Catalysis Science & Technology

CatalysisScience &Technology

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PERSPECTIVE View Article OnlineView Journal | View Issue

2814 | Catal. Sci. Technol., 2014, 4, 2814–2829 This journal is © The R

Xiaojiang Yao

Xiaojiang Yao was born inChongqing, China, in 1986. Hereceived his bachelor degree ofapplied chemistry from Chong-qing University in 2009. Now, heis studying for a doctor degree ofchemistry at Nanjing Universityunder the guidance of ProfessorLin Dong. His main researchtopic is the preparation, charac-terization and application ofsupported metal-oxide catalystsand composite oxide catalystsfor the catalytic elimination of

atmospheric molecular contaminants.

Changjin Tang

ChanAnhuireceivSchoocal Enversitof Proa poSchoojing UShouran asjingintere

tional materials and their applications

aKey Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and

Chemical Engineering, Nanjing University, Nanjing 210093, PR China.

E-mail: [email protected]; Fax: +86 25 83317761; Tel: +86 25 83592290b Jiangsu Key Laboratory of Vehicle Emissions Control, Center of Modern Analysis,

Nanjing University, Nanjing 210093, PR China

Cite this: Catal. Sci. Technol., 2014,

4, 2814

Received 30th March 2014,Accepted 23rd May 2014

DOI: 10.1039/c4cy00397g

www.rsc.org/catalysis

Research progress on the catalytic eliminationof atmospheric molecular contaminantsover supported metal-oxide catalysts

Xiaojiang Yao,ab Changjin Tang,ab Fei Gaoab and Lin Dong*ab

Catalytic elimination is an important technique to reduce the emission of atmospheric molecular

contaminants (such as CO, NOx, VOCs, HC, and PM, etc.) efficiently. In this field, the supported metal-oxide

catalysts have attracted more and more attention in recent years due to their low cost and excellent catalytic

performance. It is well known that catalytic performances are significantly dependent on the

supports, surface-dispersed components, and the pretreatment of the catalysts. In this work, we present

a brief review and propose some perspectives for supported metal-oxide catalysts according to

the above-mentioned three aspects. Meanwhile, this paper covers some interesting results about the

preparation of supported metal-oxide catalysts and the improvement of their catalytic performances for

the elimination of atmospheric molecular contaminants obtained by our research group. Moreover, we

propose the concepts of “green integration preparation (GIP)” and “surface synergetic oxygen vacancy

(SSOV)” to understand the relationship between the “composition–structure–activity” of the supported

metal-oxide catalysts, and further clarify the nature of the catalytic reactions.

1. Introduction

With the rapid development of industry, environmental pol-lution has become more and more serious in recent years,which is very harmful to human health and the ecologicalbalance. As a result, the treatment of the environmental

pollution is an urgent task. In particular, the control of atmo-spheric contamination has attracted much attention due toits wide pollution range and strong mobility. According tothe composition of pollutants, atmospheric molecular con-taminants mainly contain carbon monoxide (CO), nitrogenoxides (e.g., N2O, NO, NO2, and N2O5, etc., hereafter denotedas NOx), volatile organic compounds (VOCs), hydrocarbons(HCs), particulate matter (PM, such as soot), and sulfur com-pounds (SO2 and H2S, etc.).

1–6

Many investigation results have indicated that catalyticelimination is the most efficient approach for handling the

oyal Society of Chemistry 2014

gjin Tang was born in, China, in 1984. Heed his PhD degree from thel of Chemistry and Chemi-gineering of Nanjing Uni-y in 2011 with supervisorfessor Lin Dong, and wasstdoctoral fellow at thel of Environment of Nan-niversity with Professorong Zheng. He is currentlysociate researcher of Nan-University. His researchst is preparation of func-in environmental catalysis.

http://dx.doi.org/10.1039/c4cy00397g

http://pubs.rsc.org/en/journals/journal/CY

http://pubs.rsc.org/en/journals/journal/CY?issueid=CY004009

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above-mentioned atmospheric molecular contaminants.7–11 Itis well known that the catalyst is the key within this tech-nique, in which supported noble-metal catalysts exhibit excel-lent catalytic performances. But the scarcity of this resource,its expensive price, low hydrothermal stability, and poorsulfur resistance are major drawbacks for their wide applica-tion in the catalytic elimination of atmospheric molecularcontaminants.12–15 Therefore, as alternatives to supportednoble-metal catalysts, supported metal-oxide catalysts havebeen widely investigated in recent years due to their excellentcatalytic performance and low cost.16–20 It is well known thatthe supports, additives, and active species are the main com-ponents of supported metal-oxide catalysts. Commonly usedsupports are carbon materials, γ-Al2O3, CeO2, ZrO2, TiO2,SiO2, and their mixed oxides, e.g. CeO2, MnOx, CoOx, etc. areusually chosen as the additives due to their variable valencestates; whereas the active species mainly focused on are CuO,NiO, MnOx, CoOx, FeOx, etc.

21–27 In order to understand thenature of the catalytic reactions, it is necessary to investigatethe relationship amongst the “composition–structure–activity”of the supported metal-oxide catalysts at the molecular andatomic levels.28

It has long been considered that the properties of thesurface-dispersed components (additives and active species)are always influenced to some extent by the characteristics ofthe support.29 Therefore, understanding the interactionbetween the surface-dispersed components and support ofthe supported metal-oxide catalyst is a key step for exploringthe nature of the catalytic reactions, and to provide a valuablescientific basis for the design and preparation of novel, prac-tical, and efficient catalysts for the catalytic elimination ofatmospheric molecular contaminants. Furthermore, a lot ofinvestigation results have shown that interactions betweeneach component of the supported metal-oxide catalyst can beadjusted by many factors, which results in different catalytic

This journal is © The Royal Society of Chemistry 2014

Fei Gao

Fei Gao was born in Jiangsu,China, in 1980. He received hisPhD degree in physical chemistryunder Professor Lin Dong's guid-ance in 2008 from Nanjing Uni-versity. After graduation, hestarted to work as a facultymember in the Center of ModernAnalysis and Jiangsu Key Labo-ratory of Vehicle Emissions Con-trol, Nanjing University. Hisresearch is focused on the syn-thesis and surface modificationof nanomaterials and meso-

porous materials, as well as their applications in environmentalcatalysis (deNOx and photocatalysis, etc.) with in situ character-izations (in situ IR and ex situ XPS, etc.).

performances.30–36 These influencing factors mainly include:(1) the composition, structure, and exposed crystal planes ofthe supports; (2) the type, loading amount, preparation con-ditions, and modification of the active species; and (3) thepretreatment of the catalysts, etc.

In the present work, we summarize the application ofsupported metal-oxide catalysts in the catalytic elimination ofatmospheric molecular contaminants from the aspect of thesupport preparation, the loading of surface-dispersed compo-nents, and the catalyst pretreatment. We expect to furtherunderstand the nature of the catalytic reactions throughinvestigating the relationship between the “composition–structure–activity” of the supported metal-oxide catalysts, andto provide some theoretical basis for the design and prepara-tion of novel, practical, and efficient catalysts for the catalyticelimination of atmospheric molecular contaminants, whichis very useful for future investigations.

2. Effect of the support

It is recognized that the support, as one of the essential compo-nents of the supported metal-oxide catalyst, can influence thecorresponding catalytic performance significantly. In recentyears, investigation into supports has mainly focused on thedifferent single oxide supports, various mixed oxide supports,as well as special structures and specific exposed crystal planesof the supports. Therefore, in this section, we will discuss theeffect of the support by classification, as follows.

2.1. Different single oxide supports

In order to screen out the most suitable support for asupported metal-oxide catalyst applied for the catalytic elimi-nation of atmospheric molecular contaminants, researchershave carefully investigated the influence of different single

Catal. Sci. Technol., 2014, 4, 2814–2829 | 2815

Lin Dong

Lin Dong was born in Sichuan,China, in 1963. He received hisPhD degree from Nanjing Univer-sity in 1995 under the guidanceof Professor Yi Chen, and thenwas a postdoctoral fellow atNanjing University with Profes-sor Naiben Min. He has been aprofessor in the School of Chem-istry and Chemical Engineeringof Nanjing University since 2003.Now, he is the director ofJiangsu Key Laboratory of Vehi-cle Emissions Control, Nanjing

University. He leads a research group of ca. 20 members and hisresearch interest includes the preparation of supported catalystsand functional materials, as well as their applications in environ-mental catalysis. He has published more than 120 papers and 20patents in the field of air pollution control.


Table 1 The BET specific surface area and grain size of γ-Al2O3, ZrO2,and CeO2 supports

22

Sample SBET (m2 g−1) Grain size (nm)

γ-Al2O3 154.3 7.11ZrO2 126.8 60.89CeO2 68.0 34.67

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oxide supports (such as γ-Al2O3, CeO2, TiO2, SiO2, and ZrO2,etc.) on the corresponding catalytic performances.37–42

Wang et al.43 prepared a series of CoOx/γ-Al2O3, CoOx/SiO2,and CoOx/TiO2 catalysts for CO oxidation, and found that thecatalytic performance of CoOx/SiO2 was better than that of theCoOx/γ-Al2O3 and CoOx/TiO2 catalysts (Fig. 1). A possible reasonmight be that the interaction between CoOx and γ-Al2O3 orTiO2 was too strong, which promoted the formation of CoAl2O4

or CoTiO3 spinel, further resulting in the decrease of surfacearea, reduction behavior, and catalytic performance. Braun et al.44

compared the catalytic performances of MoO3/γ-Al2O3 andMoO3/SiO2 catalysts for soot combustion, and pointed outthat molybdenum species on the surface of γ-Al2O3 and SiO2

were in the form of MoO4− and Mo2O7

2−, respectively. Theyconcluded that the excellent catalytic performance of theMoO3/SiO2 catalyst was due to the sufficient contact betweenthe Mo2O7

2− species and soot. Furthermore, the effect of dif-ferent single oxide supports on the physicochemical proper-ties and catalytic performances of the supported metal-oxidecatalysts was also observed in the complete oxidation ofacetone over MnOx supported on Al2O3- and ZrO2-pillaredclay catalysts.45

Our research group also carried out some investigationsto explore the influence of different single oxide supportson the catalytic performances of the supported metal-oxidecatalysts.22,46 A series of CuO/γ-Al2O3, CuO/ZrO2, and CuO/CeO2

catalysts was prepared for NO reduction by CO. And thecorresponding catalytic performances showed the followingsequence: CuO/CeO2 > CuO/ZrO2 > CuO/γ-Al2O3, which wasnot consistent with the BET specific surface area and grain sizeof the γ-Al2O3, ZrO2, and CeO2 supports (Table 1). Therefore, wegave a reasonable explanation from the coordination structureof copper species to discuss the influence of the support, as fol-lows: on the surface of CeO2, the incorporated Cu2+ species wasin an unstable five-coordination structure; on the surface ofZrO2, the Cu2+ species was in an elongated environment;whereas on the surface of γ-Al2O3, the Cu2+ species was in asymmetrical and stable octahedral coordination. The variation

2816 | Catal. Sci. Technol., 2014, 4, 2814–2829

Fig. 1 Catalytic activity of CoOx/γ-Al2O3, CoOx/SiO2, and CoOx/TiO2

catalysts for CO oxidation.43

of the coordination structure of the Cu2+ species could affectthe reduction behavior significantly, and further resulted in dif-ferent catalytic performances.

It can be seen that the above-mentioned studies are mainlyabout the supported single metal-oxide catalysts. With thedeepening of investigations, researchers began to explore theinfluence of different single oxide supports on the catalyticperformance of supported dual metal-oxide catalysts.40,47,48

Pantaleo et al.40 impregnated CuO–Cr2O3 on the surfaceof γ-Al2O3 and SiO2 to obtain CuO–Cr2O3/γ-Al2O3 andCuO–Cr2O3/SiO2 catalysts, and evaluated their catalytic perfor-mance for CO oxidation. They found that SiO2 was beneficialto the generation of interaction between CuO and Cr2O3 topromote the formation of CuCr2O4 and CuCrO2, whichresulted in an excellent catalytic performance. However, therewas no evidence for such an interaction existing between CuOand Cr2O3 on the surface of γ-Al2O3. Jin et al.48 reported thatthe catalytic performance of MnOx–CeO2/TiO2 for the selectivecatalytic reduction of NO by NH3 was better than that ofMnOx–CeO2/γ-Al2O3 at low temperature (80–150 °C) due tothere being more Lewis acid sites. While the temperature washigher than 150 °C, the MnOx–CeO2/γ-Al2O3 catalyst exhibiteda superior activity over MnOx–CeO2/TiO2, because the formerpossessed more Brønsted acid sites, which was beneficial tothe oxidation of NO to NO2 at higher temperature, furtherpromoting the enhancement of the catalytic performance.

2.2. Various mixed oxide supports

Many investigation results have indicated that supportedmetal-oxide catalysts with mixed oxide supports exhibit anexcellent catalytic performance compared to the correspond-ing catalysts with single oxide supports.49–53 For example,Lin et al.50 investigated the physicochemical properties andcatalytic performance of the CuO/CeO2, CuO/Ce0.7Sn0.3O2,and CuO/SnO2 catalysts for CO oxidation through H2-TPR,XRD, CO-TPD, and the CO + O2 reaction. They found that theCuO/Ce0.7Sn0.3O2 catalyst showed the optimal catalytic perfor-mance because the introduction of Sn4+ into CuO/CeO2 pro-moted the generation of a synergistic interaction between thedispersed CuO and Ce0.7Sn0.3O2, which further resulted inthe reduced CuO/Ce0.7Sn0.3O2 catalyst that could be easily oxi-dized to supply active oxygen species.

Therefore, the investigation of supported metal-oxide cata-lysts with mixed oxide supports has attracted more attentionin recent years. Some researchers have systematically studiedthe influence of the atomic ratio of the mixed oxide supportson the catalytic performances of the supported metal-oxide



Fig. 2 Effect of the Mn/(Ce + Mn) ratio on I256/I456 calculated fromthe Raman spectra of BaO/CexMn1−xO2−y catalysts. For comparison,NO conversion (800 °C) and the normalized NO conversion (600 °C)according to the surface oxygen vacancies (I256/I456 value) were alsoplotted in the figure.60


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catalysts for the elimination of atmospheric molecularcontaminants.7,13,16,24,54–57 Wang et al.16 adopted XRD,Raman, H2-TPR, XPS and the CO + O2 reaction to investigatethe influence of the Ce/Zr ratio on the catalytic performanceof CuO/CexZr1−xO2 catalysts for CO oxidation. They concludedthat there were three kinds of copper oxide species on thesurface of the CexZr1−xO2 support, i.e., highly dispersed CuO,clustered CuO, and crystalline CuO. The Ce/Zr ratio couldaffect the dispersion behavior of CuO on the surface of theCexZr1−xO2 support, and further influence the catalytic perfor-mance of the CuO/CexZr1−xO2 catalysts because the highlydispersed CuO was the active species for CO oxidation.Ren et al.24 synthesized a series of CuO/CexMn1−xO2 catalystsfor propane combustion, and found that CuO/Ce0.6Mn0.4O2

exhibited the best catalytic performance due to the synergis-tic effect between CuO and Ce0.6Mn0.4O2, as well as theincrease of oxygen migration ability and the surface oxygendefect. Liu et al.58 compared the catalytic performances ofCuO/TixCe1−xO2 for the selective catalytic reduction of NO byC3H6. They found that the CuO/Ti0.9Ce0.1O2 catalyst showedthe best catalytic activity and N2 selectivity due to its abun-dant Lewis acid sites and adsorbed oxygen species on the sur-face of this catalyst, which provided more active sites for theadsorption and activation of NO. Furthermore, the in situFT-IR results suggested that the synergistic effect of Cu andCe was beneficial to the formation of nitrates, oxygenatedhydrocarbons, and the key intermediate isocyanate (–NCOspecies), which promoted the enhancement of the catalyticperformance. Recently, Hong et al.59 thoroughly investigatedthe effect of Fe content on the physicochemical propertiesand catalytic performance of BaO/CexFe1−xO2−y catalystsfor the direct decomposition of NO. They pointed out thatthe catalyst with the Fe/(Ce + Fe) ratio of 0.02 showed theoptimal catalytic performance due to the most isolated tetra-hedral Fe3+ ions and the increase of the concentration of sur-face oxygen vacancies. Some similar results were obtained inBaO/CexMn1−xO2−y catalysts,

60 and it was found that the cata-lyst with the Mn/(Ce + Mn) ratio of 0.25 exhibited the best cata-lytic performance. From this, the authors correlated the NOconversion to the concentration of surface oxygen vacanciesvery well, as shown in Fig. 2. However, not all supported metal-oxide catalysts with mixed oxide supports exhibit an enhancedcatalytic performance. For example, CuO/Ce1−xSmxOδ catalystsshow a lower activity than the CuO/CeO2 catalyst for ethyl ace-tate oxidation, because the incorporation of Sm3+ leads to thedeterioration of textural and redox characteristics, which inturn negatively affects the activity of ethyl acetate oxidation.61

On the other hand, adjusting the types of dopant to pre-pare various mixed oxide supports and to investigate theirinfluence on the corresponding catalytic performance of thesupported metal-oxide catalysts has become a hot topic inthe catalytic elimination of atmospheric molecular contami-nants during recent years.62–66 Rao et al.64 evaluated the cata-lytic performances of CuO/CeO2–Al2O3, CuO/CeO2–ZrO2, andCuO/CeO2–SiO2 catalysts for CO oxidation. They reported thatthe CuO/CeO2–Al2O3 catalyst exhibited the most excellent


catalytic performance due to the good dispersion and enhancedreduction behavior of the copper oxide species on the surface ofthe CeO2–Al2O3 support. They also found that the CuO/CeO2–

ZrO2 catalyst displayed the highest activity for soot combustionamong these catalysts.65 The obtained results indicated that theintroduction of Zr4+ into the CuO/CeO2 catalysts benefited thecreation of more structural defects, which could accelerate thediffusion of oxygen and induce more surface active oxygen spe-cies, further promoting the enhancement of the catalytic perfor-mance at low temperature. Bennici et al.66 pointed out that thecatalytic performance of CuO/SiO2–ZrO2 was better than that ofthe CuO/SiO2–Al2O3 and CuO/SiO2–TiO2 catalysts for the selec-tive catalytic reduction of NOx by ethane. They attributed thereason to the SiO2–ZrO2 support possessing the most acid sites,which could enhance the interaction between CuO and theSiO2–ZrO2 support, further resulting in the excellent catalyticperformance.

Recently, the influence of the atomic ratio and dopant typeof the mixed oxide support on the catalytic performance ofsupported metal-oxide catalysts has also been systematicallyinvestigated by our research group.67,68 Firstly, we loaded CuOonto a series of CexZr1−xO2 supports, and evaluated their cata-lytic performance for NO reduction by CO. The obtained resultsindicated that CuO/Ce0.8Zr0.2O2 exhibited the best catalytic per-formance, which could be attributed to the unstable five-coordination structure of Cu2+ and the synergistic interactionbetween the copper oxide species and ceria-rich phase supporteasily promoting the reduction of copper oxide species and sur-face oxygen species of the support, as well as the activation ofthe adsorbed NO species. After that, we compared the catalyticperformances of CuO/Ce0.67M0.33O2 (M = Zr4+, Ti4+, and Sn4+)for NO reduction by CO, and found that the catalytic perfor-mance of CuO/Ce0.67Zr0.33O2 was better than that of theCuO/Ce0.67Ti0.33O2 and CuO/Ce0.67Sn0.33O2 catalysts. A possiblereason is that the electronegativity of Ce (1.10) and Zr (1.33) aresmaller than that of Ti (1.54), Cu (1.90), and Sn (1.96), meaningthat it is easier to attract electrons from cerium and zirconiumspecies to copper species, causing the reduction of Cu2+ to




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form active Cu+/Cu0 species, and further promoting theenhancement of catalytic performance.

2.3. Special structures

The special structures of the supports are not only conduciveto the dispersion of the active species, but also benefit theactivation and diffusion of the reactant molecules. They canpromote the enhancement of catalytic performance of thesupported metal-oxide catalysts, and have consequentlybecome one of the hot topics in the catalytic elimination ofatmospheric molecular contaminants.

In 1997, Velev et al.69 developed a new method to preparethe SiO2 support with highly uniform and well-structuredpores of tunable size in the submicrometer region, in whichthe modified colloidal crystals were used as templates for thepolymerization of silica. And then, Holland et al.70 synthe-sized TiO2, ZrO2, and Al2O3 materials with periodic three-dimensional arrays of macropores from the correspondingmetal alkoxides by using latex spheres as templates, andfound that the resulting samples could be applied in manyfields, such as heterogeneous catalysis. After that, porousmaterials with well-structured pores of tunable size (espe-cially three-dimensionally ordered macroporous (3DOM)materials and mesoporous materials) were widely investi-gated, because they are good supports for the preparation ofsupported metal-oxide catalysts, and have the potential forapplication in heterogeneous catalysis.

For the 3DOM materials, Ji et al.71 fabricated 3DOM and bulkEu0.6Sr0.4FeO3 supports by PMMA-templating and citric acid-assisted hydrothermal methods, respectively. And then, theyloaded Co3O4 onto the surface of these supports to prepareCo3O4/3DOM-Eu0.6Sr0.4FeO3 and Co3O4/bulk-Eu0.6Sr0.4FeO3

catalysts for the combustion of toluene. The obtainedresults indicated that the catalytic performance ofCo3O4/3DOM-Eu0.6Sr0.4FeO3 was obviously better than that ofCo3O4/bulk-Eu0.6Sr0.4FeO3, which was because the formation ofthe 3DOM structure was beneficial to the increase of specificsurface area, as well as the adsorption and diffusion of reactantmolecules, further resulting in a higher adsorbed oxygen spe-cies concentration and better low-temperature reducibility.Similarly, Li et al.72 also found that Co3O4/3DOM-La0.6Sr0.4CoO3

exhibited an excellent catalytic performance for toluene combus-tion compared with Co3O4/bulk-La0.6Sr0.4CoO3. This phenome-non could be attributed to the high adsorbed oxygen speciesconcentration, good low-temperature reducibility, and synergis-tic interaction between Co3O4 and its 3DOM-La0.6Sr0.4CoO3

support, as well as the high-quality 3DOM structure. Further-more, the promotion effect of the 3DOM structure on the cata-lytic performance was also observed in the combustion oftoluene and methanol over MnOx/3DOM-LaMnO3 catalysts byLiu and co-workers.73

Recently, as a support for the supported metal-oxide cata-lysts, mesoporous materials have been widely investi-gated due to their excellent catalytic performances for theelimination of atmospheric molecular contaminants.74–77


Patel et al.75 investigated the catalytic performance of copperoxide supported on different mesoporous silica (SBA-15,MCM-41, MCM-48, and KIT-6) catalysts for NO reduction byCO. They found that CuO/SBA-15 and CuO/MCM-41 catalystsexhibited a higher catalytic activity than CuO/MCM-48 andCuO/KIT-6 samples, which resulted from the good dispersionof CuO and the excellent reduction behavior of the copperoxide species in the channels of the mesoporous SBA-15 andMCM-41. Szegedi et al.32 reported that CuO–FeOx/SBA-15showed a better catalytic performance for toluene combus-tion than the CuO–FeOx/SBA-16 catalyst. The reason for thiscould be attributed to the good dispersion of copper and ironoxides in the mesoporous channels of SBA-15 (whereas theywere on the outer surface of SBA-16, and more easily agglom-erated) was beneficial for generating a bimetallic phase, andfurther enhancing the catalytic activity and stability for tolu-ene combustion. Li et al.78 synthesized two kinds of meso-porous SBA-15 materials with different pore diameters; theythen loaded cobalt oxide into the corresponding mesoporouschannels for benzene combustion. They found that theCo3O4/SBA-15 catalyst with a larger pore diameter exhibited abetter catalytic performance due to the good dispersion ofthe cobalt oxide species.

Moreover, materials with tube-like structures have attractedmore attention in recent years due to their unique propertiesand excellent catalytic performance for the elimination ofatmospheric molecular contaminants.79–82 Jiang and Song80

pointed out that tuning the surface structures of carbon nano-tubes (CNTs) could improve the catalytic performance ofCo3O4/CNTs for toluene combustion. In particular, the surfacedefect structures of CNTs could enhance the redox propertiesof Co3O4 and increase the ratio between the adsorbed oxygenspecies and the surface lattice oxygen species, which led tothe excellent catalytic performance. Su et al.83 adopted differ-ent loading methods to obtain MnOx/CNTs catalysts withMnOx only on the outside surface or both on the inside andoutside surfaces of CNTs for the selective catalytic reductionof NO by NH3. They pointed out that MnOx confined in thechannels of the CNTs exhibited an excellent catalytic perfor-mance due to the better ability of supplying oxygen andadsorbing NO, which could be related to the electronic inter-action between MnOx species and the inner surface of theCNTs. In addition, Ren et al.81 designed a domain-confinedmacroporous catalyst (Co3O4 nanocrystals anchored on TiO2

nanotubes, denoted as Co3O4/TiO2-NTs) for soot combustion.The obtained results indicated that the Co3O4/TiO2-NTs catalystexhibited a better catalytic performance than TiO2-powder-supported Co3O4 nanocrystals, which could be attributed to thegood reduction behavior and confined macroporous structureof the Co3O4/TiO2-NTs.

For supported metal-oxide catalysts with special structuredsupports, some interesting results were obtained in ourrecent investigations.84,85 From the viewpoint of maximizedutilization of material and environmental protection,we innovatively designed the following route of green integra-tion preparation (GIP). Firstly, polyhydroxy carbohydrate




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compounds (e.g., glucose) underwent a hydrothermal treat-ment and were then filtered and washed with distilled waterto obtain hard templates (residues, such as carbon micro-spheres) and soft templates (helical carbon chains in the fil-trates). Finally, according to the individual unique propertiesof the hard and soft templates, SiO2 hollow spheres andnovel three-grade porous helical silica tubes were fabricatedby utilizing the interaction between silicon sources and tem-plates, respectively, which are displayed in Fig. 3. On the onehand, SiO2 hollow spheres were synthesized by a sol–gelmethod using carbon microspheres as hard templates, andthen used as a support to prepare the CuO/SiO2 catalyst. Wefound that the CuO species supported on SiO2 hollowspheres showed a better catalytic performance for CO oxida-tion than a commercial, SiO2-supported CuO catalyst, whichcould be because the unique hollow spherical texture wasbeneficial to the formation of more active sites and the diffu-sion of reactant molecules. On the other hand, the novelthree-grade porous helical silica tubes were prepared by aningenious multi-soft-template method, which is a promisingkind of support for supported metal-oxide catalysts. We thinkthat the active species supported on first-, second- or third-grade pores of the novel three-grade porous helical silicatubes are bound to exhibit different physicochemical proper-ties and catalytic performances. As a result, we plan to loadsome active species (such as CuO, FeOx, and CoOx, etc.) onthis material applied for the catalytic elimination of atmo-spheric molecular contaminants. We believe that the designand preparation of multi-grade porous materials as the a sup-port for supported metal-oxide catalysts will be a promisinginvestigation direction in the future.

2.4. Specific exposed crystal planes

It is well known that supports with different exposed crystalplanes lead the supported metal-oxide catalysts to exhibit dif-ferent physicochemical properties and catalytic performances.


Fig. 3 Schematic diagram of green integration preparation (GIP): the resdesired metal oxide hollow spheres; the filtrates are rich in the required hhelical structure materials.

Therefore, the influence of the support with specific exposedcrystal planes on the catalytic performance of the supportedmetal-oxide catalyst for the elimination of atmospheric molecu-lar contaminants has become a hot topic in recent years.86–89

Zhou et al.86 reported that CuO/CeO2-nanorodsexhibited a better catalytic performance for CO oxidationthan CuO/CeO2-nanoparticles. The reason might be thatthe CeO2-nanorods exposed high-energy and more reactive{001} and {110} facets, which were beneficial to the genera-tion of a synergistic interaction between the copper oxidespecies and ceria. The research group of Zhang88,89 systemati-cally investigated the influence of the support with specificexposed crystal planes on the catalytic performance of thesupported metal-oxide catalysts. Firstly, they synthesized a seriesof MnOx/CeO2–ZrO2-nanorods, MnOx/CeO2–ZrO2-nanocubes,and MnOx/CeO2–ZrO2-nanopolyhedra catalysts for the selec-tive catalytic reduction of NO by NH3. They found thatMnOx/CeO2–ZrO2-nanorods with {110} and {100} facets exhibiteda better catalytic performance than MnOx/CeO2–ZrO2-nanocubeswith {100} facets and MnOx/CeO2–ZrO2-nanopolyhedra with{111} and {100} facets, which could be attributed to the largeamounts of Mn4+ species, surface adsorbed oxygen, and oxygenvacancies associated with the exposed {110} facets. Afterthat, they further investigated the catalytic performance ofMnOx/Ce0.9Zr0.1O2-nanorods for the selective catalytic reductionof NO by NH3 through experimental and theoretical methods.They pointed out that the MnOx/Ce0.9Zr0.1O2-nanorods mainlyexposed {110} facets, which benefited the generation of inter-actions between MnOx and the Ce0.9Zr0.1O2-nanorods, as wellas the formation of oxygen vacancies and the active nitriteintermediate (NOO˙), further promoting the enhancement ofthe catalytic performance.

In addition, our research group also carried out somerelated investigations in this aspect.90,91 Firstly, the influenceof the exposed crystal planes of CeO2 on the catalytic perfor-mance of CuO/CeO2 catalysts for NO reduction by CO wasdeeply investigated. The obtained results suggested that


idues are carbon microspheres (hard templates) used to prepare theelical carbon chains (soft templates) applied for the preparation of the



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CeO2-nanopolyhedra were enclosed by {111} and {100} facets,CeO2-nanorods mainly exposed {110} and {100} facets, andCeO2-nanocubes displayed only polar {100} facets. The coor-dination environment of Cu2+ ions was different on the{111}, {110}, and {100} facets of CeO2, in which the {110}facets were the most active, so CuO/CeO2-nanorods exhibitedthe best catalytic performance. And then, we further evalu-ated the catalytic performance of CuO/Ce0.67Zr0.33O2 {110}facets and CuO/Ce0.67Zr0.33O2 {111} facets for CO oxidation. Itwas noticed that CuO/Ce0.67Zr0.33O2 {110} facets exhibited theoptimal catalytic performance. The reason for this might bethat the coordination environment of the reduced Cu+ dis-persed on the {110} facets was a stable symmetrical octahe-dral structure, which was conducive to the stabilization ofreduced Cu+, and further promoting the enhancement of cat-alytic performance due to the adsorption and activation ofCO on the Cu+ species. Supports with specific exposed crystalplanes have been widely investigated in the catalytic elimina-tion of atmospheric molecular contaminants, but their poorthermal stability has seriously limited their practical applica-tion. Therefore, how to improve the thermal stability of supportswith specific exposed crystal planes will be a key investigationarea in the future.

3. Effect of the surface-dispersedcomponents

It has been recognized that the dispersion states, valencestates, and synergistic interaction of the surface-dispersed com-ponents can inevitably affect the catalytic performance ofsupported metal-oxide catalysts. Therefore, related investiga-tions have attracted more attention in recent years, in whichthe different types of active species, various loading amounts,different preparation conditions, and the introduction of addi-tives have been adopted to adjust the dispersion states, valencestates, and synergistic interaction of the surface-dispersed com-ponents, and some interesting results have been obtained.

3.1. Different types of active species

Some research results indicate that the inherent properties ofthe active species can significantly affect the catalytic perfor-mance of supported metal-oxide catalysts for the eliminationof atmospheric molecular contaminants.92–96

Various metal-oxides (CuO, MnOx, FeOx, V2O5, MoO3,Co3O4, NiO, and ZnO) were supported on the surface ofγ-Al2O3 for toluene combustion.37 It was found thatCuO/γ-Al2O3 exhibited the best catalytic performance amongthese catalysts due to the synergistic interaction between CuOand γ-Al2O3. Bourikas et al.

94 prepared a series of V2O5/TiO2,CrO3/TiO2, MoO3/TiO2, and WO3/TiO2 catalysts for the selec-tive catalytic reduction of NO by NH3. They found that the cat-alytic performance of these catalysts followed the order ofV2O5/TiO2 > CrO3/TiO2 > MoO3/TiO2 ≥ WO3/TiO2. Theobtained results demonstrated that the catalytic performanceof these catalysts correlated well with the intensity of the


UV-vis diffuse reflectance spectroscopy (UV-vis DRS) absorp-tion band appearing at ca. 400 nm, which was considered as ameasurement of the extent of interaction between the activespecies and support in these catalysts. Doggali et al.97 com-pared the catalytic performance of FeOx/ZrO2, Co3O4/ZrO2,NiO/ZrO2, CuO/ZrO2, and MnOx/ZrO2 for CO oxidationand soot combustion. They pointed out that the catalyticperformances of these catalysts could be ranked asCo3O4/ZrO2 > MnOx/ZrO2 > CuO/ZrO2 > FeOx/ZrO2 > NiO/ZrO2,in which the optimal catalytic performance of Co3O4/ZrO2 wasattributed to the inherent property of the active Co3O4 phaserather than to other reasons. In addition, Leocadio et al.98

reported that MoO3/γ-Al2O3 exhibited a better catalytic perfor-mance for soot combustion than the V2O5/γ-Al2O3 catalyst. Thereason for this they attributed to the reaction occurringthrough the formation of carbonate species at the catalyst/sootinterface to yield CO2, and the carbonate species on the surfaceof the MoO3/γ-Al2O3 catalyst could be easily decomposed,which was evidenced by their infrared absorption spectroscopyresults of CO adsorption.

Our research group also investigated the influence of dif-ferent types of active species on the catalytic performance ofsupported metal-oxide catalysts.99 We prepared a series ofCeO2–ZrO2–Al2O3 supported metal-oxide (FeOx, Co3O4, NiO,CuO, and MnOx) catalysts for NO reduction by CO. It wasnoticed that the CuO/CeO2–ZrO2–Al2O3 catalyst showed thebest catalytic performance due to the high dispersion ofcopper oxide species, low-temperature reducibility, and moresurface oxygen vacancies, which resulted from the synergisticinteraction between CuO and CeO2–ZrO2–Al2O3.

3.2. Various loading amounts of active species

The loading amount of active species can obviously influencethe corresponding dispersion states and reduction behavior,which further results in different catalytic performances ofsupported metal-oxide catalysts. As a result, in recent yearsmany researchers have systematically investigated the effectof varying the active species loading amount.100–105

Xing et al.101 prepared a series of CrOx/γ-Al2O3 catalystswith different loading amounts of Cr for benzene combus-tion, and observed that the catalyst with a Cr loading amountof 8.5 wt% (near the dispersion capacity, 7.5 wt%) exhibitedthe best catalytic performance due to its lowest apparentactivation energy, as shown in Fig. 4. In order to observethe difference between the catalytic performances of theseCrOx/γ-Al2O3 catalysts clearly, they also gave the temperaturesof 50% (T50) and 90% (T90) benzene conversion (Table 2).Patel et al.106 reported that the catalytic performances ofCuO/SBA-15 catalysts for NO reduction by CO increased withthe increase of CuO loading amount from 4.01 to 8.67 wt%,while they declined with further increase of the CuO loadingamount to 10.1 wt% due to the formation of crystallineCuO and Cu2O at these higher CuO loading amounts. Theeffect of copper loading amount was also discussed in sootcombustion.107 It is well known that the activity of the



Fig. 4 (a) Catalytic activity, and (b) Arrhenius plots for CrOx/γ-Al2O3

catalysts with different loading amounts of Cr toward benzenecombustion.101

Table 2 The values of T50, T90, and apparent activation energy (Ea) ofthese CrOx/γ-Al2O3 catalysts for benzene oxidation101

Sample T50 (°C) T90 (°C) Ea (kJ mol−1)

γ-Al2O3 425 495 —1.7CrOx/γ-Al2O3 377 433 975.1CrOx/γ-Al2O3 333 387 828.5CrOx/γ-Al2O3 310 338 6910.2CrOx/γ-Al2O3 320 370 8411.9CrOx/γ-Al2O3 327 375 9113.6CrOx/γ-Al2O3 330 378 102


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CuO/γ-Al2O3 catalyst is dependent on the amount of easily-reduced Cu2+ species, where the amount of the most activeCu2+ species increased with the amount of copper loadingfrom 1 to 5 wt% and remained almost a constant for highercopper loading amounts. Therefore, the CuO/γ-Al2O3 catalystwith a copper loading of 5 wt% exhibited the best catalyticperformance for soot combustion. All of the above-mentionedresults indicate that supported metal-oxide catalysts with theloading amount of active species near the dispersion capacitydisplay their optimal catalytic performance for the elimina-tion of atmospheric molecular contaminants.


Indeed, there is always a threshold value for the dispersionof metal-oxide on certain supports. In the 1990s, based on theanalysis of many experimental results and relevant datareported in the literature, our research group proposed the“Incorporation Model” theory to predict the dispersion capaci-ties of active species on the surface of supports, and to describethe interaction between active species and supports, which wasvery important for the design and preparation of efficient andpractical supported metal-oxide catalysts.108,109 Furthermore,we investigated the influence of copper oxide loading amountson the catalytic performances of CuO/Ce0.5Zr0.5O2 catalysts forCO oxidation, and found that the catalyst with a copper oxideloading amount at the dispersion capacity (according to the“Incorporation Model” theory) exhibited the best catalytic per-formance, because the highly dispersed CuO was the mainactive species of copper-based catalysts for CO oxidation.110

3.3. Different preparation conditions

It is well known that the loading process of active species isvery important for the preparation of supported metal-oxidecatalysts. Recently, the influence of the loading method, pre-cursor, and calcination atmosphere of the active species onthe catalytic performance of supported metal-oxide catalystsfor the elimination of atmospheric molecular contaminantshas been investigated systematically.111–115

Ataloglou et al.112 prepared a series of Co3O4/γ-Al2O3 cata-lysts by pore volume impregnation (pvi), equilibrium deposi-tion filtration (edf), and nitrilotriacetic acid-assisted porevolume impregnation (na-pvi) methods, respectively. Theyfound that the Co3O4/γ-Al2O3 catalyst obtained by the na-pvimethod exhibited the best catalytic performance for benzenecombustion, which was because the active Co3O4 species washighly dispersed and moderately interacted with the γ-Al2O3

support. Zhang et al.116 evaluated the catalytic performanceof MnOx/TiO2 catalysts obtained by traditional impregnation(TI) and ultrasonic impregnation (UI) methods for the selec-tive catalytic reduction of NO by NH3. They found that theMnOx/TiO2-UI catalyst displayed a better catalytic perfor-mance than the MnOx/TiO2-TI catalyst, which was related tothe ultrasonic process obviously improving the dispersionbehavior and surface acid property of MnOx on the surface ofTiO2, significantly enhancing their synergistic interaction.

Harrison et al.117 discussed the influence of cobalt precur-sors (cobalt nitrate and cobalt acetate) on the catalytic perfor-mance of Co3O4/CeO2 catalysts for soot combustion. Theyreported that the Co3O4/CeO2 catalyst prepared from cobaltacetate showed a better catalytic performance due to smallercrystallite size of Co3O4. Li et al.

118 also investigated the influ-ence of different precursors (manganese nitrate and manga-nese acetate) on the catalytic performance of MnOx/TiO2

catalysts for the selective catalytic reduction of NO by NH3.They found that the MnOx/TiO2 catalyst obtained from man-ganese acetate exhibited a higher activity than that preparedfrom manganese nitrate, because the Mn species in the for-mer was highly dispersed Mn2O3 and possessed a higher




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surface Mn concentration, which was beneficial to theenhancement of catalytic performance, whereas the Mn spe-cies in the latter was mainly crystalline MnO2 accompaniedwith small amount of manganese nitrate.

Moreover, the calcination atmosphere can significantly affectthe catalytic performance of supported metal-oxide catalysts.Inaba et al.119 pointed out that CoOx/SiO2 catalysts preparedfrom cobalt acetate and calcined in N2 and air, respectively,exhibited different catalytic performances for the selective cata-lytic reduction of NO by C3H6. They found that the catalytic per-formance of the sample calcined in N2 was better than that ofthe sample calcined in air since it possessed more highly dis-persed surface Co2+ species, which was the main active speciesfor this reaction due to its solid acid properties.

Our research group also carried out some related investiga-tions to explore the influence of different preparation condi-tions on the catalytic performance of supported metal-oxidecatalysts.120,121 With regard to the method used for loadingthe active species, we synthesized a series of CuO/CeO2 cata-lysts by an impregnation method (IM), a grinding method(GM), and a mechanical mixing method (MMM) for NO reduc-tion by CO. It was noticed that the CuO/CeO2-IM catalystshowed the optimal catalytic performance due to the highestnumber of surface oxygen vacancies and Cu+ species, as well asthe excellent reduction behavior. For the precursors of activespecies, Cu(NO3)2·3H2O and Cu(CH3COO)2·H2O were chosen asthe precursors of copper oxide to prepare CuO/CeO2–ZrO2–Al2O3

catalysts, which were used for NO reduction by CO. Theobtained results indicated that the CuO/CeO2–ZrO2–Al2O3 cata-lyst prepared from Cu(CH3COO)2·H2O exhibited a better cata-lytic performance due to the presence of Cu+ species andgood reducibility (this work has not been published). Further-more, we prepared a series of CuO–CoOx/γ-Al2O3 catalystsfrom Cu(NO3)2·3H2O and Co(CH3COO)2·4H2O, and calcinedthem in N2 and air atmospheres, respectively, to investigatethe influence of calcination atmosphere on the catalytic per-formance of the CuO–CoOx/γ-Al2O3 catalysts for NO reductionby CO. It could be found that the Co species was in the formof crystalline Co3O4 in the CuO–CoOx/γ-Al2O3 catalysts cal-cined in air, whereas it was present as highly dispersed CoOin the CuO–CoOx/γ-Al2O3 catalysts calcined in N2, which wasbeneficial to the formation of Cu2+–O–Co2+ active species, andfurther promoted the enhancement of catalytic performance.Based on the above-mentioned results, we believe that thedevelopment of novel loading procedures of active species toenhance the catalytic performance of supported metal-oxidecatalysts for the elimination of atmospheric molecular con-taminants will be an important investigation direction inthe future.

3.4. Introduction of additives

Many research results have indicated that the introduction ofadditives (especially the metal-oxides with variable valencestates, such as FeOx, CoOx, MnOx, and CeO2, etc.) can signifi-cantly enhance the catalytic performance of supported


metal-oxide catalysts for the elimination of atmosphericmolecular contaminants.122–126

Todorova et al.124 investigated the effect of CoOx additiveson the catalytic performance of the MnOx/SiO2 catalyst forthe combustion of n-hexane and ethyl acetate. They foundthat the catalytic performance was significantly improvedby the introduction of cobalt oxide due to the high mobilityof lattice oxygen, the presence of the Mn4+/Mn3+ redox cou-ple, and the predominance of Co2+ on the surface of theMnOx–CoOx/SiO2 catalyst. Menon et al.127 pointed out thatthe improved catalytic performance of CuO–CeO2/γ-Al2O3 fortoluene combustion compared to the CuO/γ-Al2O3 catalystwas attributed to the formation of the CexCu1−xO2−x solidsolution, in which the oxidation of toluene occurred at Cu2+

sites whilst the reduction of oxygen took place at Ce3+ sites.In other words, the redox couples of Ce4+/Ce3+ and Cu2+/Cu+

played a key role in the toluene combustion. Drenchev et al.128

reported that the modification of MnOx/γ-Al2O3 by CeO2

led to a better dispersion of manganese oxide on theMnOx–CeO2/γ-Al2O3 catalyst compared to the MnOx/γ-Al2O3

sample, because of the partial disappearance of alumina OHgroups and the blocking of part of Al3+ Lewis acid sites,which was beneficial to the enhancement of catalytic perfor-mance for many catalytic reactions (including NO directdecomposition, NO reduction by CO, and CO oxidation, etc.).Furthermore, Khristova et al.129 systematically investigatedthe influence of CeO2 additives on the catalytic performanceof the CuO/γ-Al2O3 catalyst for NO reduction by CO. Theyfound that not only the introduction of CeO2 additivesimproved the catalytic performance of the CuO/γ-Al2O3 cata-lyst, but also the impregnation sequence of copper and ceriumprecursors strongly affected the formation of different metal-oxide phases and various active sites, further leading to differ-ent catalytic performances for NO elimination.

It has widely been reported that the introduction ofCa additives can obviously enhance the N2 selectivity ofmanganese-based deNOx catalysts, but the mechanism is stillunclear. Therefore, Liu et al.130 prepared a series ofCa-modified CeO2–MnOx/TiO2 catalysts to investigate themechanism. In-situ DRIFTS results indicated that the additionof Ca species significantly inhibited the formation of NH onthe surface of the catalyst, which limited the reaction betweenNH and NO to generate N2O. Moreover, Ca additives alsodecreased the formation of NO2, which inhibited the reactionbetween NO2 and NH3 to form N2O, and further improved theN2 selectivity of the catalysts. Based on the in-situ DRIFTSresults, they proposed a possible mechanism to understandthe suppression of Ca additives on N2O formation, as shownin Fig. 5.

Recently, our research group also systematically investi-gated the influence of additives on the catalytic performanceof supported metal-oxide catalysts.131–133 Firstly, we prepareda series of Mn2O3-modified CuO/γ-Al2O3 catalysts, and foundthat Mn2O3 grew epitaxially on the surface of the γ-Al2O3 sup-port, which led to the dispersion capacity of CuO on the sur-face of the γ-Al2O3 support increasing from 0.75 to 1.10 mmol



Fig. 5 The possible mechanism of the suppression of Ca additives onN2O formation.130


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Cu2+/100 m2 γ-Al2O3 (obtained from our previously proposed“Incorporation Model” theory), which further enhanced thecatalytic performance for NO reduction by CO. And then, wediscussed the influence of WO3 monolayer modification onthe physicochemical properties and catalytic performance ofCuO/CexZr1−xO2 catalysts. It could be observed that theseCuO/CexZr1−xO2 catalysts showed different reduction proper-ties, adsorption behaviors, and catalytic performances withthe variation of Ce/Zr ratio before WO3 monolayer modifica-tion. Whereas after WO3 monolayer modification, theyexhibited similar physicochemical properties and catalyticperformances that were independent of the variation in Ce/Zrratio due to the formation of the WO3 monolayer on thesurface of the CexZr1−xO2 support, which would block theinteraction between CuO and the CexZr1−xO2 support.Furthermore, a possible surface model of CuO dispersed onCexZr1−xO2 and monolayer WO3-modified CexZr1−xO2 supportswas proposed, which is presented in Fig. 6. Finally, we exploredthe influence of the impregnation sequence of copper andmanganese precursors on the catalytic performance ofCuO–MnO2/CeO2 catalysts for NO reduction by CO. It could befound that the catalysts prepared by a co-impregnation methodexhibited a better catalytic performance than the catalystsobtained by a stepwise-impregnation method. The reason forthis could be attributed to the co-impregnation method beingmore conducive to strengthening the interaction amongst thecomponents of the CuO–MnO2/CeO2 catalysts through moresufficient contact, which resulted in good reduction behaviors.

4. Effect of pretreatment

Pretreatment of the supported metal-oxide catalysts canadjust the valence- and coordination-states of the active spe-cies, as well as the interaction between the surface-dispersed


Fig. 6 Possible schematic diagram of surface model of CuO dispersedon CexZr1−xO2 and monolayer WO3-modified CexZr1−xO2 supports.

132

components and support, which is considered to be one ofthe most efficient approaches for improving the catalytic per-formance of supported metal-oxide catalysts.

4.1. Atmosphere pretreatment

Atmosphere pretreatment (such as oxidation pretreatment,reduction pretreatment, and reaction atmosphere pretreatment,etc.) of supported metal-oxide catalysts has been investigatedexhaustively because it can lead to different catalyticperformances.134–138 In particular, it is well known that areduction pretreatment can result in the formation of coordi-nately unsaturated cations and suspension bonds on the sur-face of the supported metal-oxide catalysts, which lead thecatalysts to being in unstable states, and further promoting theenhancement of the catalytic performance. Therefore, the influ-ence of the reduction pretreatment on the catalytic perfor-mance of supported metal-oxide catalysts for the eliminationof atmospheric molecular contaminants has attracted moreattention in recent years.36,139–142

Pan et al.36 reported that the reduction pretreatment ofCuO/γ-Al2O3 catalysts by H2 and re-oxidation by air (HA) ledto a better dispersion of copper species on the surface ofγ-Al2O3 and a larger metal area per gram of Cu, both of whichwere beneficial to the enhancement of catalytic performance ofthe CuO/γ-Al2O3 catalyst for styrene combustion (Table 3).Yang et al.140 discussed the effect of reduction pretreatment onthe catalytic performance of CuO/SBA-15 catalysts for benzenecombustion. They found that the reduced catalysts exhibited abetter catalytic performance than the unreduced catalysts, whichcould be attributed to the Cu0 species being more active thanCu2+ species for benzene combustion. Moreover, Boccuzzi et al.142

pointed out that the reduction pretreatment obviously enhancedthe catalytic performance of CuO/TiO2 catalysts for NO reduc-tion by CO, which was because the reduced state copper-basedcatalysts were beneficial to the dissociation of NO (the rate-determining step). And then, they proposed a possible reactionmechanism to further understand the improvement in catalyticperformance, as follows (note that (g) represents the gas phase,and (a) refers to the adsorbed state):

CO(g) + Cu0 → Cu0–CO(a) (1)

2NO(g) + 4Cu0 → 2Cu0–N(a) + 2Cu0–O(a) → N2(g)+ 2Cu2

+O− (2)

Cu2+O− + CO(g) → CO2(g) + 2Cu0 (3)


Table 3 The information of active species dispersion and thetemperature of 50% styrene conversion (T50) over CuO/γ-Al2O3 catalysts

36

Catalyst CuO/γ-Al2O3 CuO/γ-Al2O3–HAMetal dispersion (%) 3.35 8.75Metal surface area (m2 g−1 sample) 0.75 1.96Metal surface area (m2 g−1 metal) 21.6 56.42Active particle diameter (nm) 31.14 11.92T50 (°C) 354 325



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NO(g) + e−(TiOx) → N(a) + O−(a) (4)

NO(g) + N(a) → N2O(a) (5)

N(a) + N(a) → N2(g) (6)

CO(g) + N(a) → NCO(a) (7)

N2O(a) → N2(g) + O(a) (8)

Recently, our research group systematically explored theinfluence of the reduction pretreatment on the catalytic per-formance of supported metal-oxide catalysts for NO reductionby CO, and obtained some interesting results.143–146 We deeplyinvestigated the catalytic performance of the 0.6Cu0.3Mn/Alcatalyst (representing that the loading amounts of CuO andMn2O3 were 0.6 mmol Cu2+/100 m2 γ-Al2O3 and 0.3 mmolMn3+/100 m2 γ-Al2O3, respectively) before and after CO reduc-tion pretreatment for NO reduction by CO. The obtainedresults indicated that the CO reduction pretreatment enhancedthe catalytic performance of the 0.6Cu0.3Mn/Al catalystremarkably. In order to further understand the reason for theobvious enhancement of the catalytic performance, we gavesome reasonable explanations based on our previously pro-posed “Incorporation Model” theory, as shown in Fig. 7. Firstly,there were three kinds of Cu2+–O–Cu2+, Cu2+–O–Mn3+, andMn3+–O–Mn3+ species on the surface of the γ-Al2O3, when Cu2+

and Mn3+ were simultaneously dispersed on the surface ofγ-Al2O3. And then, XPS and EPR results showed that the


Fig. 7 The “Incorporation Model” diagram of CuO and Mn2O3 dispersedpretreatment: (a) 0.6Cu/Al, (b) 0.6Cu0.3Mn/Al, (c) 0.3Mn/Al, (a′) 0.6Cu/Al–C

dispersed Cu2+ and Mn3+ were reduced to Cu+ and Mn2+ spe-cies after CO reduction pretreatment, which suggested thatthe CO reduction pretreatment would remove the oxygenspecies between the surface-dispersed components to gener-ate Cu+– –Cu+, Cu+– –Mn2+, and Mn2+– –Mn2+ species.Furthermore, we defined the oxygen vacancy between differ-ent Cu+ and Mn2+ cations as the “surface synergetic oxygenvacancy” (SSOV). Finally, we carried out an in situ FT-IRexperiment to explore the role of the SSOV in NO reductionby CO reaction, and therefore proposed a possible reactionmechanism, which is displayed in Fig. 8. In situ FT-IR resultsindicated that CO adsorbed mainly on the Cu+ species,whereas NO primarily adsorbed on the Mn2+ species, andthe SSOV played a key bridging role between Cu+–CO andMn2+–NO, which led to the remarkable enhancement in thecatalytic performance. With the purpose of investigating theuniversality of the SSOV, we carried out the CO reductionpretreatment on other catalysts and found that the catalyticperformances of CuO–CoO/γ-Al2O3 and NiO–Mn2O3/γ-Al2O3

catalysts for NO reduction by CO were also improved obvi-ously after the CO reduction pretreatment.

4.2. Acid pretreatment

Many investigation results have indicated that the regenera-tion of deactivated catalysts, the determination of active sites,and the improvement of catalytic performance could beachieved through acid pretreatment of supported metal-oxidecatalysts.147–150 As a result, in recent years acid pretreatment


on the (110) plane of γ-Al2O3 (C-layer) before and after CO reductionO, (b′) 0.6Cu0.3Mn/Al–CO, and (c′) 0.3Mn/Al–CO.143


Fig. 8 Possible reaction mechanism of NO reduction by CO over0.6Cu0.3Mn/Al catalyst after CO reduction pretreatment.143


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has become an emerging topic for the catalytic elimination ofatmospheric molecular contaminants.

Kim and Shim147 adopted acid pretreatment of the indus-trial, deactivated, supported copper-based catalysts by differ-ent acid aqueous solutions of HNO3, CH3COOH, H2SO4, HCl,and H3PO4 to regenerate them. They observed that the cata-lytic performances of these pretreated catalysts for the com-bustion of benzene, toluene, and o-xylene could be ranked byHNO3 > CH3COOH > HCl > H3PO4 > H2SO4, in whichacid pretreatment by HNO3 exhibited the best effect dueto the efficient regeneration of active sites (copper species).Jia et al.149 investigated the catalytic performance ofCuO/CexCu1−xO2−δ catalysts for CO oxidation before and afteracid pretreatment by HNO3. They concluded that the synergis-tic effect between the oxygen vacancies in the CexCu1−xO2−δsolid solution and surface CuO species (which could beremoved by HNO3 pretreatment) was the origin of excellentcatalytic performance, because the former promoted the acti-vation of oxygen, and the latter was conducive to CO chemi-sorption. In addition, Martín et al.151 discussed the influenceof different acid pretreatments (H2SO4, H3PO4, HNO3, andHCl) on the catalytic performance of CoOx/γ-Al2O3 catalystsfor the selective catalytic reduction of NOx by CH4. Theobtained results indicated that the catalyst pretreated byH2SO4 exhibited the best catalytic performance among thesepretreated and unpretreated catalysts due to the increase ofsurface acidity and the stabilization of the active Co2+ species.

4.3. Other pretreatment

The influence of other pretreatments (including hydro-thermal aging pretreatment, microwave plasma pretreatment,etc.) on the catalytic performance of supported metal-oxidecatalysts for the elimination of atmospheric molecular con-taminants was also investigated in recent years.152,153


In particular, it is widely reported that the catalytic perfor-mance of supported metal-oxide catalysts for deNOx catalysisstrongly depends on the amount of NO2 in the exhaust,whereas the combination of microwave plasma pretreatmentand selective catalytic reduction is beneficial to the oxidationof NO to NO2, which further promotes the enhancement ofcatalytic performance.154 As a result, our research group hassystematically investigated the effect of microwave plasmapretreatment on the catalytic performance of CuO/TiO2 cata-lysts for NO reduction by CO.155 We found that the micro-wave plasma pretreatment clearly enhanced the activity andN2 selectivity of the CuO/TiO2 catalysts due to the generationof highly active oxygen species (O˙), which facilitated theoxidation of NO to NO2, and subsequently adsorbed on thesurface of CuO/TiO2 catalysts as distorted nitrate species.Furthermore, it is necessary to explore new pretreatmenttechniques to improve the catalytic performance of supportedmetal-oxide catalysts for the elimination of atmosphericmolecular contaminants in the future.

5. Conclusions and perspectives

Supported metal-oxide catalysts have been widely applied forthe catalytic elimination of atmospheric molecular contami-nants in recent years. It is well known that the support,surface-dispersed component, and pretreatment of thecatalyst can significantly affect the catalytic performance ofsupported metal-oxide catalysts. Therefore, we have carriedout a brief review and proposed some perspectives accordingto the above-mentioned three aspects in the present work.Many researchers have made great efforts to investigate thecatalytic performance of supported metal-oxide catalysts forthe elimination of atmospheric molecular contaminants, andattempted to clarify the nature of these catalytic reactions.However, the relationship amongst the “composition–structure–activity” is still not very clear. In the future, withthe development of material preparation approaches, solidcatalyst surface characterization techniques, and theoreticalcalculation methods, we can synthesize highly thermally-stabilized supports with special structures, regular morphol-ogies, and specific exposed crystal planes to simplify the cata-lyst systems, and further deeply investigate the interactionbetween surface-dispersed components and supports tounderstand the relationship amongst the “composition–structure–activity” of supported metal-oxide catalysts for thecatalytic elimination of atmospheric molecular contaminants,which can provide a valuable scientific basis for the designand preparation of novel, practical, and efficient catalysts.

Acknowledgements

The financial supports of the National Natural Science Founda-tion of China (no. 20573053, 20873060, 20973091, 21273110,and 21203091), the National Basic Research Program of China(973 program, no. 2003CB615804, 2004CB719502, 2009CB623500,




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and 2010CB732300), the Natural Science Foundation of JiangsuProvince (BK2012298), and Jiangsu Province Science and Tech-nology Support Program (Industrial, BE2011167) are gratefullyacknowledged. Furthermore, kind assistance of Dr Xi Hong,Lei Zhang, Yuan Cao, Yan Xiong, and Weixin Zou in checkingthe English and collecting the literatures is greatly appreciated.

Notes and references

1 J. L. Cao, Y. Wang, T. Y. Zhang, S. H. Wu and Z. Y. Yuan,
Appl. Catal., B, 2008, 78, 120–128.
2 P. Bera, S. T. Aruna, K. C. Patil and M. S. Hegde, J. Catal.,
1999, 186, 36–44.
3 M. Chen, L. P. Fan, L. Y. Qi, X. Y. Luo, R. X. Zhou and
X. M. Zheng, Catal. Commun., 2009, 10, 838–841.
4 F. X. Yin, S. F. Ji, B. H. Chen, Z. L. Zhou, H. Liu and
C. Y. Li, Appl. Catal., A, 2006, 310, 164–173.
5 M. E. Gálvez, S. Ascaso, I. Suelves, R. Moliner, R. Jiménez,
X. García, A. Gordon and M. J. Lázaro, Catal. Today, 2011,176, 361–364.
6 G. Y. Xie, Z. Y. Liu, Z. P. Zhu, Q. Y. Liu, J. Ge and
Z. G. Huang, J. Catal., 2004, 224, 36–41.
7 A. Hornés, P. Bera, A. L. Cámara, D. Gamarra, G. Munuera
and A. Martínez-Arias, J. Catal., 2009, 268, 367–375.
8 K. I. Shimizu, A. Satsuma and T. Hattori, Appl. Catal., B,
1998, 16, 319–326.
9 S. Krishnamoorthy, J. P. Baker and M. D. Amiridis, Catal.
Today, 1998, 40, 39–46.
10 E. E. Svensson, S. Nassos, M. Boutonnet and S. G. Järås,
Catal. Today, 2006, 117, 484–490.
11 P. Ciambelli, V. Palma, P. Russo and S. Vaccaro, J. Mol.
Catal. A: Chem., 2003, 204–205, 673–681.
12 G. R. Bamwenda, S. Tsubota, T. Nakamura and M. Haruta,
Catal. Lett., 1997, 44, 83–87.
13 R. D. Zhang, W. Y. Teoh, R. Amal, B. H. Chen and
S. Kaliaguine, J. Catal., 2010, 272, 210–219.
14 X. J. Yao, Y. Xiong, W. X. Zou, L. Zhang, S. G. Wu, X. Dong,
F. Gao, Y. Deng, C. J. Tang, Z. Chen, L. Dong and Y. Chen,Appl. Catal., B, 2014, 144, 152–165.
15 M. Dhakad, T. Mitshuhashi, S. Rayalu, P. Doggali,
S. Bakardjiva, J. Subrt, D. Fino, H. Haneda and N. Labhsetwar,Catal. Today, 2008, 132, 188–193.
16 S. P. Wang, T. Y. Zhang, Y. Su, S. R. Wang, S. M. Zhang,
B. L. Zhu and S. H. Wu, Catal. Lett., 2008, 121, 70–76.
17 X. Q. Cheng, A. M. Zhu, Y. Z. Zhang, Y. Wang, C. T. Au and
C. Shi, Appl. Catal., B, 2009, 90, 395–404.
18 M. Y. Kim, T. Kamata, T. Masui and N. Imanaka, J. Asian
Ceram. Soc., 2013, 1, 243–247.
19 X. Q. Wang, A. J. Shi, Y. F. Duan, J. Wang and M. Q. Shen,
Catal. Sci. Technol., 2012, 2, 1386–1395.
20 Z. C. Si, D. Weng, X. D. Wu, Y. Jiang and B. Wang, Catal.
Sci. Technol., 2011, 1, 453–461.
21 L. Zhang, D. S. Zhang, J. P. Zhang, S. X. Cai, C. Fang,
L. Huang, H. R. Li, R. H. Gao and L. Y. Shi, Nanoscale,2013, 5, 9821–9829.

22 L. J. Liu, J. G. Cai, L. Qi, Q. Yu, K. Q. Sun, B. Liu, F. Gao,
L. Dong and Y. Chen, J. Mol. Catal. A: Chem., 2010, 327,1–11.
23 J. Q. Lu, C. X. Sun, N. Li, A. P. Jia and M. F. Luo, Appl. Surf.
Sci., 2013, 287, 124–134.
24 T. Z. Ren, P. B. Xu, Q. F. Deng and Z. Y. Yuan, React. Kinet.,
Mech. Catal., 2013, 110, 405–420.
25 L. J. Liu, Y. Chen, L. H. Dong, J. Zhu, H. Q. Wan, B. Liu,
B. Zhao, H. Y. Zhu, K. Q. Sun, L. Dong and Y. Chen,Appl. Catal., B, 2009, 90, 105–114.
26 J. Zhu, F. Gao, L. H. Dong, W. J. Yu, L. Qi, Z. Wang,
L. Dong and Y. Chen, Appl. Catal., B, 2010, 95, 144–152.
27 M. Bellardita, M. Addamo, A. D. Paola, G. Marcì,
L. Palmisano, L. Cassar and M. Borsa, J. Hazard. Mater.,2010, 174, 707–713.
28 I. E. Wachs, Dalton Trans., 2013, 42, 11762–11769.
29 P. W. Selwood, Adv. Catal., 1951, 3, 27–106. 30 T. Sánchez, F. B. Gebretsadik, P. Salagre, Y. Cesteros,
N. Guillén-Hurtado, A. García-García and A. Bueno-López,Appl. Clay Sci., 2013, 77–78, 40–45.

31 M. Chen, L. P. Fan and X. M. Zheng, J. Rare Earths, 2006,
24, 447–450.
32 Á. Szegedi, M. Popova, K. Lázár, S. Klébert and E. Drotár,
Microporous Mesoporous Mater., 2013, 177, 97–104.
33 J. S. Yang, W. Y. Jung, G. D. Lee, S. S. Park, E. D. Jeong,
H. G. Kim and S. S. Hong, J. Ind. Eng. Chem., 2008, 14, 779–784.
34 H. Laversin, D. Courcot, E. A. Zhilinskaya, R. Cousin and
A. Aboukaïs, J. Catal., 2006, 241, 456–464.
35 C. A. Querini, M. A. Ulla, F. Requejo, J. Soria, U. A. Sedrán
and E. E. Miró, Appl. Catal., B, 1998, 15, 5–19.
36 H. Y. Pan, Z. Li, Q. B. Xia, H. X. Xi and C. He, Catal.
Commun., 2009, 10, 1166–1169.
37 S. C. Kim and C. Y. Park, Res. Chem. Intermed., 2002, 28,
441–449.
38 G. S. Pozan, J. Hazard. Mater., 2012, 221–222, 124–130.
39 E. E. Miró, F. Ravelli, M. A. Ulla, L. M. Cornaglia and
C. A. Querini, Catal. Today, 1999, 53, 631–638.40 G. Pantaleo, L. F. Liotta, A. M. Venezia, G. Deganello,

E. M. Ezzo, M. A. El Kherbawi and H. Atia, Mater. Chem.Phys., 2009, 114, 604–611.

41 J. Y. Hu, W. Chu and L. M. Shi, J. Nat. Gas Chem., 2008, 17,
159–164.
42 A. Carrascull, C. Grzona, D. Lick, M. Ponzi, E. Ponzi and
E. Ponzi, React. Kinet. Catal. Lett., 2002, 75, 63–68.
43 C. B. Wang, C. W. Tang, H. C. Tsai and S. H. Chien, Catal.
Lett., 2006, 107, 223–230.
44 S. Braun, L. G. Appel and M. Schmal, Catal. Commun.,
2005, 6, 7–12.
45 L. M. Gandía, M. A. Vicente and A. Gil, Appl. Catal., B,
2002, 38, 295–307.
46 Y. H. Hu, L. Dong, M. M. Shen, D. Liu, J. Wang, W. P. Ding
and Y. Chen, Appl. Catal., B, 2001, 31, 61–69.
47 J. Liu, Z. Zhao, C. M. Xu, A. J. Duan, L. Zhu and X. Z. Wang,
Appl. Catal., B, 2005, 61, 36–46.
48 R. B. Jin, Y. Liu, Z. B. Wu, H. Q. Wang and T. T. Gu,
Chemosphere, 2010, 78, 1160–1166.



Publ

ishe

d on

27

May

201

4. D

ownl

oade

d by

NA

NJI

NG

UN

IVE

RSI

TY

on

16/0

8/20

14 1

6:17

:18.

View Article Online

49 A. Gervasini, M. Manzoli, G. Martra, A. Ponti, N. Ravasio,
L. Sordelli and F. Zaccheria, J. Phys. Chem. B, 2006, 110,7851–7861.
50 R. Lin, M. F. Luo, Y. J. Zhong, Z. L. Yan, G. Y. Liu and
W. P. Liu, Appl. Catal., A, 2003, 255, 331–336.
51 Z. L. Zhang, Y. X. Zhang, Z. P. Wang and X. Y. Gao,
J. Catal., 2010, 271, 12–21.
52 X. J. Yao, L. Zhang, L. L. Li, L. C. Liu, Y. Cao, X. Dong,
F. Gao, Y. Deng, C. J. Tang, Z. Chen, L. Dong and Y. Chen,Appl. Catal., B, 2014, 150–151, 315–329.
53 J. F. Chen, J. J. Zhu, Y. Y. Zhan, X. Y. Lin, G. H. Cai,
K. M. Wei and Q. Zheng, Appl. Catal., A, 2009, 363,208–215.
54 M. Alifanti, M. Florea, S. Somacescu and V. I. Parvulescu,
Appl. Catal., B, 2005, 60, 33–39.
55 M. Alifanti, M. Florea and V. I. Pârvulescu, Appl. Catal., B,
2007, 70, 400–405.
56 X. Chen, S. A. C. Carabineiro, S. S. T. Bastos, P. B. Tavares,
J. J. M. Órfão, M. F. R. Pereira and J. L. Figueiredo, Appl.Catal., A, 2014, 472, 101–112.
57 T. Mishra, P. Mohapatra and K. M. Parida, Appl. Catal., B,
2008, 79, 279–285.
58 J. Liu, X. Y. Li, Q. D. Zhao, D. K. Zhang and P. Ndokoye,
J. Mol. Catal. A: Chem., 2013, 378, 115–123.
59 W. J. Hong, M. Ueda, S. Iwamoto, S. Hosokawa, K. Wada,
H. Kanai, H. Deguchi and M. Inoue, Appl. Catal., B, 2011,106, 142–148.
60 W. J. Hong, S. Iwamoto, S. Hosokawa, K. Wada, H. Kanai
and M. Inoue, J. Catal., 2011, 277, 208–216.
61 M. Konsolakis, S. A. C. Carabineiro, P. B. Tavares and
J. L. Figueiredo, J. Hazard. Mater., 2013, 261, 512–521.
62 T. J. Huang and Y. C. Kung, Catal. Lett., 2003, 85, 49–55.
63 H. Y. Cao, W. C. Song, M. C. Gong, J. L. Wang, S. H. Yan,
Z. M. Liu and Y. Q. Chen, J. Nat. Gas Chem., 2009, 18,83–87.

64 K. N. Rao, P. Bharali, G. Thrimurthulu and B. M. Reddy,
Catal. Commun., 2010, 11, 863–866.
65 K. N. Rao, P. Venkataswamy and B. M. Reddy, Ind. Eng.
Chem. Res., 2011, 50, 11960–11969.
66 S. Bennici, P. Carniti and A. Gervasini, Catal. Lett., 2004,
98, 187–194.
67 L. J. Liu, Z. J. Yao, B. Liu and L. Dong, J. Catal., 2010, 275,
45–60.
68 X. J. Yao, Q. Yu, Z. Y. Ji, Y. Y. Lv, Y. Cao, C. J. Tang, F. Gao,
L. Dong and Y. Chen, Appl. Catal., B, 2013, 130–131,293–304.
69 O. D. Velev, T. A. Jede, R. F. Lobo and A. M. Lenhoff,
Nature, 1997, 389, 447–448.
70 B. T. Holland, C. F. Blanford and A. Stein, Science, 1998,
281, 538–540.
71 K. M. Ji, H. X. Dai, J. G. Deng, X. W. Li, Y. Wang, B. Z. Gao,
G. M. Bai and C. T. Au, Appl. Catal., A, 2012, 447–448,41–48.
72 X. W. Li, H. X. Dai, J. G. Deng, Y. X. Liu, Z. X. Zhao,
Y. Wang, H. G. Yang and C. T. Au, Appl. Catal., A, 2013,458, 11–20.

73 Y. X. Liu, H. X. Dai, J. G. Deng, Y. C. Du, X. W. Li,
Z. X. Zhao, Y. Wang, B. Z. Gao, H. G. Yang and G. S. Guo,Appl. Catal., B, 2013, 140–141, 493–505.
74 M. Popova, Á. Szegedi, Z. Cherkezova-Zheleva, A. Dimitrova
and I. Mitov, Appl. Catal., A, 2010, 381, 26–35.
75 A. Patel, P. Shukla, T. Rufford, S. B. Wang, J. L. Chen,
V. Rudolph and Z. H. Zhu, Appl. Catal., A, 2011, 409–410,55–65.
76 A. Patel, P. Shukla, J. L. Chen, T. E. Rufford, V. Rudolph
and Z. H. Zhu, Catal. Today, 2013, 212, 38–44.
77 T. Tsoncheva, L. Ivanova, J. Rosenholm and M. Linden,
Appl. Catal., B, 2009, 89, 365–374.
78 J. J. Li, X. Y. Xu, Z. P. Hao and W. Zhao, J. Porous Mater.,
2008, 15, 163–169.
79 B. L. Zhu, X. X. Zhang, S. R. Wang, S. M. Zhang, S. H. Wu
and W. P. Huang, Microporous Mesoporous Mater., 2007,102, 333–336.
80 S. J. Jiang and S. Q. Song, Appl. Catal., B, 2013, 140–141, 1–8.
81 J. L. Ren, Y. F. Yu, F. F. Dai, M. Meng, J. Zhang, L. R. Zheng
and T. D. Hu, Nanoscale, 2013, 5, 12144–12149.82 C. Fang, D. S. Zhang, L. Y. Shi, R. H. Gao, H. R. Li, L. P. Ye

and J. P. Zhang, Catal. Sci. Technol., 2013, 3, 803–811.83 Y. X. Su, B. X. Fan, L. S. Wang, Y. F. Liu, B. C. Huang,

M. L. Fu, L. M. Chen and D. Q. Ye, Catal. Today, 2013, 201,115–121.

84 C. Y. Song, C. L. Wang, H. Y. Zhu, X. C. Wu, L. Dong and
Y. Chen, Catal. Lett., 2008, 120, 215–220.
85 F. Gao, L. Dong, Y. Kong, Y. H. Zhang, X. C. Wu, Y. R. Tao,
H. Y. Zhu, Y. N. Lü and Y. Chen, J. Nanosci. Nanotechnol.,2008, 8, 1497–1501.
86 K. B. Zhou, R. Xu, X. M. Sun, H. D. Chen, Q. Tian,
D. X. Shen and Y. D. Li, Catal. Lett., 2005, 101, 169–173.
87 X. L. Mou, B. S. Zhang, Y. Li, L. D. Yao, X. J. Wei, D. S. Su
and W. J. Shen, Angew. Chem., Int. Ed., 2012, 51, 2989–2993.
88 R. H. Gao, D. S. Zhang, P. Maitarad, L. Y. Shi,
T. Rungrotmongkol, H. R. Li, J. P. Zhang and W. G. Cao,J. Phys. Chem. C, 2013, 117, 10502–10511.
89 P. Maitarad, D. S. Zhang, R. H. Gao, L. Y. Shi, H. R. Li,
L. Huang, T. Rungrotmongkol and J. P. Zhang, J. Phys.Chem. C, 2013, 117, 9999–10006.
90 L. J. Liu, Z. J. Yao, Y. Deng, F. Gao, B. Liu and L. Dong,
ChemCatChem, 2011, 3, 978–989.
91 J. Zhu, L. L. Zhang, Y. Deng, B. Liu, L. H. Dong, F. Gao,
K. Q. Sun, L. Dong and Y. Chen, Appl. Catal., B, 2010, 96,449–457.
92 P. G. Smirniotis, D. A. Peña and B. S. Uphade, Angew.
Chem., Int. Ed., 2001, 40, 2479–2482.
93 S. T. Liu, A. Obuchi, J. Uchisawa, T. Nanba and
S. Kushiyama, Appl. Catal., B, 2002, 37, 309–319.
94 K. Bourikas, C. Fountzoula and C. Kordulis, Appl. Catal., B,
2004, 52, 145–153.
95 Z. Özçelik, G. S. P. Soylu and İ. Boz, Chem. Eng. J., 2009,
155, 94–100.
96 E. Finocchio, M. Baldi, G. Busca, C. Pistarino,
G. Romezzano, F. Bregani and G. P. Toledo, Catal. Today,2000, 59, 261–268.



Publ

ishe

d on

27

May

201

4. D

ownl

oade

d by

NA

NJI

NG

UN

IVE

RSI

TY

on

16/0

8/20

14 1

6:17

:18.

View Article Online

97 P. Doggali, S. Waghmare, S. Rayalu, Y. Teraoka and
N. Labhsetwar, J. Mol. Catal. A: Chem., 2011, 347, 52–59.
98 I. C. L. Leocadio, S. Braun and M. Schmal, J. Catal., 2004,
223, 114–121.
99 Q. Yu, X. X. Wu, X. J. Yao, B. Liu, F. Gao, J. M. Wang and
L. Dong, Catal. Commun., 2011, 12, 1311–1317.
100 S. S. Hong, G. H. Lee and G. D. Lee, Korean J. Chem. Eng.,
2003, 20, 440–444.
101 T. Xing, H. Q. Wan, Y. Shao, Y. X. Han, Z. Y. Xu and
S. R. Zheng, Appl. Catal., A, 2013, 468, 269–275.
102 J. Liu, Z. Zhao, J. Q. Wang, C. M. Xu, A. J. Duan, G. Y. Jiang
and Q. Yang, Appl. Catal., B, 2008, 84, 185–195.
103 R. X. Zhou, T. M. Yu, X. Y. Jiang, F. Chen and X. M. Zheng,
Appl. Surf. Sci., 1999, 148, 263–270.
104 Z. M. Liu, Y. Q. Chen, J. B. Zhong, J. L. Wang, S. H. Yan
and M. C. Gong, J. Rare Earths, 2007, 25, 585–589.
105 K. H. Chuang, Z. S. Liu and M. Y. Wey, Mater. Sci. Eng., B,
2010, 175, 100–107.
106 A. Patel, T. E. Rufford, V. Rudolph and Z. H. Zhu, Catal.
Today, 2011, 166, 188–193.
107 F. E. López-Suárez, A. Bueno-López and M. J. Illán-Gómez,
Appl. Catal., B, 2008, 84, 651–658.
108 Y. Chen and L. F. Zhang, Catal. Lett., 1992, 12, 51–62.
109 Y. Chen, L. Dong, Y. S. Jin, B. Xu and W. J. Ji, Stud. Surf.
Sci. Catal., 1996, 101, 1293–1302.110 H. L. Chen, H. Y. Zhu, Y. Wu, F. Gao, L. Dong and J. J. Zhu,

J. Mol. Catal. A: Chem., 2006, 255, 254–259.111 S. W. Moon, G. D. Lee, S. S. Park and S. S. Hong, React.

Kinet. Catal. Lett., 2004, 82, 303–310.112 T. Ataloglou, J. Vakros, K. Bourikas, C. Fountzoula, C. Kordulis

and A. Lycourghiotis, Appl. Catal., B, 2005, 57, 299–312.113 F. Wyrwalski, J. F. Lamonier, S. Siffert and A. Aboukaïs,

Appl. Catal., B, 2007, 70, 393–399.114 S. Cimino, R. Pirone and L. Lisi, Appl. Catal., B, 2002, 35,

243–254.115 J. L. Xie, D. Fang, F. He, J. F. Chen, Z. B. Fu and X. L. Chen,

Catal. Commun., 2012, 28, 77–81.116 Y. P. Zhang, X. Y. Zhao, H. T. Xu, K. Shen, C. C. Zhou, B. S. Jin

and K. Q. Sun, J. Colloid Interface Sci., 2011, 361, 212–218.117 P. G. Harrison, I. K. Ball, W. Daniell, P. Lukinskas,

M. Céspedes, E. E. Miró and M. A. Ulla, Chem. Eng. J., 2003,95, 47–55.

118 J. H. Li, J. J. Chen, R. Ke, C. K. Luo and J. M. Hao, Catal.
Commun., 2007, 8, 1896–1900.
119 M. Inaba, Y. Kintaichi, M. Haneda and H. Hamada, Catal.
Lett., 1996, 39, 269–274.
120 X. J. Yao, F. Gao, Q. Yu, L. Qi, C. J. Tang, L. Dong and
Y. Chen, Catal. Sci. Technol., 2013, 3, 1355–1366.
121 Y. Y. Lv, H. L. Zhang, Y. Cao, L. H. Dong, L. L. Zhang,
K. A. Yao, F. Gao, L. Dong and Y. Chen, J. Colloid InterfaceSci., 2012, 372, 63–72.
122 E. Kayhan, S. M. Andonova, G. S. Şentürk, C. C. Chusuei
and E. Ozensoy, J. Phys. Chem. C, 2010, 114, 357–369.
123 S. J. Yang, C. Z. Wang, L. Ma, Y. Peng, Z. Qu, N. Q. Yan,
J. H. Chen, H. Z. Chang and J. H. Li, Catal. Sci. Technol.,2013, 3, 161–168.

124 S. Todorova, A. Naydenov, H. Kolev, K. Tenchev, G. Ivanov
and G. Kadinov, J. Mater. Sci., 2011, 46, 7152–7159.
125 W. B. Li, M. Zhuang, T. C. Xiao and M. L. H. Green, J. Phys.
Chem. B, 2006, 110, 21568–21571.
126 D. Q. Yu, Y. Liu and Z. B. Wu, Catal. Commun., 2010, 11,
788–791.
127 U. Menon, H. Poelman, V. Bliznuk, V. V. Galvita,
D. Poelman and G. B. Marin, J. Catal., 2012, 295,91–103.
128 N. Drenchev, I. Spassova, E. Ivanova, M. Khristova and
K. Hadjiivanov, Appl. Catal., B, 2013, 138–139, 362–372.
129 M. Khristova, B. Ivanov, I. Spassova and T. Spassov, Catal.
Lett., 2007, 119, 79–86.
130 Y. Liu, T. T. Gu, X. L. Weng, Y. Wang, Z. B. Wu and
H. Q. Wang, J. Phys. Chem. C, 2012, 116, 16582–16592.
131 H. Q. Wan, D. Li, Y. Dai, Y. H. Hu, B. Liu and L. Dong,
J. Mol. Catal. A: Chem., 2010, 332, 32–44.
132 X. W. Li, H. Q. Wan, B. Liu, L. J. Yang, H. Y. Zhu,
H. L. Chen, X. Zhao, K. Q. Sun, L. Dong and Y. Chen, Catal.Commun., 2009, 10, 741–745.
133 X. J. Yao, Y. Xiong, J. F. Sun, F. Gao, Y. Deng, C. J. Tang
and L. Dong, J. Rare Earths, 2014, 32, 131–138.
134 X. Y. Jiang, Y. R. Jia, H. Huang and X. M. Zheng, Catal.
Lett., 2005, 104, 169–175.
135 L. F. Liotta, G. Pantaleo, G. Di Carlo, G. Marcì and
G. Deganello, Appl. Catal., B, 2004, 52, 1–10.
136 J. Jansson, J. Catal., 2000, 194, 55–60.
137 A. Martínez-Arias, M. Fernández-García, J. Soria and
J. C. Conesa, J. Catal., 1999, 182, 367–377.138 P. T. Wierzchowski and L. W. Zatorski, Appl. Catal., B,

2003, 44, 53–65.139 J. S. Yang, W. Y. Jung, S. H. Baek, K. T. Lim, S. S. Park,

G. D. Lee and S. S. Hong, React. Kinet. Catal. Lett., 2008, 93,219–226.

140 J. S. Yang, W. Y. Jung, G. D. Lee, S. S. Park and S. S. Hong,
Top. Catal., 2010, 53, 543–549.
141 W. J. Jiang, Y. Yin, X. Q. Liu, X. Q. Yin, Y. Q. Shi and
L. B. Sun, J. Am. Chem. Soc., 2013, 135, 8137–8140.
142 F. Boccuzzi, A. Chiorino, M. Gargano and N. Ravasio,
J. Catal., 1997, 165, 140–149.
143 D. Li, Q. Yu, S. S. Li, H. Q. Wan, L. J. Liu, L. Qi, B. Liu,
F. Gao, L. Dong and Y. Chen, Chem. – Eur. J., 2011, 17,5668–5679.
144 X. J. Yao, F. Gao, Y. Cao, C. J. Tang, Y. Deng, L. Dong
and Y. Chen, Phys. Chem. Chem. Phys., 2013, 15,14945–14950.
145 Y. Y. Lv, L. C. Liu, H. L. Zhang, X. J. Yao, F. Gao, K. A. Yao,
L. Dong and Y. Chen, J. Colloid Interface Sci., 2013, 390,158–169.
146 X. J. Yao, F. Gao and L. Dong, Cuihua Xuebao, 2013, 34,
1975–1985.
147 S. C. Kim and W. G. Shim, Appl. Catal., B, 2008, 79,
149–156.
148 L. Y. Hsu and H. Teng, Appl. Catal., B, 2003, 42, 69–76.
149 A. P. Jia, G. S. Hu, L. Meng, Y. L. Xie, J. Q. Lu and
M. F. Luo, J. Catal., 2012, 289, 199–209.




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150 Z. H. Zhu, L. R. Radovic and G. Q. Lu, Carbon, 2000, 38, 451–464.
151 J. C. Martín, P. Ávila, S. Suárez, M. Yates, A. B. Martín-Rojo,
C. Barthelemy and J. A. Martín, Appl. Catal., B, 2006, 67,270–278.

152 F. Lin, X. D. Wu and D. Weng, Catal. Today, 2011, 175,
124–132.

153 D. N. Tran, C. L. Aardahl, K. G. Rappe, P. W. Park and
C. L. Boyer, Appl. Catal., B, 2004, 48, 155–164.
154 M. Măgureanu and V. I. Pârvulescu, Stud. Surf. Sci. Catal.,
2007, 171, 361–396.
155 F. Gao, B. Liu, W. J. Sun, Y. Wu and L. Dong, Catal. Today,
2011, 175, 34–39.


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