US 20150291434A1 as) United States a2) Patent Application Publication co) Pub. No.: US 2015/0291434 Al Huber et al. (43) Pub. Date: Oct. 15, 2015 (54) METHOD TO REDUCE CO2 TO CO USING BOIS 23/72 (2006.01) PLASMON-ENHANCED PHOTOCATALYSIS BOLJ 23/66 (2006.01) BOIS 23/52 (2006.01) (71) Applicant: Wisconsin Alumni Research Bols 21/06 (2006.01) Foundation, Madison, WI (US) Bold 23/10 (2006.01) . (52) U.S. CL (72) Inventors: George W. Huber, Middleton, WI (US): CPC vieveeeessseee C01B 31/18 (2013.01); BOLT 21/063 Aniruddha A. Upadhye, Madison, WI (2013.01); BOLJ 21/04 (2013.01); BOLT 23/10 (US); Hyung Ju Kim, Madison, WI (2013.01); BOLT 23/72 (2013.01); BOLT 23/66 (US); Insoo Ro, Madison, WI (US); M. (2013.01); BOLT 23/52 (2013.01): BOLJ 35/004 Isabel Tejedor-Anderson, Madison, WI (2013.01) (US) : (57) ABSTRACT (73) Assignee: Wisconsin Alumni Research Foundation, Madison, WI (US) Described is a method of reducing CO, to CO using visible radiation and plasmonic photocatalysts. The method includes (21) Appl. No.: 14/248,729 contacting CO, with a catalyst, in the presence of H,, wherein the catalyst has plasmonic photocatalytic reductive activity (22) Filed: Apr. 9, 2014 whenexposedto radiation having a wavelength between 380 nm and 780 nm. The catalyst, CO, and H, are exposed to Publication Classification non-coherentradiation having a wavelength between 380 nm and 780 nm suchthat the catalyst undergoes surface plasmon (51) Int. Cl. resonance. The surface plasmon resonance increases the rate COIB 31/18 (2006.01) of CO, reduction to CO as compared to the rate of CO, BOIS 21/04 (2006.01) reduction to CO without surface plasmon resonance in the BOLJ 35/00 (2006.01) catalyst.
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US 20150291434A1
as) United States
a2) Patent Application Publication co) Pub. No.: US 2015/0291434 Al
Huberet al. (43) Pub. Date: Oct. 15, 2015
(54) METHOD TO REDUCE CO2 TO CO USING BOIS 23/72 (2006.01)PLASMON-ENHANCED PHOTOCATALYSIS BOLJ 23/66 (2006.01)
BOIS 23/52 (2006.01)(71) Applicant: Wisconsin Alumni Research Bols 21/06 (2006.01)
Foundation, Madison, WI (US) Bold 23/10 (2006.01)
. (52) U.S. CL(72) Inventors: George W. Huber, Middleton, WI (US): CPC vieveeeessseee C01B 31/18 (2013.01); BOLT 21/063
Aniruddha A. Upadhye, Madison, WI (2013.01); BOLJ 21/04 (2013.01); BOLT 23/10(US); Hyung Ju Kim, Madison, WI (2013.01); BOLT 23/72 (2013.01); BOLT 23/66(US); Insoo Ro, Madison, WI (US); M. (2013.01); BOLT 23/52 (2013.01): BOLJ 35/004Isabel Tejedor-Anderson, Madison, WI (2013.01)
(US): (57) ABSTRACT
(73) Assignee: Wisconsin Alumni ResearchFoundation, Madison, WI (US) Described is a method of reducing CO, to CO using visible
radiation and plasmonic photocatalysts. The method includes
(21) Appl. No.: 14/248,729 contacting CO, with a catalyst, in the presence ofH,, whereinthe catalyst has plasmonic photocatalytic reductive activity
(22) Filed: Apr. 9, 2014 whenexposedto radiation having a wavelength between 380
nm and 780 nm. The catalyst, CO, and H, are exposed toPublication Classification non-coherentradiation having a wavelength between 380 nm
and 780 nm suchthat the catalyst undergoes surface plasmon(51) Int. Cl. resonance. The surface plasmon resonance increases the rate
COIB 31/18 (2006.01) of CO, reduction to CO as compared to the rate of CO,BOIS 21/04 (2006.01) reduction to CO without surface plasmon resonance in the
BOLJ 35/00 (2006.01) catalyst.
Patent Application Publication Oct. 15, 2015 Sheet 1 of 12 US 2015/0291434 Al
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platinum, gold, and/or combinations thereof. The semicon-
ductor is preferably an oxide of titanium and/or an oxide of
[0046] In light of these results, using the reverse water gas
shift reaction over anAu/TiO,catalyst run plasmonically and
in the dark as a meansto reduce CO, with H, was investigated
in greater detail. FIG. 4 is a graph that depicts the rate of the
US 2015/0291434 Al
reduction reaction as a factor of temperature for both theplasmonic reactions (“light”, #) and dark reactions, @. Of
particular note in FIG. 4 is the enhancementofthe plasmonicreaction rates across all temperatures tested. As the tempera-
ture rises, the reaction rate predictably rises. The reaction isendothermic, so its rate would be expectedto rise with rising
temperature. However, the enhancement due to running the
reaction plasmonically is not expected, especially at thehigher end ofthe temperature range. Thatis, at the higher end
of the temperature range, the expectation is that the thermaleffect on catalysis would dominate and the enhancement due
to running the reaction plasmonically would decrease or dis-appear entirely. However, even at the highest temperature
tested, 400° C., FIG. 4 showsthat there is a very significant
enhancementin the reaction rate between the light reactionand the dark reaction.
[0047] FIG. 5 presents the enhancement data between the
light reaction versus the dark reaction in isolation—.e., itis agraph depicting the enhancementin rate due to running the
reaction plasmonically as a function of temperature for thereverse water gas shift reactions described above for FIG.4.
Here, the data show that in a direct comparison, the enhance-mentfactor (1.e., the rate of light reaction/rate of dark reac-
tion) is more pronounced at 100° C. and decreases in a smooth
curve to approximately a factor of 2 at 400° C. Extrapolated,these data indicate a light enhancementofa factor of7; 1.e.,
700%. These same date are presented in FIG. 6 notas a rateenhancement,but ratheras the actualdifference between CO,
reduction rate (umol/gm-cat/min) under light and dark vs.temperature that can be attributed solely to the plasmonic
influence ofthe catalyst (and not temperature). FIG. 6 indi-
cates that the maximum plasmonic-induced enhancement inthe reaction rate as a function of temperature-induced
increases in reaction rate peaks somewhere between about300° C. and about 350° C. in the Au/TiO, system. FIG. 7
corroborates these findings by showing that the light effi-
ciency versus temperature for this same reaction also reachesa peak between about 300° C. and about 350° C.In FIG.7,
light efficiency is defined as
Lightefficiency (%) =
CO, conversion rate due to lightx AMpeaction x 100% Intensityx Catalyst surface area
[0048] The salient point of FIGS. 4 through 7 takentogetheris that the visible light energy that induces plasmonic
activity in the catalyst is the cause of a very marked increasein the reaction rate ofthe reverse water-gas shift reaction. The
enhancementis achieved using simulated, non-coherent solarradiation.
[0049] Now, itcould be possible that the enhancedcatalytic
effect is not a photocatalytic effect, per se, but simply a
thermaleffect due to localized heating caused by the surfaceplasmonresonance.To investigate this possibility, an Arrhe-
nius plot (In(rate) v 1/T) was constructed for the light reac-tions described above for FIGS. 4-7 and the corresponding
dark reactions. The results are shown in FIG.8. Thus, FIG. 8is a plot depicting In(CO, reduction rate) versus 1/Temp(1/
K)x10° for the reverse water gas shift reactions. Theplots for
the light reaction versus the dark reaction clearly show dif-ferent activation energies. If the increased rate for the light
reaction werestrictly a localized heating effect, the activation
Oct. 15, 2015
energy for the light reaction versus the dark reaction shouldbe the same. However, the dark reaction (#) has an E, of
47.09+/—-0.27 kJ/mol, while the light reaction (@) has an E,, of34.93+/-0.47 kJ/mol. The change in E, indicates that it not
solely a localized heating effect that is responsible for thelight-induced enhancementofthe CO, reductionrates.
[0050] FIGS. and 10 are correspondingplots that map the
In(rate of CO, reduction) versus the In(partial pressure ofCO,) (FIG. 9) and In(rate) versus the In(partial pressure of
H,) (FIG. 10) for the light (#) and dark (@) reactions. In bothfigures, the reaction conditions were identical: Total gas flow
rate=15 sccm, P=110 psi, T=200° C., H,:CO,=2:1. In FIG. 9,
the rate equation sets up as [Rate]=Kapp-o> [PPco2|”. Thus,the exponent“m”is the reaction order andits value is depen-
dent upon the mechanism that causes the CO, reduction. InFIG.9, which is the data based on the partial pressure ofCO,,
it was foundforthe light reaction that m,,.,,=1.04; for the dark
reaction, m,,,,=0.50. These data clearly indicate that there isadistinctly different reaction mechanism forthe “light,” plas-
monically catalyzed reaction as comparedto the dark reac-tion.
[0051] The same holds true whenIn(rate) versus the In(par-
tial pressure of H,) is plotted for the light reaction versus thedark reaction. See FIG. 10. Here, the rate equation sets up as
[Rate]=Kapp;,. [PP,.]”. It was found for the light reactionthat n,,,,,-0.17; for the dark reaction, nj,,,=0.07.
[0052] FIGS. 11 and 12is a graph depicting the dependence
of light efficiency and rate enhancement on H,:CO, ratio inplasmon-enhanced water gas shift reaction over Aw/TiO,
catalyst. Experimental conditions: P=103 psi, T=200° C.,Total gas flow rate=15 sccm, catalyst amount=7.9 mg. As can
be seen in FIG.11, lowertheratio ofH,:CO,in the plasmoni-cally catalyzed reaction results in the higherlight efficiency
ofthe reaction. Thatis, at high light efficiencies, the reaction
producedincreased amounts ofH, as compared to CO. FIG.12 showsthat at low H,:CO,ratio, plasmonic rate enhance-
ment up to 1300% can be achieved.
[0053] Suitable catalysts for use in the present method may
be fabricated by the following methods. Note that these meth-
ods are exemplary andare includedsolely to provide a morecomplete disclosure ofthe method claimed herein. The exem-
plary catalysts are not limiting.
Preparation ofAu/T10, (DP) Catalyst:
[0054] The Au/TiO, DP was prepared by deposition-pre-
cipitation with NaOH (1M)'~. Titania Degussa P25 was used
as support (Sigma-Aldrich, >99.5% trace metal basis) andsolid HAuCl,.3H,O (Sigma-Aldrich, >99.9% trace metal
basis) as the precursor. Before the preparation, TiO, was driedin the air at 110° C. overnight. 100 ml of aqueous HAuCl,
solution (4.2*10-* M) washeated to 80° C.and the pH wasadjusted to 8 by drop-wise addition ofNaOH (1M). Then, 1 g
of TiO, was dispersed in the solution, and the pH wasread-
justed to 8 with NaOH. The suspension was thermostated at80° C. wasstirred for 2 h and centrifuged. The solids were
then washed, dried, and calcined at 300° C. underthe flow ofair (30 ml/min) with a heating rate of 2° C./min and main-
tained for 4h.
Preparation ofAu/CeO, DP Catalyst:
[0055] The Au/CeO, (DP)° was prepared by deposition-precipitation with NaOH (1M) which is same with Aw/TiO,
(DP)'?. Cerium (IV) oxide was used as support (Sigma-
US 2015/0291434 Al
Aldrich) and solid HAuCl,.3H,O (Sigma-Aldrich, >99.9%trace metal basis) as the precursor. Before the preparation,
CeO, was dried in the air at 110° C. overnight. 100 ml ofaqueous HAuCl1,solution (4.2*10-3 M) was heatedto 80° C.
and the pH wasadjustedto 8 by drop-wise addition ofNaOH(1M). Then, 1 g ofCeO, was dispersed in the solution, and the
pH was readjusted to 8 with NaOH. The suspension was
thermostatedat 80° C.wasstirred for 2h and centrifuged. Thesolids were then washed, dried, and calcined at 300° C. under
the flow ofair (30 ml/min) witha heating rate of2° C./min andmaintained for 4 h.
Preparation ofAu/Al,O, (DP) Catalyst:
[0056] The Au/Al,O,; (DP)* was prepared by deposition-precipitation with NaOH (1M) which is same with Au/TiO,
(DP)'?. Alumina was usedas support (Strem Chemicals) and
solid HAuCl,.3H,O (Sigma-Aldrich, >99.9% trace metalbasis) as the precursor. Before the preparation, Al,O, was
dried in the air at 110° C. overnight. 100 ml of aqueousHAuCl, solution (4.2*10-* M) washeated to 80° C.and the
pH wasadjusted to 8 by drop-wise addition of NaOH (1M).Then, 1 g ofAl,O, wasdispersed in the solution, and the pH
wasreadjusted to 8 with NaOH.The suspension was thermo-
stated at 80° C. was stirred for 2 h and centrifuged. The solidwas then washed, dried, and calcined at 300° C. under the
flow of air 30 ml/min) with a heating rate of 2° C./min andmaintained for 4 h.
Preparation of Cu/TiO, (1) Catalyst:
[0057] The Cu/TiO, (1) was prepared by impregnating 1 gof titania Degussa P25 (Sigma-Aldrich, >99.5% trace metal
basis) with a solution of 53 mg of CuSO,.5H,O (Sigma-
Aldrich, puriss, meets analytical specification ofPh. Eur., BP,USP, 99-100.5%) in 10 ml of DI water**. The slurry wasstirred for 4 h at room temperature, then all liquid was evapo-rated and the solid was dried at 110° C. overnight. The cata-
lyst was calcined at 300° C. undertheflow ofair (30 ml/min)
with a heating rate of 2° C./min and maintainedfor 4 h.
REFERENCE CITED
[0058] 1.R. Zanella, S. Giorgio, C. H. Shin, C. R. Henry
and C. Louis, J. Catal., 2004, 222, 357-367.
[0059] 2.R. Zanella, S. Giorgio, C. R. Henry and C. Louis,
J. Phys. Chem. B, 2002, 106, 7634-7642.
[0060] 3. D.L. Nguyen, S. Umbarkar, M. K. Dongare, C.Lancelot, J.S. Girardon, C. Dujardin and P. Granger, Catal.
Commun., 2012, 26, 225-230.
[0061] 4. C. Burda, X. Chen, R. Narayanan and M. A.El-Sayed, Chem. Rev., 2005, 105, 1025-1102.
[0062] 5. F. Sastre, M. Oteri, A. Corma and H. Garcia,
Energy Environ. Sci., 2013, 6, 2211-2215.
[0063] 6.F. Boccuzzi, A. Chiorino, G. Martra, M. Gargano,
N. Ravasio and B. Carrozzini, J. Catal., 1997, 165, 129-139.
Whatis claimedis:
1. A method ofreducing CO, to CO, the method compris-
ing:
(a) contacting CO, with a catalyst, in the presence of H,,
wherein the catalyst has plasmonic photocatalytic
reductive activity when exposedto radiation having awavelength between about 380 nm and about 780 nm;
and
Oct. 15, 2015
(b) exposing the catalyst, CO,, and H, to non-coherentradiation having a wavelength between about 380 nm
and about 780 nm suchthat the catalyst undergoes sur-face plasmon resonance, wherein the surface plasmon
resonanceincreasesthe rate of CO, reduction to CO ascompared to the rate of CO, reduction to CO without
surface plasmon resonancein the catalyst.
2. The methodofclaim 1, comprising, in step (b), exposing
the catalyst, CO,, and H, to solar radiation.
3. The method ofclaim 1, wherein the catalyst comprises a
metallic element have an average particle size no greater than
100 nm in combination with a semiconductor material.
4. The method of claim 3, wherein the metallic elementis
selected from the group consisting of calcium, copper,
europium, gold, lithium, magnesium, palladium, platinum,potassium, silver, sodium, rubidium, and yttrium, and com-
binations thereof; and wherein the semiconductor materialisselected from the group consisting of oxides of titanium,
aluminum,iron, silicon, zinc, and cerium, and combinationsthereof.
5. The method of claim 3, wherein the metallic element
comprises copper, silver, platinum,or gold, and the semicon-ductor material comprises titania orceria.
6. The method according to any one of claims 1 to 5,
wherein the surface plasmon resonance in the catalyst
increasesthe rate ofCO, reduction to COby a factorofat least1.8 as compared to the rate of CO, reduction to CO in the
absence of surface plasmon resonancein the catalyst.
7. The method according to any one of claims 1 to 5,wherein the surface plasmon resonance in the catalyst
increasesthe rate ofCO, reduction to COby a factorofat least3 as compared to the rate of CO, reduction to CO in the
absence of surface plasmon resonancein the catalyst.
8. The method according to any one of claims 1 to 5,wherein the surface plasmon resonance in the catalyst
increasesthe rate ofCO, reduction to COby a factorofat least4 as compared to the rate of CO, reduction to CO in the
absence of surface plasmon resonancein the catalyst.
9. The method according to any one of claims 1 to 5,
wherein the surface plasmon resonance in the catalystincreasesthe rate ofCO, reduction to COby a factorofat least
5 as compared to the rate of CO, reduction to CO in theabsence of surface plasmon resonancein the catalyst.
10. A method ofreducing CO,to CO, the method compris-
ing:
(a) contacting CO, with a catalyst, in the presence of H,,wherein the catalyst has plasmonic photocatalytic
reductive activity when exposed to non-coherentradia-tion having a wavelength between about 380 nm and
about 780 nm; and
(b) exposing the catalyst, CO,, and H, to solar radiationsuch that the catalyst undergoes surface plasmon reso-
nance, wherein the surface plasmon resonanceincreases
the rate of CO, reduction to CO as comparedtothe rateof CO, reduction to CO without surface plasmon reso-
nancein the catalyst.
11. The method of claim 10, wherein upon exposing thecatalyst, CO,, and H,to solar radiation, the catalyst achieves
a light efficiency of at least about 2%.
12. The method of claim 10, wherein upon exposing thecatalyst, CO,, and H,to solar radiation, the catalyst achieves
a solar light efficiency of at least about 3%.
US 2015/0291434 Al
13. The method of claim 10, wherein upon exposing thecatalyst, CO,, and H,to solar radiation, the catalyst achieves
a solar light efficiency of at least about 4%.14. The method ofclaim 10, wherein the catalyst comprises
a metallic element have an average particle size no greaterthan 100 nm in combination with a semiconductor material.
15. The methodofclaim 14, wherein the metallic element
is selected from the group consisting calcium, copper,europium, gold, lithium, magnesium, palladium, platinum,
potassium, silver, sodium, rubidium, and yttrium, and com-binations thereof; and wherein the semiconductor materialis
selected from the group consisting of oxides of titanium,aluminum,iron, silicon, zinc, and cerium, and combinations
thereof.
16. The methodofclaim 14, wherein the metallic elementcomprises copper, silver, platinum,or gold, and the semicon-
ductor material comprises titania or ceria.17. The method according to any one of claims 10 to 16,
wherein the surface plasmon resonance in the catalyst
increasestherate ofCO, reduction to COby a factorofat least1.8 as compared to the rate of CO, reduction to CO in the