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ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 11Applied
Catalysis A: General xxx (2015) xxxxxx
Contents lists available at ScienceDirect
Applied Catalysis A: General
jou rn al hom ep age: www.elsev ier .com/ locate /apcata
Catalytic cracking of n-hexane for producing propon MCM
Yong Wa ndoChemical Resou 226-8
a r t i c l
Article history:Received 14 SeReceived in reAccepted 10
DAvailable onlin
Keywords:Catalytic crackDealuminationLewis acid site
r proH-MC
propith am
propoun-22
andd a ca
1. Introduction
Light alkenes, in particular propylene, which are mainly
sup-plied as a by-product of ethylene production through the
thermalcracking ofin chemicalenergy intecially the Therefore, cing
attentiocatalysts givmation of lopartly via tsical bimolecracking,
thlower tempCO2 emissio
The cataane, heptancatalysts asformance omany repor
CorresponE-mail add
[email protected]
to allow discussion on the reaction mechanism and/or the effects
ofstructure of zeolites [312]. However, there are only a few
papersdealing with the catalysts working at high temperatures
above873 K which is necessary in order to obtain high alkene
yields.
http://dx.doi.o0926-860X/ this article in press as: Y. Wang, et
al., Appl. Catal. A: Gen. (2015),
http://dx.doi.org/10.1016/j.apcata.2014.12.018
naphtha, are acquiring more and more signicance industry. It is
known that the thermal cracking is annsive process, where the
product distribution, espe-ratio of propylene to ethylene, is hard
to control.atalytic cracking of naphtha has been drawing increas-n
[1]. The catalytic cracking of alkanes over acidic zeolitees a high
propylene/ethylene ratio, since the transfor-ng-chain alkanes to
short-chain alkenes occurs at leasthe carbenium ion/-scission
mechanism, i.e. the clas-cular cracking [2]. Compared with the
thermal steame catalytic cracking of naphtha which is carried out
ateratures would consume 20% less energy and reducen by
approximately 20% [1].lytic cracking of light alkanes, such as
pentane, hex-e and octane, has been studied over various
zeolite
a test reaction of naphtha cracking to clarify the per-f
catalysts and the reaction mechanism [3]. There arets on cracking
of alkanes at relatively low temperatures
ding authors. Fax: +81 45 924 5282.resses:
[email protected] (T. Yokoi),es.titech.ac.jp (T.
Tatsumi).
Among the catalysts examined for the catalytic cracking,
ZSM-5zeolite has been recognized as a prime candidate because of
its highthermal and hydrothermal stabilities and its considerable
resis-tance to deactivation caused by coking as well as its strong
acidity[1,13,14]. Yoshimura et al. [1] have carried out the
cracking of lightnaphtha in the presence of steam at 923 K and
found that the addi-tion of lanthanum (10 wt.%) to H-ZSM-5 (Si/Al =
100) enhanced theyield of ethylene and propylene up to 61 C-% and
that the ethyl-ene/propylene ratio in the product was approximately
0.7, whichcorresponds to a higher proportion of propylene than the
com-position obtained by using the current steam cracking.
Moreover,further addition of phosphorus (2 wt.%) improved the
stability.Recently, dealuminated MCM-68 catalyst with
multidimensionalchannels of 10-MR and 12-MR has also been reported
to exhibit ahigh propylene selectivity of 45 C-% [15]. However, the
selectivityto propylene is uncertain when the conversion approaches
100%.
MCM-22, a kind of layered zeolite invented by Mobil in 1990[16],
belongs to the MWW type zeolite and possesses two inde-pendent pore
systems. One consists of two-dimensional sinusoidalchannels
composed of slightly elliptical 10-MR, and the other
ischaracteristic of 12-MR supercages accessible by 10-MR
windows[17]. In addition, half supercages form surface pockets on
the outercrystal surfaces. Because of its unique structure, MCM-22
zeolite
rg/10.1016/j.apcata.2014.12.0182014 Elsevier B.V. All rights
reserved.-22 zeolites
ng, Toshiyuki Yokoi , Seitaro Namba, Junko N. Korces Laboratory,
Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama
e i n f o
ptember 2014vised form 5 December 2014ecember 2014e xxx
ing of H-MCM-22
a b s t r a c t
The catalytic cracking of n-hexane fomodel reaction of naphtha
cracking. direct or post-synthesis methods. Theratio. Dealumination
of H-MCM-22 win the increase in the catalytic life andbe attributed
to the decrease in the amresultant coke formation. Del-Al-MCMC-%)
which was higher than H-ZSM-5conversion of 95%. Moreover, it
showecatalyst.ylene
, Takashi Tatsumi
503, Japan
ducing propylene on MCM-22 catalysts was carried out as aM-22
catalysts with different Si/Al ratios were prepared byylene
selectivity was improved with an increase in the Si/Almonium
hexaurosilicate (AHFS) (Del-Al-MCM-22) resulted
ylene selectivity at a very high n-hexane conversion. This mayt
of Lewis acid sites which accelerate the hydride transfer and
(Si/Al = 62) catalyst showed a high propylene selectivity (40
H-Beta catalysts with similar Si/Al ratios at a high
n-hexanetalytic life comparable with H-ZSM-5 and longer than
H-Beta
2014 Elsevier B.V. All rights reserved.
-
Please cit , http
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 112 Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx
has been proved to be a shape-selective catalyst in the
alkyla-tion [18,19], disproportionation and isomerization [2023],
etc.Obviously, the acid properties (amount, location, type and
strength)can also play important roles in these catalytic
reactions. As weknown, thethe zeolite.
A numblite, concluof about 10lite [24,25]methods
arPost-syntheSi/Al ratios sion of deboprecursor hamount andboth
decreaobtaining hacid leachinand acid lea[20,2730],MCM-22 ar
MCM-22for FCC proas crackingless dry gasMCM-22 shratio and athat
of the in n-heptan[33], who fodue to trapcages with ing occurs tthe
supercasoidal chanimpossible Though thewas explaining the acid
In this swith differemethods ancracking ofto producecatalytic
pediscussed.
2. Experim
2.1. Catalys
H-MCM-pared by twsynthesis mAl contentssynthesizeddirecting
aaluminate (respectivelypH. DeboroMWW boroing in 6 M Hthe
crystallof 1 SiO2:0.MWW-type
post-synthesis method. Del-B-MWW zeolite was used as a Si
sourceand added into an aqueous solution of sodium aluminate and
HMIunder stirring. The resulting mixture had a molar composition
of1 SiO2:(0.0050.007) Al2O3:1 HMI:30H2O. The crystallization
was
outauto, wawideor 10-form
1 M N73 Kst-sy-22
etermlumed frs so. Thebtainto 0.066 wt wit
Cata M H
talys
catatios on spdiffraaku)tion
instr HitacM). Ttler Tmmeed oollectra oted wt in acuasorp(1.3
kmoved at
talyt
cataw ret (18tivatactor
PureactorTo int wem 1.t.
reacraphn (50e this article in press as: Y. Wang, et al., Appl.
Catal. A: Gen. (2015)
acid properties are closely related to the Si/Al ratio in
er of studies dealt with the synthesis of MCM-22 zeo-ding that
only a very narrow range of the Si/Al ratio25 is suitable for the
synthesis of pure MCM-22 zeo-. Besides the direct synthesis
methods, post-synthesise also frequently used for preparing high
silica zeolites.sis of highly crystalline MWW zeolite with
variablein a wide range (12500) through the structural
conver-ronated Si-MWW zeolite to lamellar Al-MWW zeoliteas been
studied by Liu et al. [26]. They found that the
strength of Brnsted acid sites in H-MCM-22 zeolitesed with
increasing Si/Al ratios. Another method forigh silica MCM-22
zeolites is dealumination includingg, hydrothermal treatment,
combination of steamingching, ammonium hexauorosilicate (AHFS)
treatment
etc. Obviously, the acid properties in dealuminatede dependent
on the different delamination methods.
has also proved to be a good cracking zeolite additivecess
[31,32]. Corma et al. [32] found that when used
additive, MCM-22 produced less total gases, as well ases, with a
lower loss of gasoline than ZSM-5. Moreover,owed higher
propylene/propane and butane/butane
good steam stability which was even higher thanZSM-5 zeolite.
The catalytic performance of MCM-22e cracking have been
investigated by Meloni et al.und that a very fast initial
deactivation was occurred,ping of carbonaceous compounds (coke) in
the largesmall apertures. They suggested that n-heptane
crack-hrough the classical carbenium ion chain mechanism inges,
however it occurs through protolysis in the sinu-nels, the
bimolecular reaction of hydride transfer beingin the narrow space
available near the protonic sites.
role of shape selectivity on the catalytic performanceed in the
above paper, the role of acid properties includ-
amount, strength and type was seldom investigated.tudy, the
catalytic performance of MCM-22 catalystsnt Si/Al ratios
synthesized by direct or post-synthesisd treated with AHFS was
investigated for the catalytic
n-hexane as a model reaction of naphtha cracking propylene. In
addition, the relationship between therformance and the acid
properties of the catalysts was
ental
t preparation
22 zeolite catalysts with different Si/Al ratios were pre-o
methods according to literature [26,34]. (1) Directethod was used
for the synthesis of zeolites with high
. The MCM-22 lamellar precursors were hydrothermally by using
hexamethyleneimine (HMI) as a structure-gent (SDA). Fumed silica
(Cab-o-sil M5) and sodium58.3% Al2O3, 32.3% Na2O) were used as Si
and Al sources,, and sodium hydroxide was used to adjust the
gelnated MWW (Del-B-MWW) obtained by calcination ofsilicate zeolite
at 873 K for 20 h, followed by reux-NO3 at 393 K for 20 h, was used
as seed to speed up
ization. The resulting mixture had a molar composition15
Na2O:(0.01250.025) Al2O3:0.9 HMI:45H2O. (2) The
precursors with low Al contents were synthesized by a
carriedunder lteredwith a 823 K fThe Nait withair at 7and
poH-MCMratio d
Deaobtainaqueoufor 3 hwere o0.005 Si/Al = catalyserencewith
1
2.2. Ca
TheSi/Al raemissiX-ray III (RigadsorpJapan)with a(FE-SEa
Metprograrecordwere cIR specsupporwas sewas evThe advapor then
rerecord
2.3. Ca
Thebed ocatalysand acthe re(Wakothe re6 kPa. catalysied
froamoun
Thematogcolum://dx.doi.org/10.1016/j.apcata.2014.12.018
in rotated (20 rpm) Teon-lined stainless autoclavesgenous
pressure at 423 K for 5 days. The samples wereshed, and dried at
373 K to produce lamellar precursors
range of Si/Al ratios. Direct calcination of the samples at h
resulted in the products with the 3D MWW structure.
MCM-22 was transformed into the H-form by treatingH4NO3 twice at
353 K for 2 h, followed by calcination in
for 2 h. The H-form MCM-22 zeolites prepared by directnthesis
methods were named H-MCM-22 (n) and Post-
(n), respectively, in which n denotes the Si/Al molarined by
ICP-AES analysis.
inated MCM-22 (Del-Al-MCM-22) catalysts wereom H-MCM-22 (Si/Al =
19) by the dealumination withlution of ammonium hexaurosilicate
(AHFS) at 363 K
Del-Al-MCM-22 catalysts with different Al contentsed by varying
the concentration of AHFS solution from5 M. For control, a
small-sized H-ZSM-5 catalyst withas synthesized according to
literature [13] and H-Betah Si/Al = 67 was obtained from H-Beta
(Si/Al = 12) (Ref-lyst, The Catalysis Society of Japan) by
dealuminationNO3 solution at 393 K for 1 h.
t characterizations
lysts were characterized by various techniques. Thewere
determined by inductively coupled plasma-atomicectrometer (ICP-AES)
on a Shimadzu ICPE-9000. Thection (XRD) patterns were recorded on a
Rint-Ultima
diffractometry using a Cu K X-ray source. The N2was carried out
at 77 K on a Belsorp-mini II (BELument. The crystal morphology and
size were examinedhi S-5200 eld-emission scanning electron
microscopehermogravimetric analyses (TGA) were carried out onGA/SDT
apparatus in air atmosphere. Temperature-d desorption of ammonia
(NH3-TPD) spectra weren a Multitrack TPD equipment (Japan BEL). IR
spectrated on a Nicolet NEXUS-FTIR-670 spectrometer. Thef adsorbed
pyridine were recorded as follows: a self-afer (9.6 mg cm2 in
thickness and 2 cm in diameter)
a quartz IR cell, sealed with CaF2 windows, and thented at 723 K
for 2 h before the pyridine adsorption.tion was carried out by
exposing the wafer to pyridinePa) at 423 K for 0.5 h. The
physisorbed pyridine wased by evacuation at 423 K for 1 h. The IR
spectra were
423 K.
ic cracking
lytic cracking of n-hexane was carried out with a xed-actor
under atmospheric pressure. Typically, 0.1 g of30 mesh) was put
into a tubular reactor (6 mm in i. d.)ed in an air ow of 20 ml min1
at 923 K for 1 h. After
temperature was adjusted to the desired, n-hexane Chemicals
Ind.) vapor diluted in helium was fed into. The initial partial
pressure of n-hexane was set atvestigate the effect of contact
time, the ratio of theight to the n-hexane ow rate (W/Fn-hexane)
was var-6 to 64 g-cat h/mol-n-hexane by changing the catalyst
tion products were analyzed with an on-line gas chro- (Shimadzu,
GC-14B) with an FID detector and a HP-AL/S
m 0.32 mm 8 m). The selectivities to the products
-
Please cite
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 11Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx 3
1000 A 1000 B
Fig. 1. XRD pa d) and(d).
were calculwas calculaloss from 6contents of
3. Results
3.1. Physico
All of thMWW topono impurityAs shown inBET surfaceN2
adsorptiimages of scof H-MCM-ples were cin length anmorphologygels
and thedifferent Alpatterns (Fiobserved inparent matessentially
Table 1 MCM-22 zedealuminatof the alum0.005 M AHthe Si/Al ratThe
specicMCM-22 saan increasewith an incthe micropoexternal suAHFS
treatmin a signicaber of agglohappen throneighboringa chemical
3 sh22 carol
and idiceak he act cor22 ze
of Alnto tect ocreaer he in FS trlite.SM-5cated
area (Si/e sizee of Al raimila3530252015105
d
c
b
Inte
nsity
/ cp
s
2Theta / degree
a
5
Inte
nsity
/ cp
s
tterns of H-MCM-22 samples (A) with Si/Al ration of 19 (a), 34
(b), 66 (c) and 100 (
ated based on the carbon numbers. The coke amountted by
thermogravimetric analysis (TGA). The weight73 to 1073 K in each TG
prole was dened as the
coke on the used catalyst.
and discussion
chemical characteristics of the zeolites
e H-MCM-22 zeolites synthesized in this study had thelogy and a
relatively high crystallinity, and contained
of other phase as detected by XRD patterns (Fig. 1A). Table 1,
the H-MCM-22 samples had reasonably high
areas in the range of 448540 m2 g1 as determined byon, which
indicated that they were of good quality. Theanning electron
micrographs (SEM) revealed that both22 (Si/Al = 19) and
Post-H-MCM-22 (Si/Al = 100) sam-omposed of ake-like crystals,
approximately 500 nmd 50 nm in thickness (Fig. 2a and b). Thus, the
crystal
and size were not dependent on the Si/Al ratio in the synthesis
method. The Del-Al-MCM-22 samples with
contents were further characterized by powder XRDg. 1B). After
dealumination by AHFS, little change was
their diffraction patterns compared with those of theerial.
Namely, the crystal structure of MCM-22 zeolite
Fig.MCM-these pl-peaknon-acthe h-pThus, tamounMCM-to thatrated
ithe dirwas dethe othincreasthe AH22 zeo
H-Zas indisurfaceH-Betaaveragage sizthe Si/were s this article
in press as: Y. Wang, et al., Appl. Catal. A: Gen. (2015), http
remained.lists the Si/Al ratios and textural properties of
Del-Al-olite catalysts. It can be seen that AHFS is an effectiveion
reagent for MCM-22 zeolite, and more than 40%inum atoms can be
removed by the treatment withFS solution. With an increase in the
AHFS concentration,io increased, which is consistent with the
literature [30].
surface area and micropore pore volume of of Del-Al-mples are
also listed in Table 1. It can be seen that with
in the Si/Al ratio of the Del-Al-MCM-22 samples, viz.reasing in
the AHFS concentration, the surface area andre volume of the
samples slightly decreased, while the
rface area was almost constant. On the other hand, theent,
especially with high AHFS concentration, resultednt fragmentation
of crystal morphology to form a num-merates (Fig. 2d). The
formation of agglomerates couldugh binding of the surface hydroxyl
groups (Si-OH) of
crystallites, which can be facilitated in the presence ofagent
like AHFS [35].
3.2. Catalyt
3.2.1. EffectThe effe
ing of n-heThe initial the temperity to propybetween 72ture,
appareinto aromatity to butenBTX (benzewas low coature; howthe
reactionnium ions, 3530252015102Theta / degree
d
c
b
a
Del-Al-MCM-22 samples (B) with Si/Al ratio of 34 (b), 56 (c) and
62
ows the NH3-TPD proles of H-MCM-22 and Del-Al-talysts with
different Al contents. As shown in Fig. 3, alles were composed of
two desorption peaks so-calledh-peak. The l-peak corresponds to NH3
adsorbed onOH groups and on NH4+ by hydrogen bonding,
whilecorresponds to NH3 adsorbed on true acid sites [36,37].id
amount was calculated by the area of h-peak. The acidresponded to
only 6377% of the total Al content in H-olites (Table 1). The low
concentration of acid relative
are attributed to the fact that the portion of Al incorpo-he
MCM-22 framework was not very high, regardless ofr post-synthesis
methods. Obviously, the acid amountsed with the Si/Al ratio
increased (Fig. 3A, Table 1). Onand, the acid amount was gradually
decreased with anthe AHFS concentration (Fig. 3B, Table 1), which
meanseatment is an effective dealumination method for MCM-
and H-Beta catalysts had relatively high crystallinities by XRD
patterns (not shown) and reasonably high BETs (Table 1). As shown
in Fig. 2, H-ZSM-5 (Si/Al = 66) and
Al = 67) were composed of cofn-like crystals with an of about
200 nm and sphere-like crystals with an aver-about 100 nm,
respectively (Fig. 2e and f). In addition,tio and acid amount of
H-ZSM-5 and H-Beta catalystsr to those of Del-Al-MCM-22 catalyst
(Table 1).://dx.doi.org/10.1016/j.apcata.2014.12.018
ic cracking of n-hexane over H-MCM-22 catalysts
of reaction temperaturect of the reaction temperature on the
catalytic crack-xane over H-MCM-22 (Si/Al = 19) is shown in Fig.
4.conversion of n-hexane increased with an increase inature,
achieving nearly 100% at 923 K. The selectiv-lene was almost
constant in the temperature ranging3 and 923 K. With an increase in
the reaction tempera-ntly butenes once formed were gradually
transformedic compounds, resulting in the decrease in the
selectiv-es accompanied with the increase in the selectivity tone,
toluene, and xylenes). The selectivity to ethylenempared with those
to other alkenes at low temper-ever, the value increased steeply
with an increase in
temperature. Ethylene is formed via primary carbe-regardless of
whether the monomolecular mechanism
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ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 114 Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx
Table 1Physicochemical properties of various catalysts.
Cat CAHFS/M Si/Ala Al contentb/mmol g1 Acid contentc/mmol g1
SBETd/m2 g1 S Exte/m2 g1 V microe/cm3 g1
H-MCM-22 (19) 19 0.84 0.53 517 92 0.17H-MCM-22 (34) 34 0.48 0.37
412 74 0.14Post-H-MCM-22 (66) 66 0.25 0.17 594 96 0.20Post-H-MCM-22
(100) 100 0.17 0.12 562 92 0.19
Del-Al-MCM-22 (34) 0.005 34 0.48 0.31 497 97 0.16Del-Al-MCM-22
(56) 0.02 56 0.29 0.23 466 112 0.14Del-Al-MCM-22 (62) 0.05 62 0.26
0.16 450 127 0.13
H-ZSM-5 (66) 66 0.25 0.19 445 24 0.18H-Beta (67) 67 0.25 0.18
587 201 0.15
a Molar ratio determined by ICP.b Calculated by ICP result.c
Determined by NH3-TPD.d Measured by N2 adsorption at 77 K.e
Calculated by t-plot method.
or the bimolecular mechanism operates [5,7] and therefore
theapparent activation energy for ethylene formation should be
high.Thus, the higher reaction temperature is of benet to the
higherethylene yield. Moreover, the cracking via the
monomolecularmechanism may be of more advantage in the ethylene
forma-tion. The selectivities to propane and butanes decreased with
an
increase in the reaction temperature, because the subsequent
reac-tions of propane and butanes take place at high
temperatures,resulting in the formation of alkenes, BTX and so on
[38]. In addi-tion, the selectivities to methane and ethane, which
form solely viathe monomolecular mechanism, are higher at the
higher reactiontemperatures. These ndings clearly indicate that the
cracking via
Fig. 2. SEM imH-Beta(Si/Al =e this article in press as: Y. Wang,
et al., Appl. Catal. A: Gen. (2015), http
ages of H-MCM-22(Si/Al = 19) (a), Post-H-MCM-22(Si/Al = 100)
(b), Del-Al-MCM-22(Si/A 67) (f)
samples.://dx.doi.org/10.1016/j.apcata.2014.12.018
l = 34) (c), Del-Al-MCM-22(Si/Al = 62) (d), H-ZSM-5(Si/Al = 66)
(e) and
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Please cite
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 11Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx 5
900800700600500400300
H-MCM-22(19) Del-Al-MCM-22(39) Del-Al-MCM-22(56)
Del-Al-MCM-22(62)
Temperature / K
B
900800700600500400300
H-MCM-22(19) H-MCM-22(34) Post-HMCM-22(66) Post-HMCM-22(100)
Temperature / K
A
Fig. 3. NH3-TPD proles of H-MCM-22 (A) and Del-Al-MCM-22 (B)
samples with different Si/Al ratios.
the monomolecular mechanism is more predominant at the
hightemperature.
According to the product distributions at different
reactiontemperatures, we conclude that higher reaction temperature
isbenecial toet al. report[14].
3.2.2. EffectThe effe
gated. The weight to thchange of ccracking coincreased wat the
W/Fnthe decreaspanied withBTX is formhand, primaat the highene
would butanes an
Sel
. / C
-%
Fig. 4. Effect on H-MCM-22n-hexane = 64 g-c
ethylene selectivity [38]. Meanwhile, the selectivities to
propaneand butanes decreased with an increase in the conversion,
whilethose to methane and ethane simultaneously increased.
Effect widir Si/
on tifferel conhexaic crmal e thes, th
ln(
kc isnversspecounhe li n-hexane conversion and propylene
production. Kuboed similar results in n-heptane cracking over
H-ZSM-5
of contact timect of the contact time on the reaction was
investi-contact time expressed as the ratio of the catalyste
n-hexane ow rate (W/Fn-hexane) was changed by theatalyst weight to
keep the contribution of the thermalnstant. As shown in Fig. 5, the
conversion of n-hexaneith an increase in W/Fn-hexane, achieving
nearly 100%
-hexane of 64 g-cat h/mol-n-hexane. Fig. 5 indicates thate in
the selectivities to propylene and butenes is accom-
the increase in the selectivity to BTX, suggesting thated mainly
from propylene and butenes. On the otherry carbenium ions would be
relatively easy to produce
reaction temperature of 923 K [5,7]. Therefore, ethyl-be formed
not only by n-hexane cracking but also byd/or propane cracking,
resulting in an increase in the
50 100
3.2.3. It is
on theaciditywith dof the Athat n-catalytof therand
thkinetic
kcW
F=
wherethe colyst, reacid amtures. T this article in press as: Y.
Wang, et al., Appl. Catal. A: Gen. (2015), http
9509008508007507006500
10
20
30
40
Con
v./ %
Temperature / K
0
20
40
60
80
of reaction temperature on the catalytic cracking of
n-hexane(Si/Al = 19). Reaction conditions: Cat., 0.1 g; Pn-hexane =
6 kPa; W/Fat h/mol-n-hexane; temp., 723923 K, TOS = 15 min.
Fig. 5. Effect 22(Si/Al = 19). temp., 923 K, o of Al contentely
known that acidity of zeolites is largely dependentAl molar ratios.
In order to elucidate the effect of thehe catalytic cracking of
n-hexane, H-MCM-22 zeolitesnt Si/Al ratios were employed as
catalysts. First, effecttent on catalytic activity was
investigated. We considerne cracking at such high temperatures is
the sum of theacking and the thermal cracking since the
contributioncracking is not negligible. If both the catalytic
crackingrmal cracking at high temperatures obey the rst-ordere
following equation is derived;
11 x
) ln
(1
1 xp
)(1)
the rate constant for the catalytic cracking, x and xp areion
for the n-hexane cracking with and without cata-tively [14]. Fig. 6
shows the dependence of kc on thet of H-MCM-22 catalysts at
different reaction tempera-near relationship between log kc and log
acid amount of
50 100://dx.doi.org/10.1016/j.apcata.2014.12.018
807060504030201000
10
20
30
40
Con
v. /
%
Sel
. / C
-%
W/Fn-hexane / g h mol-1
0
20
40
60
80
of contact time on the catalytic cracking of n-hexane on
H-MCM-Reaction conditions: W/F n-hexane = 6.464 g-cat
h/mol-n-hexane;thers see Fig. 4.
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ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 116 Y. Wang et
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0.0-0.2-0.4-0.6-0.8-1.0-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
logk
c
log (Acid amount)
c
b
a
Fig. 6. Dependence of kc on the acid amount of H-MCM-22
catalysts at differentreaction temperatures of 723 K (a), 823 K (b)
and 923 K (c).
H-MCM-22 catalyst was observed at every reaction temperature.
Asshown in Fig. 6, the slopes of the straight line observed in the
logkc vs. log (Acid amount) plots are 1.8, 1.6, and 1.3 at 823,
873, and923 K, respectively. The kc is almost proportional to the
acid sitedensity at 923 K; however, at lower temperatures the
effect of theacid site density is enhanced with a decrease in
reaction tempera-ture. Haag ecracking of acid site den-heptane
cSi/Al ratios
Then, thwas investselectivitiesn-hexane cdecrease inties
slightlydecreased. amount supcyclization-Thus the H-the higher
hexane. Meand/or prop
Fig. 7. Relatiocatalysts at antemp., 923 K, T
100
Fig. 8. Changecatalysts withFig. 4.
923 K was in the decrincrease inhere).
ides for a
in -22
tivityhe H) gavas tha. 80
cont wi
of min
a lae amne hich
e trag, eted ted
win increase the diffusion limitation, leading to the high
cokeion. The coke composition and the mode of deactivation int al.
reported that the catalytic activity in the catalyticn-hexane at
811 K over H-ZSM-5 is proportional to thensity [3941]. A similar
dependence of n-hexane andracking on the acid density over H-ZSM-5
with varioushas been reported by Post et al. and Kubo et al.
[6,14].e effect of the Al content on products distributionigated.
Fig. 7 shows the relationship between the
and the acid amount of H-MCM-22 catalysts at anonversion of ca.
80%. It can be seen that, with a
the acid amount, propylene and butenes selectivi- increased
while ethylene and BTX selectivities slightlyThese ndings suggest
that the decrease in the acidpressed the secondary reactions
(hydride transfer andaromatization) of propylene and butenes to
form BTX.MCM-22 catalysts with the higher Si/Al ratios
showedpropylene selectivity in the catalytic cracking of n-anwhile,
the subsequent cracking reaction of butanesane to form ethylene at
high reaction temperature of
40
50
Besfactor changeH-MCMtial acratio. Tand 34whereonly
chexanecatalysversionof 210tion ofof largsons. Osites,
whydridcouplinbe relaconnec10-MRwouldformate this article in press
as: Y. Wang, et al., Appl. Catal. A: Gen. (2015), http
0.60.50.40.30.20.10.00
10
20
30
BTX
Sel
. / C
-%
Acid amount / mmol g-1
nship between product selectivities and acid amount of H-MCM-22
n-hexane conversion of ca. 80%. Reaction conditions: Pn-hexane = 6
kPa;OS = 15 min.
n-heptane and establi22 (Si/Al = 1due to the sion of hydThese
resucontents exAl contents
In additistability. Mlyst exhibitto large extHowever, incontents
bymorphologsize on cata0
20
40
60
80
H-MCM-22(19) H-MCM-22(34) Post-H-MCM-22(66)
Post-H-MCM-22(100)
120 150 180 210 2409060300TOS / min
Coke wt./%
9.56.52.21.4
Con
v. /
%
in n-hexane conversion with time on stream (TOS) for H-MCM-22
different Si/Al ratios. Reaction conditions: temp., 923 K, others
see
reduced with a decrease in the acid amount, resultingease in the
ethylene selectivity accompanied with the
the selectivties to butanes and propane (not shown
activity and selectivity, stability is another
importantpplications of catalysts in industry. Fig. 8 shows
then-hexane conversion with time on stream (TOS) for
catalysts with different Si/Al ratios. Obviously, the ini- and
deactivation rate closely depended on the Si/Al-MCM-22 catalyst
with higher Al contents (Si/Al = 19e nearly 100% n-hexane
conversion at the initial stage,e catalyst with a lower Al content
(Si/Al = 100) showed% conversion of n-hexane. A sharp decrease in
the n-version with TOS was observed for the H-MCM-22th high Al
contents. For example, the n-hexane con-H-MCM-22 (Si/Al = 19)
decreased to ca. 60% at TOS. This deactivation was probably due to
the deposi-rge amount of coke (95 mg/g-catalyst). The formationount
of coke can be explained by two possible rea-reason may be related
to the high amount of acid
would accelerate the secondary reactions includingnsfer,
cyclization-aromatization and dehydrogenatingtc. and resultant coke
formation. Another reason mayto the special structure of MCM-22
zeolite. The non-property between 12- and 10-MR channels and thedow
openings accessible to the 12-MR
supercages://dx.doi.org/10.1016/j.apcata.2014.12.018
cracking over MCM-22 zeolite had been investigatedshed by Meloni
et al. [33]. In the case of Post-H-MCM-00) catalyst, the
deactivation rate was relative slow,smaller amount of acid sites
leading to the suppres-ride transfer and coke formation (14
mg/g-catalyst).lts indicate that H-MCM-22 catalysts with lower
Alhibit a better stability than the catalysts with higher.on, the
crystallite size might strongly affect the catalyticochizuki et al.
reported the small-sized H-ZSM-5 cata-s a higher stability in
n-hexane catalytic cracking, owingernal surface area and short
diffusion path length [13].
our present study, MCM-22 catalysts with different Al direct or
post-synthesis method had similar crystallitey and sizes (Fig.
2ad). Thus, the inuence of crystallitelytic stability could not be
examined.
-
Please cite
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 11Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx 7
120 150 180 210 24090603000
20
40
60
80
100
H-MCM-22(19) Del-Al-MCM-22(39) Del -Al-MCM-22(56) Del
-Al-MCM-22(62)
Con
v. /
%
TOS / min
Coke wt. / %
9.56.8
2.23.4
Fig. 9. Change in n-hexane conversion with time on stream (TOS)
for H-MCM-22(Si/Al = 19) and Del-Al-MCM-22 catalysts with different
Si/Al ratios. Reactionconditions: temp., 923 K, others see Fig.
4.
3.3. Catalytic cracking of n-hexane over Del-Al-MCM-22
catalysts
From the results reported above, H-MCM-22 catalysts withlower Al
contents prepared from the post-synthesis methodexhibited the
higher propylene selectivity. However, the catalytic
stability was still not satisfactory. Thus, the catalytic
performance ofseveral high-silica MCM-22 zeolites prepared by the
dealuminationwas further investigated.
Fig. 9 shows the change in n-hexane conversion with TOSfor
H-MCM-22 (Si/Al = 19) and Del-Al-MCM-22 catalysts with dif-ferent
Si/Al ratios. The stability of Del-Al-MCM-22 catalysts wasgreatly
improved by the dealumination, though the initial
n-hexaneconversion slightly decreased. In the case of
Del-Al-MCM-22(Si/Al = 62), the initial n-hexane conversion was
about 95%, andonly slightly decreased to 88% at 210 min. This also
may be dueto the smaller amount of acid sites in the Del-Al-MCM-22
catalyst,resulting in suppression of the hydride transfer and coke
forma-tion (22 mg/g-catalyst). It is noted that the catalytic
stabilities ofPost-H-MCM-22 (Si/Al = 66) and Del-Al-MCM-22 (Si/Al =
62) cata-lysts were different, though they had similar Si/Al ratios
and acidamounts. This nding indicates that some other factor than
the acidamount affects the catalytic stability, which is to be
discussed inSection 3.5. In addition, the amount of coke on the
Post-H-MCM-22(Si/Al = 66) and Del-Al-MCM-22 (Si/Al = 62) catalysts
was nearly thesame, however the stabilities were different,
indicating the differ-ent coke compositions and locations on the
two catalysts. This maybe due to the difference in the type,
strength and location of acidsites.
Fig. 10 shows the changes in selectivities to alkenes and BTXin
the n-hexane conversion on H-MCM-22 (Si/Al = 19) and Del-Al-MCM-22
catalysts with different Si/Al ratios. As shown in Fig. 10,for
H-MCM-22 (Si/Al = 19) catalyst, the selectivities to propylene
Fig. 10. Changratios. Reactio this article in press as: Y. Wang,
et al., Appl. Catal. A: Gen. (2015), http
es in selectivities to C3= (A), C2= (B), C4= (C) and BTX (D)
with n-hexane conversion on H-Mn conditions: see Fig.
5.://dx.doi.org/10.1016/j.apcata.2014.12.018
CM-22(Si/Al = 19) and Del-Al-MCM-22 catalysts with different
Si/Al
-
Please cit
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 118 Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx
Fig. 11. Chang(Si/Al = 66), H-conditions: tem
and buteneversion, whselectivity the n-hexanCompared
Al-MCM-22butenes andat high n-hlysts showen-hexane cof
Del-Al-Malmost conof 95%. Theform BTX frbutanes andature of 923was
decrea
3.4. Compawith H-ZSM
In the pr22 was alsowhich are tshows the 5, H-Beta aand acid am5
(Si/Al = 66nearly 100%during the This may bezeolite,
whideactivatiotle lower inwas still gooto coke forto its acid sof
H-ZSM-5high initial
coke formed thereon during the reaction for 210 min (107
mg/g-catalyst) was much higher than those on the other two
catalysts,leading to a signicant deactivation. Despite the milder
acidity ofH-Beta catalyst compared with H-MCM-22 and H-ZSM-5
catalysts
he po comide has y of
andf 72
cavn adve i-22
fn-l.
12 s-hexlystsectivreasecreaAl = 6nt (coreo
showtaly
of Ms indt is sic crn co
vestianc
show on
Withts, thhe dts we in n-hexane conversion with time on stream
(TOS) for H-ZSM-5Beta (Si/Al = 67) and Del-Al-MCM-22 (Si/Al = 62)
catalysts. Reactionp., 923 K, others see Fig. 4.
s were decreased along with increasing n-hexane con-ile those to
ethylene and BTX were increased. The
to propylene was decreased from 41 to 30 C-% whene conversion
was increased from 60% to nearly 100%.
with the parent H-MCM-22(Si/Al = 19) catalyst, Del- catalysts
showed high selectivities to propylene and
simultaneously low selectivities to ethylene and BTXexane
conversions. In addition, Del-Al-MCM-22 cata-d higher selectivities
to butanes and propane at highonversions (not shown here). For
example, in the caseCM-22(Si/Al = 62), the propylene selectivity
was kept
stant (ca. 40 C-%) even at a high n-hexane conversionse ndings
indicate that the secondary reactions toom propylene and butenes
and the cracking reaction of/or propane to form ethylene at high
reaction temper-
K were suppressed when the acid amount of catalyst
[42], tof coketheir wresult stabilitH-Betaature oand/or[31].
Ialso haof MCMthe co(Fig. 2)
Fig.with n22 catathe selan incBTX in22 (Si/consta95%. M95%,
itBeta caabilityndingcatalyscatalytreactio
3.5. Inperform
As closelyalysts.catalysing in tcatalyse this article in press
as: Y. Wang, et al., Appl. Catal. A: Gen. (2015), http
sed.
rison of the catalytic performance of Del-Al-MCM-22-5 and H-Beta
catalysts
esent study, the catalytic performance of Del-Al-MCM- compared
with that of H-ZSM-5 and H-Beta catalysts,he catalyst mostly used
in FCC process [31,32]. Fig. 11change in n-hexane conversion with
TOS for H-ZSM-nd Del-Al-MCM-22 catalysts with similar Si/Al
ratiosounts. Among these catalysts investigated, the H-ZSM-)
catalyst gave a high initial n-hexane conversion of
and the highest stability. The amount of coke formedreaction for
210 min was very low (29 mg/g-catalyst).
related to the tridirectional 10-MR channels in ZSM-5ch is
benecial to the mass transfer, leading to very lown. The
Del-Al-MCM-22 (Si/Al = 62) catalyst showed a lit-itial n-hexane
conversion (95%); however the stabilityd. The resistivity of
Del-Al-MCM-22 (22 mg/g-catalyst)
mation was as high as that of H-ZSM-5, probably duetrength and
density of acid sites are similar to those
[36]. Although H-Beta (Si/Al = 67) catalyst showed a n-hexane
conversion (nearly 100%), the amount of
lysts showelife than Hbe ascribedthe secondatransfer to 5
zeolite wbetter perfoethylene [4
It is welstrength anthe catalytishowed thetroscopy won the
type
Fig. 13 sent Si/Al radesorbed astretching vtwo strongexternal
siladdition, tware
assigneframework://dx.doi.org/10.1016/j.apcata.2014.12.018
lymerization of olens and the successive formationponents in the
3-dimensional 12-MR micropores and
intersections may predominantly occur [15]. A similarbeen
reported by Corma et al., who suggest that the
H-MCM-22 zeolite is intermediate between those of H-ZSM-5 in
n-heptane cracking at the lower temper-3 K, mainly because MCM-22
zeolite has larger poresities than ZSM-5 and smaller ones than Beta
zeolitedition, the crystallite size and morphology of
zeolitenuenced on the mass transfer. The ake-like crystal
zeolite is benecial to the mass transfer, compared toike crystal
ZSM-5 and sphere-like crystal Beta zeolite
hows the changes in selectivities to alkenes and BTXane
conversion on H-ZSM-5, H-Beta and Del-Al-MCM-. As shown in Fig. 12,
for H-ZSM-5 and H-Beta catalysts,ities to propylene and butenes
steeply decreased with
in n-hexane conversion, while those to ethylene andsed
drastically. However, in the case of Del-Al-MCM-2) catalyst, the
propylene selectivity was kept almosta. 40 C-%), even at an
n-hexane conversion as high asver, when the n-hexane conversion was
higher thaned a lower BTX selectivity than either H-ZSM-5 or H-
sts, which could be due to the inferior hydride transferCM-22
catalyst at high n-hexane conversions [43]. Theseicate that the
catalytic performance of Del-Al-MCM-22uperior to that of H-ZSM-5
and H-Beta catalysts in theacking of n-hexane to produce propylene
under thesenditions.
gation of the relationship between catalytice and acidity of
MCM-22 catalysts
n in Figs. 610, the catalytic performance dependedthe Si/Al
ratio of H-MCM-22 and Del-Al-MCM-22 cat-
increasing Si/Al ratio of H-MCM-22 or Del-Al-MCM-22e acid amount
was decreased (Fig. 3, Table 1), result-ecrease in the cracking
activity of catalysts. H-MCM-22ith the higher Si/Al ratios and
Del-Al-MCM-22 cata-d a higher propylene selectivity and longer
catalytic-MCM-22 catalysts with high Al contents. This could
to the decrease in the acid amount, which suppressedry reaction
of propylene and butenes and the hydrideform coke. Similarly, Zhu
et al. also reported the ZSM-ith lower acid amount (higher Si/Al
ratio) exhibitedrmance in butene catalytic cracking to propylene
and4].l know that not only the acid amount but also the acidd type
of acid site, Brnsted or Lewis acid site affectc performance.
However, the results of NH3-TPD only
change of the acid amount. So, the pyridine-IR spec-as
investigated to provide more detailed information
and amount of acid sites and their strength.hows the IR spectra
of H-MCM-22 catalysts with differ-tios before (A) and after (B)
pyridine was absorbed andt 423 K. As shown in Fig. 13A, in the
region of hydroxylibration, the H-MCM-22 (Si/Al = 19) catalyst
exhibited
bands at 3743 and 3615 cm1, which are attributed toanols and
structural Si(Al)OH hydroxyls, respectively. Ino weak bands
appeared at 3727 and 3663 cm1, whichd to internal silanols and
hydroxyls related to extra-
Al, respectively [20,34]. The 3615 cm1 band gradually
-
Please cite
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 11Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx 9
Fig. 12. Changcatalysts. Reac
Fig. 13. IR spe
decreased ia decrease Post-H-MCMcantly in in this article in
press as: Y. Wang, et al., Appl. Catal. A: Gen. (2015), http
es in selectivities to C3= (A), C2= (B), C4= (C) and BTX (D)
with n-hexane conversion on H-tion conditions: see Fig. 5.
11800
Abs
orba
nce
W
BSBAS
1.
1.
2.
2.
3200340036003800
Abs
orba
nce
Wavenumber / cm-1
a
b
c
d
0.1A
3727
36153500
37433663
ctra of H-MCM-22 catalysts with Si/Al ratio of 19 (a), 34 (b),
66 (c) and 100 (d) before (A)
n intensity with a decrease in Al content, indicatingin the
amount of Brnsted acid sites. In the case of-22 catalysts, the 3727
cm1 band increased signi-
tensity and a broad band around 3500 cm1 attributed
to hydrogedecreased. more
defecmethod.://dx.doi.org/10.1016/j.apcata.2014.12.018
ZSM-5 (Si/Al = 66), H-Beta (Si/Al = 67) and Del-Al-MCM-22 (Si/Al
= 62)
140015001600700
c
avenumber / cm-1
0.1
LAS
d
a
b
/SLAS9
9
8
6
BAS1543 1454
and after (B) pyridine was absorbed and desorbed at 423 K for 1
h.
n bonded silanols appeared when the Al content wasThese facts
indicate that Post-H-MCM-22 catalysts havet sites than the
catalysts prepared by the direct synthesis
-
Please cit
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 1110 Y. Wang
et al. / Applied Catalysis A: General xxx (2015) xxxxxx
Fig. 14. IR spe 9 (b)desorbed at 42
Then, thring-stretchas shown iattributed trespectively1543 and
1not only BrHowever, tharea of peaPost-H-MCMalysts; e.g.,
H-MCM-22tively. Thusof Lewis acdirect synthshown in Ficatalysts
exMCM-22 cathe dealumdue to the thesized MColens to etransfer
re[45].
Similarlyalysts withwas absorbally decreaswith a progthe
intensitand Lewis aluminationthe framewAHFS treatmdealuminatmore
readinot only thedealuminatminated M(Si/Al = 19) (Si/Al = 62) a
specttion he su
prois acion.
distn be
sho-22
M-22ing dthe ctes do 72ity of75% acreas
Del-creasctra of H-MCM-22 (Si/Al = 19) (a) and Del-Al-MCM-22
catalysts with Si/Al ratio of 33 K for 1 h.
e IR spectra of adsorbed pyridine in the range of pyridineing
modes after desorption at 423 K was measured,n Fig. 13B. The bands
at 1543 and 1454 cm1 wereo Brnsted acid sites (BAS) and Lewis acid
sites (LAS),. With a decrease in Al content, the intensity of
the454 cm1 band decreased simultaneously, indicatingnsted acid but
also Lewis acid decreased in amount.e ratio of BAS/LAS, which was
calculated by using theks ascribed to the Brnsted and Lewis acid
sites, for-22 catalysts was lower than that for H-MCM-22 cat-
the BAS/LAS ratios for Post-H-MCM-22 (Si/Al = 100) and (Si/Al =
19) were calculated to be 1.9 and 2.6, respec-, the Post-H-MCM-22
catalysts have higher proportionid sites than the H-MCM-22
catalysts prepared by theesis method. Based on the catalytic
performance resultsgs. 8 and 9, Section 3.2.3, although the
Post-H-MCM-22hibited better stabilities than the direct synthesized
H-talysts, their stabilities were not so high compared toinated
MCM-22 catalysts. The possible reason may behigher proportion of
Lewis acid sites in the post syn-
2.6, reproporlyst. Tlife andof Lewformat
Thesites caFig. 15H-MCMAl-MCfollowfor all acid si423 K tintensby
ca. tion incase ofwas ine this article in press as: Y. Wang, et
al., Appl. Catal. A: Gen. (2015), http
M-22 zeolites. Since the Lewis acid sites interact withnhance
their oligomerization and subsequent hydrideactions, leading to the
formation of coke products
, Fig. 14 shows the IR spectra of Del-Al-MCM-22 cat- different
Si/Al ratios before (A) and after (B) pyridineed and desorbed at
423 K. The 3615 cm1 band gradu-ed in intensity; however the 3743
cm1 band increasedress of dealumination (Fig. 14A). Fig. 14B showed
thaty of the 1543 and 1454 cm1 bands ascribed to Brnstedcid sites,
respectively, decreased with a progress of dea-. These ndings imply
that aluminum atoms not only inork but also of extra-framework are
removed by theent. Moreover the BAS/LAS ratio increased after
the
ion, which means that the Lewis acid sites are removedly than
the Brnsted acid sites. Thus, it was deduced
acid amount but also the acid type was changed withion using
AHFS treatment. The BAS/LAS ratios for dealu-CM-22 catalysts were
higher than that for H-MCM-22catalyst; e.g., the BAS/LAS ratios for
Del-Al-MCM-22nd H-MCM-22 (Si/Al = 19) were calculated to be 4.3
and
acid strengtwith that othe other hintensity ofdesorption ture
was inascribed to tively, whithan that othe
intensitunchangedPost-H-MCacid sites onDel-Al-MCMlower
stabicatalyst in nalso conclube another of Del-Al-Mcant role inmuch
heav, 56 (c) and 62 (d) before (A) and after (B) pyridine was
absorbed and
ively. Thus, the Del-Al-MCM-22 catalysts have lowerof Lewis acid
sites than the parent H-MCM-22 cata-periority of Del-Al-MCM-22
catalysts in the catalyticpylene selectivity could be due to their
smaller amountid sites which accelerate the hydride transfer and
coke
ribution of the acid strength of Brnsted and Lewis acid measured
from the thermal desorption of pyridine [46].ws the IR spectra in
the pyridine vibration region of
(Si/Al = 19) (A), Post-H-MCM-22 (Si/Al = 66) (B) and Del- (Si/Al
= 62) (C) catalysts after pyridine adsorption andesorption at
different temperatures. It is apparent thatatalysts, the intensity
of the band ascribed to Brnstedecreased with desorption temperature
increasing from3 K. For H-MCM-22 and Post-H-MCM-22 catalysts,
the
the band ascribed to Brnsted acid sites was reducednd 90%,
respectively when the temperature of desorp-ed from 423 K to 723 K.
No band was observed in theAl-MCM-22 catalyst when the desorption
temperatureed to 723 K. These facts demonstrate that the
Brnsted://dx.doi.org/10.1016/j.apcata.2014.12.018
h of Del-Al-MCM-22 catalyst is relatively low comparedf parent
H-MCM-22 and Post-H-MCM-22 catalysts. Onand, for H-MCM-22 and
Del-Al-MCM-22 catalysts, the
band ascribed to Lewis acid sites also decreased withtemperature
increased. When the desorption tempera-creased from 423 K to 723 K,
the intensity of the bandLewis acid sites was reduced by ca. 10%
and 50%, respec-ch suggests that the strength of Lewis acid is
higherf Brnsted acid in these two catalysts. It is noted thaty of
the band ascribed to Lewis acid sites was almost
with desorption temperature increased in the case ofM-22 (Si/Al
= 66), indicating that the strength of Lewis
Post-H-MCM-22 is higher than that of H-MCM-22 and-22 catalysts.
This could be a possible reason for the
lity of Post-H-MCM-22 compared with Del-Al-MCM-22-hexane
cracking. According to the above ndings, it is
ded that the decrease in the strength of acid sites wouldreason
for the higher propylene selectivity and stabilityCM-22 catalysts,
since strong acid sites play a signi-
coke formation and coke formed on strong acid sites isier than
that formed on weak acid sites [47].
-
Please cite
ARTICLE IN PRESSG ModelAPCATA-15156; No. of Pages 11Y. Wang et
al. / Applied Catalysis A: General xxx (2015) xxxxxx 11
e
0.1
d
A
e
0.1
c
d
C
140
e
-1
0.1
d
B
Fig. 15. IR spe (Si/Aadsorption and
4. Conclus
H-MCM-post-synthealytic crackacid amountion of prowas still
nothe Post-H-which accelalytic life awere improto the smalstrength
of propylene s(Si/Al = 67) cversion of 9that of H-ZS
Acknowled
This wochemistry popment Org
References
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Abs
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ctra in the pyridine vibration region of H-MCM-22 (Si/Al = 19)
(A) Post-H-MCM-22 desorption at 423 K (a), 523 K (b), 623 K (c),
and 723 K (d) for 1 h, respectively.
ions
22 catalysts with higher Si/Al ratios prepared by thesis method
showed higher propylene selectivity in cat-ing of n-hexane. This
could be attributed to the smallert, which resulted in suppression
of the secondary reac-pylene and butenes. However, the catalytic
stabilityt satisfactory. This can be explained by the fact
thatMCM-22 catalysts had more strong Lewis acid sites,erate the
hydride transfer and coke formation. The cat-nd propylene
selectivity at high n-hexane conversionsved by dealumination using
AHFS. This could be dueler amount of Lewis acid sites and the
decrease in theacid sites. Del-Al-MCM-22 (Si/Al = 62) showed a
higherelectivity (40 C-%) than H-ZSM-5 (Si/Al = 66) and
H-Betaatalysts with similar Si/Al ratios at a high n-hexane con-5%.
Moreover, the catalyst stability was comparable toM-5 and higher
than that of H-Beta catalyst.
gements
rk was partially supported by the green sustainableroject of New
Energy and Industrial Technology Devel-anization (NEDO).
[12] B.CHil
[13] H. MMic
[14] K. K126
[15] S. I[16] M.K[17] M.E
191[18] A. C[19] B. X
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Catalytic cracking of n-hexane for producing propylene on MCM-22
zeolites1 Introduction2 Experimental2.1 Catalyst preparation2.2
Catalyst characterizations2.3 Catalytic cracking
3 Results and discussion3.1 Physicochemical characteristics of
the zeolites3.2 Catalytic cracking of n-hexane over H-MCM-22
catalysts3.2.1 Effect of reaction temperature3.2.2 Effect of
contact time3.2.3 Effect of Al content
3.3 Catalytic cracking of n-hexane over Del-Al-MCM-22
catalysts3.4 Comparison of the catalytic performance of
Del-Al-MCM-22 with H-ZSM-5 and H-Beta catalysts3.5 Investigation of
the relationship between catalytic performance and acidity of
MCM-22 catalysts
4 ConclusionsAcknowledgementsReferences