Fuel 346 (2023) 128298
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0016-2361/© 2023 The Au ho (s). Published by Else ie L d. This is an open access a icle unde he CC BY-NC license (h p://c ea i ecommons.o g/licenses/by-
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E ec o wa e and me hanol concen a ion in he eed on he deac i a ion
o In
2
O
3
-Z O
2
/SAPO-34 ca alys in he con e sion o CO
2
/CO o ole ins
by hyd ogena ion
A. Po illo, O. Pa a, J. E e˜
na, A.T. Aguayo, J. Bilbao, A. A eka
*
Depa men o Chemical Enginee ing, Uni e si y o he Basque Coun y UPV/EHU, P.O. Box 644, 48080 Bilbao, Spain
ARTICLE INFO
Keywo ds:
CO
2
alo iza ion
Ole ins
SAPO-34
Tandem ca alys s
Deac i a ion
ABSTRACT
On accoun o he supe io pe o mance o In
2
O
3
-Z O
2
/SAPO-34 andem ca alys in he di ec syn hesis o ole ins
om CO, CO
2
and CO/CO
2
mix u e by hyd ogena ion, i is in e es ing o es ablish he condi ions o a oid i s
deac i a ion due o he apid coke deposi ion on SAPO-34. The co- eeding o H
2
O and/o me hanol oge he wi h
H
2
+CO
2
/CO was s udied in a packed bed eac o a : 400 ◦C, 30 ba ; CO
2
/CO
x
in he eed, 0–1; H
2
/CO
x
in he
eed, 1–3; and space ime o 5 g
ca
h mol
C
−1
, quan i ying he e olu ion wi h ime on s eam (up o 16 h) o CO
2
and
CO
x
con e sions and ole in, pa a in and CH
4
yields. The e ec s o he co- eeding on coke con en and i s na u e
we e de e mined by empe a u e p og ammed oxida ion (TPO) analyses o he spen ca alys . The esul s
highligh ed he complex e ec o he concen a ion o H
2
O and oxygena es (me hanol/dime hyl e he (DME)) on
he deac i a ion o SAPO-34 and on he p oduc s yields in he pseudo-s eady s a e o he ca alys . Co- eeding H
2
O
lessens coke deac i a ion, howe e , high H
2
O concen a ion leads o a enua e he acidi y o SAPO-34, limi ing
he pe o mance o he andem ca alys (mainly in he CO
2
con e sion). Oxygena es co- eeding concen a ion
limi alue lies on i s a o ing e ec o coke o ma ion. In addi ion o his e ec , he a o able a enua ion o
coke deac i a ion by he high H
2
concen a ion (s udied in uns wi h H
2
/CO
x
a io in he eed in he 1–3 ange)
plays a key ole in he iabili y o he p ocess, leading o a pseudo-s eady ca alys s a e in which he ac i i y is
cons an . The p o en e ec o H
2
O and me hanol concen a ions will be use ul o es ablishing new ca alys s and
eac ion condi ions a which hei p esence in he eac o will a enua e deac i a ion.
1. In oduc ion
In o de o mi iga e clima e change, he ca bon cap u e and u iliza-
ion (CCU) echnologies ha e ecei ed a g ea deal o a en ion,
encou aging he alo iza ion o CO
2
mainly h ough i s ans o ma ion
in o chemicals and uels [1–3]. Mo eo e , he join alo iza ion o CO
2
oge he wi h syngas is especially in e es ing when syngas (wi h CO and
H
2
as main componen s) is ob ained om sus ainable ou es such as
biomass gasi ica ion o e o ming o i s de i a i es [4–7]. In addi ion,
wi h biosyngas co- eeding pa o he needed H
2
is supplied.
Among he ca aly ic p ocesses o CO and CO
2
hyd ogena ion, he
di ec syn hesis o hyd oca bons o e s he ad an age o in eg a ing in
he same eac o he s ages o CO/CO
2
hyd ogena ion and he con-
e sion o he in e media es in o he a ge ed hyd oca bon p oduc s
such as uels and chemicals. The ex en o he con e sion o he in-
e media es a o s he displacemen o he equilib ium o
he modynamically limi ed eac ions, boos ing he con e sion o CO
2
.
This p ocess can be ca ied ou ia he modi ied Fische T opsch syn-
hesis o wi h me hanol/dime hyl e he (DME) as in e media es. Tan-
dem ca alys s a e used, combining me al oxides and acidic zeo ypes o
each eac ion s age [8–10].
No being limi ed by he Ande son-Shulz-Flo y (ASF) dis ibu ion,
he ou e wi h me hanol/DME as in e media es is sui able o ob aining
high ole in selec i i y [11]. Guo e al. [12] s udied he he modynamics
o he me hanol syn hesis s age, emphasizing he complex ole o CO.
Thus, in he CO
2
hyd ogena ion a equilib ium condi ions, CO o ma ion
by he e e se WGS ( WGS) had a nega i e e ec on he con e sion o
CO
2
and on me hanol yield. Whe eas co- eeding CO wi h CO
2
inc eased
hese equilib ium alues. As hese au ho s s a ed, he esul s ob ained
unde a o able he modynamic condi ions will be condi ioned by he
ac i i y and selec i i y o he ca alys s used, highligh ing ha he esul s
in he me hanol o ole ins con e sion s age a e a di ec consequence o
* Co esponding au ho .
E-mail add ess: [email p o ec ed] (A. A eka).
Con en s lis s a ailable a ScienceDi ec
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jou nal homepage: www.else ie .com/loca e/ uel
h ps://doi.o g/10.1016/j. uel.2023.128298
Recei ed 30 Janua y 2023; Recei ed in e ised o m 27 Ma ch 2023; Accep ed 31 Ma ch 2023
Fuel 346 (2023) 128298
2
he selec i i y o he zeo ype used in he andem ca alys composed o a
me allic oxide and acid zeo ype (OX/ZEO andem ca alys s). The mos
s udied ca alys s a e p epa ed mainly using oxides o In o Zn wi h Z O
2
as p omo e o me hanol syn hesis: ZnO-Z O
2
[13–15], In
2
O
3
[16–18],
In
2
O
3
-Z O
2
[19–21] o In
2
O
3
-ZnO-Z O
2
[22]. These ca alys s a e mo e
s able a he equi ed ope a ing empe a u e (≥300 ◦C o he oxygena e
con e sion in o hyd oca bons) han he con en ionally employed Cu-
based ca alys s [23]. The zeo ype ca alys s o he selec i e p oduc ion
o ole ins a e p ima ily based on he silicoaluminophospha e SAPO-34
[13,15,16,18–21,23], mainly hanks o i s se e e shape selec i i y
(wi h CHA s uc u e). Among he a emp s o imp o e he pe o mance
o SAPO-34 by modula ing i s acidi y, he addi ion o HF du ing he
syn hesis was asce ained o p o ide mo e acid s eng h o he zeoli e
and boos ligh ole ins selec i i y using a GamC Ox/H-SAPO (F) andem
ca alys , while educing CO selec i i y [24]. Al e na i ely, o he p o-
duc ion o highe hyd oca bons ca alys s based on HZSM-5 zeoli e (MFI
s uc u e) a e applied, wi h lowe se e i y o shape selec i i y [14,17].
E en i he se e e shape selec i i y o he SAPO-34 ca alys is sui able
o he selec i e p oduc ion o ligh ole ins, i is well es ablished o he
MTO/DTO p ocesses ha as a d awback i p omo es he con inemen o
he coke p ecu so in e media es [25,26] and hei e olu ion owa ds
polya oma ic s uc u es, which block he acid si es and he po ous
s uc u e [27]. I is also ema kable he o eseeable au oca aly ic na u e
o coke o ma ion, whose a e in he MTO/DTO p ocesses is dependen
on he me hanol/DME concen a ion [28]. Among he s a egies o
a enua e coke deac i a ion, he dec ease o he c ys al pa icle size and
he hie a chical o ganiza ion o he po e s uc u e o he ca alys pa icle
s and ou [29]. The concen a ion o wa e has a a o able incidence on
he a enua ion o he deac i a ion [30,31], which mo i a es i s co-
eeding [32,33], al hough compe i ion o he adso p ion o wa e and
me hanol/DME and eac ion in e media es in he acid si es also di-
minishes hei ac i i y o he p oduc ion o ole ins [34–36]. Mo eo e ,
he a o able con ibu ion o he high H
2
pa ial p essu e o a enua ing
coke deposi ion on me hanol/DME con e sion in o hyd oca bons is
no ewo hy [37–39] due o he hyd ogena ion o he coke p ecu so s
[40]. P esumably, hese e ec s will exis in he di ec syn hesis o ole ins
om CO
2
/CO hyd ogena ion, al hough he condi ions and he compo-
si ion o he eac ion medium a e di e en . Hence, he p esence o H
2
in
he di ec syn hesis o ole ins om CO
2
/CO hyd ogena ion esul s in a
lowe deac i a ion o he SAPO-34 ca alys [41].
In a p e ious wo k [42], he op imal composi ion o he In
2
O
3
-Z O
2
ca alys was de e mined (wi h an In/Z a io o 1/2), in o de o a o
he con e sion o CO
2
and CO
x
(CO
2
/CO) mix u es. This way, he sin-
e ing o In by o e - educ ion was a oided, and he seconda y me ha-
na ion eac ion was supp esed. In addi ion, he op imal condi ions
(mode a e p essu e o 30 ba , 400 ◦C, H
2
/CO
x
a io in he eed o 3),
sui able o ob aining wi h he In
2
O
3
-Z O
2
/SAPO-34 andem ca alys a
high pe pass yield o ole ins (g ea e han 4%) wi h a selec i i y g ea e
han 70 % being p opylene he majo ole in, we e de e mined [41]. I
should be poin ed ou ha he ca alys unde goes a apid ini ial deac-
i a ion, and subsequen ly eaches a pseudo-s eady s a e o cons an
ac i i y, in which coke o ma ion a e is equal o i s elimina ion a e by
hyd ogena ion.
This wo k add esses he d awback o he deac i a ion o he In
2
O
3
-
Z O
2
/SAPO-34 andem ca alys , which condi ions i s easibili y o he
di ec syn hesis o ole ins om CO
2
/CO eeds. The s udy emphasizes he
e ec o eac ion condi ions (H
2
pa ial p essu e, wa e and me hanol
concen a ion in he eac ion medium) ha will ha e an impac on he
coke deposi ion in SAPO-34 (o igin o he deac i a ion). The esul s will
be o in e es o adap he p ope ies o he ca alys and ope a ing con-
di ions wi h he objec i e o lessening he deac i a ion.
2. Expe imen al
2.1. Ca alys syn hesis and cha ac e iza ion
In
2
O
3
-Z O
2
ca alys was syn hesized ollowing a co-p ecipi a ion
me hod desc ibed in de ail in a p e ious wo k [42]. B ie ly, me allic
ni a es (In(NO
3
)
3
and Z (NO
3
)
4
, Pan eac) we e dissol ed in wa e (1 M)
in a 2/1 In/Z a io and cop ecipi a ed wi h (NH
4
)
2
CO
3
a 70 ◦C and
main aining he pH close o 7. Subsequen ly, he sample was d ied,
calcined and pelle ized. The bes con igu a ion was asce ained o be he
mix u e o indi idually pelle ized In
2
O
3
-Z O
2
(125–250 µm) and SAPO-
34 (300–400 µm) ca alys pa icles in a 2/1 mass a io dilu ed in SiC
[43]. The di e en pa icle size eases he sepa a ion o he indi idual
spen ca alys s by sie ing in o de o analyze hem.
In
2
O
3
-Z O
2
and SAPO-34 ca alys s we e cha ac e ized by N
2
adso p ion–deso p ion analyses (Mic ome i ics ASAP 2010), NH
3
- em-
pe a u e p og ammed deso p ion (NH
3
-TPD) analyses and H
2
and CO
empe a u e p og ammed educ ion (H
2
-TPR and CO-TPR). Cha ac e -
iza ion esul s a e shown in Table 1 (physical p ope ies and acidi y) and
in Suppo ing In o ma ion (Fig. S1) (TPR analyses). The high alue o
he BET su ace a ea o he SAPO-34 ca alys (651.8 m
2
g
−1
), consis e
wi h i s mic opo ous s uc u e, as well as i s high acidi y (777.6 µmol
NH3
g
ca
−1
) should be no ed. The ema kable su ace a ea o he In
2
O
3
-Z O
2
ca alys is consequence o he mesopo ous s uc u e o bo h oxides.
Thus, S
BET
accoun s o 53.4 m
2
g
−1
o In
2
O
3
and 95.4 m
2
g
−1
o Z O
2
,
and he po e olume 0.25 and 0.16 cm
3
g
−1
, espec i ely [42]. The
acidi y (122.6 µmol
NH3
g
ca
−1
) is a ibu able o Z O
2
. The esul s in Fig. S1
o In
2
O
3
-Z O
2
ca alys TPR a e in line wi h p e ious esul s [42], whe e
he highe educing capabili y o CO compa ed o H
2
is con i med, in
line wi h he li e a u e [42,44,45].
2.2. Ca aly ic ac i i y es
CO
2
/CO hyd ogena ion eac ions we e ca ied ou in a eac ion
equipmen (PID End & Tech Mic oac i i y Re e ence) desc ibed in
p e ious wo ks [42,46] equipped wi h an iso he mal s ainless s eel
packed bed eac o , wi h an e ec i e leng h o 10 cm and an inne
diame e o 9 mm and i can ope a e a condi ions up o 800 ◦C and 100
ba . I is p o ided wi h an in e nal ce amic coa ing o a oid side e-
ac ions wi h he eac o walls. Fo each un he eac o was loaded wi h
a mix u e o he desi ed ca alys amoun and SiC (up o 5 g o solid
mix u e) o a oid p e e en ial pa hways, ensu e iso he mal condi ions
and su icien bed-heigh when using small space ime alues. In o de o
analyze he p oduc s on-line, a ep esen a i e ac ion o he eac o
ou le s eam was dilu ed in He and sen o an on-line connec ed gas
ch oma og aph (Va ian CP-4900). The mic oGC is equipped wi h MS-5,
Po apak Q and CPSiL columns, allowing he quan i ica ion o com-
pounds comp ising H
2
, H
2
O, oxygena es (me hanol and DME) and hy-
d oca bons up o C
9
.
The coke deposi ed o e he spen ca alys s was s udied by empe -
a u e p og ammed oxida ion (TPO) analyses (TA Ins umen s TGA
Q5000 he mobalance), consis ing o : i) sweeping o he sample wi h He
a 120 ◦C o 30 min o emo e he humidi y, ii) s abilizing o he sample
in ai a 120 ◦C (10 cm
3
min
−1
) and iii) hea ing o he sample up o
680 ◦C wi h a hea ing a e o 7 ◦C min
−1
. The weigh o he sample was
measu ed du ing he whole expe imen o asce ain ha all humidi y
Table 1
Physical and acid p ope ies o he me allic and acid ca alys s.
Ca alys S
BET
(m
2
g
−1
)
V
mic opo e
(cm
3
g
−1
)
V
po e
(cm
3
g
−1
)
d
p
(nm)
Acidi y (µmol
NH3
g
ca
−1
)
In
2
O
3
-
Z O
2
86 0.003 0.23 9.0 122.6
SAPO-34 652 0.219 0.23 1.5 777.6
A. Po illo e al.
Fuel 346 (2023) 128298
3
was deso bed du ing he i s s ep.
The eac ion uns we e ca ied ou unde he ollowing condi ions:
350–425 ◦C; 20–50 ba ; space ime, 5 g
ca
h mol
C
−1
; H
2
/CO
x
, 1–3; H
2
/
CO
x
, 0–1. The e ec o H
2
O and me hanol con en in he eac ion me-
dium was s udied co- eeding bo h in a 5 % mola ac ion.
The esul s we e quan i ied om he mola lows a he inle and
ou le o he eac o in con ained C uni s, as ollows.
Con e sion o CO
2
(X
CO2
):
XCO2=F0
CO2−FCO2
F0
CO2
100 (1)
whe e F
0
CO2
and F
CO2
a e he CO
2
mola low a es a he inle and ou le
o he eac o , espec i ely.
The con e sion o he CO and CO
2
mix u e ( he ca bon ac ion
con e ed in o hyd oca bons o oxygena es) (X
COx
) was de ined as:
XCOx=F0
COx−FCOx
F0
COx
100 (2)
whe e F
0
COx
is inle mola low a e in C a oms, and F
COx
i s analogous a
he ou le o he eac o .
Ca bonaceous p oduc yields (Y
i
) and selec i i ies (S
i
) we e de ined
by g ouping he p oduc s in lumps: CH
4
, C
2
-C
4
ole ins, C
2
-C
4
pa a ins
and oxygena es (me hanol and DME) acco ding o he ollowing
exp essions:
Yi=niFi
F0
COx
100 (3)
Si=niFi
∑niFi
100 (4)
being n
i
he numbe o C a oms in a molecule o i componen (o
lump) and F
i
he co esponding mola low a e a he eac o ou le
s eam.
3. Resul s
3.1. Coke deposi ion o e SAPO-34
Fig. 1 shows he TPO p o iles o he wo indi idual ca alys s a e a
ce ain eac ion. I is e iden ha mos o he coke was o med o e
SAPO-34 (whe e coke amoun accoun ed up o 10.9 w % while in In
2
O
3
-
Z O
2
did no each 0.6 w %). The high coke con en o SAPO-34 is
ypical o he MTO/DTO p ocesses [26,47–49] and i is explained by he
con inemen capaci y o he in e media e a enes o med in he dual
cycle mechanism in he cages o SAPO-34 ca alys . The wide
empe a u e ange (250–650 ◦C) o he TPO p o ile co esponds o a
coke o med by he e ogeneous ca bonaceous species, whose condensa-
ion owa ds polya oma ic s uc u es du ing he eac ion and i s com-
bus ion in he TPO analysis will be limi ed by he di usional es ic ions
in he cages o he SAPO-34. On he con a y, The hyd ogena ion
capabili y o he In
2
O
3
-Z O
2
ca alys enables he hyd ogena ion o coke
p ecu so s du ing he eac ion and i s mesopo ous s uc u e eases i s
di usion ou wa ds he ca alys pa icle, explaining i s low con en in 16
h on s eam. Fu he mo e, in Fig. 1, he maximum combus ion peak is
obse ed a 450 ◦C o SAPO-34 and 270 ◦C o In
2
O
3
-Z O
2
, as he
combus ion o he coke deposi ed on he me allic oxides is ca alyzed
(which is in e es ing o acili a e i s egene a ion). In all he s udied
eac ion condi ions simila esul s o hese plo ed in Fig. 1 we e ob-
ained, poin ing o coke o ma ion o e SAPO-34 as he main esponsible
o he deac i a ion o In
2
O
3
-Z O
2
/SAPO-34 andem ca alys . Conse-
quen ly, he same species ha deac i a e SAPO-34 du ing he MTO/DTO
eac ions will p esumably be he eason o he deac i a ion o he
andem ca alys in he di ec CO/CO
2
o ole ins con e sion oo, as will
be discussed below.
3.2. E ec o he eed composi ion
3.2.1. Wa e and me hanol co- eeding wi h H
2
/CO and H
2
/CO
2
eeds
Va ious uns, whe e H
2
O, me hanol, and an equimola mix u e o
H
2
O and me hanol we e added o he H
2
+CO/CO
2
eed, we e con-
duc ed o assess he ole o H
2
O and me hanol in e media es in he di ec
hyd ogena ion o CO/CO
2
o ole ins o e he andem ca alys s. The H
2
O
low a e ed was calcula ed o simula e he same concen a ion as ha
gene a ed s oichiome ically by he WGS eac ion wi h H
2
/CO
2
eeds,
which co esponds o app oxima ely 5 mol%. Consequen ly, he e ec o
CO and CO
2
can be compa ed as in all cases H
2
O concen a ion was
simila . Fo he co- eeding o me hanol, he CO and CO
2
low a es we e
adjus ed o keep he same space ime alue. H
2
/CO
x
a io in he eed was
3 in all uns.
In Fig. 2 p oduc yields e olu ion wi h ime on s eam wi h H
2
/CO
eed is depic ed oge he wi h he esul s ob ained co- eeding H
2
O and
me hanol. Wi h he H
2
/CO eed (Fig. 2a), he ini ial deac i a ion o
SAPO-34 was e y as , which caused a dec ease in ole in and pa a in
( o med by hyd ogena ion o he o me ) yields, and led o an inc ease o
he concen a ion o oxygena es (non con e ed) and CH
4
( o med by
oxygena es c acking). These yields eached a cons an alue a e 4 h on
s eam co esponding o he ca alys emaining ac i i y.
H
2
O co- eeding (Fig. 2b) a enua ed he deac i a ion a e, delaying
he ime o acqui ing a pseudo-s eady s a e o he ca alys (up o 8 h) in
which ole in and pa a in yields we e simila o hose ob ained wi hou
H
2
O in he eed. The highe yield o oxygena es and lowe CH
4
yield
demons a e he e ec o H
2
O o a enua e he ac i i y o SAPO-34 acid
si es o he dual cycle mechanism and also o me hanol/DME c acking
[50,51]. Consequen ly, besides he lowe deac i a ion, he smalle CH
4
yield is ano he in e es ing esul ha acili a es he eci cula ion o he
p oduc s s eam and helps o ob ain highe con e sion.
On he o he hand, me hanol co- eeding (Fig. 2c), did no lead o a
highe ole in yield. Because he deac i a ion a e is di ec ly dependen
o oxygena es concen a ion. Thus, he yield o ole ins and pa a ins was
s able a e 2 h on s eam and he alues we e signi ican ly lowe han a
p e ious condi ions. In his eached ca alys s a e, he oxygena e s eam
was mainly o med by DME, because me hanol dehyd a ion ac i i y was
main ained, which only equi ed a low densi y o acid si es o educed
acid s eng h [35,52]. The high CH
4
yield ob ained when co- eeding
me hanol sugges s ha CH
4
was being o med due o he high oxygen-
a es (me hanol and DME) pa ial p essu e, which unde wen he mal
c acking a 400 ◦C (mainly DME as i is less s able han me hanol) [53].
Thus, i is obse ed ha an excessi e o ma ion o oxygena es has he
d awback o s ongly a o ing he as deac i a ion o SAPO-34 ca alys
by coke. Based on he esul s, he incidence o H
2
O co- eeding on he
deac i a ion o he SAPO-34 ca alys was simila o he well-es ablished
100200300400500600700
0.000
0.002
0.004
0.006
Ca .
In2O3-Z O2
SAPO-34
DTG ( g
c
min
-1
g
-1
ca
)
Tempe a u e ( C)
Fig. 1. Compa ison o TPO p o iles o he indi idual In
2
O
3
-Z O
2
and SAPO-34
spen ca alys s. Reac ion condi ions: 400 ◦C; 30 ba ; CO
2
/CO
x
, 0.5; space ime,
5 g
ca
h mol
C
−1
; H
2
/CO
x
, 3, and; ime on s eam, 16 h.
A. Po illo e al.
Fuel 346 (2023) 128298
4
e ec on he con e sion o me hanol/DME o ole ins (p ocesses a a -
mosphe ic p essu e and wi hou H
2
p esence). H
2
O dec eases he ac-
i i y and a enua es he deac i a ion o he ca alys , as i compe es o
he adso p ion in he acid si es wi h eac an s and coke p ecu so s
[51,52]. I is also well-es ablished o he me hanol/DME con e sion o
ole ins o e di e en acid ca alys s ha inc easing he concen a ion o
eac an oxygena es esul s in a highe coking a e [33,53].
In e ms o scaling up, i is in e es ing o compa e he yields in he
pseudo-s eady s a e o he ca alys o he di e en eeds (Fig. 2d). When
co- eeding H
2
O, ole in yield in he pseudo-s eady s a e o he ca alys
was equal (and i was e en highe be o e eaching his s a e, compa ed
o pu e H
2
/CO eeds) and highe oxygena e yield was achie ed. The
la e occu s due o he shi o he equilib ium o he me hanol o DME
dehyd a ion s ep (hampe ed by H
2
O), which esul s in highe me hanol
yield in he medium and lowe CH
4
, enligh ening ha i is o med
p e e en ially om DME he mal c acking. These e ec s (de i ed om
he p esence o H
2
O) would ake place wi hou H
2
O co- eeding when
modi ying many o he p ocess condi ions, conside ing ha H
2
O is he
p oduc o nume ous eac ions o he di ec CO
2
/CO o ole ins p ocess: i)
WGS eac ion, ii) syn hesis o me hanol om CO
2
, iii) me hanol
dehyd a ion o DME and i ) con e sion o oxygena es o ole ins.
The e ec o me hanol co- eeding in Fig. 2d shows a high oxygena e
yield and CH
4
. I is ema kable ha DME is he majo compound wi hin
he oxygena es (96 %). This occu s due o he as deac i a ion o SAPO-
34 ca alys , only capable o dehyd a ing me hanol. Mo eo e , he low
emaining ac i i y o SAPO-34 o he con e sion o me hanol/DME ia
he dual cycle mechanism a o s he CH
4
o ma ion by DME he mal
c acking. Consequen ly, his e ec mus be aken in o accoun , ope -
a ing unde condi ions in which he excess o oxygena es in he eac ion
medium is a oided.
Fig. 2d also ga he s he esul s ob ained wi h he ca alys in he
pseudo-s eady s a e wi h he join co- eeding o H
2
O and me hanol. In
his case, he excess o bo h componen s in he eac ion medium com-
bined hei nega i e e ec s, esul ing in a dec ease in ole in yield and in
an inc ease o DME yield. The CH
4
yield a ained was simila o ha
ob ained wi hou co- eeding H
2
O o me hanol, sugges ing ha he e -
ec s o co- eeding me hanol ( a o ing CH
4
o ma ion) and H
2
O (a en-
ua ing CH
4
o ma ion) we e compensa ed.
The e ec o he co- eeding o H
2
O and me hanol was also e alua ed
o H
2
/CO
2
eed (Fig. 3), compa ing he esul s wi h he a o emen ioned
o H
2
/CO eed. As obse ed p e iously in Fig. 2b wi h H
2
/CO eed, H
2
O
co- eeding led o a e y e en e olu ion o p oduc s dis ibu ion wi h
ime on s eam (Fig. 3b) compa ed o he un wi hou H
2
O co- eeding
(Fig. 3a). Howe e , he con e sion in o ole ins was s ongly penalized
by he he modynamic e ec s (a enua ion o he ex en o WGS,
me hanol o ma ion, DME o ma ion and MTO/DTO eac ions). The
esul s ob ained by me hanol addi ion (Fig. 3c) esul ed in an excess o
oxygena es ha u ned in o a high CH
4
o ma ion by DME (main
oxygena e in his case) he mal c acking.
Compa ing he p oduc yields in he pseudo-s eady s a e o he
ca alys (Fig. 3d), i is obse ed ha H
2
O co- eeding also en ailed a
nega i e e ec , in con as o ha obse ed o H
2
/CO eed (Fig. 2d).
This occu s because o H
2
/CO
2
eed he WGS eac ion is a o ed and,
hus, he H
2
O gene a ed by WGS is added o he ed H
2
O, esul ing in an
0 4 8 12 16
0
1
2
3
4
5
6
0 4 8 12 16
0
1
2
3
4
5
6
0 4 8 12 16
0
1
2
3
4
5
6
H
2
/ CO H
2
/ CO
+ H
2
O
H
2
/ CO
+ H
2
O
+ CH
3
OH
H
2
/ CO
+ CH
3
OH
0
1
2
3
4
5
6
7
8
9
Yield (%)
Ole ins
Pa a ins
Oxygena es
Me hane
d)
Ole ins
Pa a ins
Oxygena es
Me hane
Yield (%)
Time on s eam (h)
a)
Yield (%)
Time on s eam (h)
b)
Yield (%)
Time on s eam (h)
c)
Fig. 2. E olu ion o p oduc yields wi h ime on s eam o H
2
/CO eed wi hou any co- eeding (a), co- eeding H
2
O (b), co eeding me hanol (c), and hei alues a
he pseudo-s eady s a e o he ca alys (16 h on s eam) (d). Reac ion condi ions: 400 ◦C; 30 ba ; CO
2
/CO
x
, 0; space ime, 5 g
ca
h mol
C
−1
, and; H
2
/CO
x
, 3.
A. Po illo e al.
Fuel 346 (2023) 128298
5
excess o H
2
O in he medium. The e o e, he high H
2
O concen a ion
excessi ely a enua ed he ex en o he dual cycle mechanism o ole in
o ma ion. On he o he hand, analogously o wha was obse ed o he
H
2
/CO eed, co- eeding me hanol occasioned nega i e e ec s. CH
4
and
DME we e o med and ole in yield was lowe . Fu he mo e, he join co-
eeding o H
2
O and me hanol in eg a ed he nega i e e ec s. These e-
sul s a i y he impo ance o H
2
O and me hanol/DME concen a ions on
he mechanisms o he di ec syn hesis o ole ins om CO
2
and on
deac i a ion. I is also no ewo hy ha he p esence o H
2
O in a small
concen a ion had he posi i e e ec o a enua ing he deac i a ion
wi h he H
2
/CO eed. None heless, an excessi e H
2
O concen a ion wi h
H
2
/CO
2
eed in ol ed he nega i e e ec o limi ing he ac i i y o he
acid si es o SAPO-34 o be p edominan .
All hese e ec s o e he ca alys deac i a ion a e ela ed o he
di e ences in coke o ma ion on he SAPO-34 ca alys . These ends a e
clea ly obse ed in he TPOs ga he ed in Fig. 4 co esponding o he uns
wi h H
2
/CO
2
eed, wi hou and wi h co- eeding H
2
O, me hanol and a
mix u e o bo h. On he one hand, co- eeding H
2
O lessened coke con en
om 10.3 w % o 4.3 w %. Consequen ly, he no iceable limi ed ac i i y
o SAPO-34 obse ed in Fig. 3b and 3d is explained by he compe ence o
H
2
O wi h he oxygena es o i s adso p ion in he acid si es [51,52].
On he o he hand, coke con en ose up o 14.4 w % when me hanol
was co- ed. Mo eo e , in his case, TPO p o ile was displaced o highe
empe a u e ( he co esponding o he highes combus ion peak a e is
a 500 ◦C), which is in line wi h a mo e condensed coke [30,40]. This
akes place due o he highe ex en o he condensa ion eac ions o he
a enes e ained in he cages o SAPO-34, ha will e ol e in o poly-
a oma ic condensed s uc u es (coke wi h a lowe H/C a io). The join
co- eeding o H
2
O and me hanol esul ed in an in e media e coke p o ile
(compa ed o he wo indi idual eeds), bo h in a ea (coke con en 10.1
w %) and posi ion (combus ion a e peak sligh ly lowe han 500 ◦C),
e en i he nega i e e ec o inc easing me hanol concen a ion was
0 4 8 12 16
0
1
2
3
4
5
6
0 4 8 12 16
0
1
2
3
4
5
6
0 4 8 12 16
0
1
2
3
4
5
6
Ole ins
Pa a ins
Oxygena es
Me hane
Yield (%)
Time on s eam (h)
a)
Yield (%)
Time on s eam (h)
b)
Yield (%)
Time on s eam (h)
c)
H
2
/ CO
2
H
2
/ CO
2
+ H
2
O
H
2
/ CO
2
+ H
2
O
+ CH
3
OH
H
2
/ CO
2
+ CH
3
OH
0
1
2
3
4
5
6
7
8
Yield (%)
Ole ins
Pa a ins
Oxygena es
Me hane
d)
Fig. 3. E olu ion o p oduc s yield wi h ime on s eam o H
2
/CO
2
eed (a), wi h wa e co- eeding (b), wi h me hanol co- eeding (c) and hei alues a pseudo-
s eady s a e o he ca alys (16 h on s eam) (d). Reac ion condi ions: 400 ◦C; 30 ba ; CO
2
/CO
x
, 1; H
2
/CO
x
, 3, and; space ime, 5 g
ca
h mol
C
−1
.
200300400500600700
0.000
0.002
0.004
0.006
H2/CO2/CH3OH
H2/CO2/H2O/CH3OH
H2/CO2/H2O
H2/CO2
( GTD g
c
nim
-1
g
-1
ca
)
Tempe a u e ( C)
14.4%
10.1%
10.3%
4.3%
Fig. 4. E ec o he di e en co- eedings on he SAPO-34 TPO p o iles and hei
co esponding coke con en (w %). Reac ion condi ions: 400
◦C; 30 ba ; CO
2
/
CO
x
, 1; space ime, 5 g
ca
h mol
C
−1
; H
2
/CO
x
, 3; and ime on s eam, 16 h.
A. Po illo e al.
Fuel 346 (2023) 128298
6
p edominan , a o ing coke deposi ion and condensa ion. On he o he
hand, he symme y o he TPO p o iles hampe s he iden i ica ion o
di e en coke ypes by decon olu ion, which is indica i e o he coke
being deposi ed in a po ous s uc u e wi h uni o m spaces (CHA opol-
ogy wi h 10 ×6.7 ca i ies Å connec ed by 3.8 ×3.8 Å 8- ing cages) [54].
The long eac ion ime (16 h) con ibu es o he uni o mi y o he coke,
since o all he condi ions s udied, he ca alys had al eady eached a
pseudo-s eady s a e o cons an ac i i y, and p esumably he coke also
eached a pseudo-s eady s a e o condensa ion.
3.2.2. H
2
/CO
x
eeds
Conside ing he a o emen ioned di e ence in ca alys deac i a ion
o H
2
eed wi h CO and CO
2
(especially due o he highe H
2
O gene a ed
wi h CO
2
ia WGS) is in e es ing o assess he di e ences among H
2
/
CO, H
2
/CO/CO
2
and H
2
/CO
2
eeds, al hough he lowe eac i i y o CO
2
in he me hanol syn hesis should be aken in o accoun in he
compa ison.
Fig. 5 compa es he e olu ion o CO
x
con e sion wi h ime on s eam
o H
2
/CO, H
2
/CO
x
(equimola mix u e o CO
2
and CO) and H
2
/CO
2
eeds. He e, he di e ence in he ini ial deac i a ion a e was e iden , in
he o de H
2
/CO >H
2
/CO
x
>H
2
/CO
2
and can be explained by he in-
c ease o he H
2
O concen a ion in he medium wi h he p esence o CO
2
in he eed (as i a o s he g ea e ex en o he WGS) and i s a enu-
a ing e ec on coke o ma ion. Mo eo e , his e ec was also obse ed
o di e en ope a ing condi ions (di e en In
2
O
3
-Z O
2
/SAPO-34 a ios,
ope a ing empe a u es, p essu es and space ime alues) ( esul s no
shown).
The yields ob ained a e 16 h on s eam, i.e., a pseudo-s eady s a e,
a e depic ed in Fig. 6. The esul s we e ob ained wi h uns wi h CO
2
/CO
x
a ios in he eed o : 0, 0.25, 0.5, 0.75 and 1.
The maximum ole in yield alue was achie ed wi h a CO
2
/CO
x
a io
o 0.5, al hough he di e ence wi h he eeds wi h lowe CO
2
amoun
was no ema kable. I is obse ed ha , when inc easing he CO
2
amoun in he eed up o ha alue, he inc ease in H
2
O concen a ion
(as p oduc o he WGS eac ion) enhanced he p ocess by a enua ing
he deac i a ion. Indeed, wi h a CO
2
/CO
x
a io o 0.5, in pseudo-s eady
s a e, SAPO-34 main ained a su icien emaining ac i i y o he com-
ple e con e sion o oxygena es in o ole ins, a oiding hei c acking in o
CH
4
. The sligh dec ease o ole in yield o eeds wi h highe CO
2
con en
sugges s ha he e ec o he lowe eac i i y o CO
2
wi h espec o CO
[55] p edomina ed o e he expec ed highe a enua ion o
deac i a ion.
The e ec o co- eeding H
2
O and me hanol oge he wi h H
2
/CO
x
on
ca alys deac i a ion, o a CO
2
/CO
x
a io o 0.5, was also s udied. The
esul s o e olu ion o he p oduc s wi h he ime on s eam e ealed an
in e media e end o hose obse ed p e iously o he H
2
/CO and H
2
/
CO
2
eeds. Thus, he e ec o co- eeding H
2
O on he yields a he pseudo-
s eady s a e o he ca alys (Fig. 7) was in line wi h he a o emen ioned
esul s. Howe e , he un a o able e ec s obse ed o he H
2
/CO
2
eed
p edomina ed, due o he high H
2
O concen a ion (gene a ed by he
WGS eac ion) ha diminished he ac i i y o he acid si es. Acco ding
o his, H
2
O co- eeding also inhibi ed ole in o ma ion. On he o he
hand, he e ec o inc easing me hanol concen a ion, especially
wi hou he compensa ion o co- eeding H
2
O, was decisi e o in ensi y
he deac i a ion a e by coking, esul ing in he inhibi ion o me hanol
con e sion in o ole ins.
3.3. H
2
/CO
x
a io in he eed
The e ec o his a iable was analyzed sepa a ely conside ing ha ,
in addi ion o a ec ing he deac i a ion o he In
2
O
3
-Z O
2
/SAPO-34
andem ca alys (leading o pseudo-s eady s a es o di e en in e es ), i
also a ec s di ec ly he kine ics o he me hanol/DME syn hesis e-
ac ions. This di ec e ec will mask he esul s explained in he Sec ion
3.2 abou he concen a ion o H
2
O and oxygena es.
0 4 8 12 16
0
2
4
6
8
10
12
X
COX
(%)
Time on s eam (h)
H
2
/CO
H
2
/CO/CO
2
H
2
/CO
2
Fig. 5. E ec o CO
2
/CO
x
a io in he eed (0, 0.5 and 1) on he e olu ion o
CO
x
con e sion wi h ime on s eam. Reac ion condi ions: 400 ◦C; 30 ba ; H
2
/
CO
x
, 3; and space ime, 5 g
ca
h mol
C
−1
.
0 25 50 75 100
0
2
4
6
CO
2
/CO
X
(%)
Ole ins
Pa a ins
Oxygena es
Me hane
)%( dleiY
Fig. 6. E ec o CO
2
/CO
x
a io in he eed on p oduc s yield. Reac ion condi-
ions: 400 ◦C; 30 ba ; H
2
/CO
x
, 3; space ime, 5 g
ca
h mol
C
−1
; and ime on s eam,
16 h.
H
2
CO/CO
2
H
2
CO/CO
2
+ H
2
O
H
2
CO/CO
2
+ H
2
O
+ CH
3
OH
H
2
CO/CO
2
+ CH
3
OH
0
1
2
3
4
5
6
7
8
)%( dleiY
Ole ins
Pa a ins
Oxygena es
Me hane
Fig. 7. E ec o di e en co- eedings on p oduc s yield. Reac ion condi ions:
400
◦C; 30 ba ; CO
2
/CO
x
, 0.5; H
2
/CO
x
, 3, 5 g
ca
h mol
C
−1
; space ime, 5 g
ca
h
mol
C
−1
; and ime on s eam, 16 h.
A. Po illo e al.
Fuel 346 (2023) 128298
7
The esul s o he e olu ion o p oduc s yields wi h ime on s eam
shown in Fig. 8 co espond o eeds wi h H
2
/CO
x
mola a io o 1, 2 and
3 (Fig. 8a, 8b and 8c, espec i ely). I is e idenced ha he highe H
2
pa ial p essu e augmen ed he ini ial ole in yield, bu also a o ed hei
hyd ogena ion in o pa a ins. Mo eo e , he ca alys deac i a ion was
ema kably a enua ed when inc easing H
2
pa ial p essu e due o he
hyd ogena ion o coke p ecu so s [31,38]. As a consequence, by
inc easing he H
2
/CO
x
a io, he ca alys main ained a highe emaining
ac i i y in he pseudo-s eady s a e and he CO
2
and CO
x
con e sions
alues we e highe (Fig. 8d).
The a enua ion o deac i a ion wi h inc easing H
2
concen a ion
may be a ibu ed o he e ec on he con en and na u e o coke in he
SAPO-34 ca alys . In he TPO p o iles ga he ed in Fig. 9, i is obse ed
ha a highe H
2
/CO
x
a io, he coke con en dec eased. Fu he mo e,
al hough he symme y o he p o iles e idenced he a o emen ioned
uni o mi y o coke, he di e en ex en o he e olu ion owa ds
condensed s uc u es is no ewo hy. The e ec o H
2
/CO
x
a io in Fig. 9
is mode a e because in all h ee condi ions he pa ial p essu e o H
2
was
high enough o hyd ogena e coke p ecu so s [40], and consequen ly o
di icul i s condensa ion in o polya oma ic s uc u es. These hyd oge-
na ion eac ions p esumably a e ac i a ed by he In
2
O
3
-Z O
2
ca alys
si es in con ac wi h he SAPO-34 ca alys . I is no ewo hy ha he
empe a u e co esponding o he maximum combus ion a e in he TPO
p o iles was low (in he ange o 450–500 ◦C), indica ing ela i ely li le
condensed coke. Mo eo e , i should be no ed ha i was p o ed in a
p e ious wo k ha coke is pa ially elimina ed by means o an ine gas
s eam [46]. These esul s a e in good ag eemen wi h he li e a u e o
he MTO and DTO p ocesses, in which he coke is ela i ely li le
condensed unde usual condi ions (a mosphe ic p essu e) [30,35,56].
The inc ease in he H
2
/CO
x
a io in he eed on coke con en and na u e
led o he lowe deac i a ion a e o he ca alys s and i s g ea e
emaining ac i i y in he pseudo-s eady s a e in Fig. 8, due o he g ea e
ease o he eac an s o access he cages o he SAPO-34. Based on hese
esul s, an H
2
/CO
x
a io abo e 3 could be conside ed adequa e o u he
mi iga e deac i a ion. Howe e , H
2
a ailabili y mus be conside ed o
es ablish an op imal H
2
/CO
x
alue. Acco dingly, a alue o 3 a 30 ba
was se as app op ia e, achie ing a good comp omise be ween ole in
yield-selec i i y and ca alys s abili y [41], bea ing in mind ha unde
0 4 8 12 16
0
1
2
3
4
5
6
0 4 8 12 16
0
1
2
3
4
5
6
0 4 8 12 16
0
1
2
3
4
5
6
Pa a ins
Ole ins
Me hane
Oxygena es
Yield (%)
Time on s eam (h)
a)
Yield (%)
Time on s eam (h)
b)
Yield (%)
Time on s eam (h)
c)
123
0
5
10
15
20
25
30
Con e sion (%)
H
2
/ CO
X
CO
2
CO
X
d)
Fig. 8. E olu ion o p oduc s yields wi h ime on s eam o H
2
/CO
x
alues in he eed o 1 (a), 2 (b) and 3 (c), and CO
2
and COx con e sion alues a he pseudo-
s eady s a e o he ca alys (16 h on s eam) (d). Reac ion condi ions: 400 ◦C; 30 ba ; CO
2
/CO
x
0.5, and; space ime 5 g
ca
h mol
C
−1
.
100200300400500600700
0.000
0.002
0.004
0.006
( GTD gcnim 1- g1-
ca )
Tempe a u e ( C)
H
2
/CO
x
1/1
2/1
3/1
14.2%
12.5%
11.5%
Fig. 9. E ec o H
2
/CO
x
a io in he eed on he TPO p o iles o spen SAPO-34
and he co esponding coke con en (w %). Reac ion condi ions: 400 ◦C; 30 ba ;
CO
2
/CO
x
, 0.5; space ime, 5 g
ca
h mol
C
−1
, and; ime on s eam, 16 h.
A. Po illo e al.
Fuel 346 (2023) 128298
8
hese condi ions H
2
p oduced wi h PEM elec olyze s could be used
[57].
4. Conclusions
The apid deac i a ion by coke o he SAPO-34 ca alys condi ions
he pe o mance o he In
2
O
3
-Z O
2
/SAPO-34 andem ca alys in he
di ec syn hesis o ole ins om CO
2
/CO and he yield o ole ins and
byp oduc s (pa a ins and CH
4
) in he subsequen pseudo-s eady s a e.
The inc ease in H
2
concen a ion esul ed in lowe coke deposi ion
and o less condensed na u e, which con ibu es o lessen de deac i a-
ion a e and o inc ease he emaining ac i i y o he ca alys in he
pseudo-s eady s a e. Howe e , he ole o H
2
O and oxygena es (me h-
anol/DME) concen a ion on he deac i a ion o he SAPO-34 was
complex, due o he implica ion o hese compounds ( eac ion in-
e media es) in he mechanism o he main and deac i a ion eac ions
in ol ed in he con e sion o he oxygena es. Inc easing H
2
O concen-
a ion lessened he deac i a ion o he SAPO-34 ca alys o H
2
/CO
eed, boos ing ole ins yield. Howe e , his did no occu o he H
2
/CO
2
eed, because he H
2
O concen a ion was oo high a his condi ion, and
i s nega i e e ec o a enua ing he ac i i y o he acid si es o he
SAPO-34 p edomina ed. In addi ion, he excessi e concen a ion o
me hanol/DME, desi ed as eac an s o ole in p oduc ion, had he
coun e pa o a o ing deac i a ion by coke, and consequen ly he
p esence o DME and CH
4
as by-p oduc s.
These e ec s o H
2
O and me hanol concen a ion a ec he pe o -
mance o he andem In
2
O
3
-Z O
2
/SAPO-34 ca alys in he con e sion o
ole ins o CO
2
/CO mix u es, in which he H
2
O concen a ion in he eed
would also in luence he e ec o o he ope a ing condi ions ( empe a-
u e, p essu e, space ime, In
2
O
3
-Z O
2
/SAPO-34 a io) on he deac i a-
ion. Consequen ly, when s udying he e ec o he p ocess condi ions
o he in e p e a ion o he esul s, hei e ec on he H
2
O and oxy-
gena es concen a ions mus be aken in o accoun . Mo eo e , he
incidence o H
2
O and oxygena es concen a ions should be aken in o
accoun in he de elopmen o kine ic models o his p ocess, and in
pa icula , in he kine ics o deac i a ion by coke. These e ec s a e also
o in e es o p og ess in he design o new ca alys s (mo e s able in he
p esence o H
2
O and wi h lowe coke deposi ion) and eac o s. Among
he ini ia i es o modi y he acid zeo ype, he modula ion o he acid
s eng h and he gene a ion o hie a chical po ous s uc u es (wi h
mesopo es inside he c ys als o agglome a ing he zeo ype in a ma ix)
may con ibu e o a enua e coke deposi ion. To minimize he a enua-
ion o he ac i i y by he concen a ion o H
2
O, i would be easonable
o use less hyd ophilic zeo ypes and hei inco po a ion in o composi es
wi h H
2
O adso bing ma e ials. F om he pe spec i e o imp o ing he
eac o , hyd ophilic memb ane eac o s may be a good solu ion o a oid
he un a o able e ec o excess H
2
O wi h CO
2
/CO eeds.
CRediT au ho ship con ibu ion s a emen
A. Po illo: Concep ualiza ion, In es iga ion, W i ing – o iginal
d a , W i ing – e iew & edi ing. O. Pa a: Valida ion, Visualiza ion,
W i ing – o iginal d a , W i ing – e iew & edi ing. J. E e˜
na: P ojec
adminis a ion, Funding acquisi ion. A.T. Aguayo: Me hodology, Re-
sou ces, Supe ision, P ojec adminis a ion, Funding acquisi ion. J.
Bilbao: Concep ualiza ion, W i ing – o iginal d a , W i ing – e iew &
edi ing, P ojec adminis a ion, Funding acquisi ion. A. A eka:
Concep ualiza ion, W i ing – o iginal d a , W i ing – e iew & edi ing.
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing inancial
in e es s o pe sonal ela ionships ha could ha e appea ed o in luence
he wo k epo ed in his pape .
Da a a ailabili y
The au ho s a e unable o ha e chosen no o speci y which da a has
been used.
Acknowledgemen s
This wo k has been ca ied ou wi h he inancial suppo o he
Minis y o Science, Inno a ion and Uni e si ies o he Spanish Go -
e nmen (PID2019-108448RB-100); he Basque Go e nmen (P ojec
IT1645-22), he Eu opean Regional De elopmen Funds (ERDF) and he
Eu opean Commission (HORIZON H2020-MSCA RISE-2018. Con ac
No. 823745). A. Po illo is g a e ul o he Ph.D. g an om he Minis y
o Science, Inno a ion and Uni e si ies o he Spanish Go e nmen
(BES2017-081135) and O. Pa a is g a e ul o he PhD g an om he
Basque Go e nmen (PRE_2021_1_0014). The au ho s hank o ech-
nical and human suppo p o ided by SGIke (UPV/EHU).
Appendix A. Supplemen a y da a
Supplemen a y da a o his a icle can be ound online a h ps://doi.
o g/10.1016/j. uel.2023.128298.
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