H2-rich syngas production from biogas reforming: overcoming coking and sintering using bimetallic Ni-based catalysts

H 2 - ich syngas p oduc ion om biogas e o ming: O e coming coking and sin e ing using bime allic Ni-based ca alys s S. Ca asco-Ruiz a , Q. Zhang b ,J.G  anda a-Loe a , L. Pas o -P e ez a , J.A. Od iozola a,b , T.R. Reina a,b,** , L.F. Bobadilla a,* a Ino ganic Chemis y Depa men and Ma e ials Science Ins i u e, Uni e si y o Se ille-CSIC, 41092, Se illa, Spain b Depa men o Chemical and P ocess Enginee ing, Uni e si y o Su ey, Guild o d, GU2 7XH, UK highligh s g aphical abs ac H 2 - ich syngas can be ob ained e icien ly om biogas e o ming. Ni-based ca alys s a e deac i a ed by me al sin e ing and coke deposi ion. Doping wi h low Rh loadings deac i a ion can be success ully p e en ed. a icle in o A icle his o y: Recei ed 23 Augus 2022 Recei ed in e ised o m 11 Feb ua y 2023 Accep ed 20 Ma ch 2023 A ailable online 19 Ap il 2023 Keywo ds: D y e o ming H 2 - ich syngas NieRh ca alys Coking esis ance abs ac D y e o ming o me hane is a e y appealing ca aly ic ou e biogas (mainly composed by g eenhouse gases: ca bon dioxide and me hane) con e sion in o added alue syngas, which could be u he upg aded o p oduce liquid uels and added alue chemicals. Howe e , he majo culp i s o his eac ion a e coking and ac i e phase sin e ing ha esul in ca alys s deac i a ion. He ein we ha e de eloped a highly s able bime allic NieRh ca alys suppo ed on mixed CeO 2 eAl 2 O 3 oxide using low-noble me al loadings. The addi ion o small amoun s o hodium o nickel ca alys s p e en s coke o ma ion and imp o es sin e ing esis ance, achie ing high con e sions o e ex ended eac ion imes hence esul ing in p omising ca alys s o biogas upg ading. ©2023 The Au ho (s). Published by Else ie L d on behal o Hyd ogen Ene gy Publica ions LLC. This is an open access a icle unde he CC BY-NC-ND license (h p:// c ea i ecommons.o g/licenses/by-nc-nd/4.0/). *Co esponding au ho . ** Co esponding au ho . Ino ganic Chemis y Depa men and Ma e ials Science Ins i u e, Uni e si y o Se ille-CSIC, 41092, Se illa, Spain. E-mail add esses: . ami ez eina@su ey.ac.uk (T.R. Reina), [email protected] (L.F. Bobadilla). A ailable online a www.sciencedi ec .com ScienceDi ec jou nal homepage: www.else ie .com/loca e/he in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e27917 h ps://doi.o g/10.1016/j.ijhydene.2023.03.301 0360-3199/©2023 The Au ho (s). Published by Else ie L d on behal o Hyd ogen Ene gy Publica ions LLC. This is an open access a icle unde he CC BY-NC- ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). In oduc ion Figh ing global wa ming ale o mi iga e he nega i e human impac on he en i onmen is one o he u gen p io i ies o he scien i ic communi y aking op as Global Challenge p i- o i y o a sus ainable de elopmen . The g eenhouse e ec caused by he emission o ha m ul gases in o he a mosphe e is p o oking an inc ease in global empe a u e and he e o e o changing clima es causing d ough s, de o es a ion, and dese i ica ion o he plane . The ou main g eenhouse gases (GHG) a ac ing se ious global a en ion oday a e CO 2 ,CH 4, SO 2 , and N 2 O. Ca bon di- oxide is by a he mos emi ed gas in o he a mosphe e, ac- coun ing o 76% o o al emissions in 2019 [1]. Acco ding o Uni ed in Science 2020 [2], a epo compiled by he Wo ld Me eo ological O ganiza ion (WMO) unde he di ec ion o he Uni ed Na ions Sec e a y-Gene al, lockdown- ela ed all in emissions caused by COVID-19 pandemic will no educe su icien ly he CO 2 concen a ions in he a mosphe e. The g owing end o CO 2 and CH 4 emissions d i en by he in- c ease o global ene gy consump ion makes manda o y he sea ch o al e na i es o achie e GHG alo isa ion [3]. The use o enewable ene gy sou ces ep esen s “mus do” ac ion o a ou he ansi ion owa ds a low-ca bon econ- omy. He ein, biogas can play an impo an ole in he de el- opmen o he enewable ene gy ma ke nowadays, as i has a wide a ie y o applica ions compa ed o o he enewable ene gy sou ces [4]. Biogas is p oduced by anae obic diges ion o biodeg adable was es and is mainly compound by ca bon dioxide and me hane [5,6]. A e i s p oduc ion, he e a e h ee main ou es o biogas u ilisa ion (Fig. 1b). Biome hane is a nea ly pu e me hane s eam ha can be ob ained by CO 2 sepa a ion o biogas. A p esen , bio- me hane has been widely used as an engine ehicle uel in many coun ies and has b oad de elopmen p ospec s [7,8]. Biogas is a aw ma e ial o p oduce syngas (H 2 /CO gas mix u e) o indus ial syn heses o ene gy pu poses [7]. The e a e se e al ways o e o m biogas in o syngas such as D y Re o ming o Me hane o Bi-Re o ming o Me hane. G een elec ici y can be p oduced om biogas by Com- bined Hea &Powe sys em (CHP) [9]. Syngas is a combus ible gas ha can be used o p oduce elec ical ene gy in u bines and uel cells (Fig. 1c), bu he cu en ma ke demand unco e s he po en ial o syngas as a eeds ock o p oduce uels like diesel, naph ha, and gasoline, as well as o high alue-added chemical inpu s ia Fische - T opsch syn hesis (FTS) [10]. Focusing on biogas upg ading, he e se e al he mal ca a- ly ic ou es o syngas p oduc ion om biogas namely: Oxy- Re o ming o Me hane (ORM), Bi-Re o ming o Me hane (BRM) and D y Re o ming o Me hane (DRM) [11]: ORM :3CH4þCO2þO2#4CO þ6H2(Eq.1) DH0¼58 kJmol DG0¼1kJmol BRM :3CH4þCO2þ2H2O#4CO þ8H2(Eq.2) DH0¼220 kJmol DG0¼151 kJmol DRM :CH4þCO2#2CO þ2H2(Eq.3) DH0¼247 kJmol DG0¼170 kJmol Fig. 1 eBiogas li e cycle: a) Biogas p oduc ion; b) Biogas u ilisa ion; c) Syngas u ilisa ion. in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e2791727908 E en hough he ORM (Eq. (1)) is p esumably he mos a ac i e op ion gi en i s au o he mic na u e which esul s in signi ican ene gy sa ings, sa e y conce ns associa ed wi h oxygen use limi i s in e es o indus ial and la ge-scale ap- plica ions [12]. The mos popula echnologies a e he BRM (Eq. (2)) and he DRM (Eq. (3)). The i s one leads o a syngas H 2 /CO mix u e a io o a maximum o 2, meanwhile he las one can achie e a mola a io o 1 [13]. Howe e , in he con ex o a ci cula economy when a CO 2 u ilisa ion ou e is pu sued, CO 2 con e sion may p e ail o e H 2 /CO a io as selec ion c i e ia o he op imal ou e. He ein, DRM akes he edge o e BRM as epo ed elsewhe e [14]. In any case, he condi ions used o e o ming also a ou o he side eac ions (Eqs. (4)e(7)), in which ca bon deposi s (C*) a e o med as ollows [15]: Me hane decomposi ion :CH4#C*þ2H2(Eq.4) DH0¼75 kJmol Boudoua d eac ion :2CO #C*þCO2(Eq.5) DH0¼172 kJmol CO2hyd ogena ion :CO2þ2H2#C*þ2H2O(Eq.6) DH0¼90 kJmol CO hyd ogena ion :CO þH2#C*þH2O(Eq.7) DH0¼131 kJmol The o ma ion o ca bon deposi s leads o ca alys s deac- i a ion, so i is impo an o ind ma e ials capable o mini- mizing ca bon o ma ion. Besides hese eac ions ha can deac i a e he ca alys , he e is also a side eac ion ha would dec ease he H 2 yield, he Re e se Wa e Gas Shi (RWGS): RWGS eac ion :CO2þH2#CO þH2O(Eq.8) DH0¼46 kJmol When i comes o ca alys s selec ion, Ni-based ca alys s ha e shown a good ac i i y and con e sion o biogas in o syngas [16e18], bu hey a e ex book example o coking and sin e ing [19,20]. I has also been epo ed ha noble me al- based ca alys s ha e a g ea e ac i i y and con e sion, bu in addi ion, hey ha e mo e s abili y and highe coking esis- ance ye a e expensi e and less a ailable [21]. Fo hese e y easons bime allic alloys comp ised o Ni and low amoun s o noble me als (i.e. Pd, Rh, P , Ru) a e in e es ing in e o ming p ocesses. I espec i ely o he selec ed o mula ion, i is clea ha ca alys s s abili y ( esis ance o he di e en deac i a ion phenomena) is c ucial o an op imal p ocess design. F equen ly in he e ogeneous ca alysis, deac i a ion issues a e esol ed by ca alys egene a ion. Fo ins ance, he mal ea men s o emo e ca bon deposi s o ge id o po en ial sul ides [22]. The sequence o ac i i y o he DRM using M/MgO (M≡I ,Ni,Pd,P ,Rh,Ru) ca alys s is Ru >Rh >Ni »I ,P ,Pd conside ing he p esence o sul u compounds [23]. Compa ing Ru and Rh, he egene a ion o Ru ca alys s is much lowe han ha o Rh, so i seems ha he bes op ion o ou objec i e is a bime allic NieRh ca alys [24]. Beyond he ac i e phase, he suppo choice is also essen ial o ensu e an adequa e pe o mance. Fo e o ming eac ions gi en he demanding p ocess condi ions (high empe a u es) he mal and mechanical s abili y a e key ac- o s o conside . In his ega d, alumina suppo s (Al 2 O 3 ) o e s an excellen balance he mal/mechanical p ope y while also displaying high speci ic a ea which enhances me allic dispe sion. Howe e , he acidic si es o his kind o suppo s can inc ease coke o ma ion. Tha is why ce ia (CeO 2 )isan in e es ing edox p omo e . Indeed, ce ia allows a lexible unning o he acid/base p ope ies o he suppo and p o- ides excellen oxygen mobili y, p e en ing ca bon deposi ion ia oxida ion o he coke p ecu so s [13]. Se e al au ho s ha e s udied bime allic NieRh ca alys s o he DRM eac ion [25,26], ye he speci ic ole o Rh and how i bene i s ca aly ic pe o mance is no ully add essed. Pa ic- ula ly, sho - e m s abili y es and insu icien o pos - eac ion analysis in he cu en epo s pose some ques ions ega ding he undamen al ole o Rh in he bime allic o mula ion. So, unde hese p emises, his wo k ocuses on he de elopmen o an ad anced mul icomponen ca alys s NieRh/CeO 2 eAl 2 O 3 whose pe o mance is compa ed o a ba e monome allic Ni/CeO 2 eAl2O 3 sys em. Ca aly ic ac i i y and s abili y esul s as well as p e- and pos - eac ion cha ac e i- sa ion will be discussed o unde s and he bene icial e ec o noble me al addi ion. Expe imen al Ca alys s p epa a ion The suppo used was a comme cial ce ia-alumina oxidic suppo wi h 20 w % o CeO 2 (Pu alox, SASOL). The monome allic ca alys was p epa ed by we imp eg- na ion, whe e he suppo was i s imp egna ed wi h Ni(NO 3 ) 2 ·6H 2 O (Sigma-Ald ich) dilu ed in dis illed wa e , e apo a ed a educed p essu e in a o a apo , d ied o e - nigh a 100 C and calcined a 550 C o 4 h. In a simila p ocedu e, he bime allic ca alys was p epa ed by we co-imp egna ion, whe e he suppo was imp egna ed wi h Ni(NO 3 ) 2 ·6H 2 O (Sigma-Ald ich) and RhCl 3 (Sigma-Ald ich) dilu ed in dis illed wa e , e apo a ed a educed p essu e in a o a apo , d ied o e nigh a 100 C and calcined a 550 C o 4h. In all cases he NiO con en is calcula ed o be 10 w % and 0.5 w % Rh o he bime allic sample. These a ios we e cho- sen based on p e ious wo ks [27e29]. Cha ac e isa ion echniques The ex u al p ope ies o he samples we e e alua ed om ni ogen adso p ion-deso p ion iso he ms a liquid ni ogen empe a u e in a Mic ome i ics T is a II appa a us. Be o e in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e27917 27909 analysis, he samples we e degassed a 150 C o 8 h in acuum. On one hand, he speci ic su ace a ea (S BET ) was de e - mined by he B unaue -Emme -Telle (BET) me hod [30] and co esponds o he sum o he inne su ace o he po e plus he ou e su ace o he g ains. Addi ionally, he Ba e - Joyne -Halenda (BJH) me hod was used o de e mining he po e size dis ibu ion using he deso p ion iso he m. Po e olume ep esen s he inne and ou e g anula olume, and he a e age po e size was calcula ed as he a io o he po e olume and he speci ic su ace a ea and no malized using a coe icien ha depends on he po es shape [31]. Scanning elec on mic oscopy (SEM) analysis was pe - o med on he calcined samples in a acuum, using a JEOL 5400 mic oscope equipped wi h an EDS analyse (Ox o d Link). X- ay di ac ion measu emen s we e ca ied ou in a X'Pe P o PANaly ic ins umen . The di ac ion pa e ns we e eco ded a 40 mA and 45 kV using Cu-Ka adia ion (l¼0.154 nm). The 2qangle was inc eased using a s ep size o 0.05and a s ep ime o 300 s in a ange o 10 o 90. Tempe a u e p og ammed educ ion (TPR) measu emen s we e conduc ed in a con en ional U-shaped qua z eac o connec ed wi h a he mal conduc i i y de ec o (TCD), pass- ing a low o 50 mL/min o 5% H 2 dilu ed in A . TPR expe i- men s we e pe o med using app oxima ely 50 mg o each ca alys a a hea ing a e o 10 C/min om oom empe a u e (RT ¼25 C) o 900 C. A mix u e con aining ace one and d y ice was used as a cold ap o emo e he wa e o med h oughou he p ocedu e. Tempe a u e p og ammed oxida ion (TPO) expe imen s we e ca ied ou a e he long- e m s abili y es s o in es i- ga e he ca bon species deposi ed on he ca alys su ace. TPO analysis we e conduc ed in a U-shaped qua z eac o coupled o a PFEIFFER Vacuum P ismaPlus mass spec ome e . 25 mg o bo h samples we e hea ed up o 900 C a a a e o 10 C/min in a calib a ed low o 50 mL/min (5% O 2 , 95% He). Ca aly ic ac i i y and s abili y Ca aly ic pe o mance was e alua ed in a ixed-bed con in- uous- low eac o desc ibed elsewhe e [32] in which 100 mg o undilu ed ca alys we e loaded o each un. P io o he e- ac ion, he samples we e in si u educed in a low o 10% H 2 /N 2 a 850 C o 1 h. The eac ion was pe o med a a mosphe ic p essu e passing a low o 100 mL/min o CO 2 /CH 4 /N 2 (mola a io o 1:1:6) and dec easing successi ely he empe a u e om 850 C down o 550 C un il achie ing he s eady s a e each 50 C. The WHSV (Weigh Hou ly Space Veloci y) was ixed a 60 L/g ca $h. All he gases in ol ed in he expe imen s we e moni o ed by u ilising an on-line gas analyse (ABB- AO2020) which was equipped wi h bo h IR and TCD de ec o s. The ca aly ic s abili y o bo h mono and bime allic ma e- ials was also s udied. Fo his pu pose, 100 mg o each ca a- lys we e educed unde he same condi ions as o he ca aly ic ac i i y es s, and hen he eac ion condi ions we e e alua ed a a mosphe ic p essu e passing he same low condi ions as abo e a 650 C o 48 h. A second s abili y s udy was ca ied ou a 850 C o 48 h. The ca aly ic esul s ob ained ha e been exp essed in e ms o con e sions o bo h eac an gases and he H 2 /CO mola a io. The equa ions used o es ima e hese pa ame e s a e as ollows: CH4con e sion ð%Þ¼nCH4in nCH4ou nCH4in $100 (Eq.9) CO2con e sion ð%Þ¼nCO2in nCO2ou nCO2in $100 (Eq.10) H2=CO ¼nH2 nCO $100 (Eq.11) Being n he mola low o CH 4 ,CO 2 ,H 2 , and CO espec i ely and he subsc ip s in o ou co espond o he inle o he ou le eac o low. Resul s and discussion Cha ac e isa ion o solid ca alys s The ex u al p ope ies (S BET , and po e size and olume) o he ca alys s and he comme cial suppo a e summa ized in Table 1. As can be obse ed, he speci ic su ace a eas o he ca alys s a e qui e simila . This indica es a good dispe sion o he me als on he su ace o he suppo , which will ha e a posi i e e ec on he ac i i y o he ma e ials. Likewise, bo h po e olume (V po e ) and po e wid h (D po e ) a e almos iden i- cally, showing ha no agglome a ion o me al pa icles has occu ed on he ca alys and ha he po es suppo ha e no been blocked. Besides ha , he ex u al p ope ies ob ained o he ce ia- p omo ed alumina suppo sugges ha bo h Ni and Rh a e in oduced in o he po es o he suppo , so ha he speci ic su ace a ea, po e olume and po e wid h dec ease. In addi ion, he ni ogen adso p ion/deso p ion iso he ms a 77 K ha e been ob ained o bo h ca alys s as shown in Figu e S1. Acco ding o IUPAC classi ica ion [33], ou iso he m ypes a e usually ound in ca alys cha ac e isa ion, and each iso he m shape depends di ec ly on he solid po ous ex u e. In ou case, bo h iso he ms co espond o a ype IV iso he m, which is ela ed o a mesopo ous ma e ial (po e size be ween 2 nm and 50 nm). Besides, he e is also a classi ica ion o he ype o hys e esis, being he ype H1 ound in ou iso he ms. This kind o hys e esis is cha ac e is ic o solids consis ing o pa icles a e sed by quasi-cylind ical channels o consis ing o agg ega es (consolida ed) o agglome a es (unconsolida ed) o sphe oidal pa icles, and he po es may be uni o m in size and shape. Figu e S2 shows he po e size dis ibu ion ob ained by BJH me hod o bo h ca aly ic ma e ials. As can be no ed, bo h po e dis ibu ion cu es a e e y simila con i ming ha he e Table 1 eTex u al p ope ies o he suppo and p epa ed ca alys s. Sample S BET (m 2 /g) V po e (cm 3 /g) D po e ( A) CeO 2 eAl 2 O 3 159 0.39 71.9 Ni/CeO 2 eAl 2 O 3 132 0.31 67.7 NieRh/CeO 2 eAl 2 O 3 138 0.32 66.6 in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e2791727910 a e no agglome a ion o me al pa icles and he ma e ial ca i ies ha e no been blocked. The mo phology o he calcined ca alys s is shown in he SEM mic og aphs p o ided in Fig. 2. Analysing he dis ibu ion o elemen s in he di e en mappings, we can con i m ha bo h Ni and Rh a e well dispe sed and homogeneously dis ibu ed on he su ace o he ca alys s, co obo a ing a success ul syn hesis o bo h samples. The s uc u e o bo h p epa ed ca alys s was analysed by means o X-Ray Di ac ion (XRD). Bo h samples we e i s ly analysed a e calcina ion a 550 C(Fig. 3a). F om his igu e, i can be obse ed ha all samples con ain he ypical di ac- ion lines co esponding o he (111), (200), (220) and (311) c ys alline planes expec ed o he CeO 2 luo i e-like phase while he peaks co esponding o he (311) and (440) c ys al- line planes a e asc ibed o he g-Al 2 O 3 phase [34]. Fig. 2 eSEM mic og aphs o bo h calcined ca alys s: (I)Ni/CeO 2 eAl 2 O 3 ; (II)NieRh/CeO 2 eAl 2 O 3 ; whe e (a) gene al iew; (b) Ce mapping; (c) Ni mapping; (d) Al mapping; (e) Rh mapping. Fig. 3 eXRD o : a) calcined samples (550 C); b) educed samples (850 C). in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e27917 27911 Fig. 3b shows he XRD pa e ns o he samples a e educ ion in a low o 10% H 2 /N 2 a 850 C o 1 h. Hence, he di ac ion lines ela ed o me allic Ni can be clea ly seen, al hough he me allic Rh peaks we e ha dly obse ed due o he high dispe sion and/o low loading o he noble me al. An o e all idea o he edox beha iou and he me al- suppo in e ac ions was ga he ed by Tempe a u e P o- g ammed Reduc ion (TPR) analysis. The TPR p o iles ob ained o bo h ca alys s a e p esen ed in Fig. 4. No ably h ee di e en egions a e dis inguished. Fi s , aRegion (150e350 C) shows he educ ion o su ace ce ia [35e37], which is enhanced on he bime allic ca alys due o he spill-o e phenomenon [38]. The bRegion (450e650 C) exhibi s he educ ion o NiO wi h low o medium s eng h o in e ac ion wi h he suppo . Finally, he educ ion o NiO wi h high s eng h o in e ac ion wi h he suppo occu s a empe a- u es abo e 700 C(gRegion)[39]. Compa ing bo h educ ion p o iles, we can see ha he addi ion o hodium imp o es no ably he educibili y o Ni, acili a ing i s educ ion a lowe empe a u es. This highe educibili y implies be e edox p ope ies, and hese edox cha ac e is ics may enhance he ca aly ic pe o mance du ing he DRM eac ion. DRM ca aly ic ac i i y The educed ca alys s we e es ed in he DRM eac ion a a empe a u e ange o 550e850 C and a a mosphe ic p essu e wi h a CO 2 /CH 4 mola a io 1:1. As we can see in Fig. 5.a, CH 4 con e sions we e lowe han CO 2 con e sions, which may sugges ha he CH 4 ac i a ion is mo e di icul and equi es highe empe a u es in good ag eemen wi h DFT esul s [40]. The ac i a ion and clea age o CeH bonds is mo e ene ge ic han CO 2 dissocia ion. On he o he hand, compa ing he esul s be ween bo h ca alys s, no signi ican di e ences a e obse ed in he ca bon dioxide and me hane con e sions, wi h simila con e sion le els o he monome allic ca alys and he bime allic one. In e ms o he H 2 /CO mola a io (Fig. 5b), bo h ca alys s also showed simila esul s. Howe e , his mola a io s ays o e 1 h oughou he eac ions, so we can conclude ha H 2 concen a ion is highe han CO concen a ion. This is an in e es ing o biogas e o ming ia DRM since ypical H 2 /CO a e sligh ly lowe ( ypically close o 1). The main eason o his obse a ion is he p esence o mul iple pa allel eac ions desc ibed abo e in he in oduc ion sec ion ei he consuming CO o p oducing H 2 ,i.e. he RWGS/WGS p ocess which is e ec i ely ca alysed by NieCeO 2 sys ems [41]. Fig. 6 shows he XRD o he spen ca alys s. Apa om he di ac ion peaks o he me allic and suppo phases, we can obse e a highe in ensi y in he 20-402qzone o he monome allic ca alys han o he bime allic one. This es- i ies he o ma ion o ca bon deposi s as will be well dis- cussed u he below. DRM ca aly ic s abili y S abili y es s show how e icien ca alys s a e o e long e- ac ion uns and commonly s abili y is mo e impo an han ac i i y in comme cial ca alys s design since i de e mines he equency o s a -up/shu downs ope a ions and he ca alys s egene a ion cos . Fig. 4 eH 2 -TPR p o iles o bo h samples. Fig. 5 eDRM ca aly ic ac i i y: a) CO 2 &CH 4 con e sions; b) H 2 /CO mola a io. in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e2791727912 Hence, we ha e pe o med s abili y s udies a wo di e en empe a u es. This way, we will be able o s udy he ca bon deposi ion ole ance and me al sin e ing esis ance o bo h ca alys s in mo e in-dep h manne . On he hand we will assess he coking ole ance a wo di e en ope a ion egimes and on he o he hand we will e alua e he sin e ing esis ance when inc easing he he mal s ess on he ca alys 's pa icles. The i s s abili y es was pe o med a 650 C. As shown in Fig. 7, bo h me hane and ca bon dioxide con e sions o he Ni/CeO 2 eAl 2 O 3 sample dec ease wi h ime-on-s eam, while con e sions o he NieRh/CeO 2 eAl 2 O 3 sample emain p ac- ically cons an o e he 48 h o he es . This esul clea ly e idences he supe io i y o he bime allic o mula ion showcasing he posi i e impac o small amoun s o Rh. In o de o s udy he ca bonaceous deposi s o e bo h ca alys s, TPO and XRD analyses we e pe o med on he spen samples a e he s abili y es . The peaks obse ed in he TPO diag am (Fig. 8a) ep esen he gene a ion o CO 2 by he oxida ion o he ca bon deposi s o med, so i can be a i med ha he ca bon deposi ed in he NieRh ca alys is minimal compa ed o ha o he e e ence sample. The empe a u e a which he CO 2 maximums appea p o ides in o ma ion on he na u e o he ca bonaceous spe- cies deposi ed on he ca alys su ace. Gene ally speaking, ca bonaceous deposi s ha e di e en s uc u e o de s and mo phologies, and, in ou case, we can dis inguish be ween h ee ypes [42e50]: The i s peak appea s a 300e400 C and co esponds o a e y labile amo phous ca bon (C a ) which can be emo ed a low empe a u es. The second peak appea s a ~500 C and co esponds o g aphi ic ca bon (C b ) which is e y he mally s able. The C b is ha dly emo ed by gasi ica ion so i leads o se e e ca aly ic deac i a ion. Finally, he C g species we e asc ibed o ca bon nano ubes, hey appea a ~650 C. As we can see in Fig. 8.a, pos -s abili y (650 C) TPO analysis show mo e C b deposi s on he monome allic ca alys han on he bime allic one. This jus i ies he con inuous dec ease o CH 4 and CO 2 con e sions o he Ni/CeO 2 eAl 2 O 3 which is ela ed o ca bon poisoning and e idences he poo e pe o - mance o he e e ence ma e ial compa ed o he ad anced bime allic o mula ion. In addi ion, he XRD analyses o bo h spen samples (Fig. 8b) also show a clea di e ence since he e is a peak a 26app oxima ely in he monome allic sample ha i is no seen in he bime allic sample. This peak co e- sponds o g aphi ic ca bon deposi s because i has a c ys al- line s uc u e de e mined [51], hus con i ming ha he e a e mo e g aphi ic ca bon deposi s on he monome allic ca alys in ai ag eemen wi h he TPO analyses. The second s abili y es was pe o med a 850 C(Fig. 9). In his ins ance, he CO 2 con e sions dec ease as he same way o bo h ca alys s, going om almos 100%e95% a he end o he expe imen . None heless, he me hane con e sion o he Ni/CeO 2 eAl 2 O 3 sample dec eases om 97% down o 75% while he CH 4 con e sion o he NieRh/CeO 2 eAl 2 O 3 sample de- clines less, going om almos 95%e80%. E en so, hese con- e sions a e highe han hose achie ed du ing he s abili y es a 650 C gi en he endo he mic na u e o he eac ion. As in he p e ious case, he TPO analyses o he pos - s abili y samples a 850 C also ep esen h ee e y dis inc peaks co esponding o he h ee ypes o ca bon deposi s men ioned abo e (Fig. 10a). In his case, he a ea unde he cu e o NieRh/CeO 2 eAl 2 O 3 sample is signi ican ly lowe han he a ea unde he cu e o Ni/CeO 2 eAl 2 O 3 sample, which econ i ms ha he addi ion o Rh o he Ni ca alys imp o es coking esis ance. In ac , wi h a iew o acili a e i s isual- isa ion, he signal o he o me has been mul iplied by a ac o o 4, as i was di icul o sepa a e he wo peaks on a no mal scale. I mus be emphasised he ca bon deposi ion is he modynamically mo e a ou ed a lowe empe a u es be ween 600 and 750 C. In any case ou bime allic sample ou pe o med he e e ence ca alys s in bo h empe a u e egimes. Howe e , g aphi ic ca bon o ma ion was lowe on he monome allic ca alys in his es , as coke o ma ion is mo e a ou ed a lowe empe a u es. A pa icula i y o his s a- bili y es is ha i is possible o obse e how he sin e ing phenomenon a ec s he monome allic ca alys wi h he XRD Fig. 6 eXRD o spen samples. Fig. 7 e650 ºC-S abili y es esul s. in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e27917 27913 o hese samples (Fig. 10b). The peak o Ni loca ed a 51.8was used o es ima e he c ys alli e size by means o Sche e equa ion. I was ound ha he c ys alli e size is highe in he monome allic ca alys . To make a compa ison wi h he Ni c ys alli e size be o e eac ion, he same p ocedu e was pe - o med wi h he decon olu ed Ni peak o bo h educed ca a- lys s. In he case o he monome allic sample, he Ni c ys alli e size inc eased om 12 nm o 17.5 nm, while in he bime allic ca alys his alue inc eased om 11.7 nm o 13 nm. This is e idence o how he addi ion o a bime allic ac i e phase p e en s he sin e ing deac i a ion o he ca alys s since he seg ega ion o Ni species om s able bime allic o mula ions is somewha less ene ge ically a ou able in compa ison o pu e Ni pa icles [52,53]. Fig. 8 ePos cha ac e isa ion a e s abili y es a 650 C: a) TPO; b) XRD. Fig. 9 e850 ºC-S abili y es esul s. Fig. 10 ePos cha ac e isa ion a e s abili y es a 850 C: a) TPO; b) XRD. in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e2791727914 Compa ing he esul s ob ained in he s abili y es s a 650 C and 850 C, we can s a e ha he deac i a ion a 650 C is mainly caused by he o ma ion o coke, while a 850 C he deac i a ion by sin e ing p e ails, as less ca bon o ma ion is obse ed. In bo h si ua ions, he bime allic ca alys s ands ou as a p omising al e na i e. A 650 C he p edominan seconda y eac ion is me hane decomposi ion (Eq. (4)) whe e ca bon deposi s and hyd ogen a e o med om me hane. This explains he low me hane yields and ha he H 2 /CO a io emains abo e 1 a his em- pe a u e. A 850 C, howe e , he e e se eac ion o he Bou- doua d eac ion (Eq. (5)) s a s o occu , whe e he ca bon o med wi h CO 2 is con e ed o CO. This could dec ease he H 2 / CO a io, bu C b is e y he mallys able,and heCO o ma ionis no la ge enough o coun e ac he excessi e H 2 o ma ion. Conclusions Biogas con e sion o H 2 - ich syngas ep esen s a s aigh o - wa d app oach o g eenhouses alo isa ion in he con ex o a ci cula economy. He ein, a mul icomponen ca alys based on NieRh bime allic ac i e phase suppo ed on a ce ia- p omo ed alumina (NieRh/CeO 2 eAl 2 O 3 ) has been p epa ed and es ed in biogas upg ading ia DRM. The pe o mance o his ad anced sys em has been compa ed o ha o a e e - ence monome allic nickel homologue (Ni/CeO 2 eAl 2 O 3 ). Di e en p e- eac ion and pos - eac ion cha ac e isa ion es s ha e been ca ied ou , as well as a eac ion moni o ing based on he CH 4 and CO 2 con e sions and he H 2 /CO mola a io ob ained. The s a ing hypo hesis sugges ed be e pe - o mances o he bime allic ca alys han o he mono- me allic one. TPR expe imen s showed a highe educibili y o he bime allic sample compa ed o he monome allic one, which implies be e edox p ope ies, enhancing he ca aly ic pe - o mance du ing he DRM eac ion. In he ca aly ic ac i i y es , he di e ences obse ed a e negligible howe e key disc epancies a e obse ed in he ca alys s’ s abili y. The esul s ob ained in he di e en s a- bili y es s show ha he e is indeed a syne gic NieRh e ec ha imp o es ca aly ic s abili y, hus he con e sions on he bime allic ca alys emain almos cons an o e long- e m uns while he monome allic ca alys su e s a signi ican ac i i y d op showcasing i s deac i a ion. Pos -s abili y TPO expe imen s showed he o ma ion o wo di e en ca bonaceous species, an amo phous ca bon and a c ys alline ca bon, he la e being he cause o deac i- a ion as i is e y he mally s able. Ou esul s demons a e ha he monome allic sys ems nuclea e g ea e concen a- ion o ca bon han he ad anced bime allic sample being ca bon deposi ion a ou ed in he low- empe a u e ange (i.e. 650 C). Wi h he s abili y es a 850 C he sin e ing o nickel pa icles can be also obse ed, wi h a ema kable inc ease on he Ni clus e s size on he monome allic ca alys compa ed o he bime allic which demons a es a g ea e ole ance o- wa ds ac i e phase agglome a ion. O e all, his pape showcases he key ole played by he - e ogeneous ca alysis wi hin CO 2 con e sion echnologies and he esea ch s ill needed o keep e ining ca aly ic o mula- ions o a oid deac i a ion seeking o an op imal ope a ion. In pa icula , his wo k has demons a ed ha he addi ion o low amoun s o Rh signi ican ly imp o es he ca aly ic pe - o mance, educing coke o ma ion and sin e ing. A no el angle o his wo k is he p o en coking esis ance o ou mul icomponen ca alys s in he low- empe a u e DRM win- dow. This is a ema kable esul beyond he ca alys s op i- miza ion opening a new esea ch a enue o he design o low- empe a u e DRM uni s esul ing in a po en ial angible educ ion in ene gy consump ion and o e all p ocess ope a- ion cos s. In any case, he design o ad anced mul icomponen ca - alys s as he one p esen ed he ein will con ibu e o acili a e he ansi ion owa ds g eene indus ial p ocesses o p oduce low-ca bon uels and added alue chemicals. 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 . Acknowledgemen s Financial suppo o his wo k was ga he om Spanish Minis y o Science and Spanish Minis y o Science and Inno a ion h ough he p ojec s PLEC2021-008086, RYC2018- 024387-I as well as he p ojec PID2019-108502RJ-I00. This wo k was also pa ially unded by he Uni e si y o Se ille ia he VI PPIT g an scheme o alen ed esea che s. Se gio Ca asco would also like o acknowledge he Sociedad Espa- ~ nola de Ca  alisis (SECAT) o his ellowship. Funding om he Eu opean Commission h ough he BIOALL p ojec (G an Ag eemen : 101008058) SASOL is kindly acknowledged o p o iding he ca alys s'suppo s. 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.ijhydene.2023.03.301. e e ences [1] Yo o KO, Da amola MO. CO2 emission sou ces, g eenhouse gases, and he global wa ming e ec . In: Ad ances in ca bon cap u e. Else ie ; 2020. p. 3e28. h ps://doi.o g/10.1016/b978- 0-12-819657-1.00001-3. [2] Kappelle M. Uni ed in science 2020 - UN clima e epo . 2020. h ps://doi.o g/10.13140/RG.2.2.12801.28004. [3] Bouche O, F iedlings ein P, Collins B, Shine KP. The indi ec global wa ming po en ial and global empe a u e change po en ial due o me hane oxida ion. En i on Res Le 2009;4. h ps://doi.o g/10.1088/1748-9326/4/4/044007. [4] Ullah Khan I, Ha iz Dza an O hman M, Hashim H, Ma suu a T, Ismail AF, Rezaei-Dash A zhandi M, Wan in e na ional jou nal o hyd ogen ene gy 48 (2023) 27907e27917 27915