Siliceous Zeolite-supported Palladium Catalysts for Methane Oxidation

Meeting Program — January 2018

Jing Lu
Jing Lu
Staff Sci­en­tist at Clean Air Divi­sion
John­son Matthey Inc.

 

Abstract — Cat­alyt­ic oxi­da­tion of methane in the pres­ence of excess of oxy­gen is of great inter­est as a prac­ti­cal tech­nol­o­gy to reduce methane emis­sions from com­pressed nat­ur­al gas vehi­cles, engines, and tur­bines. Typ­i­cal com­mer­cial methane oxi­da­tion cat­a­lysts are alu­mi­na-sup­port­ed pal­la­di­um cat­a­lysts. When oper­at­ed at low tem­per­a­tures, these cat­a­lysts exhib­it rapid deac­ti­va­tions on stream due to water inhi­bi­tion. In addi­tion, these Pd-cat­a­lysts are sen­si­tive to sul­fur poi­son­ing, even with the pres­ence of a trace amount (≤ 1 ppm) of SO2 in the feed. Among oth­er oxide mate­ri­als, zeo­lites were also inves­ti­gat­ed as a poten­tial sup­port for pal­la­di­um – such as the effects of frame­works and exchange or impreg­na­tion meth­ods – but no sig­nif­i­cant ben­e­fits were dis­cov­ered in the past com­par­ing to con­ven­tion­al alu­mi­na-based cat­a­lysts. Here, we demon­strate the appli­ca­tion of siliceous zeo­lites (i.e. SiO2-to-Al2O3 ratio (SAR) >1200) as Pd-sup­port, the result­ing cat­a­lysts exhib­it sig­nif­i­cant­ly improved activ­i­ty and on-stream dura­bil­i­ty at low tem­per­a­tures, and are able to be regen­er­at­ed from sul­fur poi­son­ing under real­is­tic oper­at­ing con­di­tions.

Biog­ra­phy — Jing Lu received his B.S. degree in Chem­i­cal Engi­neer­ing from Uni­ver­si­ty of Cal­i­for­nia, San­ta Bar­bara. He joined John­son Matthey in 2013 after earn­ing a Ph.D. from Uni­ver­si­ty of Cal­i­for­nia, Davis where he worked with Prof. Bruce Gates. Jing is cur­rent­ly a Staff Sci­en­tist lead­ing the devel­op­ments of selec­tive cat­alyt­ic reduc­tion, ammo­nia slip con­trol and methane oxi­da­tion cat­a­lysts for diesel and nat­ur­al gas aftertreat­ment. He is an inven­tor of sev­er­al patents and author of 19 jour­nal arti­cles.

Kinetic Peculiarities of Cu-Zeolite SCR Catalysts, and Their Practical Implications

Meeting Program — November 2017

Aleksey Yezerets
Alek­sey Yez­erets
Direc­tor of Advanced Chem­i­cal Sys­tems & Inte­gra­tion
Cum­mins Inc.

 

Abstract — Cu-Zeo­lite SCR cat­a­lysts have emerged in the recent years as the lead­ing tech­nol­o­gy for meet­ing the chal­lenge of NOx reduc­tion in diesel exhaust. Despite their excel­lent per­for­mance and sta­bil­i­ty char­ac­ter­is­tics, inte­grat­ing this class of cat­a­lysts into an effec­tive and durable exhaust aftertreat­ment sys­tem has proved non-triv­ial. Such sys­tems must be capa­ble of oper­at­ing over a broad range of tran­sient con­di­tions, sur­vive a vari­ety of nom­i­nal and off-nom­i­nal aging expo­sures, and sus­tain their activ­i­ty over many years of active duty. This requires a detailed under­stand­ing of the reac­tion mech­a­nism and deac­ti­va­tion path­ways, and the abil­i­ty to trans­late those into reac­tion engi­neer­ing guid­ance to sys­tem design, feed­back con­trol algo­rithms, and on-board diag­nos­tics. In this pre­sen­ta­tion, we will share exam­ples from our recent find­ings relat­ed to the con­trol­ling regimes of oper­a­tion and to the deac­ti­va­tion mech­a­nisms of Cu-Zeo­lite cat­a­lysts – at the lev­el of cat­a­lyst mate­r­i­al, chem­i­cal func­tions, and over­all emis­sion reduc­tion per­for­mance in the con­text of a sys­tem which con­tains mul­ti­ple cat­alyt­ic ele­ments. We will fur­ther dis­cuss the advance­ments in the abil­i­ty to mod­el the behav­iors of healthy and deac­ti­vat­ed cat­a­lysts, and the respec­tive impli­ca­tions to sys­tem opti­miza­tion and con­trol.

Biog­ra­phy — As Direc­tor of Advanced Chem­i­cal Sys­tems & Inte­gra­tion with Cor­po­rate R&T Divi­sion of Cum­mins Inc., the world’s largest inde­pen­dent man­u­fac­tur­er of diesel engines and relat­ed equip­ment, Dr. Alek­sey (Alex) Yez­erets leads a team of exper­i­men­tal­ists and mod­el­ers respon­si­ble for devel­op­ing an under­stand­ing of the per­for­mance and deac­ti­va­tion of bat­ter­ies, cat­a­lysts, and sen­sors, and for pro­vid­ing guid­ance and sup­port to elec­tri­fied and low-emis­sion prod­ucts at all stages of their life­cy­cles. He also coor­di­nates a port­fo­lio of col­lab­o­ra­tive research pro­grams with indus­tri­al part­ners, Nation­al Labs, and uni­ver­si­ties. He has authored or co-authored 35 patents and 80 peer-reviewed pub­li­ca­tions, with over 2500 total cita­tions. Alex main­tains cur­ren­cy in his field by an active engage­ment in pro­fes­sion­al, edi­to­r­i­al, and grad­u­ate edu­ca­tion activ­i­ties. His tech­ni­cal con­tri­bu­tions have been rec­og­nized by awards from the Catal­y­sis Club of Chica­go, R&D100, ACS, AIChE and SAE, as well as by two Cum­mins Julius Perr awards for inno­va­tion. Alex has been elect­ed an SAE Fel­low.

Olefin Metathesis by Supported MoOx/Al2O3 Catalysts

Meeting Program — October 2017

Anisha Chakrabar­ti — Stu­dent Speak­er

Advi­sor: Israel E. Wachs
Operan­do Mol­e­c­u­lar Spec­troscopy & Catal­y­sis Lab­o­ra­to­ry
Depart­ment of Chem­i­cal and Bio­mol­e­c­u­lar Engi­neer­ing
Lehigh Uni­ver­si­ty, Beth­le­hem, PA 18015 USA
 

Abstract — The olefin metathe­sis reac­tion was com­mer­cial­ized in the late 1960s to pro­duce eth­yl­ene and 2-butene from propy­lene in the Phillips Tri­olefin Process. The reverse reac­tion, how­ev­er, is cur­rent­ly desired due to a glob­al propy­lene short­age caused by the shift to lighter feed­stocks derived from shale gas frack­ing. Het­ero­ge­neous sup­port­ed MoOx/Al2O3 cat­a­lysts are employed for olefin metathe­sis in the Shell High­er Olefin Process (SHOP) that oper­ates between room tem­per­a­ture and ~200°C.

To probe the mol­e­c­u­lar details of the sup­port­ed MoOx/Al2O3 cat­a­lysts, a mod­ern in situ spec­troscopy approach was under­tak­en. In situ UV-vis mea­sure­ments (Eg val­ues) con­firmed the pres­ence of iso­lat­ed and oligomer­ic MoOx sur­face sites, with the lat­ter increas­ing with molyb­de­na load­ing. In situ Raman spec­troscopy revealed that at low load­ings of molyb­de­na (1 Mo atoms/nm2), only iso­lat­ed dioxo (O=)2MoO2 sur­face sites are present. As the molyb­de­na load­ing is increased (1–4.6 Mo atoms/nm2), oligomer­ic mono-oxo O=MoO4 sur­face sites co-exist with the iso­lat­ed dioxo (O=)2MoO2 sur­face sites. Above mono­lay­er load­ings (>4.6 Mo atoms/nm2), crys­talline MoO3 nanopar­ti­cles are also present. In situ IR indi­cates that the iso­lat­ed dioxo MoO4 sites are anchored at more basic HO-μ1-AlIV sur­face hydrox­yls, while the sur­face oligomer­ic mono-oxo sites are anchored to more acidic HO-μ1/3-AlV/VI sur­face hydrox­yls. Propy­lene metathe­sis at reac­tion con­di­tions sug­gest that the iso­lat­ed dioxo (O=)2MoO2 sur­face site may still be present after acti­va­tion of the mono-oxo sur­face sites with propy­lene. In situ UV-vis dur­ing propy­lene metathe­sis indi­cates that Mo+6 sites are dom­i­nant dur­ing propy­lene metathe­sis due to the pres­ence of unre­duced sur­face dioxo Mo+6O4 sites and re-oxi­da­tion of reduced Mo+4 sites by propy­lene back to Mo+6=CH2 and Mo+6=CHCH3 reac­tion inter­me­di­ates. The sur­face chem­istry was chem­i­cal­ly probed by C3H6-TPSR that ini­tial­ly formed oxy­genat­ed prod­ucts (CH3CHO, H2CO, CH3COCH3, H2O and CO/CO2) dur­ing cat­a­lyst acti­va­tion. The reac­tiv­i­ty of the acti­vat­ed cat­a­lysts to butene pro­gres­sive­ly increased with molyb­de­na load­ing, indi­cat­ing that the oligomer­ic mono-oxo MoOx sites are much more active than iso­lat­ed dioxo MoO4 sites for olefin metathe­sis. The crys­talline MoO3 nanopar­ti­cles, how­ev­er, were found to be inac­tive for metathe­sis. This pre­sen­ta­tion will address the fun­da­men­tal mol­e­c­u­lar and struc­tur­al details of the sup­port­ed MoOx/Al2O3 cat­a­lysts dur­ing propy­lene metathe­sis and estab­lish their struc­ture-activ­i­ty rela­tion­ships.

Converting CO2 via Thermocatalysis and Electrocatalysis

Meeting Program — October 2017

Jingguang Chen
Jing­guang Chen
Thay­er Lind­s­ley Pro­fes­sor of Chem­i­cal Engi­neer­ing
Colum­bia Uni­ver­si­ty

 

Abstract — Ris­ing atmos­pher­ic con­cen­tra­tion of CO2 is fore­cast­ed to have poten­tial­ly dis­as­trous effects on the envi­ro­ment from its role in glob­al warm­ing and ocean acid­i­fi­ca­tion. Con­vert­ing CO2 into valu­able chem­i­cals and fuels is one of the most prac­ti­cal routes for reduc­ing CO2 emis­sions while fos­sil fuels con­tin­ue to dom­i­nate the ener­gy sec­tor. The cat­alyt­ic reduc­tion of CO2 by H2 can lead to the for­ma­tion of three types of prod­ucts: CO through the reverse water-gas shift (RWGS) reac­tion, methanol via selec­tive hydro­gena­tion, and methane by the metha­na­tion path­way. In the cur­rent talk we will first describe our efforts in con­trol­ling the cat­alyt­ic selec­tiv­i­ty for the three prod­ucts using a com­bi­na­tion of DFT cal­cu­la­tions and sur­face sci­ence stud­ies over sin­gle crys­tal sur­faces, cat­alyt­ic eval­u­a­tion of sup­port­ed cat­a­lysts, and in-situ char­ac­ter­i­za­tion under reac­tion con­di­tions. Next, we will dis­cuss our efforts in con­vert­ing CO2 with­out using H2. This is moti­vat­ed by the fact that ~95% of H2 is gen­er­at­ed from hydro­car­bon-based feed­stocks, pro­duc­ing CO2 as a byprod­uct. We will present two approach­es to avoid using H2 for CO2 con­ver­sion. The first approach involves the uti­liza­tion of light alka­nes, such as ethane, to direct­ly reduce CO2 via the dry reform­ing path­way to pro­duce syn­the­sis gas (C2H6 + 2CO2 → 4CO + 3H2) and the oxida­tive dehy­dro­gena­tion route to gen­er­ate eth­yl­ene (C2H6 + CO2 → C2H4 + CO + H2O). The sec­ond approach is the elec­trol­y­sis of CO2 to pro­duce syn­the­sis gas with con­trolled CO/H2 ratios. We will con­clude our pre­sen­ta­tion by pro­vid­ing a per­spec­tive on the chal­lenges and oppor­tu­ni­ties in con­vert­ing CO2 via var­i­ous routes in ther­mo­catal­y­sis and elec­tro­catal­y­sis.

Biog­ra­phy — Jing­guang Chen is the Thay­er Lind­s­ley Pro­fes­sor of chem­i­cal engi­neer­ing at Colum­bia Uni­ver­si­ty, with a joint appoint­ment as a senior chemist at Brookhaven Nation­al Lab­o­ra­to­ry. He received his PhD degree from the Uni­ver­si­ty of Pitts­burgh and then car­ried out his Hum­boldt post­doc­tor­al research in KFA-Julich in Ger­many. After spend­ing sev­er­al years as a staff sci­en­tist at Exxon Cor­po­rate Research, he start­ed his aca­d­e­m­ic career at the Uni­ver­si­ty of Delaware in 1998 and rose to the rank of the Claire LeClaire Pro­fes­sor of chem­i­cal engi­neer­ing and the direc­tor of the Cen­ter for Cat­alyt­ic Sci­ence and Tech­nol­o­gy. He moved to Colum­bia Uni­ver­si­ty in 2012. He is the co-author of 21 US patents and over 340 jour­nal pub­li­ca­tions with over 15,000 cita­tions. He is cur­rent­ly the pres­i­dent of the North Amer­i­can Catal­y­sis Soci­ety (NACS) and an asso­ciate edi­tor of ACS Catal­y­sis. He received many catal­y­sis awards, includ­ing the 2015 George Olah award from ACS and the 2017 Robert Bur­well Lec­ture­ship from NACS.

Structure Activity Relationships in Homogeneous Catalysis

Meeting Program — September 2017

Thomas Colacot
Thomas Cola­cot
Tech­ni­cal Fel­low & Glob­al R & D Man­ag­er
John­son Matthey

 

Abstract — Homo­ge­neous catal­y­sis is a mol­e­c­u­lar phe­nom­e­non, where the struc­ture of the cat­a­lyst plays a sig­nif­i­cant role on the activ­i­ty and selec­tiv­i­ty of a cat­alyt­ic reac­tion. Three cas­es stud­ies will be dis­cussed dur­ing the talk to explain the phe­nom­e­na. The top­ics are

  1. High puri­ty pal­la­di­um acetate vs com­mer­cial in organ­ic syn­the­sis
  2. Ir pre cat­a­lysts for C-H acti­vat­ed bory­la­tion
  3. Gen­er­a­tion of L1Pd(0) cat­a­lysts for advanced cross cou­pling.

Ref­er­ences:

  • Book: New Trends in Cross Cou­pling: The­o­ry and Appli­ca­tions, ed. Thomas J. Cola­cot, Roy­al Soci­ety of Chem­istry, Cam­bridge, UK, 2015. ISBN: 978–1-84973–896-5
  • Carin C. C. Johans­son Seechurn, Thomas Sperg­er, There­sa. G. Scrase, Franziska. Schoenebeck and Thomas. J. Cola­cot*, J. Am. Chem. Soc., 2017 (DOI: 10.1021/jacs.7b01110). This work was fea­tured in the April 5 th issue of C & EN. Please see: http://​acsmeet​ings​.cen​mag​.org/​c​h​e​m​i​s​t​s​-​g​e​t​-​b​e​t​t​e​r​-​a​c​q​u​a​i​n​t​e​d​-​w​i​t​h​-​p​a​l​l​a​d​i​u​m​-​c​a​t​a​l​y​s​ts/
  • William A. Car­ole and Thomas J. Cola­cot* Chem. Eur. J, 2016, 22, 7686 (with jour­nal cov­er graph­ics – this work was fea­tured in C & EN. page 20, May 2 nd, 2016)
  • Peter G. Gild­ner, Andrew DeAn­ge­lis, and Thomas J. Cola­cot*, Org. Lett., 2016, 18 (6), 1442–1445 DOI: 10.1021/acs.orglett.6b0037
  • William A. Car­ole, Jonathan Bradley, Mis­bah Sar­war and Thomas J. Cola­cot* Org. Lett., 2015, 17 (21), 5472–5475. DOI: 10.1021/acs.orglett. 5b02835
  • Thomas. J. Cola­cot, Angew Chem. Int. Ed. 2016, 54, 15611–15612.
  • Peter G. Gild­ner and Thomas J. Cola­cot* Organometallics, 2015, 34 (23), 5497–5508. DOI: 10.1021/acs.organomet.5b00567
  • Andrew J. DeAn­ge­lis , Peter G. Gild­ner , Ruis­han Chow , and Thomas J. Cola­cot* J. Org. Chem., 2015, 80 (13), pp 6794–6813, DOI: 10.1021/acs.joc.5b01005
  • Carin C. C. Johans­son Seechurn, Vil­vanathan Sivaku­mar, Deep­ak Satoskar and Thomas J. Cola­cot*, Organometallics, 2014, 33, 3514−3522.

Biog­ra­phy — Dr. Thomas J. Cola­cot received his Ph.D. in Chem­istry from IIT Madras in 1989, fol­low­ing a B.Sc. and M.Sc. in Chem­istry from the Uni­ver­si­ty of Ker­ala in 1981 and 1983, respec­tive­ly. After his doc­tor­al and post-doc­tor­al stud­ies in the US, Dr. Cola­cot went on to pur­sue an edu­ca­tion in man­age­ment, acquir­ing an MBA from Penn­syl­va­nia State Uni­ver­si­ty in 2005, while work­ing at John­son Matthey. Before join­ing John­son Matthey in 1995, Dr. Cola­cot had also worked as a Research Asso­ciate South­ern Methodist Uni­ver­si­ty (TX, USA) on a project fund­ed by Advanced Tech­nol­o­gy Pro­gram, as an Assis­tant Pro­fes­sor at Flori­da A&M Uni­ver­si­ty, and as a Post-Doc­tor­al/Teach­ing Fel­low at Uni­ver­si­ty of Alaba­ma. Hav­ing climbed up the ranks from Devel­op­ment Asso­ciate (bench chemist), Dr. Cola­cot is cur­rent­ly the Tech­ni­cal Fel­low at John­son Matthey, USA, the high­est tech­ni­cal rank for a sci­en­tist with reports from dif­fer­ent parts of the world.

As a researcher, Dr. Cola­cot has focused on many areas of homoge­nous catal­y­sis, par­tic­u­lar­ly becom­ing pro­fi­cient in pal­la­di­um-cat­alyzed cross-cou­pling. He also has exten­sive expe­ri­ence in organometal­lic and organ­ic syn­the­ses, and in process chem­istry. His work is reflect­ed in sev­er­al patents to his name, more than one hun­dred peer-reviewed pub­li­ca­tions, and numer­ous invit­ed lec­tures and sem­i­nars span­ning India, USA, Chi­na, and Europe. His recent­ly edit­ed book: New Trends in Cross Cou­pling: The­o­ry and Appli­ca­tions by the Roy­al Soci­ety of Chem­istry is wide­ly used in acad­e­mia and indus­try. Through his work, Dr. Cola­cot is cred­it­ed with being a lead­ing influ­ence in devel­op­ing excep­tion­al cat­alyt­ic sys­tems for the advance­ment of met­al-cat­alyzed syn­thet­ic organ­ic chem­istry for real world appli­ca­tions such as drug devel­op­ment, OLED’s/liquid crys­tals and agri­cul­ture. His empha­sis in design­ing cat­a­lysts and cat­alyt­ic process­es has been on their applic­a­bil­i­ty in indus­tri­al set­tings, par­tic­u­lar­ly per­tain­ing to agri­cul­ture, elec­tron­ics and med­i­cine. He is the finest exam­ple of a link between acad­e­mia and indus­try.

Dr. Colacot’s con­tri­bu­tions to the field have result­ed in many awards and acco­lades, amongst them the recent pres­ti­gious IIT Madras 2016 Dis­tin­guished Alum­nus Award for Tech­nol­o­gy Inno­va­tions and Chem­i­cal Research Soci­ety of India (2016 CRSI) Medal for out­stand­ing con­tri­bu­tions in Organometallics and Homo­ge­neous Catal­y­sis. He is the first Indi­an to be award­ed the Amer­i­can Chem­i­cal Soci­ety (ACS) Nation­al Award in Indus­tri­al Chem­istry in 2015. He also received the 2015 IPMI Hen­ry Alfred Award (2015) from the Inter­na­tion­al Pre­cious Met­al Insti­tute, spon­sored by the BASF. In 2014 he received the Indi­an Amer­i­can Ker­ala Cul­ture and Civic Cen­ter Award for his out­stand­ing con­tri­bu­tions in Applied Sci­ences. In addi­tion, he received Roy­al Soci­ety of Chem­istry 2012 Applied Catal­y­sis Award and Medal. He is also a Fel­low of the Roy­al Soci­ety of Chem­istry, UK.

Production of para-methylstyrene and para-divinylbenzene from furanic compounds

2017 Spring Symposium

Mol­ly Koehle and Raul Lobo, Chem­i­cal and Bio­mol­e­c­u­lar Engi­neer­ing, Uni­ver­si­ty of Delaware, Newark, DE

Abstract — Of the three iso­mers of methyl­styrene, para-methyl­styrene is high­ly desir­able because it yields poly­mers with supe­ri­or prop­er­ties over poly­styrene and mixed poly-methyl­styrene [1]. How­ev­er, con­trol­ling the sub­sti­tu­tion of methyl­styrene via direct acy­la­tion or alky­la­tion of toluene is dif­fi­cult because even though the para iso­mer is favored, meta and ortho iso­mers are also formed [1, 2], and sep­a­ra­tion of the iso­mer mix­ture is very dif­fi­cult due to their near­ly iden­ti­cal prop­er­ties.

The Diels-Alder cycload­di­tion and dehy­dra­tion of sub­sti­tut­ed furans with eth­yl­ene is a plau­si­ble route to p-methyl­styrene since it is inher­ent­ly selec­tive to para aro­mat­ic species. We have suc­cess­ful­ly devel­oped a three-step cat­alyt­ic route to p-methyl­styrene from methyl­fu­ran (Scheme 1) at high yield and very high iso­mer selec­tiv­i­ty. The process uses Friedel-Crafts acy­la­tion, selec­tive reduc­tions with hydro­gen and Diels-Alder cycload­di­tion with eth­yl­ene. The raw materials—furans, eth­yl­ene and acetic acid—can all be derived from bio­mass [3,4], thus allow­ing ‘green’ styrene pro­duc­tion from renew­able car­bon sources. This approach has also been extend­ed to the pro­duc­tion of p-divinyl­ben­zene. As the acy­la­tion step is known to be cat­alyzed by Lewis acids, recent work has focused on study­ing this step on Brøn­st­ed and Lewis acid zeo­lites and will be pre­sent­ed as well.

Scheme 1: Pro­duc­tion of para-methyl­styrene from methyl­fu­ran

Ref­er­ences:
[1] W.W. Kaed­ing and G.C. Bar­ile, in: B.M. Cul­bert­son and C.U. Pittman, Jr. (Eds.), New Monomers and Poly­mers, Plenum Press, New York, NY, 1984, pp. 223–241.
[2]“Aromatic Sub­sti­tu­tion Reac­tions.” http://​www2​.chem​istry​.msu​.edu/​f​a​c​u​l​t​y​/​r​e​u​s​c​h​/​V​i​r​t​T​x​t​J​m​l​/​b​e​n​z​r​x​1​.​htm
[3] A.A. Rosatel­la; S.P. Sime­onov; R.F.M. Frade, R.F.M..; C.A.M. Afon­so, Green Chem., 13 (2011) 754.
[4] C.H. Chris­tensen; J. Rass-Hansen; C.C. Mars­den; E. Taarn­ing; K. Ege­blad, Chem­SusChem, 1 (2008) 283.

Biog­ra­phy — Mol­ly obtained her B.S. in Chem­i­cal Engi­neer­ing from the Uni­ver­si­ty of Pitts­burgh and her M.S. in Chem­i­cal Engi­neer­ing from the Uni­ver­si­ty of Con­necti­cut. She has worked at the Catal­y­sis Cen­ter for Ener­gy Inno­va­tion in Prof. Raul Lobo’s group since 2013. Her work focus­es on trans­for­ma­tions of bio­mass to fuels and chem­i­cals with Bron­st­ed and Lewis acid zeo­lites.

The mechanism of CO2 reduction over Pd/Al2O3: a combined steady state isotope transient kinetic analysis (SSITKA) and operando FTIR investigation

2017 Spring Symposium

Xiang Wang, Hui Shi and János Szanyi, Insti­tute for Inte­grat­ed Catal­y­sis, Pacif­ic North­west Nation­al Lab­o­ra­to­ry, Rich­land, WA

Abstract — Under­stand­ing the crit­i­cal steps involved in the het­ero­ge­neous cat­alyt­ic CO2 reduc­tion has attract­ed a lot of atten­tion recent­ly. In order to ful­ly under­stand the mech­a­nism of this reac­tion the deter­mi­na­tion of both the rate-deter­min­ing steps and reac­tion inter­me­di­ates are vital. Steady-State Iso­topic Tran­sient Kinet­ic Analy­sis (SSITKA) is one of the most pow­er­ful tech­niques used to inves­ti­gate the ele­men­tary steps under steady-state reac­tion con­di­tions. This tech­nique pro­vides valu­able infor­ma­tion on mean res­i­dent life­time of sur­face inter­me­di­ates, sur­face con­cen­tra­tions of adsorbed reac­tant species and an upper bound of the turnover fre­quen­cy. Cou­pling SSITKA with operan­do-FTIR spec­troscopy allows us to dis­crim­i­nate between active and spec­ta­tor species present on the cat­alyt­ic sur­face under steady state reac­tion con­di­tions.  In the present work operan­do SSITKA exper­i­ments cou­pled with trans­mis­sion FTIR, mass spec­trom­e­try (MS) and gas chro­matog­ra­phy (GC) were per­formed to probe both the chem­i­cal nature and kinet­ics of reac­tive inter­me­di­ates over a Pd-Al2O3 cat­a­lysts and pro­vide a clear mech­a­nis­tic pic­ture of the CO2 hydro­gena­tion reac­tion by reveal­ing the rate-deter­min­ing steps for CH4 and CO pro­duc­tion.

Fig­ure 1 shows nor­mal­ized real-time sig­nals for the decay and increase of methane (a) and car­bon-monox­ide (b) in the efflu­ent at 533 K reac­tion tem­per­a­ture after the feed gas was switched at 0 s from CO2/H2/Ar mix­ture to 13CO2/H2 mix­ture.  With increas­ing tem­per­a­ture, the decay of CH4 and CO get faster.  By inte­gra­tion under the decay curves , the mean sur­face-res­i­dence times CH4 and  CO), the abun­dance of adsorbed sur­face inter­me­di­ates lead­ing to CH4 and CO prod­ucts  CH4 and  CO) at 533–573 K were cal­cu­lat­ed. At low tem­per­a­ture, CO2 metha­na­tion is slow­er than the reverse water-gas shift reac­tion, but became faster as the tem­per­a­ture was increased over 563 K.  The sim­i­lar appar­ent acti­va­tion ener­gies obtained for the hydro­gena­tion of adsorbed CO and for the for­ma­tion of CH4 indi­cates that the hydro­gena­tion of CO is the rate-deter­min­ing step dur­ing the CO2 metha­na­tion reac­tion. More­over, the sim­i­lar appar­ent acti­va­tion ener­gies esti­mat­ed for the con­sump­tion of adsorbed for­mates (FTIR) and for the for­ma­tion of CO (MS), indi­cates that the H-assist­ed decom­po­si­tion of for­mates is the rate deter­min­ing step in the reverse water gas shift reac­tion.  The rate-deter­min­ing step for CO for­ma­tion is the con­ver­sion of adsorbed for­mate, while that for CH4 for­ma­tion is the hydro­gena­tion of adsorbed car­bonyl. The bal­ance of the hydro­gena­tion kinet­ics between adsorbed for­mates and car­bonyls gov­erns the selec­tiv­i­ties to CH4 and CO. We applied this knowl­edge to design cat­a­lysts and achieved high selec­tiv­i­ties to desired prod­ucts. 


Fig­ure 1. Nor­mal­ized response of (a) CH4 and 13CH4 prod­ucts and (b) CO and 13CO prod­ucts as func­tions of time.

Biog­ra­phy — Dr. Szanyi‘s research is focused on sur­face sci­ence, spec­troscopy and kinet­ic stud­ies on het­ero­ge­neous cat­alyt­ic reac­tion sys­tems aimed at under­stand­ing struc­ture-reac­tiv­i­ty rela­tion­ships. In par­tic­u­lar, he is inter­est­ed in under­stand­ing the mech­a­nis­tic con­se­quences of very high (atom­ic) met­al dis­per­sion on dif­fer­ent sup­port mate­ri­als. Using a series of ensem­ble aver­aged spec­troscopy meth­ods he inves­ti­gates the fun­da­men­tal prop­er­ties of met­al atoms and small met­al clus­ters pre­pared under well con­trolled UHV con­di­tions. These results pro­vide infor­ma­tion on the ener­get­ics of the inter­ac­tions between high­ly dis­persed met­als and select­ed probe mol­e­cules. Apply­ing in situ RAIR spec­troscopy they study the bind­ing con­fig­u­ra­tions of adsor­bates to met­als, and iden­ti­fy sur­face species present on the met­al and sup­port mate­ri­als under ele­vat­ed reac­tant pres­sures. Simul­ta­ne­ous­ly, they are con­duct­ing detailed kinet­ics and operan­do spec­troscopy mea­sure­ments on mod­el high sur­face area sup­port­ed met­al cat­a­lysts using flow reac­tors and SSITKA/FTIR/MS tech­niques. These mea­sure­ments pro­vide detailed kinet­ic infor­ma­tion togeth­er with sur­face spe­ci­a­tion that allow them to great­ly enhance our mech­a­nis­tic under­stand­ing of het­ero­ge­neous cat­alyt­ic sys­tems, in par­tic­u­lar the reduc­tion of CO2. Dr Szanyi is also involved in research relat­ed to the fun­da­men­tal under­stand­ing of auto­mo­tive emis­sion con­trol catal­y­sis, con­duct­ing research in selec­tive cat­alyt­ic reduc­tion of NOx on zeo­lite-based cat­a­lysts, low tem­per­a­ture NO and CO oxi­da­tion on met­al oxides, and low tem­per­a­tures NOx and HC stor­age in zeo­lites.