Water Gas Shift over Industrial Cu Catalysts: A Mechanistic and Microkinetic Investigation

Meetimg Program — September 2012

Ros­tam J. Madon
BASF Cor­po­ra­tion
25 Middlesex/Essex Turn­pike
Iselin, NJ, USA 08830

Abstract — Low tem­per­a­ture water gas shift (LTS) is a com­mer­cial­ly impor­tant reac­tion that takes place over a Cu-ZnO-Al2O3 cat­a­lyst. A large num­ber of fun­da­men­tal stud­ies have been car­ried out for this reac­tion includ­ing inves­ti­ga­tions of the reac­tion mech­a­nism as typ­i­fied by Refs. [1–4]. In short, dis­cus­sions have cen­tered around (a) the redox mech­a­nism in which adsorbed H2O is dis­so­ci­at­ed to O* and OH* and the O* is removed via CO* to form CO2 – where * is an active site, and (b) for­mate as a reac­tive inter­me­di­ate. Recent­ly, Gokhale et al. [5] using a DFT inves­ti­ga­tion of the LTS reac­tion on Cu(111) pro­posed a new mech­a­nism that involves a reac­tive sur­face car­boxyl. Our study is aimed at resolv­ing which ele­men­tary steps best describe the cat­alyt­ic cycle for the LTS reac­tion. To achieve this, we used the micro­ki­net­ic mod­el­ing method­ol­o­gy pio­neered by Dumesic [6], and ana­lyzed our reac­tiv­i­ty data using all ele­men­tary steps, includ­ing those that described the redox mech­a­nism, the for­mate mech­a­nism, and the car­boxyl mech­a­nism. Thus, we ensured that there was no bias towards any par­tic­u­lar reac­tions to fit our data. We found the closed cat­alyt­ic cycle for LTS on Cu con­sists of eight ele­men­tary steps that include the for­ma­tion of COOH*, and its reac­tion with OH* to form CO2* and H2O*. The cycle does not include the reac­tion of CO2* and H* to form sur­face for­mate. How­ev­er, this is an impor­tant side reac­tion, which ensures sig­nif­i­cant cov­er­age of biden­tate for­mate species on the Cu sur­face. Biden­tate for­mate is a spec­ta­tor species whose cov­er­age increas­es with increas­ing pres­sure and decreas­es with increas­ing tem­per­a­ture. In sum­ma­ry, our inves­ti­ga­tion demon­strates that the redox and for­mate mech­a­nisms are not rel­e­vant, and that the LTS cat­alyt­ic cycle involves the for­ma­tion and reac­tion of sur­face car­boxyl. Sev­er­al relat­ed aspects of the LTS reac­tion on Cu will also be dis­cussed.


  1. Ovesen, C. V., et al. J. Catal. 158, (1996), 170.
  2. Koryabki­na, N. A. et al. J. Catal. 217, (2003), 233.
  3. Rhodes, C., Hutch­ings G.J., and Ward A.M. Catal. Today 23, (1995), 43.
  4. Her­wi­j­nen, T.V., and de Jong, W. A. J. Catal. 63, (1980), 83 and 94.
  5. Gokhale, A. A., Dumesic, J. A., and Mavrikakis, M. J. Am. Chem. Soc. 130, (2008), 1402.
  6. Dumesic, J. A., et al. “The Micro­ki­net­ics of Het­ero­ge­neous Catal­y­sis”, Amer­i­can Chem­i­cal Soci­ety, Wash­ing­ton, D. C., 1993.

Speak­er Bio — Ross com­plet­ed his under­grad­u­ate stud­ies in chem­i­cal engi­neer­ing at the Uni­ver­si­ty Depart­ment of Chem­i­cal Tech­nol­o­gy, Mum­bai, India. He did his grad­u­ate work at Stan­ford Uni­ver­si­ty, obtain­ing his Ph.D. under the guid­ance of Pro­fes­sor Michel Boudart. After com­plet­ing his post-doc­tor­al work with Pro­fes­sor W. Kei­th Hall at the Uni­ver­si­ty of Wis­con­sin — Mil­wau­kee, Ross joined Exxon Research and Engi­neer­ing Com­pa­ny. After 12 years with Exxon’s Cor­po­rate Research Lab­o­ra­to­ries, Ross joined Engel­hard Cor­po­ra­tion. Ross recent­ly com­plet­ed 25 years at Engelhard/BASF Cor­po­ra­tion where he is cur­rent­ly a Senior Research Asso­ciate.

Ross has made pio­neer­ing con­tri­bu­tions to the chem­istry and engi­neer­ing of cat­alyt­ic process­es. Ear­ly in his career with his advi­sor Michel Boudart, he devel­oped an exper­i­men­tal method to address arti­facts in kinet­ic data; a test accept­ed today as being defin­i­tive for kinet­ic con­trol in catal­y­sis. At Exxon, Ross’ stud­ies in Fis­ch­er-Trop­sch syn­the­sis demon­strat­ed the cru­cial role intra­parti­cle dif­fu­sion played in enhanc­ing hydro­car­bon chain length and in chang­ing selec­tiv­i­ty. At Engel­hard, he devel­oped impor­tant con­cepts in flu­id cat­alyt­ic crack­ing to help design com­mer­cial cat­a­lysts. He elu­ci­dat­ed the mech­a­nism by which vana­di­um caus­es struc­tur­al degra­da­tion of Y zeo­lite in FCC cat­a­lysts, and used this under­stand­ing to min­i­mize its dele­te­ri­ous effect. His stud­ies pro­vid­ed a def­i­nite assess­ment of the role of ZSM-5 addi­tives in FCC to form light olefins and high octane gaso­line. And, he defined the crit­i­cal role rare earth cations play in Y-based FCC cat­a­lysts, demon­strat­ing how the pres­ence of rare earth influ­ences hydride trans­fer reac­tions and prod­uct selec­tiv­i­ty in FCC. Most recent­ly, at BASF, Ross, togeth­er with col­leagues in acad­e­mia, elu­ci­dat­ed the mech­a­nism of the water gas shift reac­tion on cop­per, evinc­ing para­me­ters that could sig­nif­i­cant­ly improve cat­alyt­ic activ­i­ty. Impor­tant­ly, though, Ross has used his con­cep­tu­al and mech­a­nis­tic approach to cat­a­lyst research to design com­mer­cial cat­a­lysts. He is the coin­ven­tor and devel­op­er of the Redux­ion – Max­ol® fam­i­ly of FCC cat­a­lysts and of the Iso­Plus® and Ultri­um® fam­i­lies; all of which have been used com­mer­cial­ly world­wide. He coin­vent­ed the Flex-Tec® resid crack­ing cat­a­lyst which has been wide­ly and suc­cess­ful­ly deployed in demand­ing resid cat-crack­ing process­es. And most recent­ly he has devel­oped sev­er­al cop­per based cat­a­lysts for the petro­chem­i­cal indus­try.

Ross chaired the 1996 Gor­don Research Con­fer­ence on Catal­y­sis, and in 2009 was award­ed the AIChE Catal­y­sis and Reac­tion Engi­neer­ing Divi­sion Prac­tice Award.