DFT Investigation of Hydrogenation and Dehydrogenation Reactions on Binary Metal Alloys: Effect of Surface Ensembles and Composition

Meeting Program — March 2015

Fuat E Celik
Depart­ment of Chem­i­cal and Bio­mol­e­c­u­lar Engi­neer­ing
Rut­gers, The State Uni­ver­si­ty of New Jer­sey

Fuat Celik
Abstract
In sup­port­ed met­al cat­a­lysts, the trade­off between activ­i­ty and selec­tiv­i­ty presents an impor­tant chal­lenge for cat­a­lyst design. By allow­ing two dis­sim­i­lar met­als, we can attempt to tune the selec­tiv­i­ty of the cat­a­lyst by enhanc­ing bond-for­ma­tion and des­orp­tion rates through the addi­tion of a less-reac­tive ele­ment, while main­tain high bond dis­so­ci­a­tion activ­i­ty from the more active met­al. The result­ing cat­a­lyst prop­er­ties depend strong­ly on the cat­a­lyst com­po­si­tion and ratio of the two met­als (elec­tron­ic effect), but may also depend on the local struc­ture of sur­face ensem­bles of the alloy com­po­nents (geo­met­ric effect). In this talk we will explore two exam­ples of bina­ry alloys where sur­face com­po­si­tion and geom­e­try play an impor­tant role in deter­min­ing the selec­tiv­i­ty of the cat­a­lyst through den­si­ty func­tion­al the­o­ry (DFT).

In the first exam­ple, we have exam­ined the effect of plat­inum tin alloy struc­ture and com­po­si­tion on the kinet­ics and ther­mo­dy­nam­ics of dehy­dro­gena­tion and coke for­ma­tion path­ways dur­ing light alka­ne dehy­dro­gena­tion. Light alka­ne dehy­dro­gena­tion to olefins can add sig­nif­i­cant val­ue to hydro­car­bon process­es that gen­er­ate ethane and propane by con­vert­ing low val­ue com­mod­i­ty fuels to high-val­ue chem­i­cal and poly­mer pre­cur­sors. Sup­port­ed Pt cat­a­lysts are known to be active but show sig­nif­i­cant coke for­ma­tion and deac­ti­va­tion, which can be alle­vi­at­ed by alloy­ing with Sn and oth­er main group ele­ments. We aim to under­stand how the struc­ture and com­po­si­tion of these alloys affect their abil­i­ty to sup­press coke for­ma­tion. We inves­ti­gate the poten­tial ener­gy sur­faces from ethane along the desired path­way to ethene, and along the unde­sired path­ways towards sur­face carbon/coke. The effect of Pt/Sn ratio and sur­face geom­e­try is inves­ti­gat­ed. As com­pared to pure Pt, bond scis­sion is more dif­fi­cult on the alloys and des­orp­tion is more facile, and both effects are enhanced as three-fold hol­low sites con­sist­ing of only Pt atoms are elim­i­nat­ed.

In the sec­ond exam­ple, we eval­u­ate Au/Ni near-sur­face alloys as poten­tial oxy­gen reduc­tion cat­a­lysts for the direct syn­the­sis of hydro­gen per­ox­ide from O2 and H2, there­by avoid­ing the cur­rent anthraquinone process. While Au may have high­er O-H bond for­ma­tion activ­i­ty, it is a poor O2-dis­so­ci­a­tion cat­a­lyst, and like­wise Ni is very effec­tive at O2-dis­so­ci­a­tion but not oxy­gen hydro­gena­tion. Alloy­ing Au with Ni(111) low­ers H2 dis­so­ci­a­tion bar­ri­er while keep­ing the O2 dis­so­ci­a­tion bar­ri­er large rel­a­tive to O2 hydro­gena­tion. Des­orp­tion of H2O2 is sim­i­lar­ly com­pet­i­tive with H2O2 dis­so­ci­a­tion on alloy sur­faces. How­ev­er, the selec­tiv­i­ty for the OOH rad­i­cal remains a chal­lenge, with bar­ri­er­less O-O bond dis­so­ci­a­tion and large (1.3 eV) hydro­gena­tion bar­ri­ers. We fur­ther inves­ti­gate how the Au/Ni sur­face may rearrange itself to regen­er­ate three-fold hol­lows of Ni atoms in the pres­ence of strong­ly adsorb­ing sur­face species.

Methane Conversion to Methanol on Copper Containing Small Pore Zeolites

Meeting Program — February 2015

Bahar Ipek
Depart­ment of Chem­i­cal and Bio­mol­e­c­u­lar Engi­neer­ing
Uni­ver­si­ty of Delaware

Bahar Ipek
Abstract
Methan­otroph­ic bac­te­ria con­tain­ing par­tic­u­lar methane monooxy­ge­nase (pMMO), a Cu-con­tain­ing enzyme, or sol­u­ble methane monooxy­ge­nase (sMMO), an iron-met­al­loen­zyme can oxi­dize methane to methanol selec­tive­ly at ambi­ent con­di­tions 1. The zeo­lite Cu-ZSM-5 was report­ed to acti­vate the methane C-H bond—with a homolyt­ic bond dis­so­ci­a­tion ener­gy of 104 kcal/mol— at tem­per­a­tures as low as 120 °C 2 after pre­treat­ment in O2 3. The reac­tive cop­per species are believed to con­tain extra-lat­tice oxy­gen, and in the case of Cu-ZSM-5, to be a mono-μ-oxo-dicop­per com­plex ([Cu—O—Cu]2+) 4. Although a cor­re­la­tion was found between the con­cen­tra­tion of mono-μ-oxo-dicop­per species and the amount of methanol pro­duced by Cu-ZSM-5 5, no such cor­re­la­tion was found for oth­er zeo­lites that pro­duce methanol such as Cu-mor­den­ite and Cu-fer­rierite 2. We have recent­ly showed methanol pro­duc­tion on cop­per (II) exchanged small pore zeo­lites includ­ing SSZ-13 (CHA), SSZ-16 (AFX) and SSZ-39 (AEI) with yields as high as 39 μmol CH3OH/g and CH3OH/Cu ratios up to 0.09 (the largest report­ed to date).6 Here, cop­per species in these small pore zeo­lites were inves­ti­gat­ed with UV–vis and Raman spec­troscopy after O2-treat­ment at a tem­per­a­ture of 450 °C. No evi­dence of mono-μ-oxo-dicop­per species was found in the spec­tra of Cu-SSZ-13,Cu-SSZ-16 and Cu-SSZ-39 6, how­ev­er Cu—Oextralattice vibra­tions at 574 cm-1 were detect­ed in Raman spec­tra of Cu-SSZ-13 and Cu-SSZ-39 zeo­lites which is indica­tive of a dif­fer­ent Cux­Oy active species respon­si­ble for methanol pro­duc­tion in small pore zeo­lites.

Ref­er­ences
1. Han­son, R. S.; Han­son, T. E., Methan­otroph­ic Bac­te­ria. Micro­bi­o­log­i­cal Reviews
1996, 60, 439–471.
2. Smeets, P. J.; Groothaert, M. H.; Schoonhey­dt, R. A., Cu based zeo­lites: A UV–vis
study of the active site in the selec­tive methane oxi­da­tion at low tem­per­a­tures.
Catal. Today 2005, 110 (3–4), 303–309.
3. Groothaert, M. H.; Smeets, P. J.; Sels, B. F.; Jacobs, P. A.; Schoonhey­dt, R. A.,
Selec­tive Oxi­da­tion of Methane by the Bis(mu-oxo)dicopper Core Sta­bi­lized on
ZSM-5 and Mor­den­ite Zeo­lites. Jour­nal of Amer­i­can Chem­i­cal Soci­ety 2005, 127,
1394–1395.
4. Woertink, J. S.; Smeets, P. J.; Groothaert, M. H.; Vance, M. A.; Sels, B. F.;
Schoonhey­dt, R. A.; Solomon, E. I., A [Cu2O]2+ core in Cu-ZSM-5, the active site in
the oxi­da­tion of methane to methanol. Pro­ceed­ings of the Nation­al Acad­e­my of
Sci­ences of the Unit­ed States of Amer­i­ca 2009, 106 (45), 18908–13.
5. Bez­nis, N. V.; Weck­huy­sen, B. M.; Bit­ter, J. H., Cu-ZSM-5 Zeo­lites for the For­ma­tion
of Methanol from Methane and Oxy­gen: Prob­ing the Active Sites and Spec­ta­tor
Species. Catal. Lett. 2010, 138 (1–2), 14–22.
6. Wulfers, M. J.; Teke­tel, S.; Ipek, B.; Lobo, R. F., Con­ver­sion of Methane to Methanol
on Cop­per Con­tain­ing Small Pore Zeo­lites and Zeo­types. Chem Com­mun 2015, xx,
xx-xx.

Bridging Heterogeneous Catalysis and Electro-catalysis: Catalytic Reactions Involving Oxygen

Meeting Program — February 2015

Dr. Umit S. Ozkan
Depart­ment of Chem­i­cal and Bio­mol­e­c­u­lar Engi­neer­ing
The Ohio State Uni­ver­si­ty

Umit Ozkan
Abstract
Cat­alyt­ic reac­tions that involve oxy­gen can be found in a large num­ber of process­es, includ­ing those in ener­gy-relat­ed appli­ca­tions, in emis­sion con­trol and in process­es impor­tant for the chem­i­cal indus­try. Whether the cat­alyt­ic reac­tion is an oxy­gen inser­tion step as in a selec­tive oxi­da­tion reac­tion, or an oxy­gen removal step as in a hydrodeoxy­gena­tion reac­tion, oxy­gen has proven to be a very chal­leng­ing com­po­nent, often deter­min­ing the selec­tiv­i­ty of the reac­tion. Some exam­ples from our lab­o­ra­to­ries that bridge catal­y­sis and elec­tro-catal­y­sis will be dis­cussed, rang­ing from oxida­tive dehy­dro­gena­tion of alka­nes to oxy­gen reduc­tion reac­tion in fuel cells.

Challenges and Advances in Catalytic Fast Pyrolysis of Biomass using Zeolites

Meeting Program — January 2015

Dr. Julia Val­la
Chem­i­cal and Bio­mol­e­c­u­lar Engi­neer­ing Depart­ment
Uni­ver­si­ty of Con­necti­cut, Storrs, CT

Abstract
Ther­mo­chem­i­cal con­ver­sion of bio­mass to ener­gy, fuels and chem­i­cals is an attrac­tive tech­nol­o­gy for the tran­si­tion from fos­sil resources to a renew­able-based econ­o­my. Cat­alyt­ic Fast Pyrol­y­sis (CFP) of bio­mass is a par­tic­u­lar­ly inter­est­ing tech­nol­o­gy for bio­mass con­ver­sion con­sid­er­ing the already exten­sive infra­struc­ture for hydro­car­bons pro­duc­tion. How­ev­er, many chal­lenges remain unsolved before the deploy­ment of the bio­mass CFP can be real­ized, includ­ing: a) char and coke for­ma­tion, which caus­es rapid cat­a­lyst deac­ti­va­tion; and b) high oxy­gen con­tent in the bio-oil, which makes it incom­pat­i­ble with today’s hydro­car­bon fuels. With respect to the first chal­lenge, it is imper­a­tive to first under­stand the ori­gin and the for­ma­tion of char and coke dur­ing CFP. Con­sid­er­ing the sec­ond chal­lenge, it is impor­tant to under­stand which cat­a­lyst prop­er­ties can enhance the deoxy­gena­tion reac­tions and increase the bio-oil selec­tiv­i­ty to hydro­car­bons. ZSM-5 zeo­lites have been rec­og­nized as one of the most promis­ing zeo­lites for CFP due to their shape selec­tiv­i­ty and their deoxy­gena­tion abil­i­ty. How­ev­er, their micro­p­ore struc­ture can lim­it the acces­si­bil­i­ty of heavy com­pounds to the active sites of their frame­work. Mod­i­fy­ing the zeo­lite pore archi­tec­ture to cre­ate hier­ar­chi­cal struc­tures could pro­vide a solu­tion to this chal­lenge. Fur­ther­more, the CFP process design itself (in situ or ex situ) can alter the prod­uct yield and selec­tiv­i­ty and, thus, the bio-oil qual­i­ty. Dur­ing this pre­sen­ta­tion we will dis­cuss how the zeo­lite prop­er­ties and loca­tion with­in the CFP process (in situ or ex situ) can affect the coke/char for­ma­tion and the deoxy­gena­tion reac­tions for enhanced bio-oil qual­i­ty.
Julia Valla
Biog­ra­phy
Iou­lia (Julia) Val­la is an Assis­tant Pro­fes­sor in the Chem­i­cal & Bio­mol­e­c­u­lar Engi­neer­ing Depart­ment at the Uni­ver­si­ty of Con­necti­cut. She received her PhD in the field of the devel­op­ment of new zeo­lites for the decom­po­si­tion of sul­fur com­pounds in naph­tha and the pro­duc­tion of envi­ron­men­tal gaso­line from the Aris­to­tle Uni­ver­si­ty of Thes­sa­loni­ki in Greece. She has served in a lead­er­ship role with Rive Tech­nol­o­gy, Inc. on the com­mer­cial­iza­tion of a nov­el zeo­lite with ordered meso­porous struc­ture for refin­ery appli­ca­tions. Dr. Valla’s research focus­es on the mod­i­fi­ca­tion of zeo­lites struc­ture and their appli­ca­tion in catal­y­sis, adsorp­tion and ener­gy. She is the author/­co-author of 9 papers in peer-reviewed jour­nals, 1 book chap­ter and 2 patents. Dr. Val­la is the recip­i­ent of the Euro­pean Award “RUCADI, Recov­ery and Uti­liza­tion of Car­bon Diox­ide” for her study on the role of CO2 on the reform­ing of nat­ur­al gas for the pro­duc­tion of methanol. At the Uni­ver­si­ty of Con­necti­cut, Dr. Val­la received an award spon­sored by the Nation­al Sci­ence Foun­da­tion for the study “Turn­ing Tars into Ener­gy: Zeo­lites with Hier­ar­chi­cal Pore Struc­ture for the Cat­alyt­ic Removal of Tars”. The study is focused on a nov­el appli­ca­tion of hier­ar­chi­cal­ly struc­tured meso­porous bifunc­tion­al cat­a­lysts for the ther­mo­chem­i­cal upgrad­ing of unde­sir­able tars from bio­mass pyrol­y­sis or gasi­fi­ca­tion to valu­able hydro­car­bons.

Challenges and Solutions in Developing Zeolite Supported Transition Metal Catalysts for Lean-Burn NOx Emission Control

Meeting Program — September 2014

 
Hai-Ying Chen
Emis­sion Con­trol Tech­nolo­gies
John­son Matthey Inc.
Wayne, PA

chenh@​jmusa.​com
 
Abstract — Reduc­tion of NOx emis­sions from lean-burn engine exhaust has been a main top­ic of envi­ron­men­tal catal­y­sis in the past 20 years. The chal­lenge is the selec­tive con­ver­sion of a low con­cen­tra­tion of NOx (~100 ppm) in the pres­ence of large excess of O2 (~10%). Although zeo­lite sup­port­ed tran­si­tion met­al cat­a­lysts were iden­ti­fied in ear­ly 1990s as promis­ing cat­a­lysts, such a tech­nol­o­gy was not imple­ment­ed till recent­ly.

Ear­ly stud­ies main­ly focused on the devel­op­ment of zeo­lite sup­port­ed tran­si­tion met­al, pri­mar­i­ly Cu and Fe, cat­a­lysts for the selec­tive cat­alyt­ic reduc­tion of NOx with hydro­car­bons (HC-SCR). Even though the HC-SCR tech­nol­o­gy has been con­sid­ered as the “holy grail” of auto­mo­tive catal­y­sis, tech­ni­cal chal­lenges on the activ­i­ty, selec­tive and dura­bil­i­ty of the cat­a­lysts were rec­og­nized to be dif­fi­cult to over­come for the tech­nol­o­gy to be imple­ment­ed into real world appli­ca­tions. How­ev­er, the vast amount of research work, espe­cial­ly the fun­da­men­tal stud­ies on the reac­tion and the cat­a­lyst deac­ti­va­tion mech­a­nisms, demon­strat­ed that the activ­i­ty and selec­tiv­i­ty of this type of cat­a­lysts can be dras­ti­cal­ly improved if an alter­na­tive reduc­tant, NH3, is avail­able in the feed.

Exten­sive inves­ti­ga­tions on the selec­tive cat­alyt­ic reduc­tion of NOx with NH3 (NH3-SCR) began in the mid­dle 2000s aimed to enable diesel pow­ered vehi­cles to meet the US EPA 2007/2010 emis­sion reg­u­la­tions. Both Cu and Fe cat­a­lysts were con­sid­ered. Zeo­lite sup­port­ed Cu SCR cat­a­lysts are more active at low tem­per­a­ture, thus more attrac­tive for appli­ca­tions with low exhaust tem­per­a­ture. The con­ven­tion­al medi­um-pore zeo­lite (10-ring, such as ZSM-5) or large-pore zeo­lite (12-ring, such as beta) sup­port­ed Cu cat­a­lysts, how­ev­er, can­not meet the long-term dura­bil­i­ty require­ments. To over­come this major tech­ni­cal hur­dle, small-pore zeo­lite (8-ring) sup­port­ed Cu cat­a­lysts were invent­ed. On the oth­er hand, zeo­lite sup­port­ed Fe SCR cat­a­lysts are more selec­tive in uti­liz­ing NH3 for NOx reduc­tion at high tem­per­a­tures but show a strong depen­dence on the NO to NO2 ratio in the feed gas at low tem­per­a­tures. Sys­tem approach­es were devel­oped to enhance the low tem­per­a­ture SCR activ­i­ty of the Fe SCR cat­a­lysts. As such, both Cu and Fe SCR cat­a­lysts were suc­cess­ful­ly com­mer­cial­ized and applied on lean-burn diesel vehi­cles meet­ing the strin­gent US EPA 2010 emis­sion stan­dards.

Hai-Ying ChenBiog­ra­phy — Dr. Hai-Ying Chen is a Sci­en­tif­ic and Prod­uct Devel­op­ment Man­ag­er at John­son Matthey, where he leads a team of sci­en­tists to devel­op advanced emis­sion con­trol cat­a­lysts and tech­nolo­gies for both gaso­line engine and diesel engine pow­ered vehi­cles to meet the gov­ern­ment emis­sion reg­u­la­tions.

Dr. Chen received his Ph.D. in Chem­istry from Fudan Uni­ver­si­ty, Chi­na. He has pub­lished more than 50 tech­ni­cal papers in peer-reviewed jour­nals and holds 14 US/international patents. He received the Top Cit­ed Arti­cle Award by Catal­y­sis Today for arti­cles pub­lished in 1998, and was a recip­i­ent of the Amer­i­can Chem­i­cal Soci­ety Award for Team Inno­va­tion in 2009. He was named as the 2014 Her­man Pines Award in Catal­y­sis by the Chica­go Catal­y­sis Club and the 2014 Catal­y­sis Club of Philadel­phia Award by the Catal­y­sis Club of Philadel­phia.

Intrinsic Deactivation in Cobalt-Catalyzed Fischer-Tropsch Synthesis

Meeting Program — April 2014

 
Gabor Kiss, Stu­art Soled, Chris Kliew­er
Exxon­Mo­bil Res. and Eng. Co.
Annan­dale, NJ

gabor.​kiss@​exxonmobil.​com
 
Abstract — In this paper, we describe three intrin­sic deac­ti­va­tion modes observed in exper­i­men­tal cobalt Fis­ch­er-Trop­sch syn­the­sis cat­a­lysts: cobalt oxi­da­tion reversible by mild hydro­gen treat­ment, cobalt agglom­er­a­tion, and cobalt-sup­port mixed oxide for­ma­tion. All three mech­a­nisms involve redox trans­for­ma­tion of the cat­alyt­i­cal­ly active cobalt met­al.
 
Gabor_KissBiog­ra­phy — Gabor Kiss received his M.Sc. in chem­i­cal engi­neer­ing from the Uni­ver­si­ty of Veszprem (now Pan­non Uni­ver­si­ty), Hun­gary, in 1981. He worked in the Hun­gar­i­an oil indus­try for eight years before enrolling the grad­u­ate school at the Uni­ver­si­ty of Mia­mi. After receiv­ing his Ph.D. in chem­istry in 1993, he accept­ed a posi­tion at Exxon’s (now Exxon­Mo­bil) Cor­po­rate Research Lab­o­ra­to­ries in Clin­ton, NJ, where he is cur­rent­ly a Sr. Sci­en­tif­ic Asso­ciate. His research inter­ests include the kinet­ics, ther­mo­dy­nam­ics, and mech­a­nism of both homo­ge­neous and het­ero­ge­neous cat­alyt­ic process­es. He has pub­lished 26 peer-reviewed papers and has 38 patents.