Pervasiveness of Surface Metal Oxide Phases In Mixed Oxide Catalysts

Meeting Program — October 2012

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

Abstract — Mixed oxide cat­alyt­ic mate­ri­als pos­sess two or more met­al oxide com­po­nents as found in bulk mixed met­al oxides (sto­i­chio­met­ric oxides as well as sol­id solu­tions), poly­oxo meta­lates (POMs), mol­e­c­u­lar sieves, zeo­lites, clays, hydro­tal­cites and sup­port­ed met­al oxides. Although it is now well estab­lished that two-dimen­sion­al sur­face met­al oxide phas­es are present for sup­port­ed met­al oxides on tra­di­tion­al sup­ports (e.g., Al2O3, TiO2, ZrO2, SiO2, etc.), it is not cur­rent­ly appre­ci­at­ed that such sur­face met­al oxide species or phas­es are also present for oth­er types of mixed oxides. For exam­ple, recent sur­face analy­ses have demon­strat­ed that sto­i­chio­met­ric bulk mixed met­al oxides also pos­sess sur­face met­al oxide phas­es that con­trol their cat­alyt­ic activ­i­ty. For exam­ple, the cat­alyt­ic active sites for methanol oxi­da­tion to formalde­hyde over the bulk Fe2(MoO4)3 mixed oxide cat­a­lyst are sur­face MoOx species and not the bulk Fe2(MoO4)3 phase as pre­vi­ous­ly thought in the catal­y­sis lit­er­a­ture. The nanome­ter sized clus­ters in POMs also pos­sess sur­face species when a sec­ond met­al oxide com­po­nent is intro­duced (e.g., H3+xPW12-xMxO40). Depo­si­tion of met­al oxides into mol­e­c­u­lar sieves, zeo­lites, clays and hydro­tal­cites also results in the met­al oxide addi­tive usu­al­ly being present as sur­face met­al oxide species that are the cat­alyt­ic active sites for many redox and acid reac­tions. The for­ma­tion of these sur­face met­al oxide phas­es is dri­ven by their low sur­face free ener­gy and low Tam­mann tem­per­a­ture for many met­al oxides of inter­est in catal­y­sis (e.g., VOx, MoOx, CrOx, ReOx, WOx, etc.).
Biog­ra­phy — Israel E. Wachs received his under­grad­u­ate edu­ca­tion at The City Col­lege of The City Uni­ver­si­ty of New York where he grad­u­at­ed with a B.E. (ChE) in June, 1973. He received sev­er­al recog­ni­tions upon grad­u­a­tion (AIChE Award for Out­stand­ing Senior, Heller Memo­r­i­al Award for Out­stand­ing Scholas­tic Achieve­ment, and White ChE Alum­ni Award). He con­tin­ued his grad­u­ate ChE edu­ca­tion at Stan­ford Uni­ver­si­ty under the men­tor­ship of Pro­fes­sor Robert J. Madix in the area of sur­face sci­ence, and grad­u­at­ed with a PhD (ChE) in 1978. His research find­ings are con­sid­ered the first appli­ca­tion of sur­face sci­ence to catal­y­sis, and his the­sis pub­li­ca­tions are exten­sive­ly cit­ed in the sur­face sci­ence and catal­y­sis lit­er­a­ture.
INDUSTRIAL YEARS (1977–1986) — Israel joined Exxon Research & Engi­neer­ing Com­pa­ny in their Cor­po­rate Research Labs towards the end of 1977. At Exxon, he was involved with many dif­fer­ent cat­alyt­ic tech­nolo­gies over the years (selec­tive oxi­da­tion, acid catal­y­sis, syn­the­sis of syn­thet­ic fuels, hydrodesul­fu­r­iza­tion (HDS) and hydro­car­bon con­ver­sion). He obtained 100 USA and inter­na­tion­al patents dur­ing his indus­tri­al career. One of his inven­tions on the selec­tive oxi­da­tion of o-xylene to phthal­ic anhy­dride became the lead­ing inter­na­tion­al indus­tri­al cat­a­lyst for this tech­nol­o­gy and is still used around the world. At Exxon, he received the Research Incen­tive Award for one of his inven­tions on the syn­the­sis of syn­thet­ic fuels and was also select­ed to be an Exxon Fel­low for the spring semes­ter of 1986 at Cal­i­for­nia Insti­tute of Tech­nol­o­gy (Cal­Tech). He depart­ed for acad­e­mia at the end of 1986.
ACADEMIC YEARS (1987-present) — He joined the Chem­i­cal Engi­neer­ing Depart­ment of Lehigh Uni­ver­si­ty in Jan­u­ary 1987. At Lehigh, he taught many dif­fer­ent cours­es over the years: Het­ero­ge­neous Catal­y­sis, Reac­tor Engi­neer­ing, Flu­id Mechan­ics, Pro­fes­sion­al Devel­op­ment, Unit Oper­a­tions, Envi­ron­men­tal Catal­y­sis, and Air Pol­lu­tion Con­trol. He set up a world-class catal­y­sis research lab­o­ra­to­ry focus­ing on mixed met­al oxide cat­alyt­ic mate­ri­als and their char­ac­ter­i­za­tion under reac­tion con­di­tions (in situ and operan­do spec­troscopy). These stud­ies have estab­lished the foun­da­tion for the molecular/electronic struc­ture – activity/selectivity rela­tion­ships and the mol­e­c­u­lar engi­neer­ing of mixed met­al oxide cat­a­lysts. The research per­formed by Wachs and his stu­dents is well known around the world. This is reflect­ed in the many nation­al and inter­na­tion­al hon­ors he has received over the years as well as ~17,000 cita­tions to his pub­li­ca­tions with an H-index of 70 (one of the high­est among het­ero­ge­neous catal­y­sis researchers).

The cur­rent focus of Wachs’ catal­y­sis lab­o­ra­to­ry is to devel­op cat­a­lyst char­ac­ter­i­za­tion tech­niques under reac­tion con­di­tions, referred to as operan­do spec­troscopy in the recent lit­er­a­ture. The term operan­do spec­troscopy implies that the cat­a­lyst char­ac­ter­i­za­tion infor­ma­tion is being con­duct­ed simul­ta­ne­ous­ly with online prod­uct analy­sis. Along these lines, Pro­fes­sor Wachs has devel­oped instru­men­ta­tion that can simul­ta­ne­ous­ly obtain Raman, IR and UV-vis spec­tro­scop­ic infor­ma­tion and prod­uct analy­sis with an online mass spectrometer/GC sys­tem. This cut­ting-edge instru­ment is allow­ing Pro­fes­sor Wachs’ catal­y­sis research group to rapid­ly devel­op molecular/electronic struc­ture – cat­alyt­ic activity/selectivity rela­tion­ships for many dif­fer­ent cat­alyt­ic mate­ri­als and reac­tions (selec­tive hydro­car­bon oxi­da­tion, hydro­car­bon con­ver­sion with sol­id acid cat­a­lysts, gas-to-liq­uids, pho­to­cat­alyt­ic split­ting of water, enzyme catal­y­sis, CO2 cap­ture, WGS, nanocatal­y­sis, ratio­nal cat­a­lyst design, etc.).