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Per­va­sive­ness of Sur­face Met­al Oxide Phas­es In Mixed Oxide Cat­a­lysts
Israel E. Wachs
Lehigh Uni­ver­si­ty, Beth­le­hem, PA

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.).

TBA

Sup­ported Met­al Cat­a­lysts — Issues and Oppor­tu­ni­ties
Stu­art Soled, Exxon­Mo­bil

 
Oxida­tive Dehy­dro­gena­tion of Ethane to Eth­yl­ene
Anne M. Gaffney, AMG Catal­y­sis and Chem­istry Con­sult­ing, LLC
 

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Pro­gram
Sul­­fur-Resis­­tant Pd– Alloy Mem­branes for H₂ Purifi­ca­tion
Jim Miller, Carnegie Mel­lon Uni­ver­sity
 
Nature of Cat­alytic Active Sur­face Sites on Semi­con­duc­tor Pho­to­cat­a­lysts for Split­ting of Water
Som­phonh Peter Phivi­lay, Lehigh Uni­ver­sity (Stu­dent Speak­er)

TBA
John Kitchin, Carnegie Mel­lon

 

Meeting Program — April 2013

 
John Kitchin
Depart­ment of Chem­i­cal Engi­neer­ing,
Carnegie Mel­lon Uni­ver­si­ty

 
Abstract — Elec­tro­chem­i­cal water split­ting may be in inte­gral part of future ener­gy stor­age strate­gies by enabling ener­gy stor­age in chem­i­cal bonds. One of the pri­ma­ry sources of inef­fi­cien­cy in the water split­ting reac­tion is the oxy­gen evo­lu­tion reac­tion, which has high reac­tion bar­ri­ers that require addi­tion­al applied elec­tric poten­tial to dri­ve the reac­tions at prac­ti­cal rates. The most active elec­trode mate­ri­als in acid elec­trolytes include ruthe­ni­um and irid­i­um oxides, which are expen­sive but nec­es­sary for sta­bil­i­ty. In alka­line envi­ron­ments, many base met­al oxides become sta­ble, although they are still less active than Ru and Ir oxides. It has been known that small amounts of Fe can pro­mote the elec­tro­chem­i­cal activ­i­ty of nick­el oxides, mak­ing it almost as active as cobalt oxide. We have inves­ti­gat­ed the mech­a­nisms behind the pro­mo­tion using in situ Raman and syn­chro­tron spec­tro­scopies as well as ex situ char­ac­ter­i­za­tion tech­niques. Inter­est­ing­ly, we found the elec­trode changes under oxy­gen evo­lu­tion con­di­tions, turn­ing from an oxide to an oxy­hy­drox­ide phase. Fur­ther­more, the com­po­si­tion of the elec­trolyte has a sig­nif­i­cant effect on the oxy­gen evo­lu­tion activ­i­ty. We will dis­cuss these results and their impli­ca­tions in find­ing bet­ter oxy­gen evo­lu­tion elec­tro­cat­a­lysts.
 

Biog­ra­phy — John Kitchin com­plet­ed his B.S. in Chem­istry at North Car­oli­na State Uni­ver­si­ty. He com­plet­ed a M.S. in Mate­ri­als Sci­ence and a PhD in Chem­i­cal Engi­neer­ing at the Uni­ver­si­ty of Delaware in 2004 under the advise­ment of Dr. Jing­guang Chen and Dr. Mark Barteau. He received an Alexan­der von Hum­boldt post­doc­tor­al fel­low­ship and lived in Berlin, Ger­many for 1 ½ years study­ing alloy seg­re­ga­tion with Karsten Reuter and Matthias Schef­fler in the The­o­ry Depart­ment at the Fritz Haber Insti­tut. Pro­fes­sor Kitchin began a tenure-track fac­ul­ty posi­tion in the Chem­i­cal Engi­neer­ing Depart­ment at Carnegie Mel­lon Uni­ver­si­ty in Jan­u­ary of 2006. He is cur­rent­ly an Asso­ciate Pro­fes­sor. At CMU, Pro­fes­sor Kitchin is active in a major research effort with­in the Nation­al Ener­gy Tech­nol­o­gy Lab­o­ra­to­ry Region­al Uni­ver­si­ty Alliance in CO₂ cap­ture, chem­i­cal loop­ing and super­al­loy oxi­da­tion. Pro­fes­sor Kitchin also uses com­pu­ta­tion­al meth­ods to study adsor­­bate-adsor­­bate inter­ac­tions on tran­si­tion met­al sur­faces for appli­ca­tions in catal­y­sis. He was award­ed a DOE Ear­ly Career award in 2010 to inves­ti­gate mul­ti­func­tion­al oxide elec­tro­cat­a­lysts for the oxy­gen evo­lu­tion reac­tion in water split­ting using exper­i­men­tal and com­pu­ta­tion­al meth­ods. He received a Pres­i­den­tial Ear­ly Career Award for Sci­en­tists and Engi­neers in 2011.

 
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