Sur­face Reac­tions of Biomass-Derived Poly­ols on Metal Oxides and Sup­ported Metal Cat­a­lysts

2014 Spring Symposium

Carsten Siev­ers
Geor­gia Insti­tute of Tech­nol­o­gy
School of Chem­i­cal & Bio­mol­e­c­u­lar Engi­neer­ing
Atlanta, GA 30332

Abstract — Aque­ous phase process­es are expect­ed to play a key role in the pro­duc­tion of renew­able chem­i­cals and fuels from bio­mass. Facile sep­a­ra­tion makes het­ero­ge­neous cat­a­lysts an attrac­tive option for achiev­ing high effi­cien­cy in these process­es. Unfor­tu­nate­ly, lit­tle is known about the sur­face chem­istry of bio­mass-derived oxy­genates in an aque­ous envi­ron­ment. How­ev­er, this knowl­edge will be need­ed to improve the activ­i­ty, selec­tiv­i­ty, and sta­bil­i­ty of cat­a­lysts for aque­ous phase process­es to the lev­el we are used to in vapor phase reac­tions. This pre­sen­ta­tion will focus on sur­face inter­ac­tions of bio­mass-derived oxy­genates with met­al oxides (Al2O3, TiO2, ZrO2, CeO2, MgO, Nb2O5) and sup­port­ed met­al cat­a­lysts (Pt/Al2O3).

The sur­face chem­istry of aque­ous solu­tions of poly­ols on polar met­al oxides is strong­ly affect­ed by the com­pe­ti­tion between water and the poly­ols for adsorp­tion sites. Direct­ed inter­ac­tions with spe­cif­ic sur­face sites dom­i­nate. Even in the pres­ence of water, poly­ols with suf­fi­cient spa­tial sep­a­ra­tion between their alco­hol groups (e.g. glyc­erol) can chemisorb on Lewis acid sites form­ing sta­ble mul­ti­den­tate sur­face species. The fre­quen­cies of C-O stretch­ing vibra­tions of par­tic­i­pat­ing groups scale lin­ear­ly with the elec­troneg­a­tiv­i­ty of the met­al atom pro­vid­ing an indi­ca­tion for reac­tiv­i­ty trends in acid cat­alyzed reac­tions, such as dehy­dra­tion. The sur­face species described here can also sta­bi­lize met­al oxides like γ-Al2O3 against hydrol­y­sis in hot liq­uid water that would oth­er­wise dete­ri­o­rate the mate­r­i­al. Direct dehy­dra­tion of adsorbed glyc­erol on the Lewis acid sites of Nb2O5 yields hydrox­y­ace­tone as the main prod­ucts, where­as acrolein is formed when Brøn­st­ed acid sites are involved in the con­ver­sion.

In-situ spec­tro­scop­ic stud­ies pro­vide addi­tion­al insight into the kinet­ics of the con­ver­sion of oxy­genates in water. Specif­i­cal­ly, ATR-IR spec­troscopy is used to demon­strate that Pt/Al2O3 read­i­ly acti­vates bio­mass-derived oxy­genates, such as glyc­erol, to form sur­face bound CO on the Pt par­ti­cles. The num­ber of avail­able sur­face sites is increased when Pt/γ-Al2O3 is cleaned by hydro­gen and oxy­gen sat­u­rat­ed water. After this pre­treat­ment, some of the Pt sites that bind bridg­ing CO show activ­i­ty for the water-gas-shift reac­tion even at room tem­per­a­ture.
Model Release-YESBiog­ra­phy — Carsten Siev­ers obtained his Diplom and Dr. rer nat. degrees in Tech­ni­cal Chem­istry at the Tech­ni­cal Uni­ver­si­ty of Munich, Ger­many. Under the guid­ance of Prof. Johannes A. Lercher he worked on het­ero­ge­neous cat­a­lysts for var­i­ous process­es in petro­le­um refin­ing includ­ing hydro­gena­tion of aro­mat­ics in Diesel fuel, alky­la­tion, alka­ne acti­va­tion, and cat­alyt­ic crack­ing. Addi­tion­al research projects includ­ed nov­el cat­alyt­ic sys­tem, such as sup­port­ed ion­ic liq­uids. In 2007, he moved to the Geor­gia Insti­tute of Tech­nol­o­gy to work with Profs. Christo­pher W. Jones and Pradeep K. Agraw­al as a post­doc­tor­al fel­low. His pri­ma­ry focus was the devel­op­ment of cat­alyt­ic process­es for bio­mass depoly­mer­iza­tion and syn­the­sis of bio­fu­els. He joined the fac­ul­ty at the Geor­gia Insti­tute of Tech­nol­o­gy in 2009. His research group is devel­op­ing cat­alyt­ic process­es for the sus­tain­able pro­duc­tion of fuels and chem­i­cals. Spe­cif­ic foci are on the sta­bil­i­ty and reac­tiv­i­ty of sol­id cat­a­lysts in aque­ous phase, sur­face chem­istry of oxy­genates in water, applied spec­troscopy, physic­o­chem­i­cal char­ac­ter­i­za­tion of sol­id mate­ri­als, syn­the­sis of well-defined cat­a­lysts, methane con­ver­sion, pyrol­y­sis, and gasi­fi­ca­tion. He is Pres­i­dent of the South­east­ern Catal­y­sis Soci­ety and Pro­gram Chair of the ACS Divi­sion of Catal­y­sis Sci­ence & Tech­nol­o­gy.