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

carsten.sievers@chbe.gatech.edu
 
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.