Ceria and ceria-zirconia supports are commonly used in supported metal catalysts. In many cases, these materials are chosen as redox active supports, but the observed reactivity is predominantly associated with supported metal particles. However, pure ceria catalysts also can be active for reactions that are typically metal catalyzed, for example the hydrogenation of acetylene [1]. In the present work, it is shown that ceria and ceria-zirconia can heterolytically dissociate molecular hydrogen under mild conditions [2]. The most active sites for this reaction are oxygen vacancies, which catalyze the isotopic H2-D2 exchange reaction with activation energies of 22-25 kJ/mol. At temperatures above 200 °C, a second type of sites starts to be kinetically relevant. It is suggested that these sites are located at the edges of ceria-zirconia crystallites. The activation energy at the second type of sites is in the range of 62 to 88 kJ/mol, and it decreases with decreasing crystallite size due to increased strain on the edge sites. Using results from reactivity studies and detailed physico-chemical characterization, structure-property relationships and a kinetic model are obtained. Oxygen vacancies on ceria-based catalysts are also able to catalyze hydrodeoxygenation (HDO) of guaiacol at 300-400 °C [3]. The removal of the first functional group occurs more readily than complete deoxygenation, while no products with saturated aromatic rings are formed. The activation energy for HDO over these materials is comparable to sulfated NiMo or CoMo catalysts 1. G. Vile, B. Bridier, J. Wichert, J. Perez-Ramirez, Angew. Chem. Int. Ed. 51 (2012) 8620. 2. S.M. Schimming, G.S. Foo, O. LaMont, A.K. Rogers, M.M. Yung, A.D. D’Amico, C. Sievers, J. Catal. 329 (2015) 335. 3. S.M. Schimming, O. LaMont, M. König, A.K. Rogers, A. D'Amico, M.M. Yung, C. Sievers, ChemSusChem 8 (2015) 2073.

Hydrogen activation and hydrodeoxygenation over ceria-zirconia catalysts

251st National Meeting (2016)

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