Role of Ceria in Oxidative Dehydrogenation on Supported Vanadia Catalysts Maria Veronica Ganduglia-Pirovano,* ,†,‡ Cristina Popa, † Joachim Sauer, † Heather Abbott, § Alexander Uhl, § Martin Baron, § Dario Stacchiola, § Oleksandr Bondarchuk, § Shamil Shaikhutdinov,* ,§ and Hans-Joachim Freund § Institute of Chemistry, Humboldt UniVersita ¨t zu Berlin, Unter den Linden 6, 10099 Berlin, Germany, and Chemical Physics Department, Fritz Haber Institut der Max Planck Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany Received December 15, 2009; E-mail: vgp@chemie.hu-berlin.de; shaikhutdinov@fhi-berlin.mpg.de Abstract: The effect of the suppport on oxidative dehydrogenation activity for vanadia/ceria systems is examined for the oxidation of methanol to formaldehyde by use of well-defined VO x /CeO 2 (111) model catalysts. Temperature-programmed desorption at low vanadia loadings revealed reactivity at much lower temperature (370 K) as compared to pure ceria and vanadia on inert supports such as silica. Density functional theory is applied and the energies of hydrogenation and oxygen vacancy formation also predict an enhanced reactivity of the vanadia/ceria system. At the origin of this support effect is the ability of ceria to stabilize reduced states by accommodating electrons in localized f-states. 1. Introduction Vanadium oxide is the major active component of catalysts for selective oxidation reactions. 1-4 The activity of supported vanadia is strongly affected by the specific oxide used as a support. 2,3,5,6 In oxidative dehydrogenation (ODH) reactions, vanadia supported on ceria shows a remarkably high activity as compared to silica- and alumina-supported catalysts. 2,6,7 Although cerium oxide is known for its ability to store, release, and transport oxygen ions, 8 the origin of the promoting effects of ceria in oxidation reactions has yet to be elucidated. In this work, we focus on understanding the support effect on the ODH activity for vanadia/ceria catalysts. We employ a well-defined VO x /CeO 2 (111) model system, for which the atomic surface structure has been determined, 9 and we study the selective oxidation of methanol to formaldehyde as a prototype ODH reaction, because alkane oxidation typically requires high pressures and temperatures. Nevertheless, in both alcohol and alkane ODH on metal oxides the rate-limiting step is a reduction-oxidation (redox) process, which involves C-H bond cleavage. 10-12 For vanadium oxide species supported on silica, previous calculations based on density functional theory (DFT) have indeed shown that the rate-determining step is H abstraction from a C-H bond, 13,14 as found in many other cases including homogeneous and enzymatic catalysis. 15 Before this can happen, the reactant molecule needs to bind onto the surface. 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