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Selective Oxidation Catalysis on Multiple Length Scales: Surfaces, Nanoparticles and Bulk Oxides for Propane Oxidation to Acrylic Acid

Professor Vadim Guliants
Department of Chemical Engineering - Coal Preparation
University of Cincinnati
Cincinnati, OH

Thursday, April 21, 2005 - 4:00 pm
Ben Bandy Conference Room
UK Center for Applied Energy Research

The current abundance and low cost of light alkanes have generated much recent interest in the oxidative catalytic conversion of alkanes to olefins and oxygenates in the petroleum and petrochemical industries [1,2]. Recently discovered multicomponent Mo-V-M-O (M= combinations of Nb, Te, Sb, etc.) catalytic system appears to be the most active and selective for one-step propane oxidation to acrylic acid and ammoxidation to acrylonitrile [2,3]. These catalysts consist of so-called M1 and M2 phases, which possess orthorhombic and pseudohexagonal structures, respectively. The studies of propane (amm)oxidation indicated that the orthorhombic M1 phase was more active and selective in these transformations, although a synergism due to cooperation between these phases was suggested by some at high propane conversion [2].

In order to elucidate the origins of the activity and selectivity of the Mo-V-M-O catalytic system in propane oxidation, we investigated the surfaces, nanoparticles and bulk oxide phases present in the following M1 phase Mo-V-M-O catalysts: (1) the bulk Mo-V-O catalyst promoted with Te, Sb and Nb oxide species at sub-monolayer surface coverage; (2) the bulk Mo-V-Te-O catalysts; and (3) the bulk Mo-V-Te-Nb-O catalysts. This study indicated that the surfaces of these catalysts are terminated with an active and selective monolayer, which possesses different elemental composition from that of the bulk. The rates of propane consumption and formation of propylene and acrylic acid depended on the topmost surface V concentration. These findings suggested that the bulk Mo-V-Te-O structure may function as a support for the unique active and selective surface monolayer in propane oxidation to acrylic acid. The results of this study have important practical consequences for the development of improved selective oxidation catalysts by introducing surface metal oxide components to form new surface active V-O-M sites for propane oxidation to acrylic acid. 1. 1. M. Lin, Appl. Catal., A 207 (2001) 1. 2. 2. R.K. Grasselli, J.D. Burrington, D.J. Buttrey, P. DeSanto, Jr., C.G. Lugmair, A.F. Volpe, Jr., and T. Weingand, Topics in Catal. 23 (2003) 5, and refs. therein. 3. 3. V.V. Guliants, R. Bhandari, J.N. Al-Saeedi, V.K. Vasudevan, R.S. Soman, O. GuerreroPérez, M.A. Bañares, Appl. Catal. A 274 (2004) 123, and refs. therein