Catalysis Letters 16 (1992) 231-239 231 Relationship between structure and point of zero surface charge for molybdenum and tungsten oxides supported on alumina S.D. Kohler, J.G. Ekerdt * Department of Chemical Engineering, The University of Texas at Austin, Austin, TX 78712, USA D.S. Kim and I.E. Wachs Zettlemoyer Center for Surface Studies, Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA Received 21 May 1992; accepted 12 August 1992 Laser Raman spectroscopywas used to characterize alumina-supported molybdenum and tungsten oxides at loadings ranging from 0.5 to 15 wt% Mo and 0.5 to 30 wt% W. The structure of calcined Mo6+/AI203 and W6+/A1203 was governed by the point of zero surface charge of each system, with the point of zero surface charge being dependent on metal loading. The structures formed by the molybdenum and tungsten overlayers at the sample point of zero surface charge were found to be analogous to the structures formed by molybdenum and tungsten oxyanions in aqueous solution at a solution pH equal to the sample point of zero surface charge. Keywords: Molybdenum oxide; tungsten oxide; Raman spectroscopy; alumina; point of zero surface charge 1. Introduction Laser Raman spectroscopy (LRS) has been used extensively to determine the structures of the molybdenum [1-14] and tungsten [15-19] oxide overlayers that form when one metal oxide component is deposited upon a different metal oxide support such as A1203, SiO2, and TiO 2. Although there have been differences in opinion involving the structure of the oxide overlayers in the past, it has been recently demonstrated that the structure of the overlayers under ambient conditions is analogous to the structure of the metal oxyanion in * To whom correspondence should be addressed. 9 J.C. Baltzer A,G. Scientific Publishing Company