Solid-State Defect Mechanism in Vanadyl Pyrophosphate Catalysts: Implications for Selective Oxidation
Pratibha L. Gai 1 and
K. Kourtakis 1
1 DuPont Science and Engineering Laboratories, Central Research and Development, Wilmington, DE 19880, USA.
High-resolution and in situ electron microscopy of vanadyl pyrophosphate catalysts reacted in alkane (n-butane) and other reducing environments have shown evidence for surface structure modifications accompanied by two sets of symmetry-related extended defects. Defect analysis reveals that the defects are formed by pure (glide) shear mechanism. The defect mechanism suggests the presence of basal (coplanar) anion vacancies, associated with Lewis acid centers, at oxygen sites linking corner-sharing phosphorus tetrahedra and vanadyl octahedra in the active plane. These in-plane defect sites may be key to the activation of the alkane, especially in the dehydrogenation.
Submitted on September 13, 1994
Accepted on December 5, 1994
