Novel Tungsten Oxide Materials

Enrique Iglesia, Professor of Chemical Engineering, University of California at Berkeley and Faculty Scientist, Lawrence Berkeley Laboratory

This project explores the nature of reaction intermediates, rate-determining steps, and Bronsted acid sites in three types of strong solid acids based on nanoclusters of tungsten oxide: tungstated zirconia, supported heteropolyanions, and oxygen-modified tungsten carbides. WOx-ZrO2 materials developed in our laboratory catalyze the isomerization of C6+ alkanes with unprecedented selectivity at 400-500 K. These solids also catalyze o-xylene isomerization at similar low temperatures. This unique catalytic behavior requires oxidative treatments at 1000-1100 K during synthesis, which lead to the formation of WOx domains of intermediate size and strong Bronsted acidity. Such domains consist of distorted octahedral WO x2O3 and from bulk WO3. The unique acid properties of small WOx domains may be related to their ability to form W+(6-n)-O-n(H +) reduced centers during catalytic reactions carried out in the presence of H2. Dihydrogen is involved in the formation of Bronsted acid centers and in the desorption of carbocations by hydrogen transfer before undesired cracking and oligomerization reactions. This project combines kinetic and isotopic tracer studies of reactions pathways with in-situ ultraviolet-visible, Raman, and X-ray absorption spectroscopic studies of cluster structures required for strong Bronsted acidity. These materials are potential replacements for liquid acids and for stoichiometric Friedel-Crafts reagents in alkylation, isomerization, acylation, and related chemical reactions. This project is a collaboration with Dr. Stuart L. Soled (Exxon Research and Engineering Co.), Dr. George D. Meitzner (Edge Analytical) and Professor Gustavo A. Fuentes (UAM, Mexico).

Novel Tungsten Oxide Materials as Strong Solid Acid Catalysts

RESEARCH GROUP: Laboratory for the Science and Applications of Catalysis