Key Catalyst Support Parameters Identified

By conducting a detailed comparison of silica materials used as palladium-catalyst supports, researchers in the U.K. have uncovered key criteria that make some supports far superior to others in selective alcohol oxidations. The team also identified the catalytically active species that mediate conversion of allylic alcohols to the corresponding aldehydes, an industrially significant process (ACS Catal., DOI: 10.1021/cs200145n). Christopher M. A. Parlett, Adam F. Lee, and Karen Wilson of Cardiff University, Wales, and coworkers in England prepared palladium catalysts on four types of silica that widely vary in pore architectures and surface areas (200–950 m²/g). Through a series of microscopy, spectroscopy, and other types of measurements that probed the catalysts and monitored formation of cinnamaldehyde and separately crotonaldehyde, the team found that the best supports feature the highest surface areas and a three-dimensional network of interconnected channels. Some high-surface-area silicas lack 3-D interconnectivity, which is needed for maximizing palladium dispersion and enhancing mass transport, the group says. Additionally, they found that Pd²⁺ species (PdO) are responsible for the rate-limiting oxidative dehydrogenation step.