Impact of noble-metals on the catalytic stability of cobalt nanoparticles for the acceptorless dehydrogenation of alcohols

摘要

Three different types of unsupported Co catalysts are prepared by the polyol process and investigated for the oxidation of alcohols through an acceptorless dehydrogenation pathway: cobalt spheres with a predominantly face-centered cubic structure, pure cobalt nanorods and Ru-decorated cobalt nanorods, both with a hexagonal compact structure. All the catalysts display a high chemoselectivity for the oxidation of long-chain model alcohols since only secondary alcohols can be transformed into the corresponding ketones. Besides the ketone generated, the highly valuable hydrogen molecule is produced as the only by-product. Irrespective of the shape, similar high conversions and high selectivities are measured for the first catalytic tests. Nevertheless, when the three types of particles are recycled, significant differences in terms of catalytic stability and morphological evolution are observed. All the Co crystal habits are substantially modified during catalysis although well-isolated particles are recovered after three consecutive runs. The highest catalytic stability is found for Co nanorods decorated by Ru nanoparticles.