Effects of preparation variables of supported-cobalt catalysts on the selective hydrogenation of α,β-unsaturated aldehydes

Abstract

The effects of starting salts, supports, added amount of Na 2CO 3, and other precipitation variables on catalytic properties of supported cobalt catalysts were studied for the hydrogenation of cinnamaldehyde and crotonaldehyde by using TGA, XRD, and XPS. The catalysts prepared from cobalt chloride always exhibited high selectivities to unsaturated alcohols irrespective of the support employed. The amount of surface chlorine remaining after H 2-reduction of the CO/SiO 2 precursors prepared from cobalt chloride decreased with increasing amount of Na 2CO 3 added as the precipitant, and both activity and selectivity reached maxima at around Cl/Co = 0.2 in the catalyst surface. The enhanced selectivity of the catalyst prepared from cobalt chloride was explained by the effects of residual chlorine both in the HZ-reduction stage and in the reaction stage; the former leads to a favorable crystallite size distribution (CSD) of cobalt and the latter depresses the hydrogenation of CC double bond. The difference in activities and selectivities of various supported catalysts prepared from cobalt nitrate was discussed based on the difference in the strength of metal-support interaction which leads to different CSDs of cobalt in these catalysts.