Preparation of Coimpregnated Cu−Zn on Zn-Modified Silica: Influence of the Basicity of the Support and of the Nature of Zinc Species on the Catalyst Properties

Abstract

In this paper, we showed that the addition of zinc on silica support by impregnation with zinc nitrate or chloride (10 wt % Zn) followed by calcination at 450 °C modifies the properties of the oxide surface and induces different basic properties as determined by the test-reaction of conversion of methylbutynol. Basicity depends on the zinc species formed during calcination, zinc silicate of hemimorphite-type (Zn4Si2O7(OH)2·H2O) for the zinc nitrate precursor and isolated grafted zinc species ((≡SiO)2ZnCl(O), with (O) = OH or H2O) for the zinc chloride precursor. Basicity of the support favors the formation of hydroxy-compound during further impregnation with copper or copper−zinc nitrate. The dispersion and crystallinity of these precursors directly govern the final state of the catalyst after reduction, i.e., the copper particle size and the extent of the Cu0−ZnII interactions; the latter is attested through the test-reaction of selective hydrogenation of crotonaldehyde.