Effect of preparation variables on enantioselectivity of supported nickel catalysts modified with tartaric acid

Abstract

Enantioselective hydrogenation of methyl acetoacetate to methyl 3-hydroxybutyrate on various supported nickel catalysts modified with ( R,R)-tartaric acid was studied under mild reaction conditions in order to examine the effects of preparation variables on the enantioselectivity and activity of resulting catalysts. The selectivity of the supported nickel catalysts was strongly dependent on the precipitation conditions. The effect of reduction conditions on the selectivity depended on the kind of support. Even Ni-alumina catalysts, when reduced under relatively mild conditions, had high enantioselectivity although their hydrogenation activity was low. Ni-silica catalysts, precipitated under optimum conditions and reduced at 400–500 °C for 1–3 h, were much more active than the other catalysts with similar, high enantioselectivity. Various extents of the selectivity of supported nickel catalysts were explained in terms of the effect of preparation conditions on the crystallite size distributions of nickel.