Tartaric acid–Ni supported catalysts obtained from hydrotalcite-like compounds: Effects of catalyst preparation variables on enantioselectivity

Abstract

The catalytic properties of tartaric acid–nickel supported catalysts obtained from hydrotalcite-like compounds have been assessed in the enantioselective hydrogenation of methyl acetoacetate. Ni particle size above a minimum threshold of ca. 20nm was found to influence enantioselectivity. For materials with similar Ni crystallite size, e.e. progressively lowers as Mg is incorporated to Ni/Al, whereas incorporation of Zn improves e.e. for all Ni/Zn ratios. In general, activity is higher on Ni/Mg/Al than on Ni/Zn/Al series. Moreover, the synthetic method to obtain hydrotalcite-like compounds affects the catalytic properties of the resultant catalysts. For a series of materials of the same composition, the urea hydrolysis method leads to catalysts with enantiodifferentiation ability, whereas the coprecipitation method does not. Variables of reaction during chiral modification, such as pH and tartaric acid concentration, proved not to have a major effect on enantioselectivity. Furthermore, no direct correlation between the amount of tartaric acid adsorbed onto, or Ni leached from the surface, and the enantiodifferentiation ability of the catalysts was found.