Selective hydrogenation of α,β-unsaturated aldehydes over Au/Mg xAlO hydrotalcite catalysts

Abstract

Liquid-phase reduction of α,β-unsaturated aldehydes (UALs) to the corresponding α,β-unsaturated alcohols (UOLs) was investigated on gold catalysts supported on a solid base of Mg x AlO hydrotalcite ( x = Mg/Al molar ratio). The Au/Mg x AlO catalysts were prepared using a modified deposition precipitation method without adjusting the pH of the initial HAuCl 4 solution. The effects of various parameters involved in preparation of catalysts were also studied, including the Mg/Al molar ratio and the calcination temperatures of the Mg x AlO support and Au/Mg x AlO catalyst. The Mg/Al ratio of Mg x AlO affected the pH of the final solution, and determined the actual gold loading in the catalyst. Calcination temperatures of the Mg x AlO support and Au/Mg x AlO catalyst determined the ratio of gold states (Au 3+/Au 0) on the catalyst. A correlation between the gold states (Au 3+/Au 0) and the activity and selectivity of UAL to UOL was found. Increasing the Au 3+/Au 0 ratio of the catalysts increased the activity and selectivity of UAL to UOL. The different performances of the Au/Mg x AlO catalysts from Group VIII metals due to the effects of temperature, pressure and steric structures of UALs were discussed.