Liquid-phase reduction of alpha,beta-unsaturated aldehydes (UALs) to the corresponding alpha,beta-unsaturated alcohols (UOLs) was investigated on gold catalysts supported on a solid base of MgxAlO hydrotalcite (x = Mg/Al molar ratio). The Au/MgxAlO catalysts were prepared using a modified deposition precipitation method without adjusting the pH of the initial HAuCl4 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 MgxAlO support and Au/MgxAlO catalyst. The Mg/Al ratio of MgxAlO affected the pH of the final solution, and determined the actual gold loading in the catalyst. Calcination temperatures of the MgxAlO support and Au/MgxAlO catalyst determined the ratio of gold states (Au3+/Au-0) on the catalyst. A correlation between the gold states (Au3+/Au-0) and the activity and selectivity of UAL to UOL was found. Increasing the Au3+/Au-0 ratio of the catalysts increased the activity and selectivity of UAL to UOL. The different performances of the Au/MgxAlO catalysts from Group VIII metals due to the effects of temperature, pressure and steric structures of UALs were discussed. (C) 2009 Elsevier B.V. All rights reserved.
