Effect of nickel particle size on alumina supported nickel catalysts for p-nitrophenol hydrogenation

The catalytic hydrogenation of p-nitrophenol to p-aminophenol was investigated over alumina supported nickel catalysts prepared by impregnation reduction method and mechanical mixing method. The catalysts were characterized by XRD and FESEM. The results show that the nickel particle diameter of alumina supported nickel prepared by impregnation reduction method (denoted as Ni/Al₂O₃) is slightly smaller than that of alumina supported nickel prepared by mechanical mixing method (denoted as Ni+Al ₂O₃), and the catalytic activity of Ni+Al ₂O₃ is higher. The nickel particle size of Ni+Al ₂O₃ would increase as Ni+Al₂O₃ is reduced in hydrogen for 2 h at 270 °C and 600 °C, respectively, and its catalytic activity correspondingly decreases. These imply that the reaction is structure sensitive and the smaller nickel particle diameter is beneficial to obtain a higher catalytic activity. However, the nickel particle diameter almost has no influence on the catalytic selectivity of the p-nitrophenol hydrogenation to p-aminophenol.