Chin. J. Chem. Eng., 15(6) 884—888 (2007) Effect of Alumina Particle Size on Ni/Al 2 O 3 Catalysts for p-Nitrophenol Hydrogenation * CHEN Rizhi(陈日志) a , DU Yan(杜艳) b , XING Weihong(邢卫红) a and XU Nanping(徐南平) a, ** a State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engi- neering, Nanjing University of Technology, Nanjing 210009, China b College of Environmental Sciences, Nanjing University of Technology, Nanjing 210009, China Abstract The catalytic hydrogenation of p-nitrophenol to p-aminophenol was investigated over Ni/Al 2 O 3 catalyst on alumina support with different particle size. It is found that support particle size has significant influences on physiochemical properties and catalytic activity of the resulting Ni/Al 2 O 3 catalyst, but little influence on the selec- tivity. At a comparable amount of Ni loading, the catalytic activity of Ni/Al 2 O 3 prepared with alumina support of smaller particle size is lower. The reduction behavior of the catalyst is a key factor in determining the catalytic ac- tivity of Ni/Al 2 O 3 catalyst. The supported nickel catalyst 10.3Ni/Al 2 O 3 -3 improves the life span of the membrane by reducing fouling on the membrane surface compared to nano-sized nickel. Keywords p-nitrophenol, catalytic hydrogenation, p-aminophenol, Ni/Al 2 O 3 catalysts, ceramic membrane filtra- tion 1 INTRODUCTION p-Aminophenol is of great commercial impor- tance as an intermediate for the preparation of analge- sic and antipyretic drugs[1—4]. In view of the grow- ing demand for p-aminophenol, direct catalytic hy- drogenation of p-nitrophenol to p-aminophenol be- comes important, because this could be an efficient and greener route[5]. Up to now, some works have been reported on the liquid phase p-nitrophenol hy- drogenation over Raney nickel[6], nano-sized nickel[7,8] and several noble metal catalysts such as Pt/C[5]. Our previous works have shown that the catalytic properties of nano-sized nickel have been proved to be superior to those of Raney nickel[8]. However, during the application of nano-sized nickel to membrane-based catalyst separation, it was found that nano-sized nickel particles would easily adsorb on the surface of pipeline, tank and membrane, which caused the decrease of catalyst concentration in reac- tion slurry and led to consequent decline in reaction rate and permeate flux of the membrane[9]. Due to their low cost and high catalytic activity, supported nickel catalysts are widely used in various reac- tions[10 — 13]. Moreover, compared to nano-sized nickel catalysts, the supported nickel catalysts are easy to be recovered by membrane separation process. More significantly, it is efficient to maintain high flux of membrane. So it is desired to find a supported nickel catalyst with better membrane filtration per- formance and comparable catalytic activity to replace nano-sized nickel. There are few reports on the cata- lytic hydrogenation of p-nitrophenol over supported nickel catalysts[14]. Therefore, this work is attempted to perform the catalytic hydrogenation of p-nitrophenol to p-aminophenol over Ni/Al 2 O 3 catalysts. The catalysts were prepared by liquid-phase chemical reduction method, and were characterized by inductively coupled plasma (ICP), X-ray powder diffraction (XRD), X-ray photoelectron spectra (XPS) and temperature-programmed reduction (TPR) in order to correlate the catalytic activity with the characteristics of the catalysts. The effect of alu- mina support particle size on the physiochemical and catalytic properties of Ni/Al 2 O 3 catalysts was studied. At the same time, the membrane filtration perform- ance of Ni/Al 2 O 3 suspension and nano-sized nickel suspension was compared. 2 EXPERIMENTAL 2.1 Catalyst preparation A series of Ni/Al 2 O 3 samples were prepared by a liquid-phase chemical reduction method. Nonporous Al 2 O 3 supports of three different mean particle sizes, i.e., 1.3μm, 11.2μm, 22.8μm, measured by Mastersizer 2000 (Malvern, UK), were supplied by Zhengzhou Fuwei New Materials Co., China and designated as Al 2 O 3 -1, Al 2 O 3 -2, Al 2 O 3 -3, respectively. 10g of Al 2 O 3 calcined at 500℃ for 4h in stagnant air was impreg- nated with 45ml of 0.42mol·L －1 aqueous NiSO 4 solu- tion for 8h under low magnetic stirring, was dried at 110℃ under gentle stirring overnight to exclude re- sidual water. 5g precursor was reduced by adding 8ml of hydrazine hydrate (N 2 H 4 ·H 2 O) alkaline solution, during which the mole ratio of N 2 H 4 ·H 2 O to Ni 2+ was controlled at 2 ︰ 1 and the mixture was vigorously stirred. The resulting Ni/Al 2 O 3 catalyst was washed with deionized water at first, then by ethanol, and fi- nally dried at 80℃ in oven to get the black powders of supported nickel. The nickel content in all samples was analyzed by inductively coupled plasma (ICP, Optima 2000DV, PerkinElmer, USA) after extraction with nitric acid. The resulting catalysts were denoted as xNi/support, where x is the actual nickel loading. Received 2007-06-22, accepted 2007-09-23. * Supported by the Special Funds for Major State Basic Research Program of China (No.2003CB615702), the National Natural Science Foundation of China (No.20636020) and the Natural Science Foundation of Jiangsu Province (No.BK2006722). ** To whom correspondence should be addressed. E-mail: npxu@njut.edu.cn