Effect of alumina grinding on the properties of alumina supported palladium catalysts in selective hydrogenation of acetylene

Abstract

In this study, the effects of alumina grinding and mixed oxides (ZnO-Al2O3 and NiO-Al2O3) grinding with various Zn/Al and Ni/Al molar ratios (0.1 and 0.5) prepared by an attrition ball mill on catalytic performance of alumina supported Pd catalysts for selective hydrogenation of acetylene were investigated. It was found that catalytic performances of the Pd catalyst supported on Al2O3 milled for 12 h were superior compared to those of Pd-supported on the unmilled Al2O3. However, all the catalysts prepared from milled mixed oxides presented lower acetylene conversion and ethylene selectivity than that of the catalyst prepared from alumina milled for 12 h. From X-ray diffraction, it was suggested that varying milling time directly affected the crystallite size, surface area and acidity of alumina supports. As revealed by CO chemisorption, milling of Al2O3 supports could increase metal active sites of Pd/Al2O3 catalysts without change in the interaction between Pd and the alumina support so that the catalysts exhibited higher acetylene activity and ethylene selectivity. Moreover, increasing of acidity affected coke formation on the catalysts.