Effect of Fe- and Co-modified Al[subscript 2]O[subscript 3] on the properties of Pd/Al[subscript 2]O[subscript 3] catalyst in selective acetylene hydrogenation reaction

Abstract

In this study, the effect of Fe- and Co-modified Al[subscript 2]O[subscript 3] prepared by sol-gel and solvothermal methods with various Fe/Al and Co/Al molar ratios (0, 0.1, 0.3 and 0.5) on the catalytic performances of supported Pd catalysts for selective hydrogenation of acetylene have been studied. It was found that all the Pd catalysts supported on Fe-modified [alpha]-Al[subscript 2]O[subscript 3] that were prepared by sol-gel method exhibited higher activity and ethylene selectivity than the unmodified while those prepared by solvothermal method, only the catalyst with Fe/Al=0.1 showed improvement. Acetylene conversion and ethylene selectivity depended on the average Pd particle size which itself was a function of crystallite size of the supports (both [alpha]-Al[subscript 2]O[subscript 3]and [alpha]-Fe[subscript 2]O[subscript 3]). NH3-TPD results suggest that acidity of Fe-modified [alpha]-Al[subscript 2]O[subscript 3]was lower than the unmodified supports so the modified catalysts exhibited lower coke formation. For Co-modified [alpha]-Al[subscript 2]O[subscript 3]supported Pd catalysts, those prepared by solvothermal method resulted in CoAl[subscript 2]O[subscript 4] formation at lower Co/Al ratio than sol-gel method because solid-solution occurred more easily by solvothermal method. However, for both techniques, dispersion of Pd decreased when CoAl[subscript 2]O[subscript 4] was formed. In most cases, Pd catalysts on the Co-modified [alpha]-Al[subscript 2]O[subscript 3]supports showed better performance than on the unmodified supports especially at nearly 100% conversion of acetylene. The effect of Co-modified Al[subscript 2]O[subscript 3] on coke formation, however, was not clearly shown.