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

Abstract

In this study, the effect of Ni-modified Al[subscript2]O[subscript3] prepared by sol-gel and solvothermal methods with varying Ni/Al molar rations on catalytic performances of supported Pd catalysts for selective hydrogenation of acetylene has been studied. It was found that catalytic performances of the Pd catalyst supported on Ni-modified Al[subscript2]O[subscript3] were superior compared to those of Pd-supported on commercial a-Al[subscript2]O[subscript3]. For the sol-gel-made samples, when Ni/Al ratio was 1, the highest ethylene selectivity was achieved whereas for the solvothermal-made samples, the utmost ethylene selectivity was obtained when Ni/Al ratio was 0.3. For a similar Ni/Al ratio (0.5), ethylene selectivity of the sol-gel-made samples was higher than that of solvothermal-made. From X-ray diffraction, it is suggested that varying Ni/Al ratio directly affected the crystalline phases of alumina supports and formation of nickel-alumina compounds. A revealed by NH[subscript3] temperature programmed desorption studies, incorporation of Ni atoms into a-Al[subscript2]O[subscript3] resulted in a significant decrease of acid sites on the alumina supports hence reducing coke deposition on the catalyst surface. Moreover, formation of NiAlAl[subscript2]O[subscript4] could modify the properties of Pd surface so that high ethylene selectivities were obtained.