Influence of Preparation Method on the Nanocrystalline Porosity of α-Al₂O₃ and the Catalytic Properties of Pd/α-Al₂O₃ in Selective Acetylene Hydrogenation

Abstract

Nanocrystalline α-Al2O3 powder with average crystallite sizes of 34−68 nm have been synthesized by three different methods, namely, solvothermal, sol−gel, and precipitation. Although the smallest crystallite size of α-Al2O3 was obtained via the sol−gel synthesis, the α-Al2O3 sol−gel possessed the least amount of specific surface area and pore volume. A narrow pore size distribution with an average pore diameter of 15 nm can be obtained via solvothermal method, whereas the precipitation method yielded α-Al2O3 with larger pore size and a wider pore size distribution. When used as a support for palladium catalysts, the α-Al2O3 solvothermal provided the highest palladium dispersion and the best catalyst performance in selective hydrogenation of acetylene. The catalytic properties of Pd/α-Al2O3 solvothermal were improved, in terms of both acetylene conversion and ethylene selectivity. As shown by temperature program studies, the use of solvothermal-derived α-Al2O3 facilitated H2 reduction at low temperature and the desorption of ethylene and CO.