Ethylene epoxidation over Ag catalysts: effects of support, second metal, promoter, and diluent gas

Abstract

The ethylene epoxidation reaction was conducted in a packed-bed tubular reactor to produce ethylene oxide in this work. The effects of oxide supports (α-Al2O3, Al2O3 C, Al2O3, Acid, SiO2 90, TiO2, SrTiO3, MgTiO3, CaTiO3, and BaTiO3), second metals (Au, Cu, Ba, Pd and Sn), and the diluent gases in the reactant feed (He, Ar, N2, CH4, and CH4 balanced with He) were investigated in order to find the optimum reaction conditions for the epoxidation of ethylene, leading to an improvement of the catalytic activity in terms of both EO selectivity and EO yield. Among the investigated supports, SrTiO3 was found to be the best support, relating to Sr atoms that are incorporated in the SrTiO3 support that made this support more selective in EO formation. The most effective catalyst was the bimetallic 1.39 wt% Cu-17.16 wt.% Ag/SrTiO3 catalyst with 0.32 wt.% Sn promoter. The superior performance of this catalyst might be due to its high oxygen and ethylene uptakes. Moreover, the tin promoter enhanced the long-term stability of the catalyst, resulting from the decrease in the rate of carbonaceous species formation. Under the optimum experimental conditions, the EO selectivity was found to be extremely high up to 99.5 % at 6 h and could maintain at 96 % after 7 days of time on stream, together with the maximum EO yield of 5.5 % at 6 h and 4.9 % at 7 days of time on stream.