Catalytic Oxidation of Benzene in the Gas Phase over Alumina-Supported Silver Catalysts

Abstract

Catalytic properties of Ag/Al₂O₃ for complete oxidation of benzene with ozone at 295−373 K were studied and compared with those of Mn/Al₂O₃. At the reaction temperature of 295 K, the Ag/Al₂O₃ catalysts showed selectivity to CO_x (ca. 80%) higher than that of the oxide of metals in the first transition series (Fe, Mn, Co, Ni, Cu) supported on Al₂O₃, which had selectivities of 28−62%. The catalyst showed gradual deactivation from accumulation of byproduct compounds on the catalyst surface. FTIR studies revealed that the byproduct compounds consisted of easily decomposable species and hardly decomposable species. The rate for benzene oxidation linearly increased with Ag loadings (∼15 wt %) and was not improved at higher loading levels. The ratios of ozone decomposition to benzene oxidation and ozone decomposition to CO_x selectivity were evaluated to be 7.5 and 80%, respectively, and they were independent of benzene conversion. The Ag/Al₂O₃ catalyst showed steady-state activities at a reaction temperature of 313−373 K, and the conversion increased with the increase in the reaction temperature. The presence of water vapor in the reaction gas inhibited the catalyst deactivation, and steady-state activity was obtained at a reaction temperature of 295 K, while it did not affect the activities for benzene oxidation but improved the CO₂ selectivity.