The Effect of Cesium Dopant on Catalytic and Chemical-Physical Properties of V/Ti/O, Catalysts for the Selective Oxidation of o-Xylene to Phthalic Anhydride

摘要

Titania-supported vanadia (V/Ti/O) systems were modified by addition of cesium oxide for application as catalysts in the selective oxidation of o-xylene to phthalic anhydride. Catalytic tests demonstrated that cesium is a strong promoter of activity and of selectivity to PA, but that this effect is evident only under well-defined reaction conditions. Samples with a Cs content lower than 0.35 wt.% CS2O exhibited a strong increase of conversion as compared with the undoped V/Ti/O system. Catalytic tests made by varying the o-xylene and the oxygen concentrations in feed demonstrated that in Cs-doped V/Ti/O catalysts the rate-determining step is the re-oxidation of vanadium by molecular oxygen. Thermal-programmed reduction and re-oxidation tests evidenced that the addition of Cs decreases the vanadium reducibility and increases the re-oxidizability of reduced vanadium sites.