Transient study of oxidative dehydrogenation of propane

Abstract

Kinetics and the mechanism of the oxidative dehydrogenation of propane were investigated using various transient techniques. Results support a redox reaction mechanism in which propane and intermediate products react with lattice oxygen, reducing the catalyst surface, which is reoxidized by gas-phase O 2. Partial reduction of the catalyst occurs during the start-up to a steady state. Successive pulsing with C 3H 8 reduced V 5+ in the magnesium ortho-vanadate phase to V 2+. Carbon-containing species were observed upon interruption of the reaction, although only minute amounts were formed. Cycling increases the amount of the carbon deposited, but this carbon is reactive and most of it is oxidized in the succeeding O 2 pulse. Temperature-programmed oxidation (TPO) experiments on the catalyst used in steady-state operation revealed mainly strongly bound carbonaceous matter on the catalyst, but this carbon deposition did not affect catalyst activity. Thus, adsorbed oxygen is an important source of total combustion. Our experiments show, however, that lattice oxygen also produces total oxidation. Propene selectivity of the reaction in the absence of gas-phase O 2 was superior to steady-state selectivity, at the same propane conversion. Propene selectivity could be further improved by increasing the degree of reduction of the catalyst.