Transient study of oxidative dehydrogenation of propane

Kinetics and the mechanism of the oxidative dehydrogenation of propane were investigated using various transient techniques. Results support a redox r eaction mechanism in which propane and intermediate products react with lat tice oxy gen, reducing the catalyst surface, which is reoxidized by gas-pha se O-2. Partial reduction of the catalyst occurs during the start-up to a s teady state. Successive pulsing with C3H8 reduced V5+ in the magnesium orth o-vanadate phase to V2+ Carbon-containing species were observed upon interr uption of the reaction, although only minute amounts were formed. Cycling i ncreases the amount of the carbon deposited, but this carbon is reactive an d most of it is oxidized in the succeeding O-2 pulse. Temperature-programme d oxidation (TPO) experiments on the catalyst used in steady-state operatio n revealed mainly strongly bound carbonaceous matter on the catalyst, but t his carbon deposition did not affect catalyst activity. Thus, adsorbed oxyg en is an important source of total combustion. Our experiments show, howeve r, that lattice oxygen also produces total oxidation, Propene selectivity o f 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. (C) 1999 Elsevier Science B.V. All rights reserved.