A comparison of steady-state and unsteady-state reaction kinetics of n-butane oxidation over VPO catalysts using a TAP-2 reactor system

The reaction of n-butane with 'reactor-equilibrated' (VO)(2)P2O7 based catalysts has been investigated using a combination of low-pressure transient response experiments and atmospheric-pressure steady-flow reaction experiments. The activation energy for n-butane conversion in both steady-flow and transient response experiments was a function of the oxidation stare of the catalyst. Under steady-flow conditions an activation energy of 17 +/- 2 kcal/mol was obtained for 'reactor-equilibrated' catalysts, and 13 +/- 2 kcal/mol for an oxygen-treated catalyst. The activation energy for n-butane conversion in transient-response experiments varied between 12 +/- 1 and 23 +/- 2 kcal/mol. An analysis of the transient response curves of the reaction products shows that the rates of formation and desorption of products are strong functions of the catalyst oxidation state. Analysis of the kinetic results indicated that the same sites are involved in the steady-state and unsteady-state conversion of n-butane.