Direct decomposition of nitric oxide over perovskite-type catalysts: Part I. Activity when no oxygen is added to the feed Original Research Article

The direct decomposition of nitric oxide over several La1−xSrxM1−yMy′O3−δ (M=Co, Ni, Cu) perovskites, having specific surface area between 9 and 22 m2/g, was studied at a steady state in a plug-flow reactor with 1 g catalyst and flow rates between 10 and 200 ml/min of 1–10% NO in helium, at temperatures from 723 to 923 K. No oxygen was added to the feed. The studied perovskites exhibit an activity better than most of other metal oxides, including previously studied perovskites, but at 773 K are much less active than the best copper zeolites. Analysis of the collected data suggests inhibition by both nitric oxide and oxygen formed by decomposition and a change of kinetics at temperatures between 820 and 870 K, depending on the catalyst composition. Oxygen inhibition appears to be very strong at high temperatures (>800 K), but comparatively weak at low temperatures. Several kinetic models were tested. For the low temperature range, for majority of the studied perovskites, the best fit was obtained with a model in which oxygen is an inhibitor, but also reactant. This suggests that some surface oxygen species plays a role of an active site. For higher temperature range (823–923 K) two limiting values of the apparent activation energies may be derived, with the difference of about 40 kJ/mol.