Kinetics of the NO/H2 reaction on Pt/LaCoO3: A combined theoretical and experimental study

This paper reports an extensive kinetic investigation of the overall reduction of NO by H2 over platinum supported on LaCoO3. Particular attention has been given to the influence of reductive pretreatment under pure H2 at 250 or 450 °C. According to temperature conditions, a partial or extensive reduction of the support occurs that drastically changes the kinetic behaviour. Prereduction at 250 °C leads to metallic platinum particles in weak interaction with LaCoO3. In that case, only Pt catalyses the NO/H2 reaction, which obeys a conventional Langmuir–Hinshelwood mechanism. On the other hand, extensive reduction of LaCoO3 into La2O3 and CoOx(x<1)(x<1) at 450 °C leads to peculiar interactions between metallic Pt particles and CoOx, correlated with different kinetics features. A bifunctional mechanism involving anionic vacancies at the vicinity of platinum particles likely occurs. Subsequent comparisons of adjusted kinetic and thermodynamic constants on supported Pt and Pd explain the changes in their intrinsic catalytic performance.