Can isotopic transient and formal steady-state kinetics lead to a converging surface chemistry analysis? Case study on the selective reduction of NO by CH4 over Co-ZSM-5 catalysts

The surface coverage analysis derived from two formal steady-state kinetic models is compared to values directly obtained from steady-state isotopic transient analysis (SSITKA) for the selective catalytic reduction (SCR) of NO by CH₄ over Co-ZSM-5 catalysts. It is shown that the most abundant reacting intermediates are NO _x adspecies, though no clear differentiation between the various adspecies identified by DRIFT spectroscopy was achieved. Less numerous carbon containing adspecies were identified and quantified in the reacting system, essentially as methoxy species. Nitromethane-like intermediates remained undetectable due to a very rapid transformation into N₂ and CO₂. On the basis of these converging kinetic analyses related to each elementary step of the SCR process, a microkinetic model can be derived, which allows describing transient operation, in view of a non steady-state application.