Molecular dynamics and kinetic modelling of the CO and H2 oxidation pattern of a composite MnCeOx catalyst

Abstract

The CO and H2 oxidation functionality of a composite MnCeOx catalyst with large exposure of Mn(IV) sites has been investigated in a wide range of experimental conditions (T, 293–533 K; pCO/p0 or pH2/p0, 0.00625–0.025; pO2/p0, 0.00625–0.20) to ascertain the mechanistic clues of a peculiar preferential CO oxidation pattern. The MnCeOx shows high CO oxidation activity in the range of 293–533 K, while a large activation energy hinders the H2 oxidation at T < 373 K. Computational analysis of adsorption and activation energies on a model Mn4O8 cluster, and unchanging energy barriers of CO2 and H2O formation, in absence and in the presence of O2, indicate that the abstraction of lattice O-atoms is the rate limiting step (r.l.s.) of the CO and H2 oxidation. This reactivity pattern relies on strong chemical affinity of Mn(IV) sites toward CO enabling the easy abstraction of lattice O-atoms, while H2 oxidation occurs via an extrafacial reaction path driven by diatomic oxygen species produced by spillover and adsorption processes at T > 373 K. Mechanistic clues were synthesized into macrokinetic models predicting the CO and H2 oxidation activity of the MnCeOx catalyst under any conditions.