Scientific and engineering issues of the CO oxidation on nanocomposite MnCeOx catalysts

Since many decades, the oxidative conversion of carbon monoxide is one of the most common "model" reactions in Catalysis, with also great environmental and technological concerns due to high toxicity of CO, also boosting the formation of ozone in metropolitan areas, and the fact that CO behaves as a poison in some important catalytic technologies (e.g., Ammonia, Fuel Cells, etc.). Although supported noble metals currently dominate the catalyst market for environmental applications, including total and preferential CO oxidation in hydrogen streams (PROX), an incessant research interest is devoted to transition metal oxide (TMO) systems, for obvious economic reasons and a performance at low-medium temperature (<573K), actually comparing to metal catalysts [1]. In fact, metals and TMO's feature a CO oxidation pattern depending on different interactions with substrate and oxygen, even though catalyst chemistry and reaction environment (i.e., temperature, reagent pressure and molar ratio) control mechanism and activity [1]. Therefore, this work is aimed at providing a thorough overview of the CO oxidation pattern of a nanocomposite MnCeOx catalyst (M5C1; Mnat/Ceat, 5) in wide ranges of temperature (293-533K), CO-O2 pressure (0.00625-0.025atm), CO/O2 molar ratio (0.25-4.0), CO2 co-feeding (0.0-0.10 atm) and conversion level (0-100%) [2]. Systematic activity data under kinetic regime and mechanistic evidences signal the occurrence of competitive adsorption phenomena, although the abstraction of O-atoms from the MnIV active sites is rate-determining (r.d.s.). A concerted redox mechanism, L-H type, of five elementary steps leads to formal rate equations explaining empiric kinetics and fully predicting the reactivity pattern of the studied catalyst in the range of 293-533K (Fig. 1).