Reaction mechanism and kinetics of NOx reduction by propene on CoOx/alumina catalysts in lean conditions

The effect of the preparation method and the Co loading on the performance of alumina supported CoOx for NOx reduction by propene was studied in the presence of excess oxygen. Cobalt impregnated on sol–gel γ-alumina (Co/Al-sg) showed higher activity than cobalt on conventional γ-alumina. Co2+ was proposed to be the most reactive cobalt phase by catalyst characterization (XRD, XPS). The optimal calcination temperature and Co loading in respect of the NOx efficiency was found in the specified lean conditions. In general, the calcination temperature of 700°C and the Co loading in the range of 0.8–1.8 wt.% was the optimum by the activity. Static FTIR studies showed the occurrence of several gas phase or surface intermediates like nitrates, oxygenated hydrocarbons and nitrogen–carbon–hydrogen containing species in reaction sequences. The final reactants in the dinitrogen formation have been proposed to be adsorbed NO and an exactly defined nitrogen containing compound denoted as NRO (RCH2) in the kinetic model. A derived kinetic model based on reaction experiments and FTIR studies was able to simulate the observed activity results. All the detected gas phase concentrations and proposed surface species coverage were simulated along the Co/Al-sg catalyst bed as a function of temperature with the presented mechanistic kinetic model.