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 p resence of excess oxygen, Cobalt impregnated on sol-gel gamma-alumina (Co/A l-sg) showed higher activity than cobalt on conventional gamma-alumina, Co2 + was proposed to be the most reactive cobalt phase by catalyst characteriz ation (XRD, XPS). The optimal calcination temperature and Co loading in res pect of the NOx efficiency was found in the specified lean conditions. In g eneral, the calcination temperature of 700 degrees C and the Co loading in the range of 0.8-1.8 wt.% was the optimum by the activity. Static FTIR stud ies showed the occurrence of several gas phase or surface intermediates lik e nitrates, oxygenated hydrocarbons and nitrogen-carbon-hydrogen containing species in reaction sequences. The final reactants in the dinitrogen forma tion have been proposed to be adsorbed NO and an exactly defined nitrogen c ontaining compound denoted as NRO (R=CH2) in the kinetic model. A derived k inetic model based on reaction experiments and FTIR studies was able to sim ulate the observed activity results. All the detected gas phase concentrati ons and proposed surface species coverage were simulated along the Co/Al-sg catalyst bed as a function of temperature with the presented mechanistic k inetic model. (C) 2000 Elsevier Science B.V. All rights reserved.