CH4-SCR of NO over Co and Pd ferrierite catalysts: Effect of preparation on catalytic performance

Selective catalytic reduction of NO with methane (CH4-SCR) in the presence of oxygen excess and water vapour was studied over two bimetallic cobalt/palladium-based FER catalysts, which differ on the order of introduction of metal ions. H2-TPR and UV–vis analysis showed that the simple change in the order of addition of metals to catalyst, gives rise to totally diverse species (Co2+ ions, Co oxides, Co-oxo cations and Pd species) both in type and quantity but also in location within zeolite framework. Experiments of TPD and TPSR of NO and NO2 provided important information to establish a relation between the various active sites formed on both catalysts and their function in the reaction mechanism. The importance of NO2 in the mechanism of NO reaction with CH4 and O2 was explored and the catalyst with a higher capacity to retain adsorbed NO2 is the less active for deNOx. The preparation of a bimetallic catalyst active for NO reduction must provide the proximity between Co and Pd species, and the presence of Co-oxo cations together with palladium species seem to be essential. Furthermore, a suitable amount of cobalt oxides must exist in order to originate NO2 that is the main reaction intermediate. Nevertheless, an excessive amount of these Co species can lead to an increase of adsorbed NO2, which reduces the rate of the reaction of some of the mechanism steps.