CH 4-SCR of NO over Co and Pd ferrierite catalysts: Effect of preparation on catalytic performance

Abstract

Selective catalytic reduction of NO with methane (CH 4-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. H 2-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 (Co 2+ 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 NO 2 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 NO 2 in the mechanism of NO reaction with CH 4 and O 2 was explored and the catalyst with a higher capacity to retain adsorbed NO 2 is the less active for deNO x . 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 NO 2 that is the main reaction intermediate. Nevertheless, an excessive amount of these Co species can lead to an increase of adsorbed NO 2, which reduces the rate of the reaction of some of the mechanism steps.