Selective catalytic reduction of NO with propane over CoZSM-5 containing alkaline earth cations

Selective catalytic reduction (SCR) of nitric oxide (NO) with propane is studied over CoZSM-5 catalysts with a series of exchanged cobalt concentrations (0.9-7.5 wt.-%). The overall activity for SCR of NO is found to increase linearly with the cobalt content in the range below the maximum exchange capacity (CoAl= 0.5). However, when the cobalt loading exceeds the exchange capacity of the zeolite, viz.CoAl 0.5, the combustion of propane is favored significantly, resulting in a decrease of the NO conversion. The presence of excess Co²⁺ in zeolite appears to bring about the marked falls in adsorption of NO. In this case cobalt oxide particles are presumed to form, which promote the oxidation of propane. Nevertheless, the addition of alkaline-earth metal cations (Ba, Ca) resulted in the suppression of propane oxidation over CoZSM-5, and improved the NO conversion dramatically.