Reduction of nitric oxide by propene and propane on Ni-exchanged mordenite

The reduction of NO over Ni-exchanged mordenite in the presence of excess oxygen using propane and propene as reducing agents was studied. During ion exchange of the zeolite with Ni²⁺, Brønsted acid sites were formed resulting from the hydrolysis of divalent Ni²⁺ ions. The chemical state of the Ni ions and the density and strength of the acid sites strongly determine the activity and selectivity of the catalysts for the NO reduction. Non-reduced catalysts showed a high selectivity to N₂, while after partial reduction of the Ni ions significant concentrations of NO₂ and N₂O were formed. In addition, low concentrations of NO₂ were formed during reduction of NO with propane and related to the more demanding activation of the alkane. An optimum concentration of acid sites, which in turn depends on the nickel loading, is required to obtain high NO conversion with propane. Deactivation due to deposition of carbonaceous species was observed during the NO reduction with propene for samples with high concentration of acid sites.