CATALYTIC REDUCTION OF NITROGEN-OXIDES WITH METHANE IN THE PRESENCE OF EXCESS OXYGEN - A REVIEW

Interest in new approaches to NO, removal were stimulated by the discovery that certain zeolites were very active for NO decomposition and reduction by C-2s and C-3s. Initially, NO could not be reduced by methane with this early generation of zeolites. Later it was discovered that Co-ZSM-5 demonstrated uniquely high activity for NOx reduction by methane in the presence of O-2. Given the world's plentiful supply of natural gas, methane would certainly be a hydrocarbon of choice to reduce NO. Since the breakthrough work with Co-ZSM-5, a number of other materials were reported to be catalysts for this reaction. This review summarizes the work in this topical area and attempts to relate the activities of all these potential catalysts. Direct comparisons regarding the relative performance of many of these newer catalysts are not always possible, often because rates are not reported and the data are collected under different conditions. With the current information at hand, it appears that the most active catalyst under simulated sulfur-free, wet exhaust conditions is Co-ferrierite.