CONVERSION OF NITRIC-OXIDE AND METHANE OVER PD ZSM-5 CATALYSTS IN THEABSENCE OF OXYGEN/

We have studied the conversion of nitric oxide and methane on several H- and Na-ZSM-5 zeolite catalysts in the absence of oxygen. Our result s suggest that the NO-CH4 reaction can be explained in terms of a mech anism that starts with a nitric oxide decomposition step followed by t he surface reaction of methane with the product oxygen regenerating th e active site, We have found that reduced Pd/ZSM-5 catalysts are activ e for the nitric oxide decomposition reaction but deactivate rapidly d ue to self-poisoning by product oxygen. By contrast, in the presence o f methane these catalysts can exhibit high activity and stability unde r certain conditions. For instance, when the nitric oxide decompositio n and the reaction of methane with the surface oxygen proceed at compa rable rates the catalyst is stable but when the methane conversion is lower than that required to remove all the oxygen produced (stoichiome tric methane conversion) the catalyst rapidly deactivates. Under some conditions the methane conversion may be higher than the stoichiometri c requirement leading to the deposition of carbonaceous species. These carbonaceous deposits can promote the reaction by helping to remove t he product oxygen.