NO Reduction by CH4in the Presence of O2over Pd-H-ZSM-5

Abstract

An investigation of the interaction of NO and NO2with Pd-H-ZSM-5, as well as the reduction of NO by CH4, has been conducted using mass spectrometry andin situinfrared spectroscopy. Prior to reaction most of the Pd in Pd-H-ZSM-5 (Pd/Al=0.048) is present as Pd2+cations. NO reduction by CH4in the absence of O2results in the progressive reduction of Pd2+cations above 610 K and the formation of small Pd particles. Reduction of Pd2+cations is significantly suppressed when O2is added to the feed of NO and CH4.In situinfrared spectroscopy reveals the presence of NO+and NO as the principal adsorbed species. NO+is present as a charge-compensating cation (e.g., Z−NO+) and is believed to be formed via the reaction 2 Z−H++2 NO+1/2 O2=2 Z−NO++H2O. NO+does not react with CH4at temperatures up to 773 K. Adsorbed NO reacts with CH4above 650 K and CN species are observed as intermediates. The latter species react with both NO, O2, and presumably NO2. Based on the accumulated data, a mechanism is proposed to explain the reduction of NO by CH4both in the presence and absence of O2.