Potential synergic effect between MOR and BEA zeolites in NOx SCR with methane: A dual bed design approach

Abstract The selective catalytic reduction of NO x with methane (NO x CH 4 –SCR) under lean conditions was investigated with catalysts based on two different zeolite structures (MOR and BEA) containing Pd and Ce. The catalytic performance for NO oxidation to NO 2 reaction, considered an important first key step in the NO x CH 4 –SCR mechanism, was also assessed. Pd(0.3)Ce(2)–HBEA was found to be very active for NO oxidation but exhibits poor activity for NO x CH 4 –SCR. Conversely, Pd(0.3)Ce(2)–HMOR presents modest activity for NO oxidation, compared to Pd(0.3)Ce(2)–HBEA, but exhibits mild activity for NO x CH 4 –SCR reaction. Characterisation by H 2 –TPR, DRS UV–vis, TEM/EDS and FTIR-CO allowed the identification of palladium stabilised as Pd 2+ ions in exchange positions in both monometallic and bimetallic MOR based catalysts, whereas, in BEA catalysts, it is presented as PdO clusters. Cerium is stabilised in Pd(0.3)Ce(2)–HMOR as small CeO 2 particles, whereas, in Pd(0.3)Ce(2)–HBEA, it is present as large clusters. Catalysts were also tested in dual bed configuration, in which Pd(0.3)Ce(2)–HBEA was placed as first layer and Pd(0.3)Ce(2)–HMOR as second layer in the catalytic bed. The catalytic performance was significantly improved (higher NO x conversion into N 2 and higher CH 4 selectivity to SCR reaction), when compared to the catalytic performance of each catalyst individually, suggesting the existence of a synergic effect. This synergy is explained by the complementary roles that each catalyst play in HC–SCR mechanism.