Book Description
In the last annual reports, we reported Cu-exchanged pillared clays as superior selective catalytic reduction (SCR) catalysts. During the past year we explored the possibilities with MCM-41, a new class of molecular sieve. In this report, Rh exchanged Al-MCM-41 is studied for the SCR of NO by C3H6 in the presence of excess oxygen. It shows a high activity in converting NO to N2 and N2O at low temperatures. In situ FT-IR studies indicate that Rh-NO species (1910-1898 cm−1) is formed on the Rh-Al-MCM-41 catalyst in flowing NO/He, NO+O2/He and NO+C3H6+O2/He at 100-350 C. This species is quite active in reacting with propylene and/or propylene adspecies (e.g., [pi]-C3H5, polyene, etc.) at 250 C in the presence/absence of oxygen, leading to the formation of the isocyanate species (Rh-NCO, at 2174 cm−1), CO and CO2. Rh-NCO is also detected under reaction conditions. A possible reaction pathway for reduction of NO by C3H6 is proposed. In the SCR reaction, Rh-NO and propylene adspecies react to generate the Rh-NCO species, then Rh-NCO reacts with O2, NO and NO2 to produce N2, N2O and CO2. Rh-NO+ and Rh-NCO species are two main intermediates for the SCR reaction on Rh-Al-MCM-41 catalyst.