In situ FTIR characterization of NH3 adsorption and reaction with O2 and CO on Pd-based FCC emission control additives Original Research Article

The adsorption of NH3 and its reaction with O2 and CO over Cen+/Na+/γ-Al2O3 and Pd/Cen+/Na+/γ-Al2O3 was examined by FTIR spectroscopy in a wide range of temperatures. Ammonia undergoes decomposition on the surfaces of these materials at elevated temperatures with a fraction of the NH3 species being oxidized by lattice oxygen to NOx, which is trapped on the surface in the form of nitrites. The presence of O2 in the feed accelerates the formation of surface nitrite and nitrate species. The reaction of these species with ammonia at 400 °C is fast, producing N2. The presence of CO in the gaseous feed leads to the formation of surface isocyanates, presumably through the reaction with partially dehydrogenated surface NHx species. The PdO component mildly promotes the formation of these isocyanate species. Both the NCO and NO3−/NO2− species identified on the surfaces of these materials at elevated temperatures are active intermediates, participating in further reactions which ultimately lead to the reduction of NOx and CO emissions. The contribution of these intermediates to a possible N2 formation reaction network should be accounted for when FCC regenerators are operating under partial or incomplete burn combustion modes.