In situ FTIR characterization of NH 3 adsorption and reaction with O 2 and CO on Pd-based FCC emission control additives

Abstract

The adsorption of NH 3 and its reaction with O 2 and CO over Ce n+ /Na +/γ-Al 2O 3 and Pd/Ce n+ /Na +/γ-Al 2O 3 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 NH 3 species being oxidized by lattice oxygen to NO x , which is trapped on the surface in the form of nitrites. The presence of O 2 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 N 2. The presence of CO in the gaseous feed leads to the formation of surface isocyanates, presumably through the reaction with partially dehydrogenated surface NH x species. The PdO component mildly promotes the formation of these isocyanate species. Both the NCO and NO 3 −/NO 2 − 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 NO x and CO emissions. The contribution of these intermediates to a possible N 2 formation reaction network should be accounted for when FCC regenerators are operating under partial or incomplete burn combustion modes.