Carbonate formation and stability on a Pt/BaO/γ-Al2O3 NOX storage/reduction catalyst

There has been recent debate regarding the role or influence of BaCO3 species on the performance or operation of Pt/BaO/Al2O3 model NOX storage/reduction (NSR) catalysts. This influence is primarily regarded as negative, but the extent of its impact is not clear. For this reason, the formation and stability of barium carbonate species on a Pt/BaO/Al2O3 model NSR catalyst were characterized using Fourier transform infrared (FTIR) spectroscopy. The catalyst sample was exposed to CO2, CO, and CO + O-2 at various temperatures, from 300 to >500 K. Bidentate carbonate species readily form under all conditions, while at higher temperatures, unidentate species were also observed and likely formed from bidentate species as a result of a change in their coordination to the oxide surface. Reaction of COX species with residual hydroxide species on the catalyst led to the formation of bicarbonates, and when the sample was exposed to CO at low temperature, formate species were also formed. These formate species decomposed at elevated temperatures and contributed to the formation of carbonates. H2O exposure resulted in the agglomeration of various COX-containing phases to larger particles.