Carbonate Formation and Stability on a Pt/BaO/γ-Al₂O₃ NO_<i>X</i> Storage/Reduction Catalyst

Abstract

There has been recent debate regarding the role or influence of BaCO 3 species on the performance or operation of Pt/BaO/Al 2 O 3 model NO X 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/Al 2 O 3 model NSR catalyst were characterized using Fourier transform infrared (FTIR) spectroscopy. The catalyst sample was exposed to CO 2, 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 CO X 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. H 2 O exposure resulted in the agglomeration of various CO X -containing phases to larger particles.