Catalytic Post-Treatment of Automotive Exhaust Gas from Natural Gas Combustion Engines: Potential Interest of Perovskite Materials

This study reports an investigation of the surface properties of Pd-modified perovskite catalysts for NO _x removal from Natural Gas engines. H₂ production from reforming and water-gas-shift reactions can be profitably used for the reduction of NO _x . Particular attention has been paid to the nature of interactions between Pd and LaCoO₃ according to in situ reductive thermal treatments. The catalytic properties have been investigated by temperature-programmed NO desorption and temperature-programmed NO/H₂ reaction. Different experiments performed on partially and extensively reduced catalysts lead to changes in surface reactivity. Interestingly, beneficial interactions with a significant selectivity enhancement to the production of nitrogen is observed on pre-reduced Pd/LaCoO₃ under smooth conditions at 250 °C particularly in the presence of oxygen. More extensive reduction at 450 °C leads to the loss of the structural properties of LaCoO₃ accompanied with partial segregation of CoO _x and La₂O₃. Such structural changes lead to a detrimental effect on the catalytic performances.