Catalytic NO reduction by CO over ceria-cobalt oxide catalysts

A series of ceria-cobalt oxide (Co_100-xCe_x) catalysts with controlled metal molar ratios were tested for the catalytic performance of NO reduction by CO. The structural property, and surface chemistry were investigated by nitrogen adsorption, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photo-electron spectroscopy, and temperature-programmed reduction by hydrogen. The flow reactor studies revealed that the Co₉₈Ce₂ catalyst can achieve 99% N₂ selectivity at a relatively low temperature (260 °C), and the Co₁₅Ce₈₅ catalyst exhibits ∼100% N₂ selectivity at a high temperature (580 °C). Notably, the tandem use of Co₉₈Ce₂ and Co₁₅Ce₈₅ catalysts (molar ratio 1 : 1) achieved 99.6% conversion of NO and 99.7% selectivity of N₂ for a wide temperature range from 250 to 680 °C. The synergistic effects of Ce and Co were evidenced in this work. The Co²⁺/Co³⁺ ratio was increased with 2% Ce incorporation, which could promote NO adsorption at low temperature; the Ce-O-Co solid solution formed rich surface oxygen that may promote CO oxidation through the Mars-van Krevelen mechanism on surfaces and oxygen vacancies would be replenished when adsorbed NO molecules were reduced to N₂. The rich O/(Ce + Co), Co²⁺/Co³⁺, and Ce⁴⁺/Ce³⁺ pairs on the surface of Co_100-xCe_x promoted sustainable activity for NO decomposition to N₂. This study provides a promising avenue for boosting the conversion of polluted exhaust gas via designing suitable tandem catalysis systems.