Catalytic NO reduction by CO over ceria-cobalt oxide catalysts

A series of ceria-cobalt oxide (Co100-xCex) 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% N-2 selectivity at a relatively low temperature (260 degrees C), and the Co15Ce85 catalyst exhibits similar to 100% N-2 selectivity at a high temperature (580 degrees 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 N-2 for a wide temperature range from 250 to 680 degrees 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 N-2. The rich O/(Ce + Co), Co2+/Co3+, and Ce4+/Ce3+ pairs on the surface of Co100-xCex promoted sustainable activity for NO decomposition to N-2. This study provides a promising avenue for boosting the conversion of polluted exhaust gas via designing suitable tandem catalysis systems.