NO decomposition over sodium-promoted cobalt oxide

The catalytic decomposition of NO over cobalt oxide was significantly enhanced by the addition of alkali promoters. The promotional effect was the highest with Na and the optimal Na/Co atomic ratio was 0.015. The reaction rate increased with increasing temperature up to 650°C. At 550°C, the rate measured at low conversions for the most active catalyst was 0.28 μmol N₂/g s. In contrast, very low decomposition rate was observed when Na was added to ZrO₂. This suggests that both Na⁺ and Co₃O₄ are necessary for the high NO decomposition activity. In ¹⁵NO temperature programmed desorption, the presence of Na in the sample resulted in the appearance of desorption peaks of NO, O₂ and N₂ at temperatures higher than 450°C. X-ray diffraction of a post-reaction sample detected a NaNO₃ phase. It was proposed that the presence of Na facilitated the desorption of oxygen from Co³⁺ to form Co²⁺ via the formation and decomposition of NaNO₃, and Co²⁺ was the active site for NO decomposition.