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 w as the highest with Na and the optimal Na/Co atomic ratio was 0.015. T he reaction rate increased with increasing temperature up to 650 degre es C. At 550 degrees C, the rate measured at low conversions for the m ost active catalyst was 0.28 mu mol N-2/g s. In contrast, very low dec omposition rate was observed when Na was added to ZrO2. This suggests that both Na+ and Co3O4 are necessary for the high NO decomposition ac tivity. In (NO)-N-15 temperature programmed desorption, the presence o f Na in the sample resulted in the appearance of desorption peaks of N O, O-2 and N-2 at temperatures higher than 450 degrees C. X-ray diffra ction of a post-reaction sample detected a NaNO3 phase. It was propose d that the presence of Na facilitated the desorption of oxygen from Co 3+ to form Co2+ via the formation and decomposition of NaNO3, and Co2 was the active site for NO decomposition. (C) 1998 Elsevier Science B .V. All rights reserved.