Effects of hydrothermal aging at high and low temperatures on the selective catalytic reduction of NOx with NH3 over Cu/SAPO-34

Abstract

Effects of hydrothermal aging at 80 and 850 °C on catalytic performance and stability of Cu/SAPO-34 catalysts with different Cu loadings were examined, and their catalytic activities were investigated for the selective catalytic reduction (SCR) of NOx with ammonia. Over the fresh catalysts, the NH3-SCR activity increased with the loading of copper in the low-temperature range and decreased in the high-temperature range. Both of the isolated Cu2+ ions and CuO synergistically influenced the SCR behavior of the Cu/SAPO-34 catalysts, which gave rise to the distinct trends of catalytic activity in the two temperature ranges. Structural damage and dealumination, however, were observed in the aged samples, leading to a severely decreased amount in acid site and a loss in crystallinity. After hydrothermal aging at 850 °C, there was some aggregation in Cu species and the redox capacity of the 0.8Cu/SAPO-34-850 catalyst was improved. It is found that the isolated Cu2+ ions were transformed into the Cu–AlOx species after hydrothermal aging at 80 °C. These results clearly demonstrate that the change in the state of copper species and the damage in structure led to different catalytic activity of the sample.