Promoted activity of the selective catalytic reduction of NOx with propene by H2 addition over a metal-monolithic anodic alumina-supported Ag catalyst

The effect of H2 addition on the selective catalytic reduction of NOx with propene (C3H6-SCR of NOx) was investigated using a metal-monolithic anodic alumina-supported Ag catalyst. The de-NOx activity of the Ag/Al2O3 catalyst at low temperature was markedly enhanced by the addition of a small amount of H2; the enhancement was associated with the improved propene activation at low temperatures. The addition of H2 greatly promoted the nitrate decomposition at low temperatures, which was believed to alleviate nitrate poisoning and to initiate the SCR reaction at low temperatures, because of the formation of free silver sites. Furthermore, it is suggested that a small amount of H2 addition will further reduce the freed Ag+ species into Agnδ+ and will eventually lead to the improved de-NOx activity, because Agnδ+ is more active for the propene activation than Ag+ at low temperatures. However, excess H2 and high Ag loading mainly promoted the nonselective combustion of propene with oxygen, rather than the selective oxidation of propene with NOx. Additionally, a combination of this H2 promotion effect and electrical heating produced a favorable de-NOx system with a quick response, a wide temperature-window and a high de-NOx activity.

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► A metal-monolithic anodic alumina-supported Ag catalyst was used.
► Hydrogen was added to promote the SCR activity at low temperatures.
► The addition of H2 greatly promoted nitrate decomposition to free silver sites.
► An electrical-heating pattern gave a quick SCR system response.