Catalysts based on pillared interlayered clays for the selective catalytic reduction of NO

The reactivity of an Al-pillared interlayered clay (PILC) (AZA) and a mixed Fe/Al-PILC (FAZA), used as references by the Concerted European Action-Pillared Layered Structure (CEA-PLS), was investigated in the selective catalytic reduction (SCR) of NO by NH3 or propane, as either catalysts or as supports of Cu ions. Both AZA and FAZA, either with or without Cu were found to be inactive in the reduction of NO with propane and oxygen. This is different from the behaviour with alumina with or without Cu, because of the different surface acidity properties. Good NO conversions were observed for both PILCs using NH3. The best catalytic performances were shown by FAZA, but the activity of AZA was also remarkable. The addition of Cu ions to both AZA and FAZA leads to an improvment in the activity in NO conversion and a reduction in the side formation of N2O. The catalytic behaviour was found to depend on the method of Cu addition, the Cu loading and the nature of the PILC. With AZA the best results were obtained for a Cu content up to 2 wt%, while further increases in the amount of Cu resulted in a considerable decrease in the conversion of NO. With FAZA, on the other hand, a high activity was observed at up to 3% of Cu introduced by ion exchange. By comparison with other Cu containing catalysts, Cu-FAZA allows operation in a wider range of reaction temperatures due to the reduced rate of side ammonia combustion. The surface acidity properties of AZA and FAZA were also characterized to interpret the above effects.