Effects of hydrothermal aging on NH ~3-SCR reaction over Cu/zeolites

摘要

The effects of hydrothermal treatment on model Cu/zeolite catalysts were investigated to better understand the nature of Cu species for the selective catalytic reduction of NO _x by NH _3. After hydrothermal aging at 800 °C for 16 h, the NO _x reduction performance of Cu-ZSM-5 and Cu-beta was significantly reduced at low temperatures, while that of Cu-SSZ-13 was not affected. When the zeolite framework aluminum species were probed using solid state 27Al MASNMR, significant reduction in the intensities of the tetrahedral aluminum peak intensity was observed for Cu-ZSM-5 and Cu-beta, although no increase in the intensities of the octahedral aluminum peak was detected. When the redox behavior of Cu species was examined using H _2-TPR, it was found that Cu ~(2+) could be reduced to Cu ~+ and to Cu ~0 for Cu-ZSM-5 and Cu-beta catalysts, while Cu ~(2+) could be reduced only to Cu ~+ in Cu-SSZ-13. After hydrothermal aging, CuO and Cu-aluminate species were found to form in Cu-ZSM-5 and Cu-beta, while little changes were observed for Cu-SSZ-13.