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 ~(27)Al 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.