PNNL

Abstract

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 NOx by NH3. After hydrothermal aging at 800°C for 16 h, the NOx reduction performance of Cu-ZSM-5 and Cu-beta were 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-NMR, significant reduction in the intensities of the tetrahedral aluminum peak was observed for Cu-ZSM-5 and Cu-beta, although no increase in the intensities of the octahedral aluminum peak was observed. When the redox behavior of Cu species was examined using H2-TPR, it was found that Cu2+ could be reduced to Cu+ and to Cu0 fir Cu-ZSM-5 and Cu-beta catalysts, while Cu2+ could be reduced to Cu+ only for 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.