Effect of Cu loading content on the catalytic performance of Cu-USY catalysts for selective catalytic reduction of NO with NH3

Abstract

Series of Cu-USY zeolite catalyst with different Cu loading content were synthesized through simple impregnation method. The obtained catalysts were subjected to selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) performance evaluation, structural/chemical characterizations such as X-ray diffraction (XRD), N₂ adsorption/desorption, H₂ temperature-programmed reduction (H₂-TPR), NH₃ temperature-programmed desorption (NH₃-TPD) as well as detailed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments including CO adsorption, NH₃ adsorption and NO+O₂ in situ reactions. Results show that Cu-USY with proper Cu loading (in this work 5Cu-USY with 5 wt.% Cu) could be promising candidates with highly efficient NH₃-SCR catalytic performance, relatively low byproduct formation and excellent hydrothermal stability, although its SO₂ poisoning tolerability needs alleviation. Further characterizations reveal that such catalytic advantages can be attributed to both active cu species and surface acid centers evolution modulated by Cu loading. On one hand, Cu species in the super cages of zeolites increases with higher Cu content and being more conducive for NH₃-SCR reactivity. On the other hand, higher Cu loading leads to depletion of Brønsted acid centers and simultaneous formation of abundant Lewis acid centers, which facilitates NH₄NO₃ reduction via NH₃ adsorbed on Lewis acid centers, thus improving SCR reactivity. However, Cu over-introduction leads to formation of surface highly dispersed CuO_x, causing unfavorable NH₃ oxidation and inferior N₂ selectivity.

Keywords: Brønsted/Lewis acid centers; Cu species; Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS); NH(3)-SCR; USY zeolite.