Excellent selective catalytic reduction of NOx by NH3 over Cu/SAPO-34 with hierarchical pore structure

Abstract

SAPO-34 with hierarchical pore structure (SAPO-34-H) was first prepared by a hard-template method using CaCO3 as template. The xCu/SAPO-34-H (x = 1.1 wt%, 1.9 wt%, 2.7 wt% and 3.2 wt%) catalysts were synthesized by ion-exchanged method and applied for selective catalytic reduction (SCR) of NOx with NH3. XRD, XRF, SEM, TEM, UV–vis-DRS, NH3-TPD, XPS, NMR, EPR and in situ DRIFTS were used to characterize the physiochemical properties of the catalysts. The SCR activity results demonstrate that 100% NOx conversion can be achieved over the 2.7 wt%Cu/SAPO-34-H catalyst at about 150 °C in the GHSV of 40,000 h−1. Furthermore, NOx conversion under the testing conditions of H2O and SO2 was slightly influenced over the 2.7 wt%Cu/SAPO-34-H catalyst after high-temperature hydrothermal aging at 700 and 800 °C, respectively. NOx convention presents above 90% at 170–480 °C even introducing 10% H2O for 10 h, and it can be maintained 90% by introducing 200 ppm SO2 and 12% H2O over 2.7 wt%Cu/SAPO-34-H. In the meantime, 2.7 wt%Cu/SAPO-34-H was investigated through the low-temperature hydration treatment at 80 °C, it also displays superior hydration treatment resistance for low-temperature. The outstanding performance is ascribed to the hierarchical pore structure of 2.7 wt%Cu/SAPO-34-H, which can promote the diffusion of reaction gas and generation of active sites. EPR results indicate that the Cu2+ species mainly locates the site I in 2.7 wt%Cu/SAPO-34-H, while the Cu2+ species mainly locates the site III for the conversional 2.7 wt%Cu/SAPO-34. Moreover, the in situ DRIFTS results indicate that the Lewis acid sites are easy to participate in NH3-SCR reaction for 2.7 wt%Cu/SAPO-34-H, which mainly follows the Eley-Rideal (E-R) reaction mechanism at 200 °C for 2.7 wt%Cu/SAPO-34-H.