Enhancing catalytic performance of Cu-SSZ-13 for the NH3-SCR reaction via in situ introduction of Fe3+ with diatomite

Abstract

The SSZ-13 zeolite supported Cu catalyst is highly efficient in eliminating NO_x and introduction of Fe³⁺ ions can significantly improve the high-temperature activity and the hydrothermal stability of Cu-SSZ-13. However, the exact role of Fe species has not been investigated yet. In this work, we synthesized highly crystalline SSZ-13 with a silicon source of Fe³⁺-containing diatomite (SSZ-13-D) and silica sol (SSZ-13-S). The crystallization time of SSZ-13-D was only half that of SSZ-13-S. Investigation of the crystallization processes revealed that the intrinsic six-membered ring in diatomite was responsible for the significant shortening of the crystallization time. The fresh Cu-SSZ-13-D exhibited better catalytic activity than the fresh Cu-SSZ-13-S from 175–500 °C, especially at 200 °C, where the NO conversion of Cu-SSZ-13-D was 10% higher than that of Cu-SSZ-13-S. After hydrothermal ageing, the temperature window of T₉₀ for Cu-SSZ-13-D_HTA was narrowed to 250–350 °C, while the maximum NO conversion of aged Cu-SSZ-13-S_HTA was reduced to 88%. TEM, XPS, EPR, UV-Vis DRS, NH₃-TPD, and H₂-TPR characterization demonstrated that the extra-framework Fe³⁺ in SSZ-13-D could suppress the aggregation of Cu²⁺ in the fresh Cu-SSZ-13-D at high reaction temperature and promoted the transformation of Cu(OH)⁺ species to Cu²⁺ during the hydrothermal ageing leading to a better catalytic performance. The investigation of the role of Fe species in enhancing the catalytic performance of the Cu-SSZ-13 catalyst provides guidance for the preparation of efficient bimetallic Cu-based zeolite catalysts for the NH₃-SCR reaction.