Effect of mass ratio on micro-mesoporous Cu-SSZ-13/CeWTi composite catalysts for the selective catalytic reduction of NO with ammonia

Abstract

A series of micro-mesoporous SSZ-13/CexWyTiz composites with different zeolite/oxide ratios were synthesized using a one-step crystallization method. The effects of the mass ratio on the crystal form, specific surface area, pore structure, surface element properties, redox properties, surface acidity and deNO_x performance of the Cu-SSZ-13/CeWTi composite catalysts were investigated using X-ray diffractometry (XRD), Brunauer–Emmett–Teller analysis (BET), X-ray photoelectron spectroscopy (XPS), H₂ temperature programmed reduction (H₂-TPR) and NH₃ temperature programmed desorption (NH₃-TPD). The results reveal that the Cu-SSZ-13/CeWTi composite catalysts formed a micro-mesoporous structure. The increase in the mass ratio leads to the increased microporous ratio of the composite catalysts, the improved crystal structure of SSZ-13 and a higher specific surface area and pore volume, which is conducive to enhancing the low-temperature deNO_x activity, but its high-temperature performance (450 °C and above) decreases. The introduction of micropores into mesoporous materials can result in the production of more Ce⁴⁺, surface chemisorption oxygen species O_α and acid sites. The Cu-SSZ-13/CeWTi composite catalyst with a mass ratio of 1 : 4 demonstrated the best micro-mesoporous ratio, low-temperature selective catalytic reduction (SCR) performance and hydrothermal stability.