Highly Engineered Cr-In/H-SSZ-39 Catalyst for Enhanced Performance in CH4-SCR of NOx

The selective catalytic reduction of NOxwith CH4(CH4-SCR) holds the potential to simultaneously abate harmful NOxand CH4greenhouse gases. In this study, a series of bimetallic M-In/H-SSZ-39 catalysts (where M represents Cr, Co, Ce, and Fe) were prepared via an ion exchange method and subsequently evaluated for their CH4-SCR activity. The influences of the preparation parameters, including the metal ion concentration and calcination temperature, as well as the operating conditions, such as the CH4/NO ratio, O2concentration, water vapor content, and gas hourly space velocity (GHSV), on the catalytic activity of the optimal Cr-In/H-SSZ-39 catalyst were meticulously examined. The results revealed that the Cr-In/H-SSZ-39 catalyst exhibited peak CH4-SCR catalytic performance when the Cr(NO3)3concentration was 0.0075 M, the In(NO3)3concentration was 0.066 M, and the calcination temperature was 500 °C. Under optimal operating conditions, namely GHSV of 10,000 h−1, 400 ppm NO, 800 ppm CH4, 15 vol% O2, and 6 vol% H2O, the NOxconversion rate reached 93.4%. To shed light on the excellent performance of Cr-In/H-SSZ-39 under humid conditions, a comparative analysis of the crystalline phase, chemical composition, pore structure, surface chemical state, surface acidity, and redox properties of Cr-In/H-SSZ-39 and In/H-SSZ-39 was conducted. The characterization results indicated that the incorporation of Cr into In/H-SSZ-39 enhanced its acidity and also facilitated the generation of InO+active species, which promoted the oxidation of NO and the activation of CH4, respectively. A synergistic effect was observed between Cr and In species, which significantly improved the redox properties of the catalyst. Consequently, the activated CH4could further interact with InO+to produce carbon-containing intermediates such as HCOO−, which ultimately reacted with nitrate-based intermediates to yield N2, CO2, and H2O.