Insights into the different catalytic behavior between Ce and Cr modified MCM-41 catalysts: Cr2S3 as new active species for CH3SH decomposition

Abstract

High sulfur resistance and high stability of catalysts are crucial for the catalytic decomposition of sulfur-containing volatile organic compounds. In this work, compared to 5Ce-MCM-41, the 5Cr-MCM-41 catalyst exhibited ultra-stability (no activity loss at 600 h) and higher sulfur resistance. The physical structure and chemical characteristics of the catalysts were analyzed by XRD, H2-TPR, NH3-TPD, CO2-TPD, XPS, and TEM. Combining the characterization results, we found that the 5Cr-MCM-41 catalyst presented outstanding catalytic performance due to superior reducibility and appropriate acidity, which results in the conversion of most of the C and S elements in the CH3SH to the gas-phase coke- and sulfur-containing products rather than accumulating on the catalyst surface. Meanwhile, the catalytic performance, reaction path, and deactivation mechanism of rare earth metal (Ce) and transition metal (Cr) modified MCM-41 catalysts were systematically investigated by in situ DRIFTS and DFT calculations. Additionally, a new active phase (sulfide state Cr2S3) was proposed and proved via accurately designed experiments, which plays a significant role in the collaborative removal of CH3SH with hexavalent chromium (Cr(VI)). These findings are beneficial for designing high sulfur resistance catalysts for the removal of CH3SH and other sulfur-containing products.