Using Transient XAS to Detect Minute Levels of Reversible S-O Exchange at the Active Sites of MoS₂-Based Hydrotreating Catalysts: Effect of Metal Loading, Promotion, Temperature, and Oxygenate Reactant

Modulation excitation spectroscopy (MES) coupled with time-resolved X-ray absorption (XAS) was applied to unpromoted and Co-promoted Mo-based hydrotreating catalysts (i.e., Mo CoMo catalysts) for investigating the minute as well instantaneous differences in active site composition under influence of H2S H2O. Transient experiments during alternating sulfur- water-rich conditions were performed at temperatures between 400 500 °C using varying Co/Mo metal loadings study correlative effect these factors on stability sites. For both types catalysts, features demodulated K-edge spectrum matching difference spectra MoS2 MoO3 references indicate a reversible oxidation–sulfidation process H2O/H2S cycling. In case increasing loadings, transient XAS K- Co revealed levels S-O exchange sulfided sites, although 26 47% bound stable CoAl2O4, which does not form bulk sulfide. Thus, even presence multiple phases (oxide sulfide) low number sites relative total atoms, can successfully detect changes occurring over Furthermore, comparison amplitude showed that atoms are more prone temperature, while promotion stabilized molybdenum MES-coupled 1-propanol evaluate degree another oxygenate reactant higher affinity water toward compared 1-propanol.