Surface Structure and Catalytic Activity of MoO3/Al2O3 Catalysts in the Hydrodesulfurization of Thiophene Studied by X-ray Photoelectron Spectroscopy

Article abstract of DOI:10.1021/j100451a019

The relationships between surface structure and catalytic activity of MoO3/Al2O3 catalysts in the hydrodesulfurization of thiophene (at 400 deg C and atmospheric pressure of thiophene/H2) were investigated by X-ray photoelectron spectroscopy (XPS), coupled with various physicochemical techniques including pyridine adsorption experiments.It was found that the intrinsic activity of molybdenum (thiophene conversion/g of MoO3) depended simply on the sulfidation degree of molybdenum determined by XPS regardless of the loading amount of MoO3 (2.4-23.1 wt percent MoO3), the calcination temperature (500 and 700 deg C), and the pretreatment conditions (prereduction with H2, presulfidation with CS2/H2 and nonpretreatment).The intrinsic activity showed a maximum at S/Mo=1 (atomic ratio), forming a good volcano-type correlation.In the low sulfur content region (S/Mo<1), it was revealed by XPS that S/Mo(IV)=1.0+/-0.2.To interpret consistently these features, pyridine adsorption results, and sintering behavior of molybdenum, it is proposed that a molybdenum species (1) having a composition of S/Mo(IV)=1 is present in the sulfided catalysts as well as MoS2.Species 1 shows much higher intrinsic activity for the reaction than MoS2 because of the higher anion vacancy concentration in it, induced by better dispersion.The structure of species 1 and the hydrodesulfurization mechanism on species 1 are suggested on the basis of the above observations.The surface structures of oxidic and sulfided MoO3/Al2O3 catalysts are discussed mainly on the basis of the XPS results.