Studies on Characterization of Active Sites of Sulfided PtMo/γ-Al₂O₃ Catalysts by Using Low Temperature FTIR Spectroscopy of Adsorbed CO and Their Thiophene HDS Activity

A series of sulfided PtMo/γ-Al₂O₃ catalysts[w(Mo) = 9. 0%] with different contents of Pt were characterized by using low-temperature FTIR spectroscopy of adsorbed CO, while their HDS activity was investigated with thiophene as a model substrate. Experimentally, it was found that no existence of the bands related to the surface complexes of Al³⁺←CO and Pt⁰←CO→Pt⁰ was observed at 77 K and that the rate of the thiophene HDS reaction (573 K) is well linearly proportional to the area of the Pt⁰←CO band at 2 093 cm^-1 with a higher extrapolated HDS rate compared to that of sulfided Mo/γ-Al₂O₃ catalyst at the zero content of platinum. On the basis of the results here, the conclusion may be made that the active monolayer phase of Pt-Mo-S may be formed over sulfided PtMo/γ-Al₂O₃ catalysts during the sulfidation process and that both Mo²⁺ and Pt⁰ sites for CO adsorption should be the active reaction centers of thiophene HDS.