Low Temperature IR Spectroscopic Study on the Surface Structure of Sulfided MoO₃/γ-Al₂O₃ Catalyst

The adsorption characterization and the surface structure of sulfiled MoO₃（15wt.%）/γ-Al₂O₃ catalyst were investigated by in situ low temperature infrared spectroscopy, using CO and NO as IR probe molecules.
For NO and CO alternate adsorption, the IR spectra showed that when the sample was preadsorbed by NO(1790, 1690cm^-1), it could still adsorb CO(2120cm^-1); however, when the sample was preadsorbed by CO, it could not adsorb NO at all. Similar phenomena were observed for O₂ and CO alternate adsorption and for H₂ and NO alternate adsorption. For H₂ and CO alternate adsorption, the IR spectra showed that once the sample was preadsorbed by H₂, it could not adsorb CO.
According to the results mentioned above, it was suggested that there were two kinds of Mo（CUS） （denoted as Mo_A（CUS） and Mo_B（CUS）） existing on the surface, Mo_A（CUS） might adsorb all of CO, NO, O₂ or H₂, Mo_B（CUS） might adsorb CO or H₂ only. The fraction of the former in the two kinds of Mo（CUS） was very amall. The possible states of the two kinds of Mo（CUS） were discussed.