Hydrodesulfurization of Dibenzothiophene Over Ni-Mo Sulfides Supported by Proton-Exchanged Siliceous MCM-41

Strong acid sites on the surface of mesoporous MCM-41 were generated by ion-exchanging siliceous MCM-41 with dilute HNO₃ solution (0.5 M). The XRF determination indicates that most of the sodium cations contained in MCM-41 can be removed by the proton exchange, and dealuminization was observed during the proton exchange. The acidity of the mesoporous materials was characterized by means of NH₃-TPD and the Hammett indicators. It is revealed that new strong acid sites (-5.6 > H₀ > -8.2) were generated after the first 2 h of ion exchange and that the following ion exchanges had little effect on the acidic properties. XRD patterns of the mesoporous materials indicate that the structure of siliceous MCM-41 was improved by HNO₃ ion exchange. When Ni-Mo sulfides were supported on the prepared solid acid (H⁺-MCM-41), high performance in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was observed. However, the HDS activity was decreased while the selectivity of biphenyl (BP) was increased, when H⁺-Si-MCM-41 was ion exchanged with Na₂CO₃ aqueous solution. TPR profiles of the supported Ni-Mo oxides reveal that the acidic properties of the supports greatly influence the hydrogenation activities of the bimetallic oxides. The high performance of H⁺-MCM-41-supported Ni-Mo catalysts may be attributed to the enhanced hydrogenation activity. The introduction of Na cation into the support led to the decrease of the HDS activity due to the poor hydrogenation ability of the supported bimetallic oxides. The HDS activity is well correlated with the low H₂ consumption temperature in the TPR profiles.