Abstract
The effect of the preparation method of monometallic Pd and Pt and bimetallic Pd-Pt/Al2O3-TiO2catalysts on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was investigated in this study. The synthesis was accomplished using three methods: (A) impregnation, (B) metal organic chemical vapor deposition (MOCVD), and (C) impregnation-MOCVD. The bimetallic Pd-Pt catalyst prepared by the impregnation-MOCVD method was most active for the HDS of DBT compared to those prepared by the single impregnation or MOCVD method due to the synergetic effect between both noble metals. The greater selectivity toward biphenyl indicated that this bimetallic Pd-Pt catalyst preferentially removes sulfur via the direct desulfurization mechanism. However, the bimetallic Pd-Pt catalyst prepared using the single MOCVD method did not produce any cyclohexylbenzene, which is most likely associated with the hydrogenation/dehydrogenation sites.
Highlights
The hydrodesulfurization (HDS) of straight run gasoil (SRGO) is receiving considerable attention due to stringent environmental requirements, such as a lower sulfur content and the elimination of aromatic compounds in diesel fuel [1,2,3,4]
The bimetallic PdPt catalyst prepared by the impregnation-metal organic chemical vapor deposition (MOCVD) method was most active for the HDS of DBT compared to those prepared by the single impregnation or MOCVD method due to the synergetic effect between both noble metals
The HDS activity of the better bimetallic catalyst was four times higher than that obtained from the catalysts prepared with either the single IMP or MOCVD method (Figure 8(a)), which indicated that the catalytic activity was strongly improved when Pt0 is dispersed or deposited on the PdO particles that were previously incorporated onto the Al2O3-TiO2 support rather than being incorporated in one step
Summary
The hydrodesulfurization (HDS) of straight run gasoil (SRGO) is receiving considerable attention due to stringent environmental requirements, such as a lower sulfur content and the elimination of aromatic compounds in diesel fuel [1,2,3,4]. DBT is desulfurized via the DDS route while 46DMDBT is desulfurized via the HYD route [7, 8] In this case, strong hydrogenating catalytic sites are preferable for the successful removal of refractory sulfur compounds, such as 46DMDT. Conventional supported Ni-Mo sulfide hydrotreating catalysts become active in the HYD route only at high pressure due to the thermodynamic limitation [9] Precious metals, such as Pd and Pt, have exhibited a higher hydrogenation ability at lower temperatures compared to metallic sulfides in hydrotreating catalysts. For the synthesis of HDS catalysts, conventional wet impregnation has been the most frequently employed method for metal incorporation This process requires several steps in the preparation and has several limitations to good metallic dispersion [22]. We try to explain the HDS catalytic activity as a function of the reducibility or hydrogenating properties and the particle size of the bimetallic catalysts
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