Tailoring of alumina surfaces as supports for NiMo sulfide catalysts in the ultra deep hydrodesulfurization of gas oil: Case study of TiO 2-coated alumina prepared by chemical vapor deposition technique

Abstract

The present paper gives a detailed review of the different studies under investigation in our laboratory concerning the use of TiO2 and TiO2-Al2O3 composites prepared by chemical vapor deposition (CVD) as support for sulfide catalysts in the HDS of dibenzothiophene (DBT) derivatives. The supports investigated here are: TiO 2 (from Degussa, 50m2/g), Al2O3 (Nikki, 186m2/g) and TiO2-Al2O3 supports prepared by CVD of TiCl4 on alumina. Using several characterization techniques, we have demonstrated that the support composite presents a high dispersion of TiO2 over γ-Al2O 3 without forming precipitates up to ca. 11wt.% loading. Moreover, the textural properties of the support composite are comparable to those of alumina. XPS investigations of Mo and NiMo catalysts supported on the different carriers show that Mo-oxide species exhibit a higher degree of sulfidation on the surface of TiO2 and TiO2-Al2O3 than on alumina. The HDS tests of 4,6-DMDBT under mild operating conditions (573K, 3MPa) show that sulfide catalysts supported on the composite support (ca. 11wt.%) are more active than those supported on to TiO2 or Al 2O3. This higher HDS catalytic activity is attributed to the promotion of the hydrodesulfurization pathway, whereby the pre-hydrogenation of one of the aromatic rings adjacent to the thiophenic one may reduce the steric hindrance caused by the two methyl groups adjacent to the sulfur atom during the C-S bond cleavage. © 2003 Elsevier B.V. All right reserved.