New NiO-MoO3/Al2O3-MnO catalysts for dibenzothiophene hydrodesulfurization

Abstract

Obtaining fuels with ultra-low sulfur content requires new, more active catalysts. There are three ways to improve the activity of the catalysts: 1) With the development of new supports, 2) improve the NiMoS active phases and 3) the use of new active phases such as carbides, nitrides or phosphides. Carbides or nitrides are prone to resulfurization under reaction conditions, and consequently generate low activity. The phosphides are very active and stable during the reaction, but the emission of PH3 after the transformation of the phosphate or phosphide precursors becomes a serious problem.
NiMoS phases are traditionally formed by MoS2 or WS2 promoted by Ni or Co and supported on γ-Al2O3. The promotion for Ni or Co can be lost due to an interaction with the support. Therefore, to control the promoter effect, new supports have been sought that allow an optimal Ni-Mo-support interaction that favors the formation of NiMoS phases and prevents the formation of species such as NiSx, MoS2 and NiMoOSx.
The mixed oxides of TiO2-Al2O3, ZrO2-Al2O3 have been used for this purpose, but the acidity of these supports has a negative effect since they favor the presence of nitrogenous molecules and the formation of coke. One solution to this problem is to use mixed oxides formed from Al2O3 and a basic oxide. In this work we present a detailed study from the solution and the effect of Mn on polymolybdates formed after impregnation in basic medium and of Ni on MnO-Al2O3 supports with 1 and 5 mol% of MnO. UV-Vis and Raman diffuse reflectance spectroscopy results showed that Mn allows a high dispersion of Mo as MoO42- and Ni with local octahedral symmetry, but the formation of a NiMnO spinel was also observed. The use of Mn oxides in hydrodesulfurization has not been reported in the literature, it has only been reported as a NiMnMo/Al2O3 supported bulk catalyst, where it is reported for ultrahydrodesulfurization. In this work, the kinetic results of hydrodesulfurization of dibenzothiophene show that Mn is a favorable agent for the support that allows greater activity than the industrial catalyst.