Effect On Oxidative Desulfurization Activity Of The Modification Of MoO₃/SiO₂

As the environmental pollution caused by SOX has become more and more severe which was produced along with the sulfur-bearing oil, various countries strict limit diesel oil the sulfur content. Because of the low activity of DBTs with large steric hindrance in the diesel in conventional hydrodesulfurization(HDS), it is difficult to remove. If HDS is used to remove these sulfocompounds, Severe HDS operating conditions are required which will result in high operating expenses. Oxidative desulfurization (ODS) as a new desulphurization technology with mild reaction conditions, high desulphurization efficiency, low operating cost and simple technical process becomes a foucs of the research.In this paper, MoO3/SiO2 Supported catalysts were prepared by incipient wet impregnation method and modified by the introduction of citric acid (CA), oxalic acid (OA) and CeO2, respectively. MoO3/SiO2 and modified catalysts were characterized by the ultraviolet-visible diffuse reflection spectrum (UV-vis), X-ray photoelectron spectrum (XPS), Transmission electron microscope(TEM) and nitrogen adsorption isotherm method. Inductively coupled plasma (ICP) was used to determine MoO3 capacity after reaction.The research of catalytic oxidation to remove DBT from model diesel composed of DBT(2000 ppm)and toluene was taken in a fixed bed flow reactor under 50℃, and cumene hydroperoxide(CHP) was used as the oxidant (O/S=4, molar ratio). The results indicated that 20% MoO3/SiO2 had low catalytic activity to the DBT oxidation, and the maximum conversion of DBT was around 65%.The catalysts prepared by impregnation method using citric acid or oxalic acid had high activities and the maximum conversion of DBT was raised to above 80%. Through the characterization and analysis of these catalysts, it was thought that the introduction of CA or OA could promote the dispersion of MoO3, which would enhance catalytic activity. The catalytic activities of catalysts modified by CA or OA using a post-treatment method also have been improved, and the maximum conversion of DBT was raised to 80%. Through the characterization and analysis, it was thought that citric acid or oxalic acid not only affected the interaction of active species and the carrier, but also possibly took the reducing agent effect in the heat-treatment process, promoting the formation of a few Mo5+ species, which could affect the catalyst performance. However, Mo5+ could be oxidized by CHP in the reaction process, which caused the decrease of catalytic activity. The catalysts of 20% MoO3-CeO2/SiO2 prepared by impregnation method could make the maximum conversion of DBT raise to above 90%. It was thought that CeO2 could promote the dispersion of MoO3 and cause the formation of defect sites on the surface, which could promote the formation of active oxygen. The activity had a further promotion by the introduction of CA or OA. Through the analysis, it was thought that the CA or OA also promoted the formation of Mo5+, and CeO2 could promote the catalytic activity of Mo5+...