Preparation Of MoO_3-x/o-CNTs Catalyst And Its Application In Oxidative Desulfurization

China is rich in coal resources which play a crucial role as energy reserves.Direct coal liquefaction（DCL）offers clean and efficient coal utilization.The oil derived from DCL contains 0.05～2.5%sulfur.As a result,the deep processing of such oil products causes the poisoning of downstream catalysts,severe equipment corrosion,and increased production cost.It emphasizes the importance of deep desulfurization of coal-based oil,both practical and theoretical.This dissertation,dibenzothiophene（DBT）,a refractive and primary sulfur compound in coal-based oil,is taken as a model compound.Considering the harsh conditions required for hydrodesulfurization,the mild oxidative desulfurization（ODS）method is chosen to remove the sulfur-containing compounds from the oil.The traditional ODS often requires the addition of organic extractant,which is not environmentally friendly.The different catalytic systems were investigated to improve the desulfurization of ODS.The impacts of adding aromatic hydrocarbons/nitrogen-containing compounds to the ODS system were also studied.The main results and conclusions are summarized as follows:（1）Preparation and catalytic activity of hydrophilic MoO_3-x/SiO₂ and hydrophobic MoO_3-x/o-CNTs catalysts.The addition of extractant promotes product desorption from the surface of the hydrophilic MoO_3-x/SiO₂ catalyst,increasing the ODS activity.Contrary to this,adding extractant to hydrophobic MoO_3-x/o-CNT catalyst suppresses the ODS activity due to the enhanced mass transfer resistance.Therefore,for the MoO_3-x/CNT catalyst,a better ODS performance is attained without adding extractant,i.e.,98.9 and 99.2%sulfur removal（S=500ppm）is achieved for DBT 4,6-DMDBT,respectively.The MoO_3-x/o-CNTs catalyst not only adsorbs the reactant DBT but also facilitates the product desorption in the absence of extractant.The addition of aromatic hydrocarbon compounds has no significant influence on the removal of DBT,while the addition of nitrogen-containing compounds inhibits the removal of DBT.（2）Effects of active phases present in MoO_3-x/o-CNTs catalysts.The increase of hydrothermal synthesis temperature enhances the amount of Mo⁵⁺in the resultant catalysts,enhancing the ODS activity.The solution with more acidity（c（H⁺）=1.5 M）supports the generation of more Mo⁶⁺species in the catalysts that require more oxidant（H₂O₂）to exhibit a good ODS performance.Amidst the pH range（2≤pH≤4）,the lower pH value increases Mo⁵⁺content in the catalysts to reach better ODS activity.The catalyst with maximum Mo⁵⁺content is obtained when the pH value of the synthetic solution is 2 and shows the highest ODS performance（99.5%DBT removal）.The pH of the solution higher than the isoelectric point of o-CNT is not suitable to reach the maximum ODS activity.（3）Preparation and activity of amphiphilic Pickering emulsion catalysts.With the increase of water and oil proportion,the size of emulsion droplets is gradually decreased.The emulsion types belong to the O/W type.Water has a noticeable inhibitory effect on the ODS,i.e.,the ODS performance is negatively correlated with the water content.According to the theoretical calculations,it is due to the facile adsorption of water than DBT on the catalyst,which decreases the ODS activity.According to the theoretical calculations,due to interaction between the water and the oxygen containing functional groups of o-CNTs and SiO₂,the adsorption of water is much easier than DBT on the catalyst,thus resulting in the decreasing ODS activity.