Study On Hydrodesulfurization Performance Of Heteroatom-modified Catalysts

With the rapid development of society and economy,human consumption demand for petroleum products is increasing.Large-scale mining consumption makes poor-qualitilization and heavy-qualitilization of crude oil resources more serious,resulting in the content of impurities such as sulfur and nitrogen compounds in the raw materials for processing gasoline and diesel has also increased.During the use of fuel oil,the release of large quantities of sulfides into petroleum products has caused pollution and damage to the natural environment.Since 2019,China has implemented the National VI clean fuel standard,which indicated that the sulfur content should be lower than 10 ppm for the diesel products.This means that the sulfur-containing compounds in the oil need to be deeply removed during the oil processing.Hydrodesulfurization is the most commonly used oil desulfurization technology in industry,and its core is to develop high-activity and high-selectivity hydrodesulfurization catalysts.With its excellent pore structure and mechanical strength,γ-Al₂O₃ has become the most widely used hydrodesulfurization catalyst support in industry.However,a strong force is formed betweenγ-Al₂O₃ and the active metal,which limits the performance of the catalyst for hydrogenation,and it is difficult to meet the processing requirements of ultra-low sulfur products under normal conditions.Therefore,it is one of the important research directions in this field to improve the reaction performance of catalysts by adjusting the catalyst structure.In this paper,a series of Ni Mo/Al₂O₃ catalysts with different Si O₂ contents were prepared using Si modified alumina as support.The changes in the properties and structures of the modified catalysts were explored by XRD,BET,NH₃-TPD,Py-IR,H₂-TPR,HRTEM and XPS characterizations,and the desulfurization activity of the catalysts was evaluated using dibenzothiophene（DBT）.Through the characterization and analysis of the Si modified catalysts,it was found that the introduction of silicon weakened the metal-support interaction,changed the porous structure and surface acidity of the catalyst.It also improved the active phase dispersion and metal sulfidation,thereby,promoted the formation of more Type II Ni Mo S active phases.The evaluation results confirm that Si modification improved the reaction performance of the catalysts,and the catalyst has the best effect when the Si content was6%.At this time,the activation energy of DBT was 91.4 k J/mol,and the reaction rate constant was 5.25×10^-4 mol/（g·h）.The comparison of the desulfurization products distribution of DBT conversion ratio 50%showed that the introduction of silicon significantly affected the reaction path selectivity of the catalyst,and the DDS selectivity increased from 83.69%（unmodified catalyst）to 92.89%（the content of 6%）.The characterization results of Ti-modified catalysts showed that Ti modification changed the pore size distribution of the supports and catalysts,increasing the proportion of effective pores of 4～10 nm.The amount of weak acid on the catalysts surface was increased and new active sites were created.In addition,more easily reducible Mo species were generated,which increased the Mo sulfurization degree and the ratio of Ni Mo S active phases.The evaluation results showed that Ti modification improved the hydridesulfurization performance of the catalysts.The desulfurization effect of the catalyst was the best when the addition amount of Ti O₂ was 8%,and the corresponding activation energy and reaction rate constant of DBT were 79.2 k J/mol and 3.96×10^-4 mol/（g h）,respectively.The comparison of the desulfurization products distribution of DBT conversion ratio 50%showed that the BP was still the main product of DBT,and the desulfurization path selectivity of DDS increased from 83.69%（unmodified catalyst）to91.97%（the content of 8%）.