摘要/Abstract

由于国家对石油产品中含硫量的严格控制，原油脱硫已成为石油化工生产中的一项紧迫任务.硫化钼作为高效加氢脱硫催化剂而被广泛研究.过渡金属Co掺杂提高了传统钼基硫化物加氢脱硫催化剂的催化活性，目前被广泛应用于原油催化脱硫.本文采用密度泛函理论，对Co修饰MoS₂三角形团簇边缘不饱和活性位（CUS）的形成及甲硫醇的催化脱硫过程进行了理论研究.结果表明，活性位形成过程中，氢气裂解的活性位为Mo原子和S原子，随后形成硫化氢并脱附.甲硫醇倾向于吸附在CUS的Top^Co位.通过电荷布居及前线轨道分析发现，Co的引入改变了表面原子电荷及CUS的LUMO轨道分布，并且Co表现出强吸电子能力，从而促进甲硫醇的吸附.CH₃SH最优脱硫路径为先后断裂S—H和C—S键形成甲烷实现脱硫，其中形成甲烷的基元步骤为整个脱硫反应的速率控制步骤，其能垒为1.51 eV.
关键词: 二硫化钼, 甲硫醇, 脱硫, 不饱和活性位, 密度泛函理论
With the advent of increasingly stringent regulations on sulfur containing in oil products, desulfurization of crude oil has become an urgent task for petrochemical production. Molybdenum sulfide (MoS₂) have been extensively studied as one of the most efficient hydrodesulfurization catalysts. Co-doped molybdenum sulfides are usually used in desulfurization processes of sulfur-containing compounds, in which the transition metal Co could promote its catalytic performance. Herein, density functional theory was employed to investigate the formation of coordinative unsaturated active sites (CUS) and the catalytic desulfurization process of methanethiol (CH₃SH) at the Co-doped MoS₂ triangular clusters. Results showed that Co was not the effective reaction site on hydrogenation process, and Mo and S atoms acted as the active sites of hydrogen dissociation during the formation of CUS sites, followed by the H₂S generation and desorption. The charge population analyses showed that Co promoted the hydrogenation process indirectly. CH₃SH prefered to be adsorbed at the Top^Co site with a high adsorption energy of -1.44 eV. The charge population and frontier orbitial analyses illustrated that Co can alter the distribution of the surface atoms' charge and the LUMO orbital of CUS and showed the strong electrophile and thus strengthening the CH₃SH adsorption. When CH₃SH was adsorbed at the Co-doped MoS₂ clusters, electrons transfered from CH₃SH to the surface atoms of MoS₂. In this work, three desulfurization pathways of CH₃SH at the Co-doped MoS₂ were investigated, namely, the C-S bond initial scission, the S-H bond initial scissions, and the C-S and S-H scissions simultaneously. The competitive route during the CH₃SH desulfurization process started with the S-H and C-S bond scissions successively, followed by the methane formation in the terms of thermodynamics and kinetics, and the formation of methane was the rate-determining step with the energy barrier of 1.51 eV.
Key words: molybdenum disulfide, CH₃SH, desulfurization, coordinative unsaturated active site, density functional theory


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