Applied Catalysis A: General ( IF 5.5 ) Pub Date : 2018-05-28 , DOI: 10.1016/j.apcata.2018.05.033 Seyyedmajid Sharifvaghefi , Bo Yang , Ying Zheng
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Experimental and computational studies were performed to investigate the effect of varying sulfur coverage over MoS2 in hydrodesulfurization (HDS) of dibenzothiophene (DBT). Hematite and iron particles were employed as H2S scavengers. MoS2 showed high hydrogenation (HYD) preference in HDS of DBT which was explained by the DFT calculations showing that HYD pathway is more favorable in brim adsorption. The addition of hematite drastically shifted this preference to direct desulfurization (DDS) pathway. DFT calculations showed that MoS2 forms edges with 25% sulfur coverage in presence of hematite. The hydrogen dissociation was found to be energetically unfavorable (deactivated) over the Mo-edge with such sulfur coverage and becomes exothermic (reactivated) only after sigma adsorption of DBT on a vacancy site. In agreement with experimental results, calculations also showed that in the presence of vacancies, the sigma adsorption of DBT and therefore DDS pathway is more favorable. MoS2 with iron particles present, favored the HYD reaction route, however, compared to MoS2 the biphenyl (BP) selectivity increased while the selectivity for isomerized products was reduced. DFT calculations showed that in the presence of iron, Mo-edge has 37% coverage with a vacancy site formed over this edge which explains the higher DDS activity for this catalyst compared to MoS2. A difference was observed in the ability of H2 and H2S in creation of acid sites upon their dissociation at the edges. This was attributed to the difference in SH bond energies in each molecule and the change in oxidation sate of neighboring Mo atoms.
中文翻译:
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H 2 S和硫空位在MoS 2边缘上的二苯并噻吩加氢脱硫中的作用的新见解
进行了实验和计算研究,以研究在MoS 2上变化的硫覆盖率对二苯并噻吩(DBT)的加氢脱硫(HDS)的影响。赤铁矿和铁颗粒用作H 2 S清除剂。MoS 2在DBT的HDS中显示出较高的氢化(HYD)偏好性,这通过DFT计算表明,HYD途径在帽沿吸附方面更有利。赤铁矿的加入将这种偏好急剧转移到直接脱硫(DDS)途径。DFT计算表明,MoS 2在赤铁矿存在下形成含25%硫覆盖率的边缘。发现氢解离在具有这样的硫覆盖率的Mo-边缘上在能量上不利(失活),并且仅在σBT在空位上吸附后才放热(重新激活)。与实验结果一致,计算结果还表明,在存在空位的情况下,DBT的σ吸附以及因此DDS途径更为有利。但是,与MoS 2相比,含铁颗粒的MoS 2更有利于HYD反应路线联苯(BP)选择性增加,而异构化产物的选择性降低。DFT计算表明,在铁的存在下,Mo-edge具有37%的覆盖率,在该边缘上形成空位,这说明与MoS 2相比,该催化剂的DDS活性更高。观察到H 2和H 2 S在边缘解离后产生酸位的能力有所不同。这归因于每个分子中S H键能的差异以及相邻Mo原子的氧化态的变化。