Surface/Interface Morphology Effect Of Molybdenum Based Materials And Their Catalytic Performances Of Hydrodesulfurization And Hydrogen Evolution Reaction

As a typical transition metal sulfide,MoS2 plays an important role in the fields of environment and energy catalysis because of its special layered structure and physical-chemical properties.Specially,in the catalysis of hydrodesulfurization(HDS)and electrochemical hydrogen evolution reaction(HER),MoS2 has been the main active component of the catalyst.In this paper,the surface/interface morphology effect of Mo-based catalysts was studied from three aspects:?-Al2O3 carrier,nano-MoS2 particles and Ni-Mo component distribution.HDS and HER tests were used to evaluate the catalytic activities of Mo-based catalysts,which built the structure-activity relationship of Mo-based catalysts.In addition,the connections between HDS and HER catalytic reactions were also discussed.Firstly,the support effect on Mo-based catalysts were studied.Two different kinds of y-AL2O3 precursors:nano stick-like AACH and nano leaf-like AIO(OH)could be selectively synthesized via a facile hydrothermal method by just adjusting reaction temperature.Comparative tests and characterizations proved that the synthesis temperature was the key factor to decide the kinds of products,and the selective synthesis mechanism of AACH and AIO(OH)was also described.After heat treatment,y-Al2O3 with two different morphologies(nano stick-like ACH and nano leaf-like AOH)were synthesized and used as supports for CoMo HDS catalysts.4,6-dimethyldibenzothiophene,and the mixture of thiophene and 1-hexene were used to evaluate the catalytic activities of CoMo/Al2O3.The results showed that CoMo/ACH and CoMo/ACH both had better activities and selectivities.XRD,H2-TPR,XPS,HRTEM characterizations were used to studied the effect of support,compared with other ?-A12O3,ACH and AOH had smaller crystalline aggregation ratios,there were less Lewis acid on ACH and AOH,which caused more Co-Mo-S active phases formed on CoMo/ACH and CoMo/AOH,so CoMo/ACH and CoMo/AOH catalyst had better HDS activities,and proved that the morphological effect of support had a significant effect on the activity of Mo-based catalysts.Secondly,the effect of MoS2 morphology on the activity of Mo-based catalysts were studied.The morphology of MoS2 was controlled by adding thiophene during the hydrothermal synthesis process.It was found that thiophene molecule could aggravate the aggregation of MoS2 nanosheets in the process of MoS2 synthesis,resulting in the formation of MoS2 spherical particles,and gave MoS2 special surface structure,thus the prepared MoS2 catalyst had a larger surface area and more active sites.The catalytic activities of MoS2 catalysts for HDS and HER reaction were both studied,the results showed that the MoS2 catalyst prepared with.200 ?L thiophene(MoS2-200)had the most edge active sites and the best catalytic activity for HDS and HER reaction.With the increase of additive amount of thiophene,the number of active sites and the catalytic activity of MoS2 catalyst would increase,and reached the highest value with 200 ?L thiophene;when the thiophene content was more than 200 ?L,the number of active sites and the catalytic activity of MoS2 catalyst decreased due to the excessive accumulation of MoS2 nanosheets.The HDS and HER tests proved that the catalytic activity of the MoS2 catalyst was highly consistent for the two reactions and proved that the morphological of MoS2 had a significant effect on the activity of Mo-based catalysts.Lastly,the effect of Ni-Mo component distribution on Mo-based catalysts were studied.Ni promoter was introduced into the Mo-S/CNT catalyst by one-step and mechanical mixing methods,respectively.When Ni promoter was introduced by mechanical mixing method,Ni element hardly interacted with MoS2,and basically existed in the form of Ni3S4 phase;when Ni promoter was introduced by one-step method,most of Ni element interacted with MoS2 to form Ni-Mo-S structure.Thiophene HDS test and HER experiment were used to investigate the influence of Ni promoter on the activity of Mo-S/CNT catalysts.It was found that when Ni element existed in the form of Ni3S4 phase,the catalytic activity of MoS2 could not be obviously improved.However,when Ni existed in the presence of Ni-Mo-S structure,the catalytic activity of MoS2 could be improved for both HDS and HER reactions at the same time,which reflected the important effect of the interfacial effect between Ni-S and Mo-S on the activity of Mo-based catalyst.In addition,the DFT was also used to simulate and calculate the binding energies needed for HDS and HER on MoS2 structure and Ni-Mo-S structure,respectively.It was found that the required binding energy for C-S bond breaking and H2 generation on Ni-Mo-S structure were both significantly lower than that of MOS2 structure.Therefore,it was proved theoretically that compared with MoS2 structure,Ni-Mo-S structure had better catalytic activity for both HDS and HER.