| Integrated gasification combined cycle (IGCC) is an advanced power generation system and has become a significant path to the efficient utilization of coal resource. Among IGCC, desulfurization process of coal-based gases is one of the key technologies. Carbonyl sulfide (COS), as an organic sulfur-containing compound, which is inevitably existed in the coal gasification as well as other coal transformation processes, is much more difficult to be directly removed because of its stability and neutral nature. Hydrodesulfurization (HDS) is a highly effective strategy to reduce COS, meanwhile hydrogen existed in coal gas can act as reducing agent and hydrogenation agent without additional gas source. Generally, the oxides of Ni, Co and Mo supported on γ-Al2O3are used as catalysts for the COS hydrogenation. However, there are several defects for these traditional catalysts, for example, the HDS reaction conducts only at high temperature (>320℃), and the oxides catalysts need presulfurizing treatment to transform into activated sulfides, which severely limit their catalytic performance and applications. Therefore, the developing of new support materials and/or the modifying of active components for HDS catalysts is very important.As a typical transition-metal dichalcogenide, molybdenum disulfide (MoS2) exhibits excellent catalytic activity and has been widely applied in various hydrogenation reactions. Graphene is a new carbon material which possesses a plate-like structure with a large specific surface area. The unique large basal plane structure, coupled with its excellent thermal, electronic and mechanical features, makes graphene an attractive substrate for the deposition of inorganic nanoparticles to produce highly dispersed composite catalysts. At present, the outstanding activities for graphene-based catalysts have been demonstrated in the applications of electrocatalysis of fuel cell, carbon-carbon coupling reaction and photocatalysis, etc. Hence, due to the current situation of traditional HDS catalysts, the target of this work has been focused on the preparation of MoS2/graphene composites as a new type of HDS catalysts for carbonyl sulfide. The dependency of the catalytic performance on the composition and structure of the synthesized composites has been investigated and a series of novel research works are described as follows.Firstly, a facile and rapid process to prepare MoS2/graphene (M-MoS2/GS) composite catalysts via a solid micro wave-assisted (MWI) route using functionalized graphene sheets as microwave susceptor and ammonium tetrathiomolybdate (ATTM) as the precursor of MoS2 has been described. Compared to other MoS2catalysts, including unsupported MoS2, MoS2/GS and MoS2/activated carbon prepared by traditional thermal approach, the resulting M-MoS2/GS hybrid exhibits superior catalytic activity and stability in the HDS reaction of COS. Detailed characterizations reveal that the excellent performance of M-MoS2/GS catalyst should be ascribed to the highly uniform distribution of small MoS2nanoparticles (20nm) on GS substrate, which is derived from the strong microwave absorption of FGS leading to rapid temperature elevation and the subsequently fast decomposition of ATTM in short radiation time, which promotes the formation of small sized MoS2nanoparticles without aggregation. The high catalytic efficiency over M-MoS2/GS composites demonstrates that microwave irradiationis helpful for the preparation of graphene-based catalysts with enhanced catalytic activity.Secondly, three-dimensional MoS2/graphene monoliths catalysts (3D-MoS2/G) have been fabricated via an in situ hydrothermal route by employing graphite oxide (GO) and ATTM asprecursors. By comparison with the MoS2/G catalysts prepared by impregnation-pyrolysis method and solution reduction route, as well as conventional MoS2/γ-Al2O3catalyst,3D-MoS2/G shows more excellent activity for COS hydrodesulfurization, which should be attributed to its peculiar structure and the synergetic effect between MoS2and graphene. In addition, the influence of microwave irradiationon the property of3D-MoS2/G catalyst has also been investigated. The HDS result indicates that MWI treatment is helpful for the activity improving of monolith catalyst.Finally, stable2D nanosheet crystals with the structure similar to graphene, such as transition metal chalcogenides have been emerging as new appealing materials thanks to their unique properties. While in the range of our knowledge, there have been no reports about graphene-like MoS2being applied in catalysis. Therefore, few-layer MoS2unsupported catalysts and few-layer MoS2/graphene monoliths have been synthesized through solid sulfurization route (MoS2-S) and hydrothermal methods (MoS2-H,3D-FL-MoS2/G). Their HDS catalytic performances for COS removal have been evaluated. Besides, the supported and unsupported multi-layer MoS2catalyst and conventional presulfurizing MoS2catalyst are also prepared as contrast. The results show that the new type catalysts of few-layer MoS2can display superior catalytic activities than others. Among them, MoS2-H catalyst obtained from hydrothermal route demonstrates predominant low-temperature activity which could reach nearly100%COS conversion at240℃. |
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