Preparation Of MoS₂-Composite Oxide Catalysts And Study Of Carbonyl Sulfide Hydrogenation Performance

Integrated Gasification Combined Cycle（IGCC）power generation technology is considered to be the most promising technology for the clean and efficient use of coal.However,the carbonyl sulfide（COS）formed in the gasification reaction is chemically stable and difficult to remove,not only polluting the ecosystem but also causing corrosion of downstream reaction equipment.Therefore,the removal of carbonyl sulfide from feedstock syngas is critical to the successful application of IGCC systems.Hydrodesulfurization makes direct use of the hydrogen in the gas and is often considered to be an effective method of removing COS from gas.Traditional hydrodesulfurization（HDS）catalysts usually use activated alumina as the support and molybdenum disulfide promoted by cobalt or nickel as the active component.However,there are some disadvantages such as strong metal-support interaction（MSI）,high reaction temperature（>320℃）and pre-vulcanization,which greatly limit their application.Therefore,research on new HDS catalysts focuses on the development of support materials with good performance or modification of the active components.Composite oxide carriers with active alumina as the main component,i.e.retain the performance advantages of the components in the composite oxide carrier,while significantly improving the defects of the single active alumina carrier.Nickel oxide is widely used as a catalyst active centre or catalyst carrier in the catalytic reactions of organic substances and has shown excellent performance.Based on this,this thesis carried out a study on the low-temperature hydrogenation of carbonyl sulfide using Ni O-Al₂O₃ composite oxide as a carrier loaded with Mo S₂ catalyst,and the following main findings were obtained:Firstly,through the screening of the support and the study of preparation conditions,it is concluded that the hydrodesulfurization activity of Mo S₂-Ni O/Al₂O₃ catalyst prepared with composite oxide（Ni O-Al2O3）as the support,nickel oxide content of 10 wt.%and calcination temperature of 600°C is the best.At the reaction temperature of 220°C,COS can be completely removed and H₂S selectivity is 100%.Characterization showed that the Mo S₂-Ni O/Al₂O₃ catalyst prepared at a Ni O content of 10 wt.%and a roasting temperature of 600°C did not form Mo O₂and had a higher percentage of Mo⁴⁺（Mo S₂）.In addition,the active phase of the catalyst was very stable and achieved a COS removal efficiency of more than 99%in 22 h of hydro conversion reaction.Secondly,the effect of reaction conditions on the hydrodesulfurization activity of Mo S₂-Ni O/Al₂O₃ catalysts was investigated.When the CS₂ concentration in the reaction system is in the range of 0-50 ppm,CS₂ has essentially no effect on the HDS activity of the catalyst,but the H₂S selectivity of the catalyst increases with increasing CS₂ concentration.When the H₂S concentration in the reaction system was in the range of 0-75 ppm,H₂S had little effect on the catalyst HDS activity,and the hydroconversion efficiency of COS started to decrease when the H₂S concentration was continued to increase to 100 ppm.The catalyst stability was good in the range of 22000 h^-1 to 32000 h^-1 airspeed and the catalyst HDS activity decreased when the airspeed was continued to increase to 37000 h^-1 and 42000 h^-1.The optimum H₂ content for the hydroconversion of COS over Mo S₂-Ni O/Al₂O₃ catalysts is 25 vol%and the optimum relative humidity is 35%.The experimental combined with characterization analyses revealed that the hydroconversion of COS over Mo S₂-Ni O/Al₂O₃ catalysts was carried out in two steps,with the sulfide vacancies on the catalysts being the active sites for hydrodesulfurization.The introduction of nickel oxide increased the polarization of the alumina carrier,weakened the interlayer interaction of Mo S₂loaded on the Ni O-Al₂O₃ carrier and promoted the formation of more multilayers of Mo S₂ over the catalyst.in addition,the use of Ni O-Al₂O₃ as the catalyst carrier weakened the metal-carrier interaction and facilitated the reduction of more ammonium tetrathiomolybdate to Mo S₂ during the preparation process.this conferred Mo S₂-Ni O/Al₂O₃ catalyst with more edge-active sites and higher Mo S₂ occupancy,which facilitates the COS HDS activity.Moreover,the Ni O-Al₂O₃composite as Mo S₂ carrier can significantly increase the catalyst surface alkaline strength and enhance the COS chemisorption process.