Preparation Of MoZrO_x@m-ZrO₂/NaZSM-5 Tandem Catalytic H₂S/CO₂/H₂ To Methyl Mercaptan

Focusing on the simultaneous resource utilization of industrial acid gases H₂S and CO₂,the paper proposes the design and development of MoZrO_x bimetallic oxide catalysts in view of the existing technical bottleneck of low selectivity in the one-step synthesis of methanethiol from H₂S/CO₂/H₂ mixture and the good sulfur resistance of molybdenum（Mo）based hydrodesulfurization catalysts,combined with the oxygen vacancy defects of zirconium（Zr）oxide and the excellent adsorption and activation ability of CO₂ molecules by abundant alkali sites on the surface.For the special catalytic reaction path of MoZrO_x bimetallic oxide,the paper proposes the preparation of MoZrO_x@m-ZrO₂/NaZSM-5 tandem catalyst using m-ZrO₂/NaZSM-5compounded with MoZrO_x,coupling the two-step process to enhance the process,forming a thermodynamic and kinetic environment conducive to the efficient conduct of the two-step tandem reaction,exploring the catalyst active phase and reaction conversion behavior,and obtaining high catalytic reaction performance.The thesis pioneered the preparation,characterization and catalytic performance evaluation of MoZrO_x bimetallic oxide around the one-step synthesis of methyl mercaptan process from H₂S/CO₂/H₂ mixture.The effects of MoO₃ doping,compounding method and precipitating agent on the physical and chemical properties and catalytic performance of MoZrO_x catalysts were investigated.The results showed that the 60%MoZrO_x catalyst made by the co-precipitation method with ammonium carbonate as the precipitant had high catalytic reactivity when the MoO₃ doping was60%.Under the reaction conditions of T=320℃,P=2.0 MPa,V（H₂S）:V（CO₂）:V（H₂）=2:1:3,GHSV=18000 mL·gcat^-1·h^-1,and H₂S pre-sulfuration for 3 h,the CO₂ conversion was as high as 23.3%,but the selectivity of the target product methanethiol was only 24%.after the MoZrO_x catalyst was pre-sulfurized.The improvement of the reactivity was directly related to the significant increase of oxygen vacancies and the formation of the"Mo(Mo⁵⁺,Mo⁴⁺)-S"active phase.To address the problem of low selectivity of methanethiol in the MoZrO_xcatalytic system and to combine the characteristics of methanol products appearing in the process,the paper carried out the preparation,characterization and catalytic performance of the ZrO₂/NaZSM-5 composite catalyst based on the group’s previous research on the process of methanethiol production by hydrogen sulfide/methanol,in order to further improve the catalytic performance of the process.The effects of ZrO₂crystalline phase structure,compounding method and compounding ratio on the physical and chemical properties and catalytic performance of the fabricated ZrO₂/NaZSM-5 composite catalyst were investigated.The results showed that the m-ZrO₂/NaZSM-5 composite catalyst was produced by a hydrothermal coating process with a mass ratio of m-ZrO₂:NaZSM-5 of 1:1,which provided the possibility to expose its abundant acid（0.078 m mol/g）and base（0.081 m mol/g）active centers due to its large specific surface area（360 m²/g）and pore volume（0.52 cm³/g）.possibility to exhibit shorter induction period and better catalytic performance.Not only does it exhibit a high conversion of 96%to methanol,but also shows a selectivity of up to 95%to methyl mercaptan.Compared with t-ZrO₂,in the NaZSM-5hydrothermal synthesis system,m-ZrO₂ is more likely to dissolve out Zr⁴⁺into the molecular sieve causing greater desilylation of the skeleton.Also,the hydrothermal encapsulation method enriched the acid-base activity species of the composite catalysts due to the hydrothermal modification effect compared with the composite effect of impregnation and mechanochemical methods.Focusing on the one-step synthesis of methanethiol from H₂S/CO₂/H₂ mixture,the thesis concludes with the preparation,characterization and catalytic performance evaluation of MoZrO_x@m-ZrO₂/NaZSM-5 tandem catalyst.The effects of the tandem two-phase composite mode,ratio and ball milling time on the physical and chemical properties and catalytic performance of MoZrO_x@m-ZrO₂/NaZSM-5 tandem catalyst were investigated,the tandem reaction process conditions were optimized,and the MoZrO_x@m-ZrO₂/NaZSM-5 catalytic active phase and catalytic reaction path were explored.The results showed that the MoZrO_x@m-ZrO₂/NaZSM-5 tandem catalysts were produced by mechanochemical method with MoZrO_x:m-ZrO₂/NaZSM-5 mass ratio of 2:1 and ball milling for 10 min exhibited excellent catalytic performance.Under the reaction conditions of T=320℃,P=2.0 MPa,V（H₂S）:V（CO₂）:V（H₂）=2:1:3,GHSV=18000 mL·gcat^-1·h^-1,and H₂S pre-sulfuration for 3 h,the CO₂ conversion and methanethiol selectivity were as high as 58%and 72%,respectively.MoZrO_x@m-ZrO₂/NaZSM-5 tandem The significant improvement of catalytic performance after the pre-sulfuration treatment was directly related to the significant increase of oxygen vacancies and the concentration of the"Mo(Mo⁵⁺,Mo⁴⁺)-S"active phase.The MoZrO_x phase of the tandem catalyst is mainly responsible for the CO₂activation conversion,and it is preliminarily revealed that the reactions on the MoZrO_x phase follow the"COS-Intermediates"and"CH₃OH-Intermediates"pathways,respectively.The tandem phase of m-ZrO₂/NaZSM-5 enhances the conversion of"CH₃OH-Intermediates"to methyl mercaptan,while the tandem thermodynamic and kinetic effects synergistically promote the conversion of"COS-Intermediates"to methyl mercaptan.Intermediates"conversion to methyl mercaptan was also promoted synergistically by tandem thermodynamic and kinetic effects.The appropriate two-phase ratio and tandem spacing are the keys to the high catalytic performance of MoZrO_x@m-ZrO₂/NaZSM-5 tandem catalyst.