Preparation Of ZSM-5@t-ZrO₂ Core-shell Structure Catalysts And Catalytic Synthesis Of Methanethiol

For the problem that the yield of the target product is low and the reaction life of the catalyst is short in the process of synthesizing methanethiol by the hydrogen sulfide methanol method,the key is to solve the contradictory problem of how to coordinate methanol and methanethiol require different dissociation transformations and reactions to generate environmental conditions.In order to solve the problem of simultaneously increasing methanol conversion and methanethiol selectivity requiring different reaction temperature,the paper proposes to enhance the dissociative adsorption of methanol at lower temperatures by forming B-L acid synergistic catalytic center on the catalyst surface.At the same time,in order to solve the problem of long life of the catalyst and requiring different active centers,the paper proposes to construct core-shell distinct reaction path based on the meso-microporous structure.The effects of different composite preparation methods on the structural properties of ZSM-5@t-ZrO₂ core-shell catalysts and the catalytic performance of synthesis of methanethiol were systematically studied.The effects of two-phase mass ratio,ZrO₂ phase state,t-ZrO₂ powder fineness,ZSM-5 silica-alumina ratio,roasting temperature,roasting heating rate and other hydrothermal coating process conditions on structure properties of core-shell catalyst and catalytic performance of synthesis of methanethiol were further investigated.XRD,SEM,FT-IR,Visible/UV-Raman,BET,NH₃/CO₂-TPD,NH₃-IR,and TEM were used to reveal the structure-activity relationship of ZSM-5@t-ZrO₂ core-shell catalysts.The results show that the composite preparation method has a great influence on the structural properties of the ZSM-5@t-ZrO₂ core-shell catalyst.Using liquid phase coating method,t-ZrO₂ as the coating phase and ZSM-5 as the core phase,the composite catalyst was prepared without forming a complex phase.Although the composite catalyst prepared by physical blending method has ZSM-5 phase and t-ZrO₂ phase,it does not form cladding core-shell composite phase.Using hydrothermal coating method,under the conditions that ZSM-5 was used as the coating phase,t-ZrO₂ calcined at 450?for 2h was used as the core phase,ZSM-5:t-ZrO₂ mass ratio 1:7,200 mesh t-ZrO₂ powder,ZSM-5 silica-alumina ratio 360,calcination temperature 550?,roasting heating rate5?·min^-1,ZSM-5@t-ZrO₂ core-shell catalyst was prepared to form cladding core-shell composite phase and meso-microporous structure(microporous specific surface area 114.12m²/g,mesoporous specific surface area 125.08m²/g,total specific surface area 239.20m²/g,total pore volume 0.38cm³·g^-1).At the same time,ZSM-5@t-ZrO₂ core-shell catalyst has B acid(1430cm^-1,1450cm^-1),L acid(1630cm^-1)and L alkali center?total acid amount up to 0.072mmol/g,total alkali amount up to0.077mmol/g?.At reaction pressure of 1.0MPa and reaction temperature of 370?,the core-shell catalyst exhibits longer catalytic lifetime of 20h.In order to reveal the inactivation of core-shell catalysts,the coking sulfur behavior of ZSM-5@t-ZrO₂ was studied.With the help of Visible-Raman,FT-IR,O₂-TPO and other characterization methods,the effect of reaction temperature and reaction time for the catalytic synthesis of methanethiol on the coking sulfur of core-shell catalysts was investigated.The oxygen consumption of coking sulfur of ZSM-5@t-ZrO₂,ZSM-5 and t-ZrO₂ after 8h of reaction was analyzed and compared.The results show that different reaction temperatures make carbon and sulfur species present in the core-shell catalysts.At 310-430?,as the reaction temperature increases,the oxygen consumption of coking sulfur will decrease first and then increase.The lowest total oxygen consumption was found at 370?until deactivation,and6.144mmol/g.At 370?,with the reaction time increases,the amount of coking sulfur gradually increases.Core-shell catalysts have similar deposition inactivation species as single ZSM-5 and t-ZrO₂,however,the oxygen consumption of core-shell catalyst was reduced by 51.9%compared with ZSM-5 after 8h of reaction?ZSM-5inactivation?.The effects of different reaction temperature,reaction pressure,H₂S/CH₃OH molar ratio,feed airspeed,N₂ flow on methanol conversion,methanethiol selectivity and reaction life of ZSM-5@t-ZrO₂ core-shell catalyst were systematically investigated.The results show that under the conditions,reaction temperature 370?,reaction pressure 1.0MPa,raw material feed velocity 1.5h^-1,H₂S/CH₃OH molar ratio2:1,N₂ flow rate 90ml·min^-1,methanol conversion,methanethiol selectivity and catalytic lifetime were 92.07%,90.89%and 20h,respectively.