Study On Pre-vulcanization And Deactivation Behavior Of Catalytic Reaction Of Methanol And Hydrogen Sulfide By ZSM-5@t-ZrO₂

In view of the excellent catalytic performance of ZSM-5@t-ZrO₂ core-shell catalyst,it is based on the design and development of new structural catalysts and industrial catalytic applications.In order to further reveal the pre-vulcanization mechanism and deactivation behavior of the catalyst,the paper firstly studied the effect of pre-vulcanization conditions on the physicochemical properties and catalytic properties of ZSM-5@t-ZrO₂ core-shell catalyst,and revealed the mechanism of pre-vulcanization.Taking t-ZrO₂,ZSM-5 and ZSM-5/t-ZrO₂ physical mixed catalysts as reference,the effects of reaction conditions on the amount and species of carbon and sulfur deposition of ZSM-5@t-ZrO₂ core-shell catalysts were studied,and the inactivation rules of carbon and sulfur deposition of core-shell catalysts were revealed.The paper firstly investigated the effect of different pre-vulcanization time on the thiolation performance of ZSM-5@t-ZrO₂ core-shell catalyst.The methanol conversion and methanethiol selectivity of ZSM-5@t-ZrO₂ core-shell catalyst were92.09%and 90.95%after pre-vulcanization for 3h.Methanol conversion and methanethiol selectivity were increased by 3.83%and 3.32%,respectively,compared to the unpre-vulcanization catalyst.Taking ZSM-5/t-ZrO₂ physical mixed catalysts as reference,ZSM-5@t-ZrO₂ core-shell catalyst was extensively characterized by TEM?XRD?XPS?NH₃/CO₂-TPD and NH₃/CO₂-IR techniques to investigate its physicochemical properties of unpre-vulcanization and pre-vulcanization 3h.The results indicated that the pre-vulcanization has little effect on the crystal phase composition of the coated ZSM-5@t-ZrO₂ core-shell catalyst,but it has a great influence on the surface acidity and alkalinity.The pre-vulcanization increased the strength of the weak acid and medium-strong acid of the core-shell catalyst,and the total acid amount increased to 0.078 mmol·g^-1,while the strength of the weak base and medium-strong base decreased,and the total alkali amount decreased to 0.067mmol·g^-1.The combination of NH₃/CO₂-IR and XPS analysis showed that the pre-vulcanization process directly modifies t-ZrO₂ in the catalyst shell phase,resulting in the increase of L acid and the decrease of L base.The special reaction path of shell?t-ZrO₂,L-base active site?-nucleus?ZSM-5,B-acid active site?formed after pre-vulcanization and the suitable synergistic active center of L-B acid formed on the interface of composite solid solution phase are the main reasons for the high activity of the catalyst in thiolation reaction.Taking t-ZrO₂,ZSM-5 and ZSM-5/t-ZrO₂ physical mixed catalysts as reference,the effects of reaction time and temperature on carbon and sulfur deposition and species of ZSM-5@t-ZrO₂ core-shell catalysts were studied.ZSM-5@t-ZrO₂core-shell catalyst was extensively characterized by TPO-MS?TG-IR?Raman?XRF?XPS?NH₃/CO₂-TPD?GC and GC-MS techniques to investigate its variation rules of carbon and sulfur deposition and species.The results indicated that the amount of carbon and sulfur deposited by t-ZrO₂,ZSM-5,ZSM-5/t-ZrO₂ and ZSM-5@t-ZrO₂were28.39mg/g_catalyst,28.12mg/g_catalyst,25.96mg/g_catalystatalyst and16.62mg/g_catalyst,respectively.The formation rates of carbon and sulfur deposited were 2.37mg/g_catalyst·h,3.52mg/g_catalyst·h,2.16mg/g_catalyst·h and 0.83mg/g_catalyst·h,respectively.ZSM-5@t-ZrO₂core-shell catalyst has the lowest amount of carbon and sulfur deposits and the minimum rate of formation of carbon and sulfur deposits.With the increase of reaction temperature,the formation rate of carbon and sulfur deposited on ZSM-5@t-ZrO₂ core-shell catalyst increased gradually.Carbon and sulfur species on catalysts is mainly composed of polymethylbenzene,polymethyl naphthalene,compounds containing C-S and S-S bonds,cyclic elemental sulfur.With the increase of reaction time,the species of carbon and sulphur deposited were transferred from medium low temperature to high temperature.The species of carbon deposited were transferred from medium low temperature to high temperature with the increase of reaction temperature.The sulfur species tended to transfer to high-temperature species at temperatures below 370?,but to low-temperature species at temperatures above370?.ZSM-5@t-ZrO₂ catalyst has a higher proportion of cyclic sulfides and more sulfur species with large molecular size compared with ZSM-5/t-ZrO₂ catalyst.This may be related to the special micro-mesoporous system with core-shell structure catalyst having enough space for cyclization reaction and allowing more cyclic sulfides to be formed.At the same time,the micro-mesoporous system can help to weaken the restriction of molecular diffusion,delay the deactivation rate of carbon and sulfur deposits on catalysts,and show excellent anti-carbon and sulfur deposits deactivation ability.