Study On Preparation And Catalytic Reaction Of Syngas Directly Aromatization Catalysts

In order to achieve clean and efficient use of coal,reduce the dependence on petroleum resources and ensure the energy security of the country.At the same time to meet the growing demand for production capacity in the domestic aromatics market,there is an urgent need to find a non-petroleum route to increase aromatics production.Although the non-petroleum route of producing aromatics from coal as a raw material to produce syngas,then from syngas to methanol and finally from methanol to aromatics has been sufficiently developed in recent decades,there are still many problems.For this reason,researchers have proposed direct syngas to aromatics in lighting of maximizing thermodynamic utilization and economic efficiency.In this study,a bifunctional catalyst with activations of syngas and catalytic aromatization of intermediate products was designed based on the catalysts for methanol from syngas and aromatization from methanol.The relationship among the structural properties,combination,reaction process and the aromatization performance of the catalyst is also investigated.The reaction mechanism of syngas direct aromatization was also explored and studied.（1）Nano-Ti O₂、Zr O₂ and Hf O₂ were prepared by supercritical method.The structural properties of the single-component titanium subgroup metal oxides Ti O₂,Zr O₂,Hf O₂ and and the adsorption and dissociation properties of metal oxides for CO and H₂ were systematically investigated.It was clarified that the concentration of oxygen vacancies on the surface of metal oxides and the binding energy of oxygen vacancies are the key factors for CO adsorption and dissociation.The comparison of in situ IR results revealed that the intermediate product CH_xO*contributes to the selectivity of methanol in metal oxides and aromatics in bifunctional catalysts.（2）The structural properties and adsorption-dissociation properties of MZr O_xmetal oxides with different M metal ions(Cr⁶⁺,Mo⁶⁺,W⁶⁺,Cu²⁺,Zn²⁺,Ga³⁺)and Cu Zn Zr O_x metal oxides with different Cu contents were compared in detail.It was found that the doping of different metal ions all could promote the oxygen vacancy concentration of the metal oxides MZr O_x,and a certain amount of Cu could helpfully increase the oxygen vacancy concentration in Cu Zn Zr O_x metal oxides.Combining the binding energy of oxygen vacancies in MZr O_x and Cu Zn Zr O_x with the results of in situ IR,it was found that the low-valent metal ions help to increase the binding energy of oxygen vacancies in MZr O_x and promote the formation of the intermediate product CH_xO*.With the increase of Cu content in Cu Zn Zr O_x,the oxygen vacancy binding energy gradually increases leading to the decrease of bond energy of CO and CO₂carbon oxygen bonds adsorbed on the oxygen vacancy and the increase of catalyst reactivity.It was further clarified that the intermediate product CH_xO*contributes to improve the selectivity of methanol in metal oxides and aromatics in bifunctional catalysts.（3）The combination method of the bifunctional catalyst was the grinding of the calcined metal oxide and ZSM-5 with a mass ratio of 1:2,which were be found by exploring the combination method and mixing ratio of Cu0.5Zn1Zr50 metal oxide and ZSM-5 zeolite on the reaction activity as well as product distribution.The reaction temperature（T）,reaction pressure（P）,and H₂/CO ratio of the bifunctional catalyst were investigated in detail,and it was found that the conversion of CO was 23.17%and the selectivity of aromatics could reach up to 70.71%at T=360℃,P=3 Mpa,and H₂/CO ratio of 2:1.Under the above conditions,the reaction activity and product selectivity of the catalyst remained stable when the catalyst continued to react for 300 h.（4）The effects of the structural properties of ZSM-5 zeolite with different silica-alumina ratios in bifunctional catalysts on the reactivity and catalytic product distribution of syngas aromatization were investigated.It was clarified that the reactivity and product distribution of bifunctional catalysts were related to the acidity of ZSM-5.The effects of impregnation modification and surface deposition modification on the structural properties and acidic distribution of ZSM-5 were investigated in detail,and it was found that Zr combined with the acidic sites of the modified ZSM-5,the acidity of the zeolite decreased,and the Zr-modified ZSM-5 can be helped to improve the reactivity of the bifunctional catalyst and the selectivity of BTX in the catalytic products.（5）The twin-crystal structure of ZSM-5 zeolite was designed for catalytic syngas aromatization.The effects of the morphological structure and acid distribution of ZSM-5 on the bifunctional catalytic reaction activity and catalytic product distribution were systematically investigated.The relationship among the acidity of ZSM-5 and the silica-alumina ratio of the zeolite,and the effect of the addition of n-butylamine on the distribution of the B-acid site of the twinned ZSM-5 zeolite were elaborated by the quantification results of NH₃-TPD and pyridine infrared.It was confirmed that the reactivity of the bifunctional catalyst was correlated with the acidity of the twinned ZSM-5 zeolite,besides,the decrease of the acidity of the outer surface of the twinned ZSM-5 zeolite contributed to the improvement of the selectivity of BTX and the decrease the selectivity of C₉⁺in the catalytic products.In summary,the aromatization of syngas was achieved by designing the structural properties of metal oxides and ZSM-5 zeolite.It was found that the high concentration and high binding energy oxygen vacancies on the surface of the metal oxides could help catalyze the CO hydrogenation to produce the intermediate product CH_xO*,and the CH_xO*diffused into ZSM-5 could carry out the aromatization reaction to produce BTX,and the reduction of B acid sites on the outer surface of ZSM-5 helps reduce the selectivity of C₉⁺aromatics in the catalytic product.This study not only provides a reference for the design of catalysts for direct aromatization of syngas,but will also help to achieve increased aromatics production from coal to aromatics in non-petroleum routes.There are 58 figures,21 tables and 311 references.