Synthesis Of Organic-functionalized Zeolites With Hierarchically Porous Structure For Catalytic Liquid Phase Alkylation Of Aromatic Hydrocarbon

Alkylation of aromatic compounds is an important reaction process in the production of high value-added fine chemicals such as oxidants,heating resistant films,coating materials,adhesives,liquid crystal polymers,and so on.However,current reaction systems using microporous ZSM-5 and mesoporous MCM-41 as catalysts have problems such as low reaction efficiency,low alkylation product yield,and relatively harsh reaction conditions.Therefore,development of new,efficient,and sustainable catalysts and green catalytic reaction systems has become the focus of research.Herein organic functionalized zeolite catalystswith hierarchicallyporous structure have been conducted through various synthesis strategies and appliedfor the liquid phase catalyticalkylation of aromatic hydrocarbons,and efficient catalytic liquid phase alkylation reaction systems for aromatic hydrocarbons have been explored through the study of structure-effect relationships and catalytic mechanisms.The research work can be divided into the following three aspects.Firstly,the hierarchically porous structure was first introduced into microporous zeolite molecular sieves through post treatment modification,and then organically functionalized to obtain organically functionalized hierarchical pore zeolite molecular sieves,which were applied to catalyze the liquid phase alkylation of naphthalene.Firstly,the hierarchical pore SAPO-44 zeolite molecular sieve was prepared by alkali treatment,and then the organically functionalized hierarchical pore SAPO-44 zeolite molecular sieve was prepared through different routes of organic functionalization.Compared to other types of commercial microporous zeolites,pure inorganic microporous SAPO-44,and hierarchical pore SAPO-44 zeolite molecular sieves,methylfunctionalized hierarchical pore SAPO-44 zeolite molecular sieve(MT-CHA-H)shows the best catalytic performance in the alkylation of 1,3-diisopropylbenzene and naphthalene.Further,effects of organosilylation reagent types,catalytic reaction temperature,and catalytic reaction time on naphthalene conversion and alkylation product selectivity had been systematically investigated.It was found that76.9%conversion of naphthalene and nearly 100% selectivity of alkylation can be reached by using MT-CHA-H as catalyst.49.8%selectivity for1-isopropylnaphthalene,45.8%selectivity for 2-isopropylnaphthalene,and 4.4%selectivity for 2,6-diisopropylnaphthalene were reached.On the one hand,this was due to the fact that the hierarchical pore structure was conducive to the diffusion and mass transfer of large substrate molecules,greatly improving the effective active sites of zeolite molecular sieves.On the other hand,the organic groups on the surface of zeolite molecular sieves significantly improved the affinity and wettability between the catalyst and the organic molecular substrate,which was conducive to the enrichment of substrate molecules on the surface of the catalystand had a positive catalytic effect on the reaction,The above respectshad promoted greatly the contact of substrate molecules with effective acidic catalytic active sites and thereby promoted the reaction.Secondly,silicoaluminahollownest-structured zeolite(HSZ)was prepared by a one-step hydrothermal synthesis method,and then subjected to dual modifications of phosphotungstic acid and organic functionalization to prepare organic-functionalized zeolite with hierarchically porous structure,which were used to catalyze the liquid phase alkylation of p-cresol.Si-Al type hollow zeolite(Al-HSZ)was prepared by a method similar to that of combining titanium containing hollow zeolite in the subject,and then modified by phosphotungstic acid loading and organic functionalization through a one-step post-treatment method to obtain hierarchical pore zeolite molecular sieves.Compared to Al-HSZ,phosphotungstic acid supported Al-HSZ,and organic functionalized Al-HSZ,phosphotungstic acid supported organic-functionalized AlHSZ-H exhibited the best catalytic performance in the alkylation of p-cresol and tert-butanol.Further,the effects of organosilylation reagent types,phosphotungstic acid loading,catalytic reaction temperature,and catalytic reaction time on the conversion of p-cresol and the selectivity of alkylation products were systematically investigated.It was found that the optimal catalyst for dimethyl functionalization was the 10 wt% phosphotungstic acid supported HSZ catalyst,which could realize 70.7%conversion rate of cresol and 90.6%selectivity for total alkylation products(52.2% for 2,6-di-tert-butyl-4-methylphenol and 38.4%selectivity for 2-tert-butyl-4-methylphenol).The good catalytic performance of the catalyst,on one hand,was ascribed to the unique hollownest structure of the catalyst,which was conducive to the diffusion and mass transfer of large substrate molecules,greatly improving the effective active sites of zeolite molecular sieves.On the other hand,it was ascribed to the organic groups on the surface of catalyst,which further enhanced the wettability and affinity between the catalyst and substrates,which was conducive to the enrichment of substrate molecules on the surface of the catalyst,and had a positive catalytic effect on the reaction,The loading of certain amount of phosphotungstic acid over HSZ played a role to adjust the acid strength of zeolite to the extent suitable for the reaction,which facilitated the activation of substrate molecules and promoted the reactiongreatly.Thirdly,MOR zeolite molecular sieves modified with transition metals and organic groups were prepared by one-step hydrothermal method and applied to the alkylation of phenol and 1-octene.The effects of organosilylation reagent types,transition metal types,and their different amounts on the crystallization and catalytic performance of zeolite molecular sieves were systematically investigated.Compared with the solely modified zeolite catalyst,nickel and dimethyl functionalized MOR zeolite molecular sieves exhibited the best catalytic performance,with phenol conversion up to 72.8% and alkylation product selectivity up to 81.9%.This was ascribed to,on one hand,the fact that the organic groups on the surface of zeolite molecular sieves significantly improve the wettability and affinity between the catalyst and the organic substratemolecular,which was conducive to the enrichment of substrate molecules on the surface of the catalyst,and had a positive catalytic effect on the reaction.On the other hand,the introduction of a certain amount of transition metals had tuned the acid strength of zeolite to a proper degree,whichwas suitable for the activation of substrate molecules and promoted the reaction.