Synthesis And Characterization Of Hierarchical Mordenites And Their Performance In The Benzylation Of Benzene With Benzyl Alcohol

Hierarchical zeolites, combining good selectivity, acidity, hydrothermalstability of microporous zeolites and excellent mass transport ability ofmesoporous materials, exhibit excellent catalytic performance in the reactionsinvolving large molecules. Recently, the fabricatinon of hierarchical zeoliteswith homogeneous mesopores by adding organic soft-templates asmesoporogens into typical zeolite synthesis gels is the most fascinating methodin in-situ synthesis of hierarchical zeolites. Post-treatment methods,dealumination and desilication, are the main industrial strategies employed tofabricate hierarchical zeolites.Mordenite consists of12-membered ring (MR) pore channels of0.67×0.70nm interconnected by8-MR pores of0.34×0.48nm. Due to the8-MRchannels are too small for most molecules to enter in, mordenite is generallyconsidered as a one-dimensional pore system, which may induce diffusionlimitations in its applications. In spite of this, mordenite is widely used inindustry, especially in alkylation, hydroisomerization, dewaxing and otherreactions. To improve mass transfer ability in the one-dimensional channels of traditional mordenite, the introduction of additional mesopores is undoubtedly afast and ideal method.In the present work, hierarchical mordenites were achieved by a sequentialacid-base post-treatment method and soft-templating strategies by employing adiquaternary ammonium-type surfactant and a type of organosilanes asmesoporous templates. The detailed results are summarized as follows:1. The preparation of hierarchical mordenite by employing diquaternaryammonium-type surfactant C18-6-6Br2as a mesoporogenHierarchical mordenite zeolite was synthesized through a soft-templatingmethod using a special diquaternary ammonium-type surfactant as amesoporogen. The influence factors of synthesis were investigated, such aspre-crystallization, crystallizing time, silicon source, etc. The structure andphysicochemical properties of the hierarchical zeolite samples werecharacterized by XRD, SEM, TEM, N2physisorption, TG-DTG and NH3-TPDtechniques. The results show that pre-crystallization has significant influence onthe morphology and grain size of the samples while silicon source has littleimpact on the synthesis of hierarchical mordenite. Hierarchical mordenite zeolitesamples with high crystallinity, large mesopore volume and strong acidity wereprepared in suitable reaction conditions such as suitable crystallizing time andtemplate amount. Moreover, the prepared hierarchical mordenite catalysts werehigh-efficienct for the conversion of benzyl alcohol into diphenylmethane due tothe superior mass transfer ability resulting from the introduction of additional mesopores, macropores and large amount of accessible acid sites.2. The preparation of hierarchical mordenite zeolite by employing amphiphilicorganosilane TPHAC as a mesoporogenHierarchically structured mordenite zeolites were synthesized underhydrothermal synthesis condition by adding organosilane TPHAC as amesoporogen. The influence factors of synthesis were investigated, such ascrystallizing temperature, crystallizing time, TPHAC content, etc. The sampleswere characterized by XRD, FT-IR, N2physisorption, SEM and NH3-TPDtechniques. The results show that the hierarchical mordenite samples have largemesopore volume and uniform mesoporous diameter. Whereas the amount ofacid sites of hierarchical mordenite is smaller than those of its conventionalcounterpart. In spite of this, the prepared hierarchical mordenite zeolite catalystsdisplayed good catalytic activity in the benzylation of benzene with benzylalcohol. This can be ascribed to the improved mass transfer ability resultingfrom the introduction of mesopores.3. The preparation of hierarchical mordenite zeolite by sequential acid-basepost-treatment methodHierarchical mordenite zeolites were achieved by sequential acid-basepost-treatment method. The structure and physicochemical properties of thesynthetic samples were characterized by XRD, FT-IR, N2physisorption, SEM,and NH3-TPD techniques. The results show that large mesopore volume andsurface area were obtained through sequential acid-base post-treatment. Treatment conditions have significant influence on the pore structure and acidityof the products. The prepared hierarchical mordenite catalysts exhibited goodcatalytic performance in the benzylation of benzene with benzyl alcohol.Post-treatment method is easy to handle, low-cost and has large possibilityto realize large-scale industrialized production. Therefore, it has importantpractical significance for the deep research of this method. The use of organicsilane and the diquaternary ammonium-type surfactant provides a feasible wayfor the preparation of other types of hierarchical zeolites. This not only hasenriched the synthesis strategies of hierarchical zeolite materials, but alsoprovides new ideas and new research perspective for the study and developmentof new materials.