Pore Structure,Acidity And Benzylation Of Naphthalene Over Mesopores Beta Zeolite

Beta zeolite is the only zeolite molecular sieve with a three-dimensional macroporous structure,and the larger pore size and strong acidity make it exhibit high catalytic activity in the aromatization of aromatics.However,in the catalytic reaction involving larger molecules,the pore size of 0.7 nm still can not meet the requirement of macromolecule reaction.A large number of studies have shown that hierarchical zeolites are a class of superior catalysts which contain simultaneously interconnected mesopores and micropores.The zeolitic micropores bear the catalytic function,while the additionally created larger mesopores ensure accessibility of acid sites for larger molecules and intracrystalline diffusion.Similarly,mesopores Beta zeolite not only posses strong acid but also shorter diffusion path and higher accessibility of acid,which make it have higher catalyst activity especially involving the macromolecular reaction.However,the introduction of the mesopores has a great influence on the pore structure and surface acidity of zeolite molecular sieve,especially on the surface acid type,the strength of the acid,acid concentration and the distribution of acid sites.The mesopore beta zeolite as the research object was characterized through the X-ray diffraction,N2 adsorption stripping,scanning electron microscopy.The results show that the mesopores Beta zeolite samplescrystallinity decreased and pores are mainly distributed in 3 to 10 nm.The change of pore structure and morphology affect its acidity.Their acidic properties were characterized via NH3-TPD and FT-IR spectra in combination with probe molecules of different sizes.The amount of total acid and acid strength characterized through the NH3-TPD technique.Research results show that,acid center removal towards low temperature with the increase of external surface area,and the acid amount obviously decreased.MHB4 samples of ATH/ATL value dropped to 1.76,which is the 1/2 of microporous sample HB.In addition,the acid strength and acid concentration of different acid types on the surface pore zeolite zeolite were characterized by pyridine in situ infrared technique.Two different size probe molecules,2,6-di-tert-butylpyridine and trimethylacetonitrile were used to characterized the distribution of acid sites.The results show that the accessibility of Br?nsted acid and Lewis acid increases with the increase of surface area.In order to investigate the effect of the change of acidity and pore structure on the catalytic activity of aromatization of aromatic hydrocarbons,the catalytic activity of macromolecular naphthalene and benzyl chloride was evaluated.The results show that the microporous zeolite catalyst HB has a relatively high initial conversion rate,but is gradually deactivated as the reaction progresses.But the mesoporous zeolite samples MHBn and GHBn all showed high catalytic activity.And with the increase of the surface area,the catalytic activity gradually increased.In addition,for different mesoporous zeolite samples,the weaker acidity facilitates the progress of the reaction.In the Br?nsted acid and Lewis acid have higher progressability of the catalyst,showing a higher catalytic activity.Indicating that Br?nsted acid and Lewis acid synergistically promote aromatization of benzylation.