title: Tailoring the structure of hierarchically porous zeolite beta through modified orientated attachment growth in a dry gel system.
abstract: The crystallization of zeolite beta in a dry gel system is found to follow the orientated attachment growth route, escorted with a temporal morphology change from bulky gel, through aggregation of the particulate to large zeolitic crystals. Modification of the precrystallized gel with organosilanes can be used to tune the morphology of the ultimate beta. When hexadecyltrimethoxysilane (HTS) is employed to modify precrystallized gel, a resumed secondary growth produces a hybrid mesocrystal of agglomerated nanozeolites. Combustive removal of organics leads to the formation of hierarchically porous zeolite beta of 100 to 160 nm, composed of nanocrystal building units ranging from 20 to 40 nm, with a noticeable micropore volume of 0.19 mL g(-1) and a meso/macropore size between 5 and 80 nm. Conversely, when 1,8-bis(triethoxysilyl)octane (BTO) is utilized to modify the same precrystallized gel, assemblages of discrete beta nanozeolite of around 35 nm are generated. These assemblages construct a hierarchical zeolite beta with a micropore volume of 0.20 mL g(-1) and auxiliary pores ranging from 5 to 100 nm. Both organosilanes bring about well-connected hierarchical pore networks. HTS has little effect on the Brønsted/Lewis acidity, whereas BTO causes a substantial reduction of strong Brønsted acid sites. The hierarchical beta zeolite-supported Pt catalyst exhibits improved catalytic performance for the hydroisomerization of n-heptane.
authors.affiliation: State Key Lab of Chemical Engineering, School of Chemical Engineering, East China University of Science and Technology, 130 Meilong road, Shanghai 200237 (P.R. China).
authors.forename: Jiao
authors.initials: J
authors.lastname: Chen
authors.forename: Weiming
authors.initials: W
authors.lastname: Hua
authors.forename: Yu
authors.initials: Y
authors.lastname: Xiao
authors.forename: Qisheng
authors.initials: Q
authors.lastname: Huo
authors.forename: Kake
authors.initials: K
authors.lastname: Zhu
authors.forename: Xinggui
authors.initials: X
authors.lastname: Zhou
keywords: alkanes; isomerization; mesoporous materials; synthetic methods; zeolites