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Studies on Synthesis, Characterization and Catalytic Application of Porous magadiite-Based Heterostructures

Author: ZhangCong
Tutor: ZhangHui
School: Beijing University of Chemical Technology
Course: Chemical Engineering and Technology
Keywords: Porous magadiite-based heterosrtuctures (PMH) supported catalysts Al-magadiite homogeneous precipitation SOsup>2---ZrO2/PMH esterification postsynthesis grafting Al/PMH Friedel-Crafts alkylation
CLC: O621.3
Type: Master's thesis
Year: 2012
Downloads: 41
Quote: 0
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Abstract


In the present work, porous magadiite-based heterosrtuctures (PMH)and porous Al-magadiite-based heterosrtuctures (PAMH) as alternativelycatalyst supports were prepared by combination of ion-exchange andgallery-template method upon the prepared hydrous sodium silicatesmagadiite and Al-magadiite and systematically characterized by XRD,SEM/EDS, FTIR, TEM/HRTEM, TG, and BET techniques. Two novelsupported catalysts of SZ/PMH and Al/PMH were obtained by loading Zrand grafting Al on PMH. The novelty and major content of the thesis aredetailed as follows:Hydrothermal synthesized layered host magadiite is prepillared bycetyl trimethyl ammonium bromide (CTMABr) via ion-exchange leadingto an organoclay QM with basal spacing of2.83nm. With a mixture ofQM, n-decylamine (DA) and TEOS at QM/DA/TEOS ratio of1:20:150,upon CTMA+-DA co-surfactant function together with the basic catalysisof DA, TEOS was hydrolyzed and condensation polymerized within thegalleries of magadiite leading to sound interlayer self-assembly followed calcinations giving a novel porous support PMH. The resultants PMHpossesses a super-gallery height of3.01nm, the pore size distributionfrom supermicropores to small mesopores (1.4-4.3nm), large specificsurface area of729.2m2/g and high thermal stability up to750℃.A novel supported catalysts were prepared by homogeneous pre-cipitation with varied amount of SO42-/ZrO(2SZ)on as-synthesized PMH.The esterification reaction of citric acid with n-butyl alcohol to producetirbutyl citrate (TBC) was carried out over synthetic SZ/PMH. Theamount of acid sites is greatly enhanced compared to PMH, and its Lewisacid sites more than Bronsted acid sites. Among investigated catalysts,the30wt%SZ/PMH shows the best catalytic activity with the citric acidconversion of93.4%, TBC yield of90.2%and TBC selectivity of96.6%.It can be attributed to the uniformly dispersed ZrO2on the internal poresurface of PMH, making more catalytic active center exposed, benefitingcatalytic properties of the catalyst.A series of Al/PMH catalyst are prepared by postsynthesis graftingof aluminum into the mesostructural intragallery silica framework ofPMH generating much more acid sites compared with PMH. TheFriedel-Crafts alkylation of catechol with tert butyl alcohol to produce4-tert-butyl catechol (4-TBC) was performed over the Al/PMH catalysts.Among the studied catalysts, the catechol conversion is decreased withincreasing Al amount can be related to an increase in the intragallery wall thichness of PMH upon Al incorporation leading to large steric hindrancemaking part of active center unaccessible. The10(Si/Al molar ratio)-Al/PMH presents higher selectivity for4-TBC (76.3%) than otherx-Al/PMH samples, implying its proper shape-selecting catalysisfunction.Directly hydrothermal synthesized Al-containing host Al-magadiite(PAMH) can be prepillared by CTMABr, followed CTMA+-DA co-surfactant function and TEOS interlayer hydrolysis and condensationpolymerization as well as high temperature calcination giving in a novelporous Al-magadiite-based heterosrtucture PAMH. The PAMH possessesa super-gallery height of3.20nm, the narrow pore size distribution1.4-2.7nm, large specific surface area of741.2m2/g and high thermalstability. The incorporation of Al into the host matrix greatly enhance theamount of Lewis acid sites in PAMH implying potential applications inacid catalysis field.

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