The Synthesis, Characterization And Catalytic Applications Of Mesoporous Solid Acid And Base Catalysts

Mesoporous materials possess large surface areas, uniform pore sizes and variedcomponents from inorganic heteroatoms to organic groups, and thus have thepotential as heretogeneous catalysts or catalyst supports. Since many fine chemicalsare prepared by acid or base catalysis, here our attentions are mainly focused on thesynthesis and characterization of mesoporous solid acid and base catalysts, and ontheir catalytic applications in the preparations of fine chemcials.Alkylation reaction of phenol with tert-butanol is a typical acid-catalyzedreaction, and main products such as 4-tert-butyl phenol (4-TBP) and 2,4-tert-butylphenol (2,4-DTBP) are widely used as intermediates in industry. When classicmesoporous aluminosilicates are used as catalysts, both phenol conversion and2,4-DTBP selectivity are very low. In the chapter two, by two-step crystallizationprocedure zeolite Beta precursors are assembled into ordered mesoporousaluminosilicates with hexagonal p6mm and cubic Ia3d structures (denoted as MB41and MB48 respectively). IR spectra show that the walls of MB41 and MB48 containsecondary structural units of zeolite Beta. IR spectra of pyridine adsorption indicatethat both Lewis and Br?nsted acid sites are present over HMB41 and HMB48.NH₃-TPD measurements indicate that HMB41 and HMB48 have larger amounts ofstrong acid sites than HAl-MCM-41 and HAl-MCM-48. In the alkylation reaction ofphenol with tert-butanol, HMB41 and HMB48 display higher catalytic activities thanHAl-MCM-41 and HAl-MCM-48. At the reaction temperature of 145 oC, phenolconversion and 2, 4-DTBP selectivity are 85.7% and 43.1% over HMB41, 91.0%and 49.0% over HMB48, but those are only 61.3% and 13.2% over HAl-MCM-41and 65.7% and 17.6% over HAl-MCM-48. These results indicate that the presence ofstrong acid sites favors the improvement of both phenol conversion and 2,4-DTBPselectivity.In the chapter three, templated by triblock copolymer, phenyl-functionalizedlarge-pore Ia3d mesoporous materials have been synthesized by the co-condensationof phenyltriethoxysilane (PTES) and tetraethoxysilane (TEOS) under acid conditions.During the synthesis procedure, the amount of PTES added is very crucial to thepreparation of Ia3d structure. If the amount is 3-10 %, ordered Ia3d mesoporousmaterials are prepared. If the amount is samller than 3%, ordered hexagonalmesoporous materials are synthesized. However if the amount is 15% or more, onlydisordered materials are obtained. In addition, the prehydrolysis of PTES is also veryimportant for the synthesis of Ia3d materials. If TEOS is prehydrolyzed instead ofPTES, only hexagonal materials are obtained. After being treated with fumingsulfuric acid, sulfonic acid groups could be introduced into the channels ofphenyl-functionalized mesoporous materials. In tert-butylation reactions of phenol,mesoporous solid arenesulfonic acid catalysts display higher conversion of phenolthan microporous zeolites and acid mesoporous aluminosilicates, however, thesearenesulfonic acid catalysts are rapidly deactivated. In the liquid condensation ofphenol with acetone, these mesoporous solid arenesulfonic acid catalysts displayhigher selectivity to p,p′-Bisphenol A than homogeneous para-toluene sulfonic acidcatalyst.Flavanone is an important polyphenolic substance, which is widely used innumerous pharmacological applications for antimalarial, anticancer, anti-inflam-matory, cytotoxic, antibacterial, and anti-AIDS. Flavanone is usually synthesized viathe Claisen-Schmidt condensation between benzaldehyde with 2′-hydroxy-acetopheone and the subsequent isomerization of 2′-hydroxychalcone intermediatesunder homogeneous basic or acidic conditions. Up to now, many solid catalysts likeMgO, Al2O3, Ba(OH)2 and NaNO3 have been used for the synthesis of flavanone. Inthe chapter four, aminopropyl-functionalized SBA-15 (APS-SBA-15) materials areprepared by postgrafting method. By adjusting the amount of aminopropyl-triethoxysilane, the amount of aminopropyl loaded can be changed. The pore sizes ofAPS-SBA-15 can be tuned by using SBA-15 with different pore sizes as parentmaterials. In this chapter, APS-SBA-15 catalysts display high activities for thesynthesis of flavanone. With increasing the content of benzaldehyde, the conversionof 2′-hydroxyacetopheone gradually decreases. In addition, it is found that higheramount of amino groups loaded, larger pore size and longer reaction time favor theimprovement of 2′-hydroxyacetopheone conversion and keeping high flavanoneselectivity.In the chapter five, bifunctional SH-MCM-41-NH2 has been synthesized by theco-condensation of 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilaneand tetraethoxysilane under basic conditions with cetyltrimethylammonium bromideas the template. After extracting the template, protecting NH2 groups, oxidating SHgroups and deprotecting NH2, bifunctional acid and base mesoporous catalyst HSO3-MCM-41-NH2 is prepared.