| Aromatic ketone compounds are important chemical intermediates,which have been widely used in the fields of pesticide,medicine,spice and so on.Traditionally,the synthesis of aromatic ketones is achieved through the Friedel-Crafts acylation(FCA)of arenes with acyl chloride,in presence of homogeneous Lewis acid catalyst such as Al Cl3.However,this method has some serious drawbacks,such as difficulty in catalyst recovery and high environmental pressure.For solving these problems,recent efforts have been devoted to developing environmentally friendly solid acid catalysts,and significant progresses have been made.Among the numerous investigated catalysts,zeolites Beta has shown relatively high catalytic activity for some FCA reactions,and has been commercially applied in the acylation of anisole and veretrole with anhydride.However,the synthesis period of Beta zeolites is usually long,and their activation capacity for bulky aromatic hydrocarbons(e.g.containing more substituents)is poor,and the deactivation rate is very fast.Therefore,it is still a very significant subject to develop more simple and effective methods for synthesizing highly efficient Beta zeolite catalyst applied in various FCA reactions.In this thesis,the synthesis methods of Beta zeolites were optimized by introducing polyethylene glycol(PEG)additive into the synthetic sol-gel system and by adjusting the crystallization process.The structure,morphology and acidity of the resultant Beta zeolites were studied by a variety of characterization techniques.The main results are as follows:1.A series of Beta zeolites with small particle size were synthesized by hydrothermal crystallization through adding an appropriate amount of PEG into the initial sol-gel synthesis system.The effect of PEG addition and crystallization time on the crystallization process of Beta zeolites was investigated.The results showed that addition of small amount of PEG could obviously decrease the crystal size of Beta zeolites with average particle size of 200-300 nm.With further increasing the PEG adding amounts,the particle size of the zeolites increases somewhat(up to about 600 nm),but is still smaller than the Beta zeolites obtained by conventional method(without using additives).These small-sized Beta zeolites exhibit higher catalytic activity for the acylation of veratrole with acetic anhydride and selectivity to 3,4-dimethoxy acetophenone,much better than the conventional Beta zeolites.The improvement of catalytic performance is mainly attributed to the fact that the small particle size make it easier for the reactant molecules to access the acid site in zeolites,which facilitates the reaction proceeding.The catalytic activity of the spent Beta zeolites could be fully recovered by high-temperature calcination,showing excellent recyclability and regenerability.2.Another series of Beta zeolites were synthesized by combining the usage of PEG additive and the steam-assisted crystallization strategy.The addition amount of PEG could affect the crystallization time and the grain size of the zeolites.The introduction of an appropriate amount of additives combined with steam-assisted conversion may considerably shorten the crystallization time of the zeolites,which can complete the crystallization of Beta zeolites within 12-48 hours.Characterization results confirmed that the Beta zeolites synthesized by this method have relatively high crystallinity and much smaller grain size(below 100 nm).The resultant Beta zeolite catalyst showed very high catalytic activity for the acylation of veratrole with acetic anhydride.The decrease in grain size of zeolite crystals may enlarge the external surface area,and increase the accessible acid sites,thus significantly the catalytic performance for the FCA reaction. |
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