Synthesis Of Heteroatom Aluminophosphate Molecular Sieve By Solvent-Free Method Using Carbon As Medium And Their Catalytic Performance

Zeolites are a kind of important inorganic crystal materials.Because of their controllable morphology and pore structure,zeolites are widely used in the fields of industrial catalysis,adsorption separation,ion exchange and so on.Aluminum phosphate molecular sieve?AlPO₄-5?is an important part of zeolite family,which has been widely studied by scholars at home and abroad since it was first reported in 1982.The introduction of Si or transition metal elements into the framework of aluminum phosphate molecular sieves can make the originally electrically neutral aluminum phosphate molecular sieves show specific acidity or ion exchange properties.Generally,the traditional molecular sieve synthesis method is hydrothermal or solvothermal,which wastes a lot of water resources,at the same time,high vapor pressure and the use of a large number of organic solvents also cause great safety risks and environmental pressure.With the emergence of solvent-free method,these problems have been solved.Different from the traditional hydrothermal method,this green synthesis method has many advantages,such as low autogenous pressure,high product yield,simple synthesis and so on.Once it appeared,it aroused great interest from researchers.In this paper,AFI aluminum phosphate molecular sieves containing different heteroatoms were synthesized by solvent-free method using activated carbon as hard template and reaction medium under microwave irradiation,the main research contents are as follows:Firstly,SAPO-5 molecular sieve was synthesized by microwave-assisted solvent-free method using activated carbon as reaction medium.The synthesis was optimized by changing silicon source,activated carbon treatment method,grinding method and time,reaction time,Si/Al ratio and heating method,and the effects of the above conditions on the synthesis were discussed.The crystallinity,purity,morphology and pore structure of SAPO-5 molecular sieve were analyzed by XRD,SEM,N₂ physical adsorption/desorption,EDS and FT-IR.The results show that the grinding method has a great influence on the synthesis of SAPO-5 molecular sieve in this system,and the samples with higher relative crystallinity and purity can be obtained by mechanical grinding.SEM analysis shows that the main morphology of the samples synthesized by this method is irregular nano-particle aggregates accompanied by a small number of large particles,and there are a variety of crystal morphologies in the samples.Finally,the catalytic performance of SAPO-5 molecular sieve synthesized in this system was investigated by using the alkylation of benzene with benzol to diphenylmethane as a probe reaction.The results show that the catalytic effect of the sample is not ideal,and the low BET surface area makes the selectivity of the sample Si2-M20-t2-S0.3-raw only 38.9%.Similarly,FeAPO-5 molecular sieve was synthesized by microwave-assisted solvent-free method using activated carbon as reaction medium.The synthesis was optimized by changing iron source,activated carbon treatment method,template type,grinding method and Fe-Al ratio,and the effects of these conditions on the synthesis were discussed.The crystallinity,purity,morphology and pore structure of FeAPO-5 molecular sieve were analyzed by XRD,SEM and N₂ physical adsorption/desorption.Finally,the catalytic performance of FeAPO-5 molecular sieve synthesized in this system was investigated by using alkylation of benzene with benzyl chloride and hydroxylation of phenol as probe reaction.The results show that the selection of iron source has a great influence on the structure of the sample,and the crystallinity and purity of the synthesized sample can be greatly improved by using the double template strategy,but when the ratio of template is 4:4,the Fe/Al ratio range has a greater impact on the sample.The sample Fe3-DT44-S0.2-HNO₃ with the highest crystallinity and purity has 41.2%benzyl chloride conversion and 62.2%diphenylmethane selectivity in benzene alkylation,and 50%maximum phenol conversion and 60.2%catechol selectivity in phenol hydroxylation,which is due to its high BET specific surface area and mesoporous volume.