关键词: 磷酸 ,  HZSM-5 , 热稳定性 , 密度泛函理论

Abstract: The interaction of orthophosphoric acid and zeolite HZSM-5 was investigated. It is found that chemisorption of orthophosphoric acid and cationic species including H₅P₂O⁺₇ and H₄PO⁺₄ are possible structures of P/HZSM-5 before calcination or steaming, adsorption energy with -49.31， -45.96 kJ/mol are negative, it shows that adsorption is an exothermic process, the reason is the hydrogen bonding is the major form of interaction in between. After calcination or steaming, dehydration reaction occurs, two different models are proposed, thats to say, P species are combined with the framework of zeolite by one or two bridged oxygen atoms. It is show that the energy barrier, for the reaction: a oxygen bridge to two oxygen bridges, is 125.73 kJ/mol for forward reaction; while 47.59 kJ/mol for reversed one, so the model with only one bridged oxygen atoms is the energetically stable one, which is regarded as the major model after dehydration, the lower energy barrier makes two oxygen bridges easy into an oxygen bridge structure.

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