Synthesis And Catalytic Properties Of Mesoporous Aluminophosphates And Nickel Phosophates Materials

Mesoporous metal phosphates are a most important part of mesoporous molecular sieve materials.This materials have a wide range of applications in photoelectronics,catalysis,and electromagnetics due to their multiple and abundant elements of the inorganic frameworks. These unique properties are not found in siliceous,aluminosilicate mesoporous molecular sieves.However,their thermal stability is poor compared with silica-based materials.In order to extend the application fields,it is very necessary to improve the thermal stability of mesoporous metal phosphates and develop novel transitional metal phosphate mesoporous materials.This thesis presents two types mesoporous phosphate materials,including mesoporous aluminophosphates(AlPO)and nickel phosophates(NiPO),which were synthesized by cationic surfactant self-assembly method.(1)Highly condensed mesoporous AlPO have been rapidly synthesized by using ultrasonic irradiation method.Compared with mechanical stirring method,the reaction time reduced drastically from 48 to 2 hours by using ultrasounic technique.It was found that when the ultrasond was employed in crstallization process,the high quality mesoporous AlPO would be evidently promoted.(2)It was proposed that combined programmed temperature calcination is the optimal method to remove template,and the hard inorganic framework of mesoporous AlPO completely formed during the calcination process.Compared with one-step and two-step calcination methods,the thermal stability,the condensation and ordered structures,surface acidity of mesoporous AlPO were dramatically improved by the combined programmed temperature calcination method.The thermal stability of mesoporous AlPO is over 800℃. The material calcined combined programmed temperature method showed a good catalyitic activity in oxidative desulfurizaion of DBT.Besides,this calcination method can be extended to the preparation of metal-substituted mesoporous AlPO with good thermal stability.(3)High-thermally stable tungsten-substituted mesoporous aluminophosphates have been synthesized by in situ hydrothermal method and removed templates by combined programmed temperature calcination.Compared with the synthsis of W-MCM-41,the tungsten is more effectively induced and dispersed into the framework of mesoporous AlPO and form tetrahedral[WO₄]^2-.The W-AlPOs were applied to oxidative desulfurizalon of DBT and showed much higher activity than W-MCM-41.Besides,it is concluded that the tetrahedral tungsten in the mesoporous structrues plays an active role in the oxidative desulfurizaion of DBT reaction.(4)Two novel tubular mesoporous nickel phosphate materials(NiPO-1 and NiPO-2)have been synthesized by using a cationic surfactant as template.The base,TMAOH or aqueous ammonia,determines the materials with distinct textural characteristics such as pore structures,morphologies,and inorganic composition of inorganic framework.NiPO-1 and NiPO-2 can keep their mesoporous character up to 400℃in heat-treatment.Both mesoporous materials possess a relatively high BET surface area(205～292 m² g^-1)and the pore diameters are between 3.7 and 3.9 nm.These novel materials show high catalytic activity in the epoxidation of cyclic olefins using H₂O₂ aqueous solution as an oxidant.In the reaction of cyclohexene,the conversions are over 80%with both materials.For cyclododecene, heat-treated NiPO-1 and NiPO-2 exhibited high activity(＞50%)and high selectivity to epoxide(99.0%and 95.6%).Moreover,no destruction of the mesoporous structures in NiPO-1 or NiPO-2 was observed,and no leaching of the active species was detected after reactions.