Synthesis And Characterization Of Cerium Aluminophosphate Molecular Sieve

Wilson and his colleagues firstly synthesized a new serials of molecular sieve——Aluminophosphate molecular sieves in 1982 and their framework substituted analogs in 1986. Its framework is composed of [AlO4] and [PO4] tetrahedrons which are strictly alternated . It has lower acidity and is neutral without free cation so that it is not of good catalysis activity. The Al3+ and P5+ atoms in the tetrahedrons can be substituted by silicon atoms to form SAPO-n (where n denotes particular type) and also by other metals to form MeAPO/MeAPSO materials. These materials have potential redox molecular sieves and bifunctional cataysts, because they have both acid sites and redox active sites.In this work, Ce which has the ability of storing oxygen has been used to substituted part of Phosphorus or Aluminum in the framework.It has come into the negative ion tetrahedron structure of oxygen in order to obtain a kind of heteroatom molecular sieve which has acidity to some degree. Introducing Ce into their frameworks provides CeAPO-5 molecular sieve both acid sites and redox actives sites, and makes them to be potential redox molecular sieves. It's obvious that the appearance of the new Aluminophosphate molecular sieve develops a new field for the Aluminophosplate molecular sieves.In this work, CeAPO-5 molecular sieve was hydrothermally synthesized using pseudo-boehmite, orthophosphoric acid, cerium carbonate as raw materials and triethylamine as templating agent. The effects of the ratio of raw materials, nature of aluminum sources, triethylamine dosage, and the pH value of reaction system, crystallization time, and crystallization temperature on as-synthesized CeAPO-5 molecular sieve were carefully investigated. Further more, the effects of calcinations conditions on CeAPO-5 molecular sieve were tested. The results show that the nature of aluminum feed is justified to be one of key factors for as-synthesis of pure CeAPO-5 molecular sieve. The selective tests of Al sources prove that pseudo-doehmite is a suitable feed. The pure CeAPO-5 molecular sieve can be produced with material ratio of n(Et3N):n(Al2O3):n(P2O5):n(Ce2O3):n(H2O)=0.26:0.8:1.0:0.5:60,crystallization at 150℃for 72h and the value of pH is 5.8-6.7. The results show that both higher temperature and longer time can lead to formation of impurity. Calcination conditions greatly affect the properties of final products. Thermal treating below 550℃can not completely remove the template, but higher thermal temperature may result in the collapse of the framework. The optional way to remove the template and bound water is temperatured programmed calcination. The products were characterized by XRD,SEM,TEM,XRF,FI-IR,TG-DTA,BET and so on. The primary results showed that , all of the samples had the same structure as aluminophosphate molecular sieves,the doped element Ce has entered the framework of the molecular sieves. By the way, they have good heat stability and catalytic activity. The CeAPO-5 molecular sieves were applied to catalytic oxidation of styrene in order to test their catalytic performance. The CeAPO-5 molecular sieves achieves a styrene conversion of 42%,benaldehyde selectivity of 96%. The results prove that CeAPO-5 molecular sieve is a new environmental friendly catalyst and has better catalytic activity. What is more, different reaction conditions can affect the catalytic oxidation of styrene to some extent.