Study On The Synthesis And Catalytic Application Of CoAPO-5 Molecular Sieve

Wilson and his colleagues firstly synthesized a new serials of molecular sieve Aluminophosphate(APOs) molecular sieves in 1982 and their framework substituted analogs(MAPOs) in 1986. Introducing transition metal cations into their frameworks provide MAPOs both acid sites and redox active sites, and make them to be potential redox molecular sieves and bifunctional catalysts. Many works focused on CoAPO-5 have been reported because of its good stability and comparatively large pore opening. In this work, CoAPO-5 molecular sieve was hydrothermally synthesized using pseudo-boehmite, orthophosphoric acid(85%), tetrahydrate cobaltous acetate as raw materials and N,N-diehtyl-ethanolamine as templating agent. The effects of N,N-di-ethyl-ethanolamine dosage, crystallization temperature, crystallization time on as-synthsized CoAPO-5 molecular sieve were carefully invistigated. Furthermore, the effects of calcination temperatures and calcination times on CoAPO-5 product were tested. The results show that pure CoAPO-5 can be synthesized at a wide temperature range (150~200℃) with a ratio of R/Al2O3 at 1.25. Larger grain size CoAPO-5 was obtained under higher crystallization temperatures. However, a higher temperature leads to the formation of impurity. Crystallizing at 200℃for 48 hrs obtained a grain size up to 242.44 angst. Calcination conditions greatly affect the properties of final products. Thermal treating below 500℃can not completely remove the templates, but thermal treating beyond 600℃may result in the collapse of the framework. An optimal temperature for calcination is 500-600°C. Transition of Co+2 to Co+3 is a slow process, so the samples was calcinated at 550℃in a muffle furnace for 10 hrs. Redox catalytic behaviors of CoAPO-5 in liquid-phase oxidation of alkyl arene with different oxidants were investigated in a variety of reaction media. The results indicate that the CoAPO-5 exhibits no catalytic activity in toluene, ethylbenzene and benzyl alcohol oxidation with TBHP in chlorobenzene at ambient pressure. And even acetate acid used as promoter, no catalytic activity was observed in the oxidation of toluene using TBHP as oxidant, neither. However, CoAPO-5 exhibits good redox catalytic activity in oxidations of both toluene oxidation and ethylbenzene by using oxygen as an oxidant under 1.5 MPa. These oxidation reactions conducted in a semi-batch autoclave at 135~145℃. The conversion of toluene is up to 11% in 4 hrs and the selectivity to benzyl aldehyde is 17%, they were much higher than those in absence of CoAPO-5. CoAPO-5 also exhibited a high catalytic activity for the oxidation of ethylbenzene. The conversion of ethylbenzene reached 28.9% in 4 hrs, and the selectivities to hypnone and benzyl acetate were 30.2% and 16.3%, respectively.