Studies On The Synthesis Of MeAlPO₄-5 And Their Catalytic Properties In Cyclohexanone Ammoximation

ε-Caprolactam is an important material for the organic chemistry industry.The one-step ammoximation of cyclohexanone intoε-caprolactam is one of the novel rounts in green chemistry.The heteroatoms substituted aluminophosphate sieves(MeAlPO₄-5) have special channel structure and various functional heteroatoms,also acid sites and redox active sites. These make them to be potential multi-functional catalysts.In this paper,various MeAlPO₄-5 molecular sieves were hydrothermally synthesized and their physical-chemical properties were characterized by many spectroscopy methods.At the same time,their catalytic activities were tested in cyclohexanone ammoximation.Various MeAlPO₄-5 molecular sieves were hydrothermally synthesized,here Me= Co,Mn,Fe,Mg,Zn,Cu,V,Cr.The effects of the aluminium source,templating agent amount,various metal amount,crystallization temperature,crystallization time on as-synthesized MeAlPO₄-5 molecular sieve were carefully invistigated.The results show that pseudo-boehmite has good water solubility;pure MeAlPO₄-5 can be synthesized at 200℃for 48 h with a ratio of R/Al at 0.89(R= N,N-diethyl-ethanolamine) or R/Al at 0.80(R=Triethylamine).The template agent and water can be removed at 550℃in a tubular furnace for 10 h and also transition of Me²⁺ to Me³⁺.XRD,FT-IR,nitrogen adsorption-desorption,NH₃-TPD and UV-Visible diffusion reflectance spectra were used to characterize the crystal structure and acid quantity of the MeAlPO₄-5 molecular sieves as well as the chemical state of Co or Mn in the framework of molecular sieves.The results show that the molecular sieves have the crystal structure of AlPO₄-5,and the acid quantity and intensity of the molecular sieves were enhanced because of the transition metal atoms entering framework of molecular sieves.The tetrahedral Co²⁺ or Mn²⁺ in the lattice framework of molecular sieves,which could be partially oxidized to Co³⁺ or Mn³⁺ to form redox centers upon calcination. The catalytic properities of MeAlPO₄-5 in cyclohexanone ammoximation show that CoAlPO₄-5 exhibits higher catalytic activity than other MeAlPO₄-5;MeAlPO₄-5 molecular sieves prepared by the pseudo-boehmite and N,N-diehty-ethanolamine as raw materials, calcinated at 550℃in a tubular furnace for 10 h,Under the conditions of reaction temperature 80℃,amount of NH₃ 2.2 g,content of catalysts 0.5 g,reaction time 4 h,and by using dry air as an oxidant under 3.5 MPa,the yield and selectivity of cyclohexanone oxime are 1.00%and 1.57 %,respectively.