Heteroatom Aluminum Phosphate Molecular Sieve Synthesis And Catalytic Performance

With good thermal stability and hydrothermal stability, the aluminum phosphate molecular sieves are composed of TO4 tetrahedra (T=Al, P, etc), the elements containing in the framework of microporous materials, which can be substituted with different valence states of nonmental or mental elements, and resulting materials are so-called heteroatom-aluminum phosphate molecular sieves with intrersting structures. Due to good redox activity and acidic property, heteroatom-aluminum phosphate molecular sieves have evoked keen attention in the field of catalysis as redaox and bifunctional catalyst. The present works were applied to synthesize a novel class of aluminum phosphate molecular sieves by hydrothermal crystallization employing diethylenetriamine (DETA) as template. In the present work, phosphoric acid, aluminum hydroxide, cobalt acetate, zinc acetate, manganese acetate and magnesium acetate were used in the syntheses as starting materials. The main research contents and conclusion are as follows:Firstly, by adjusting the usage of templates, crystallization time and temperature, pH value and the amount of metallic acetates under the traditional hydrothermal condition, molecular sieve have been synthesized. The resulting products are so called heteroatom-aluminum phosphate molecular sieves (metal= Co, Zn, Mn or Mg), which were calcined in tne muffle furnace at 500℃for 3 h. Finally, heteroatom-aluminum phosphate molecular sieves were obtained.Secondly, chemical analysis was carried out by a series of analysis methods. Phosphomolybdate bismuth blue photometry were applied to determine the contents of P, respectively. The elemental analysis was performed on Vario ELⅢelemental analyzer in order to measure contents of C, H and N. Metal elements were determined with EDTA titration method.Thirdly, metal-doped aluminum phosphate molecular sieves were characterized by powder X-ray diffraction(XRD) and scanning electron microscope(SEM) for studying its structure and crystal morphology. DTA-TG analysis showed that the framework of CoAPO-101, ZnAPO-101, MnAPO-101 and MgAPO-101 were collapsed at about 700℃. The solids were characterized by CCD method, which showed that CoAPO-101 and ZnAPO-101 are all belonged to rhombohedral system and R-3 space group. The lattice parameters are given:a=b=13.795(3), c=15.162(7) A,α=β=90°,γ= 120°, V=2498.8(13) A3, the molecular structure formula is [Co(C4H13N3)2]2+·[(Al4Co2P6)O24]3-·(H3O)+for CoAPO-101, and a=b=13.8017(18), c=15.142(4) A,α=β= 90°,γ= 120°, V=2497.9(8) A3, the molecular structure formula is [Co(C4H13N3)2]2+·[(Al4.67Zn1.33P6)O24]3-·(H3O)+for ZnAPO-101, separately. Fourthly, MTO reaction performance of CoAPO-101 was studied by using fixed bed reactor. The results showed that the selectivity of ethylene and propylene are about 50.00 wt%,35.00 wt%, respectively, and their overall selectivity is about 80.00 wt%, and that methanol conversion rate is about 55% for CoAPO-101 molecular sieve at 450℃. After molecular sieve is regenerated four times, it still has.acceptable methanol conversion and high olefin selectivity.