Triethylenetetramine Aluminosilicate Molecular Sieves As The Template Synthesis Of Metal Phosphate

Silicoaluminophsphate molecular sieves (SAPOs) have been extensively used as adsorbents, catalysts and catalyst carriers, with high shape selectivity, hydrothermal stability and good thermal stability. Recently, scientists have carried on a series of modification and doping by introducing hetero-atoms into zeolite framework, the hetero-atoms can not only modulate molecular sieves'ion exchange capacity, surface acidity, thermal stability and hydrothermal stability, but also often show high activity in catalytic reaction. Thus, hetero-atoms molecular sieves can be widely used in the field of catalysis, electricity, optical, magnetism, host-guest assembly and so on. The present works were applied to synthesize a novel class of silicoaluminophsphate molecular sieves by hydrothermal crystallization employing triethylenetetramine (TETA) as template, phosphoric acid, aluminum hydroxide, ethylorthosilicate, acetic zinc, ammonium ferrous sulfate and nickel sulfate were used in the syntheses as starting materials, moreover, many techniques were also used to characterize them. The main research contents and conclusions are as follows:Firstly, by adjusting the crystallization time, crystallization temperature, pH value, the amount of metallic salts and templates, molecular sieve raw powder have been synthesized under the hydrothermal condition. The resulting products are so called metal-doped silicoaluminophsphate molecular sieves (metal=Zn, Fe or Ni), which were calcined in the muffle furnace at 500℃for 3～5 h. Finally, metal-doped silicoaluminophsphate molecular sieves were obtained.Secondly, chemical analysis was carried out by a series of analysis methods. Phosphomolybdate bismuth blue photometry and silicon molybdenum blues photometry were applied to determine the contents of P and Si, respectively. The elemental analysis was performed on Vario EL III elemental analyzer in order to measure contents of C, H and N. Metal elements were determined with EDTA titration method.Thirdly, the results of SEM and XRD analyses indicated that the synthetic product had a high purity, crystallinity and large crystal size, the compounds are all belonged to cubic system, space group I (-4)3m, with lattice parameters a=16.7515(7) A,V=4701.2(10) A3 for ZnSAPO-102, a= 16.648(2) A, V=4614.1(8) A3 for FeSAPO-102, and a=16.7913(3) A, V=4734.3(15)A3, respectively.Fourthly, the BET specific surface areas of ZnSAPO-102 and NiSAPO-102 were found to be 331.2 m2/g and 329 m2/g, and with the median pore width of 4.75 A and 4.801 A, respectively. DTA-TG analysis showed that the framework of ZnSAPO-102, FeSAPO-102 and NiSAPO-102 were collapsed at about 700℃,680℃and 650℃. The surface acidity of molecular sieves were studied by temperature programmed desorption, the results indicated that these three kinds of metallic molecular sieves have stronger surface acidity.Fifthly, methanol conversion reaction performance of ZnSAPO-102, FeSAPO-102 and NiSAPO-102 were studied by using fixed bed reactor. The results showed that these three kinds of metallic silicoaluminophsphate molecular sieves have extremely low selectivity of light olefins in the methanol conversion reaction, while the contents of methane in gaseous phase products is very high.