摘要
采用XRD、SEM、FT IR、TG DTA等表征手段 ,对分别以正磷酸、拟薄水铝石和硅溶胶为磷源、铝源和硅源 ,用五种模板剂合成的SAPO 34分子筛进行了表征 .不同模板剂合成的SAPO 34分子筛在晶粒粒度分布上有相当大的差异 .通过TEAOH Et3 N或者TEAOH Morpholine复合模板剂法可以有效地调节晶粒粒度 .不同模板剂合成的SAPO 34分子筛的红外骨架振动相似 ;而模板剂分子与分子筛骨架的作用方式有区别 .模板剂种类对SAPO 34分子筛骨架热稳定性没有影响 。
Triethylammine (Et3N), Morpholine, tetraethylammonium hydroxide (TEAOH), TEAOH-Et3N dual template and TEAOH-Morpholine dual template can all be used to synthesize pure SAPO-34 molecular sieve. The SAPO-34 molecular sieve samples are synthesized with the five kinds of templates mentioned above and characterized with XRD, SEM, FTIR, NMR and TGA techniques, etc. And the samples are also evaluated by methanol-to-olefins (MTO) reaction. The SAPO-34 sample synthesized with single Et3N has the defects in the crystal lattice which could be proved by the undistinguished low peaks at 2theta value 26degrees, 31degrees and the lower characteristic peaks in the XRD pattern. These defects can be effectively improved by using the dual template TEAOH-Et3N system as is shown by the two more distinct double peaks at 2theta value 26degrees, 31degrees and the higher characteristic peaks. The relative crystallinity of sample synthesized with the dual template TEAOH-Morpholine (Et3N) is between the sample with single TEAOH and that with single Morpholine (Et3N). This phenomenon shows an interesting 'additional effect'. Different templates could synthesize SAPO-34 molecular sieves with different crystal sizes. TEAOH is favourable to produce the small crystal SAPO-34, while Morpholine would synthesize big crystals and Et3N forms the crystals whose size is between TEAOH one and Morpholine one. The crystal size can be adjusted by the dual template method effectively. The SAPO-34 molecular sieve samples with the use of TEAOH have far smaller crystal sizes than the samples with single Morpholine or Et3N no matter TEAOH is the sole template or a composite template. Framework vibrancy modes of SAPO-34 molecular sieve samples synthesized from different templates are similar, while their interaction modes between templates molecules and framework are different. TEAOH is more effective in the formation of SAPO-34 structure, and it is more favourable to enter the pore system of SAPO-34 and easier to react with the negative charge of the structure of SAPO-34 to form the protonated molecules which are thermally decomposed at a higher temperature. The amount of Morpholine and Et3N is more than that of TEAOH in the initial gel, so the main role of Morpholine or Et3N is filling the cavity of SAPO-34. The SAPO-34 synthesized from different templates has the same thermal stability as their structures all thermally collapse at ca. 1155degreesC. The SAPO-34 molecular sieve synthesized with the dual template system has higher (C-2(=) + C-3(=)) selectivity in MTO reaction than the sample with single Morpholine or single Et3N, while it is still lower than the TEAOH sample. This phenomenon also shows a kind of the additional effect.
