SAPO-34 molecular sieves synthesized using calcined kaolin as partial raw material under three-stage of high-low-high temperature hydrothermal condition are explored . Especially, the effect of kaolin calcination temperature on the crystallization mechanism of SAPO-34 and the methanol to olefin performance are investigated thoroughly. It is found that the sample (SP-500) synthesized by using kaolin calcined at 500 °C (MK-500) demonstrates clean cubic structure, large specific surface area and mild acidity, providing the initially activated Si and Al source for the synthesis of SAPO-34 molecular sieve due to the well scattered structure of MK-500. From the crystallization mechanism consideration, it can be proposed that the SAPO-34 molecular sieves will be controlled by the low degree of Si aggregation in metakaolin and quantity of Si (3Al,1Si) species. As a result, SP-500 displays excellent catalytic lifetime during methanol to olefin reaction for its special Si coordination environment, showing the highest stable light olefin yield of 80.6 % and a methanol conversion above 90 % for more than 720 min. In contrast, SP-800 sample with the most strong acid sites is only 390 min, even if showcasing the highest selectivity of light olefins (84.5%).

中文翻译：

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高岭土煅烧温度对甲醇制烯烃SAPO-34分子筛制备及结晶机理的影响

探索了以煅烧高岭土为部分原料，在高-低-高温三阶段水热条件下合成SAPO-34分子筛。特别是，深入研究了高岭土煅烧温度对SAPO-34结晶机理和甲醇制烯烃性能的影响。结果发现，采用500 ℃煅烧高岭土（MK-500）合成的样品（SP-500）表现出干净的立方结构、大的比表面积和温和的酸性，为合成SAPO-34 分子筛得益于 MK-500 良好的分散结构。从结晶机理考虑，可以提出SAPO-34分子筛将受到偏高岭土中Si聚集程度低和Si(3Al,1Si)物种数量的控制。因此，SP-500因其特殊的Si配位环境，在甲醇制烯烃反应过程中表现出优异的催化寿命，表现出最高的稳定轻质烯烃产率80.6%，甲醇转化率超过90%，持续时间超过720分钟。相比之下，具有最强酸位点的 SP-800 样品仅 390 分钟，即使显示出最高的轻质烯烃选择性 (84.5%)。