合成气经费托合成反应直接制低碳烯烃是极具开发前景的合成气直接制烯烃技术, 其关键是通过产物分布的调控提高低碳烯烃的选择性. 本工作将疏水性Fe基费托合成催化剂与SAPO-34分子筛进行复合, 制备了一系列不同SAPO-34分子筛含量的Fe@Si/S-34复合催化剂. 采用X射线衍射、扫描电子显微镜、N₂吸附-脱附、NH₃程序升温脱附和水接触角测量仪考察了SAPO-34分子筛含量对催化剂物化性质的影响. 结果表明SAPO-34分子筛的含量对催化剂的表面积、孔体积、酸性和疏水性具有显著的影响. 随着SAPO-34分子筛含量的增加, 催化剂的比表面积和总孔体积增加, 弱酸和中强酸位点增加, 疏水性减弱. 催化性能评价结果表明, Fe@Si/S-34复合催化剂明显降低了C₅₊产物选择性, 增加了C₂~C₄烃类的选择性, 适量的SAPO-34分子筛能够显著提高C₂~C₄烯烃的选择性. 本研究将Fe@Si催化剂的疏水性和SAPO-34分子筛对C₅₊烃的裂解活性耦合在一起, 在抑制水煤气变换(WGS)反应, 降低CO₂选择性的同时获得较高的C₂~C₄烯烃选择性, 为费托合成制烯烃催化剂的研制提供了一条新的策略.

The direct synthesis of light olefins from syngas via Fischer-Tropsch synthesis reaction is a promising technology for direct synthesis of olefins from syngas. The key is to improve the selectivity of light olefins through the regulation of product distribution. In this work, the hydrophobic Fe@Si catalyst was prepared by room temperature solid state method- Stöber-silylation method, and then the catalyst was combined with SAPO-34 molecular sieves with different contents to prepare Fe@Si/S-34 composite catalysts. The effects of SAPO-34 molecular sieve content on the physicochemical properties of the catalysts were investigated by X-ray diffraction, scanning electron microscopy, N₂ adsorption-desorption, NH₃ temperature programmed desorption and water contact angle measurement. The results showed that the content of SAPO-34 molecular sieve has significant influence on the surface area, pore volume, acidity and hydrophobicity of the catalysts. With the increase of SAPO-34 molecular sieve content, the specific surface area and total pore volume of the catalyst increased, the weak acid and medium-strong acid sites increased, and the hydrophobicity weakened. The catalytic performance evaluation results showed that the Fe@Si/S-34 composite catalyst decomposed C₅₊ hydrocarbons into light hydrocarbons, significantly reduced the selectivity of C₅₊ products and increased the selectivity of C₂~C₄ hydrocarbons. Appropriate SAPO-34 molecular sieve could significantly improve the selectivity of C₂~C₄ olefins. When the mass ratio of Fe@Si catalyst to SAPO-34 is 2, the C₂~C₄ olefin selectivity of Fe@Si/S-34 catalyst is the highest, the conversion of CO is 80.0%, the selectivity of CO₂ in the product is 8.9%, and the selectivity of C₂~C₄ olefins is 31.1%. In this study, the hydrophobicity of Fe@Si catalyst and the cracking activity of SAPO-34 molecular sieve for C₅₊ hydrocarbon were coupled together to inhibit the water-gas shift (WGS) reaction, reduce the CO₂ selectivity and obtain higher C₂~C₄ olefin selectivity, which provided a new strategy for the development of catalysts for Fischer-Tropsch synthesis to olefins.