合成气直接制低碳烯烃用Fe/K/Mg-O-Al催化剂

Fe/K/Mg-O-Al catalysts for direct production of lower olefins from syngas

传统费托合成着眼于制取蜡/油等长碳链饱和烃,其催化剂的"金属/酸性氧化物"界面可以极化和稳定反应中间体,从而促进加氢和C-C偶合,有助于较长链烷烃的生成。为了从合成气直接获取高附加值的低碳烯烃,催化剂设计理念应该与以制取较长链烷烃为目的的传统费托催化剂取法相异。该文着眼于"弱加氢金属/固体碱型载体"费托合成制低碳烯烃催化剂的基础研究,采用表面碱性的载体和碱性的钾助剂,逆转上述传统催化剂中"金属/酸性氧化物"之间界面的状况,削弱对加氢和C-C偶合的促进,达到抑制加氢、抑制C-C偶合的目的。所测Fe/K/Mg-O-Al系列催化剂的烯烷比取决于强碱性位的数量及其占总碱性位的比值。在1200℃钝化处理条件下,与简单MgO担载的弱碱性催化剂相比,复合氧化物MgAl2O4担载的强碱性催化剂将低碳烯烃(C2^=~C4^=)产物分布值显著提高了84%,将C2~C4烯烷比显著提高了266%。

Traditional Fischer-Tropsch synthesis focuses on the production of long chain saturated hydrocarbons such as wax/oil, whose catalyst’s "metal/acidic oxide" interface can polarize and stabilize the reaction intermediates, thus promoting hydrogenation and C-C coupling, and contributing to the formation of longer chain alkanes. In order to obtain high value-added lower olefins directly from syngas, the concept of catalyst design should be different from that of the traditional Fischer-Tropsch method to produce long-chain alkanes. Therefore, the basic research of catalysts for Fischer Tropsch synthesis of low-carbon olefins with "weak hydrogenation metal/solid base support" was carried out. Base support and potassium promoter were adopted to reverse the status of above-mentioned interface between "metal/acid oxide" in the traditional catalysts, weaken the promotion of hydrogenation and C-C coupling, and achieve the purpose of inhibiting hydrogenation and C-C coupling. The ratio of olefin to paraffin(O/P) of Fe/K/Mg-O-Al series catalysts depended on the number of strong basic sites and their ratio to the total basic sites. Under the same passivation treatment at 1200 ℃, compared with those in the weak base catalyst supported by simple MgO, the hydrocarbon product distribution value of C2^=~C4^= hydrocarbon was increased by 84% in the strong base catalyst supported by composite oxide MgAl2O4, and the C2~C4 olefin/paraffin ratio was increased by 266%.