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

摘要:

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。然而，低碳烯烃是不饱和短碳链烃，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，与简单氧化物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C2=-C4=烃产物分布值显著提高了84%，将C2-C4烯烷比显著提高了266%。

Abstract:

The traditional Fischer-Tropsch synthesis focuses on the production of long chain saturated hydrocarbons such as wax/oil, of which the “metal/acidic oxide” interface of the catalysts can polarize and stabilize the reaction intermediates, thus promoting hydrogenation and C—C coupling, and contributing to the formation of longer chain alkanes. However, lower olefins are unsaturated short-chain hydrocarbons. In order to obtain high value-added lower olefins directly from syngas, the design concept should be the opposite of the traditional Fischer-Tropsch method for the purpose of producing long-chain alkanes. Therefore, we focus on the fundamental research of the "weak hydrogenation metal/solid base support" Fischer-Tropsch to olefins catalysts, use the surface basic support and basic potassium promoter 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 a Fe/K/Mg—O—Al series catalyst depends on its integral area of the high temperature peak in CO2-TPD profile. Under the same passivation treatment at 1200℃, compared with the weak base catalyst supported by simple oxide MgO, the strong base catalyst supported by composite oxide MgAl2O4 significantly increased the hydrocarbon product distribution value of C2=-C4= hydrocarbon by 84%, and the C2-C4 olefin/paraffin ratio by 266%.