通过结合时间分辨原位表征和微动力学分析了解 α-Fe2O3 在 CO2 加氢中的命运,ACS Catalysis

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通过结合时间分辨原位表征和微动力学分析了解 α-Fe2O3 在 CO2 加氢中的命运
ACS Catalysis ( IF 11.3 ) Pub Date : 2023-06-24 , DOI: 10.1021/acscatal.3c01340
Qingxin Yang ₁ , Vita A. Kondratenko ₁ , Andrey S. Skrypnik ₁ , Henrik Lund ₁ , Stephan Bartling ₁ , Jana Weiss ₁ , Angelika Brückner ₁ , Evgenii V. Kondratenko ₁

Affiliation

在铁基催化剂上进行CO _{2加氢是减少这种温室气体排放的一种有前途的途径，并为无原油生产化学品和燃料提供了可能性。}了解 (i) 工作催化剂中晶相或/和表面物质的作用，(ii) 在反应条件下影响其形成的因素，以及 (iii) 气相产物表面前体的种类和反应性至关重要用于控制CO ₂加氢的效率。在本研究中，我们应用时间分辨原位表征技术来监测 Fe ₂ O _3还原、CO₂启动过程中的相变加氢，稳态操作，最后催化剂失活。_{不同运行时间后获得的结构信息与从H 2}和CO ₂活化的时间分析以及稳态同位素瞬态动力学分析(SSITKA)获得的动力学数据相关。Fe ₂ O ₃在300℃以上很容易被还原为Fe ₃ O _4和H₂中的Fe 。Fe ₅ C ₂和Fe ₃ C，在CO _{2下由金属Fe/Fe}₃ O ₄快速形成在氢化条件下，在环境压力条件下，随着反应流的时间增加，不会发生氧化。然而，催化剂失去了其初始活性，特别是对碳氢化合物的选择性，而有利于CO。因此，我们没有证实通过碳化铁氧化进行CO/CO ₂加氢的公认的失活机制。相反，通过原位拉曼和伪原位XPS测量鉴定的表面碳质物质被认为会由于阻碍催化剂从H ₂和CO ₂生成表面物质的能力而导致催化剂失活和去选择性。_{具体而言，CO 2}的强度在碳沉积物存在的情况下，吸附和将吸附的CO ₂解离为吸附的CO的催化剂活性降低。SSITKA 测试的动力学评估表明，(i) 在反应流上 1.5 小时后仅存在一种产生气相 CO 的表面中间体，但 (ii) 至少有两种（短寿命和长寿命）参与的表面中间体平行地形成CH _{4 。}碳沉积物似乎堵塞了负责形成短期中间体的位点。

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Understanding of the Fate of α-Fe2O3 in CO2 Hydrogenation through Combined Time-Resolved In Situ Characterization and Microkinetic Analysis

CO₂ hydrogenation over Fe-based catalysts is a promising pathway to mitigate emissions of this greenhouse gas and provides a possibility for crude-oil-free production of chemicals and fuels. Understanding of (i) the role of crystalline phases or/and surface species in the working catalysts, (ii) the factors affecting their formation under reaction conditions, and (iii) the kind and reactivity of surface precursors of gas-phase products is vital for controlling the efficiency of CO₂ hydrogenation. In this study, we applied time-resolved in situ characterization techniques for monitoring phase transformations during Fe₂O₃ reduction, starting of CO₂ hydrogenation, steady-state operation, and finally catalyst deactivation. The obtained structural information after different times on stream was related to kinetic data obtained from temporal analysis of H₂ and CO₂ activation as well as from steady-state isotopic transient kinetic analysis (SSITKA). Fe₂O₃ is easily reduced to Fe₃O₄ and Fe in H₂ above 300 °C. Fe₅C₂ and Fe₃C, which are quickly formed from metallic Fe/Fe₃O₄ under CO₂ hydrogenation conditions, do not undergo oxidation with rising time on the reaction stream under ambient-pressure conditions. Nevertheless, the catalyst loses its initial activity and, particularly, the selectivity to hydrocarbons in favor of CO. Thus, we do not confirm the well-recognized deactivation mechanism of CO/CO₂ hydrogenation through oxidation of iron carbides. Instead, surface carbonaceous species identified by in situ Raman and pseudo in situ XPS measurements were concluded to cause catalyst deactivation and deselectivation due to hindering the catalyst ability to generate surface species from H₂ and CO₂. Specifically, the strength of CO₂ adsorption and the catalyst activity to dissociate adsorbed CO₂ to adsorbed CO decrease in the presence of carbon deposits. Kinetic evaluation of SSITKA tests revealed the presence of (i) only one kind of surface intermediate yielding gas-phase CO after 1.5 h on reaction stream but (ii) at least two kinds (short-lived and long-lived) of surface intermediates participating in CH₄ formation in parallel. Carbon deposits seem to block the sites responsible for the formation of short-lived intermediates.

更新日期：2023-06-24

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