Wang Haozhi, Nie Xiaowa, Liu Yuan, Janik Michael J, Han Xiaopeng, Deng Yida, Hu Wenbin, Song Chunshan, Guo Xinwen
State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China.
Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, China.
ACS Appl Mater Interfaces. 2022 Aug 24;14(33):37637-37651. doi: 10.1021/acsami.2c07029. Epub 2022 Aug 15.
Converting CO into value-added chemicals and fuels is one of the promising approaches to alleviate CO emissions, reduce the dependence on nonrenewable energy resources, and minimize the negative environmental effect of fossil fuels. This work used density functional theory (DFT) calculations combined with microkinetic modeling to provide fundamental insight into the mechanisms of CO hydrogenation to hydrocarbons over the iron carbide catalyst, with a focus on understanding the energetically favorable pathways and kinetic controlling factors for selective hydrocarbon production. The crystal orbital Hamiltonian population analysis demonstrated that the transition states associated with O-H bond formation steps within the path are less stable than those of C-H bond formation, accounting for the observed higher barriers in O-H bond formation from DFT. Energetically favorable pathways for CO hydrogenation to CH and CH products were identified which go through an HCOO intermediate, while the CH* species was found to be the key C intermediate over χ-FeC(510). The microkinetic modeling results showed that the relative selectivity to CH is higher than CH in CO hydrogenation, but the trend is opposite under CO hydrogenation conditions. The major impact on C hydrocarbon production is attributed to the high surface coverage of O* from CO conversion, which occupies crucial active sites and impedes C-C couplings to C species over χ-FeC(510). The coexistence of iron oxide and carbide phases was proposed and the interfacial sites created between the two phases impact CO surface chemistry. Adding potassium into the FeC catalyst accelerates O* removal from the carbide surface, enhances the stability of the iron carbide catalyst, thus, promotes C-C couplings to hydrocarbons.
将一氧化碳转化为增值化学品和燃料是缓解一氧化碳排放、减少对不可再生能源的依赖以及将化石燃料对环境的负面影响降至最低的一种有前景的方法。这项工作使用密度泛函理论（DFT）计算结合微观动力学模型，以深入了解碳化铁催化剂上一氧化碳加氢制烃的机理，重点是理解选择性烃生产的能量有利途径和动力学控制因素。晶体轨道哈密顿布居分析表明，该路径中与O-H键形成步骤相关的过渡态比C-H键形成的过渡态稳定性更低，这解释了从DFT观察到的O-H键形成中更高的势垒。确定了一氧化碳加氢生成CH和CH产物的能量有利途径，该途径通过HCOO中间体，同时发现CH物种是χ-FeC(510)上关键的C中间体。微观动力学模型结果表明，一氧化碳加氢中对CH的相对选择性高于CH，但在一氧化碳加氢条件下趋势相反。对C烃生产的主要影响归因于一氧化碳转化产生的O的高表面覆盖率，它占据了关键活性位点并阻碍了χ-FeC(510)上C-C偶联生成C物种。提出了氧化铁和碳化物相的共存，并且两相之间形成的界面位点影响一氧化碳表面化学。向FeC催化剂中添加钾可加速O*从碳化物表面的去除，增强碳化铁催化剂的稳定性，从而促进C-C偶联生成烃。
