Operando XAS和NAP-XPS研究Co3O4和CeO2-Co3O4催化剂上优先CO氧化的过程,Journal of Catalysis

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Operando XAS和NAP-XPS研究Co3O4和CeO2-Co3O4催化剂上优先CO氧化的过程
Journal of Catalysis ( IF 6.5 ) Pub Date : 2016-09-24 09:45:01
Liliana Lukashuk, Karin Föttinger, Elisabeth Kolar, Christoph Rameshan, Detre Teschner, Michael Hävecker, Axel Knop-Gericke, Nevzat Yigit, Hao Li, Eamon McDermott, Michael Stöger-Pollach, Günther Rupprechter

Co ₃ O ₄是用于通过优先CO氧化（PROX）从H ₂流中除去CO的有前途的催化剂。通常建议采用Mars-van-Krevelen氧化还原机理，但通常缺少对反应条件下催化活性表面氧化态的详细了解。因此，我们利用操作X射线吸收光谱法检查了PROX期间的结构和氧化态，以及在低光电子动能下接近大气压XPS的情况，从而检查了表面敏感度的高表面敏感性。纯CO的表面还原非常容易（已经从〜100°C开始）和O ₂易于再氧化这表明分子吸附的CO与晶格氧反应，晶格氧由气相O ₂补充。然而，即使对于XPS检测，反应条件下氧空位的稳态浓度也太低，以至于在PROX过程中Co ₃ O ₄的体积和表面都被完全氧化。另外，研究了向C ₃ O ₄中添加CeO ₂（活性物质少）的效果。用10wt％的CeO ₂促进Co ₃ O ₄可以提高CO和H ₂的还原温度并增强PROX活性。从CeO _2开始由于是活性较低的材料，这只能由Co-O-Ce界面的较高活性来解释。

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Operando XAS and NAP-XPS studies of preferential CO oxidation on Co3O4 and CeO2-Co3O4 catalysts

Co₃O₄ is a promising catalyst for removing CO from H₂ streams via the preferential CO oxidation (PROX). A Mars-van-Krevelen redox mechanism is often suggested but a detailed knowledge especially of the oxidation state of the catalytically active surface under reaction conditions is typically missing. We have thus utilized operando X-ray absorption spectroscopy to examine structure and oxidation state during PROX, and near atmospheric pressure-XPS at low photoelectron kinetic energies and thus high surface sensitivity to monitor surface composition changes. The rather easy surface reduction in pure CO (starting already at ∼100°C) and the easy reoxidation by O₂ suggest that molecularly adsorbed CO reacts with lattice oxygen, which is replenished by gas phase O₂. Nevertheless, the steady state concentration of oxygen vacancies under reaction conditions is too low even for XPS detection so that both the bulk and surface of Co₃O₄ appear fully oxidized during PROX. Furthermore, the effect of adding CeO₂ (a less active material) to Co₃O₄ was studied. Promotion of Co₃O₄ with 10wt% CeO₂ increases the reduction temperatures in CO and H₂ and enhances the PROX activity. Since CeO₂ is a less active material, this can only be explained by a higher activity of the Co-O-Ce interface.

更新日期：2016-09-25

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