The Structural Evolution and Dynamics of an In2O3 Catalyst for CO2 Hydrogenation to Methanol: an Operando XAS-XRD and in situ TEM Study,Journal of the American Chemical Society

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The Structural Evolution and Dynamics of an In2O3 Catalyst for CO2 Hydrogenation to Methanol: an Operando XAS-XRD and in situ TEM Study
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2019-07-19 , DOI: 10.1021/jacs.9b04873
Athanasia Tsoukalou ₁ , Paula M. Abdala ₁ , Dragos Stoian ₂ , Xing Huang ₃ , Marc-Georg Willinger ₃ , Alexey Fedorov ₁ , Christoph R. Müller ₁

Affiliation

We report an operando examination of a model nanocrystalline In2O3 catalyst for methanol synthesis via CO2 hydrogenation (300 oC, 20 bar) by combing X-ray absorption spectroscopy (XAS), X-ray powder diffraction (XRD) and in situ TEM. Three distinct catalytic regimes are identified during CO2 hydrogenation: activation, stable performance, and deactivation. The structural evolution of In2O3 nanoparticles (NPs) with time on stream (TOS) followed by XANES-EXAFS-XRD associates the activation stage with a minor decrease of the In-O coordination number and a partial reduction of In2O3 due to the formation of oxygen vacancy sites (i.e. In2O3-x). As the reaction proceeds, a reductive amorphization of In2O3 NPs takes place, characterized by decreasing In-O and In-In coordination numbers and intensities of the In2O3 Bragg peaks. A multivariate analysis of the XANES data confirms the formation of In2O3-x and, with TOS, metallic In. Notably, the appearance of molten In0 coincides with the onset of catalyst deactivation. This phase transition is also visualized by in situ TEM, acquired under reactive conditions at 800 mbar pressure. In situ TEM revealed an electron beam assisted transformation of In2O3 nanoparticles into a dynamic structure in which crystalline and amorphous phases co-exist and continuously interconvert. The regeneration of the deactivated In0/In2O3-x catalyst by re-oxidation was critically assessed revealing that the spent catalyst can be re-oxidized only partially in a CO2 atmosphere or air yielding an average crystallite size of the resultant In2O3 that is approximately an order of magnitude larger than the initial one.

中文翻译：

用于 CO2 加氢制甲醇的 In2O3 催化剂的结构演变和动力学：Operando XAS-XRD 和原位 TEM 研究

我们通过结合 X 射线吸收光谱 (XAS)、X 射线粉末衍射 (XRD) 和原位 TEM，报告了通过 CO2 加氢（300 oC，20 bar）合成甲醇的模型纳米晶 In2O3 催化剂的操作检查。在 CO2 加氢过程中确定了三种不同的催化机制：活化、性能稳定和失活。In2O3 纳米颗粒 (NPs) 随运行时间 (TOS) 和 XANES-EXAFS-XRD 的结构演变将活化阶段与 In-O 配位数的轻微减少和因形成氧而导致的 In2O3 部分减少相关联空位（即 In2O3-x）。随着反应的进行，发生了 In2O3 NPs 的还原非晶化，其特征是 In-O 和 In-In 配位数和 In2O3 布拉格峰的强度降低。XANES 数据的多变量分析证实了 In2O3-x 和 TOS 金属 In 的形成。值得注意的是，熔融 InO 的出现与催化剂失活的开始一致。这种相变也可以通过原位 TEM 可视化，在 800 毫巴压力下的反应条件下获得。原位 TEM 揭示了电子束辅助 In2O3 纳米粒子转变为动态结构，其中结晶相和非晶相共存并不断相互转化。通过再氧化对失活的 In0/In2O3-x 催化剂进行了严格评估，结果表明，废催化剂只能在 CO2 气氛或空气中部分再氧化，生成的 In2O3 的平均微晶尺寸约为一个数量级幅度比最初的大。

更新日期：2019-07-19

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