In Situ Multimodal 3D Chemical Imaging of a Hierarchically Structured Core@Shell Catalyst.
In Situ Multimodal 3D Chemical Imaging of a Hierarchically Structured Core@Shell Catalyst.
复制标题
DOI：
10.1021/jacs.7b02177
复制
发表时间：
2017-05
影响因子：
15
通讯作者：
T. Sheppard;S. W. T. Price;F. Benzi;S. Baier;M. Klumpp;R. Dittmeyer;W. Schwieger;J. Grunwaldt
中科院分区：
文献类型：
--
作者：
T. Sheppard;S. W. T. Price;F. Benzi;S. Baier;M. Klumpp;R. Dittmeyer;W. Schwieger;J. Grunwaldt
采用同步辐射显微X射线荧光（μ-XRF）、X射线衍射（μ-XRD）和扫描透射X射线显微镜（STXM）计算机断层成像（CT）技术，对Cu/ZnO/Al2O3@ZSM-5核壳型催化剂合成气一步制二甲醚（DME）活性进行了同步原位成像。逐步成像相同的样品体积，首先在氧化和还原气氛下（模拟煅烧和活化过程），然后在DME合成的模型反应条件下（H2：CO：CO2比例为16：8：1，高达250 °C）。多模态成像方法提供了对催化剂内的活性金属结构和形态的深入了解，并允许在单次采集中对催化剂核和沸石壳进行成像。在还原过程中观察到纳米级Cu物种分散在催化剂芯中，在芯-壳界面处形成亚稳Cu+相。在DME反应条件下，在1巴，在活性催化剂的核心与部分氧化的Cu物种的共存被解开。沸石壳和核-壳界面在所有条件下保持稳定，保持了催化剂的双功能性质。这些观测结果是无法使用标准的散装技术，如X射线吸收光谱（XAS）和XRD，展示了多模态原位X射线CT的潜力，用于表征分层设计的材料，这将大大受益于这种三维空间分辨测量。
A Cu/ZnO/Al2O3@ZSM-5 core@shell catalyst active for one-step conversion of synthesis gas to dimethyl ether (DME) was imaged simultaneously and in situ using synchrotron-based micro X-ray fluorescence (μ-XRF), X-ray diffraction (μ-XRD), and scanning transmission X-ray microscopy (STXM) computed tomography (CT) with micrometer spatial resolution. An identical sample volume was imaged stepwise, first under oxidizing and reducing atmospheres (imitating calcination and activation processes), and then under model reaction conditions for DME synthesis (H2:CO:CO2 ratio of 16:8:1, up to 250 °C). The multimodal imaging methods offered insights into the active metal structure and speciation within the catalyst, and allowed imaging of both the catalyst core and zeolite shell in a single acquisition. Dispersion of nanosized Cu species was observed in the catalyst core during reduction, with formation of a metastable Cu+ phase at the core-shell interface. Under DME reaction conditions at 1 bar, the coexistence of Cu0 in the active catalyst core together with partially oxidized Cu species was unraveled. The zeolite shell and core-shell interface remained stable under all conditions, preserving the bifunctional nature of the catalyst. These observations are inaccessible using standard bulk techniques like X-ray absorption spectroscopy (XAS) and XRD, demonstrating the potential of multimodal in situ X-ray CT for characterization of hierarchically designed materials, which stand to benefit tremendously from such 3D spatially resolved measurements.