Scientists reveal the reality of the reaction state of bimetallic catalyst based on in-situ electron microscopy

Recently, Liu Wei and Yang Bing, associate researchers of the electron microscopy technology research group of the Energy Research Technology Platform of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, and the team of Gao Wei, a researcher from the Shanghai Advanced Research Institute of the Chinese Academy of Sciences, and Gu Meng, an associate professor of the Southern University of Science and Technology, observed and confirmed The catalyst has made progress on the real surface in the CO2 hydrogenation reaction.

In catalytic studies, conventional static microanalysis can only provide structural information before or after the catalyst reaction. However, under the action of thermal vibration, gas molecule adsorption / desorption, the surface atoms of the catalyst will inevitably migrate and cause surface reconstruction. The changed surface is the real surface related to the catalytic reaction activity. With the help of in situ characterization technology. Especially for the multi-metal catalytic system that is prone to surface reconstruction, the atomic structure of the catalyst in the reaction atmosphere cannot be observed in situ, the true surface contributing catalytic activity cannot be confirmed, and a reliable catalytic structure-activity relationship cannot be established. In previous studies, in-situ spectroscopy with macro-statistics has made pioneering explorations of dynamic catalytic processes from a fine energy dimension, such as in-situ FTIR, in-situ XPS (AP-XPS), and in-situ XAS . On this basis, the direct observation of the surface atomic arrangement of the catalyst in the reaction in real space is a long-term goal pursued by researchers. In response to this problem, environmental transmission electron microscopy (ETEM) was born. ETEM is an in-situ method mainly based on TEM imaging. It is suitable for tracking the structural evolution of catalysts in gas-solid reactions under atomic resolution.

In this work, the research team studied the process of CO2 hydrogenation catalyzed by NiAu / SiO2 system based on environmental transmission electron microscopy and a specially designed mbar-level negative pressure quantitative gas mixing system. The initial static microscopy results show that the catalyst has Ni as the core and 2 to 3 Au atom shells on the surface, which is a typical Ni @ Au core-shell configuration. Considering that Ni has strong hydrogenation activity, which will lead to CH4 selectivity of the reaction, the core-shell configuration can reasonably explain the CO selectivity of CO2 hydrogenation of up to 95% in this work. However, in-situ observations of environmental transmission electron microscopy found that under the reaction atmosphere and temperature, the inner core Ni atoms will gradually segregate to the surface and alloy with Au; when the reaction is stopped at a lower temperature, it will dealloy to return to the Ni @ Au core-shell structure . The results of in situ spectroscopy (including in situ FTIR and in situ XAS) confirm the above microscopic observations. Theoretical calculations and in-situ FTIR results show that the in-situ CO and NiAu surface alloying in the reaction play a key and subtle mutual promotion role, which is the reason for the evolution of the catalyst configuration and high CO selectivity. This work provides inspiration for the study of the core-shell bimetallic catalytic process. For example, does the core-shell surface actually exist under the reaction conditions and does it contribute catalytic activity? Another example is it necessary to pursue the construction of the core-shell surface in the preparation of catalysts? This work is a set of comprehensive application cases of microstructure characterization and macroscopic state statistics under in-situ environment, while highlighting the local atomic structure microscopic observation, with the help of in-situ spectroscopy, especially in-situ XAS technology, to ensure electronic display Confidence level of micro-discovery and the performance of the material under macroscopic conditions. This provides an example for the development of in situ, dynamic, and high-spatial resolution catalytic characterization new methods and technologies, and also provides reference and thinking for the design and construction of specific structural and functional new catalytic materials. In addition, the journal specially invited reviewers to write and independently publish a work review (news & views) entitled The dynamic of the peel, to show the unique inspiration of this work for catalytic research.

Related results were published in "Nature-Catalysis" (Nature Catalysis). The work was supported by the National Natural Science Foundation of China, the Dalian Talent Project, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and especially the strong support of researcher Su Dangsheng.

Scientists reveal true active surface under bimetallic catalyst reaction state based on in-situ electron microscope

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