Advanced Electron Microscopy and ... - Wiley Online Library

DOI: 10.1002/cctc.201501174

Editorial

Advanced Electron Microscopy and Spectroscopy for Catalysis Bingsen Zhang* and Dang Sheng Su*[a]

Identifying and illustrating the fine structures of active sites

play an important role for tuning selectivity, conversion and stability of the catalysts.[1, 2] With the development of nanoscience and nanotechnology, many novel approaches have been developed to tailor and control morphology, architecture, and surface/interface structure of the complex solid catalysts at atomic level. All of the investigations need high-resolution characterization methods to detect the active site/phase of a catalyst.

Electron microscopy (EM) enables us to obtain significant de-

tails at atomic and sub-electron-volt scales, ranging from the morphology, elemental distribution, bulk/surface/interface structure, chemical and crystallographic information, and valence state, to dynamic process (e.g., the sintering of nanoparticles in heating and the structure evolution simulated by elec-

tron beam), as shown in Figure 1. Traditionally, to explore the structure–function relationship of a given catalyst, and to aid in the understanding of the mechanism, catalyst structures were compared before and after a reaction by analyzing the evolution of the active sites. Analysis could be achieved with a variety of modes on routine TEMs (e.g., high-resolution transmission EM (HRTEM), scanning TEM (STEM) and electron diffraction (ED) or affiliated spectroscopy techniques (e.g., energy dispersion X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS)).

It should be mentioned that TEM and STEM images are two-

dimensional (2D) projections derived from 3D objects. The interpretation of S/TEM images combining with image simulation and quantitative analysis are essential and give invaluable information about the structural features of complex nanocata-

Figure 1. Electron microscopy as a toolbox for revealing the microstructure of the solid catalysts and exploring the structure-function relationship. The figure is composed of components from several references.[3]

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Editorial lysts. Now, 3D tomography (e.g., electron tomography and Xray fluorescence tomography) can provide 3D information of catalysts, for instance, the composition distribution, the decorated location of nanoparticles on supports, or the pore distribution of mesoporous materials. The resolution needs to be improved for real catalysts and the typical damage caused by electron beam irradiation may well be avoided in future.[1, 2, 4] These characterization methods make great contributions to the catalysis development.

Scanning

tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) microscopy, and fluorescence microscopy are also capable of providing surface/interface structure, chemical composition, electronic and magnetic structure, which are included in this Special Issue. Apart from microscopy that directly observes and reveals the microstructure of catalysts, spectroscopic methods, such as ultraviolet, Raman, infrared, XPS, and synchrotron radiation, are also indispensable characterization methods for probing the fine structures of catalysts, such as studying the vibrational modes associated with different types of point defects and the real surface termination in solid catalysts. Aggregating all of the information gathered will Bingsen Zhang completed his Ph.D. at the Northeastern University (P.R. China) in 2009, and then went to the Fritz Haber Institute (FHI) of the Max Planck Society (MPS) in Berlin (Germany) as a postdoctoral fellow in the Department of Inorganic Chemistry. In 2011, he received an IMR SYNL-T.S. KÞ Research Fellowship founded by the Shenyang National Laboratory for Materials Science (SYNL) and joined the Institute of Metal Research (IMR), Chinese Academy of Sciences (CAS). Now he is a professor of SYNL, IMR CAS (P.R. China). His current research interests are the advanced transmission electron microscopy investigation of carbon, catalysts, and energy conversion and storage materials. Dang Sheng Su completed his Ph.D. at the Technical University of Vienna (Austria) in 1991, and then moved to the FHI of the MPS in Berlin (Germany), as a postdoctoral fellow in the Department of Electron Microscopy. After a short stay at the Hahn Meitner Institut GmbH and the Humboldt Universitt zu Berlin (Berlin, Germany), he rejoined the FHI in 1999, where he worked on electron microscopy and nanomaterials in heterogeneous catalysis and energy storage until 2011. He is now a Professor and Head of the Catalysis and Materials Division of the SYNL (P.R. China). His research interests are nanomaterials and nanocatalysis, energy storage and conversion, electron microscopy, and electron energy-loss spectroscopy.

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greatly increase the clarity over the morphology, crystallographic, and electronic structures of solid catalysts from macro down to micro scales. This greater clarity will open the door to pinpoint catalytic processes and reveal various physical and chemical effects.

In general, observations by microscopy and spectroscopy are

performed in high vacuum or air/inert atmosphere, and the samples are not in a reactive environment (Figure 2, upper part). Care, therefore, must be taken when interpreting the TEM images and correlating them to performance. Exploring

Figure 2. The development and aim of electron microscopy and spectroscopy: unraveling the microstructures at atomic and sub-electron-volt level under realistic reaction conditions with real-time analysis of reaction products.

the structural evolution of catalysts in a real environment (the “black box”) is essential to unravelling the structure–function relationship, which provides direct information for a rational design of the highly efficient catalysts. The in situ dynamic EM and spectroscopy are our versatile tools for tracing the temporally and spatially resolved status of the structural evolution of active sites at working conditions. The effort and attention to developing in situ methods are increasing, from heating via environmental TEM (ETEM) with differential pumping system or windowed gas/liquid environmental cell to operando, and to furthermore combine these data with the structural features revealed by in situ spectroscopy—future structure–function relationships could be evidenced and illustrated in real-time and real-space.[1, 5] Based on the development of environmental electron microscopy and spectroscopy (Figure 2, lower part), the morphological, crystallographic, compositional, electronic structures can be tuned towards synthesizing the solid catalysts with desired structure and optimal performance.

Following the 1

and 2nd international symposiums on advanced electron microscopy for catalysis,[6, 7] the 3rd symposium on this topic and combing with spectroscopy for catalysis was held in Kloster Seeon, Germany. Many scientists and young scholars have participated in the symposium and gave presentations and posters focusing on their recent progresses. These results highlight the crucial of microscopy and spectroscopy in

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Editorial the catalysis field and outline some challenges and opportunities in developing solid catalysts. Some representative results are published in this Special Issue—Advanced Electron Microscopy and Spectroscopy for Catalysis. We would like to thank all the contributors for their wonderful articles in this Special Issue. We also thankfully acknowledge the referees and the editors of ChemCatChem. Bingsen Zhang and Dang Sheng Su Keywords: heterogeneous catalysis · microscopy nanocatalysis · spectroscopy · structure-activity relationships

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[1] D. S. Su, B. Zhang, R. Schloegl, Chemical Reviews 2015, 115, 2818 – 2882. [2] B. Zhang, D. S. Su, Comptes Rendus Physique 2014, 15, 258 – 268. [3] a) R. C. Tiruvalam, J. C. Pritchard, N. Dimitratos, J. A. Lopez-Sanchez, J. K. Edwards, A. F. Carley, G. J. Hutchings, C. J. Kiely, Faraday Discuss. 2011, 152, 63 – 86; b) M. G. Willinger, W. Zhang, O. Bondarchuk, S. Shaikhutdinov, H.-J. Freund, R. Schlçgl, Angew. Chem. Int. Ed. 2014, 53, 5998 – 6001; Angew. Chem. 2014, 126, 6108 – 6112; c) D. S. Su, T. Jacob, T. W. Hansen, D. Wang, R. Schlçgl, B. Freitag, S. Kujawa, Angew. Chem. Int. Ed. 2008, 47, 5005 – 5008; Angew. Chem. 2008, 120, 5083 – 5086; d) S. I. Sanchez, M. W.

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[4] [5]

[6] [7]

Small, S. Sivaramakrishnan, J.-g. Wen, J.-M. Zuo, R. G. Nuzzo, Anal. Chem. 2010, 82, 2599 – 2607; e) E. D. Boyes, M. R. Ward, L. Lari, P. L Gai, Ann. Phys.-Berlin 2013, 525, 423 – 429; f) B. Zhang, W. Zhang, D. S. Su, ChemCatChem 2011, 3, 965 – 968; g) D. J. Flannigan, A. H. Zewail, Acc. Chem. Res. 2012, 45, 1782 – 1791. B. Zhang, D. S. Su, Angew. Chem. Int. Ed. 2013, 52, 8504 – 8506; Angew. Chem. 2013, 125, 8662–8664. S. B. Vendelbo, C. F. Elkjaer, H. Falsig, I. Puspitasari, P. Dona, L. Mele, B. Morana, B. J. Nelissen, R. van Rijn, J. F. Creemer, P. J. Kooyman, S. Helveg, Nature Materials 2014, 13, 884 – 890. D. S. Su, ChemCatChem 2013, 5, 2543 – 2545. D. S. Su, ChemCatChem 2011, 3, 919 – 920.

[a] Prof. B. Zhang, Prof. D. S. Su Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences 72 Wenhua Road, Shenyang 110016 (P.R. China) Fax: (+) 86 24 8397 0019 E-mail: [email protected] [email protected]

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