Electron energy loss spectroscopy catalyst characterization

Many of these requirements are met by INS spectroscopy, and INS investigations of catalysts have been carried out for more than 30 years (7-9). INS has emerged as an attractive technique to extend and supplement characterizations by surface science techniques, such as high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). INS complements infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectroscopies, especially when the electrical conductivity and absorption of visible and IR light by metals or supports, hinders, or prevents, the use of the full analytical power of these methods. 

Over the past 10 years a multitude of new techniques has been developed to permit characterization of catalyst surfaces on the atomic scale. Low-energy electron diffraction (LEED) can determine the atomic surface structure of the topmost layer of the clean catalyst or of the adsorbed intermediate (7). Auger electron spectroscopy (2) (AES) and other electron spectroscopy techniques (X-ray photoelectron, ultraviolet photoelectron, electron loss spectroscopies, etc.) can be used to determine the chemical composition of the surface with the sensitivity of 1% of a monolayer (approximately 1013 atoms/cm2). In addition to qualitative and quantitative chemical analysis of the surface layer, electron spectroscopy can also be utilized to determine the valency of surface atoms and the nature of the surface chemical bond. These are static techniques, but by using a suitable apparatus, which will be described later, one can monitor the atomic structure and composition during catalytic reactions at low pressures (< 10-4 Torr). As a result, we can determine reaction rates and product distributions in catalytic surface reactions as a function of surface structure and surface chemical composition. These relations permit the exploration of the mechanistic details of catalysis on the molecular level to optimize catalyst preparation and to build new catalyst systems by employing the knowledge gained. 

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