Catalytically active sites Fourier transforms

Based on X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), electron spin resonance (ESR), Mbssbauer, and extended X-ray absorption fine structure spectroscopy (EXAFS) , van Veen and collaborators concluded that the thermal treatment at temperatures where catalytic activity is maximum ( 500-600°C) does not lead to complete destruction of the macrocycles, but rather to a ligand modification which preserves the Me-N4 moiety intact. Furthermore, the stability of this catalytic site is improved because the reactive parts of the ligands are bound to the carbon support and thus are no longer susceptible to an oxidative attack. Thermal treatments at higher temperatures (up to 850°C) led to some decomposition of the Me-N4 moiety, and thus to a decrease of the catalytic activity, and to the reduction of some of the ions to their metallic state. 

Recent advances in the preparation of ceria-based gold catalysts for hydrogen production by the WGS and PROX reactions are reviewed in this chapter. Considerable emphasis is placed on the catalyst characterization by a number of physicochemical methods X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The relation between the structure, properties, and catalytic activity, as well as the nature of the active sites is also discussed. 

The active site (MMS) redox response, which apparently occurs in a fast, quasi-reversible manner, is usually of low magnitude and overlaps with, and is not easily distinguished from, the capacitive double layer response. Eurthermore, when an electrocatalytic process takes place, mediated by the active site species, the catalytic process usually dominates the dc response, i.e., the redox behavior of the active site is not at all obvious. In such circumstances advantage may be taken of ac voltammetry techniques to investigate the vital role of the active sites at the interface [8]. Large amplitude Fourier transformed ac (LAFT-ac) voltammetry has been explored, at both a theoretical and experimental level [9-11], by Bond and co-workers, and the application of this technique to the study of gold surfaces in aqueous acid and base was described recently [12]. 

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