Characterization studies sites transformation

Investigations of the acidity of specific surface sites may be accomplished by studies coordinated with spectroscopic methods, such as infrared (JR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, or mass spectrometry (MS). Surface characterization with Fourier transform infrared (FTIR) spectroscopy can provide quantitative results with experimental methods that are easily performed. However, the transmission sampling techniques traditionally employed for infrared studies may introduce experimental artifacts on the analyzed surface (10,... 

The activity of a series of Pt/VK /SIO for the NO-CO reaction has been studied using in-situ Fourier Transform Infrared Spectroscopy. It was found that high loadings of WO3 promote the activity of Pt for this reaction. Catalyst characterization studies, conducted by x-ray diffraction, x-ray photoelectron spectroscopy, CO chemisorption, and transmission electron microscopy, indicate that Pt was decorated by an overlayer of partially reduced W0X. The increased activity can be quantitatively related via a two site mechanism involving Pt sites and adlineation sites formed at the interface between the overlayers and Pt. 

The aim of this study is to develop model reaction for the characterization of the acidity and basicity of various transition aluminas, the experimental conditions being close to that for catalysis use. Among various model reactions, the transformation of cyclopentanol and cyclohexanone mixture was chosen for this work. Indeed, this reaction was well known for estimating simultaneously the acid-base properties of oxide catalysts [1], Two reactions take place the hydrogen transfer (HT) on basic sites and the alcohol dehydration (DEH) on acid sites. The global reaction scheme is shown in Figure 1. 

Some very important surface properties of solids can be properly characterized only by certain wet chemical techniques, some of which are currently under rapid improvement. Studies of adsorption from solution allow determination of the surface density of adsorbing sites, and the characterization of the surface forces involved (the energy of dispersion forces, the strength of acidic or basic sites and the surface density of coul-ombic charge). Adsorption studies can now be extended with some newer spectroscopic tools (Fourier-transform infra-red spectroscopy, laser Raman spectroscopy, and solid NMR spectroscopy), as well as convenient modern versions of older techniques (Doppler electrophoresis, flow microcalorimetry, and automated ellipsometry). 

In summary, the compilation of relevant case studies shows that XRD of working catalysts is a widely applicable technique. It gives rich and useful information about synthesis and activation of catalysts as well as deactivation by structural transformations. The pertinent question about the structure of the active sites is not accessible directly by this method despite such claims in the literature. It must be pointed out that this shortcoming of a technique involving characterization of samples in reactive atmospheres is common to all methods when one is concerned with high-performance catalysts in which the active sites are a small fraction of the active surface. Model systems do a better job in this respect, provided that they are active for the reaction of interest and not only in proxy reactions. 

Hydrogenation of C02 over Rh ion exchanged zeolite catalysts (RhY) was studied. The RhY catalyst showed high activity for hydrogenation of C02. The main product transformed from methane to CO and formation of ethanol was promoted in accordance with Li addition. Characterization of surface sites and adsorbed species was performed. 

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