Catalyst characterization spectroscopic methods

While in situ techniques encompass all characterization/spectroscopic methods that can be used to probe the surface chemistry of an operating practical catalyst, its entirety is too large to cover in any real detail. Therefore the methods covered in this review were chosen based on their prevalence and use in the field and the potential for significant observations during reaction cycles. Some methods, such as ATR, TAP and catalytic shock tube, were chosen based on the potential of these methods and the likelihood that they will become more widely used as they are integrated with evolving spectroscopic techniques. 

B. M. Weckhuysen, Phys. Chem. Chem. Phys. 5, 4351 (2003)) to the characterization of catalysts by spectroscopic methods with simultaneous measurements of catalytic activity (and/or selectivity and/or stability). Unfortunately, many authors have used this term more loosely, for example, without reporting any catalyst performance data, and it seems to be at risk of becoming as vague in usage as in situ we largely avoid it in this set of volumes. 

This work discusses the vibrational features associated with the insertion of tetrahedral Ti in the MFI zeolite lattice. The understanding of these features forms the base for the technical characterization of Ti containing silicate catalysts using spectroscopic methods, which is of capital importance in industrial catalysis. A combination of spectroscopic and computational techniques is used in order to assign the main vibrational features of Ti-silicalite, also taking into account the presence of hydroxylated defects. 

Catalysts were synthesized by hydrothermal treatment and characterized by various spectroscopic methods. Bio-ethanol containing 5 ppm sulfur was used as a... 

The same polymeric arenes that served as metallation catalysts in equation 119 can also be used for silylation in Barbier-type reactions (equation 131). The polymer is presumably converted to a lithium arene adduct that activates metallic lithium for metallation of the halogenated substrates, before addition of an electrophile to achieve the synthetic goal. Equations 132-135 illustrate some of the cases investigated. The products can be characterized by the usual spectroscopic methods . 

Volume 57A Spectroscopic Characterization of Heterogeneous Catalysts. Part A Methods of... 

The purpose of the present paper is to offer a contribute to the understanding of the mechanisms of these reactions by using an IR spectroscopic method and well-characterized "monolayer" type vanadia-titania (anatase) as the catalyst. We will focus our paper in particular on the following subjects i) the nature of the activation step of the methyl-aromatic hydrocarbon ii) the mechanism of formation of maleic anhydride as a by-product of o-xylene synthesis iii) the main routes of formation of carbon oxides upon methyl-aromatic oxidation and ammoxidation iv) the nature of the first N-containing intermediates in the ammoxidation routes. 

Table I lists the major characterization techniques which have been applied to the molybdena catalyst. They may be grouped into two broad categories nonspectroscopic and spectroscopic methods. Space does not permit a full discussion of the theory, experimental techniques, or interpretation of results of these techniques—we give here only the author s interpretations of their results. The reader is referred to any number of standard texts or reviews on the specific technique for a more complete description.

A catalyst surface may be assumed to be characterized by specific poisoning if the number of adsorption sites, the strength (or the strength distribution) of the adsorbate-catalyst interaction, and the nature of this interaction as well as the chemical nature of the adsorbed species can be determined. All three properties are equally important to characterize fully, i. e., qualitatively and quantitatively, a catalyst surface. The number of adsorption sites may be determined from the adsorbed amount of poison as measured by conventional techniques, whereas thermoanalytical methods have to be applied for a quantitative characterization of the adsorption bond strength. Spectroscopic methods will be most suitable for studies of the chemical nature of the adsorbed species and the nature of the adsorbate-surface interaction. 

A number of modern physical techniques are used to characterize heterogeneous catalysts. These methods range from techniques probing the interaction of catalysts with probe molecules, to in situ surface characterization techniques as well as structural elucidation under both in situ and ex situ conditions. In general, interaction of catalysts with probe molecules is followed using some spectroscopic property of the probe molecule itself and/or the changes induced by the heterogeneous catalyst. The spectroscopic techniques used include vibrational spectroscopies, NMR spectroscopy, UV-Vis spectroscopy and mass spectrometry to name a few examples. Similarly, in situ techniques tend to use properties of probe molecules but also combined with structural techniques such as X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). In recent years XAS has been widely used in the characterization of catalysts and catalyst surfaces. 

Spectroscopic Characterization of Heterogeneous Catalysts. Part A. Methods of Surface Analysis. Part B. Chemisorption of Probe Molecules, J.L.G. Fierro. Ed.. Elsevier (1990). (Part A on surface structure methods, surface groups on oxides. X-ray, Mdssbauer Part B on Infrared, NMR, EPR, thermal desorption,. ..)... 

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