Characterization oxygen chemisorption

Another way of investigating structure is through the classical method on metals of varying catalyst particle size. The key to this method is to measure active catalyst surface areas in order to determine changes in turnover rates with ensemble size. In recent years several chemisorption techniques have been developed to titrate surface metal centers on oxides (25). In this volume Rao and Narashimha and Reddy report on the use of oxygen chemisorption to characterize supported vanadium oxide. 

The surface structure and reactivity of vanadium oxide monolayer catalysts supported on tin oxide were investigated by various physico-chemical characterization techniques. In this study a series of tin oxide supported vanadium oxide catalysts with various vanadia loadings ranging from 0.5 to 6. wt.% have been prepared and were characterized by means of X-ray diffraction, oxygen chemisorption at -78°C, solid state and nuclear magnetic resonance... 

Vanadium Catalysts Supported on Titanium (Anatase) Characterized by Ammonia and Low-Temperature Oxygen Chemisorption... 

The experimental apparatus and the silver catalyst preparation and characterization procedure is described in detail elsewhere (10). The porous catalyst film had a superficial surface area of 2 cm2 and could adsorb approximately (2 +. 5) 10-b moles O2 as determined by oxygen chemisorption followed by titration with ethylene (10). The reactor had a volume of 30 cm3and over the range of flowrates used behaved as a well mixed reactor (10, 11). Further experimental details are given in references (10) and (11). 

One of the best ways of characterizing a supported catalyst is determination of dispersion and effective surface area of the catalyticaUy active component. The dispersion of metal oxide catalysts can be determined by selective chemisorption of oxygen at appropriate temperatures [14-16]. The dispersions obtained from oxygen chemisorption measurements on various catalysts are presented in table 1. The N2 BET surface areas of various samples are also shown in this table. As can be noted, dispersion for 20 wt% catalyst is similar, within experimental limitations, irrespective of their origin. The BET surface area measurements also reveal that both the preparation methods yield similar type of catalysts in terms of physico-chemical characteristics. These catalysts were further evaluated for selective oxidation of / -methox doluene to p-... 

Characterization of Supported Metal Catalysts. - Chemisorption of different probe molecules and Temperature Programmed Reduction (TPR) studies are frequently used to study the metal dispersion, surface composition and oxidation state of metals in mono- and bimetallic supported catalysts. Combined use of CO, hydrogen and oxygen chemisorption as well as oxygen-hydrogen titration can provide information about the dispersion and surface composition of metal nanoclusters. TPR studies of bimetallic catalysts can give information about the type, the reducibility, and the oxidation state of metal components. In addition, the position of TPR peaks can be used to characterize the type of interactions of the metal species in the catalysts. - ... 

Chary, K.V.R., Rama Rao, B., and Subrahmanyam, V.S. Characterization of supported vanadium oxide catalysts by a low-temperature oxygen chemisorption technique, ni. The V205/Zr02 sysi m.. Appl Catal 1991, 74, 1-13. 

The existence of various temperature intervals characterized by predominant manifestation of one of above interactions can be detected from thermal desorption spectra. For instance, the thermal desorption spectrum obtained in [71] for a cleaved ZnO (1010) monocrystal following its interaction with oxygen (Fig. 1.4) indicates the availability of such typical temperature intervals as interval of physical adsorption (a), chemisorption (b), interval of formation of surface defects (c) and, finally, the domain of formation of volume defects (d). 

In order to understand the catalytic behaviour of oxygen-treated WC and Mo2C, a characterization of the catalysts was performed. The BET surface areas and amounts of CO chemisorption are reported in Table 21.3. 

Wolkenstein and Kogan 114) have given a generalized treatment of the influence of irradiation on chemisorption on semiconductors, and their theory does in fact provide for the dual existence of photodesorption and photoadsorption in one and the same chemical system. This treatment relates the direction of the photoeffect to the concentrations of adsorbed particles in the weak and strong forms of chemisorption which characterize Wolkenstein s theory of catalysis. For the case of oxygen (an electron... 

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