Low-temperature oxygen chemisorption

Monolayer coverage of vanadium oxide on tin oxide support was determined by a simple method of low temperature oxygen chemisorption and was supported by solid-state NMR and ESR techniques. These results clearly indicate the completion of a monolayer formation at about 3.2 wt.% V2O5 on tin oxide support (30 m g" surface area). The oxygen uptake capacity of the catalysts directly correlates with their catalytic activity for the partial oxidation of methanol confirming that the sites responsible for oxygen chemisorption and oxidation activity are one and the same. The monolayer catalysts are the best partial oxidation catalysts. 

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

In this communication, the results of a systematic study of ammonia chemisorption on V2O -Ti02 (anatase) catalysts of different vanadia loading is reported." Low temperature oxygen chemisorption is also utilized to determine the monolayer loading of 20 on Ti02 (anatase). Partial oxidation of methanol to formaldehyde is studied as a model reaction on these catalysts and the activities of the catalysts are correlated with NH and O2 uptakes. 

Low Temperature Oxygen Chemisorption. The same volumetric high vacuum system used for NH chemisorption with the facility for reducing the samples in situ by flowing hydrogen, was used for the study of oxygen chemisorption. The quantity of chemisorbed... 

A similar relationship can be observed with promoted M0S2. Each family of catalysts has its own linear correlation, which cannot be compared to each other directly because of the corrosivity problem. More recently, low-temperature oxygen chemisorption has been claimed to be more reliable, but it also lacks a well-determined stoichiometry (52). Oxygen chemisorption has also been applied to tungsten and rhenium sulfides, as well as promoted molybdenum and tungsten sulfides. In the isotropic class, it has been applied only to ruthenium sulfide, in which case it gives approximately the same result as a BET measurement due to the isotropic nature of this sulfide (41). 

The morphology and surface structure of molybdenum sulfide on two commercial HDN catalysts have been examined. Transmission electron microscopy results indicated that the M0S2 stack length increased and the stack density decreased after commercial use. The changes of the amount of low temperature oxygen chemisorption on HDN catalyst samples showed that the destruction of the microstructure of Mo species took place during the reaction. The reasons of the HDN catalyst deactivation have been discussed. 

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. 

Whilst hydrogen enters into a chemisorptive bond with charcoal at very low temperatures, oxygen remains physically adsorbed unless relatively high temperatures are reached. At liquid-air temperatures the adsorption entropy of oxygens shows that the adsorbed molecules are completely free to move and rotate over the surface 168). 

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