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Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

“…Isolated and highly dispersed transition metal ions/oxide on oxide supports (e.g., Al 2 O 3 and SiO 2 ) are frequently the active sites or the phases of catalysts for many kinds of reactions including the selective oxidation of hydrocarbons [12,13]. Similar to the transition metal ions substituted in molecular sieves, the characterization of the active sites in isolated and highly dispersed forms is also important in gaining insight into their catalytic natures.…”

Antimony Oxide-Modified Vanadia-Based CatalystsPhysical Characterization and Catalytic Properties

“…This is consistent with the complete disappearance of Sb 2 O 3 Raman lines and the very strongly reduced intensities of Raman lines characterizing V 2 O 5 . The reason for this observation is the spreading of both oxides across the support anatase surface as already demonstrated by XPS . The spreading process is more efficient in the presence of 10 wt % H 2 O during milling.…”

“…Most industrial catalysts used for PA synthesis are V/TiO 2 modified by antimony oxide, − which is believed to enhance the PA selectivity and vanadium antimonate-type catalysts are known as selective oxidation and ammoxidation catalysts. − Despite the technical importance of the ternary Sb−V/TiO 2 catalyst system, the structure and physical characteristics of this material have only sparely been investigated. , …”

Selective oxidation of o-xylene to phthalic anhydride: from conventional catalysts and technologies toward innovative approaches

“…The amount of cesium oxide, one key promoter, decreases from the top downwards, to the bottom layer; other important promoters are K, P and Sb. 46,47 The main roles of dopants are: (a) to moderate the activity in the top layer and enhance it in the bottom layer, thus helping to avoid excessively high temperatures in hot spots; (b) to inhibit the parallel oxidative degradation reactions to carbon oxides and maleic anhydride byproducts in the top layer, and limit the consecutive hydrolysis and oxidative degradation occurring on PA in the bottom layer; and (c) to accelerate the subsequent steps from o-xylene to PA, by facilitating the re-adsorption and oxidation of intermediates. In some cases, promoters may have a significant effect even when present in low amount; this is the case of Cs, and this effect is likely due to a delocalized effect (collective properties) rather than to a specific interaction with active sites (e.g.…”