Desorption uranium oxides

Uranium oxides have been investigated as catalysts and catalyst components for selective oxidation. They are more commonly used as catalyst components, but there are also reports of uranium oxide alone as a selective oxidation catalyst The oxidation of ethylene over UO3 has been studied by Idriss and Madhavaram [40] using the technique of temperature programmed desorption (TPD). Table 13.3 shows the desorption products formed during TPD after ethylene adsorption at room temperature on UO3. The production of acetaldehyde from ethylene indicates... 

Madhavaram H, Idriss H (1997) Temperature programmed desorption of ethylene and acetaldehyde on uranium oxides. Evidence of furan formation from ethylene. Stud Surf Sci Catal 110 265... 

Temperature Programmed Desorption of Ethylene and Acetaldehyde on Uranium Oxides. Evidence of Furan Formation from Ethylene. 

In comparison to the bismuth molybdate and cuprous oxide catalyst systems, data on other catalyst systems are much more sparse. However, by the use of similar labeling techniques, the allylic species has been identified as an intermediate in the selective oxidation of propylene over uranium antimonate catalysts (20), tin oxide-antimony oxide catalysts (21), and supported rhodium, ruthenium (22), and gold (23) catalysts. A direct observation of the allylic species has been made on zinc oxide by means of infrared spectroscopy (24-26). In this system, however, only adsorbed acrolein is detected because the temperature cannot be raised sufficiently to cause desorption of acrolein without initiating reactions which yield primarily oxides of carbon and water. 

The sorption and desorption behavior of uranium is similar to neptunium. Figure 3 shows that hysteresis is more important for uranium sorption under reducing conditions than under oxidizing conditions. Values of Ng/Nd are 10 and approximately 200 for oxidizing and reducing conditions, respectively. 

Figure 3. Sorption and Desorption Isotherms for Uranium Sorption on Mabton Interbed Solids, (a) Oxidizing Conditions, (b) Reducing Conditions.

Another example is found in the analysis of the mineral zircon. We had previously published [4] a spectrum of a positive ion laser desorption spectrum of a sample of the mineral zircon (zirconium silicate) showing uranium as 238U+, present in the sample at a level of approximately 15 parts-per-million [41]. The spectrum, which showed mixed zirconium oxides and hydroxides as the most intense peaks in the spectrum, was taken with a four second delay between the laser pulse and ion detection, in order to allow neutrals to be pumped out of the cell. These conditions had been found adequate for analysis of organic compounds. However, it was found that the reactivity of zirconium was such that the mixed oxides and hydroxides were produced as ion-molecule reaction products during the long trap period. 

Several examples for desorption of this type are given below 1) desorption of organics from activated carbon by methanol (Sudo and Suzuki, 198S), 2) concentrating desorption of uranium from the resin adsorbent used for recovery of uranium from sea water by using an acid solution (Suzuki et al, 1986), and 3) desorption of ammonium ion from the clinoptilolite used for water treatment by sodium chloride solution (Ha and Suzuki, 1984). Also, alkaline desorption for phenols adsorbed on the activated carbons or acid desorption of phosphate trapped on zirconium oxide adsorbent and many other examples may be analyzed by similar methods... 

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