Desorption, oxidative

Figure 4 Temperature-programmed desorption/oxidation spectra for benzene, toluene, p-xylene, and mesitylene adsorbed on TiOi. (From Ref. 43.)...

Figure 5 Temperature-programmed desorption/oxidation for (a) ethanol and (b) acetaldehyde on TiO2. (From Ref. 48.)...

Reactions such as dissolution, hydrolysis, precipitation, photolysis, adsorption/desorption, oxidation-reduction, ion exchange, complexation, biodegradation, polymerization, and others taking place in the environment, may affect the solubility of pollutants and therefore their mobility, specia-tion, and toxicity. This, in turn, can define to a great extent the dispersion, bioavailability, and risk associated with them. 

Through redistribution of species in different phases. For instance, through dissolution-precipitation, adsorption-desorption, oxidation-reduction, and complexation and dissociation of coordinated species. 

Temperature programmed desorption Oxidation degree of active sites Activation energy related to oxidation... 

Many solids have foreign atoms or molecular groupings on their surfaces that are so tightly held that they do not really enter into adsorption-desorption equilibrium and so can be regarded as part of the surface structure. The partial surface oxidation of carbon blacks has been mentioned as having an important influence on their adsorptive behavior (Section X-3A) depending on conditions, the oxidized surface may be acidic or basic (see Ref. 61), and the surface pattern of the carbon rings may be affected [62]. As one other example, the chemical nature of the acidic sites of silica-alumina catalysts has been a subject of much discussion. The main question has been whether the sites represented Brpnsted (proton donor) or Lewis (electron-acceptor) acids. Hall... 

Bonn M, Funk S, Hess C, Denzier D N, Stampfl C, Soheffler M, Wolf M and ErtI G 1999 Phonon versus eleotron-mediated desorption and oxidation of CO on Ru(OOI) Science 285 1042... 

The first step consists of the molecular adsorption of CO. The second step is the dissociation of O2 to yield two adsorbed oxygen atoms. The third step is the reaction of an adsorbed CO molecule with an adsorbed oxygen atom to fonn a CO2 molecule that, at room temperature and higher, desorbs upon fomiation. To simplify matters, this desorption step is not included. This sequence of steps depicts a Langmuir-Hinshelwood mechanism, whereby reaction occurs between two adsorbed species (as opposed to an Eley-Rideal mechanism, whereby reaction occurs between one adsorbed species and one gas phase species). The role of surface science studies in fomuilating the CO oxidation mechanism was prominent. 

Figure A3.10.25 Arrhenius plots of CO oxidation by O2 over Rli single crystals and supported Rli/Al203 at PCO = PO2 = 0.01 atm [43]. The dashed line in the figure is the predicted behaviour based on the rate constants for CO and O2 adsorption and desorption on Rli under UHV conditions.

Fig. 4.25 Adsorption isotherms showing low-pressure hysteresis, (a) Carbon tetrachloride at 20°C on unactivated polyacrylonitrile carbon Curves A and B are the desorption branches of the isotherms of the sample after heat treatment at 900°C and 2700°C respectively Curve C is the common adsorption branch (b) water at 22°C on stannic oxide gel heated to SOO C (c) krypton at 77-4 K on exfoliated graphite (d) ethyl chloride at 6°C on porous glass. (Redrawn from the diagrams in the original papers, with omission of experimental points.)...

Pulse radiolysis results (74) have led other workers to conclude that adsorbed OH radicals (surface trapped holes) are the principal oxidants, whereas free hydroxyl radicals probably play a minor role, if any. Because the OH radical reacts with HO2 at a diffusion controlled rate, the reverse reaction, that is desorption of OH to the solution, seems highly unlikely. The surface trapped hole, as defined by equation 18, accounts for most of the observations which had previously led to the suggestion of OH radical oxidation. The formation of H2O2 and the observations of hydroxylated intermediate products could all occur via... 

A more simplified description is a unit that combusts materials in the presence of oxygen at temperatures normally ranging from 800 to 1650°C. A typical configuration of an incinerator is shown in Figure 9. Typical types of incineration units that are discussed herein are catalytic oxidation, fluidized beds, hquid injection, multiple hearth furnaces, and rotary kiln. Thermal desorption is also discussed. However, an overview of the main factors affecting incinerator performance is presented first, below. 

Ethylene oxide Lab method using charcoal absorbent tubers, solvent desorption and gas chromatography 26... 

A secondary fan draws the air and forces it through the secondary heat exchanger, where the reduced air volume temperature is raised to the required desorption temperature. The preheated air is then used to desorb the air in one portion of the wheel. As the air exits the desorption section the organic concentration is approximately 10 times the concentration of the original process stream. This low volume, higher concentration stream then enters the induced draft section of a catalytic or thermal recuperative oxidizer, where the organics are destroyed. 

The ZGB lattiee gas model is an oversimplified approaeh to the aetual proeesses involved in the eatalytie oxidation of CO. Consequently several attempts have been made in order to give a more realistie deseription. Some of them are the following (i) The inelusion of A desorption [19,38-40] eauses the first order IPT to beeome reversible and slightly rounded, in qualitative agreement with experiments (Fig. 3). (ii) The influenee of lateral interaetions between reaetants adsorbed on the eatalyst surfaee have been eonsidered by various authors, e.g., [38,41,42]. (iii) Studies on the influenee of the fraetal nature of the eatalyst surfaee were motivated by the faet that most eatalysts are eonstituted by small fraetal (metallie) elusters dispersed on a fraetal support. The fraetal surfaees have been modeled by means of... 

---