Reactions of environmental importance

Silica-alumina has been used to support the CuO coupled with Ga203, and Sn02 dispersed phases to enhance the catalytic properties of CuO-based catalysts in reactions of environmental importance (hydrocarbon combustion, NO and N2O decomposition and reduction [88]). The acidic properties of such oxide systems were studied from a qualitative (nature of the acid sites) and quantitative (number, acid strength, and strength distribution of acid sites) points of view through the adsorption and desorption of two basic probes (ammonia and pyridine) by coupled volumetric-calorimetric technique and XPS and FT-IR spectroscopy. 

R.M. Lambert, M. Tikhov, A. Palermo, I.V. Yentekakis, and C.G. Vayenas, Electrochemical Promotion of Environmentally Important Catalytic Reactions, Ionics 1, 366-376 (1995). 

Demonstrations of Environmentally-Important Reactions. Classroom demonstrations make an important contribution to students understanding. "NOx and SOx" is a series of demonstrations illustrating the preparation and properties of... 

An HPLC-CL determination of environmentally important chlorophenols was reported by using 10-methyl-9-acridinium carboxylate as a CL label. A two-step derivatization was used to produce the CL derivatives (Fig. 10). Following the separation under reversed-phase conditions, the CL reaction was performed by the base-catalyzed postcolumn oxidation. The quantum efficiency was dependent on the species of analytes. The detection limit of chlorophenols (S/N = 3) ranged from 300 amol to 1.25 fmol per injection (Fig. 11) [52],... 

Lin, S. and Carlson, R.M. Susceptibility of environmentally important heterocycles to chemical disinfection reactions with aqueous chlorine, chlorine dioxide, and chloramine. Environ. Sci. Technol, 18(10) 743-748, 1984. 

We begin with a discussion of the most common minerals present in Earth s crust, soils, and troposphere, as well as some less common minerals that contain common environmental contaminants. Following this is (1) a discussion of the nature of environmentally important solid surfaces before and after reaction with aqueous solutions, including their charging behavior as a function of solution pH (2) the nature of the electrical double layer and how it is altered by changes in the type of solid present and the ionic strength and pH of the solution in contact with the solid and (3) dissolution, precipitation, and sorption processes relevant to environmental interfacial chemistry. We finish with a discussion of some of the factors affecting chemical reactivity at mineral/aqueous solution interfaces. 

Colloidal semiconductor particles have been found to act as heterogeneous photocatalysts in a number of environmentally important reactions. 

Semiconductor particles and films have been found to act as heterogeneous photocatalysts in a number of environmentally important reactions. Materials such as Ti02 and CdS have been found to be efficient in laboratory-scale pollution abatement systems, reducing both organic and inorganic pollutants/impurities to harmless species (see [1-35] and references therein). Photocatalysts have been shown to be useful for decomposition of O3 [36], destruction of bacteria [37-39] and viruses [40], purification of air [41], photosplitting of water [42,43] and clean-up of oil spills [44,45]. Photocat-... 

Temperature dependence of environmentally important reaction rate constants. (A) CO2 reaction with H2O or OH in seawater. The data are plotted so that the sfope of the line is the Arrhenius activation energy, divided by the gas constant, R (8.315 J mor deg ) (Johnson, 1982). (B) HS oxidation (Millero et a/., 1987a). (C) Fe(ll) oxidation in seawater (Millero et o/., 1987b). (D) The dissolution rate constants for opal as a function of temperature. The values plotted here are normalized to a constant area volume ratio, A /V = I0cm . The high dissolution rate constants (circles) are for acid-cleaned siliceous sediments (Hurd, 1972) the squares are data for peroxide and acid-washed plankton (Lawson et a/., 1978) and the other results (triangles) are for two untreated single species of diatom (Kamatani, 1982). 

Classical chemistry literature provides comprehensive lists of rate data that can also be applied for predicting abiotic reaction rates of environmental importance when the pathways are well identified. For some reactions, such as hydrolysis or OH radical reactions, enough data are available to determine siructure-reactivity correlations that enable one to interpolate within series of chemically related compounds of known reactivity [for review, see Brezonik (Chapter 4, this volume) and Lyman et al. (1982)]. The aquatic chemist is, however, more often confronted with the fact that many classical studies have been performed in organic solvents, but that the speciation of many dissolved chemicals in aquatic systems may vary with pH (caboxylic acids, phenols, etc.) and with ligand concentrations (e.g., all dissolved heavy metal species) or that the chemical species may be adsorbed on surfaces or absorbed by colloidal organic materials. In all these cases, reaction-rate constants must be determined for each individual aqueous species contributing to the overall kinetics. The equilibrium distribution of these species must also be accounted for. Reductions of the... 

Electrophilic aromatic substitutions are reactions of great importance for industry and ionic liquids have been used in these reactions as alternative reaction media, mainly with the aim of reducing the environmental impact of these processes. Only few reactivity data, which might be used to quantitatively estimate the effect of the ionic reaction medium on these reactions, have been collected. 

Bc2 produced by flash photolysis of seawater decays by parallel first- and second-order reactions. The environmentally important exponential decay is a pseudo first-order reaction of Br2 with the carbonate/ bicarbonate system in seawater. A chemical speciation model for the free ions and ion-pairs in seawater and in solutions at seawater ionic strength allowed us to measure the dependence of the pseudo first-order rate term, a, on individual C02-containing species. A predictive equation based on reaction of Br2 with free C03 and the hgC03°, NaC03 and CaC03 ion pairs accounts for the mean seawater a at pH 8.1 within experimental uncertainty. The reaction productfs) are unknown. 

Sparks DL, Fendorf SE, Zhang PC, Tang L. (1993). Kinetics and mechanisms of environmentally important reactions on soil colloidal surface. In Migration and Fate of Pollutants in Soils and Subsoils, Vol. 32, NATO ASI Series G (eds. D Petruzzeli, F Helfferich). Berlin, Germany Springer-Verlag, pp. 141-168. 

Nguyen QT, Manning BA (2003) Spectroscopic and modeling study of lead adsmption and precipitation reactions on mineral soil. Biogeochemistry of environmentally important trace... 

Accordingly, to accurately predict the fate, mobility, speciation, and bioavailability of environmentally important metals and semi-metals in terrestrial and water environments, one must understand the kinetics and mechanisms of the reactions. This chapter focuses on nonequilibrium aspects of metal sorption/desorption and the confirmation of reaction mechanisms using in-situ atomic/molecular level spectroscopic and microscopic techniques. 

---