Catalytic ozonation

Since the recognition of the role of chlorine in catalytic ozone destruction, increasing effort has been devoted to finding replacements. In most cases reported so far, the replacements are partially halogenated molecules that retain one or more hydrogen atoms (HCFCs and HFC s). The presence of H-atoms gives HO a handle (via H-atom abstractions such as R4) for their tropospheric... 

This simple oxygen-only mechanism consistently overestimates the O3 concentration in the stratosphere as compared to measured values. This implies that there must be a mechanism for ozone destruction that the Chapman model does not account for. A series of catalytic ozone-destroying reactions causes the discrepancy. Shown below is an ozone-destroying mechanism with NO/NO2 serving as a catalyst ... 

It is interesting to compare the rate constants of the oxygen-only ozone destruction reaction with those of the catalytic ozone destruction cycle. The rate constants for reactions 4-6 at 30 km are given below in units of cm molecules s . 

In 1974, Cicerone and Stolarski suggested that if there were sources of atomic chlorine in the stratosphere, the following catalytic ozone destruction cycle... 

Halogen atoms released by photolysis give rise to catalytic ozone depletion in cycles such as [1,14]... 

Volk et al. (1997) assessed the effects of ozone, ozone/hydrogen peroxide, and catalytic ozone by changes in the organic constituents of a synthetic solution of fulvic acids. Initial dissolved organic carbon (DOC) and... 

Figure 14.26). The oxidation system that generated the highest BDOC concentration was ozone/hydrogen peroxide, while catalytic ozone produced the lowest concentrations with ozone doses greater than 3.5 mg/L, BDOC levels were 0.90, 0.80, and 0.60 mg/L for ozone/hydrogen peroxide, ozone, and catalytic ozone, respectively. Catalytic ozone induced oxidation of ozone by-products into COz. 

DOC reduction vs. applied ozone dose for a fulvic acid solution treated with ozone, ozone/ hydrogen peroxide, or catalytic ozone. Contact time = 10 min pH = 7.5 initial DOC = 2.84 mg/ L. (From Volk, C. et al., Water Res., 31(3), 650-656, 1997. With permission.)... 

Ni, C.H. and Chen, J.N., Heterogeneous catalytic ozonation of 2-chlorophenol aqueous solution with alumina as a catalyst, Water Sci. Technol., 43(2), 213-220,2001. 

Volk C, Roche P, Joret JC, Paillard H. Comparison of the effect of ozone, ozone-hydrogen peroxide system and catalytic ozone on the biodegradable organic matter of a fulvic acid solution. Water Res 1997 31 650-656. 

Legube B, Karpel Yel Leitner N. Catalytic ozonation a promising advanced oxidation technology for water treatment. Catal Today 1999 53 61-72. 

Theoretical and experimental studies of the interactions between water molecules and hydrogen chloride are of fundamental importance for the understanding of the production of stratospheric chlorine molecules which, in turn, take part in the catalytic ozone depletion reactions. This mainly heterogeneous atmospheric reaction begins with the adsorption of the HCl molecules on the surface of water icicles is the source of the stratospheric chlorine atoms in the polar regions380 - 382. Chlorine molecules are photolysed by solar radiation and the resultant chlorine atoms take part in the destruction of the stratospheric ozone. The study of the (H20) HC1 clusters is an important step towards understanding of the behavior of the HCl molecule on the ice surface383- 386. 

Bromine compounds, when diffused to and photolyzed in the stratosphere, can produce Br atoms that participate in catalytic ozone destruction that can reach efficiencies that are 40-50 times more effectively than Cl atoms [9,22-24]. The stratospheric chemistry of brominated organic compoimds is similar to that of... 

Delanoe F., Acedo B., Karpel N., Leitner V., Legube B. et al.. Relationship between the structrre of Ru/CeOj catalysts and their activity in the catalytic ozonation of succinic acid aqueous solution. Appl. Catal. B Environ., 29 (2001)pp. 315-325. 

The major chemical cycles describing catalytic ozone destruction by HOx, NOx and ClOx are now reasonably well characterized. The development of sophisticated computational models has facilitated the unification of field studies with laboratory experiments. At high altitudes where the... 

Catalytic Ozonation. Ozonation is a well established method especially for drinking water and is substituting in many applications the use of chlorine-based reactants for water sterilization. The interest in combining ozone with the use of... 

The data by Orcutt et al. (06) for catalytic ozone decomposition have been processed in the same manner. Those by van Swaay and Zuiderweg (V7, V8) for ozone decomposition are treated as follows. Their data are presented in terms of an apparent HTU, (//ob)app. as defined by... 

With the catalytic ozone analyzer described, ozone concentration can be measured by the temperature differential between two thermistors placed in the gas stream. One of the thermistors is coated with a catalyst promoting the decomposition of ozone the other is uncoated and is used as reference to the temperature of the gas. The two thermistors are part of a bridge circuit, the output of which is fed directly to a recorder. The instrument is not affected by the presence of water vapor, carbon monoxide, chlorine, nitrogen dioxide, sulfur dioxide, organic peroxides, hydrocarbon vapors, and combustion smokes at their usual concentrations in polluted atmospheres. 

Treatment of Lamffill Leachates. Landfill leachate contains large quantities of nonbiodegradable and toxic constituents. Some heterogenous catalytic ozonation processes (Ecoclear or Catazone systems) can successfully treat landfill leachates. " In addition, ozone-based AOPs have also been successfully used to remove COD or TOC either as pretreatment or at the final stage of the treatment. Both heterogenous catalytic ozonation and the AOP processes are introduced below. 

In fact, heterogenous catalytic ozonation introduced above is a novel type of AOP, because a large amount of radicals are produced during the processes. ... 

Legube, B. Leitner, N.K.V. Catalytic ozonation a promising advanced oxidation technology for water treatment. Catal. Today 1999, 53, 61-72. Rice, R.G. Graham, D.M. U.S. FDA Regulatory approval of ozone as an antimicrobial agent— what is allowed and what needs to be understood. Ozone News 2001, 29, 22-31. 

Zhang, T. and Ma, J., Catalytic ozonation of trace nitrobenzene in water with synthetic goethite, J. Mol. Catal. A, 279, 82, 2008. 

The first of these reactions will result in the generation of a single ozone molecule. The second reaction produces the NO that leads to catalytic ozone destruction. The relative rates of these two reactions is in an approximate ratio of 9 1, favoring the first. Since NO is a catalyst for O2 destruction (a single NO will destroy many ozone molecules before being removed), N2O is believed to exert a significant control on stratospheric O3 concentrations. 

As in the discussion of gas-phase chemistry, a complete understanding of ozone depletion requires consideration not only of how much CIO is present (i.e., C10/Cly), but also of the catalytic cycles in which CIO may engage. Solomon et al (1986) emphasized the catalytic ozone destruction initiated by the reaction between HO2 and CIO. However, this process cannot destroy enough ozone early enough in the spring season to be consistent with the seasonality of the ozone loss process as shown above in Figure 6.11. 

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