Decomposition ozone

The presence of ozone (O3) in the upper atmosphere is beneficial since it absorbs ultraviolet radiation. However, the presence of ozone, which can be emitted by equipment, such as photocopiers and laser printers, close to the ground is harmful, as it causes respiratory illness and enhances photochemical pollution [2,543]. The allowable concentration in a working environment and regulation threshold level for allowable exposure is 0.1 ppm [543]. 

Ozone is useful since it is a powerful oxidising agent, but the molecule itself is toxic to both animal and plant life and its release into the environment must be avoided. The problem of ozone decomposition is therefore technologically important. For example, ozone needs to be reduced in airplane cabins, submarines and office environments. Discharges from sterilisation, odour removal and waste water treatment units must also have their ozone levels lowered [466,544]. 

Activated carbon and zeolite have been used in adsorbent filters and need regeneration. Catal3dic decomposition has no such disadvantages and, therefore, has attracted great interest. Most of the catalysts are reported in patent literature [547-549]. Research carried out in a variety of catalysts showed insufficient activity and stability when they are used under severe conditions such as a high ozone concentration, large space velocity and in the presence of moisture. 

This group also used gold catalysts for the simultaneous removal of ozone and CO. Petrov did the same and reported that gold and a transition metal-oxide supported on ceria and titania achieved 100% ozone decomposition [551]. 

Engelhard Co. (USA) markets a base metal catalyst system, which converts ozone into oxygen when coated onto a car radiator at the moderate temperatures generated by the radiator [553]. Prom the limited amount of information on the properties of gold catalysts currently available, inclusion of gold in such a catalyst system could make them really effective [543]. 

Although the decomposition of ozone to dioxygen is a thermodynamically favoured process,126 it is thermally stable up to 523 K and catalysts are needed to decompose it at ambient temperature in ventilation systems, in the presence of water vapour and at high space velocity. A limited number of catalysts have been evaluated and active components are mainly metals such as platinum, palladium and rhodium, and metal oxides including those of manganese, cobalt, copper, iron, nickel and silver. Supports that have been used include 7-alumina, silica, zirconia, titania and activated carbon.125,170 

Activated carbon and zeolites have been used in absorbent filters and need to be regenerated but catalytic decomposition has no such 

About 3% Au/V205 supported on titania and zirconia catalysts (c au = 5nm) were very active for the decomposition of ozone at 293 and 303 K, respectively.84,126 

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Only about 10 percent of the input energy is effectively used to produce the ozone. Inefficiencies arise primarily from heat production and, to a lesser extent, from light and sound. Since ozone decomposition is highly temperature dependent, efficient heat-removal techniques are essential to the proper operation of the generator. 

In the schemes considered to this point, even the complex ones, the products form by a limited succession of steps. In these ordinary reaction sequences the overall process is completed when the products appear from the given quantity of reactants in accord with the stoichiometry of the net reaction. The only exception encountered to this point has been the ozone decomposition reaction presented in Chapter 5, which is a chain reaction. In this chapter we shall consider the special characteristics of elementary reactions that occur in a chain sequence. 

Mechanism II begins with fast reversible ozone decomposition followed by a rate-determining bimolecular collision of an oxygen atom with a molecule of NO. The rate of the slow step is as follows Rate = 2[N0][0 This rate expression contains the concentration of an intermediate, atomic oxygen. To convert the rate expression into a form that can be compared with the experimental rate law, assume that the rate of the first step is equal to the rate of its reverse process. Then solve the equality for the concentration of the intermediate ... 

The net reaction for this two-step mechanism is the conversion of an O3 molecule and an oxygen atom into two O2 molecules. In this mechanism, chlorine atoms catalyze ozone decomposition. They participate in the mechanism, but they do not appear in the overall stoichiometry. Although chlorine atoms are consumed in the first step, they are regenerated in the second. The cyclical nature of this process means that each chlorine atom can catalyze the destruction of many O3 molecules. It has been estimated that each chlorine atom produced by a CFC molecule in the upper stratosphere destroys about 100,000 molecules of ozone before it is removed by other reactions such as recombination CF2 Cl -b Cl CF2 CI2... 

The cataiysis of ozone decomposition by chiorine atoms occurs entirety in the gas phase. Chlorine is classified as a homogeneous catalyst because the cataiyst and the reactants are present in the same phase, in this case the gas phase. A heterogeneous catalyst, on the other hand, is in a different phase than the one where the reaction occurs. A heterogeneous cataiyst is usuaiiy a soiid, and the reactants are gases or are dissolved in a liquid solvent. 

C15-0051. Do the following for the ozone decomposition mechanism (a) Express the rate in terms of O2 formation, (b) Relate the rate of O3 consumption to the rate of O2 production, (c) If O2 forms at a rate of 2.7 X 10" M, state how fast ozone disappears. 

The quantum yield of ozone decomposition at 334 nm (L2) is 4, indicating that one of the products must be an excited species capable of decomposing 0 further. The primary process of the 0 photolysis at 334 nm occurs according to the reactions ... 

Van Swaaij, W. P. M., andZuiderweg, F. J., Investigation of Ozone Decomposition in Fluidized Beds on the Basis of a Two-phase Model, Chemical Reaction Eng., Proc. 5th European/2ndInt. Symp. Chem. Reaction Eng., Elsevier, Amsterdam/London/New York (1972)... 

The enthalpy of ozone decomposition AH=Do2—o = 107kJ mol-1. The most probable reaction of initiation by ozone in solution is the abstraction reaction [133] ... 

Due to high activity in reactions with free radicals, ozone undergoes the chain decomposition in solutions also. The chain reaction of ozone decomposition was evidenced in 1973 in the kinetic study of cyclohexane and butanone-2 oxidation by a mixture of 02 and 03 [146-151], It was observed that the rate of ozone consumption obeys the equation [112] ... 

So, three different chain reactions of ozone decomposition were observed in solutions ... 

Regarding ozonization, it is only applied in a limited number of WWTPs after secondary treatment [61]. Several investigations have proven that it is a very effective technique to eliminate pharmaceutical [25, 62, 63]. Oxidation reactions take place due to direct reaction with ozone (03), which are very selective or with free OH radicals, which are generated by ozone decomposition and are very powerful and not selective oxidants. In advanced oxidation processes, 03 is completely transformed onto OH radicals and they are recommended when compounds are ozone resistant. 

Gaseous ozone, decomposition of, 17 770-771 Gaseous pollutants disposal of, 26 690 sampling, 26 674... 

Ozone bleaching technology, 21 46 for recycled pulps, 21 51-52 Ozone contactors/dispersion devices, 17 801-802 Ozone decomposition in acidic solution, 17 773 hydroxyl ion initiated, 17 771—772 Ozone deficit problem, 17 785 Ozone delignification technology, 21 46 Ozone-depleting substances, in release agents, 21 598... 

A knowledge of the kinetics of the decomposition of ozone is essential for the understanding of the chemistry of some important processes which occur in earth s atmosphere. Yet, in spite of numerous studies and the structural simplicity of ozone, the mechanism of its ultraviolet photolysis is still uncertain. Electronically and vibrationally excited species are involved in ozone decomposition and the current knowledge of the chemical behavior of such intermediates is still in its infancy. 

Alder, M. G., and G. R. Hill. The kinetics and mechanism of hydroxide ion catalyzed ozone decomposition in aqueous solution. J. Amer. Chem. Soc. 72 1884-1886, 1950. 

Mechanism of ozone decomposition in water depends on the presence of chemical species that can initiate, promote and/or inhibit its decomposition. The most accepted ozone decomposition mechanism is given in Figrtre 3. 

Figure 3. Scheme of ozone decomposition mechanism in water. P = promoter (e.g. ozone, methanol), S = scavenger or inhibitor (e.g. /-butanol, carbonate ion), I = initiator (e.g. hydroxyl ion, perhydroxyl ion) (adapted by Beltran [35]). 

Tomiyasu, H Fukutomi, H Gordon, G. Kinetics and mechanism of ozone decomposition in basic aqueous soiution. inorganic Chemistry, 1985 24 (19), 2962-2966. 

Rogg, B., A. Linan, and F. A. Williams. 1986. Deflagration regimes of laminar flames modeled after the ozone decomposition flame. Combustion Flame 65 79-101. 

Chain reactions are a t3q)e of overall reactions, which require two or more steps to accomplish. They are also known as consecutive reactions or sequential reactions. Examples of chain reactions include nuclear hydrogen burning, nuclear decay chains, ozone production, and ozone decomposition. Some steps of a chain reaction may be rapid and some may be slow. The slowest step is the ratedetermining step. During a chain reaction, some intermediate and unstable species may be produced and consumed continuously. 

Hanning-Lee, M. A., B. B. Brady, L. R. Martin, and J. A. Syage, Ozone Decomposition on Alumina Implications for Solid Rocket Motor Exhaust, Geophys. Res. Lett, 23, 1961-1964 (1996). 

Note that since the atomic chlorine consumed in reaction 8.5 is regenerated in 8.7, it acts as a catalyst for ozone decomposition. Reaction 8.6 represents the decomposition of ozone by ultraviolet light, so that reactions 8.6 and 8.2 form a dynamic system that accounts for the absorption of ultraviolet light by the ozone layer. 

An explanation begins with chlorofluorocarbons such as Freon-12 (CC12F2), formerly used in refrigerators and air conditioners. These long-lived compounds, which are not found in nature,2 diffuse to the stratosphere, where they catalyze ozone decomposition. 

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