Heterogenous Kinetics

A homogeneous reaction occurs in one phase. Heterogeneous kinetics have been studied much less. 

G. R. Belton and W. L. Worrel, eds., Heterogeneous Kinetics at Elevated Temperatures, Plenum Press,... 

Kenji O, Kazuya I, Yoshihiro Y, Hiroshi B, Rokuro N, Yasuaki M (2005) Sonochemical degradation of azo dyes in aqueous solution a new heterogeneous kinetics model taking into account the local concentration of OH radicals and azo dyes. Ultrason Sonochem... 

Hence, the macroscopic model of Bond and Hill reinterpreted the data in Figure 3.96 in terms of a cross-over between the limiting forms of mass transport, i.e. linear to radial diffusion, and not in terms of a slowing down in the heterogeneous kinetics. 

In this chapter we consider the problem of the kinetics of the heterogeneous reactions by which minerals dissolve and precipitate. This topic has received a considerable amount of attention in geochemistry, primarily because of the slow rates at which many minerals react and the resulting tendency of waters, especially at low temperature, to be out of equilibrium with the minerals they contact. We first discuss how rate laws for heterogeneous reactions can be integrated into reaction models and then calculate some simple kinetic reaction paths. In Chapter 26, we explore a number of examples in which we apply heterogeneous kinetics to problems of geochemical interest. 

Heterogeneous kinetic rate law, 25 286 Heterogeneous nuclear RNA (hnRNA), 22 454... 

In analyzing the kinetics of surface reactions, it will be illustrated that many of these processes are rate-controlled at the surface (and not by transport). Thus, the surface structure (the surface speciation and its microtopography) determine the kinetics. Heterogeneous kinetics is often not more difficult than the kinetics in homogeneous systems as will be shown, rate laws should be written in terms of concentrations of surface species. 

Laurendeau N.M., Heterogeneous Kinetics of Coal Char Gasification and Combustion , Prog. Energy Combust. Sci. 4, 221-270(1978). 

Here sub/superscripts 1 and 2 denote carbon oxidation by oxygen and by carbon dioxide, respectively Ai, Tsi), Aci (Tsi), Ac2 Tsi) are the Arrhenius functions for heterogeneous kinetics depending on the surface temperature... 

Adsorption phenomena are important in most Ziegler-Natta polymerizations, and this requires treatment by heterogeneous kinetics [Bohm, 1978 Boor, 1979 Chien and Ang, 1987 Chien and Hu, 1987 Cooper, 1976 Keii, 1972 Tait and Watkins, 1989]. The exact form of the resulting kinetic expressions differs depending on the specific adsorption... 

X-ray diffraction, 39 160-161, 164-165 Radial factor, 22 214-218 Radiation, see also Irradiation cosmic, see Cosmic radiation terrestial origin, 3 288-293 Radiation chemistry, heterogeneous kinetics of, 3 198-203... 

While many techniques have evolved to evaluate surface intermediates, as will be discussed below, it is equally important to also obtain information on gas phase intermediates, as well. While the surface reactions are interesting because they demonstrate heterogeneous kinetic mechanisms, it is the overall product yield that is finally obtained. As presented in a text by Dumesic et al. one must approach heterogeneous catalysis in the way it has been done for gas phase systems, which means using elementary reaction expressions to develop a detailed chemical kinetic mechanism (DCKM). DCKMs develop mechanisms in which only one bond is broken or formed at each step in the reaction scheme. The DCKM concept was promoted and used by numerous researchers to make great advances in the field of gas phase model predictions. 

Because of the gaseous nature of many of the important primary and secondary pollutants, the emphasis in kinetic studies of atmospheric reactions historically has been on gas-phase systems. However, it is now clear that reactions that occur in the liquid phase and on the surfaces of solids and liquids play important roles in such problems as stratospheric ozone depletion (Chapters 12 and 13), acid rain, and fogs (Chapters 7 and 8) and in the growth and properties of aerosol particles (Chapter 9). We therefore briefly discuss reaction kinetics in solution in this section and heterogeneous kinetics in Section E. 

However, if one applies the heterogeneous kinetics reported by Takagi et al. (1986), one can calculate that methyl nitrite concentrations of the order measured in the exhaust sample could arise by reactions of unburned methanol and N02 on the walls of the sampling bag prior to analysis (Finlayson-Pitts et al., 1992). 

Fenter, F. F., F. Caloz, and M. J. Rossi, Heterogeneous Kinetics of N205 Uptake on Salt, with a Systematic Study of the Role of Surface Presentation (for N205 and HNO,), ./. Phys. Chem., 100, 1008-1019 (1996). 

If, however, carbon anodes are used, the initial radicals RCHCH2N, are only weakly adsorbed and not stabilized in the adsorbed state. The adsorption of the intermediate radicals that are formed in consecutive steps is predominant and the adsorbed radicals are readily oxidized. The consecutive reactions of the carbenium cations then proceed according to heterogeneous kinetics at the surface of the carbon anode (218, 219). 

The Ru problem was treated in detail by Nicholson [36] using theoretical methods. He found that the IRU term has approximately the same effect on LSV and CV waves as quasi-reversible charge transfer [36]. Thus, an effective means of handling this problem is of especial importance to heterogeneous kinetic studies. 

Experimental data for the reduction of benzonitrile in lV,N-dimethyl-formamide (DMF)—Bu4NBF4 (0.1 M) are given in Table 4 and the results of the two correlation methods are summarized in Tables 5 and 6. This system will be discussed in the section dealing with heterogeneous kinetics. 

Variation of cyclic voltammetry peak potential separation with the heterogeneous kinetic parameter i//... 

HETEROGENEOUS KINETICS OF THE REDUCTION OF PERYLENE IN APROTIC SOLVENTS... 

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