Homogeneous activation

All our measurements i/ere carried out in rooms with i < 1 hr1 and the radon concentration outdoors (c 5 Bq nr 3) i/as always much smaller than indoors (cj > 100 Bq m 3). Assuming a constant radon emanation, a homogeneous activity distribution and 100 % prefiltering of the free fractions of the incoming air, the radon, the free and attached radon daughter activity concentrations indoors (cj cjf cja) and outdoors (eg c f c a) under steady conditions are ... 

Additional insight can be obtained by comparing the electrochemical and homogeneous activation parameters. Table II... 

Figure 1. Homogeneous activation of commercial hydrogen peroxide (7 mM H2O2) in 50mMNa2SO4 acid solution ( pH 2 and room temperature), in the presence of ( ) 1 mMFe, ( ) ImMFe. ...

Polanyi (27) as early as 1921 suggested that the activated state consists of free atoms which are adsorbed or bound by large affinities (heat of adsorption or diminution of the homogeneous activation energy) to the catalyst. A more quantitative treatment became possible after the theory of wave mechanics presented equations for the mutual interaction of different covalent bonds. London (28) showed that the total interaction energy of three atoms X, Y, and Z is... 

Many transition metal complexes catalyze homogeneous activation of molecular hydrogen in solution, forming hydrido complexes. Such complexes include pentacyanocobaltate(II) anion, [Co(CN)5], many metal carbonyls, and several complexes of rhodium, iridium, and palladium. 

According to the classification [5], the spatial structures existing in homogeneous active (in particular, chemical) media are as follows ... 

Data are expressed as percent of homogenate activity per gram liver recovered in each fraction. Recovery is total percent of homogenate activity recovered in the various subcellular fractions. Assays were carried out at pH 6.5 and 38°. Animals had been fasted for 12 hr before use. 

The MWDs of polyolefins produced with some soluble catalysts such as Cp2TiCl2 (Cp = cyclopentadienyl anion)/ A1(C2H5)2C154) and VCljAlfC Hj Cl55) were found to be expressed by Eq. (13). As will be shown in later sections, various soluble catalysts based on titanium and vanadium compounds yield polymers with Q values (Kfw/Mn) near 2.0, indicating that the polymerization of olefin with the respective soluble catalyst proceeds on uniform (homogeneous) active centers. 

Summary of Catalytic Homogeneous Activation of Molecular Hydrogen... 

While geometric factors are undoubtedly of considerable influence in many catalytic systems, it is likely that for homogeneous activation of hydrogen the geometric factor is not prominent, although it may be responsible for lack of activity observed on addition of certain complexing agents to otherwise active systems. 

Grauel and Krischer also detected similar stationary domains during the oxidation of H2 on a Pt ring electrode in sulfuric acid [182]. As can be seen in the cyclic voltammogram in Fig. 46a, in this case the homogeneous active branch coexisted with the oxide covered passive branch, and thus the homogeneous dynamics were bistable. The stationary structure displayed in Fig. 46b spontaneously formed when a... 

Fig. 57. Numerical, one-parameter bifurcation diagram displaying the global current of stable solutions as a function of the applied potential. In the case of the standing waves (SW), the global current is oscillatory and the open circles denote maximum and minimum of the oscillations. (hom.a. = homogeneous active stationary state hom.p. = homogeneous passive stationary state.) (Reproduced from J. Lee, J. Christoph, P. Strasser, M. Eiswirth and G. Ertl, J. Chem. Phys. 115 (2001), 1485 by permission of the American Institute of Physics.)...

A. Ozaki, K. Aika Catalytic Activadon of Dinitrogen The third chapter is a comprehensive and critical review of studies on the catalytic activation of dinitrogen, including chemisorption and coordination of dinitrogen, kinetics and mechanism of ammonia synthesis, chemical and instrumental characterization of active catalysts, and homogeneous activation of dinitrogen including metal complexes (353 references). 

The complex heterogeneous structure of fiber is replaced with an effective homogeneous structure having an equivalent rate of mass transfer. Coefficient of mass diffusion through the effective homogeneous activated carbon fiber is defined as the effective diffusivity (Defr). Detr is then used to explain the mass transfer of adsorbed vapors through the original activated carbon fiber complex structure [6]. 

Furthermore, soluble catalytic systems containing homogeneous active centres yield polymers with very narrow MWD (Q 2) even when they are used in hetero-phasic processes (see Section 4.1.1). 

By solving a differential equation system which describes the above polymerization model for homogeneous active centres (kp = const.), a polydispersity Q value between 1 and 2 was obtained, which cannot explain the MWD of the experimentally obtained polymers (Q = 2.5-5.0). On the other hand, even an exponential distribution... 

For example, Soga et al. > found, by examining propylene polymerization in toluene in the temperature range 0-65 °C with an apparently soluble catalyst such as tetrabenzylzirconium, that the isotactic index and the polydispersity of the polymer increased as the polymerization temperature increased. Furthermore, the value of Q > 30 was much greater than that predicted for homogeneous active centres. From these results the authors concluded that the catalyst should be made up of small invisible colloid-type particles. The same interpretation is valid for the surprising results (Q 40) obtainedfor polyethylene, in Isopar solution at 200 °C, with the originally soluble tetrabenzylzirconium-water catalyst. 

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