Site densities, rate determining steps

Site Density and Entropy Criteria in Identifying Rate-Determining Steps in Solid-Catalyzed Reactions... 

For Example 9 the order is 0.7, suggesting a model for which the logL value is between that for Step 2 (0.5 order, log L = 15) and Step 1 (1.0 order, log L = 22). Thus, the rate-determining step may be a reaction on a partially filled surface. Since the log L value calculated in this way for 0.7 order is rather large, some surface mobility and/or rotation is indicated. The zero-order reactions of Examples 11 and 19 are clearly surface reactions for which expected site densities are obtained. For Example 11 Tottrup (25) suggested that the rate-determining step is C-O scission in adsorbed CO. 

Site Density and Entropy Criteria in Identifying Rate-Determining Steps in Solid-Catalyzed Reactions Russell W. Maatman Organic Substituent Effects as Probes for the Mechanism of Surface Catalysis M. Kraus... 

It is assumed that this is also a rate determining step for the overall reaction. The activation energy of reaction (4) and the site density of oxygen active centers were the only adjustable parameters of the model. In general, a C-H bond scission for reactants and products of the methane dimerization process occurs by an Eley-Rideal (E-R) type mechanism to form a gas-phase alkyl radical and a hydroxyl surface site (HO ) ... 

Copper(I) complexes catalyse a variety of organic reactions which are of synthetic and industrial importance.305 In such processes that involve halide abstraction from aryl or alkyl halides, the abstraction step by a Cu(I) catalyst is believed to be the rate-determining step. In order to circumvent the property of facile disproportionation of Cu, various methods of stabilising Cu(I) and influencing reaction rates were considered.306 A kinetics study of ligand (L) effects on the reactivity of Cu(I)L complexes towards C13CC02 was undertaken. The results indicated that the rate of the chlorine abstraction reaction was affected by several factors. These were the redox potential of the Cu(II/I)L couple, the hybridisation on Cu(I) in the Cu(I)L complex, steric hindrance, and electron density on the central Cu(I) cation at the binding site of the chlorine atom to be abstracted. The volume of activation,... 

The results demonstrate that the rate of the chlorine abstraction reaction (Eq. (47)), which is usually the rate determining step in this process, is affected by (a) the redox potential of the Cu L couple (solvents such as acetonitrile, that form complexes with Cu and anodically shift its redox potential, decrease the reactivity), (b) the hybridization on Cu in the Cu L complex, (c) steric hindrance, (d) electron density on the central Cu cation, at the binding site of the chlorine atom to be abstracted (149). However for the complex Cu(I)L, which is the strongest reducing agent studied, the stability of the L Cu -CCl2C02 transient is increased considerably and its decomposition becomes the rate determining step (149). 

The hysteresis effect in the anode potential vs. current density curves is attributed to the fact that water (or OH") does not easily discharge on occupied sites. With the experimental evidence discussed, Conway and Dzieciuch have concluded for the aqueous formate reaction that the lower slope region corresponds to the rate-determining step... 

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