Heterogeneous Reaction Parameter Research Articles

Immobilization of denatured DNA to macroporous supports: II. Steric and kinetic parameters of heterogeneous hybridization reactions

The accessibility of immobilized DNA has been shown to depend more crucially on the method of immobilization than on the type of support used for fixation. When sonicated denatured DNA is coupled via diazotization or via cyanogen bromide reaction to solid Sephadex G-25 and Cellex 410 or to macroporous Sephacryl S-500 and Sepharose C1-6B its accessibility varies from 100 to 24 percent. Generally the loss of accessibility is linked to a depression of the melting temperature of DNA helices formed on the support. This correlation shows a characteristic course for a particular coupling method. DNA coupled under denaturing conditions may become totally inaccessible when only 3 percent of its bases are involved in the covalent linkage. Kinetic experiments with sonicated E.coli DNA have shown that the rate constants for renaturation or hybridization reactions are very similar for DNA immobilized by different methods to solid or macroporous supports. Generally the second order rate constant for a heterogeneous reaction (between mobile and immobilized DNA) is about one order of magnitude smaller than that of the analogous homogeneous reaction (in solution).

Effects of an external circuit on the dispersion of soluble matter in a magnetohydrodynamic channel flow with homogeneous and heterogeneous reactions

An analysis of the effects of the first-order homogeneous irreversible chemical reaction and the heterogeneous chemical reaction on the effective Taylor diffusion coefficient is carried out in a magnetohydrodynamic channel flow characteritic of a MHD generator. On taking into account the external circuit, the effects of M (the Hartmann number), γ (homogeneous reaction rate parameter), β (heterogeneous reaction parameter), R ∗ (resistance), and V g ∗ (generator voltage) are discussed quantitatively in all cases of the magnetohydrodynamic channel flows. Results are compared with those when γ = 0, β = 0. It is observed that the effective Taylor diffusion coefficient is affected more significantly by the first-order homogeneous chemical reaction than that by the heterogeneous chemical reaction.

The static microreactor technique a new, simple method for determination of kinetic parameters of gas-phase heterogeneous catalytic reactions

The dehydrogenation of methanol on a silver catalyst was studied in a static microreactor at 376–457°C, with initial methanol partial pressures of 60–90 Torr. The apparent activation energy agrees well with literature data. The experimental data suggest that the static microreactor is a suitable means for the rapid acquisition of preliminary kinetic data.

Sur des causes d'erreurs lors de determinations par analyse thermogravimetrique des parametres cinetiques de diverses reactions

Thermogravimetric analysis is widely used to determine the kinetic parameters of heterogeneous reactions. When this method is applied, the experimental conditions are chosen so that the study is not disturbed by external diffusion. In this paper some other sources of error are emphasized which can affect the determination of the kinetic parameters, and which are related to the influence of the atmosphere in which the reaction takes place and to the physico-chemical mechanism of the reaction itself.