| Popis: |
In the present paper the final goal is to use the hydrogenolysis of hydrocarbons as a diagnostic tool for characterizing the metallic surface, i.e. to give a technique for drawing conclusions about the character of a metallic surface itself from the observed kinetic parameters. The main features are as follows: Surface properties of a transition metal are essentially determined by the electron structure and geometry of the bulk, members of the group VIII metals possess, therefore, apriori activity in the hydrogenolysis of a given hydrocarbon. Vulcano shaped curves observed in the hydrogenolysis of ethane, n-pentane, may, therefore, be an indication that neither too strong, nor too weak interaction between the catalyst surface and the substrate is good for the optimum catalyst performance. In addition to the ability of a metal in the “weak” to “strong” type of interconvension conceptualized earlier, the kinetic parameters may be influenced by some additional factors e.g. temperature, hydrogen pressure and the aging of the catalyst. A systematic change in the catalyst structure of platinum and ruthenium results in a characteristic variation in the activity of ethane and n-butane hydrogenolysis as well as in selectivity. By carefully analysing the limiting factors mentioned the effect of different supports, metallic dispersion, impregnating substrate, alloying with iron and rhenium and adsorbed sulphide on the activity and selectivity was determined. |
