Chemical effects at the solid/solid phase boundary

The phase boundary between solid/solid bodies affects kinetic or catalytic properties although, of course, thermodynamic potentials are unaffected. For example, the activation energy in the formic acid reaction over silver is lowered if supported on a p-type semiconductor and raised if supported on an n-type semiconductor. The effect is found if there is a much larger proportion of semiconductor so that the lower electron concentration can have an effect on the metal. Similar effects have been found for the inverse such as in the oxidation of carbon monoxide over an oxide supported on a metal. Also, similar boundary layer effects are found in the reactions of solids with each other. The experimental evidence for the boundary layer changes in the direction indicated by the catalytic studies is provided by two types of experiments. The one is based on rectifying effects and the other on conductivity measurements.