Correlation of nucleation- and growth modes with wetting, alloy segregation, catalyst preparation and strong-metal support interaction

Abstract

A simple thermodynamical model has been derived earlier, that enables to predict the growth mode (monolayer - or crystallite growth) for solid adsorbates on solid substrates. The influence of pseudomorphism on the model is discussed. It will be shown that the model can also be used for predicting the behaviour of liquids and gases on solid substrates. The terms cohesion and adhesion are valid for adsorbates of all states of aggregation. A scheme is presented, which correlates the thermodynamics of nucleation- and growth modes for metals on metallic substrates with parameters that determine surface segregation in binary alloys. This scheme allows a prediction of alloy segregation, when thermo-chemical data are lacking, by examination of the growth modes for both components of the alloy deposited onto each other. The behaviour of ionic solids deposited on ionic solids and the miscibility of organic compounds is discussed in relation to this scheme. Catalyst preparation methods, resulting in metal particles dispersed on a carrier, can be understood in terms of the behaviour of ionic solids and metals on ionic solid substrates. The recently found Strong Metal Support Interaction effects (S.M.S.I.) in heterogeneous catalysis may be expected to occur, within the framework of the present model, at a temperature at which an adhesive component becomes mobile.