ABSTRACT
A catalyst is a substance that increases the rate at which chemical reaction approaches equilibrium without, itself, becoming permanently involved in the reaction. The key word in this definition is permanently since there is ample evidence showing that the catalyst and the reactants interact before a reaction can take place. Since a catalyst merely increases the rate of a reaction it cannot be used to initiate a reaction that is thermodynamically unfavorable. The enthalpy of the reaction as well as other thermodynamic factors are function of the nature of reactants and the products only and, thus, cannot be modified by the presence of a catalyst. It has to be recognized that adsorption on a catalyst surface must be energetically favorable, have a relatively low activation energy and lead to the formation of reactive surface species. In most catalytic reactions the selectivity is generally determined by the nature of the catalyst being used with the other reaction parameters having secondary importance.
