Chapter Heterogeneous Catalysis and Surface Reactions
The defi nition of a catalyst, as per the International Union of Pure and Applied Chemistry (IUPAC), is that “a catalyst is a substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction” . The chemical process of increase of the reaction rate is called catalysis and the catalyst is both a reactant and a product of the reaction. That is, the catalyst is restored after each catalytic act. Besides, the catalyst does not infl uence the fi nal equilibrium composition after the cessation of the reaction.