Solid acid catalysis. Part II, Catalytic chemistry of proton activation

A catalytic reaction is a complex cyclic reaction network of a sequence of elementary reactions. The initial part of this article considers the rate of elementary reactions where organic molecules are activated by zeolite protons. It will be seen that protonated intermediates as carbonium or carbenium cations are part of transition states are activated intermediates in solid acid catalysis. In part I an analysis of the proton affinity as a function of zeolite composition has been given. In this article we will emphasize the importance of confinement, that relates to match of molecular dimension and zeolite micro-cavity. Confinement causes large differences in adsorption free energies when zeolite structure is varied. A kinetic analysis is given that leads to the definition of a catalytic analogue of the classical Hammett function of acidity. Selected examples of catalytic reaction cycles are chosen that illustrate the interplay of confinement and proton affinity in the comparison of zeolites with different structures and composition.