Solid acid catalysis; part I, the zeolite protonic site

Physical chemical properties of the zeolite proton are reviewed as deduced from spectroscopy, quantum-chemical calculation and kinetic studies. Emphasis is on relation of zeolite proton affinity with zeolite composition and structure. As long as Al/(Al + Si) zeolite composition ratio is less than 10% and protonic zeolites are not promoted by exchange with inorganic cations proton affinity is not composition or structure dependent. However for higher Al/(Al + Si) ratio's the dependence of proton affinity on structure can be significant. Proton reactivity may strongly depend on zeolite structure when in contact with a reactant molecule. Then match of molecular dimensions and zeolite cavity becomes important. This is the confinement effect.