ACIDIC AND CRACKING PROPERTIES OF OFFRETITE

The acidic and catalytic properties of offretite zeolites have been studied as a function of potassium content. NH3 thermodesorption and ir studies of pyridine adsorption have shown that the weaker protonic acid sites arise from the exchange of the first of the three potassium cations located in gmelinite windows. The progressive removal of the last two cations creates strong acid sites and allows the reaction molecules to enter the gmelinite cages. There is evidence for two types of Lewis acidity. One of them is suggested to arise from a partial dehydroxylation during pyridine evacuation. Both Lewis sites are strong. The isooctane cracking selectivity is modified and gives a high C3 C4 ratio at the expense of iso C4 when the ion content is small enough to allow a diffusion of molecules through the gmelinite cavities. © 1979.