Acidity of isomorphically substituted crystalline silicic acids with layer structure .1. H-magadiite

Pure crystalline silicic acid prepared from magadiite does not contain acid sites detectable by IR spectroscopic methods, ammonia TPD and adsorption heat measurements. Isomorphic substitution of silicon by aluminum or gallium in the framework of magadiite creates strong Bronsted-acid sites. Part of the incorporated aluminum, released upon heat treatment from the framework of ammonium-exchanged magadiite, occupies cationic lattice sites and forms strong Lewis sites. Ion exchange with hydrochloric acid results in extraction of a considerable part of the framework Al by acid leaching. Incorporation of Ga into the crystal sheets of magadiite results in materials with stronger Bronsted- and Lewis-type acid sites than that found in the respective aluminum varieties. Ga containing silicic acid with magadiite structure proved to be also more resistent to heat treatments and acid leaching.