A NEW MICROPOROUS MATERIAL - ALUMINATED SEPIOLITE

It was shown previously that the stability of the porous structure of sepiolite, a fibrous magnesio-silicate formed of staggered talc sheets , was improved by isomorphic replacement of silicon by aluminum in the tetrahedral sheet and some replacement of magnesium by aluminum in th e octahedral sheet. Alumination was carried out using a caustic soluti on of sodium aluminate. Here, it is shown that further improvement can be achieved by aluminating with a caustic solution of potassium alumi nate. As the number of substitutions in the tetrahedral layer increase s, the cation-exchange capacity corresponding to the increase of the l attice negative charge reaches 0.55 mequiv./g. The microporosity is pr eserved up to 400 degrees C while it collapsed at 150 degrees C in the original sepiolite. The calcined ammonium-exchanged aluminated sepiol ite contains mostly Lewis acid sites, contradictory to the expectation to observe some Bronsted sites. Because of the rather high cation-exc hange capacity, cations with redox properties (such as Ag+) can be exc hanged, leading to a bifunctional catalyst.