Adsorption of carbon dioxide, ammonia and pyridine on sodium-modified silicalite

Abstract

The surface properties of sodium-modified silicalite have been investigated by ESCA, i.r. spectroscopy, adsorption of carbon dioxide and ammonia, and temperature-programmed desorption. The results of carbon dioxide adsorption show that number of basic sites in sodium-modified silicalite is very small, although the existence of sodium ions enhances the adsorption. It has been observed that sodium-modified silicalite adsorbs ammonia and pyridine more stably compared with non-modified silicalite, but the t.p.d. profiles of adsorbed ammonia and i.r. spectra of adsorbed pyridine show that strong acid sites do not exist in the sodium-modified silicalite. These molecules are adsorbed on the silanol groups on the external surface of the silicalite and also on the sodium ions in the silicalite.