USE OF BUT-1-YNE AS A PROBE FOR THE CHARACTERIZATION OF THE BASICITY OF ALKALI-EXCHANGED ZEOLITES

But-1-yne has been adsorbed at room temperature on a series of LiNa, N a and CsNaX and Y zeolites and also on CsNaX,9Cs and CsNaY,9Cs samples containing nine Cs atoms occluded by a unit cell. An IR study of the 3000-2800 cm(-1) frequency range clearly showed that but-1-yne isomeri zed into but-2-yne on CsNaX,9Cs whereas the observation of a band near 1950 cm(-1) in the case of CsNaY,9Cs characterized the formation of b uta-1,2-diene. Such partial transformation of but-1-yne to isomers did not occur on LiNa and Na samples, allowing one to study the basicity of such zeolites from the nu(=CH) shift which decreases in the followi ng order: NaX > LiNaX > NaY > LiNaY. The main feature is the observati on of at least two perturbed nu(ECH) bands for the NaX and NaY samples , revealing the heterogeneity of the basic sites. This result is discu ssed taking into account the presence of cations in different position s.