FTIR MICROSCOPY WITH POLARIZED IR RADIATION FOR THE ANALYSIS OF SAPO-5 AND P-XYLENE-LOADED SAPO-5

Using an optimized procedure, large SAPO-5 single crystals (up to 250 X 75 mu m) with a very high optical quality could be synthesized. NMR spectroscopy proved the perfect incorporation of silicon on phosphorus sites. IR microscopy with polarized IR radiation revealed that both t ypes of OH groups, with absorption bands at 3627 and 3519 cm(-1), ate oriented almost perpendicularly to the crystal c-axis, thus protruding into the 12-membered and the 6-membered ring channels, respectively. Adsorbed p-xylene reacts with both types of OH groups, giving rise to one broad band for the OH vibration at 3233 cm(-1), which indicates a- shift of the proton from the 6-membered ring to the 12-membered ring. From the dichroic ratios of the bands due to the p-xylene, it can be i nferred that the long axis of the p-xylene molecule is oriented parall el to the channel axis of the molecular sieve.