F. Schuth et al., FTIR MICROSCOPY WITH POLARIZED IR RADIATION FOR THE ANALYSIS OF SAPO-5 AND P-XYLENE-LOADED SAPO-5, Journal of the American Chemical Society, 116(3), 1994, pp. 1090-1095
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.