EFFECT OF EXTRA-LATTICE ALUMINUM SPECIES ON THE ACTIVITY, SELECTIVITYAND STABILITY OF ACID ZEOLITES IN THE LIQUID-PHASE ISOMERIZATION OF ALPHA-PINENE

The liquid phase isomerisation of alpha-pinene was studied on a number of zeolite catalysts at 150 degrees C. The primary reaction products were camphene, tricyclene and p-menthadienes. Catalyst samples with la ttice Si/Al ratios ranging from 1.46 to ca. 200 were prepared by hydro thermal treatment of zeolites Y and X. The nature of extra-framework a luminium species was investigated by Al-27-MAS-NMR spectroscopy. For h igh values of N-Al (number of framework aluminium atoms per unit cell) extra-lattice aluminium (EFAL) species have a promoting effect on the catalytic activity. On the other hand, for the highly dealuminated sa mples the catalytic activity decreases with N-Al. However it does not seem to become zero for zero Bronsted acidity, suggesting that Lewis a cid sites are also active on alpha-pinene isomerisation. Selectivity t owards camphene is also strongly affected by EFAL species, decreasing at high values of N-Al and increasing for the catalyst samples with hi gh EFAL content. The different distribution of EFAL species in the cat alysts prepared at different temperatures would cause this effect on s electivity.