Gas- versus liquid-phase alpha-pinene transformation over faujasite-like zeolites and an amorphous silicoaluminate

The transformation of alpha-pinene was studied in both gas and liquid phase over a series of faujasite-like zeolites having different framework compos ition. A comparison with an amorphous silicoaluminate having 13 wt% of Al2O 3 (SA) was made. Camphene + limonene were the major products observed in li quid phase at 393 K at conversion levels lower than 90%. At 473 K, where th e reaction in gas phase took place, limonene suffered an ulterior transform ation mainly into terpinenes and terpinolenes and a faster deactivation of the zeolite catalysts as compared to the one in liquid phase was observed. This behaviour contrasts with the high stability shown by SA in gas phase. Over the wider pore system of SA undesired heavy products were formed in li quid phase at the expenses of the terpene isomers. However, in gas phase th is ulterior transformation of monoterpenes was minimised. A maximum activit y for the zeolite catalysts was observed when the number of Al-IV per unit cell reached about 17, a value where the population of Si(0Al) sites has be en shown to reach the maximum.