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

Abstract:

The transformation of α-pinene was studied in both gas and liquid phase over a series of faujasite-like zeolites having different framework composition. A comparison with an amorphous silicoaluminate having 13 wt% of Al2O3 (SA) was made. Camphene + limonene were the major products observed in liquid phase at 393 K at conversion levels lower than 90%. At 473 K, where the reaction in gas phase took place, limonene suffered an ulterior transformation 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 liquid phase at the expenses of the terpene isomers. However, in gas phase this ulterior transformation of monoterpenes was minimised. A maximum activity for the zeolite catalysts was observed when the number of AlIV per unit cell reached about 17, a value where the population of Si(0Al) sites has been shown to reach the maximum.