THEORETICAL AND EXPERIMENTAL-STUDY ON THE SELECTIVITY OF DEHYDROGENATION OF ALPHA-LIMONENE IN ZSM-5 AND ZEOLITE-Y

Dehydrogenation of the natural terpene cu-limonene to the industrially important p-cymene was studied over two zeolite-supported Pd catalyst s, ZSM-5 and zeolite-Y. Reactor tests indicate that transalkylation of the p-cymene product can be avoided by employing the shape-selective properties of a medium-pore ZSM-5 catalyst. The diffusion properties o f the three isomers of cymene were then calculated in the two zeolites using molecular mechanics. In case of ZSM-5, p-cymene was found to ha ve the lowest barrier of the three isomers for diffusion through the s traight, spherical channel of the zeolite. For zeolite-Y, differences in diffusivity for the three isomers were very small. Theory and exper iments showed, in excellent agreement, that only ZSM-5 selectively pro duces p-cymene. This work shows that molecular mechanics is a powerful and reliable method for the screening of zeolites for performing shap e-selective catalysis.