The dehydrogenation of the natural terpene alpha-limonene to the industrially important p-cymene was studied over zeolite supported Pd catalysts. Transalkylation of the product p-cymene can be avoided by employing a medium-pore ZSM-5 catalyst via the well known product selectivity. The addition of a Ce promoter leads to an enhanced p-cymene selectivity and a slower catalyst deactivation. Surprisingly deactivation can be drastically reduced by the addition of hydrogen to the carrier gas.