Abstract
Silica-supported zinc oxide possessing acid and dehydrogenation functions is an efficient, noble-metal-free bifunctional catalyst for the environment-friendly synthesis of p-Cymene from renewable monoterpene feedstock by gas-phase dehydroisomerisation of alpha-pinene and limonene in a fixed-bed reactor. The reaction involves acid-catalysed terpene isomerisation to p-menthadienes followed by dehydrogenation to form p-Cymene. Dehydroisomerisation of alpha-pinene produces p-Cymene with 90% yield at 100% conversion at 370 degrees C and WHSV = 0.01-0.020 h(-1). The reaction with limonene gives a 100% p-Cymene yield at 325 degrees C and WHSV = 0.080 h(-1). ZnO/SiO2 catalyst shows stable performance for over 70 h without co-feeding hydrogen.