α-Pinene isomerisation over heteropoly acid catalysts in the gas-phase

Article abstract of DOI:10.1016/j.apcata.2010.10.018

The isomerisation of α-pinene was studied in the gas phase over solid heteropoly acid (HPA) catalysts in a fixed-bed continuous flow reactor at 200 °C and ambient pressure. The catalysts included bulk and SiO ₂-supported H₃PW₁₂O₄₀ and bulk Cs_2.5H_0.5PW₁₂O₄₀ possessing strong Br?nsted acid sites, as well as composites prepared by supporting 15 wt% H₃PW₁₂O₄₀ on Nb₂O₅, ZrO₂ and TiO₂ possessing both Br?nsted and Lewis acid sites of moderate strength. The reaction yielded camphene as the main product in a mixture with monoterpene by-products such as limonene, terpinolenes, terpinenes, β-pinene, p-cymene and others. The HPA catalysts with strong Br?nsted acid sites exhibited high initial activities, but suffered from catalyst deactivation, resulting in low camphene yields. Conversely, the HPA catalysts supported on Nb₂O₅, ZrO ₂ and TiO₂, although weaker acids, showed more stable performance in α-pinene isomerisation. The HPA catalyst supported on TiO₂ gave a camphene yield of 51% and a total camphene and limonene yield of 58%.