A Comparative Study of Solvent-Free and Highly Efficient Pinene Hydrogenation over Pd on Carbon, Alumina, and Silica Supports
Résumé
Solvent-free catalytic hydrogenation of pinene over Pd on carbon, alumina, and silica supports were compared. Despite the absence of solvent, Pd catalyst on all three supports yields to a quantitative conversion of pinene to pinanes and a higher selectivity for the cis isomer (72-89%). The temperature affected similarly the selectivity of the reaction for all three catalysts in favor of the cis-pinane isomer. However, recycling of the Pd on the three tested supports varied greatly. If Pd/C and Pd/alumina were successfully recycled 13 and 14 times, respectively, Pd/silica could be used only once to convert pinenes into pinanes. Remaining very effective during all 13 cycles, Pd/C was the best catalyst/support of the three tested ones for the solvent-free hydrogenation of pinene. The influence of H-2 pressure on pinene conversion rates were investigated for Pd/C catalyst. An extremely low leaching rate of palladium in pinenes and pinanes determined by ICP/MS confirmed the heterogeneous nature of this catalytic solvent-free reaction. The hydrogenation reaction presented in this paper is an alternate environmentally friendly pathway for pinane synthesis.