Abstract

The transformation of alcohols to aldehydes or ketones is one of the most essential reactions in organic synthesis. An interesting alternative to aerobic conditions to produce oxygenated products, such as aldehydes and ketones, can be the dehydrogenation of alcohols under anaerobic conditions with the utilization of unsaturated organic molecules as hydrogen acceptors, instead of molecular oxygen. In this case, the oxidative dehydrogenation is changed to transfer dehydrogenation, which overcomes the safety limitations of aerobic oxidation. The influence of varying the stabilizer type (PVA, PVP, and THPC) during the synthesis of palladium nanoparticles via sol-immobilization technique on the resulted particles, and their catalytic activity on the liquid phase transfer dehydrogenation of 1-phenylethanol (1-PhEt) has been investigated for the first time. The chemical composition and morphology of the fresh and used catalysts were determined using XRD, XPS, BET, SEM-EDX, and TEM. By evaluating the catalytic activity of the series of 1% Pd/TiO₂ catalysts prepared using different PVA/Pd weight ratio, the results illustrate that two main parameters can mainly control the catalytic activity of 1% Pd/TiO₂ in the liquid phase transfer dehydrogenation of 1-PhEt, these are Pd(0)/Pd(II) ratio and the particle size of the catalyst. The results show that two different regimes can be identified during the liquid phase transfer dehydrogenation of 1-PhEt. At the initial time, the particle size parameter appears to control the catalytic performance of 1-PhEt while the effect of Pd oxidation state starts to take place after reaching iso-conversion, where the percentage of Pd(0)/Pd(II) increases while the reaction proceeds.