Selective Oxidation of Benzyl Alcohol catalyzed by CeO2-Nanorods Supported Palladium

Selective oxidation of benzyl alcohol (BA) to benzaldehyde (BZ) is considered as a crucial functional group transformation, since the product is a key intermediate for the synthesis of fine chemicals, in the perfume, pharmaceutical and dyestuff industries. This oxidation reaction is conventionally performed by various stoichiometric oxygen donors such as chromates, permanganates, and peroxides which are expensive and highly toxic. Therefore, from environmental point of view, and to reduce the overall production cost, there is a great interest in the development of heterogeneous catalysts capable of utilizing air or O2 as greener oxidants. Supported noble-metal catalysts has been investigated in numerous studies and showed promising potential to carry out selective oxidation of BA to BZ; however, various issues such as catalyst deactivation and BZ selectivity must be overcome for the industrial implementation of this reaction. In this research work, the selective oxidation of BA to BZ was studied using Palladium supported on CeO2 Nanorods (NR) as catalyst, and atmospheric air as greener oxidant. CeO2-NR were prepared according to previously published hydrothermal method [10]. Palladium oxide was deposited by wet-impregnation on CeO2-NR using Pd(NO3)2 • 2H2O and calcination at 400 °C (PdO/CeO2-NR). The effect of oxidation state of palladium on the catalytic activity was also investigated by using the reduced form of the catalyst (Pd/CeO2-NR-H2). Structural, morphological and redox properties of the synthetized materials were studied by mean of XRD, TEM, SEM, TPR and BET methods. Catalytic oxidation of benzyl alcohol using PdO/CeO2-NR or Pd/ CeO2-NR-H2 was conducted in toluene and in ethanol solvents under air flow (20ml/min). Effect of temperature (60-110 °C), BA concentration and catalyst/BA ratio (1/1, 2/1, 3/1) on catalytic activity and BZ yield was studied. Reactant and products were analyzed by GC-MS. The results showed that in toluene, catalyst deactivation occurred and high BZ yield was not achieved. In ethanol as solvent, BZ was produced with up to 99% yield and considerable selectivity. The oxidation rate increased with the catalyst/substrate ratio and with the BA concentration.