Understanding the effect of support surface properties in Pd catalyzed liquid-phase oxidation of benzyl alcohol: an in situ ATR-IR study

The liquid phase oxidation of alcohols to the corresponding carbonyl compounds over supported metal catalysts has been extensively studied in the last decade. Recent studies have shown that the support plays an important role in enhancing the activity and ruling the selectivity of the noble metal catalyzed reactions. In this work, the effect of the support for the Pd catalyzed benzyl alcohol oxidation to benzaldehyde was investigated in a batch reactor and by attenuated total reflection infrared (ATR-IR) spectroscopy in a flow reactor cell under similar conditions. Pd catalysts (5 wt%) were prepared by immobilizing polyvinyl alcohol (PVA) protected Pd nano-particles on Al2O3, TiO2 and NiO. Pd/TiO2 exhibited the best catalytic performance. The dehydrogenation and oxidation pathways of alcohol oxidation were followed by ATR-IR. The study demonstrated a clear difference of the distribution of benzaldehyde and adsorbed benzoic acid on the catalyst surface according to the basicity of the support. As expected, the catalysts showed that a higher amount of adsorbed species caused more rapid deactivation. Unlike a conventional Pd/Al2O3, the absence of adsorbed CO excluded the decarbonylation pathway and confirmed the high selectivity of the PVA capped Pd nano-particles.