Synergistic Catalysis of Interlayer-Ordered PtFe Nanoalloy and Pd Nanoparticles: High-Efficiency Oxidation of p-Cresol to p-Hydroxybenzaldehyde under base-free Conditions

Abstract

The efficient oxidation of p-cresol to p-hydroxybenzaldehyde (p-HBA) under base -free conditions is a significant challenge in industry. We supposed that the sluggish kinetic problems due to the lack of hydroxide ions (OH-) may be addressed if reactive oxygen species (ROS, such as H2O2, O2•−, 1O2, HO• et.al.) can be introduced. Over optimized active sites in catalyst, molecular oxygen (O2) can be adsorbed and activated into nucleophilic ROS and facilitate the oxidation of p-cresol to p-HBA under base-free conditions. Herein, an ordered intermetallic PtFe nano-catalyst supported over active carbon (PtFe/C) and supported Pd catalyst over S doped carbon (Pd/S-C) with varied size from singe atom catalyst (SAC) to ca. 5.58 nm nanoparticles (NPs) were developed and employed in aerobic oxidation of p-cresol into p-HBA. Highest p-HBA yield up to >99% was obtained over PtFe/C and Pd/S-C combining catalysts, much higher than literature reported results. Radical quenching experiments and EPR spectroscopy confirmed that singlet oxygen (1O2), superoxide radicals (O2•−), and hydroxyl radicals (HO•) participated into the reaction path. Based on experiments data, a new catalytic mechanism for aerobic oxidation of p-cresol into p-HBA, involving ROS, was proposed. In this mechanism, Pd/S-C and PtFe/C catalysts played key roles in O2 adsorption, activation, ROS transformation and synergistic facilitated the oxidation of p-cresol to p-HBA.