N-doped carbon-modified palladium catalysts with superior water resistant performance for the oxidative removal of toxic aromatics

Abstract

The supported palladium catalysts perform well in the oxidative removal of hazardous aromatic hydrocarbons. However, water vapor can seriously deactivate the catalysts especially in the low-temperature regime. Hence, improving moisture resistance of the Pd-based catalysts is full of challenge in the removal of aromatics. Herein, we report a new type of Pd@NC/BN catalysts featured with nitrogen-doped carbon layers modified Pd supported on hexagonal boron nitride (h-BN), and the relationship between structure and water resistance of the catalysts. The results show that in the presence of 10 vol% H2O in the feedstock, the Pd@NC/BN catalyst could effectively oxidize o-xylene (with an almost 87% removal efficiency), whereas o-xylene conversion declined from 69% to 20% over the conventional Pd/Al2O3 at a reaction temperature of 210 °C and a space velocity of 40,000 mL/(g h). The adsorption of H2O was significantly inhibited on the nitrogen-doped carbon layers due to the hydrophobic nature. Meanwhile, the oxygen species active for o-xylene oxidation were not only from the adsorbed gas-phase oxygen but also from the new active oxygen (*OOH and *OH) species that were generated via the interaction of O2 and H2O in the presence of water in the feedstock. It is concluded that the reactive oxygen species that accelerated the activation and cleavage of C−H bonds significantly facilitated the conversion of key intermediate species (from benzaldehyde to benzoic acid), thus playing a decisive role in o-xylene oxidation. The present work provides a direction for developing the superior water resistance catalysts with hydrophobic nature and good water activation ability in the oxidative removal of volatile organic compounds.