Carbon Defects on N-Doped Carbon Promote Catalytic Activity of Pd Nanoparticles for the Selective Hydrogenation of Quinoline

Abstract

The activation process is a key step in preparing porous carbon. Herein, three kinds of green activators were separately used to successfully prepare N-doped porous carbons through a two-step strategy: hydrothermal carbonization and chemical activation using microcrystalline cellulose as the carbon source and urea as the nitrogen source. Palladium was deposited on these N-doped microcrystalline cellulose-based carbons (NMC-X, where X represents the activator) via a traditional deposition–precipitation method, and the resulting Pd nanoparticle catalysts (Pd/NMC-X) showed high activity in the selective hydrogenation of quinoline under mild conditions, particularly Pd/NMC-ZC (ZC, zinc carbonate), which achieved complete conversion of quinoline within 100 min at 40 °C and 4 atm H₂. Characterization results suggest that the high activity of Pd/NMC-ZC is mainly attributed to the special electronic structure of its Pd species, particularly the distribution of valence states and reducibility of Pd and the high hydrogen spillover capacity between Pd and NMC-ZC. The chemical activation by ZC leads to the formation of multiple defect sites on the carbon skeleton, modifying the carbon surface properties to enhance hydrogen spillover. This also provides an excellent environment for Pd nanoparticle anchoring, thus increasing the Pd-support interactions and regulating the electronic structure of Pd.