Ultrafine Pd Particles Embedded in Nitrogen-Enriched Mesoporous Carbon for Efficient H2 Production from Formic Acid Decomposition

It remains a grand challenge to prepare highly efficient and stable Pd/C catalyst for catalytic H-2 production from formic acid (FA). Here through a simple deposition precipitation method, we constructed a catalyst of ultrafine Pd particles uniformly embedded in N-enriched mesoporous carbon (Pd/NMC) by integrating N-doping, mesopore confinement and small size effects into one composite. The results showed that Pd nanoparticles were distributed in a narrow range (1.2-1.4 nm) and evenly dispersed on the NMC with high dispersion (90%-96%) compared to Pd/MC with large size (similar to 8 nm). The content of N-containing functionalities, determined by XPS could reach as high as 18.7 at. %. More importantly, Pd/NMC demonstrated not only over 12 times higher H-2 production amount than Pd/MC but also very promising stability (>95% retention efficiency within 4 cycles 8 h running) without any generation of a CO byproduct. It was also found that carbonization temperature of NMC greatly influenced the type and content of N species and thus the Pd particle size, distribution, and dispersion through the interaction between Pd and N containing functionalities. Both N-containing functionalities (particularly pyridinic N) and metallic Pd sites played critical roles in determining the turnover frequency (TOF) of FA. The catalytic performance of Pd/NMC was correlated with catalyst structure, surface chemistry, and reaction conditions (such as reaction temperature and FA feeding concentration). Findings reported in this work could shed insights into the design of efficient and stable metal/carbon catalysts for energy and environmental applications.