Design, Characterization And Application Of New Pd/Support Hybrid Catalysts

Supported Pd catalysts play an important role in energy conversion, contaminant degradation and fine chemical synthesis. How to design and prepare supported Pd hybrid materials and optimize their performance in various systems is of significance in nanomaterial synthesis. Based on the effects of support on the catalyst performance, we take the structure and component of support and the activation of the hybrid materials into consideration to enhance the activity and the durability of the catalysts. Material synthesis, performance evaluation and mechanism elucidation have been performed and new approaches have been established. As a result, new supported Pd catalysts have been prepared and useful information for efficient energy conversion and material utilization have been obtained. Main works and achievements are listed below:1. We prepare a unique self-supporting Pd-Cu bimetallic catalyst with3D porous structure using a facile double-template fabrication process and evaluate its performance as an ORR catalyst. This catalyst is found to possess an electrochemically active surface area of80.2m2/gpd, a peak current of17.4mA/cm2and an unusual limiting current density of12mA/cm2. Meanwhile, the fabricated bimetallic catalyst exhibits a better long-term stability than the state-of-the-art Pt/C catalyst. These results provide useful information on the facile preparation of cost-effective cathodic catalysts for chemical or microbial fuel cells in a controllable way.2. A model bactrium, Shewanella is used as an environmentally friendly factory for nano-sized Pd preparation and a precursor for multifunctional carbon support with functionalized surface and heteroatom dopant. With simple KOH activation at420℃, a highly-porous heteroatom-doped carbon with well-dispersed Pd nanoparticles is derived from the microbial cells. The as-synthesized material exhibits a2.2-times larger specific mass catalytic activity (at-0.1V vs. Ag/AgCl) towards oxygen reduction reaction, better durability and higher methanol tolerance than commercial Pt/C catalyst. Density functional theory calculations provide a molecular-level insight into the ORR mechanism, and suggest that its great catalytic activity is ascribed mainly to the high reactivity of Pd4cluster and the N-and O-doped carbon support with vacancy. This work opens a facile, low-cost and eco-friendly approach for hybrid electrocatalyst preparation and provides implications for the expanded application of biogenic nano-sized metal nanoparticles.3. Biogenic palladium activated with KOH at elevated temperatures is applied for catalyzing the reduction of4-nitrophenol to4-aminophenol. Among the three annealing temperatures, activated samples at400℃have a remarkable apparent kinetic constant of5.0×10-3s-1for4-nitrophenol reduction, which is12times greater than that of the raw biogenic palladium and comparable to that of the commercial Pd/C. Changes of the Pd nanoparticle aggregation, ratio of palladium to sulfur, surface area of the support are tracked to explore the improvement mechanisms associated with the KOH-activation at elevated temperatures. Such an activation approach is also successfully applied for improving the catalytic activity of biogenic Au. This work offers an cost-effecrive and efficient approach to activate biogenic metal nanomaterials to act as an active nanocomposite catalyst for organic conversion.