Synthesis And Application Of Graphene-Based Palladium Catalysts

Graphene has attracted an increasing attention as a zero bandgap, sp2-hybridizedcarbon material. Metal graphene composite is promising for many applications, suchas molecular electronics, sensors, supercapacitor, solar cell. It is of great significanceto synthesize the metal graphene composises with controllable size, shape andstructure. In addition, due to the random distribution of carbon-vacancy defect and thefunctional groups in chemical derived graphene, it is difficult to control the compositestructure. However, the metal ions can be adsorbed and intercalated into graphenesheets to form thermal stable composite materials, and the interaction can also beutilized to regulate the nucleation and crystal growth and prepare the structurecontrolled composites. Herein, several reduction methods are employed to synthesizehighly dispersed and structure controlled palladium nanoparticles （Pd NPs） on thegraphene sheet without any stabilizer and dispersant. And the Pd structure and sizeeffect towards CO oxidation activity and mechanism are also investigated.Pd-graphene catalysts have been prepared using the plasma reduction, hydrogenreduction and chemical reduction method. The density functional theory （DFT） studyand the catalyst characterization using Raman and XPS confirm that the oxygencontaining groups play an important role in stabilizing Pd clusters on graphene. Thefirst layer of the metal particle mainly presents as PdOx. The TEM, HRTEM and XRDresults demonstrated that highly dispersed Pd NPs are formed on the graphene sheets,and the Pd crystals are twin crystal, single crystal and polycrystal, respectively.Both the Pd structure and particle size have an obvious effect towards COoxidation activity, where the catalyst active center is Pd0. The graphene supported Pdcatalyst shows good catalytic activity and high stability for CO oxidation.The kinetic test and DFT studies indicate that CO oxidation over the graphenesupported Pd catalyst follows the Langmuir-Hinshelwood （L-H） mechanism, wherethe chemisorbed CO reacts with the chemisorbed oxygen. The rate determining step isthe O₂adsorption dissociation, and the activation energy is the O₂dissociation energy.