Preparation Of Platinum Group Metallic Nanomaterials With High Catalytic Properties

Noble metals of platinum group have attract increasing attentions due to their distinctive properties in heterogeneous catalysis, electro-catalytic reaction, oxygen reduction reaction and proton exchange membrane fuel cells. Generally, the catalytic properties are closely related with crystal surface, compositions and structures of nanocrystals. The hybridization among different metals can significantly change the electronic structure and the synergistic effect is proved to have enhanced catalytic properties. Also the hybrid materials with other transition metals can also effectively reduce the amount of platinum used in the catalysts.In this article, a serials of hybrid nanomaterials containing Pt, Pd and Rh were designed and some simple preparation ways have been developed, for which the catalytic properties in heterogeneous catalysis and electro-catalytic oxidation of formic acid were highly investigated. The results may be helpful for the designing of platinum group nanocatalysts. The main information is as follows:1. The controllable growth of RhAg on gold nanorods is achieved from the dumbbell-like RhAg-tipped nanorods to the brushy RhAg-coated nanorods, or the rod-like Au@Ag-Rh nanorattles. These different growth modes of RhAg on gold nanorods are correlated with the coreducing kinetics of RhC13 and AgNO3. In view of the promising catalytic properties of Rh, gold nanorods modified by RhAg in different structures are examined as catalysts for the oxidation of o-phenylenediamine. It is found that brushy RhAg-coated nanorods present a higher catalytic efficiency than dumbbell-like RhAg-tipped nanorods and rod-like Au@Ag-Rh nanorattles. These results would benefit the overgrowth control on the one-dimensional metallic nanorods and the rational design of new generation heterogeneous catalysts and optical devices.2. Bimetallic Pd-Rh nanoframes and nanoboxes are synthesized by selective removing of Pd cores from different Pd-Rh nanocubes prepared by a hydrothermal reaction of PdC12, RhC13 and CH2O. CH2O in the recipe alters the reaction kinetics and the growth behavior of Pd and Rh, resulting in different nanocubes that determine the following hollow nanostructures, nanoframes or nanoboxes. The catalytic properties of the hollow nanostruetures are investigated using the oxidation of o-phenylenediamine (OPDA) to 2, 3-diaminophenazine (DAP) as a model reaction. The resultant bimetallic nanoframes and nanoboxes show enhanced conversion efficiencies than their solid counterparts. This method offers a convenient way for mass production of bimetallic hollow nanomaterials.3. Au-Ag@Rh-Ag nanorattles and Rh-Ag hollow nanospheres are successfully prepared by one-pot reaction. Temporal evolution of Rh-Ag hollow spheres reveals that Ag spheres were obtained in the first minutes and galvanic replacement were subsequently occurred between Ag spheres and Rh+. The catalytic oxidation of OPDA shows that the catalytic property of Au-Ag@Rh-Ag nanorattles is better than Rh-Ag hollow spheres. The enhanced catalytic property may be related with the active surface of Rh.4. The transformation of five-fold twinned Pd nanowires to trimetallic PtPdCu concave nanocubes was first successfully achieved. The detailed control experiments reveals that five-fold twinned Pd nanowires were corroded first and Pt+, Pd2+, Cu2+ co-reducted to obtain PtPdCu concave nanocubes. The corrosion of five-fold Pd nanowires is related with lattice strain caused by the defects in twinned structures. The electro-catalytic oxidation of formic acid shows that PtPdCu concave nanocubes have enhanced catalytic activity and stability than commercial Pt/C catalyst.