Synthesis Of Pt-based Nanoparticles And Their Catalysis For The Hydrolytic Dehydrogenation Of Ammonia Borane

Pt and Pt-based nanomaterials have attracted more and more attention due totheir good catalytic activity in various fields such as fuel cells, sensors, petrochemicaland automotive industries. Unfortunately, the cost of Pt is extremely high due to itsrare storage in the earth. So most of the recent efforts have focused on decreasing Ptutilization and increasing its catalytic activity. Ammonia borane is a good hydrogenstorage material, showing the potential commercial value because of the high amountof hydrogen and the good stability. Pt-based catalysts show a high catalytic activityfor hydrolytic dehydrogenation of ammonia borane, but its commercialization processhas been affected by its limited storage capacity and high prices. In this thesis, thepreparation method, the composition and its effect on the corresponding catalyticperformance of Pt-based catalysts have been studied; the main contents are as follows:1.To develop a simple and rapid method for the synthesis of Pt nanospheres withcontrollable sizes by reducing H2PtCl6and other metal-salt solution at roomtemperature with N2H4H2O.The as-prepared Pt nanospheres are of uniform size andgood dispersity, and the size, morphology, composition and structure could becharacterized by TEM and XRD. In addition, the impact of different types anddifferent valence states of other metal-salts on the reaction process has been studied,too. The results demonstrate that bivalent metal-salts have a main effect on the size ofPt nanospheres. Also, the influence of different surfactants (PVP and CTAB) on themorphology and structure has been explored. 2. A simple and universal method has been demonstrated to successfully preparePt-M (M=Fe, Co, Ni) bimetallic nanoparticles in aqueous solution under mildconditions. The contrast experiments and optimized results show that thenanoparticles with uniform size and good dispersity could be obtained when PVP andNaBH4are used as the surfactants and the reducing agent, respectively. Thecharacterization and analytic results of TEM, XRD and XAFS show that theas-prepared nanoparticles are not the mixture of two kinds of metallic nanoparticles,but bimetallic nanoparticles based on Pt fcc structure. Then Pt-M (M=Fe, Co, Ni)bimetallic nanoparticles could be applied in the hydrolysis of ammonia borane. Pt-Ninanoparticles (Pt:Ni=4:1) have shown the highest hydrogen-release rate in all samples,which is even higher than that of pure Pt nanoparticles prepared under the sameconditions. The XAFS results implies that Ni in Pt-Ni (4:1) NPs shows more metallicfeature compared to that in Pt-Ni (1:1) and Pt-Ni (1:4) NPs, which is better for thesynergistic effect on Pt and might be responsible for the best catalytic activity.3. Pt-M (M=Fe, Co) bimetallic nanomaterials with core-shell or hollow structurehave been synthesized and preliminarily explored, for example, Pt-Co core-shellnanostructures, Pt-Fe nanospheres and Pt-Fe hollow nanospheres. During thesestructures, Pt-Co core-shell nanostructures show good catalytic performance in thehydrolysis of ammonia borane.