Studies On The Synthesis Of Palladium Hydride Nanocrystals And Their Catalytic Properties

The unique character and excellent catalytic properties of a noble metal nano-materials have received much attention,yet their limited reserves greatly impede their applications.As an important material,noble metal Pd is widely applied to catalytic reaction and fuel cell production.It is of great significance to improve its catalytic activity,stability and use efficiency.On the other hand,despite many studies on Pd-based alloy nanocrystals at present,due to the large difference in atomic radius and standard reduction potential between Pd and other transition metals,it is still difficult to obtain Pd-based alloy with other metal with different compositions.The studies in this thesis were conducted with Pd-H and Pd-Cu alloy nanocrystals as the reseach object,and focused on its surface structure,composition regulation and structure-function relationship.The main contents and research achievements are summarized as follows:1.The formation of stable palladium hydride and its unique physical/chemical properties have received great attentions.Herein,by simply heat-treating commercial Pd black simply with butylamine solvent,a clean,stable,composition-tunable PdHx was successfully prepared.We found that PdH0.43 could decrease oxidation overpotential by 180 mV and improve catalytic activity by roughly 3 times in comparison with Pd black in the electro-catalytic oxidation of formic acid.2.Nanocrystal with a well-defined surface structure is the basis for studies of the structure-function relationship.Successively,we synthesized PdH,nanocrystal with different surface structures,and studied their electro-catalytic properties over oxidation of formic acid.The order of electro-catalytic properties follows:icosahedra with twin crystal {111} plane>cubes with exposed {100} crystal plane>octahedra with exposed{111} crystal plane>Pd black.More importantly,PdHx nanocrystalline could significantly decrease oxidation peak potential for formic acid electro-oxidation compared with Pd nanocrystals.3.Due to the change of the electronic structure of Pd in PdHx,PdHx might have unexpected catalytic properties.Therefore,we investigated other catalytic properties of PdHx,and found that PdHx could enhance the catalytic activity of formic acid decomposition,which is twice as high as commercial Pd black.In hydrogenation reaction for nitrobenzene and phenylacetylene,PdHx showed high selectivity for specific resultants.36.8%nitrosobenzene was obtained in nitrobenzene hydrogenation and 27.7%styrene was obtained in phenylacetylene hydrogenation.4.Pd and transitional metal Cu underwent a co-reduction reaction to generate icosahedral Pd-Cu alloy nanocrystalls with different compositions by using N-octanol to regulate the reduction potential.The resulted products improved the catalytic activity of ethanol electrooxidation.