Controlled Synthesis Of Rh-/Pt-Based Nanocrystals With Specific Surface/Interface Structures And Their Catalytic Properties

The catalytic performance of noble metal nanocatalysts are closely related to the composition and distribution of surface elements,as well as the flow of material and energy at the catalyst surface/interface.For many catalytic reactions happening at the surface/interface of the noble metal nanocrystals,it has been corroborated that the controllable structure of the nanocatalysts surface/interface is vital for the improvement of catalysts utilization and the development of high quality catalysts.Therefore,an understanding of the catalytic mechanisms at a molecular level under the instruction of structure-activity relationship is becoming the mainstream direction in the research of nanocatalysts.In this dissertation,we systematically studied the Rh and Pt nanocrystal from the structure design to the controllable synthesis,and from the catalytic performance investigation to the mechanistic research.In addition,we also discussed the relationship between the catalyst structure(the heterogeneous structure and the alloying structure)and the catalytic activity in depth.Based on such discussion,we further proposed the catalytic mechanism of reactions promoted by these nanocatalysts.The main research contents and results are summarized as follows.We started from the investigation of growth regularity and structure-activity relationship of the Cu-Rh bimetallic heterostructure nanocrystals.In this work,we successfully synthesized the super branched Rh-on-Cu nanoscale sea urchins(NSUrs)with a high density of Cu-Rh interfaces by reversing the reduction sequences of the Rh3+and Cu2+ precursors through a selective coordination of Rh3+ with ascorbic acid(AA)in a one-pot strategy.The resulting Rh-on-Cu NSUrs are obtained by an epitaxial growth of Rh atoms on the early formed Cu cores.In addition,by tracking the structure evolution and analyzing the UV-vis spectra,we elaborated the selective coordination between AA and Rh3+ cations,which enhanced our understanding into the growth mechanisms of the Rh-on-Cu NSUrs.Moreover,we combined the in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)into the catalytic application toward CO oxidation reaction(COR).The DRIFTS research elucidated the effective decoupling of the competitive adsorption and activation of CO and O2 on the heterogeneous Rh-on-Cu nanostructure,resulting in the selective adsorption of CO on the Rh branches and the adsorption and activation of O2 on the Cu cores.This improved the interaction between the activated COads and Oads in close proximity at the interfaces,giving rise to the remarkably accelerated COR on the Cu-Rh NSUrs catalysts.Then,we further undertook the integrated design and synthesis of the Pt-based nano-catalysts under the guidance of the structure-activity relationship for the electrocatalytic oxidation of small organic molecules,such as methanol,formaldehyde and formic acid.The catalytic activity of the different doping content Rh-doped Pt3Ni0.sCo0.5 electrocatalysts for the above reactions in the acid media was evaluated in order to correlate the catalyst surface structure and composition with electrocatalytic behavior.We found that incorporation of trace rhodium(i.e.1%)present the best specific and mass activity,with an extended durability.To further investigated the relationship between the surface composition as well as electronic effect and electrocatalytic performance,we also made the surface state element analysis and the valence state analysis according to the XPS measurement.Furthermore,the reaction intermediate of methanol and formic acid were further studied by in situ electrochemical Fourier transform spectroscopy.