Controlled Synthesis And Catalytical Performance Of Nanocrystals

Nanocatalysts are materials with nanometers(1-100 nm)in size.They have unique advantages such as large surface area,high surface energy,and effective active center.Nanocatalysts have far-reaching significance for improving the catalytic reaction kinetics,activity and selectivity,so researches of catalytic properties of nanomaterials(morphology,size,and surface structure)have a guiding role in the development and design of high-performance nanocatalysts.Nowadays,with the rapid development of in-situ technology,scientists may have a deep understanding of the factors which have an important effect on the performance of nanocatalysts.Furthermore,they can identify distribution of the active site and structure-activity relationship of catalysts at the single particle level,in order to optimize the performance of nanomaterials.In this dissertation,the non-precious metal catalysts were chosen as the model system.As a results,we investigated the influence of the surface structure and the defects of the nanomaterials as well as the structure-activity relationship in various reactions.These results revealed the structure-activity relationship(SAR)and atomic and molecular model of the catalytic process,and also provided deep insights into the design of nanocatalysts for various catalytic reactions.The specific findings are summarized as follows:In chapter 1,the research progress of nanocatalysts is briefly introduced.The specific applications of nanocatalysts in the field of catalytic energy are summarized,and some factors affecting the catalytic performance of nanocatalysts are introduced.Therefore,people can reasonably design corresponding catalysts according to application requirements.In chapter 2,we report a facile one-pot synthesis of CuPt-Cu2S,Pt-Cu2S HNCs.and CuPt nanocubes by simply changing the Pt precursor types.1-Hexadecanethiol(HDT)was employed in this system to mediate the reduction of metal precursors and also as capping agent and sulfur source.Moreover,CuPd-Cu2S and Au-Cu2S HNCs were successfully prepared by using this one-step method.The catalytic properties of the obtained three nanocrystals were investigated in hydrogenation of cinnamaldehyde.Results show that CuPt-Cu2S HNCs exhibited the highest conversion rate and the highest selectivity toward hydrocinnamaldehyde while 3-phenyl-1-propanol was the only product over Pt-Cu2S HNC.In chapter 3,we synthesized WO3 nanosheets with rich O vacancies by liquid exfoliation.Electronic transport measurements disclose the nature of degenerate semiconductor for the WO3 nanosheets with O vacancies,consistent with our theoretical calculation results.The WO3 nanosheets rich in O vacancies exhibit a superior HER catalytic performance with a small overpotential of 38 mV at a current density of 10 mA cm-2 and low Tafel slope of 38 mV dec-1.Such activity was comparable to that of the commercial Pt/C.The high activity derived from the large surface area of the two-dimensional morphology and the O vacancies which rendered high electrical conductivity and appropriate ?GH.In chapter 4,we target at R-P LanSrNinO3n+1(n=1,2,3 and ?)perovskite series,in which A site is partially occupied by Sr ions.The R-P LanSrNinO3n+1(n=1,2,3 and ?)per ovskite series can maintain the valence stability of the B sites without the impact of the dimensionality.Through manipulating their structural dimensionality which is semi-quantitatively represented by the value n,we could effectively regulate their OER performance.The temperature-dependent resistivity curves showed that the conductivity of LanSrNinO3n+1 increased with n,accompanied with an insulator-metal transition.Besides,the hybridization of Ni-O was strengthened with larger n accompanied with the O 2p character shifting closer to the Fermi level as revealed by the X-ray Absorption Spectra(XAS),and thus opens up the possibility of LanSrNinO3n+1 perovskites for lattice oxygen redox activity.Consequently,the OER activities of LanSrNinO3n+1 were significantly enhanced as the value n increased due to higher conductivity and stronger hybridization of Ni-O.