| In this thesis,our research was concentrated on the influence and mechanism of preparation method and the addition of Au,Ag on the peroxide species(O22-)generated by the lattice oxygen(O2-)and molecule oxygen(O2)over cubic Nd2O3(c-Nd2O3).In part 1,three Nd2O3 samples were synthesized by hydrolysis,hydrothermal and combustion methods.A comparative study of the photo-induced formation of peroxide species on the three Nd2O3 samples was carried out at room temperature in air using Raman spectroscopy with a 325 nm laser as excitation source.A variety of experimental technologies have been applied to characterize the key factors affecting the formation of peroxide ions over above samples.In part 2 and 3,we used impregnation method to prepare the Au and Ag supported c-Nd2O3 synthesized by the combustion method,the promotion effects of Au and Ag and the influence factors such as noble metal loading,laser power,sample temperature,calcination temperature and reduction temperature on the formation of peroxide species over Au/c-Nd2O3 and Ag/c-Nd2O3 under the irradiation of 325 nm and 514 nm were carefully investigated.The promotion mechanism of noble metal was studied by XRD,TEM,UV-Vis,etc.The main results are summarized as follows:(1)Three Nd2O3 samples with cubic phase being the main component phase were synthesized by hydrolysis,hydrothermal,and combustion methods.The purity of the Nd2O3 synthesized by combustion methods was highest,while the Nd2O3 synthesized by hydrolysis and hydrothermal methods contained a small amount of hexagonal structure.Peroxide species was detected in all Nd2O3 samples,after irradiation with the laser of 325 nm at room temperature in air.However,the rate of peroxide formation over Nd2O3 synthesized by combustion methods was much faster than that over the other two samples.As evidenced by the results of O2-and CO2-temperature-programmed desorption(TPD)characterizations,Nd2O3 synthesized by combustion methods contained greater number of surface lattice oxygen(O2-)species with low coordination numbers than the other two samples.Moreover,the basicity of the surface O2-species in Nd2O3 synthesized by combustion methods is stronger than the other two samples.Both these factors favor the reaction of lattice oxygen with molecular oxygen to generated peroxide species under photo irradiation.(2)Au and Ag can promote the formation of peroxide species over c-Nd2O3 under the irradiation of 325 nm and 514 nm.It was found that 0.25wt%Au or Ag catalyst exhibited the highest performance of formation of peroxide species.TEM and UV-Vis characterizations showed that the rise of calcination or reduction temperature caused the increase of Au or Ag nanoparticles size,the particle sizes of noble metal over Au/c-Nd2O3 or Ag/c-Nd2O3 reduced by H2 decreased slightly compared with samples calcined in air at the same temperature.The intensity of photo-induced peroxide species Raman bands over Au/c-Nd2O3 or Ag/c-Nd2O3 samples calcined in air at 200 °C or reduced by H2 at 200 °C was the largest.With the increase of calcination temperature,the intensity of peroxide band decreased.The phenomenon can be explained by that the rise of calcination temperature resulted in the increase of Au or Ag nanoparticles size,large particle size of-Au or Ag nanoparticles may be unfavorable to the activation of molecular oxygen,which is bad for the formation of oxygen species.The silver species over Ag/c-Nd2O3 reduced by H2 mainly exist in the form of metallic silver,which is more favorable to the formation of peroxide species.As the temperature was raised to 400 °C,the intensity of the peroxide Raman bands over Au/c-Nd2O3 began to decrease,the peroxide ion decomposed totally when heated to 450 °C.Besides,high laser power can also lead to the decomposition of peroxide species.We have verified that the illumination and molecule oxygen are the two requirements of photo-induced formation of peroxide species over Au/c-Nd2O3,which revealed that its mechanism remains unchanged with the addition of Au. |
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