| As a fundamental driving force for the developing economy,catalysis keeps attracting great expectations.Being closely connected with production and our livelihood,a bunch of progresses have been and will be achieved in the field of applied catalysis,which focus on "What".On the other hand,however,the so called"Black Box" of the dynamic change during catalytic reaction remains a big challenge for scientists because of the complexity of industrial catalysts,which focuses on"Why".Briefly speaking,changes of the catalytically active phases that happen under different reaction gases and temperature range over components,valence states,morphologies,and so on.In the following catalysts systems or progresses we mainly focus on in this dissertation,consensus has not been achieved on the whole dynamic pictures during catalytic reaction.So,by using a combination of modern surface sensitive techniques,we are endeavoring to learn the dynamic process for catalytically active phases more precisely.Being a classic example for high dispersion of active phase on supports,few reports have been published for the morphology change during oxidation/reduction treatment for CuOx/?-Al2O3 catalysts.Also catalytic reactivity of the pre-reduced Cu/?-Al2O3 for CO oxidation has not been reported yet.We here prepared CuO/?-Al2O3 with different Cu loadings by wetness incipient impregnation.Using LEISS&XPS?CO oxidation reaction?H2-TPR?XRD,great difference of the dispersion of Cu species in reduced and oxidized states were deduced quantitively.The oxidation of Cu and wetting of CuOx take place spontaneously.One dimensional line of Cu-O species,the structure of which proposed in the literatures,was confirmed and it kept wetting the ?-Al2O3 surface until a dispersion limit was achieved.The highly dispersed Cu-O phase,being very stable,was found with very low activity toward CO oxidation.The pre-reduced Cu/Al2O3 catalyst,however,shows a much higher activity for CO oxidation.Detailed characterization of the active phase for Cu/Al2O3 during catalytic reaction shows that a different kind of CuOx species involved under reaction conditions.SiO2 has been considered as an inert support in most cases.However,different changes were found for Pd/Si02 and Cu/Si02 catalysts during UHV annealing.PdxSiy species involved and returned to Pd/SiO2 after oxidation or reduction,while a little mount of Si was left on the surface.The morphology of Pd species did not change a lot during these processes.On the other hand,no copper silicide was found during UHV annealing of Cu/SiO2.But the topmost surface Cu signal increased obviously indicating a wetting behavior of the Cu nanoparticles.More interestingly,we found that under high vacuum annealing condition,a highly dispersed Cu+ species developed from either Cu0 or Cu2+.By carefully comparison with the spectroscopic characteristics of Cu silicate,the highly dispersed CuOx species was found to be inserted in the surface Si-O lattice with only Si-O-Cu linkage and without Cu-O-Cu structure.Nano-sized Au exhibits great catalytic activities for many reactions,mainly due to its particle size?morphology?charging state?interaction with supports.Most researchers corelated the catalytic activity with the structure of Au before or after catalytic reaction,while much fewer researchers were focused on the dynamic changes of Au under different pre-treatment,especially under reductive conditions.We firstly discovered that Au nanoparticles grow in a much more flat mode on the pre-reduced ordered TiO2(110)-2×1 surface,compared with on the pre-oxidized TiO2(110)-1×1 surface,indicating a much stronger interaction between Au and the oxygen defeat structure.Different morphological changes were found for the Au/TiOx/Mo(100)model surface under different reduction conditions.Moreover,sintering and re-dispersing(or wetting)of Au nanoparticles were achieved over a realistic Au/Ti02 catalyst by different treatments. |
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