| Supported Au catalysts,as new-type materials in the great potential application of industrial and environmental catalysis,can remove the trace amounts of CO in the environment and CO of the H2-rich in the proton exchange membrane fuel cell at low temperature.The study has attracted wide interest in the past three decades and how to improve its catalytic performance is still a worthy goal.Based on the congnition of(1)the electrons-rich on Au surfaces in favour of the adsorption,activation and the promoted oxidation of CO in the process of CO oxidation for Au catalysts;(2)the interaction between the support and active component;(3)the produced hot electrons induced by the located surface plasma resonance(LSPR)of Au nanoparticles under visible light irradiation,the paper has systematically studied the effect of visible light and electron promoters on the catalytic oxidation of CO(or selective oxidation).Firstly,in this paper the relationship between the typical "active"support TiO2 and "inert" support Al2O3 for the catalytic proformance of CO under.visible light irradiation was compared,which revealing the structure-function relationship of electron transfer action,chemical adsorption and catalytic activity by the characaterizations of the component and structure,photo-response,the chemisorption behavior of reactants and active species of the samples.And then the researchs about the promoted role of different organic or inorganic electron promoters towards the catalytic performance of CO on the Au/TiO2 under visible light irradiation were carried out and the obtained main results are as follows:(1)Visible light could simultaneously promote the oxidation of CO and CO selective oxidation in the H2-rich stream on Au/TiO2,but it only promoted the oxidation of CO and suppressed CO selective oxidation in the H2-rich stream on Au/Al2O3.This is mainly attributed to the difference of the electron transfer induced by the LSPR effect of Au nanoparticles and the following chemisorption of CO and O2 in the two catalysts.(2)The introduction of the organic conducting polymer polyaniline(PANI)with the visible light response on Au/TiO2 can promote the CO selective oxidation in the H2-rich stream.The analysis suggests that PANI with the electron transition from ?to ?*orbit of benzenoid or quinonoid unit with p-7c delocalized conjugated N atoms has the donating electron effect,which enabling the elevation of the Fermi level and the increased surface electron densities of Au surfaces in the Au/TiO2-PANI system,and then promoting the efficient activation of CO.And also the dissociating hydrogen on Au sites could overflow to the support and had a protonizing effect on PANI,whch played an important role the inhibition of H2 oxiation.(3)Graphite C3N4 in the high conduction band and the precursor of titanium ethylene glycol could prepare the TiO2 microspheres-C3N4 nano-heterojunction by the hydrothermal method.The better contact between the support and Au could provide a better physical basis for high efficient electron transfer among the interface of TiO2,C3N4 and Au NPs to maintain the high electron densities of Au surfaces under visible light irradiation and promote the CO oxidation.(4)Different from the promoted role of alkaline earth metal oxide(AEMO)as structural stability in the previous study,we had an insight into AEMO as electron promoters on Au/TiO2 to lift up the Fermi level of the support to change the electron structures of the catalysts by DFT calculation and different characterization views.And also the visible light can further reinforce the promoting role.(5)CuO was conducted as structural promoter and electron promoter for CO selective oxidation on Au/TiO2 under visible light irradiation.The analysis suggests that the appropriate CuO thin layer which was grafted on three-dimensional urchin-like miro/nano hierarchical(well-organized)TiO2 microspheres by the co-precipitation method with the precursor of chloroauric acid and copper nitrate under alkaline conditions didn't benefit to the dispersion of Au nanoparticles on the support,but also could strengthen the interaction of electron transfer between Au and support.Visible light could increase the surface electron densities of Au?CuO and TiO2 surfaces,in favour of the adsorption and activation of CO on Au surfaces and 02 on the CuO or TiO2 surfaces,which enhancing the catalytic performance.In a word,the introduction of electron promoters,the LSPR effect of Au nanoparticles,the photo-response behavior of the samples and the accommodation of the Fermi level on semi-conductor support can utilize the effect of electron transfer between the support and active component to improve the electron densities of Au surfaces and further promote the activity and selectivity of CO oxidation.The study maybe serve as a probable approach for the design or modification of the catalysts and other involving electron transfer reaction in heterogeneous catalysis. |
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