| Carbon monoxide is one of the main pollutants in atmosphere, and the existence of CO has raised serious problems for environment and human health. Furthermore, CO will poison Pt electrode in fuel cell which will lead to decrease of efficiency. The oxidation of CO is an effective way to wipe off CO in atmosphere, especially its application in low temperature is very important in practical application, such as:indoor air purification, gas masks and CO sensors. Moreover CO oxidation can be used as probe reaction to study mechanism of catalytic reaction. So CO oxidation is important for both actual application and theoretical research.Au nanocatalyst is the most widely used catalyst in CO oxidation, and it has raised attraction all over the world for its high activity and stability. Bimetallic catalysts based on gold also received considerable attention, since bimetallic catalysts combined with two different metals’properties demonstrate improved performance due to the strong synergetic effect when compared to their monometallic counterparts. Photodeposition was regarded as a promising and green approach to prepare catalysts supported on several metal oxides. The particle size can be readily controlled by altering the illumination intensity, irradiation time, initial solution concentration and the pH value. The bimetallic Au-Ag/TiO2-NB catalyst supported on TiO2 nanobelts (TiO2-NB) were synthesized by a successive two-step photodeposition method which can be assembled to porous nanopaper. The nanopaper catalyst was applied in CO low temperature oxidation.1. The Au-Ag/TiO2-NB nanostructures were synthesized by two-step photodeposition method and SEM, TEM, ICP, XRD, XPS and UV-Vis diffuse reflectance spectra were used to characterize the structure and composition. We can see from the SEM image that TiO2 nanobelts overlapped and obtain larger specific area and porosity. The Au-Ag nanoparticles were well dispersed on TiO2 nanobelts and the size of bimetallic nanoparticles supported on TiO2 nanobelts showed a bimodal distribution. The small nanoparticles dispersed on the surface of TiO2 nanobelts had an average diameter ～2.0 nm.2. The Au-Ag/TiO2-NB was applied in CO low temperature oxidation, and the influence of pH value, pretreated condition and preparation methods were discussed. The Au/TiO2-NB nanopaper obtained the highest activity when prepared with a pH value 10. At high pH values, the surface of the TiO2 nanobelts is negatively charged, the amount of gold deposited on the support decreased to obtain small nanoparticles. Furthermore, AuCl4 will hydrolyze and the Cl- can be replaced by OH- which led to higher activity. Moreover, we studied the influence of the Au/Ag ratio and pretreated temperature. The Au-Ag/TiO2-NB nanostructures with an Au/Ag ratio of 1:0.8 which obtained the best performance pretreated at 400 ℃ in 11% H2/N2 flow. The deactivation phenomenon of nanostructure with time on stream was also discussed.3. We found that smaller Au nanoparticles with a greater surface to volume ratio show higher catalytic activity. However, smaller Au nanoparticles are easily aggregate during reaction due to their higher surface energy, resulting in a remarkable reduction in their catalytic activities. To overcome these disadvantages, increasing effort has been aimed to prepare well dispersed Au nanoparticles with low spatial density. We prepared size and spatial density controllable nanoparticles by altering the photodeposition time and precursor concentration. The CO conversion over Au/TiO2-NB irradiated for 10 seconds with 1 mL HAuCl4 · 4H2O as precursor can achieve 100% at room temperature with a average diameter ～2.5 nm. When the precursor concentration decreased to 0.1 mL, the Au/TiO2-NB nanostructure size is only 1.4 nm with good activity for CO oxidation. |
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