Fabrication And Catalytic Properties Of Au-based BimetallicAu-M/TiO₂-NB Nanostructured Catalysts

TiO2-NB, a kind of one-dimensional nanomaterial with remarkable thermal stability, high surface area and smooth surface, has been widely used as catalyst support. One-dimensional TiO2-NB was more and more widely applied with the studying of TiO2-NB as catalyst support. For nano-sized catalysts supported on TiO2-NB, it is well dispersed and the catalytic activity and stability are excellent.Recently, as the noble metal catalysts becoming a hot spot, much attention has been devoted to the supported bimetallic nanocatalyst. Owning to the existence of bimetallic synergy, the bimetallic nanoparticle catalyst presented synergistically enhanced activity and improved stability compared to their monometallic counterparts. For the supported bimetallic nanocatalyst, small metal particle size and large surface area are benefit to the catalytic activity. During the catalyst preparation process, the structure and composition of the mixed second metal will affect the physical and chemical properties of catalysts. Moreover, the bimetallic nanoparticles will form variety kinds of structures, such as core-shell structure, sub-cluster segregated, alloy, etc. Catalysts with different bimetallic structures will have different binding sites and active sites, which is the main cause of the differences of catalytic activities. So, It is particularly important to control the preparation process of bimetallic nanoparticle catalysts.In this paper, photodeposition-galvanic replacement method and deposition-precipitation route were used to prepare four kinds of bimetallic nanocatalysts supported on one-dimensional TiO2-NB, namely as Au-Cu/TiO2-NB, Au-Ag/TiO2-NB, Au-Pd/TiO2-NB, Au-Pt/TiO2-NB. The as-synthesized samples were characterized by scanning electron microscope(SEM), transmission electron microscopy (TEM), X-ray photoelectron apectroscopy(XPS), X-ray diffraction (XRD) and inductively coupled plasma spectrometer (ICP), the catalytic activities of which were evaluated by using the aerobic oxidation of benzyl alcohol and methanol as probe reaction. The detail contents are as follows:Au-Cu bimetallic nanoparticles supported on TiO2-NB have been designed and synthesized by one pot photodeposition-galvanic replacement method. The TEM observation revealed that small-sized metal nanoparticles (less than 2 nm) uniformly and finely dispersed on TiO2-NB. Characterization by XRD coupled with XPS demonstrated that the Au-Cu bimetallic nanoparticles are composed with an Au-rich core/CuOx shell structure. The as-synthesized one dimensional Au-Cu/TiO2-NB nanostructure can be easily assembled into paper-like porous monolithic catalyst and applied in the heterogeneous catalysis. The formed bimetallic nanopaper catalyst presented synergistically enhanced activity and improved stability for catalyzing the aerobic oxidation of benzyl alcohol compared to their monometallic counterparts. It is likely that the Au-CuOx heterostructure is responsible for the superior catalytic properties of the bimetallic Au-Cu/TiO2-NB catalysts, and the catalytic activity can be significantly affected by the Au/Cu ratio. The uniform and high dispersion of metal nanoparticles on TiO2 nanobelts are also believed to contribute to the stability of Au-Cu/TiO2-NB catalysts, suggesting that the one-dimensional TiO2-NB are desirable support for the preparation of nanoscale metal catalysts.In this paper, photodeposition-galvanic replacement method and deposition-precipitation method were used to prepare four kinds of supported bimetallic nanoparticle catalyst loaded on the one-dimensional TiO2-NB, like Au-Cu/TiO2-NB, Au-Ag/TiO2-NB, Au-Pd/TiO2-NB, Au-Pt/TiO2-NB. SEM, TEM, XPS, XRD and ICP characterization methods have been used to characterize the composition, structure and catalytic active of the as-synthesized samples. The aerobic oxidation of methanol was used a probe reaction to evaluate their catalytic properties. It is demonstrated that Au-Pd/TiO2-NB has a higher catalytic activitycompared to three other kinds of bimetallic nanocatalysts supported on one-dimensional TiO2-NB. It is interesting that the catalytic activity and selectivity of the as-synthesized Au-Pd/TiO2-NB can be controlled by adjusting the ratios of Au/Pd and alcohol/oxygen.