双金属RhAu_x/γ-Al_2O_3催化剂的CO催化氧化反应活性

Activity of bimetal RhAu_x/γ-Al_2O_3 catalysts for CO catalytic oxidation

采用超声辅助膜扩散法制备了双金属RhAu/γ-Al_2O_3催化剂(x=0、0.25、0.5、1.0、2.0和4.0),研究了该系列催化剂的CO催化氧化反应活性。采用程序升温还原(TPR)、X射线衍射(XRD)、原位DRIFTS和电子透射显微镜(TEM)等技术对催化剂的结构、形貌和物化性能进行了表征。结果表明,双金属RhAu/γ-Al_2O_3催化剂具有良好的CO催化氧化活性,催化活性的变化规律为:RhAu_4/γ-Al_2O_3≈RhAu_2/γ-Al_2O_3≈RhAu/γ-Al_2O_3≈RhAu_0.5/γ-Al_2O_3>RhAu0.25/γ--Al_2O_3>Rh/γ-Al_2O_3>Au/γ-Al_2O_3。在RhAux/γ-Al_2O_3催化剂体系中,Au对于催化剂上RhAu_x金属纳米粒子的粒度分布、氧化还原性能、CO吸附行为和CO催化氧化活性具有重要的调节作用。Rh与Au原子之间存在一定的相互作用,经过H_2还原处理,催化剂表面上的RhAu_x金属纳米粒子发生Au表面偏析,形成一定的壳核结构,覆盖了部分金属Rh的活性中心,使还原后的RhAu_x/γ-Al_2O_3催化剂活性降低。

Abstract： RhAux/γ-Al2O3 （ x = 0,0.25,0.5,1.0,2.0,4. 0） catalysts were prepared by the ultrasound- assisted membrane reduction method. The activity of the catalysts for CO catalytic oxidation was investigated. RhAux/γ-Al2O3 catalysts were characterized by TPR, XRD, in-situ DRIFTS and TEM techniques. The results showed that RhAux/γ-Al2O3catalysts possessed higher activity for CO oxidation than Rh/γ-Al2O3 catalyst. The activity of CO catalytic oxidation decreased as the following order of RhAu4/γ-Al2O3 RhAu2/γ-Al2O3≈ RhAu/γ-Al2O3 ≈ RhAu0.5/γ-Al2O3 〉 RhAu0.25/γ-Al2O3 〉 Rh/γ-Al2O3〉 Au/γ-Al2O3. Au in RhAux/γ-Al2O3 catalysts had significantly adjusting effects on the distribution of RhAux metal nanopartiele size, redox properties, CO adsorption and the catalytic activity for CO oxidation. The experimental results showed that there was an interaction between Rh and Au atoms. After H2 reduction, the segregation phenomenon of Au in RhAux nanoparticles on the surface of the catalysts occurred. A certain structure of core-shell was formed and Rh active sites were covered by Au atoms, arousing the decrease of in catalytic activity for CO oxidation as the RhAux/r - A1203 catalysts were reduced by H2.