摘要
采用液相氢气两步还原法制备了双金属Au@Pt核壳纳米粒子,通过直接吸附法将纳米粒子均匀地分散于载体上,制备出低负载量的双金属Au@Pt/Al_2O_3催化剂,并且评价了催化剂对甲苯的催化氧化性能。通过TEM、XRD、XPS、N_2吸附-脱附和H_2-TPR等对催化剂进行了表征。结果表明,与单金属Au和Pt催化剂相比,双金属Au@Pt核壳催化剂表现出更高的催化活性,具有很好的稳定性和选择性,在甲苯体积分数为1×10~(-3),气体空速为18 L·g~(-1)·h~(-1)的条件下,Au_1@Pt_2/Al_2O_3核壳催化剂具有优异的催化氧化性能,其中甲苯实现98%的转化率的温度(T_(98))为195℃。由XPS结果可知,在Au和Pt之间存在电子转移促进了Pt上活性氧物种的形成,催化剂的活性组分主要以Au~0和Pt~0的形式存在,并广泛分布在载体的表面上。Au@Pt纳米粒子与载体Al_2O_3之间的强相互作用也是提高甲苯催化氧化活性的重要因素。
Highly active bimetallic Au@Pt core-shell catalysts were prepared by using direct-adsorption method,in which uniformly dispersed Au@Pt nanoparticles synthesized using two-step liquid-phase hydrogen reduction method were directly loaded on support. The performance of the catalysts for catalytic oxidation of toluene was evaluated. The catalysts were characterized by transmission electron microscopy(TEM) in conjunction with energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), N_2 adsorption-desorption and temperature-programmed reduction(H_2-TPR). As a result, the bimetallic Au@Pt coreshell catalysts exhibited higher catalytic activity compared with monometallic Au or Pt catalyst, and the Au_1@Pt_2/Al_2 O_3 core-shell catalyst showed outstanding catalytic activity, selectivity and stability among the bimetallic catalysts. The temperature for conversion of 98% toluene(T_(98)) was 195 ℃ under the condition of toluene volume fraction at 1 ×10~(-3) and the gas hourly space velocity of 18 L·g~(-1)·h~(-1).The XPS results illustrated that the enhancement of catalytic activity is attributed to the presence of Au underneath Pt shell where electron exchange from Au to Pt has promoted the formation of active oxygen species on Pt, which facilitates the oxidation of toluene. In addition, the active components of the catalyst mainly existed in the form of Au~0 and Pt~0, and the strong interaction between the Au@Pt nanoparticles and the support was observed.
引文
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