Au负载OMS-2催化剂的制备及其低温催化氧化性能

摘要

通过前掺杂法(QI),浸渍法(IM)和沉积-沉淀法(DP)3种方法制备了Au负载氧化锰八面体分子筛(OMS-2)Au/OMS-2催化剂,研究了制备方法和制备条件对其催化氧化CO活性的影响.采用X射线衍射(XRD)和BET比表面积测定等技术对所制样品进行表征.结果表明,沉积-沉淀法制备的Au/OMS-2-DP催化剂活性明显高于前掺杂法和浸渍法制备的催化剂,这与Au/OMS-2-DP催化剂比表面积较大和负载Au颗粒较小有关.制备条件(沉淀剂种类、制备溶液pH、Au负载量和催化剂焙烧温度)明显影响Au/OMS-2-DP催化剂的催化活性.对于各种不同的沉淀剂,以KOH为沉淀剂制备的催化剂活性最高,这可能与其无钝化作用,而且形成的Au颗粒较小有关；制备溶液的为最佳,当pH值过高或过低容易导致Au颗粒的聚集和Au沉淀量较少;XRD结果表明,当Au负载量为5wt％催化剂和催化剂焙烧为300℃时,所制备的催化剂颗粒最小,所得的催化剂活性最高.最佳条件制备的Au/OMS-2-DP催化剂活性较好,CO完全转化(100％)的温度为67℃.%Au/OMS-2 catalysts were prepared by pre-incorporation (QI), typical wet impregnation (IM) and deposition-precipitation (DP) methods. The influences of prepared methods and conditions on the catalytic activity of CO oxidation were studied. The samples were characterized by X-ray diffraction (XRD) and Brunaner-Emmett-Teller (BET). As compared with pre-incorporation and typical wet impregnation methods, Au/OMS-2-DP prepared from deposition-precipitation (DP) method revealed the highest activity, due to the largest surface area and the smallest Au particle size. A study was conducted on the effects of different preparation conditions (I.e., precipitating agents, pH of solution, Au loading and calcinations temperature) on the catalytic oxidation of CO over Au/OMS-2-DP. Effects of precipitating agents on catalytic activity were obvious. The best catalytic activity was shown by the Au/OMS-2-DP catalyst prepared with KOH as a precipitating agent, which could be explained in terms of the smallest Au particle size. A pH of 9 generated greater amounts of Au loading and smaller Au particles on OMS-2 than other pH value. The sample calcined at 300 °C showed the highest activity, which may be due to the sample's calcined at 200 °C inability to decompose completely to metallic gold while the sample calcined at 400"C had larger particles of gold deposited on the support. Au/OMS-2-DP prepared from a gold solution with KOH as a precipitating agent, pH of 9, Au loading at 5 wt%, and a calcination temperature of 300 °C provides the optimum catalytic activity for CO oxidation, I.e. 100% CO conversion at 67 ℃.