Au/Al_2O_3催化剂的制备及其在CH_4/CO_2重整反应中的催化活性

PREPARATION OF Au/Al_2O_3 CATALYST AND ITS CATALYTIC ACTIVITY IN CO_2 REFORMING OF CH_4

采用浸渍法和沉积 沉淀法制备了四种不同的Au/Al2 O3 催化剂 ,测定了它们在氢气还原前后及催化反应后的金含量及比表面积。结果表明 ,制备方法明显影响催化剂的金含量。应用X 光粉末衍射技术研究了这些催化剂经还原处理及反应后的物相变化 ,金以Au0 物相存在 ,没有发现氧化态的金物相。考察了该催化剂在CH4/CO2 重整反应中的催化活性 ,发现金催化剂的活性取决于金粒子的大小。浸渍法制备的金催化剂具有较大的金晶粒尺寸 ,催化活性低 ;沉积 沉淀法制备的金催化剂金晶粒尺寸较小 ,催化活性较高。以尿素为沉淀剂制备的催化剂给出 10 73K时的CH4与CO2 转化率分别为 8 1%和 17 6 %。高温反应不仅导致金晶粒的聚集 ,而且存在明显的金流失现象。

Four different Au/Al 2O 3 catalysts were prepared via impregnation method at ambient temperature and 343?K and deposition precipitation method at 343?K using Na 2CO 3 and NH 2(CO)NH 2, respectively Gold amounts and BET surface areas of these gold catalysts were measured The catalytic activity of gold catalyst was investigated for CO 2 reforming of CH 4 It has been found that the preparation technique of gold catalysts have a large influence on Au amounts, Au particles size and their catalytic activities The catalyst prepared by impregnation method had large gold particles size but low activity while the catalyst prepared by deposition precipitation method, especially using NH 2(CO)NH 2 as precipitating agent, had small gold particles size and relatively high activity with 8 1% conversion of CH 4 and 17 6% conversion of CO 2 X ray diffraction was used to determine the gold phases of the catalysts reduced at 573?K and that of the catalysts used at 1?123?K For the impregnation prepared gold catalyst reduced, Au 0 phase is present as Au (111), Au (200), Au (220) and Au (311) faces, but dominant Au (111) face is present for the gold catalyst prepared by deposition precipitation However, oxidizing gold phases do not exist for all gold catalysts prepared Larger size of gold particles and stronger diffraction peaks are observed for the four gold catalysts used possibly due to aggregation of gold particles In addition, some losing of gold is found in the catalyst after reaction at high temperature