Cu/SiO2纳米气凝胶的组成及催化氧化CO性能研究

以硝酸铜、 正硅酸乙酯和硝酸铈为原料, 利用溶胶-凝胶-超临界流体干燥技术制备了不同n(Cu)/n(Si)的用于CO催化氧化的Cu/SiO2系列气凝胶催化剂. 利用TEM、 XRD、 物理吸附、 微型反应器和气相色谱等对试样进行了表征. TEM观察结果显示, 试样中含有介孔的气凝胶结构, 5 nm左右的Cu粒子均匀地分布在SiO2的网络组织中. BET分析结果表明, 试样的比表面积均在140 m2/g以上. XRD分析结果显示, 添加铈前后, 试样的物相发生了从Cu 2+ →Cu+ →Cu的转变, 使试样的催化活性进一步提高. 试样的催化氧化CO活性表明, 组分中铜含量的不同及铜的不同物种直接影响试样的催化氧化CO的活性, 当组分中n(Cu)/n(Si)=2时, Cu/SiO2试样上CO完全氧化的温度降为210 ℃; 于400 ℃低温焙烧, 可使试样中有效活性组分全部转变成纳米晶CuO, 并进一步降低了CO完全转变成CO2的温度; 添加少量铈组分, 使试样催化氧化CO的tstart, t50及t90温度提前20 ℃以上, Cu/SiO2试样催化氧化CO动力学研究结果显示, 试样降低CO氧化温度的实质是降低了CO氧化的反应活化能.

Composition of Cu/SiO2 Nanometer Aerogel and Its Catalytic Properties for CO Oxidation

A series of Cu/SiO2 nanometer aerogel catalysts with different molar ratios of Cu to Si were prepared by sol-gel-SCFD methods and characterized by TEM, XRD, physisorption analysis instrument, micro-reactor and gas chromatogram. It was found that SiO2 was amorphous and Cu was highly dispersed on the SiO2 particles, and the structure consists of mesopores. The BET analysis indicates that the samples have a high specific surface area more than 140 m2·g-1. The catalytic activities investigation show that the content of copper and the different phases of reactive species all affected the activities of the samples. When n(Cu)/n(Si)=2, the temperature of entire oxidation of CO upon the sample was reduced to 210 ℃. After calcination at a low temperature, the nanometer particles of Cu and Cu2O transformed into nanometer CuO, the temperature of CO full conversion to CO2 was further decreased. Adding small amounts of cerium dopant into the composition can change the reactive species from CuO, Cu2O to Cu, which can further reduce the temperature of tstart, t50 and t90 of the samples. The kinetics research demonstrates that essential of the decrease of the CO oxidation temperature was the decrease of activation energy of CO oxidation reaction.