Mo/ZrO_2催化剂上甲烷选择氧化制甲醛  

Selective Oxidation of Methane to Formaldehyde over Mo/ZrO_2 Catalysts

作　　者：张昕[1] 贺德华[1] 张启俭[1] 叶青[1] 徐柏庆[1] 朱起明[1] 

机构地区：[1]清华大学化学系一碳化学与化工国家重点实验室,北京100084

出　　处：《催化学报》2003年第1期22-26,共5页

基　　金：国家重点基础研究发展规划项目 (G19990 2 2 40 0 6)

摘　　要：制备了一系列甲烷选择氧化制甲醛的Mo/ZrO2 催化剂 .采用催化剂性能评价、BET比表面积测定、XRD、共焦显微激光拉曼光谱、H2 TPR和XPS等方法研究比较了不同Mo担载量催化剂的性能及其结构和性质 .实验结果表明 :Mo/ZrO2 催化剂具有催化选择氧化甲烷制甲醛的性能 ,且对甲醛有较高的选择性 .在所考察的范围内 ,随着催化剂Mo担载量的增加 ,甲烷的转化率增加 ,甲醛的选择性增加 ,甲醛的比活性增加 .随着反应温度的升高 ,甲烷的转化率增加 ,甲醛的选择性降低 ,甲醛比活性升高 .Mo/ZrO2 催化剂中主要含有ZrO2 和Zr(MoO4 ) 2 .催化剂的性能和性质与催化剂中Zr(MoO4 ) 2 的性质密切相关 .随着Mo担载量的增加 ,Zr(MoO4 ) 2 晶粒尺寸增大 ,并且其含量增加 ;ZrO2 晶粒尺寸基本不变 .Zr(MoO4 ) 2 晶粒尺寸增大和含量增加导致催化剂的比表面积降低 ,使甲烷选择氧化生成甲醛的钼氧物种增多 ,催化剂的还原温度升高和表面Mo的配位不饱和程度降低 .从而使得Mo含量较高的催化剂 (12 %Mo/ZrO2 )A series of Mo/ZrO_2 catalysts were prepared by impregnating ZrO_2 powder with an aqueous solution of (NH_4)_6Mo_7O_ 24. ZrO_2 powder was prepared by alcohol-sol/gel method. The catalytic performance of the Mo/ZrO_2 catalysts in selective oxidation of methane to formaldehyde has been investigated. The results show that the Mo/ZrO_2 catalysts possess high selectivity for formaldehyde in selective oxidation of methane to formaldehyde. With increasing Mo loading on the investigated catalysts, methane conversion and formaldehyde selectivity as well as formaldehyde specific activity increased. The reaction temperature had great influence on the catalytic performance of these catalysts. The methane conversion increased and formaldehyde selectivity decreased and formaldehyde specific activity increased as the reaction temperature rising. The comparative characterization on physicochemical properties of Mo/ZrO_2 catalysts has been made by BET, XRD, confocal microprobe LRS, H_2-TPR and XPS techniques. The Mo/ZrO_2 catalysts are mainly composed of ZrO_2 and Zr(MoO_4)_2. With the increase of Mo loading, the amount and the crystal size of Zr(MoO_4)_2 increased, but the crystal size of ZrO_2 almost kept constant. Zr(MoO_4)_2 is close relative to physicochemical properties and catalytic performance of these catalysts. The increase of the amount and the crystal size of Zr(MoO_4)_2 resulted in reducing the BET specific surface, decreasing the coordination unsaturated Mo, increasing the amount of active Mo species for selective oxidation of methane to formaldehyde, and decreasing the reducibility of the catalysts. All that enhanced formaldehyde selectivity and formaldehyde specific activity. However, much Mo=O and Mo-O-Mo species led to deep oxidation of methane and formaldehyde. In the case of the investigated catalysts, hence, the formaldehyde selectivity and the formaldehyde specific activity and the CO_x specific activity all increased in selective oxidation of methane to formaldehyde with increase of Zr(MoO_4)_2 in Mo/ZrO_2

关 键 词：Mo/ZrO2催化剂 甲烷 选择氧化 甲醛 超细氧化物 钼 二氧化锆 负载型催化剂 催化活性 

分 类 号：O643.3[理学—物理化学]