Characterization and reactivity of molybdenum oxide catalysts supported on Nb2O5-TiO2
Characterization and reactivity of molybdenum oxide catalysts supported on Nb2O5-TiO2
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DOI：
10.1016/j.molcata.2004.01.029
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发表时间：
2004-12
影响因子：
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通讯作者：
K. Chary;K. R. Reddy;Chinthala Praveen Kumar;D. Naresh;V. V. Rao-V.;G. Mestl
中科院分区：
文献类型：
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作者：
K. Chary;K. R. Reddy;Chinthala Praveen Kumar;D. Naresh;V. V. Rao-V.;G. Mestl
制备了一系列Mo负载量为1~10wt.%的Mo/Nb2O5-TiO2催化剂，并用X射线衍射仪、脉冲氧化学吸附、激光拉曼光谱和程序升温还原等方法对催化剂进行了表征。X射线衍射图表明，在Nb2O5-TiO2光催化剂上存在超过7wt.%Mo的MoO_3晶相。在较低的钼载量下，钼以高度分散的状态存在。脉冲氧化学吸附结果表明，当Mo负载量达到5wt.%时，吸氧量增加，而在较高负载量时则趋于平稳。H_2的程序升温还原表明，催化剂的还原分为两个阶段。Mo/Nb2O5-TiO2催化剂的还原性能随载体上Mo负载量的增加而降低。激光拉曼光谱表明，在低Mo负载量(~lt；5%Mo)时，存在表面钼酸盐物种，而在Mo负载量为7wt%及以上时，观察到MoO_3晶态。当钼负载量增加到5wt.%时，甲苯氨氧化反应的催化活性增加，这相当于单层覆盖率，在较高的钼负载量下保持不变。催化剂的活性与氧的化学吸附位置之间存在线性关系。
A series of Mo/Nb2O5–TiO2catalysts with Mo loadings ranging from 1 to 10wt.% were prepared and characterized by X-ray diffraction (XRD), pulse oxygen chemisorption, laser Raman spectroscopy (LRS) and temperature-programmed reduction (TPR). XRD patterns indicate the presence of a crystalline MoO3phase beyond 7wt.% Mo on Nb2O5–TiO2. Molybdena is found to be present in a highly dispersed state at lower Mo loadings. Pulse oxygen chemisorption results reveal that the oxygen uptake is found to increase with Mo loading up to 5wt.% and levels off at higher loadings. Temperature-programmed reductions of H2suggest that reduction of the catalysts occurs in two stages. The reducibility of Mo/Nb2O5–TiO2catalysts decreases with increase of Mo loading on the support. Laser Raman spectra shows that the surface molybdate species are present at low Mo loading (<5% Mo) and crystalline MoO3bands are observed from 7wt.% of Mo and above loadings. The catalytic activity during ammoxidation of toluene increases with molybdena loading up to 5wt.%, which corresponds to monolayer coverage and remains unchanged at higher Mo loadings. A linear correlation is observed between catalytic activity and oxygen chemisorption sites.