CATALYTIC OXIDATION OF METHANE OVER Pd-MeOx (Me = Mn, Co, Ni, Ce) CATALYSTS - INFLUENCE OF METAL OXIDES
CATALYTIC OXIDATION OF METHANE OVER Pd-MeOx (Me = Mn, Co, Ni, Ce) CATALYSTS - INFLUENCE OF METAL OXIDES
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发表时间：
2014
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通讯作者：
S. Todorova;P. Stefanov;A. Naydenov;H. Kolev
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作者：
S. Todorova;P. Stefanov;A. Naydenov;H. Kolev
研究了金属氧化物(MeOx；Me=Ni，Co，Ce，Mn)对Pd/Al_2O_3催化剂的改性活性。采用Me(NO3)2.6H2O和Pd(NO3)22H2O水溶液顺序浸渍Al_2O_3制备催化剂。用X射线衍射仪、热重分析和X射线光电子能谱对样品进行了表征。甲烷在空气中燃烧的结果表明，添加Co、Ni和Co-Ce、Co-Mn混合氧化物可以显著提高氧化铝负载钯的催化性能。这主要归因于PdO对催化剂载体的稳定作用。Pd与Me氧化物之间的紧密接触可以增加表面氧物种对Pd的浓度，从而导致PdO在表面上的稳定。对于含Ce的样品，提高催化活性的另一个因素是CeO2的储氧能力。CeO_2可能是氧的“储存库”，这与Ce3+和Ce4+在还原/氧化条件下的动态平衡有关。与Pd/Al_2O_3相比，Pd/Mn/Al_2O_3催化剂的活性较低，其原因是锰改性后的活性中心数量减少，这可能是由于Pd从锰氧化物中部分修饰所致。此外，添加锰的样品(Pd/Mn/Al_2O_3和Pd/CoMn/Al_2O_3)在时效后出现明显的失活现象。
The activity of Pd/Al2O3 catalysts modified with metal oxides (MeOx ; Me = Ni, Co, Ce, Mn) was studied. The catalysts were prepared by sequential impregnation of Al2O3 with aqueous solutions of Me(NO3)2.6H2O and Pd(NO3)22H2O. All samples were characterized by XRD, TPR and XPS. Results on methane combustion in air show that the catalytic performance of the palladium supported on alumina can be improved significantly by addition of Co, Ni and mixed Co-Ce, Co-Mn oxides. The effect has been attributed to the stabilization of PdO on the catalytic support. The close contact between Pd and Me-oxides could increase the concentration of the surface oxygen species towards the Pd thus leading to stabilization of PdO on the surface. Another factor which increases the catalytic activity in the case of cerium containing sample is the oxygen storage capacity of CeO2. Ceria may acts as oxygen “reservoir” and this is related with dynamic equilibrium between Ce 3+ and Ce 4+ at reduction/oxidation conditions. The observed low activity of Pd/Mn/Al2O3 in comparison with that Pd/Al2O3 can be explained by the decrease in the number of active centers after modification with manganese due to possible partial decoration of Pd from manganese oxide. Further, a significant deactivation after aging was observed with the samples promoted with manganese (Pd/Mn/Al2O3 and Pd/CoMn/Al2O3 ).