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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Effect of palladium on the reducibility of Mn based materials: correlation with methane oxidation activity
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Effect of palladium on the reducibility of Mn based materials: correlation with methane oxidation activity

机译：钯对锰基材料还原性的影响：与甲烷氧化活性的关系

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Mn-based oxide supports were synthesized using different procedures: (i) carbonate co-precipitation method, leading to the formation of a hexaaluminate crystallized solid (La_(0.2)Sr_(0.3)Ba_(0.5)MnAl_(11)O_(19)) and (ii) solid-solid diffusion method, leading to the formation of a doped θ-Al2O3 crystallized solid (nominal composition: 60 wt% La_(0.2)Sr_(0.3)Ba_(0.5)MnAl_(11)O_(19) + 40 wt% Al2O3). Impregnation of 1.0 wt%Pd was carried out on both oxides. The solids were tested for the catalytic methane combustion up to 700 °C. It was observed that adding palladium resulted in an important increase in the catalytic activity. The combined use of H2-TPR and XPS techniques reveals that only Mn~(3+)/Mn~(2+) redox "couple" is present in the solids, whatever the synthesis procedure used. The fraction Mn~(3+)/Mn is proportional to the total Mn content in the solid support, whatever the sample structure (hexaaluminate or doped θ-Al2O3) and its morphology (large crystals or aggregates of small particles, respectively). Pd impregnation and further calcination at 650 °C has no significant effect on the Mn~(3+) /Mn fraction. However, some changes in Mn~(3+) reduction profile are observed, depending on the solid structure. Indeed, palladium addition strongly affects the manganese reducibility with an important shift of the reduction process to lower temperatures (～100 °C). On the basis of redox properties observed for the different catalysts, a Mars-van-Krevelen redox mechanism, with oxygen transfer from support oxides to palladium particles, is proposed to explain the difference in terms of catalytic conversion and stability with respect to a 1.0 wt%Pd/Al2O3 reference sample.
机译：锰基氧化物载体的合成采用不同的程序：（i）碳酸盐共沉淀法，导致形成六铝酸盐结晶固体（La_（0.2）Sr_（0.3）Ba_（0.5）MnAl_（11）O_（19） ）和（ii）固-固扩散方法，导致形成掺杂的θ-Al2O3结晶固体（标称成分：60 wt％La_（0.2）Sr_（0.3）Ba_（0.5）MnAl_（11）O_（19） + 40 wt％Al2O3）。在两种氧化物上进行1.0重量％Pd的浸渍。测试了固体在高达700°C的催化甲烷燃烧。观察到添加钯导致催化活性的重要增加。 H2-TPR和XPS技术的结合使用表明，无论采用何种合成方法，固体中仅存在Mn〜（3 +）/ Mn〜（2+）氧化还原“偶”。 Mn〜（3 +）/ Mn分数与固体载体中总Mn含量成正比，无论样品结构（六铝酸盐或掺杂的θ-Al2O3）及其形态（分别是大晶体或小颗粒的聚集体）如何。 Pd的浸渍和在650°C下进一步煅烧对Mn〜（3+）/ Mn分数没有显着影响。然而，根据固体结构，观察到Mn〜（3+）还原曲线的某些变化。确实，钯的添加对锰的还原性有很大的影响，还原过程向较低的温度（约100°C）转移了重要的一步。根据在不同催化剂上观察到的氧化还原特性，提出了一种将氧气从载体氧化物转移到钯颗粒的Mars-van-Krevelen氧化还原机理，以解释1.0 wt％催化剂在催化转化率和稳定性方面的差异。 ％Pd / Al2O3参考样品。

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