Insight into phase structure-dependent soot oxidation activity of K/MnO2 catalyst.
Insight into phase structure-dependent soot oxidation activity of K/MnO2 catalyst.
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DOI：
10.1016/j.jes.2022.05.038
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发表时间：
2022-06
影响因子：
6.9
通讯作者：
Changlong Zheng;Shidong Bao;Danjun Mao;Zhaoyi Xu;Shourong Zheng
中科院分区：
文献类型：
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作者：
Changlong Zheng;Shidong Bao;Danjun Mao;Zhaoyi Xu;Shourong Zheng
本研究制备了两种具有β相和δ相结构的纳米MnO2以及不同K负载量的钾负载MnO2催化剂（记为K/MnO2）。采用松散接触模式下的程序升温氧化和等温反应来检查所制备的催化剂的烟灰氧化活性。表征结果表明，与β-MnO2相比，δ-MnO2具有更大的表面积和更高的羟基含量。在 K 负载后，δ-MnO2 中丰富的羟基有效地螯合 K 阳离子，形成结合的 K 物质，而游离 K 物质仅在 K 负载量高于 3.0 wt.% 时才可用。相比之下，由于羟基含量非常低，即使钾负载量为 1.0 wt.%，大多数钾形态仍以游离态存在于 β-MnO2 中。 O2程序升温脱附(O2-TPD)表明，含有游离K物种的催化剂表现出很强的活化气态O2的能力，而仅含有结合K的催化剂表现出较小的O2活化能力。因此，尽管 β-MnO2 的活性略低于 δ-MnO2，但 K/β-MnO2 催化剂的活性明显高于具有相同 K 负载量的 K/δ-MnO2 催化剂。本研究的结果清楚地表明，对于 MnO2 基催化剂，烟灰氧化催化活性的增强高度依赖于 K 负载量，并且这种依赖性与 MnO2 的相结构密切相关。
In the present study, two nanosized MnO2with β and δ phase structures and potassium loaded MnO2catalysts with varied K loading amounts (denoted as K/MnO2) were prepared. Temperature programmed oxidation and isothermal reactions in loose contact modes were employed to examine the soot oxidation activity of the as-prepared catalysts. Characterization results show that as compared with β-MnO2, δ-MnO2has larger surface area and higher content of hydroxyl groups. Upon K loading, abundant hydroxyl groups in δ-MnO2effectively sequestrate K cation to form bound K species and free K species are available only at K loading above 3.0 wt.%. In contrast, the majority of K species present as free state in β-MnO2even at a K loading of 1.0 wt.% due to its very low hydroxyl group content. The O2temperature-programmed desorption (O2-TPD) demonstrates that the catalysts with free K species exhibit strong ability in activating gaseous O2, whereas the catalysts only having bound K display minor O2activation capability. As a result, despite of slightly lower activity of β-MnO2than δ-MnO2, the K/β-MnO2catalysts exhibit substantially higher activities than K/δ-MnO2catalysts with identical K loadings. The finding in this study clearly demonstrates that for MnO2based catalysts, the enhancement of catalytic activity for soot oxidation is highly K loading amount dependent and the dependency is strongly associated with the phase structure of MnO2.