Reduction of NO by hydrogen versus reduction by CO over Pt, Pd and Rh clusters in NaX zeolite
Reduction of NO by hydrogen versus reduction by CO over Pt, Pd and Rh clusters in NaX zeolite
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DOI：
10.1016/s0926-3373(00)00260-5
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发表时间：
2001-03
影响因子：
22.1
通讯作者：
J. Nováková
中科院分区：
文献类型：
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作者：
J. Nováková
分别采用室温下的D2+H2平衡和170℃下的13CO+C18O加扰来考察氢气和CO的活化，并用室温下NO的吸附及其TPD来表征NO的活化。将这些反应与一氧化碳和氢气还原 NO 进行比较。看来，M/NaX簇（M=Pt、Rh或Pd）在这两种还原剂的NO还原中表现出相反的行为：对于CO，序列是Rh⪢Pd≅Pt，而当使用氢气时，铂（Pt/NaX）是最活跃的催化剂（Pt⪢Pd>Rh）。发现 CO 扰动在 Pt 上最快，而 NO 的吸附和解离在 Rh 上最广泛；在 CO 还原 NO 的过程中，Rh 上较弱的 CO 活化被强的 NO 解离所压倒。另一方面，Rh对NO的广泛吸附和解离阻碍了氢的解离，导致H2还原NO的活性最低，并中间形成N2O。但 Pt 的情况并非如此，在 Pt 上，容易解离的氢与可能分子吸附的 NO 发生反应。在室温下，氢对 N2O 的还原在所有金属簇上都很容易进行，因此，要么具有与 NO+H2 反应相同的活性，要么甚至比 Pd 特别是 Rh 具有更高的活性。 N2O 容易被氢气还原，这与 CO 的还原效果不一致，CO 的还原效果比 NO 的还原效果更差。在某些情况下，还使用双金属物质（PtRh/NaX、PtPd/NaX、PdRh/NaX）以及氧化的 M 簇。
The activation of hydrogen and CO was examined using D2+H2equilibration at room temperature and by13CO + C18O scrambling at 170°C, respectively, the adsorption of NO at room temperature and its TPD were used to characterise the activation of NO. These reactions were compared with the NO reduction by carbon monoxide and by hydrogen. It appeared that the M/NaX clusters (M=Pt, Rh or Pd) exhibit opposite behaviour in the NO reduction by these two reductants: with CO the sequence was Rh⪢Pd≅Pt, while platinum (Pt/NaX) was the most active catalyst (Pt⪢Pd>Rh) when hydrogen was employed. The CO scrambling was found to be most rapid over Pt, while the adsorption and dissociation of NO was most extensive over Rh; in the NO reduction by CO the weak CO activation over Rh was overwhelmed by the strong NO dissociation. On the other hand, the extensive NO adsorption and dissociation over Rh hindered the dissociation of hydrogen, which resulted in the lowest activity in the NO reduction by H2accompanied by an intermediate formation of N2O. This was not the case with Pt, over which easily dissociated hydrogen reacted with probably molecularly adsorbed NO. The reduction of N2O by hydrogen proceeded readily over all metallic clusters at room temperature, being thus, either of the same activity as that of NO+H2reaction, or even of higher activity over Pd and especially over Rh. The easy reduction of N2O by hydrogen does not agree with the reduction by CO, which was found to proceed worse than that of NO. In some cases, also bimetallic species (PtRh/NaX, PtPd/NaX, PdRh/NaX) were employed, as well as oxidized M clusters.