Oscillation in low-temperature NO–H2–O2 reactions over Pt catalysts supported on NOx-adsorbing material, TiO2–ZrO2
Oscillation in low-temperature NO–H2–O2 reactions over Pt catalysts supported on NOx-adsorbing material, TiO2–ZrO2
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DOI：
10.1016/j.jcat.2004.06.019
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发表时间：
2004-10
影响因子：
7.3
通讯作者：
M. Machida;S. Ikeda
中科院分区：
文献类型：
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作者：
M. Machida;S. Ikeda
在90℃条件下，研究了0.08% NO-0.28% H2-10% o2在1 wt% Pt/ tio2 - zro2催化剂上的振荡反应（W/F=0.24 s g cm−3），并考察了载体氧化物的吸附性能。在稳态流中诱导约20 h后，随着进料中H2in浓度的不同，出现了不同周期和振幅的振荡。在振荡过程中，NO和h2s的转化率较稳态同时下降，而相应的N2/N2O产率高于反应化学计量学的估计。平行TPD测量结果表明，振荡开始时催化剂上硝态氮（NO3）的积累量最大。原位漂移检测到两种不同的硝酸盐，它们具有不确定和双齿结构，它们吸附在两种氧化物成分边界形成的基本位点上。基于硝酸盐在载体上的表面覆盖与振荡周期相关的事实，提出了一种机制，即积累的硝酸盐的表面结构域阻碍了气态NO的吸附，导致催化活性突然下降。但随着Pt与H2反应脱硝的进展，Pt吸附NO可以重新启动NO的催化还原。
The oscillatory behavior of 0.08% NO–0.28% H2–10% O2reactions in a flowing He (W/F=0.24 s g cm−3) over 1 wt% Pt/TiO2–ZrO2catalyst has been studied at 90 °C with attention to the NOxadsorption property of the support oxide. After an induction period of ca. 20 h in a steady-state flow, oscillations appeared with different periods and amplitudes depending on the concentration of H2in the gas feed. During the oscillation, the conversions of both NO and H2were decreased simultaneously from the steady state, whereas the corresponding N2/N2O yields were more than estimated from the reaction stoichiometry. The parallel TPD measurement revealed that the amount of nitrate (NO3) accumulation on the catalyst became largest when the oscillation started. In situ DRIFTS detected two different nitrates species with unidentate and bidentate structures, which adsorbed on basic sites forming at the boundary of two oxide components. Based on the fact that the surface coverage of nitrate on the support is correlated to the oscillation period, a mechanism is suggested in which the surface domains of accumulated nitrates block the adsorption of gaseous NO, leading to a sudden drop of the catalytic activity. However, with the progress of nitrate removal by the reaction with H2, the adsorption of NO onto Pt can restart the catalytic NO reduction.