Catalytic reduction of NO by CO over rhodium catalysts. 2. Effect of oxygen on the nature, population, and reactivity of surface species formed under reaction conditions
Catalytic reduction of NO by CO over rhodium catalysts. 2. Effect of oxygen on the nature, population, and reactivity of surface species formed under reaction conditions
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DOI：
10.1006/jcat.1999.2785
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发表时间：
2000-04
影响因子：
7.3
通讯作者：
D. I. Kondarides;Tarik Chafik;X. Verykios
中科院分区：
文献类型：
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作者：
D. I. Kondarides;Tarik Chafik;X. Verykios
采用FTIR和瞬态MS技术研究了氧对Rh/TiO_2催化剂上CO还原NO过程中形成的表面物种的性质、数量和反应活性的影响。已经发现，Rh的活性受到来自NO分解的表面氧和进料中的气相氧的积累的阻碍。在Rh颗粒附近吸附的CO和还原的TiO 2 −x物质作为氧原子清除剂，在富燃料条件下，从表面去除原子氧并恢复催化性能。本研究的结果提供了额外的证据，即N2的产生与吸附的Rh-NO−的解离有关，而N2 O的产生与Rh（NO）2的存在有关。还原Rh 0位点的存在对于两种还原产物的形成是必要的。在进料中不存在氧的情况下，在反应条件下也观察到表面异氰酸酯物质。它们的形成需要相邻的Rh 0-CO和还原Rh 0位点的存在。虽然这些物种是有利的条件下，NO转化为还原产物的观察，没有证据表明，他们是催化活性物种。
The effect of oxygen on the nature, population, and reactivity of surface species formed during reduction of NO by CO over Rh/TiO2 catalysts has been examined employing FTIR and transient MS techniques. It has been found that the activity of Rh is hindered by accumulation of surface oxygen originating from NO decomposition and gas-phase oxygen in the feed. Adsorbed CO and reduced TiO2−x species in the vicinity of Rh particles act as oxygen atom scavengers and, under fuel-rich conditions, remove atomic oxygen from the surface and restore the catalytic properties. Results of the present study provide additional evidence that production of N2 is related to dissociation of adsorbed Rh–NO− while production of N2O is related to the presence of Rh(NO)2. The presence of reduced Rh0 sites is necessary for the formation of both reduction products. In the absence of oxygen in the feed, surface isocyanate species are also observed under reaction conditions. Their formation requires the presence of adjacent Rh0–CO and reduced Rh0 sites. Although these species are favored under conditions in which NO conversion to reduction products is observed, there is no evidence that they are catalytically active species.