The catalytic role of water in CO oxidation
The catalytic role of water in CO oxidation
复制标题
DOI：
10.1063/1.1602053
复制
发表时间：
2003-09-22
影响因子：
4.4
通讯作者：
Raval, R
中科院分区：
文献类型：
--
作者：
Gong, XQ;Hu, P;Raval, R
水是地球上最常见的物种之一，可以在许多反应中发挥催化作用，包括多相催化反应。在最近的实验工作中，Bergeld，Kasemo和Chakarov证明了水能够在低温（类似于200 K）下促进CO氧化。在这项研究中，我们选择了CO氧化Pt（111）在水的存在下作为一个模型系统，以解决水的催化作用的表面反应一般使用密度泛函理论。研究了低温下CO在Pt（111）上氧化的许多可能的基元步骤。我们发现以下情况。首先，在水的存在下，CO氧化势垒降低到0.33 eV（没有水时，势垒为0.80 eV）。这种势垒降低主要是由于H2O中的H与过渡态（TS）的O之间的氢键合，其稳定了TS。第二，CO可以容易地与OH反应，势垒为0.44 eV，而COOH解离产生CO2并不容易（势垒为1.02 eV）。第三，在H2O+OH混合相中，CO可以容易地转化为CO2。它通过两个步骤发生：CO与OH反应，形成COOH; COOH将H转移到附近的H2O，同时H2O中的H转移到OH，导致CO2形成。该过程的反应势垒在CO覆盖度为1/6 ML时为0.60 eV，在CO覆盖度为1/3 ML时为0.33 eV。讨论了CO低温氧化的机理。根据我们的计算，我们提出水的促进作用一般可分为两类：（1）在CO+O+ H_2O →> CO_2 + H_2O反应中，H_2O通过H与负电子物种如O之间的氢键作用，稳定反应的TS，从而降低势垒。(ii)H_2O首先分解为H和OH，然后OH或H直接参与反应，诱导出新的反应机理，OH或H可作为中间体参与反应。(C)2003年，美国物理学会。
Water, one of the most popular species in our planet, can play a catalytic role in many reactions, including reactions in heterogeneous catalysis. In a recent experimental work, Bergeld, Kasemo, and Chakarov demonstrated that water is able to promote CO oxidation under low temperatures (similar to200 K). In this study, we choose CO oxidation on Pt(111) in the presence of water as a model system to address the catalytic role of water for surface reactions in general using density functional theory. Many elementary steps possibly involved in the CO oxidation on Pt(111) at low temperatures have been investigated. We find the following. First, in the presence of water, the CO oxidation barrier is reduced to 0.33 eV (without water the barrier is 0.80 eV). This barrier reduction is mainly due to the H-bonding between the H in the H2O and the O at the transition state (TS), which stabilizes the TS. Second, CO can readily react with OH with a barrier of 0.44 eV, while COOH dissociation to produce CO2 is not easy (the barrier is 1.02 eV). Third, in the H2O+OH mixed phase, CO can be easily converted into CO2. It occurs through two steps: CO reacts with OH, forming COOH; and COOH transfers the H to a nearby H2O and, at the same time, an H in the H2O transfers to a OH, leading to CO2 formation. The reaction barrier of this process is 0.60 eV under CO coverage of 1/6 ML and 0.33 eV under CO coverage of 1/3 ML. The mechanism of CO oxidation at low temperatures is discussed. On the basis of our calculations, we propose that the water promotion effect can in general be divided into two classes: (i) By H-bonding between the H of H2O and an electron negative species such as the O in the reaction of CO+O+H2O-->CO2+H2O, H2O can stabilize the TS of the reaction and hence reduce the barrier. (ii) H2O first dissociates into H and OH and then OH or H participates directly in the reaction to induce new reaction mechanism with more favorable routes, in which OH or H can act as an intermediate. (C) 2003 American Institute of Physics.