The adsorption and decomposition of formic acid on Cu{110}
The adsorption and decomposition of formic acid on Cu{110}
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DOI：
10.1016/0039-6028(95)01069-6
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发表时间：
1996-04-01
期刊：
影响因子：
1.9
通讯作者：
Haq, S
中科院分区：
文献类型：
--
作者：
Bowker, M;Rowbotham, E;Haq, S
使用分子束系统、TPD、LEED 和 STM 研究了甲酸 (HCOOH) 在掺氧 Cu(110) 上的反应吸附。在低温下，反应强烈依赖于氧覆盖度。所有覆盖率都会导致甲酸发生高反应概率（室温下为 0.8），并且对于少于 0.25 个单层氧，氧气会被完全清除，从而使甲酸盐以 c(2 X 2) 结构留在表面上。在更高的覆盖率下，情况更加复杂，一些氧气仍然与甲酸盐共吸附。然后，两种吸附物主要相分离成c(6 X 2)氧和(3 X 1)甲酸盐岛。由于相边界处的压力，两相相互压缩。在此温度范围内，反应化学计量为2:1甲酸:氧原子。在较高温度 (> 450 K) 下，甲酸盐本身不稳定并在吸附过程中分解，导致反应化学计量发生变化；一分子甲酸以水的形式除去一个氧原子，氢气停止析出。在 350 到 420 K 之间的温度范围内，反应变得非常困难，反应概率下降到大约 0.1。据认为，这是由于少量的甲酸盐将大部分氧吸附层快速压缩成不反应的 c(6 x 2) 结构。该反应通过表面上高度移动、弱保持的“前体”状态进行，该状态能够寻找表面上的活性位点，这些活性位点在高氧水平下覆盖率较低。这些活性位点是氧岛中的末端氧原子（在[001]方向），它们仅存在于0.5单层氧覆盖率的台阶边缘或相边界处。
The reactive adsorption of formic acid (HCOOH) on oxygen dosed Cu(110) has been studied using a molecular beam system, TPD, LEED and STM. At low temperature the reaction is strongly oxygen coverage dependent. All coverages result in high reaction probability (0.8 at room temperature) for formic acid and, for less than 0.25 monolayers of oxygen there is complete oxygen clean-off, leaving formate on the surface in a c(2 X 2) structure, At higher coverages the situation is more complex, with some oxygen remaining coadsorbed with the formate. The two adsorbates are then mainly phase separated into islands of c(6 X 2) oxygen and (3 X 1) formate, The two phases mutually compress each other due to pressure at the phase boundaries. The reaction stoichiometry is 2:1 formic acid:oxygen atoms in this temperature range. At higher temperatures (> 450 K) the formate itself is unstable and decomposes during adsorption which results in a change of stoichiometry of the reaction; one molecule of formic acid removes an oxygen atom as water, and hydrogen evolution ceases. There is a range of temperature between 350 and 420 K for which the reaction becomes very difficult, and the reaction probability drops to similar to 0.1. It is proposed that this is due to rapid compression of much of the oxygen adlayer into the unreactive c(6 x 2) structure by small amounts of formate. The reaction proceeds through a highly mobile, weakly held, ''precursor'' state on the surface, which is able to seek out the active sites on the surface, which are low in coverage at high levels of oxygen, These active sites are the terminal oxygen atoms in the oxygen islands (in the [001] direction), which are only present at step edges or phase boundaries at 0.5 monolayers coverage of oxygen.