Reaction kinetics of H2O adsorption on Ce surface
Reaction kinetics of H2O adsorption on Ce surface
复制标题
Ce表面吸附H2O的反应动力学
DOI：
10.1016/s0925-8388(03)00266-4
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发表时间：
2003
影响因子：
6.2
通讯作者：
H. Uchida
中科院分区：
文献类型：
--
作者：
D. Katsuya;R. Suzuki;Fujio Suzuki;D. Tabuse;Y. Tajima;H. Uchida
在超高真空条件下制备了铈（Ce）薄膜，定量测定了气体H2O与Ce表面的反应活性，测定了在298 K下的反应概率rh2o和反应气量nh2o。在清洁的Ce表面上，即使在298 K的温度下，水的吸附也以最高的反应速率进行。随着反应活性的降低，观察到表面有明显的H2gas解吸现象。通过对解吸h2气体分压的测定，得到了H2O分子中H原子的反应概率r2H/H2O。从吸附速率的压力依赖性出发，估计了控制速率的步骤。从反应开始到反应结束，控制反应速率的是Ce表面的H2O分子的解离。当rH2O=1时，吸附活化能基本为零，当rH2O<1时，吸附活化能增大。在r2H/H2O=1时，H原子表面反应（氢化物和/或氢氧化物生成）的活化能几乎为零，当r2H/H2O<1时，随着NH2O的增加，活化能急剧增加。H2O与H原子的表面反应被强烈抑制，H原子的再组合变得活跃。在此基础上，讨论了水在Ce表面吸附的复杂机理。
Cerium (Ce) thin films were prepared under an ultra high vacuum condition, and the reactivity of H2O gas with the Ce surface was quantitatively measured for the reaction probability rH2Oand the gas amount NH2Oreacted at 298 K. The H2O adsorption proceeded at the highest reaction rate even at 298 K on a clean Ce surface. As the H2O reactivity drops, a marked desorption of H2gas from the surface was observed. From the measurement of the partial pressure of the desorbed H2gas, the reaction probability r2H/H2Oof the H atoms from H2O molecules were obtained. From the pressure dependence of the H2O adsorption rate, the rate controlling step was estimated. The rate controlling step was found to be the dissociation of H2O molecules on the Ce surface from the start to the end of the reaction. The activation energy for the H2O adsorption was almost zero at rH2O=1, and then increased at rH2O<1. The activation energy for the surface reactions (hydride and/or hydroxide formations) of the H atoms from H2O was almost zero at r2H/H2O=1, and then sharply increased at r2H/H2O<1 with increasing NH2O. The surface reactions of the H atoms from H2O become strongly inhibited, and the recombination of the H atoms become active. Based on these data, complicated mechanisms of the H2O adsorption on the Ce surface are discussed.