甲烷在Ni表面及La薄膜上激活解离化学吸附

利用分子束技术改变甲烷的平动能E_k来研究E_k及其法向分量E_n对甲烷在Ni表面及La薄膜上激活解离吸附的影响。对CH_4/Ni及CH_4/La系统, 当甲烷的平动能E_k分别低于58.5 kJ·mol~(-1)及52.3 kJ·mol~(-1)时, 没观察到甲烷的解离吸附。当甲烷的平动能超过此阈值时, 即对CH_4/Ni系统, 当Ek=58.5增至63.8 kJ·mol~(-1)时, 初始沾着几率s_0由0至0.54线性增加; 对CH_4/La系统, 当E_k=52.3增至63.8 kJ·mol~(-1)时, S_0由0至0.49线性增加。这些结果表明, 两个系统的化学吸附是不经过前趋态的直接化学吸附。最后求出CH_4/Ni, CH_4/La系统的表观活化能分别为46.8 kJ·mol~(-1)和38.1 kJ·mol~(-1)。

ACTIVATED CHEMISORPTION OF CH_4 ON Ni SURFACE AND La FILM

The effect of translational kinetic energy E_k on the activated chemisorption of CH_4 on Ni (polycrystal) surface and La film has been investigated using supersonic molecular beam technique. No dissociative adsorption was observed for CH_4/Ni system when E_k≤58.5 kJ·mol~(-1) and for CH_4/La system when E_k≤52.3 kJ·mol~(-1). Above these threshold values, the initial sticking probability s_0 increases linearly from 0 to 0.54 for CH_4/Ni system as E_k increases from 58.5 to 63.8 kJ·mol~(-1) and from 0 to 0.49 for CH_4/La system as E_k increases from 52.3 to 63.8 kJ·mol~(-1). These results indicate that a rather direct chemisorption process, rather than a classical precursor mechanism proceeds in these systems. Finally the apparent activation energies obtained are 46.8 kJ·mol~(-1) and 38.1 kJ·mol~(-1) for CH_4/Ni and CH_4/La systems respectively.