Wang Wenji
College of Chemistry & Pharmacy, Northwest A&F University, Yangling, Xianyang 712100, Shaanxi Province, P. R. China.
J Phys Chem A. 2020 Oct 22;124(42):8724-8732. doi: 10.1021/acs.jpca.0c06130. Epub 2020 Oct 12.
Water dissociation is a key step in many industrial catalytic processes. The dissociation of HO on a rigid Ni(100) surface was investigated by the quantum instanton method with a full-dimensional potential energy surface. The calculated free-energy barrier maps showed that the free-energy barrier varied dramatically with the surface site. The free-energy well map demonstrated that the physisorption well of HO was existent at all of the surface sites, and HO could be dissociated by both the direct and steady-state processes. The calculated direct dissociation rate constants at different surface sites decreased rapidly in the order transition state (TS) > bridge > top > hollow. The steady-state dissociation rate constants had the same trend as that of the direct process but the steady-state dissociation rate constant at the top site became the largest at high temperatures. The direct dissociation rate constants were always larger than those of the steady-state process at a given temperature. The calculated kinetic isotope effects for the direct and steady-state processes were extremely large at low temperatures, which was caused by the zero-point energy correction and remarkable quantum tunneling. From low temperature to high temperature, HO would undergo stable molecular adsorption at the top site, steady-state dissociation at the TS site, direct rupture at the TS site, and direct decomposition at the impact site.
水的离解是许多工业催化过程中的关键步骤。采用具有全维势能面的量子瞬子方法研究了HO在刚性Ni(100)表面的离解。计算得到的自由能垒图表明，自由能垒随表面位点的变化很大。自由能阱图表明，HO在所有表面位点都存在物理吸附阱，并且HO可以通过直接过程和稳态过程离解。计算得到的不同表面位点的直接离解速率常数按过渡态(TS)>桥位>顶位>空位的顺序迅速降低。稳态离解速率常数与直接过程具有相同的趋势，但在高温下顶位的稳态离解速率常数变得最大。在给定温度下，直接离解速率常数总是大于稳态过程的速率常数。计算得到的直接过程和稳态过程的动力学同位素效应在低温下极大，这是由零点能校正和显著的量子隧穿引起的。从低温到高温，HO将在顶位发生稳定的分子吸附，在TS位点发生稳态离解，在TS位点直接断裂，在碰撞位点直接分解。
