Physisorbed State Regulates the Dissociation Mechanism of H2O on Ni(100)

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 124; no. 42; pp. 8724 - 8732
• Main Author: Wang, Wenji
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22.10.2020
• Subjects: A: Spectroscopy, Molecular Structure, and Quantum Chemistry
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.0c06130

Water dissociation is a key step in many industrial catalytic processes. The dissociation of H2O 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 H2O was existent at all of the surface sites, and H2O 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, H2O 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.