Enhancing dissociative chemisorption of H ₂ O on Cu(111) via vibrational excitation

Abstract

The dissociative chemisorption of water is an important step in many heterogeneous catalytic processes. Here, the mode selectivity of this process was examined quantum mechanically on a realistic potential energy surface determined by fitting planewave density functional calculations spanning a large configuration space. The quantum dynamics of the surface reaction were characterized by a six-dimensional model including all important internal coordinates of H 2 O and its distance to the surface. It was found that excitations in all three vibrational modes are capable of enhancing reactivity more effectively than increasing translational energy, consistent with the "late" transition state in the reaction path.heterogeneous catalysis | mode specific chemistry | reaction dynamics T he dissociative chemisorption of H 2 O on transition-metal surfaces, which produces chemisorbed H and OH species, is an important and often obligatory step in many heterogeneous catalytic processes, such as the water-gas shift (WGS) reaction and steam reforming (1). Given our dwindling fossil fuel resources and health-threatening pollution, these reactions have become increasingly important in generating environmentally friendly hydrogen fuels for various high-efficiency applications, such as fuel cells (2). In low-temperature WGS on copper catalysts, for example, the dissociative chemisorption of H 2 O has been identified as the rate-limiting step (3). A better understanding of the reaction dynamics and the ultimate control and/or enhancement of the process could potentially benefit many industrial processes that involve H 2 O. Despite our increasing understanding of the adsorption and dissociation of water on various metal surfaces, however, few experimental studies have been reported (to the best of our knowledge) on the dynamics of water-metal interaction, and none on dissociative chemisorption (4). In this work, we explore a potentially useful scheme based on mode selectivity to enhance dissociative chemisorption on a copper surface.Controlling reactivity of a chemical reaction by selecting reactant internal quantum states is a holy grail in chemical dynamics (5). This mode selectivity and related bond selectivity have been experimentally demonstrated for only a few reactive systems in the gas phase (6-13) and on surfaces (14-21). For example, it was shown that both the kinetics and dynamics of the H þ H 2 O reaction depend sensitively on the vibrational state of the H 2 O reactant (6). Similarly, different vibrational excitations of CH 4 have been demonstrated to have varying efficacies in promoting its dissociative chemisorption on transition-metal surfaces, some more effective than translational energy (22). These observations underscore the importance of quantum dynamical effects and inadequacy of statistically based transition state theory for describing mode-and bond-specific chemistry.A key question in mode-and bond-selective chemistry is whether energy in vibrational coordinates is more effective in promoting reaction than t...

Prediction of Mode Specificity, Bond Selectivity, Normal Scaling, and Surface Lattice Effects in Water Dissociative Chemisorption on Several Metal Surfaces Using the Sudden Vector Projection Model

“…2−4 Given the "lateness" of the barrier, it can be expected that excitations in water stretching modes would promote the reaction more effectively than translational energy. 5 This expectation has indeed been confirmed recently in a combined experimental -theoretical study of the dissociative chemisorption of D 2 O on Ni(111). 6 Similar mode specificity and related bond selectivity have also been observed experimentally in the dissociative chemisorption of methane.…”

“…5,30,34 Similar underestimations have been found in some gas phase reactions as well, 38 which could presumably be considered as a weakness of the SVP model. Given the lower frequency of the bending mode, it is conceivable that a much faster IVR is associated with the angular coordinates near the transition state.…”

Six-dimensional quantum dynamics study for the dissociative adsorption of HCl on Au(111) surface

“…zhangdh@dicp.ac.cn six-dimensional quantum dynamics calculations of H 2 O on Cu(111) [37][38][39] and eight-dimensional calculations of CH 4 on Ni(111). 40 Accurate PESs were fit by the permutationally invariant polynomial approach of Bowman and co-workers 41,42 based on energy points from density functional theory (DFT) calculations.…”

Communication: Enhanced dissociative chemisorption of CO2 via vibrational excitation

“…31 This approach has been previously used to study the DC of both methane and water with success. 25,[32][33][34][35][36][37] A global PES allows not only a large number of trajectories to achieve good statistics but also quantum dynamics important for describing quantum effects such as tunneling. 31 However, an analytical high-dimensional representation of the DFT points distributed in a large configuration space is rather challenging.…”