Water dissociation and COOH formation on Fe modified Cu(100) surface: A density functional theory study

Water splitting has emerged as a promising route for sustainable hydrogen production. In this research paper, adsorption and dissociation of H2O accompanied with dissociated constituents reactions with CO2 and CO have been investigated on Fe modified Cu(100) surface employing density functional theory (DFT) at GGA-PW91 level. The adsorption and other reactions carried out on Fe2-Cu(100) surfaces gave very promising results. The adsorption of H2O on Fe top of this surface occurs yielding Eads -1.73 eV, which highlights a favorable adsorption on the Fe-modified Cu(100) surface. The activation energy for the water splitting reaction is found to be 0.65 eV, suggesting a feasible pathway for hydrogen evolution. The process also accompanies reaction energy of -0.54 eV. Furthermore, the interaction between carbon dioxide (CO2) and the H-atom on the surface lead to the formation of COOH through surmounting an activation barrier of 1.09 eV. The final position of COOH gets further stabilization having exothermicity of -0.43 eV. Another route for COOH formation from CO + OH operates on the Cu(100) part of the surface with a small activation barrier of 0.14 eV through exothermic process of -0.29 eV, however, diffusion of CO and OH from Fe to Cu is energetically expensive. This study signifies the consumption of CO and CO2 in addition to water splitting giving birth to useful products.

Theoretical Calculations on Metal Catalysts Toward Water-Gas Shift Reaction: a Review

Water-gas shift (WGS) reaction offers a dominating path to hydrogen generation from fossil fuel, in which heterogeneous metal catalysts play a crucial part in this course. This review highlights and summarizes recent developments on theoretical calculations of metal catalysts developed to date, including surface structure (e. g., monometallic and polymetallic systems) and interface structure (e. g., supported catalysts and metal oxide composites), with special emphasis on the characteristics of crystal-face effect, alloying strategy, and metal-support interaction. A systematic summarization on reaction mechanism was performed, including redox mechanism, associative mechanism as well as hybrid mechanism; the development on chemical kinetics (e. g., molecular dynamics, kinetic Monte Carlo and microkinetic simulation) was then introduced. At the end, challenges associated with theoretical calculations on metal catalysts toward WGS reaction are discussed and some perspectives on the future advance of this field are provided.

Mechanism Investigations on Water Gas Shift Reaction over Cu(111), Cu(100), and Cu(211) Surfaces

Cu-based catalysts are commonly applied in low-temperature water gas shift (WGS) reactions, owing to their low cost and high catalytic activity. The influence of different Cu surfaces on catalytic activity and mechanism over the WGS reaction remains unclear. In this work, the effect of different structures of surfaces on the WGS mechanism is studied using density functional theory (DFT). Three surface terminations (Cu(100), Cu(111), and Cu(211)) of Cu are considered, and the coordination number (CN) of the active Cu site is in the range from 7 to 9. The most stable surface is Cu(211). Then, d-band center values are calculated, which decrease in the following sequence: Cu(211) > Cu(100) > Cu(111). This shows that d-band center values decrease with increasing coordination number. The increase in the centers of the d-band leads to an increase in the adsorption strength of CO and H₂O adsorbates, which is in line with the theory of the d-band center. In addition, the further calculated mechanism for WGS reaction over three different Cu surfaces illustrates that the carboxyl path is the most favorable mechanism, and the rate-determining step is H₂O dissociation. Cu(211) shows excellent WGS catalytic performance, better than the Cu(100) and Cu(111) surfaces. This work provides theoretical insights into the rational design of highly active Cu-based catalysts toward WGS reaction.

Direct Visualization of a Gold Nanoparticle Electron Trapping Effect

A new atomic-scale anisotropy in the photoreaction of surface carboxylates on rutile TiO₂(110) induced by gold clusters is found. STM and DFT+U are used to study this phenomenon by monitoring the photoreaction of a prototype hole-scavenger molecule, benzoic acid, over stoichiometric (s) s-TiO₂, Au₉/s-TiO₂, and reduced (r) Au₉/r-TiO₂. STM results show that benzoic acid adsorption displaces a large fraction of Au clusters from the terraces toward their edges. DFT calculations explain that Au₉ clusters on stoichiometric TiO₂ are distorted by benzoic acid adsorption. The influence of sub-monolayers of Au on the UV/visible photoreaction of benzoic acid was explored at room temperature, with adsorbate depletion taken as a measure of activity. The empty sites, observed upon photoexcitation, occurred in elongated chains (2 to 6 molecules long) in the [11̅0] and [001] directions. A roughly 3-fold higher depletion rate is observed in the [001] direction. This is linked to the anisotropic conduction of excited electrons along [001], with subsequent trapping by Au clusters leaving a higher concentration of holes and thus an increased decomposition rate. To our knowledge this is the first time that atomic-scale directionality of a chemical reaction is reported upon photoexcitation of the semiconductor.