We present a density functional theory study on the adsorption and decomposition mechanisms of monomeric formic acid (HCOOH) on a Cu(111) surface. We used Perdew-Burke-Ernzerhof (PBE) functional, PBE with dispersion correction (PBE-D2), and van der Waals density functionals (vdW-DFs). We found that the adsorption energy of HCOOH by using the PBE functional is smaller than the experimental value, while the PBE-D2 and vdW-DFs give better agreement with experimental results. The activation energies of decomposition calculated by using PBE-D2 and vdW-DFs are lower compared with desorption energies, seemingly in contradiction with experimental findings at room temperature, in which no decomposition of HCOOH on Cu(111) is observed when the surface is exposed to the gas phase HCOOH. We performed the reaction rate analysis based on the first-principles calculations for desorption and decomposition processes to clarify this contradiction. We found that the desorption of monomeric HCOOH is faster than that of its decomposition rate at room temperature because of a much larger pre-exponential factor. Thus, no decomposition of monomeric HCOOH should take place at room temperature. Our analysis revealed the competition between desorption and decomposition processes of HCOOH.

Formic acid (HCOOH) can be catalytically decomposed into H2 and CO2 and is a promising hydrogen storage material. As H2 production catalysts, Cu surfaces allow selective HCOOH decarboxylation; however, the on‐surface HCOOH decomposition reaction pathway remains controversial. In this study, the temperature dependence of the HCOOH/Cu(111) adsorption structures is elucidated by scanning tunneling microscopy and non‐contact atomic force microscopy, establishing the adsorbate chemical species using density functional theory. 2D HCOOH islands at 80 K, linear chains of HCOOH and monodentate formate at 150 K, chain‐like assemblies of monodentate and bidentate formate at 200 K, and bidentate formate clusters at 300 K are observed. At each temperature, the adsorbates experience attractive interactions among themselves. Such aggregation stabilizes them against desorption and decomposition. Thus, accurate evaluation of intermolecular interactions is essential to understand catalytic reactivity.

We have studied the dissociation process of nitric oxide (NO) on Cu(110) and the influence of the hydrogen bond with water by means of density functional theory calculations. We have found that an upright NO adsorbed at a short-bridge site and a side-on NO at a hollow site connecting two short-bridge sites are the two most stable molecularly adsorbed states, and the latter is the precursor for the dissociation process. Various NO dissociation pathways under the influences of the hydrogen bonds with water have been investigated. We have found that hydrogen bonds efficiently reduce the activation energy of NO dissociation by the introductions of a water dimer to O and water dimers to both sides of the side-on NO, respectively. More importantly, the promoting effect of water molecules on NO dissociation is dominant only when one of water molecules in a water dimer forms a hydrogen bond with O of the side-on NO. Our results provide a physical insight into the promoting effect of hydrogen bonds with water, which may be helpful in improving the catalytic activity as well as designing novel catalysts for NO reduction.

Identifying the origin of carbon deposition in reactions, such as dry reforming of methane (DRM) over cobalt (Co) nanocatalysts, is an important yet challenging issue in heterogeneous catalysis. In this study, we used density functional theory (DFT) calculations to investigate the surface reactions of CO2 with C* at the flat and step sites of face-centered cubic (FCC) Co [(111), (110), (100), (211), and (221)], which represent the major surfaces of Co nanoparticles. The results were being compared with Ni nanoparticles. Hereby, we identified that the high degree of preference for C–C coupling over CO* formation, especially on Co(111), serves as the origin of carbon graphitization. This finding is similar to that on Ni(111). Furthermore, we reported for the first time that the significant difference between Co and Ni is due to CO2 activation, which is far more favored on Co than on Ni, accounting for the lower carbon deposition on Co. On the other hand, within the investigated surfaces of Co, step and less common surfaces, namely, Co(211), Co(221), and Co(100), do not favor C–C coupling. Based on our findings, we proposed that high-index-facet, surface-modified, and/or promoted Co nanoparticles be used for DRM to restrict C–C coupling.

The reaction mechanism of the CH3OH synthesis by the hydrogenation of CO2 on Cu catalysts is unclear because of the challenge in experimentally detecting reaction intermediates formed by the hydrogenation of adsorbed formate (HCOOa). Thus, the objective of this study is to clarify the reaction mechanism of the CH3OH synthesis by establishing the kinetic natures of intermediates formed by the hydrogenation of adsorbed HCOOa on Cu(111). We exposed HCOOa on Cu(111) to atomic hydrogen at low temperatures of 200–250 K and observed the species using infrared reflection absorption (IRA) spectroscopy and temperature-programmed desorption (TPD) studies. In the IRA spectra, a new peak was observed upon the exposure of HCOOa on Cu(111) to atomic hydrogen at 200 K and was assigned to the adsorbed dioxymethylene (H2COOa) species. The intensity of the new peak gradually decreased with heating from 200 to 290 K, whereas the IR peaks representing HCOOa species increased correspondingly. In addition, small amounts of formaldehyde (HCHO), which were formed by the exposure of HCOOa species to atomic hydrogen, were detected in the TPD studies. Therefore, H2COOa is formed via hydrogenation by atomic hydrogen, which thermally decomposes at ∼250 K on Cu(111). We propose a potential diagram of the CH3OH synthesis via H2COOa from CO2 on Cu surfaces, with the aid of density functional theory calculations and literature data, in which the hydrogenation of bidentate HCOOa to H2COOa is potentially the rate-determining step and accounts for the apparent activation energy of the methanol synthesis from CO2 on Cu surfaces.