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Energy transfer dynamics of formate (HCOO ) decomposition on a Cu(110) surface has been studied by measuring the angle-resolved intensity and translational energy distributions of CO emitted from the surface in a steady-state reaction of HCOOH and O . The angular distribution of CO shows a sharp collimation with the direction perpendicular to the surface, as represented by cos θ (n=6). The mean translational energy of CO is measured to be as low as 100 meV and is independent of the surface temperature (T ). These results clearly indicate that the decomposition of formate is a thermal non-equilibrium process in which a large amount of energy released by the decomposition reaction of formate is transformed into the internal energies of CO molecules. The thermal non-equilibrium features observed in the dynamics of formate decomposition support the proposed Eley-Rideal (ER)-type mechanism for formate synthesis on copper catalysts.

The formation of two-electron chemical bonds requires the alignment of spins. Hence, it is well established for gas-phase reactions that changing a molecule’s electronic spin state can dramatically alter its reactivity. For reactions occurring at surfaces, which are of great interest during, among other processes, heterogeneous catalysis, there is an absence of definitive state-to-state experiments capable of observing spin conservation and therefore the role of electronic spin in surface chemistry remains controversial. Here we use an incoming/outgoing correlation ion imaging technique to perform scattering experiments for O(3P) and O(1D) atoms colliding with a graphite surface, in which the initial spin-state distribution is controlled and the final spin states determined. We demonstrate that O(1D) is more reactive with graphite than O(3P). We also identify electronically nonadiabatic pathways whereby incident O(1D) is quenched to O(3P), which departs from the surface. With the help of molecular dynamics simulations carried out on high-dimensional machine-learning-assisted first-principles potential energy surfaces, we obtain a mechanistic understanding for this system: spin-forbidden transitions do occur, but with low probabilities.

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.

Energy transfer dynamics of formate (HCOO a ) decomposition on aC u(110) surface has been studied by measuring the angle-resolved intensity and translational energy distributions of CO 2 emitted from the surface in asteady-state reaction of HCOOH and O 2 .The angular distribution of CO 2 shows as harp collimation with the direction perpendicular to the surface,a srepresented by cos n q (n = 6). The mean translational energy of CO 2 is measured to be as lowas100 meV and is independent of the surface temperature (T s ). These results clearly indicate that the decomposition of formate is athermal non-equilibrium process in which al arge amount of energy released by the decomposition reaction of formate is transformed into the internal energies of CO 2 molecules.T he thermal non-equilibrium features observed in the dynamics of formate decomposition support the proposed Eley-Rideal (ER)-type mechanism for formate synthesis on copper catalysts.Energy transfer and bond rupture/formation are two important events in ac hemical reaction. [1,2] Consequently,t he reaction mechanism must be examined with both aspects in mind. Forg as-phase bimolecular reactions,e nergy transfer processes have been extensively examined by applying crossed molecular beam techniques,w here detailed dynamical parameters (such as total momentum, energy,and angular momentum, before and after the collision events) can describe the partitioning of energy into each available mode of the products. [3,4] On the other hand, characterizing the energy-transfer processes in gas-surface chemical reactions is challenging because of the large number of degrees of freedom available to the surface atoms.T oa nalyze ag assurface chemical reaction, angle-resolved (AR) analysis of the desorbed products from the surface is one of the direct methods used because it relates to the transition state (TS) structure of the reaction. [5][6][7] In this communication, we report the angle-resolved intensity and translational energy distributions of the CO 2 produced from the decomposition of formate during the steady-state reaction of HCOOH with O 2 on Cu(110).Formate (HCOO a )i sa ni mportant intermediate in the synthesis of methanol, and is formed on copper surfaces during the initial elementary CO 2 hydrogenation step, namely:C O 2 + 1/2 H 2 !HCOO a . [8][9][10] Formate synthesis is unique in terms of reaction mechanism and dynamics,a s well as its structure-insensitive kinetics.W ehave proposed an ER-type mechanism for formate synthesis,b ased on experimental kinetic analysis and theoretical calculations, [11,12] in which CO 2 directly reacts with the adsorbed hydrogen atoms (H a )o nt he copper surface without the involvement of trapping states and adsorption precursors.T his,i nt urn, implies that the formate production rate can only be enhanced by controlling the energy of the CO 2 molecules in terms of at hermal non-equilibrium character.T he dynamics of formate decomposition on copper catalysts is thus interesting as the reverse reaction of formate synthesis: HCOO a ...