Mechanism of the Surface Hydrogen Induced Conversion of CO₂ to Methanol at Cu(111) Step Sites

Cu/ZnO/Al₂O₃ is an industrially important heterogeneous catalyst for the conversion of CO₂ to methanol, which is in worldwide demand, and for the solution of the activation mechanism of catalytically inactive CO₂. Recent studies have achieved numerous improvements in active sites of catalysts for this process, which can be described as “active copper with step sites” decorated with ZnO_<i>x</i>. In spite of these improvements, the mechanism of this process is still unknown, and even its initial stage remains unclear. In this study, we simplified the catalytic system to bare Cu(111) and Cu(775) surfaces in order to systematically determine the mechanistic effects of step sites. The reaction was conducted by using a CO₂/H₂ gas mixture at 1 Torr at various temperatures and characterized with infrared reflection absorption spectroscopy (IRRAS). The initial activation of CO₂ was found to occur only with the coadsorption of hydrogen; it cannot on its own be converted into other activated species. This coadsorbed hydrogen induces the dissociation of CO₂ and converts it into CO, surface oxygen (O*), and surface hydroxyl (HO*). These species are subsequently converted to carbonate (CO₃*), bicarbonate (HCO₃*), and formate (HCOO*). One significant observation is that the number of these formate species on step sites continuously decreases with increases in the number of CH₂ species during stepwise heating. In addition, a continuous reaction is obtained from formate transfer from terrace to step. Also, an instantaneous feature of methoxy (CH₃O*) was observed during the evacuation process. These phenomena strongly indicate that formate is an essential intermediate, especially on steps, for the conversion of CO₂ to methanol and that the reduction in its level during this process is due to step-by-step hydrogenation

Effects of Hydrogen Partial Pressure in the Annealing Process on Graphene Growth

Graphene domains with different sizes and densities were successfully grown on Cu foils with use of a chemical vapor deposition method. We investigated the effects of volume ratios of argon to hydrogen during the annealing process on graphene growth, especially as a function of hydrogen partial pressure. The mean size and density of graphene domains increased with an increase in hydrogen partial pressure during the annealing time. In addition, we found that annealing with use of only hydrogen gas resulted in snowflake-shaped carbon aggregates. Energy-dispersive X-ray spectroscopy (EDX) and high-resolution photoemission spectroscopy (HRPES) revealed that the snowflake-shaped carbon aggregates have stacked sp² carbon configuration. With these observations, we demonstrate the key reaction details for each growth process and a proposed growth mechanism as a function of the partial pressure of H₂ during the annealing process

Additional file 1: of Enhancement of Photo-Oxidation Activities Depending on Structural Distortion of Fe-Doped TiO2 Nanoparticles

Supplementary material. Digital images and SEM images of Fe@TiO2 nanoparticles, XRD, and Raman intensity plot. Figure S1. Digital images of the Fe@TiO2 dispersed solution with several of Fe dopant concentration. Figure S2. SEM images as the morphologies varying the doping level of Fe: (a) 1 wt %, (b) 3 wt %, (c) 5 wt %; and their high-resolution images (a′), (b′), and (c′), respectively. Figure S3. EDX spectra with Fe peak (marked by black arrows) of big particles: (a) 1 wt% Fe@TiO2, (b) 3 wt% Fe@TiO2, and (c) 5 wt% Fe@TiO2. Figure S4. (a) XRD peak position and correspond lattice constant of (101) plane of anatase TiO2 structure and (b) Raman intensity ratio of I410 (α-Fe2O3 Eg) to I144 (anatase TiO2 Eg). Figure S5. Spectral subtraction of valence band spectra by bare TiO2 peak: (a) 1 wt% Fe@TiO2, (b) 3 wt% Fe@TiO2, and (c) 5 wt% Fe@TiO2

Comparison and Contrast Analysis of Adsorption Geometries of Phenylalanine versus Tyrosine on Ge(100): Effect of Nucleophilic Group on the Surface

The discrepancy of geometric configuration between phenylalanine and tyrosine adsorbed on Ge(100) surfaces was investigated using scanning tunneling microscopy (STM) in conjunction with density functional theory (DFT) calculations and core-level photoemission spectroscopy (CLPES). The study focused on the role of nucleophilic group (hydroxyl group) on phenyl ring of tyrosine, and we elucidated the difference of the adsorption geometry between phenylalanine and tyrosine on Ge(100) surfaces. We first confirmed that the “O–H dissociated–N dative bonded structure” was the most favorable structure in both molecules at low coverage by results of CLPES and DFT calculations. Geometric differences for the adsorption configurations between phenylalanine and tyrosine were observed: the phenyl ring of phenylalanine was aligned axially with respect to the Ge(100) surface, whereas that of tyrosine was tilted, as determined by DFT calculations. In sequence, we found out the results of STM images to confirm DFT results. We determined the different geometric configurations are attributed to the nucleophilic hydroxyl group of tyrosine, which creates an uneven charge distribution