Carbon dioxide reduction on Ir(111): stable hydrocarbon surface species at near-ambient pressure

Abstract

Stable hydrocarbon surface species in the carbon dioxide hydrogenation reaction on Ir(111) were identified by means of infrared-visible sum-frequency generation vibrational spectroscopy and X-ray photoelectron spectroscopy under near-ambient pressure conditions (0.1 mbar). By introducing gas phase binary and ternary mixtures of CO2, CO, and H2 into the reaction chamber, stable ethylidyne and ethynyl species were found at the metal surface above 425 K, in remarkable analogy with that observed during the ethylene decomposition process yielding graphene. In addition, upon increasing temperature (up to 600 K depending on the reaction conditions), vibrational and electronic spectroscopic fingerprints appeared that could be attributed to the nucleation of aromatic hydrocarbons at the edge of metastable graphenic clusters interacting with the metal surface.

Vibrational fingerprint of localized excitons in a two-dimensional metal-organic crystal

“…3–6 ) identifies four contributions at 1986, 1992, 2005, and 2011 cm −1 . The SFG signal was deconvoluted by means of an established least-square fitting procedure 32 , according to an effective description of the nonlinear second-order susceptibility (the complete set of fitting parameters is reported in Supplementary Tables 1 and 2 ). The surface density of the Fe centers is very low due to the large size of the FePc molecules (about 0.03 ML with respect to the underlying Ir metal surface).…”

“…IR-Vis sum-frequency generation vibronic spectroscopy measurements were performed in a dedicated setup 32 . A UHV system with a base pressure of 5 × 10 −11 mbar hosts standard surface science preparation and characterization techniques, and it is directly connected to a high-pressure cell for in situ IR-Vis SFG spectroscopy.…”

“…The excitation source (Ekspla) delivers a 532 nm (2.33 eV, 30 ps, 50 Hz, 0.01 mJ pulse −1 at 1% power) visible beam and tunable IR radiation in the 1000–4500 cm −1 range. After normalization to the IR and visible excitation intensities, the SFG spectra were analyzed by least-squares fitting to a parametric, effective expression of the nonlinear second-order susceptibility 32 , 49 . The expression (reported here below) well reproduces the observed lineshapes, accounting for the resonant IR-Vis vibronic transitions and for the nonresonant background, and describing all the interference terms: where, A NRes and A k account for the amplitudes of the nonresonant and k th -resonant contributions, respectively, Δ φ k is the phase difference between the k th -resonant and nonresonant signals, ω k is the energy position of the line, and Γ k its Lorentzian broadening, related to the dephasing rate, which in turn stems from the energy lifetime and from the elastic dephasing of the excited vibronic state 50 .…”

“…These plots directly put in evidence the amplitude and the relative phase for each of the resonances. Further details can be found in our previous work 32 . In the present study, all spectra were collected in the ppp polarization configuration (SFG-visible-infrared).…”

Tetrapyrroles at near-ambient pressure: porphyrins and phthalocyanines beyond the pressure gap

“…The presence of the N-species on the carbon substrate both stabilizes the active Fe(II) centers hindering further reduction of Fe, thus inhibiting the hydrogen evolution, and allows coordination of the reactive CO 2 -related species related with the liquid phase [142]. Interestingly, it is found that the latter (H 2 CO 3 , HCO 3 − , CO 3 − ) consistently differ with respect to their counterpart in the case of the solid/gas reaction [68][69][70][71][72][144][145][146]. Metal-nitrogen coordinated electrocatalytic systems offer the capability of electron donation/ withdrawal to/from the carbonaceous ligand, thus with improved and tunable activity [147][148][149][150].…”