Abstract:We present a new high-pressure x-ray photoelectron spectroscopy system dedicated to probing catalytic reactions under realistic conditions at pressures of multiple bars. The instrument builds around the novel concept of a "virtual cell" in which a gas flow onto the sample surface creates a localized high-pressure pillow. This allows the instrument to be operated with a low pressure of a few millibar in the main chamber, while simultaneously a local pressure exceeding 1 bar can be supplied at the sample surface… Show more
“…In particular, we can find a small spectral shoulder at 307.9 eV, as displayed in the overlapping comparison plot of CO(g) and CO 2 (g) in Supplementary Fig. 7 , which implies that the surface Rh 3 d core-level shifts get involved in the adsorbate‒Rh atoms bonding formation properties by reactive molecule collisions and electronic charge redistribution on the Rh(111) surface 44 – 46 . Fig.…”
Utilization of carbon dioxide (CO2) molecules leads to increased interest in the sustainable synthesis of methane (CH4) or methanol (CH3OH). The representative reaction intermediate consisting of a carbonyl or formate group determines yields of the fuel source during catalytic reactions. However, their selective initial surface reaction processes have been assumed without a fundamental understanding at the molecular level. Here, we report direct observations of spontaneous CO2 dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO2. The linear geometry of CO2 gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO2 and surface Rh atoms. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy at near-ambient pressure, and computational calculations, we reveal strong evidence for chemical bond cleavage of O‒CO* with ordered intermediates structure formation of (2 × 2)-CO on an atomically flat Rh(111) surface at room temperature.
“…In particular, we can find a small spectral shoulder at 307.9 eV, as displayed in the overlapping comparison plot of CO(g) and CO 2 (g) in Supplementary Fig. 7 , which implies that the surface Rh 3 d core-level shifts get involved in the adsorbate‒Rh atoms bonding formation properties by reactive molecule collisions and electronic charge redistribution on the Rh(111) surface 44 – 46 . Fig.…”
Utilization of carbon dioxide (CO2) molecules leads to increased interest in the sustainable synthesis of methane (CH4) or methanol (CH3OH). The representative reaction intermediate consisting of a carbonyl or formate group determines yields of the fuel source during catalytic reactions. However, their selective initial surface reaction processes have been assumed without a fundamental understanding at the molecular level. Here, we report direct observations of spontaneous CO2 dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO2. The linear geometry of CO2 gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO2 and surface Rh atoms. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy at near-ambient pressure, and computational calculations, we reveal strong evidence for chemical bond cleavage of O‒CO* with ordered intermediates structure formation of (2 × 2)-CO on an atomically flat Rh(111) surface at room temperature.
“…S3). The precise measurement by using ARPES can open new opportunities to monitor the work function on the surface, for example, in ambient conditions [52][53][54][55] , under controlled application of strain 56,57 , during phase transitions or crossovers [58][59][60] and upon irradiation of intense femtosecond pulses 30,[61][62][63][64] .…”
Electron emission can be utilised to measure the work function of the surface. However, the number of significant digits in the values obtained through thermionic-, field- and photo-emission techniques is typically just two or three. Here, we show that the number can go up to five when angle-resolved photoemission spectroscopy (ARPES) is applied. This owes to the capability of ARPES to detect the slowest photoelectrons that are directed only along the surface normal. By using a laser-based source, we optimised our setup for the slow photoelectrons and resolved the slowest-end cutoff of Au(111) with the sharpness not deteriorated by the bandwidth of light nor by Fermi-Dirac distribution. The work function was leveled within ±0.4 meV at least from 30 to 90 K and the surface aging was discerned as a meV shift of the work function. Our study opens the investigations into the fifth significant digit of the work function.
“…24 Reasonable distances for lab-based systems are typically in the range of 500–800 µm, 14,25–27 while for synchrotron applications this distance can be reduced to 150–300 µm 28 and for some specific cases, including the system used herein, down to 30 µm. 13,29 At these distances, a small change in distance of 1 µm can have a substantial effect on the pressure over the sample, the pressure in the differentially pumped section, and the signal from the sample. To date, few systems have been able to achieve pressures over 50 mbar.…”
Section: Introductionmentioning
confidence: 99%
“…For all differentially pumped systems, the sample-to-aperture distance is monotonically related to the pressure in the differential pumping stage. 13,30 Therefore, maintaining a constant pressure in the first differential pumping stage also maintains a constant sample-to-aperture distance. A pressure gauge in this stage is an ideal source of information for developing a position feedback loop, to maintain a constant separation due to the pressure depending on the sample-to-aperture distance yet being measured independently.…”
Section: Introductionmentioning
confidence: 99%
“…Figure 1 shows a mockup of the sample and aperture, indicating that the gas is approaching the sample from within the analyzer cone. Typical separation under reaction conditions is 30 µm; for more details, see Amman et al 13 Figure 1.A mockup of the sample and aperture, indicating that the gas is approaching the sample from within the analyzer cone. Typical separation under reaction conditions is 30 µm.…”
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