Desulfurization-Related Surface Chemistry on Two-Dimensional Silica Films: Adsorption of Thiophene and Short-Chain Alkanes on Silicatene

Abstract

The kinetics of thiophene and alkane adsorption on silicatene (i.e., on two-dimensional atomically thin and crystalline silica films) was studied by employing (multimass) thermal desorption spectroscopy (TDS) at ultrahigh vacuum. The monoatomic SiO2 film is grown on a Mo(112) support. Thiophene is a standard probe molecule for hydrodesulfurization (HDS); alkanes typically form as reaction products; Mo is a catalyst for HDS. The samples were characterized by Auger electron spectroscopy and low-energy electron diffraction as well as the silica film additionally by water TDS. The silicatene film is hydrophobic. All probe molecules adsorbed nondissociatively on silicatene. Two TDS peaks in the monolayer range are evident as well as a condensation structure. Thiophene binds with 42.6 ± 0.5 kJ/mol in the limit of zero coverage. Using a Redhead analysis and assumed pre-exponential of 1 × 1013/s, the (low coverage) binding energy of the alkanes (isobutane, n-pentane, and n-heptane) increases from 34.1 to 46.8 (±0.5) kJ/mol with the chain length. A more sophisticated data analysis (direct inversion of the Polanyi–Wigner equation) reveals a chain-length-dependent pre-exponential and binding energy. In addition, the adsorption dynamics of butane was characterized by molecular beam scattering. The adsorption probabilities and binding energies are systematically smaller for silicatene than for polycrystalline bulk silica wafer.

Adsorption and Reaction of Thiophene on Graphene/Ruthenium: Experiment and Theory

“…The α-peak (at 133 or 139 K, solid lines in Figure A or B), with a peak position independent of C 4 H 4 S exposure, is assigned to molecular desorption in the monolayer coverage range. The c-peak at 130 K (dashed lines) indicates condensation of C 4 H 4 S. Condensation temperatures of 130–150 K have been reported before for thiophene . The α- and c-peak are not well separated.…”

“…The UHV chamber is equipped with a cylindrical mirror analyzer-based Auger electron spectroscopy (AES) system and a mass spectrometer for thermal desorption spectroscopy (TDS) (equipped with a funnel-shaped front-end, Feulner cup), among the usual equipment for sample cleaning and gas dosing. The thermocouple was calibrated (±10 K) in comparison to earlier data of H 2 formation while making graphene (main desorption at 436–432, Figure S1 in ref 8) as well as the condensation of pentane (125 K) and thiophene (130 K) . Binding energies, E d , were determined from the TDS peak positions using Redhead analysis with an uncertainty of ±2.5 kJ/mol (±10 K).…”

“…For thiophene on nonreactive SiO 2 , thiophene's binding energy was within the range of 35−55 kJ/mol (i.e., comparable with the current results), but it did depend on the coverage, 53 similar to thiophene adsorption on silicatene (2D SiO 2 ). 34 Thiophene has indeed a rather small dipole moment, 54 i.e., small lateral interactions leading to only small or no peak shifts may be expected unless polarization effects of the substrate are present. That may be the case for less conducting SiO 2 .…”

“…The thermocouple was calibrated (±10 K) in comparison to earlier data of H 2 formation while making graphene (main desorption at 436−432, Figure S1 in ref 8) as well as the condensation of pentane (125 K) 33 and thiophene (130 K). 34 Binding energies, E d , were determined from the TDS peak positions using Redhead analysis with an uncertainty of ±2.5 kJ/mol (±10 K). The heating rate amounts to β = 1.6 K/s.…”

Comparative Study of the Flue Gas Desulfurization Using Different‐Grade Natural Manganese Oxides

“…In detail, the Mn distribution is sparse and scattered in the low‐grade manganese ores (A and B), and some of the dark areas observed on the ore surfaces would result from enrichment of impurities such as SiO 2 . The SiO 2 has a 2D/3D‐frame‐like structure and it can play the role of a bridge‐like material to support the internal structure and further strengthen the dispersivity of the MnO 2 in the ores. A large amount of exposed MnO 2 enlarges the direct contact area with SO 2 and fully promotes the desulfurization reactions.…”