Sulfur-Accelerated Ceria Catalyst for Efficient CH₄/CO₂ Reforming: Unraveling the Special Role of Redox Functions and Its Reaction Mechanism

Sulfur poisoning remains a severe problem in industrial applications for CH4 dry reforming, and developing a highly active and durable catalyst is of great environmental importance. Meanwhile, designing a Lewis acid catalyst of CeO2 to replace traditional metal Ni for the challenging activation of CH4 is interesting. Herein, valuable insights into the role of H2S in promoting the catalytic activity of ceria catalysts for the dry reforming of methane are presented. Moreover, the special role of redox functions over the sulfur-accelerated CeO2 catalyst and its reaction mechanism are unraveled by using quasi in situ XPS, in situ CH4/CO2-TPSR, and in situ DRIFTS and DFT calculations. This work gives a distinctive example of a sulfur-accelerated ceria catalyst for efficient CH4/CO2 reforming

Ethylene Glycol and Its Mixtures with Water and Electrolytes: Thermodynamic and Transport Properties

A comprehensive thermodynamic model has been developed for calculating thermodynamic and transport properties of mixtures containing monoethylene glycol (MEG), water, and inorganic salts and gases. The model is based on the previously developed mixed-solvent electrolyte (MSE) framework, which has been designed for the simultaneous calculation of phase equilibria and speciation of electrolytes in aqueous, nonaqueous, and mixed solvents up to the saturation or pure solute limit. In the MSE framework, the standard-state properties of species are calculated from the Helgeson–Kirkham–Flowers equation of state, whereas the excess Gibbs energy includes a long-range electrostatic interaction term expressed by a Pitzer–Debye–Hückel equation, a virial coefficient-type term for interactions between ions and a short-range term for interactions involving neutral molecules. Model parameters have been established to reproduce the vapor pressures, solubilities of solids and gases, heat capacities, and densities for MEG + H₂O + solute systems, where the solute is one or more of the following components: NaCl, KCl, CaCl₂, Na₂SO₄, K₂SO₄, CaSO₄, BaSO₄, Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, CaCO₃, HCl, CO₂, H₂S, and O₂. In particular, emphasis has been put on accurately representing the solubilities of mineral scales, which commonly appear in oil and gas environments. Additionally, the model predicts the pH of mixed-solvent solutions up to high MEG contents. On the basis of speciation obtained from the thermodynamic model, the electrical conductivity of the MEG + H₂O + NaCl + NaHCO₃ solutions is also calculated over wide ranges of solvent composition and salt concentration. Additionally, associated models have been established to compute the thermal conductivity, viscosity, and surface tension of aqueous MEG mixtures

Photoenhanced Uptake of NO₂ and HONO Formation on Real Urban Grime

Nitrous acid (HONO) is one of the most important photochemical precursors of the hydroxyl radical in the sunlit urban atmosphere. The sources of HONO, however, are still poorly characterized, yet there is a disagreement between the field observations and the model results. Here, we show that light-induced NO2 heterogeneous chemistry on authentic urban grime can make an important contribution to the total HONO levels in the urban atmosphere. The obtained results indicate that the effective uptake coefficients of NO2 on urban grime in the presence of ultraviolet light [2.6 × 1015 photons cm–2 s–1 (300 nm < λ < 400 nm)] increased markedly from (1.1 ± 0.2) × 10–6 at 0% relative humidity (RH) to (5.8 ± 0.7) × 10–6 at 90% RH, exhibiting the following linear correlation with RH: γ­(NO2) = (7.4 ± 3.3) × 10–7 + (5.5 ± 0.6) × 10–8 × RH%. The flux densities of HONO mediated by light-induced heterogeneous conversion of NO2 (46 ppb) on urban grime were enhanced by ∼1 order of magnitude from (2.3 ± 0.2) × 109 molecules cm–2 s–1 at 0% RH to (1.5 ± 0.01) × 1010 molecules cm–2 s–1 at 90% RH. This study promotes light-induced NO2 chemistry on urban grime being an important source of HONO and suggests that further experiments be performed in the future

Production of Volatile Organic Compounds by Ozone Oxidation Chemistry at the South China Sea Surface Microlayer

Ozone (O3) oxidation chemistry on proxy compounds of the sea surface microlayer (SML) generates volatile organic compounds (VOCs) in the atmosphere. To shed light on the proposed significance of this chemistry, we investigated the formation of VOCs through heterogeneous chemistry of O3 (100 ppb) with authentic SML collected from 10 sites in the South China Sea using a reactor coupled to proton transfer reaction–time of flight–mass spectrometry (PTR–TOF–MS) and subsequently identified by off-line techniques. On the basis of the semi-quantitative data of the identified compounds, we estimated the production rates of acetone, acetaldehyde, propanal, hexanal, heptanal, octanal, and nonanal, which correspond to the experimental conditions applied in this study. These results provide a significant update to our understanding of abiotic formation of VOCs in the marine atmosphere, which should be considered in future model studies to properly evaluate the VOC contribution of ozone heterogeneous chemistry with the SML

Inorganic Ions Enhance the Number of Product Compounds through Heterogeneous Processing of Gaseous NO₂ on an Aqueous Layer of Acetosyringone

Methoxyphenols represent important pollutants that can participate in the formation of secondary organic aerosols (SOAs) through chemical reactions with atmospheric oxidants. In this study, we determine the influence of ionic strength, pH, and temperature on the heterogeneous reaction of NO2 with an aqueous film consisting of acetosyringone (ACS), as a proxy for methoxyphenols. The uptake coefficient of NO2 (50 ppb) on ACS (1 × 10–5 mol L–1) is γ = (9.3 ± 0.09) × 10–8 at pH 5, and increases by one order of magnitude to γ = (8.6 ± 0.5) × 10–7 at pH 11. The lifetime of ACS due to its reaction with NO2 is largely affected by the presence of nitrate ions and sulfate ions encountered in aqueous aerosols. The analysis performed by membrane inlet single-photon ionization-time-of-flight mass spectrometry (MI-SPI-TOFMS) reveals an increase in the number of product compounds and a change of their chemical composition upon addition of nitrate ions and sulfate ions to the aqueous thin layer consisting of ACS. These outcomes indicate that inorganic ions can play an important role during the heterogeneous oxidation processes in aqueous aerosol particles

Resolving the Formation Mechanism of HONO via Ammonia-Promoted Photosensitized Conversion of Monomeric NO₂ on Urban Glass Surfaces

Understanding the formation processes of nitrous acid (HONO) is crucial due to its role as a primary source of hydroxyl radicals (OH) in the urban atmosphere and its involvement in haze events. In this study, we propose a new pathway for HONO formation via the UVA-light-promoted photosensitized conversion of nitrogen dioxide (NO2) in the presence of ammonia (NH3) and polycyclic aromatic hydrocarbons (PAHs, common compounds in urban grime). This new mechanism differs from the traditional mechanism, as it does not require the formation of the NO2 dimer. Instead, the enhanced electronic interaction between the UVA-light excited triplet state of PAHs and NO2–H2O/NO2–NH3–H2O significantly reduces the energy barrier and facilitates the exothermic formation of HONO from monomeric NO2. Furthermore, the performed experiments confirmed our theoretical findings and revealed that the synergistic effect from light-excited PAHs and NH3 boosts the HONO formation with determined HONO fluxes of 3.6 × 1010 molecules cm–2 s–1 at 60% relative humidity (RH) higher than any previously reported HONO fluxes. Intriguingly, light-induced NO2 to HONO conversion yield on authentic urban grime in presence of NH3 is unprecedented 130% at 60% RH due to the role of NH3 acting as a hydrogen carrier, facilitating the transfer of hydrogen from H2O to NO2. These results show that NH3-assisted UVA-light-induced NO2 to HONO conversion on urban surfaces can be a dominant source of HONO in the metropolitan area

Unraveling the Synergistic Reaction and the Deactivation Mechanism for the Catalytic Degradation of Double Components of Sulfur-Containing VOCs over ZSM-5-Based Materials

The competitive adsorption behavior, the synergistic catalytic reaction, and deactivation mechanisms under double components of sulfur-containing volatile organic compounds (VOCs) are a bridge to solve their actual pollution problems. However, they are still unknown. Herein, simultaneous catalytic decomposition of methyl mercaptan (CH3SH) and ethyl mercaptan (C2H5SH) is investigated over lanthanum (La)-modified ZSM-5, and kinetic and thermodynamic results confirm a great difference in the adsorption property and catalytic transformation behavior. Meanwhile, the new synergistic reaction and deactivation mechanisms are revealed at the molecular level by combining with in situ diffuse reflectance infrared spectroscopy (in situ DRIFTS) and density functional theory (DFT) calculations. The CH3CH2* and SH* groups are presented in decomposing C2H5SH, while the new species of CH2*, active H* and S*, instead of CH3* and SH*, are proved as the key elementary groups in decomposing CH3SH. The competitive recombining of SH* in C2H5SH with highly active H* in dimethyl sulfide (CH3SCH3), an intermediate in decomposing CH3SH, would aggravate the deposition of carbon and sulfur. La/ZSM-5 exhibits potential environmental application due to the excellent stability of 200 h and water resistance. This work gives an understanding of the adsorption, catalysis, reaction, and deactivation mechanisms for decomposing double components of sulfur-containing VOCs

Evolution of Indoor Cooking Emissions Captured by Using Secondary Electrospray Ionization High-Resolution Mass Spectrometry

Cooking emissions represent a major source of air pollution in the indoor environment and exhibit adverse health effects caused by particulate matter together with volatile organic compounds (VOCs). A multitude of unknown compounds are released during cooking, some of which play important roles as precursors of more hazardous secondary organic aerosols in indoor air. Here, we applied secondary electrospray ionization high-resolution mass spectrometry for real-time measurements of VOCs and particles from cooking peanut oil in the presence of 300 ppbv nitrogen oxides (NOx) generated by a gas stove in an indoor environment. More than 600 compounds have been found during and after cooking, including N-heterocyclic compounds, O-heterocyclic compounds, aldehydes, fatty acids, and oxidation products. Approximately 200 compounds appeared after cooking and were hence secondarily formed products. The most abundant compound was 9-oxononanoic acid (C9H16O3), which is likely the product formed during the heterogeneous hydroxyl (OH) radical oxidation of oleic acid (C18H34O2) or linoleic acid (C18H32O2). Real-time detection of an important number of organic compounds in indoor air poses a challenge to indoor air quality and models, which do not account for this extremely large range of compounds