Optimization of Reduced Chemical Mechanisms Using Graph Theory-Assisted Gradient Descent

Reutilization of Cr-Y zeolite obtained by biosorption in the catalytic oxidation of volatile organic compounds

The work presents Pd-containing catalysts for practical application with enhanced low-temperature activity in the complete oxidation of volatile organic compounds (VOCs) using innovative combinations of reduced graphene oxide (RGO) and alumina. The catalysts were characterized by XRD, SEM, TEM, XPS, low-temperature N2-adsorption, and CO chemisorption. The tests on complete catalytic oxidation of different VOC (propane, butane, hexane, dimethyl ether, toluene, propylene) and CO were carried out. The reaction kinetics and the mechanism of the reaction of complete oxidation of toluene are being investigated in detail. The results show that the new catalyst design makes it able to completely oxidize the studied VOCs and CO at low temperatures (100–350 °C) with long-term stability. Using a variety of instrumental methods, it was established that for high activity and long-term stability, the optimal ratio Pd/PdO should be close to 1:1. The most probable mechanism of complete toluene oxidation is the mechanism of Langmuir–Hinshelwood. The high activity and the weak effect of water on the catalyst performance leads to further perspectives for the application of the currently developed approach for the preparation of large-scale monolithic catalytic systems for air pollution control.

General study of catalytic oxidation of various VOCs over La0.8Sr0.2MnO3+x perovskite catalyst—influence of mixture

The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds

<strong class="journal-contentHeaderColor">Abstract.</strong> Particulate matter (PM) largely consists of secondary organic aerosol (SOA) that is formed via oxidation of biogenic and anthropogenic volatile organic compounds (VOCs). Unambiguous identification of SOA molecules and their assignment to their precursor vapors are challenges that have so far only succeeded for a few SOA marker compounds, which are now well characterized and (partly) available as authentic standards. In this work, we resolve the complex composition of SOA by means of a top-down approach based on the newly created <i>Aerosolomics</i> database, which is fed by non-target analysis results of filter samples from oxidation flow reactor experiments. We investigated the oxidation products from the five biogenic VOCs <span class="inline-formula"><i>α</i></span>-pinene, <span class="inline-formula"><i>β</i></span>-pinene, limonene, 3-carene, and <i>trans</i>-caryophyllene and from the four anthropogenic VOCs toluene, <i>o</i>-xylene, 1,2,4-trimethylbenzene, and naphthalene. Using ultrahigh-performance liquid chromatography coupled to a high-resolution (Orbitrap) mass spectrometer, we determine the molecular formula of 596 chromatographically separated compounds based on exact mass and isotopic pattern. We utilize retention time and fragmentation mass spectra as a basis for unambiguous attribution of the oxidation products to their parent VOCs. Based on the molecular-resolved application of the database, we are able to assign roughly half of the total signal of oxygenated hydrocarbons in ambient suburban PM<span class="inline-formula">_2.5</span> to one of the nine studied VOCs. The application of the database enabled us to interpret the appearance of diurnal compound clusters that are formed by different oxidation processes. Furthermore, by performing a hierarchical cluster analysis (HCA) on the same set of filter samples, we identified compound clusters that depend on sulfur dioxide mixing ratio and temperature. This study demonstrates how <i>Aerosolomics</i> tools (database and HCA) applied to PM filter samples can improve our understanding of SOA sources, their formation pathways, and temperature-driven partitioning of SOA compounds.

Catalytic oxidation of toluene and m-xylene by activated carbon fiber impregnated with transition metals

Abstract. Particulate matter (PM) largely consists of secondary organic aerosol (SOA) that is formed via oxidation of biogenic and anthropogenic volatile organic compounds (VOCs). Unambiguous identification of SOA molecules and their assignment to their precursor vapors are challenges that have so far only succeeded for a few SOA marker compounds, which are now well characterized and (partly) available as authentic standards. In this work, we resolve the complex composition of SOA by means of a top-down approach based on the newly created Aerosolomics database, which is fed by non-target analysis results of filter samples from oxidation flow reactor experiments. We investigated the oxidation products from the five biogenic VOCs α-pinene, β-pinene, limonene, 3-carene, and trans-caryophyllene and from the four anthropogenic VOCs toluene, o-xylene, 1,2,4-trimethylbenzene, and naphthalene. Using ultrahigh-performance liquid chromatography coupled to a high-resolution (Orbitrap) mass spectrometer, we determine the molecular formula of 596 chromatographically separated compounds based on exact mass and isotopic pattern. We utilize retention time and fragmentation mass spectra as a basis for unambiguous attribution of the oxidation products to their parent VOCs. Based on the molecular-resolved application of the database, we are able to assign roughly half of the total signal of oxygenated hydrocarbons in ambient suburban PM2.5 to one of the nine studied VOCs. The application of the database enabled us to interpret the appearance of diurnal compound clusters that are formed by different oxidation processes. Furthermore, by performing a hierarchical cluster analysis (HCA) on the same set of filter samples, we identified compound clusters that depend on sulfur dioxide mixing ratio and temperature. This study demonstrates how Aerosolomics tools (database and HCA) applied to PM filter samples can improve our understanding of SOA sources, their formation pathways, and temperature-driven partitioning of SOA compounds.

Secondary Organic Aerosol (SOA) production and chemical composition play a crucial role in the urban air pollution. Here, we used observations from two summer campaigns in Beijing in 2017 and 2023 to show that nighttime production of NOz (NOy - NOx) is particularly enhanced in specific conditions and that can play a significant role for SOA the next day. The observations showed nocturnal peaks of NOz&amp;#160;of about 40 ppb, correlated with very high NO and NO2. We employed the Framework for 0-D Atmospheric Modeling (F0AM) model, based on the Master Chemical Mechanism (MCM), running simulations to investigate the organic nitrates (ONs) speciation, and founding that during the night the alkyl nitrates is the most abundant ONs, produced by oxidation of volatile organic compounds (VOCs) by the nitrate radical (NO3). Finally, we used the Framework for 0-D Atmospheric Modeling- Washington Aerosol Module (F0AM-WAM) model, which couple the gas phase chemistry with the SIMPOL representation for the particle phase, to correlate the nocturnal ONs peaks, that we suggested to be mainly in gas phase, to the diurnal particle growth events registered in Beijing.

Space‐confined catalysis can help create unique nanoscale chemical environments partitioned from the surrounding bulk space and has become a feasible strategy for designing high‐efficiency catalysts for various reactions. Confinement effects can affect both the reacting molecules and confined metal/metal‐oxide nanoparticles. This review mainly documents the progress in the design and applications of confined catalysts used in environmental catalysis (selective catalytic reduction (SCR) of NOx with ammonia, catalytic oxidation of CO and volatile organic compounds (VOCs), photocatalytic oxidation of VOCs, and photocatalytic CO2 reduction). Throughout the review, the impact of confinement effects on the activity, selectivity, and stability of catalysts is emphasised. Materials such as carbon nanotubes (CNTs), titanate nanotubes (TNTs), zeolites, mesoporous TiO2, and metal−organic frameworks (MOFs) are common confined hosts. In the NH3‐SCR reaction, confined catalysts, which are non‐noble metals confined in titanate/carbon nanotubes catalysts, have been widely studied. The protection offered by the confined space can shield metal/metal‐oxide nanoparticles from toxic components (e. g., SO2, alkali metals, and heavy metals), while improving the activity of the catalysts. In the field of catalytic oxidation of CO and VOCs, noble metals are always confined in the host without aggregating, sintering, or poisoning and show enhanced activity. In the photocatalytic oxidation of VOCs and photocatalytic reduction of CO2, the application of confined catalysts can prolong the contact time of reactants and improve visible‐light absorption and electron transfer, leading to better catalytic performance.

With the rapid development of urbanization and industrialization, environmental pollution has become more severe. Volatile organic compounds (VOCs) could be originated from the following sources: domestic, mobile and industrial sources. As important air pollutants, VOCs could cause serious harm to the environment and human health. Therefore, removing VOCs has become a priority research direction of ecological issues. Among the many elimination methods, catalytic oxidation approaches are among the most effective and economical methods which can transform VOCs into CO2 and H2O. MnOx catalysts are among the most active catalysts, which can be further modified by different cations such as Cu2+, Co2+, Cr3+, Ni2+ and Ce4+ to form mixed oxides to improve the catalytic oxidation of VOCs activity. Moreover, MnOx can be loaded on the carrier, improving the redox and oxygen storage capacity and improving its stability and activity. This review explores the structure, preparation and oxidation state of Mn-based catalysts.

ABSTRACTA photocatalytic paint based on carbon‐doped titanium dioxide as a pigment replacement was tested for the oxidation of volatile organic compounds (VOCs) under visible‐light illumination in indoor environments. The photocatalytic paint was characterized by X‐ray photoelectron spectroscopy, scanning and transmission electron microscopy, and diffuse reflectance and transmittance spectral measurements. The effects of environmental conditions, including inlet concentration, relative humidity (RH), incident radiation flux, and residence time, on the degradation of toluene, an aromatic VOC, were investigated. At certain operating conditions, toluene degradation efficiency increased, from 38% to 61%, with the rise in the incident radiation flux from 6.86 to 42.34 W/m2, while it declined with increasing RH from 10% to 70%. A one‐directional heterogeneous model predicted these trends, highlighting the opposing effects of incident radiation flux and humidity on toluene oxidation kinetics. In binary mixtures of toluene and acetaldehyde, representing aromatic and aliphatic VOCs, respectively, the presence of acetaldehyde had a negligible effect on toluene conversion, whereas acetaldehyde degradation was significantly reduced—by 36% and 65%—when co‐fed with 3.5 and 6.5 ppmv of toluene, respectively, indicating a strong competitive effect between pollutants. This study highlights the benefit of using photocatalytic paint for indoor air decontamination and provides new insights into its performance under more realistic environmental conditions, particularly in the presence of mixed VOCs.

Inter-comparisons of VOC oxidation mechanisms based on box model: A focus on OH reactivity

Oxygenated organic molecules (OOMs) originate from both direct emissions and secondary formation via the oxidation of volatile organic compounds (VOCs) emitted from biogenic and anthropogenic sources. OOMs are suggested to play a crucial role in the nucleation and growth of newly formed particles, which in turn influence climate, health and air quality. However, OOMs and the associated nucleation and growth of aerosols in the boundary layer aloft are not considered in atmospheric chemistry models owing to limited observation data. Here, by using unique measurements on the top of a 528 m building tower in Beijing, we show that a variety of OOMs existed, dominated by C6-7 and C5 compounds, which probably arose from multigeneration oxidation of aromatic compounds and isoprene, respectively. Consequently, five possible formation pathways of OOMs were identified using a machine learning approach combined with their diurnal patterns. Further analysis suggested that OOMs, together with sulfuric acid and ammonia, are highly involved in the formation of nanoparticles. Our results complement the current mechanism of ammonia-sulfuric acid nucleation in the boundary layer aloft of anthropogenically influenced regions, highlighting the important role of OOMs in the nucleation and growth of aerosol. We suggest that OOMs should be considered in atmospheric chemistry models for better prediction accuracy.

In the atmosphere, a significant fraction of organic aerosol (OA) makes up the particulate matter. Since OA consists of thousands of complex molecules, uncertainties remain concerning their sources and atmospheric processes leading to their transformation (Hallquist M et al. Atmos Chem Phys 9:5155–5236, 2009). OA are, in principle, divided into two categories: primary organic aerosol (POA), which is emitted directly into the atmosphere, and secondary organic aerosol (SOA), which is formed by the photo-chemical oxidation of volatile organic compounds (VOC). VOC emissions and consequently OA formation are strongly linked to the season of the year. To that purpose, simulations were performed in autumn (September 2008) and summer (June 2010) with the WRF-CHEM model including more precisely RACM (Stockwell WR et al. J Geophys Res 102:25847–25879, 1997) chemical mechanism for gas phase associated with MADE for aerosols (Ackermann IJ et al. Atmos Environ 32(17):2981–2999, 1998) and VBS (Ahmadov et al. J Geophys Res 117:D06301, 2012) for SOA. Moreover, model outputs are compared with measurements performed during each season (Freney EJ et al. Atmos Chem Phys 11:13047–13059, 2011) at the puy de Dôme monitoring site which is located in central France (45°46 N 2°57 E) and is a part of the ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure) and GAW (Global Atmospheric Watch) network.KeywordsSecondary Organic AerosolVOCs ConcentrationVolatile Organic Compound EmissionBiogenic EmissionAtmos Chem PhysThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Three‐dimensional modeling studies have been performed to investigate the short‐timescale photochemical generation of carbon monoxide (CO) on a regional basis in two very distinct areas of the United States: New England (mixed biogenic and anthropogenic influence) and the South Coast Air Basin (SoCAB, dominated by anthropogenic influence) of California. For the New England study, the Caltech Atmospheric Chemistry Mechanism (CACM) was incorporated into the Community Multiscale Air Quality model and applied to 3–4 August 2004. For the SoCAB, CACM was applied to 8–9 September 1993 using the California Institute of Technology three‐dimensional regional atmospheric model. Results indicate that in each location, on a relative scale, the photochemical generation of CO is responsible for less than 10% (3–9% for the eastern United States and approximately 1% in the SoCAB) of the total simulated mixing ratio for the respective dates based on domain‐wide, calendar‐based 24‐hour averages. In the eastern United States, simulations indicate that isoprene is the major volatile organic compound (VOC) source for CO and that VOC oxidation can lead to up to approximately 20 parts per billion by volume (ppb) of CO in New England. In the SoCAB, anthropogenic short‐chain alkenes lead to the greatest amount of photochemical CO generation; VOC oxidation in its entirety can lead to up to approximately 45 ppb of photochemically generated CO in the SoCAB. Therefore studies on the regional scale that use CO as a marker of primary combustion emissions may overestimate the importance of primary emissions, depending on location and time.