Gas-phase Products Research Articles

Gas-phase production equation for CBM reservoirs: Interaction between hydraulic fracturing and coal orthotropic feature

The efficient development of coalbed methane (CBM) reservoirs entails the accurate evaluation of production behavior, particularly for the gas phase performance. However, subjected to complexity arising from the coal inherent heterogeneous properties and dynamic gas-water two-phase flow, pursuit of high prediction accuracy remains challenging. Although massive excellent contributions have been devoted to addressing this issue, several key factors fail to be captured, and in-depth analysis is lacking, involving coal orthotropic feature, as well as associated interaction with hydraulic fractures. In light of the current knowledge status, the research has developed a robust gas-phase productivity equation for CBM wells, putting the emphasis on the coupling influence from coal orthotropic feature as well as hydraulic fracture. Also, gas-water two-phase flow mechanism is captured by incorporating the relationship between pressure and fluid saturation in coal cleat system. Moreover, traditional factors are considered as well, including gas desorption, stress dependence, matrix shrinkage. Numerical simulation is utilized to clarify the reliability of the proposed equation at the stable state, and desirable agreements can be achieved. Results show that (a) Augment effect, induced by enlarging intersection angle, on gas production rate is evident, and the calculation case suggests the optimized angle is 90°, requiring further investigations; (b) The inherent orthotropic feature acts the detrimental role for gas production performance, and fortunately hydraulic fracturing, treated with suitable intersection angle, is able to alleviate the influence; (c) Gas desorption ability lays the profound basis for evaluation of the CBM development, supposed to be selected as the prominent index for the favorable target development area.

Redistribution of total reactive nitrogen in the lowermost Arctic stratosphere during the cold winter 2015/2016

Abstract. During winter 2015/2016, the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with a very strong polar vortex and with the occurrence of extensive polar stratospheric clouds. From mid-December 2015 until mid-March 2016, the German research aircraft HALO (High Altitude and Long-Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than 20 flights have been conducted out of Kiruna, Sweden, and Oberpfaffenhofen, Germany, covering the whole winter period. Besides total reactive nitrogen (NOy), observations of nitrous oxide, nitric acid, ozone, and water were used for this study. Total reactive nitrogen and its partitioning between the gas and particle phases are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. The vertical redistribution of total reactive nitrogen was evaluated by using tracer–tracer correlations (NOy–N2O and NOy–O3). The trace gases are well correlated as long as the NOy distribution is controlled by its gas-phase production from N2O. Deviations of the observed NOy from this correlation indicate the influence of heterogeneous processes. In early winter no such deviations have been observed. In January, however, air masses with extensive nitrification were encountered at altitudes between 12 and 15 km. The excess NOy amounted to about 6 ppb. During several flights, along with gas-phase nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid-containing particles, leading to redistribution of total reactive nitrogen at lower altitudes. Remnants of nitrified air masses have been observed until mid-March. Between the end of February and mid-March, denitrified air masses have also been observed in connection with high potential temperatures. This indicates the downward transport of air masses that have been denitrified during the earlier winter phase. Using tracer–tracer correlations, missing total reactive nitrogen was estimated to amount to 6 ppb. Further, indications of transport and mixing of these processed air masses outside the vortex have been found, contributing to the chemical budget of the winter lowermost stratosphere. Observations within POLSTRACC, at the bottom of the vortex, reflect heterogeneous processes from the overlying Arctic winter stratosphere. The comparison of the observations with CLaMS model simulations confirm and complete the picture arising from the present measurements. The simulations confirm that the ensemble of all observations is representative of the vortex-wide vertical NOy redistribution.

Secondary organic aerosol formation from photooxidation of γ-butyro and γ-valero-lactone: A combined experimental and theoretical study

The formation of secondary organic aerosol (SOA) generated by OH-photooxidation of γ-butyrolactone (GBL) and γ-valerolactone (GVL) in the presence of OH, NO, H2O vapour and aerosol seeds ((NH4)2SO4 and CaCl2) has been investigated for the first time. Experiments were conducted in a smog chamber at 298 K and atmospheric pressure. Lactone's decay was followed by gas chromatography with a mass spectrometric detector (GC-MS), and the temporal evolution of the SOA was monitored using a fast mobility particle sizer (FMPS). The SOA yield increases slightly when the initial GVL concentration increases. On the other hand, SOA formation is minor for GBL, and it rises slightly at low concentrations. In the case of GVL, the organic aerosol formation can be tentatively expressed by a one-product gas/particle partitioning absorption model. The particle number concentration, mass and yield decrease in the presence of NO but increase at higher relative humidity (RH) and seed surface area within the studied range. Acetic acid and succinic anhydride for GVL, and succinic anhydride for GBL were experimentally identified as oxidation products both in gas and particle phase using thermal desorption followed by GC-MS. Moreover, the theoretical studies carried out to complement the experimental results indicate that H-abstraction at the carbon site adjacent to the heterocyclic oxygen is the predominant pathway, being even more favourable when H2O was added. Also, under atmospheric conditions, the opening of the ring of the corresponding oxy-radicals and their subsequent fragmentation could be the possible explanation for the formation of detected products and the higher yield of SOA in the presence of H2O and absence of NO. Considering these results, the formation of SOA from the use of both lactones as potential biofuels is few significative, although SOA generation may be enhancement by particle-phase heterogeneous reactions catalyzed by humidity and the acidity of seed aerosols present in real atmosphere.

Machine learning analysis of gas phase photocatalytic CO2 reduction for hydrogen production

In this work, the gas phase photocatalytic CO2 reduction was analyzed via machine learning, and the results were compared with those obtained in liquid phase process. Total 549 data points (268 for gas and 281 for liquid phase) were extracted from 80 published papers for this purpose. The general trends in the literature were analyzed using simple descriptive statistics first; then, the random forest (RF) regression was used for the band gap prediction while the decision tree (DT) classification was utilized to deduce heuristics for higher CO2 reduction rates. It was found that H2, CO, and CH4 are the main products in gas phase while CH3OH production is more dominant in liquid phase. Random forest prediction was quite successful in predicting the band gap with the root mean square error of 0.15 for testing. Decision tree models for the total gas production rates were also successful; for example, the accuracy rates for training and testing were 80% and 79% respectively for the gas phase processes. The high precision for the high gas production class allowed to deduce some rules indicating the semiconductor and co-catalysts options for high CO2 photoreduction rates while the reaction temperatures was also found to be influential in the liquid phase.

Spectro-kinetics of the methanol to hydrocarbons reaction combining online product analysis with UV–vis and FTIR spectroscopies throughout the space time evolution

The well-studied methanol to hydrocarbons reaction over a ZSM-5 zeolite catalyst has been used to develop a spectro-kinetic approach to obtain an overall reaction mechanism involving both retained species and gas-phase products. We combined two in situ spectroscopic techniques (ultraviolet–visible and Fourier-transform infrared spectroscopies) with online product analysis to obtain the time- and space time-resolved evolution of the entire reaction media. A ZSM-5 zeolite catalyst was tested in two commercial spectroscopic cells at 400 °C using different space times (different inlet flow rates). Specifically, our work focusses on the effect of the space time (key parameter in any kinetic study) and how to tune other parameters such as partial pressure of methanol to resolve, from the spectroscopic and gas-phase points of view, the mechanisms of reaction and deactivation. Our approach reinforces the previous interpretation of these two combined networks in the selected reaction, thus, proving that the spectro-kinetic approach is a robust methodology to simultaneously build overall reaction and deactivation mechanisms.

Kinetic Analysis of Recovering Zinc from Electric Arc Furnace Dust by Vacuum Carbothermic Reduction at 20 Pa

Electric arc furnace dust (EAFD) presents a contamination hazard due to its heavy metal leachability. The traditional disposal methods of landfill or stacking not only pose a threat to the environment but also waste metal resources. This paper adopted vacuum carbothermic reduction to dispose of EAFD and the zinc metal could be obtained as a product. The reduction ratios of the EAFD were carried out under various reaction temperatures and times at 20 Pa. Furthermore, the kinetics of the reduction process was also studied. The reduction ratio of the reaction process can be facilitated through increasing the temperature or lengthening the time and can reach up to 99.6% under the condition of 1373 K with 60 min. The zinc ferrite and zinc oxide were reduced first and then iron oxide reduction occurred. The reduction process could be divided into three stages: Stage 1 involved the direct reduction of zinc ferrite and zinc oxide, and the control step was the phase boundary reaction with the apparent activation energy of 48.54 kJ/mol; Stage 2 involved the reduction of zinc oxide and iron oxide, and the control step was also the phase boundary reaction with the apparent activation energy of 56.27 kJ/mol; Stage 3 involved the escape of gas phase products and the control step was diffusion with the apparent activation energy of 105.3 kJ/mol.

Photoinduced release of odorous volatile organic compounds from aqueous pollutants: The role of reactive oxygen species in increasing risk during cross-media transformation

Photoinduced volatile organic compounds (VOCs) release from fatty alcohols at the air-water interface, has attracted considerable attention. This paper comprehensively explores the release of odorous VOCs from aqueous micropollutants under photoirradiation, especially in terms of the important role of the reactive oxygen species (ROS) in increased risk by cross-media transformation. The formation and distribution of photoinduced VOCs produced by aqueous benzyl alcohol (BzOH), a common ingredient in personal care products, were monitored in situ by online gas chromatography equipped with mass spectrometry and flame ionization detector (GC–MS/FID). The photoreaction of BzOH followed first-order kinetics with a rate constant of 0.0158/min under air. After 180 min of ultraviolet irradiation, the accumulated output of the gas-phase products benzene and benzaldehyde (BA) reached 3.8 μmol and 2.6 μmol respectively, being approximately 10 times that under nitrogen. According to electron paramagnetic resonance measurements, singlet oxygen mainly promoted the oxidation of BzOH to BA, which was an important intermediate producing benzene via photocleavage. Odorous alicyclic hydrocarbons were also generated through photorearrangement under nitrogen. On the other hand, the Henry's law constants of the main products were much lower than those of BzOH, indicating that the photoproducts would volatilize from the aqueous phase into the gas phase. The odor threshold of gas-phase products decreased to varying degrees after photoirradiation. Especially for BA, one of the main products, its odor threshold decreased 130 times compared with BzOH. This study shows that the risk of cross-media pollution could significantly increase due to the transformation of aqueous pollutants into odorous VOCs under photoirradiation and provides new insight into its risk prevention.

Investigation of Ni catalyst activation during plasma-assisted methane oxidation

Atmospheric pressure plasma has shown promise in improving thermally activated catalytic reactions through a process termed plasma-catalysis synergy. In this work, we investigated atmospheric pressure plasma jet (APPJ)-assisted CH4 oxidation over a Ni/SiO2 .Al2O3 catalyst. Downstream gas-phase products from CH4 conversion were quantified by Fourier transform infrared spectroscopy. The catalyst near-surface region was characterized by in-situ diffuse reflectance infrared Fourier transform spectroscopy. The catalyst was observed to be activated at elevated temperature (500 °C) if it was exposed to the APPJ operated at large plasma power. ‘Catalyst activation’ signifies that the purely thermal conversion of CH4 using catalysts which had been pre-exposed to plasma became more intense and produced consistently CO product, even if the plasma was extinguished. Without the application of the APPJ to the Ni catalyst surface this was not observed at 500 °C. The study of different exposure conditions of the activated catalyst indicates that the reduction of the catalyst by the APPJ is likely the cause of the catalyst activation. We also observed a systematic shift of the vibrational frequency of adsorbed CO on Ni catalyst when plasma operating conditions and catalyst temperatures were varied and discussed possible explanations for the observed changes. This work provides insights into the plasma-catalyst interaction, especially catalyst modification in the plasma catalysis process, and potentially demonstrates the possibility of utilizing the surface CO as a local probe to understand the plasma-catalyst interaction and shed light on the complexity of plasma catalysis.

Study on the reaction of 3-methyl-2-butenal and 3-methylbutanal with Cl atoms: kinetics and reaction mechanism

The reaction of Cl atoms with two C5 aldehydes (3-methyl-2-butenal and 3-methylbutanal) were investigated by proton-transfer-reaction mass spectrum (PTR-MS) using smog chamber at 298 ± 1 K and 760 Torr. A relative rate method was used to determine the rate constants of the title reactions with m-xylene and trans-2-butene as reference compounds: (3.04 ± 0.18) × 10−10 and (2.07 ± 0.14) × 10−10 cm3/(molecule⋅sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identified by PTR-MS, and the possible reaction mechanisms were proposed basing on the identified products. The detected gas-phase products are similar for two C5 aldehydes reactions, mainly including small molecules of aldehydes, ketones and chlorinated aldehyde compounds. The atmospheric lifetimes (τ) calculated for 3-methyl-2-butenal (τ = 7.0 hr, marine boundary layer (MBL)) and 3-methylbutanal (τ = 10.3 hr, MBL) according to the obtained rate constants. The results indicate that Cl atoms at MBL are competitive with OH radicals for the degradation contribution of C5 aldehyde compounds.

Experimental investigation on the production of hydrogen from discarded circuit boards in supercritical water

Circuit boards are indispensable components of electronic products. They are difficult to burn as they capture active free radicals, therefore the traditional disposal methods for discarded circuit boards are inefficient and polluting. In this work, discarded circuit boards were gasified in supercritical water. The operating conditions employed were as follows: temperature 500–750 °C; reaction time 1–30 min; feedstock concentration 1–10 wt%; and pressure 23 MPa. Analysis of the components in the gasification products showed that the increase of the reaction temperature and reaction time improved the gasification performance. Furthermore, the reduction in the feedstock concentration could also significantly enhance the conversion rates of both the carbon and hydrogen. It can be concluded that the efficient and economical working condition were as follows: temperature 700 °C; reaction time 10 min; feedstock concentration 5% and the addition of a catalyst. The conversion efficiencies for both carbon and hydrogen were 84.67% and 146.77% under these conditions, representing an increased efficiency with reduced costs. Finally, the conversion process of the bromine atoms in the tetrabromobisphenol A epoxy resin was examined and the bromine atoms in the raw material were converted into the gas phase product, hydrogen bromide, the solid phase products copper bromide and other bromides, and the liquid phase products bromide ions and bromine-containing organic molecules.

The potential energy profile of the decomposition of 1,1-diamino-2,2-dinitroethylene (FOX-7) in the gas phase.

1,1-Diamino-2,2-dinitroethene (FOX-7) is an energetic material with low sensitivity and high detonation performance, thus it has been considered as a potential replacement for traditional nitro-based energetic materials. In a recent publication (J. Phys. Chem. A, 2022, 126, 4747), the initial decomposition steps of FOX-7 were studied using reflectron time-of-flight mass spectrometry and infrared spectroscopy. The experimental study was complemented with quantum chemistry calculations, which demonstrated the gas phase potential energy surface to be indicative of the reaction process in the condensed phase. The computation in J. Phys. Chem. A, 2022, 126, 4747 focuses on the primary decomposition - but in this manuscript, the full decomposition pathway on the singlet surface, consisting of 54 intermediates and 37 transition states, is characterized at an unprecedented detail. The calculations show that the nitro group, instead of the amine group, is primarily responsible for the sensitivity and endothermicity of FOX-7 decomposition. This result sheds light on how to critically optimize the performance of FOX-7 and design the next generation of nitro-based energetic materials. A comprehensive roadmap, initiated from FOX-7, covers the chemical space of the entire decomposition thus providing a holistic demonstration of various key decomposition pathways leading to various small, gas phase products such as NO, NO2, NH2, CO2, and CO.

Real-time measurements of product compounds formed through the reaction of ozone with breath exhaled VOCs.

Human presence can affect indoor air quality because of secondary organic compounds formed upon reactions between gaseous oxidant species, e.g., ozone (O3), hydroxyl radicals (OH), and chemical compounds from skin, exhaled breath, hair and clothes. We assess the gas-phase product compounds generated by reactions of gaseous O3 with volatile organic compounds (VOCs) from exhaled human breath by real time analysis using a high-resolution quadrupole-orbitrap mass spectrometer (HRMS) coupled to a secondary electrospray ionization (SESI) source. Based on the product compounds identified we propose a reaction mechanism initiated by O3 oxidation of the most common breath constituents, isoprene, α-terpinene and ammonia (NH3). The reaction of O3 with isoprene and α-terpinene generates ketones and aldehydes such as 3,4-dihydroxy-2-butanone, methyl vinyl ketone, 3-carbonyl butyraldehyde, formaldehyde and toxic compounds such as 3-methyl furan. Formation of compounds with reduced nitrogen containing functional groups such as amines, imines and imides is highly plausible through NH3 initiated cleavage of the C-O bond. The detected gas-phase product compounds suggest that human breath can additionally affect indoor air quality through the formation of harmful secondary products and future epidemiological studies should evaluate the potential health effects of these compounds.

Light olefins from biomass-derived butyric acid by tandem deoxygenation reactions

The feasibility of using a series of Zn-Zr mixed oxides for the gas-phase production of light olefins from butyric acid, a platform molecule derived from biomass processing, was investigated. These materials with Zn/Zr molar ratios of 0.11–0.66 were prepared by incipient wetness impregnation of Zn on Zr(OH)4 and characterized by BET, XRD and CO2 and NH3 TPD. At full butyric acid conversion conditions, a range of C2-C7 olefins was obtained. The molecular weight of the olefin pool as well as the total olefin yield depend on the catalyst composition and experimental conditions. The catalyst acid-base properties can be tuned for optimal olefin yield by generating a high number of Zn-O-Zr species and oxygen vacancies resulting from incorporation of Zn2+ to the ZrO2 lattice. The best olefin yield coincides with the catalyst showing the highest acid site number and moderate basic properties. Also, the reaction temperature and reactor contact time were varied to improve the olefin yield. A total olefin yield of 60.7% was obtained with a catalyst having 11.1 wt% Zn (Zn/Zr=0.25) at 723 K and 835 h g cat./mol. Ethylene (52%) and isobutene (33%) were the main components of the olefin fraction, the other 15% being pentene, isohexene and heptene. The olefin yield can be further improved to 65.8% by increasing the contact time to 1500 h g cat./mol. Butyric acid transformation proceeds with the intermediate formation of different ketones (heptanone, pentanone and acetone), each of which gives rise to a particular olefin. Isobutene forms through tandem butyric acid ketonization/C-C bond rupture by McLafferty rearrangement/aldol condensation/breaking of the aldol adduct reactions. Ethylene is generated during the McLafferty step. The pathways toward other olefins may involve deoxygenation steps such as reduction of unsaturated bonds by in-situ generated hydrogen species, followed by dehydration. Acetic and propionic acids, formed in minor amounts, participate in further tandem sequences. No catalyst deactivation was observed during standard and extended catalytic tests because water co-feeding and hydrogen generation prevent heavy product formation and active site loss.

Mechanistic study of methanol oxidation on Pt(1 1 1) single crystal

The oxidation of methanol on a Pt(111) single crystal was studied using X-ray photoelectron spectroscopy and polarization-modulation infrared reflection absorption spectroscopy in a temperature range between 300 and 600 K. It was shown that the oxidation starts at approximately 350 K, and methanol is oxidized mainly to CO2 and methyl formate. CO was not found among gas-phase products in the whole temperature range. A small amount of formaldehyde was detected in the gas phase only at 350–450 K. On the platinum surface, methyl formate, CO, formates, carbonates, and carbon atoms were detected under reaction conditions. Their concentrations depended on the reaction temperature and the methanol/oxygen molar ratio. Formates were detected only at 300 K, indicating their low thermal stability. Both CO and formate are the key intermediates in the total oxidation of methanol, which can proceed via two different pathways: a CO-based route and a non-CO-included route. Carbonates are formed from formates and demonstrate extremely high thermal stability. This leads us to propose that not only CO but also carbonates can poison the platinum surface and prevent the oxidation of methanol. The overall mechanism of the oxidation of methanol on platinum is discussed.

Determination of oxidation rates and volatile oxidation products for HTGR graphite matrix material exposed to steam atmospheres

High-temperature gas-cooled reactors (HTGRs) in operation use tristructural isotropic (TRISO) particles embedded in graphite and carbonized resin matrix to form the fuel element. This graphite matrix material serves as a supportive structural element, heat transfer medium, and neutron moderator. In HTGR designs, fuel compacts are exposed to helium coolant, which facilitates high outlet temperatures (750°C<T<950°C) and subsequently greater thermal efficiency than current commercial power reactors. However, data pertaining to the oxidation resistance of graphite matrix material in HTGR accident or off-normal conditions (<50k kPa pH2O, 800°C<T<1600°C) is limited. In this study, both the oxidation behavior of matrix graphite material and its gas-phase products, including CO, CO2, and H2, are quantified in varied oxidant atmospheres using a coupled thermogravimetric analyzer and mass spectrometer. Oxidation rates reported here for varied steam (H2O [g]) atmospheres are predominantly linear and comparable with literature values in the range of tested temperatures (800–1200°C). Changes in dominant matrix oxidation products from primarily CO to a mixture of CO, CO2, and H2 were observed at higher temperatures (≥1000°C) and steam atmospheres (≥5 kPa pH2O). Kinetic data indicates that there was no shift in oxidation regime with chemical oxidation occurring at all temperatures and H2O (g) atmospheres tested. These data provide insight into the oxidation behavior of graphite matrix material and will inform future testing conditions, notably mixed atmospheric conditions, of HTGR fuel elements.

Gas- and Particle-Phase Products and Their Mechanisms of Formation from the Reaction of Δ-3-Carene with NO3 Radicals.

Monoterpenes are a major component of the large quantities of biogenic volatile organic compounds that are emitted to the atmosphere each year. They have a variety of structures, which influences their subsequent reactions with OH radicals, O3, or NO3 radicals and the tendency for these reactions to form secondary organic aerosol (SOA). Here we report the results of an environmental chamber study of the reaction of Δ-3-carene, an abundant unsaturated C10 bicyclic monoterpene, with NO3 radicals, a major nighttime oxidant. Gas- and particle-phase reaction products were analyzed in real time and offline by using mass spectrometry, gas and liquid chromatography, infrared spectroscopy, and derivatization-spectrophotometric methods. The results were used to identify and quantify functional groups and molecular products and to develop gas- and particle-phase reaction mechanisms to explain their formation. Identified gas-phase products were all first-generation ring-retaining and ring-opened compounds (ten C10 and one C9 monomers) with 2-4 functional groups and one C20 dinitrooxydialkyl peroxide dimer. Upon partitioning to the particle phase, the monomers reacted further to form oligomers consisting almost entirely of C20 acetal and hemiacetal dimers, with those formed from a hydroxynitrate and hydroxycarbonyl nitrate comprising more than 50% of the SOA mass. The SOA contained an average of 0.94, 0.71, 0.15, 0.11, 0.16, 0.13, and 7.80 nitrate, carbonyl, hydroxyl, carboxyl, ester, peroxide, and methylene groups per C10 monomer and was formed with a mass yield of 56%. These results have important similarities and differences to those obtained from a previous similar study of the reaction of β-pinene and yield new insights into the effects of monoterpene structure on gas- and particle-phase reactions that can lead to the formation of a large variety of multifunctional products and significant amounts of SOA.

Direct Observation of Plasma-Stimulated Activation of Surface Species Using Multimodal In Situ/Operando Spectroscopy Combining Polarization-Modulation Infrared Reflection-Absorption Spectroscopy, Optical Emission Spectroscopy, and Mass Spectrometry.

Nonthermal plasmas (NTPs) produce reactive chemical environments, including electrons, ions, radicals, and vibrationally excited molecules, that can drive chemistry at temperatures at which such species are thermally inaccessible. There has been growing interest in the integration of conventional catalysis with reactive NTPs to promote novel chemical transformations. Unveiling the full potential of plasma-catalytic processes requires a comprehensive understanding of plasma-catalytic synergies, including characterization of plasma-catalytic surface interactions. In this work, we report on a newly designed multimodal spectroscopic instrument combining polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS), mass spectrometry, and optical emission spectroscopy (OES) for the investigation of plasma-surface interactions such as those found in plasma catalysis. In particular, this tool has been utilized to correlate plasma-phase chemistry with both surface chemistry and gas-phase products in situ (1) during the deposition of carbonaceous surface species via NTP-promoted nonoxidative coupling of methane and (2) during subsequent activation of surface deposits with an atmospheric pressure and temperature argon plasma jet on both nickel (Ni) and silicon dioxide (SiO2) surfaces. For the first time, the activation of carbonaceous surface species by a NTP on Ni and SiO2 surfaces to form hydrogen gas and C2 hydrocarbons was directly observed, where both PM-IRAS and OES measurements suggest that they may form through different pathways. This unique tool for studying plasma-surface interactions could enable more rational design of plasma-stimulated catalytic processes.

Identification of Adsorbed Species and Surface Chemical State on Ag(111) in the Presence of Ethylene and Oxygen Studied with Infrared and X-ray Spectroscopies

Using a combination of two surface-sensitive spectroscopy techniques, the chemical state of the Ag(111) surface and the nature of the adsorbed species in the presence of ethylene and oxygen gases are identified. In the 10 mbar pressure range and 25–200 °C studied here, Ag(111) remains largely metallic even in O2-rich conditions. The only adsorbed molecular species with a low but discernible coverage is surface carbonate, which forms due to further oxidation of produced CO2, in a similar manner to its formation in ambient air on Ag surfaces. Its formation is also pressure-dependent, for instance, it is not observed when the total pressure is in the 1 mbar pressure range. Production of carbonate, along with carbon dioxide and water vapor as the main gas-phase products, suggests that an unpromoted Ag(111) surface catalyzes mainly the undesired full oxidation reaction.

Fire retarded polyurethane foam composites based on steel slag/ammonium polyphosphate system: A novel strategy for utilization of metallurgical solid waste

AbstractA series of FR‐RPUF composites were prepared by a one‐step water foaming process with ammonium polyphosphate (APP) and steel slag (SS) as flame retardants. Thermogravimetric analysis (TG), limiting oxygen index (LOI), UL‐94 vertical combustion test, microscale combustion calorimetry (MCC), TG‐Fourier transform infrared spectrometry (TG‐FTIR), scanning electron microscopy (SEM), Raman spectra and FTIR were used to investigate the thermal stability, flame retardancy, combustion performance, gas phase products, and char residue morphology of FR‐RPUF composites. TG test results showed that the initial decomposition temperature (T‐5wt%) and char residue rate at 700°C of RPUF/APP/SS composites were significantly enhanced by the addition of APP and SS, and the thermal stability of the composites was improved. Flame retardant test results confirmed the significantly increased LOI values of RPUF/APP/SS composites with V‐0 rating. TG‐FTIR also confirmed the obviously decreased release of toxic gases and flammable gases in the combustion of RPUF/APP/SS composites. SEM and Raman spectra of char residues for the composites suggested that APP/SS system improved the compactness and graphitization degree of char layer for RPUF/APP/SS composite. The above researches provide a new strategy for the utilization of SS in fire safety engineering.

A facile strategy to achieve efficient flame-retardant cotton fabric with durable and restorable fire resistance

Novel, durably flame-retardant cotton fabrics with fascinatingly restorable fire resistance were prepared by simple grafting of phosphate and melamine, which contributed to a phosphorous-nitrogen (P/N) synergism. During the preparation process, phosphate was grafted with the hydroxyl groups of cellulose to form P-O-C bonds; subsequently, melamine reacted with the aldehyde groups of cellulose generated from phosphorylation to form P/N modified fabrics (P/N-Cotton). The P/N synergistic effect endowed cotton fabric with prominent fire resistance and durability. The Limit oxygen index (LOI) was as high as 51.1 ± 0.3% and was maintained at 32.7 ± 0.8% after 50 laundering cycles (LCs). The total heat release (THR) and peak values of heat release rate (pHRR) of P/N-Cotton were significantly reduced by 70.11% and 64.19%, respectively. Amazingly, the modified cotton fabrics exhibited restorable fire resistance once immersed into the acetic acid solution due to the ion exchange between Na+ from detergent and H+ from acetic acid. The LOI of P-Cotton and P/N-Cotton after 50 LCs can be restored to 32.4 ± 0.7% and 35.7 ± 0.7% from 20.8 ± 0.7% and 32.7 ± 0.8%, respectively. The analysis of gas-phase products and residual char demonstrated that the incorporation of phosphate and melamine facilitated cellulose fibers to convert to dense and stable graphitized carbon layers and carbon-nitrogen heterocycles, effectively protecting the fabric from decomposing to flammable gases.