On-line Mass Spectrometer Research Articles

Research on the effect of CO2 and H2O on NO reduction of biomass char by the equivalent characteristic spectrum method via an on-line mass spectrometer

Despite extensive experimental studies on NO reduction by biomass char, the impact of high concentrations of CO2 and H2O on the NO-char reaction remains insufficiently understood. This study investigates the effects of CO2, H2O, and CO2+H2O atmospheres on NO reduction by biomass char in a micro-fluidized bed (MFB). Experiments were conducted at 900 °C, with CO2 concentrations ranging from 20 % to 80 % and H2O concentrations from 10 % to 40 %. The results show that increasing concentrations of CO2 and H2O accelerate the NO reduction rate. However, under high CO2 and H2O concentrations, both the maximum NO reduction efficiency and the mass consumption of nitrogen decrease. In a CO2 atmosphere, nearly all nitrogen from NO converts to N2, but this conversion efficiency declines in the presence of H2O. When both CO2 and H2O are present, H2O predominantly governs the NO consumption rate. Additionally, the apparent activation energy for NO reduction is higher in an H2O atmosphere compared to a CO2 atmosphere at similar concentrations.

Indoor Emission, Oxidation, and New Particle Formation of Personal Care Product Related Volatile Organic Compounds.

Personal care products (PCPs) contain diverse volatile organic compounds (VOCs) and routine use of PCPs indoors has important implications for indoor air quality and human chemical exposures. This chamber study deployed aerosol instrumentation and two online mass spectrometers to quantify VOC emissions from the indoor use of five fragranced PCPs and examined the formation of gas-phase oxidation products and particles upon ozone-initiated oxidation of reactive VOCs. The tested PCPs include a perfume, a roll-on deodorant, a body spray, a hair spray, and a hand lotion. Indoor use of these PCPs emitted over 200 VOCs and resulted in indoor VOC mixing ratios of several parts per million. The VOC emission factors for the PCPs varied from 2 to 964 mg g-1. We identified strong emissions of terpenes and their derivatives, which are likely used as fragrant additives in the PCPs. When using the PCPs in the presence of indoor ozone, these reactive VOCs underwent oxidation reactions to form a variety of gas-phase oxidized vapors and led to rapid new particle formation (NPF) events with particle growth rates up to ten times higher than outdoor atmospheric NPF events. The resulting ultrafine particle concentrations reach ∼34000 to ∼200000 cm-3 during the NPF events.

Insights into the Phases Transformation of Copper and Nickel Catalysts during Partial Oxidation and Steam Reforming of Methane

AbstractThe paper shows the structural changes of copper and nickel catalysts in the presence of strong (O2) and weak (H2O) oxidizing agents and their influence on the course of methane conversion. The changes in oxidation states of investigated catalysts were studied during partial oxidation and steam reforming of methane using an X‐ray reactor chamber (XRD) coupled with an online mass spectrometer. Also, the susceptibility of these catalysts to oxidation and reduction by individual reaction components was investigated using TPR, TPO, and in situ XPS techniques. The obtained results indicated the distinct catalytic behavior of copper and nickel catalysts depending on their oxidation state and the importance of coke formation in the activation of the partial oxidation process. The mechanism of re‐reduction of catalysts under reaction conditions and a method to increase the activity of nickel catalysts are proposed.

Quantification of O2 Crossover and Concurrent Faradaic Efficiency Loss of H2 Production Via PEM Water Electrolysis

PEM water electrolyzers (PEMWEs) are considered to be a key technology for the decarbonization of major sectors by being able to store fluctuating renewable energy as chemical energy in the form of hydrogen gas. While the scarcity of the necessary iridium catalyst on the anode limits widespread application minding the high loadings still needed today,1 there are additional efficiency losses that are still to be fully understood.By employing a proton exchange membrane, PEMWEs are able to produce hydrogen at elevated pressure on the cathode while keeping the balance of plant costs low as the anode can still be operated with liquid water at close to ambient pressure. Hydrogen crossover to the anode compartment through the membrane is significantly increased at elevated cathode pressures, which is majorly considered a safety issue. As the anode catalyst does not serve as a good hydrogen oxidation reaction catalyst, explosive mixtures of hydrogen and oxygen can form at the anode (and its exhaust) depending on the membrane type and thickness, current density, temperature, hydrogen partial pressure at the cathode, cathode catalyst layer structure etc.2-4 Aside of safety concerns – which can be bypassed by the use of recombination interlayers in the membrane5 – gas crossover also reduces the Faradaic efficiency of the system as parts of the hydrogen produced cannot be used further because it does not reach the cathode exhaust.A so far not majorly considered additional Faradaic efficiency loss stems from oxygen crossover from the anode to the cathode. As the platinum based cathode catalyst is very active for the oxygen reduction reaction, basically all of the oxygen crossing over to the cathode compartment recombines with the hydrogen present, forming liquid water.6 The permeability of oxygen through common PEM materials is significantly lower than that of hydrogen.7 But due to the osmotic drag from the anode to the cathode as well as possibly high bubble pressures of oxygen at the anode catalyst layer / membrane interface,8 oxygen crossover deserves closer attention.In this study we show quantification of the oxygen crossover in operating PEMWE single cells by a full balance of the gases detected at both the anode and cathode exhaust using an online mass spectrometer. A direct correlation of Faradaic efficiency of the oxygen and hydrogen produced matches the expected chemical recombination on the cathode, which serves as a direct measure of the oxygen crossover to the cathode compartment during PEMWE operation. Depending on the exact operating conditions the Faradaic efficiency loss caused by oxygen crossover can easily be in the percentage range, stressing the importance of having a closer look at the oxygen crossover characteristics of PEMWE cells in order to improve the Faradaic efficiency of the system. Taie, Z.; Peng, X.; Kulkarni, D.; Zenyuk, I. V.; Weber, A. Z.; Hagen, C.; Danilovic, N., Pathway to Complete Energy Sector Decarbonization with Available Iridium Resources using Ultralow Loaded Water Electrolyzers. ACS Appl Mater Interfaces 2020, 12, 52701-52712.Bernt, M.; Schröter, J.; Möckl, M.; Gasteiger, H. A., Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 2020, 167.Ito, H.; Miyazaki, N.; Ishida, M.; Nakano, A., Cross-permeation and consumption of hydrogen during proton exchange membrane electrolysis. Int. J. Hydrogen Energy 2016, 41, 20439-20446.Trinke, P.; Keeley, G. P.; Carmo, M.; Bensmann, B.; Hanke-Rauschenbach, R., Elucidating the Effect of Mass Transport Resistances on Hydrogen Crossover and Cell Performance in PEM Water Electrolyzers by Varying the Cathode Ionomer Content. J. Electrochem. Soc. 2019, 166, F465-F471.Zhang, Z.; Han, Z.; Testino, A.; Gubler, L., Platinum and Cerium-Zirconium Oxide Co-Doped Membrane for Mitigated H2 Crossover and Ionomer Degradation in PEWE. J. Electrochem. Soc. 2022, 169.Schalenbach, M.; Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D., Pressurized PEM water electrolysis: Efficiency and gas crossover. Int. J. Hydrogen Energy 2013, 38, 14921-14933.Schalenbach, M.; Hoefner, T.; Paciok, P.; Carmo, M.; Lueke, W.; Stolten, D., Gas Permeation through Nafion. Part 1: Measurements. The Journal of Physical Chemistry C 2015, 119, 25145-25155.Weber, C. C.; Wrubel, J. A.; Gubler, L.; Bender, G.; De Angelis, S.; Buchi, F. N., How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis. ACS Appl Mater Interfaces 2023, 15, 34750-34763.

A new quantitative method via on-line mass spectrometer: Application in biomass char/NO reaction

A novel quantitative analysis method via on-line mass spectrometer (OMS) was developed to calculate the mass flows of the reactants and products for the reaction between NO and biomass char in micro-fluidized bed. The experimental results showed that the quantitative method could accurately calculate the mass flow rate of each gas even though there were ion currents overlapping at mass-to-charge ratio (m/z) = 12,16, and 28 when CO, CO2 and N2 were simultaneously present in OMS. Furthermore, the method facilitated the quantitative analysis of gaseous reactants and products, thereby enabling the assessment of mass conversions of carbon (C) and nitrogen (N) in the NO reduction reaction. It was observed that CO was the predominant carbon-containing product in the reaction involving biomass char and NO at 900 °C, with over 96 % of nitrogen in NO participating in the reduction reaction being converted to N2. This study also revealed that increasing the fluidization number, NO concentration, and temperature in the micro-fluidized bed could significantly accelerate the conversion processes of C and N in the reduction of NO by biomass char. The peak mass flow rates of CO, CO2, and N2 were found to increase correspondingly with higher NO concentrations and temperature levels. The NO reduction process over sawdust char was compared to that of corncob char, showing a higher maximum NO reduction efficiency. The reaction order with respect to NO concentration was determined to be 0.82 for corncob char and 0.68 for sawdust char. Additionally, the apparent activation energies were determined to be 92.35 kJ/mol for corncob char and 125.60 kJ/mol for sawdust char, respectively.

Multifold nanotwin-enhanced catalytic activity of Ni-Zn-Cu for hydrazine oxidation

The hydrazine oxidation reaction (HzOR) plays a critical role in direct hydrazine fuel cells and presents a promising alternative to the kinetics-sluggish oxygen evolution reaction in water reduction. Engineering catalysts with high-density multifold nanotwin structures has emerged as a compelling strategy to enhance catalytic activity. However, the exploration of multifold nanotwins for HzOR applications remains absent. Herein, we report the successful synthesis of a porous Ni-Zn-Cu catalyst featuring high-density twofold and fivefold nanotwins. The Ni-Zn-Cu catalyst supported on Ni foam (Ni-Zn-Cu/Ni foam) exhibits exceptionally high catalytic activity and stability toward the HzOR, achieving a current density of 204.3 mA cm−2 at 0.0 V vs. RHE and retaining up to 89.1 % after 20 h of continuous electrolysis. Online mass spectrometer (MS) analysis indicates that the Ni-Zn-Cu coating facilitates NN bond cleavage of N2H4. This study offers valuable insights into the development of multifold nanotwin catalysts for advancing HzOR applications.

Study on the secondary oxidation behavior and microscopic characteristics of oxidized coal gangue.

Spontaneous combustion of coal gangue (CG) hills has caused varieties of secondary disasters that seriously endanger the ecological environment of the world. The emission law of index gases and their oxidation kinetics during the secondary oxidation process of CG with different ranks of oxidation were studied by using the temperature programmed device and online mass spectrometer (MS). Fourier transform infrared spectroscopy (FTIR) was used to reveal the changes of the CG internal active functional groups. The results showed that the energy required for the combustion of CG with low rank of pre-oxidation was significantly lower than that of the raw sample. However, as the oxidation rank increased, due to amounts of volatile components were released in the process of oxidation reaction, the CG in the combustion process of the emission of index gases and its oxygen consumption rate gradually reduced; the rapid oxidation stage shifted to the direction of the high temperature. In this study, the risk of spontaneous combustion of CG after oxidation at 80℃ under 3% oxygen concentration was the strongest. The results of this paper are of great guiding significance for exploring the spontaneous combustion characteristics of CG hills and their prevention by traditional covering method.

Online water vapor removal membrane inlet mass spectrometer for high-sensitivity detection of dissolved methane

Underwater mass spectrometry is characterized by excellent consistency, strong specificity, and the ability to simultaneously detect multiple substances, making it a valuable tool in research fields such as aquatic ecosystems, hydrothermal vents, and the global carbon cycle. Nevertheless, current underwater mass spectrometry encounters challenges stemming from the high-water vapor content, constituting proportions of nearly 90%. This results in issues such as peak overlap, interference with peak height, decreased ionization efficiency and, consequently, make it difficult to achieve low detection limits for extremely low concentrations of gases, such as methane, and impede the detection of background CH4 levels. In this study, we optimized the design of the sampling gas path and developed a high gas-tightness, high pressure-resistant membrane inlet system, coupled with a small-volume, low-power online water vapor removal system. This innovation efficiently eliminates water vapor while maintaining a high permeation flux of the target gases. By elevating the vacuum level to the order of 1E-6 Torr, the ionization efficiency and detection performance were improved. Based on this, we created an online water vapor removal membrane inlet mass spectrometer and conducted experimental research. Results indicated that the water removal efficiency approached 100%, and the vacuum level was elevated by more than 2 orders of magnitude. The detection limit for CH4 increased from over 600 nmol/L to 0.03 nmol/L, representing an improvement of over 4 orders of magnitude, and reaching the level of detecting background CH4 signals in deep-sea and lakes. Furthermore, the instrument exhibited excellent responsiveness and tracking capability to concentration changes on the second scale, enabling in situ analysis of rapidly changing concentration scenarios.

Tracking the Impact of Koch‐Carbonylated Organics During the Zeolite ZSM‐5 Catalyzed Methanol‐to‐Hydrocarbons Process

AbstractA methanol‐based economy offers an efficient solution to current energy transition challenges, where the zeolite‐catalyzed methanol‐to‐hydrocarbons (MTH) process would be a key enabler in yielding synthetic fuels/chemicals from renewable sources. Despite its original discovery over half a century ago over the zeolite ZSM‐5, the practical application of this process in a CO2‐neutral scenario has faced several obstacles. One prominent challenge has been the intricate mechanistic complexities inherent in the MTH process over the zeolite ZSM‐5, impeding its widespread adoption. This work takes a significant step forward by providing critical insights that bridge the gap in our understanding of the MTH process. It accomplishes this by connecting the (Koch‐carbonylation‐led) direct and dual cycle mechanisms, which operate during the early and steady‐state phases of MTH catalysis, respectively. To unravel these mechanistic intricacies, we have performed catalytic and operando (i.e., UV/Vis coupled with an online mass spectrometer) and solid‐state NMR spectroscopic‐based investigations on the MTH process, involving co‐feeding methanol and acetone (cf. a key Koch‐carbonylated species), including selective isotope‐labeling studies. Our iterative research approach revealed that (Koch−)carbonyl group selectively promotes the side‐chain mechanism within the arene cycle of the dual cycle mechanism, impacting the preferential formation of BTX fraction (i.e., benzene‐toluene‐xylene) primarily.

Tracking the Impact of Koch-Carbonylated Organics During the Zeolite ZSM-5 Catalyzed Methanol-to-Hydrocarbons Process.

A methanol-based economy offers an efficient solution to current energy transition challenges, where the zeolite-catalyzed methanol-to-hydrocarbons (MTH) process would be a key enabler in yielding synthetic fuels/chemicals from renewable sources. Despite its original discovery over half a century ago over the zeolite ZSM-5, the practical application of this process in a CO2 -neutral scenario has faced several obstacles. One prominent challenge has been the intricate mechanistic complexities inherent in the MTH process over the zeolite ZSM-5, impeding its widespread adoption. This work takes a significant step forward by providing critical insights that bridge the gap in our understanding of the MTH process. It accomplishes this by connecting the (Koch-carbonylation-led) direct and dual cycle mechanisms, which operate during the early and steady-state phases of MTH catalysis, respectively. To unravel these mechanistic intricacies, we have performed catalytic and operando (i.e., UV/Vis coupled with an online mass spectrometer) and solid-state NMR spectroscopic-based investigations on the MTH process, involving co-feeding methanol and acetone (cf. a key Koch-carbonylated species), including selective isotope-labeling studies. Our iterative research approach revealed that (Koch-)carbonyl group selectively promotes the side-chain mechanism within the arene cycle of the dual cycle mechanism, impacting the preferential formation of BTX fraction (i.e., benzene-toluene-xylene) primarily.

Online Electrochemical Mass Spectrometry on Large-Format Li-Ion Cells

Significant progress has been made in real-time analysis methodologies for batteries, particularly with regards to the development of Operando Electrochemical Mass Spectrometry (OEMS) [1]. OEMS provides unprecedented selectivity and sensitivity in analysing the release of volatile species, enabling the detection of side reactions during battery cycling which can provide crucial information about the Solid Electrolyte Interface (SEI) and processes that limit battery life. However, most research thus far has been conducted on model battery systems (~1 mAh) that do not accurately reflect conditions within large-format commercial cells (~10,000 mAh) particularly in terms of electrode areas, electrolyte volumes, and stack pressures. Additionally, the atmosphere within the cell is altered through either continuous flow [2] [3] (in the open approach) or purging [4] (in the semi-closed approach [5]). In both cases, gas is being withdrawn from the cell (10% of cell volume/measurement point) during operation and replaced with a carrier gas (usually Ar). This dilutes the existing environment and prevents further reactions, making it difficult to compare the results to real-life situations.In this work, the development and validation of an entirely closed OEMS system that can be interfaced with large-format commercially available batteries is showcased. Instead of replacing the removed gas, a small amount (0.2 % of cell volume/measurement point) is periodically removed, causing a gradual pressure drop in the cell. Experiments are limited by a minimum internal cell pressure of 700 mbar due to the sensitivity of the pressure sensor and vapour pressures of the electrolyte. Apart from this pressure drop, the internal cell environment is therefore relatively constant allowing us to observe side reaction products that have occurred within a realistic cell environment.We additionally provide a detailed description of an adapter design for interfacing large format prismatic cells with our intermittently closed OEMS (ICEMS) setup. The adapter is placed over a hole in the cell (produced with a drill) and can be easily scaled for different cell geometries. Using this ICEMS setup, we provide operando pressure and gassing data from a calendared BAK PHEV2 cell. The pressure within the cell changes depending on the level of lithiation in the cathode (NMC) and anode (graphite), revealing the multiple phase transitions that occur in both materials during cycling. These transitions can be divided into four regions of interest, where graphite dominates regions I and III (with large pressure increases during charge) and NMC dominates regions II and IV (with pressure decreases during charge). By analysing the gas produced during these transitions, it is clear that structural changes within both electrodes result in side reactions. When graphite undergoes large volume changes (from 1L to 2L and 2 to 1, regions I and III), H2 and C2H4 are released as SEI reformation products, while the c lattice collapse in NMC (during the H2 to H3 transition, region IV) results in CO2 evolution (through O2 release that subsequently reacts with the electrolyte). In addition, we suggest that Lewis bases formed on the graphite through the reduction of electrolyte species ring open EC, forming CO2 [6]. The results of this study suggest that the internal chemistry of commercially available prismatic rechargeable batteries can be studied effectively using ICEMS without significantly altering the battery's chemistry.[1] A. M. Tripathi, W. N. Su, and B. J. Hwang, “In situ analytical techniques for battery interface analysis,” Chem. Soc. Rev., vol. 47, no. 3, pp. 736–751, 2018, doi: 10.1039/c7cs00180k.[2] P. Novák et al., “Advanced in situ characterization methods applied to carbonaceous materials,” J. Power Sources, vol. 146, no. 1–2, pp. 15–20, 2005, doi: 10.1016/j.jpowsour.2005.03.129.[3] N. Tsiouvaras, S. Meini, I. Buchberger, and H. A. Gasteiger, “ A Novel On-Line Mass Spectrometer Design for the Study of Multiple Charging Cycles of a Li-O 2 Battery ,” J. Electrochem. Soc., vol. 160, no. 3, pp. A471–A477, 2013, doi: 10.1149/2.042303jes.[4] R. Lundström and E. J. Berg, “Design and validation of an online partial and total pressure measurement system for Li-ion cells,” J. Power Sources, vol. 485, no. December 2020, 2021, doi: 10.1016/j.jpowsour.2020.229347.[5] L. A. Kaufman and B. D. McCloskey, “Surface Lithium Carbonate Influences Electrolyte Degradation via Reactive Oxygen Attack in Lithium-Excess Cathode Materials,” Chem. Mater., pp. 1–7, 2021, doi: 10.1021/acs.chemmater.1c00935.[6] N. Gogoi et al., “Silyl-Functionalized Electrolyte Additives and Their Reactivity toward Lewis Bases in Li-Ion Cells,” Chem. Mater., vol. 34, no. 8, pp. 3831–3838, 2022, doi: 10.1021/acs.chemmater.2c00345.

Mapping the Methanol-to-Gasoline Process Over Zeolite Beta.

Decarbonizing the transportation sector is among the biggest challenges in the fight against climate change. CO2 -neutral fuels, such as those obtained from renewable methanol, have the potential to account for a large share of the solution, since these could be directly compatible with existing power trains. Although discovered in 1977, the zeolite-catalyzed methanol-to-gasoline (MTG) process has hardly reached industrial maturity, among other reasons, because maximizing the production of gasoline range hydrocarbons from methanol has proved complicated. In this work, we apply multimodal operando UV/Vis diffuse reflectance spectroscopy coupled with an online mass spectrometer and "mobility-dependent" solid-state NMR spectroscopy to better understand the reaction mechanism over zeolites H-Beta and Zn-Beta. Significantly, the influential co-catalytic role of oxymethylene species is linked to gasoline formation, which impacts the MTG process more than carbonylated species.

Mapping the Methanol‐to‐Gasoline Process Over Zeolite Beta

AbstractDecarbonizing the transportation sector is among the biggest challenges in the fight against climate change. CO2‐neutral fuels, such as those obtained from renewable methanol, have the potential to account for a large share of the solution, since these could be directly compatible with existing power trains. Although discovered in 1977, the zeolite‐catalyzed methanol‐to‐gasoline (MTG) process has hardly reached industrial maturity, among other reasons, because maximizing the production of gasoline range hydrocarbons from methanol has proved complicated. In this work, we apply multimodal operando UV/Vis diffuse reflectance spectroscopy coupled with an online mass spectrometer and “mobility‐dependent” solid‐state NMR spectroscopy to better understand the reaction mechanism over zeolites H‐Beta and Zn‐Beta. Significantly, the influential co‐catalytic role of oxymethylene species is linked to gasoline formation, which impacts the MTG process more than carbonylated species.

Catalyst-Free Oxidation Reactions in a Microwave Plasma Torch-Based Ion/Molecular Reactor: An Approach for Predicting the Atmospheric Oxidation of Pollutants.

The atmospheric oxidation of chemicals has produced many new unpredicted pollutants. A microwave plasma torch-based ion/molecular reactor (MPTIR) interfacing an online mass spectrometer has been developed for creating and monitoring rapid oxidation reactions. Oxygen in the air is activated by the plasma into highly reactive oxygen radicals, thereby achieving oxidation of thioethers, alcohols, and various environmental pollutants on a millisecond scale without the addition of external oxidants or catalysts (6 orders of magnitude faster than bulk). The direct and real-time oxidation products of polycyclic aromatic hydrocarbons and p-phenylenediamines from the MPTIR match those of the long-term multistep environmental oxidative process. Meanwhile, two unreported environmental compounds were identified with an MPTIR and measured in the actual water samples, which demonstrates the considerable significance of the proposed device for both predicting the environmental pollutants (non-target screening) and studying the mechanism of atmospheric oxidative processes.

Synergistic and Antagonistic Effects of the Co-Pyrolysis of Plastics and Corn Stover to Produce Char and Activated Carbon.

The physicochemical properties of char and activated carbon produced from the co-pyrolysis of corn stover (CS) and plastics, polystyrene (PS) and polyethylene terephthalate (PET), were studied. Non-isothermal gas analysis of the volatiles was conducted using an online mass spectrometer to correlate the thermal degradation of gaseous byproducts to the formation of pores in the char materials. The findings determined that the addition of PS or PET promotes the formation of the solid char product with either higher than average pore sizes or surface areas compared to control samples. The addition of PET to corn stover increases the surface area of the char formed. The char formed from a CS:PET mass ratio of 1:1 produced char with a surface area of 423.8 ± 24.8 m2/g at 500 °C and a duration of 2 h. The surface area of the chars formed from CS and PET decreased as the amount of PET decreased, showing a tendency for PET to increase the surface area of the char materials synergistically. The addition of PS to corn stover promoted the formation of chars with, on average, larger pore sizes than the control char samples. The chars were chemically activated with potassium hydroxide, and the activated carbon that formed had lower surface areas but comparable surface functional groups to the control samples. Vanillin adsorption testing showed that activated carbon from corn stover performed the best at removing 95% of the vanillin after 2 h. In contrast, the activated carbon from the chars produced from the co-pyrolysis of corn stover and polystyrene or corn stover and polyethylene terephthalate removed 45% and 46% of vanillin after 2 h, respectively. The findings suggest that plastics have a synergistic relationship in producing char precursors with improved porosity but antagonistically affect the activated carbon adsorbent properties.

Atomic Scale Characterization of the Reaction Mechanism of Moisture in Coal Matrix Acting on Coal Spontaneous Combustion

ABSTRACT It is imperative to have an in-depth understanding of the mechanism of action for the role of moisture in a coal matrix during coal spontaneous combustion, not only for preventing fires in the coal industry but also for reducing emissions of hazardous gases. In this study, the method of isotope tracing was first introduced to study the mechanism of moisture in the spontaneous combustion of coal. Moisture in a coal matrix was labeled separately using D2O and H2 18O, and the coal samples with internal moisture and external moisture were prepared by controlling the drying temperature. Coal samples with different isotopic moisture were heated using a spontaneous combustion apparatus. The gaseous products (CO2, CO, and CH4) were measured using a GC-950 gas chromatography equipped with a flame photometric detector, and simultaneously, the isotopic gases (including C18O, C18O2, CH3D) were timely monitored using an online mass spectrometer. The appearance of isotopic gases directly proved that the moisture could participate in the spontaneous combustion of coal in atomic level, and the moisture in the coal matrix is involved in the spontaneous combustion of coal through chemical reaction. Based on the experimental results, the pathways of the oxygen atom and H atom from the moisture participating in the production of isotopic gases were investigated. The reaction mechanism of moisture participating in the spontaneous combustion of coal was also explored based on the migration law of oxygen and hydrogen atoms of H2O molecule in coal matrix.

Comparisons of GC-Measured Carboxylic Acids and AMS m/z 44 Signals: Contributions of Organic Acids to m/z 44 Signals in Remote Aerosols from Okinawa Island

An intercomparison study was conducted to evaluate the contributions of carboxylic acids to m/z 44 (COO+) signals obtained by an on-line aerosol mass spectrometer (AMS) during a field campaign at Cape Hedo, Okinawa, in the western North Pacific Rim. We report for the first time that carboxylic acids (diacids, oxoacids, benzoic acid, and fatty acids) significantly contribute to m/z 44 signals with a strong correlation (R = 0.93); oxalic acid accounts for 16 ± 3% of the m/z 44 signals and 3.7 ± 0.9% of organic mass measured by AMS. We also found that about half of AMS m/z 44 signals can be explained by diacids and related compounds, suggesting that the remaining signals may be derived from other organic acids including monocarboxylic acids (e.g., formate and acetate) in aerosol phase. This study confirms that AMS-derived m/z 44 can be used as a surrogate tracer of carboxylic acids, although the signals cannot specify the types of carboxylic acids and their molecular compositions.

Chemical looping gasification characteristics and kinetic analysis of Chlorella and its organic components

Chemical looping gasification (CLG) characteristics and kinetic analysis of Chlorella (CHL), simulated Chlorella (V-CHL) and medium-chain triglycerides (MCT) were investigated using a thermogravimetric analyzer coupled with an online mass spectrometer. The apparent activation energy was obtained via Kissinger-Akahira-Sunose (KAS) method. In the result of the weightless behavior, the addition of oxygen carrier inhibited the decomposition of V-CHL at lower temperatures but promoted its decomposition at high temperatures. The values of chemical looping process characteristic parameters showed that a 10 wt% oxygen carrier would maximize the release of volatile products in the CLG of MCT, with 5.12 × 10−6 %·min−1·oC−3. Oxygen carriers also affected gaseous products. The LHV of gaseous products of CHL reached the largest when the oxygen carrier was 10 wt%, which was 8.13 MJ/m3. And the gaseous product of MCT had the largest LHV with 30 wt% oxygen carrier, which was 8.83 MJ/m3. According to the kinetic analysis, the minimum value of apparent activation energy of MCT chemical looping gasification was 89.54 kJ·mol−1 with the oxygen carrier of 30 wt%, which was 50% less than that of MCT pyrolysis. And the minimum value for V-CHL was obtained when the mass fraction of Fe2O3 was 50 wt%. This paper could provide a reference for the choice of algae, the design of reactors, and the targeted regulation of the gaseous product for the algae CLG process.

Effect of operating cell voltage on the NaCl poisoning mechanism in polymer electrolyte membrane fuel cells

The mechanism of NaCl poisoning in polymer electrolyte membrane fuel cells (PEMFCs) depends on the operating cell voltage. Both the Pt dissolution and the liberation of Cl2 and CO2 gases are monitored using an on-line mass spectrometer to differentiate between the different poisoning mechanisms. The changes in the particle size and composition of the catalyst are measured by high-resolution transmission electron microscopy and energy dispersive spectroscopy. At a cell voltage of 0.6 V the degradation of performance due to NaCl poisoning is primarily attributed to blockage of the active sites of the catalyst by the adsorption of Cl−. This reduced performance can be fully restored by removing Cl− in the form of Cl2 while slowing down the carbon corrosion reaction. However, NaCl poisoning at a high cell voltage of 0.9 V results in Cl−-induced dissolution of the Pt catalyst, which prevents performance recovery. Thus, it has been demonstrated that the NaCl poisoning mechanism and the reversibility of the performance loss depends largely on the operating cell voltage of the PEMFC.

Mixed-potential ammonia sensor using Ag decorated FeVO4 sensing electrode for automobile in-situ exhaust environment monitoring

High-performance YSZ-based mixed potential NH3 sensor has been developed and utilized with the prospect of excellent applications in in-vehicle SCR (Selective Catalytic Reduction) systems. In order to further lower the detection limit and improve the sensitivity to NH3, we prepared Ag decorated FeVO4 as sensing electrode material through the NaBH4 reduction method in this work. Electrochemical methods such as cyclic voltammetry (CV), linear sweep voltammetry (LSV) and I-t curves are used to explore and compare the electrochemical catalytic activity of electrode materials. 3 mol% Ag decorated FeVO4 was considered as the best sensing electrode material because of its highest electrochemical catalytic activity and reliable stability. Also, the reaction product under the sensor’s working condition was confirmed by the online mass spectrometer. The sensor attached with 3 mol% Ag decorated FeVO4-SE could give a response of − 57 mV to 50 ppm NH3 in 3s and recover to base line in 16s, exhibiting its rapid detection ability at high temperature of 550 °C. Moreover, it displayed good selectivity and a low detection limit of 200 ppb. Additionally, the stability of the sensor under different oxygen concentration and humidity was studied in detail.