On-line Gas Research Articles

Design, simulation, and manufacturing of analyzer optical cell for detection and measurement of injectable odorant at pressure reduction stations.

The absence of a mercaptan compounds analyzer in natural gas pressure reduction stations (PRS) odorizer leads to inaccuracies in the injection dosage, often resulting in quantities beyond standard limits and consequently increasing odorant consumption. Insufficient odorant levels in natural gas can pose safety risks to consumers, as the gas may become odorless at the end of the pipeline. Therefore, accurate determination of the concentration of key odorant compounds in natural gas can reduce both costs and environmental risks. In this study, a hybrid UV-IR analyzer for detecting key odorant compounds was designed and developed. Initially, regional conditions were examined, and various natural gas and odorant samples were analyzed to identify compound percentages, which were then used to prepare calibration gas cylinders. Based on the results of simulated conditions, the analyzer's structure was designed, and technical specifications of components were determined. The analyzer consists of mechanical and optoelectronic units, connected via fiber optics. Subsequently, an optical cell was designed and manufactured, and the performance of the analyzer's components was evaluated in laboratory testing systems. This device can measure two key compounds, tert-butyl mercaptan and isopropyl mercaptan, separately, simultaneously, or in mixtures, making it comparable to an online gas chromatograph (GC). Installing this analyzer in PRSs enables precise adjustment of odorant injection dosages based on the analyzer's real-time results.

Pollution investigation of wintertime VOCs in the coastal atmosphere of the Yellow Sea: Insights from on-line photoionization-induced CI-TOFMS.

Volatile Organic Compounds (VOCs) are pivotal in tropospheric atmospheric chemistry, significantly impacting the formation of photochemical smog, fine particle pollution, and the atmospheric oxidizing potential, all of which affect air quality. Chemical ionization time-of-flight mass spectrometry, renowned for its exceptional sensitivity, precision, and swift response time, has proven to be exceptionally effective for real-time VOCs monitoring. In this study, a custom-built photoionization-induced CI-TOFMS was deployed to individually detect 116 VOCs standard gases specified by the United States Environmental Protection Agency, quantifying their responses and establishing a distinctive mass spectrogram database. A 12-day comparative analysis with online gas chromatography coupled with a flame ionization detector and mass spectrometer demonstrated the high reliability of the PICI-TOFMS, confirming its effectiveness for field VOCs monitoring. During two months of stationary monitoring, the PICI-TOFMS could further refine the timing of pollution events with high temporal resolution and identified four distinct air pollution episodes, including local emissions, coal burning, sand and dust transport and festival-related pollution. Employing a Hysplit model, the Concentration Weighted Trajectory model, and a source apportionment method based on tracer gases, the air trajectories were calculated and contributions from different potential source areas were quantified. Our findings reveal that transport was the main contributor to pollution in December 2022, while burning was the primary source in January 2023. This study refines our understanding of the dynamics of air pollution, providing valuable insights into the temporal and spatial distribution of VOCs and their sources.

(Invited) Photocatalytic CO2 Reduction Using Water As an Electron Donor

Photocatalytic CO2 reduction is a promising CCU reaction to solve resources, energy, and environment issues, and achievement of carbon neutrality. In the photocatalytic reaction, water should be an electron donor and a hydrogen source for the CO2 reduction [1]. This reaction is regarded as artificial photosynthesis because light energy is converted to storable chemical energy. In the present paper, various metal oxide and sulfide photocatalysts and semiconductor photoelectrodes for CO2 reduction using water as an electron donor are introduced and discussed.Photocatalysts were prepared by a solid-state reaction, a polymerizable complex method, or a liquid-solid-state reaction. Cocatalysts were loaded on photocatalysts by a liquid-phase-reduction or an impregnation method. Photocatalytic CO2 reduction was carried out using a gas-flow system. CO2 gas (1 atm) was bubbled into an aqueous solution. Evolved gas products were quantified by using online gas chromatographs.NaTaO3:Ba of a single particulate photocatalyst was active for CO2 reduction to form CO using water as an electron donor when Ag cocatalyst was loaded on the surface [2]. The Ag/NaTaO3:Ba photocatalyst gave ca. 90% of the selectivity for CO formation by the CO2 reduction accompanied with water oxidation to form O2 in an aqueous medium. As the next step, it is challenging to demonstrate CO2 reduction to form CH4 of an eight-electron reduction product using water as an electron donor. A single particulate Rh-Ru/NaTaO3:Sr photocatalyst continuously produced CH4, H2, and O2 under UV irradiation [1,3]. The selectivity for CH4 formation based on the number of reacted electrons was about 10%. An e–/h+ ratio estimated from obtained products was 1.1 and TON based on the CH4formation to Rh and Ru cocatalysts was 2.0. These results have proven that CH4 was obtained by photocatalytic CO2reduction using water as an electron donor over the Rh-Ru/NaTaO3:Sr. C2H6 and C3H8 successfully evolved accompanied with O2 evolution by further development of dual cocatalysts. Notably, about 59 % of a selectivity (electronic efficiency) was obtained for formation of hydrocarbons.We also demonstrated photocatalytic CO2 reduction using water as an electron donor under visible light irradiation by a Z-scheme photocatalyst and a photoelectrochemical cell using bare (CuGa)0.5ZnS2 powder prepared by a flux method as a CO2-reducing photocatalyst [4]. The Z-scheme system employing the bare (CuGa)0.5ZnS2 photocatalyst and RGO-(CoOx/BiVO4) as an O2-evolving photocatalyst produced CO of a CO2 reduction product accompanied with H2 and O2in a simple suspension system without any additives under visible light irradiation and 1 atm of CO2. When a basic reagent (i.e. NaHCO3, NaOH etc.) was added into the reactant solution (H2O + CO2), the CO formation rate and the CO selectivity increased. The selectivity for the CO formation of the Z-schematic CO2 reduction reached 10 – 20% in the presence of the basic reagent even in an aqueous solution and without loading any cocatalysts on the (CuGa)0.5ZnS2metal sulfide photocatalyst. It is notable that CO was obtained accompanied with reasonable O2 evolution indicating that water was an electron donor for the CO2 reduction. The present Z-scheme system also showed activity for solar CO2 reduction using water as an electron donor. The bare (CuGa)0.5ZnS2 powder loaded on an FTO glass was also used as a photocathode for CO2 reduction under visible light irradiation. CO and H2 were obtained on the photocathode with 20% and 80% of Faradaic efficiencies at 0.1 V vs. RHE, respectively.References Yoshino, T. Takayama, Y. Yamaguchi, A. Iwase, A. Kudo, Acc. Chem. Res., 2022, 55, 966.Nakanishi, K. Iizuka, T. Takayama, A. Iwase, A. Kudo, ChemSusChem, 2017, 10, 112.Soontornchaiyakul, S. Yoshino, T. Kanazawa, R. Haruki, D. Fan, S. Nozawa, Y. Yamaguchi, A. Kudo, J. Am. Chem. Soc., 2023, 145, 20485.Yoshino, A. Iwase, Y. Yamaguchi, T. M. Suzuki, T. Morikawa, A. Kudo, J. Am. Chem. Soc., 2022, 144, 2323.

Comprehensive Analytical Method with a Standardized Data Pipeline Enables Parallel Experiments in Electrochemical CO2 Reduction

The electrochemical reduction of CO2 (eCO2R) is a promising way to convert detrimental CO2 emissions into sustainable fuels and chemicals, and thus to achieve a net zero or net negative carbon economy. 1 Depending on catalyst type and reaction conditions, different gaseous and liquid products can be obtained during eCO2R, with their production rates significantly varying over time. Thus, for any catalytic performance analysis, it is key to assess the product distribution online during eCO2R. 2,3 However, while gaseous products are readily analyzed online by gas chromatography, liquid products are typically only assessed at the end of the reaction due to the lack of suitable automated liquid sampling and analysis methods. In addition, relevant reaction parameters such as CO2 flow rates, electrolyzer temperatures and flow pressures are seldom recorded, causing the loss of important information on catalysts, electrodes, and electrolyzer behavior.In this work, we overcome these issues by assembling a comprehensive analytical system coupling online gas and liquid product analysis by gas and liquid chromatography (leveraging a special automated liquid sampling valve) with electrochemical protocols that assess CO2RR performance, electrolyzer cell resistance and electrode surface area. In addition, we record CO2 volumetric flow rates, electrolyzer temperatures, as well as gas and liquid flow pressures. 4 To rapidly and reproducibly handle the large and heterogeneous data volume obtained we implement a standardized data pipeline based on our own open-source software,5 which automatically parses the numerous different raw data files, composes a data set following FAIR practices,6 and post-processes and plots the data in a standard way. We validate this analytical system by carrying out eCO2R at 200 mA/cm2 on Cu gas diffusion electrodes, following the changes in selectivity with reaction time for > 12 gaseous and liquid products while recording volumetric flow rates, electrolyzer cell resistance, electrode surface area, electrolyzer temperatures and flow pressures. The modular nature of our analytical system, combined with the standardized data pipeline, allows us to freely increase the number and type of sensors used with minimal impact on the data analysis time, as well as to multiplex our analysis to 8 parallel electrolyzer cells, providing a deep understanding of the function of eCO2R catalysts, electrodes, and electrolyzers, and paving the way to accelerated discoveries.

Quantifying H2 Crossover in PEM Water Electrolyzers Operating at High Differential Pressure

Large-scale deployment of proton exchange membrane water electrolyzers (PEMWEs) is crucial for producing clean and economically viable hydrogen to create hydrogen-based energy ecosystems that can replace existing carbon-intensive processes. Efficient operation of PEMWEs requires the use of thinner membranes to reduce ohmic losses as well as the differential pressure operation to increase the overall system efficiency. The high differential pressure operation of PEMWEs with thin membranes results in significant hydrogen crossover from cathode to anode. This crossover-H2 has considerable implications on PEMWE performance, durability, as well as operational safety.In this work, we develop a method to accurately quantify hydrogen crossover rates in PEMWEs operating at high differential pressure. Our analysis shows that crossover-H2 is oxidized at the anode catalyst layer resulting in measurable hydrogen oxidation reaction (HOR) currents. We combine this HOR current measurement with online gas chromatography with thermal conductivity detector to determine H2 concentration in the anode outlet and also calculate H2 crossover rates at various operating current and differential pressures (up to 30 bar). Further, we use this methodology to evaluate the effect of porous transport layer (PTL) coatings (Pt, Ir, and Au) on the HOR current as well as the hydrogen crossover rate in PEMWEs.Acknowledgment: This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office (HFTO) through the Hydrogen from Next-generation Electrolyzers of Water (H2NEW) consortium.

Operando Grazing Incidence XAS Study of Pd-Nanoparticle and -Aerogel Catalysts for the Electrochemical Reduction of CO2

As global warming takes place at an unprecedented pace, it becomes increasingly important to develop negative emission (i.e., CO2-depleting) technologies to achieve the hoped-for net-zero target in 2050. The electrochemical CO2-reduction reaction (CO2RR) to carbon monoxide (CO) or formate is expected to be an economically viable approach to close the carbon cycle while reducing greenhouse gas emissions.[1] In this context, palladium (Pd) has been identified as an interesting CO2RR-catalyst owing to its ability to selectively produce formate vs. CO in the lower vs. higher overpotential regimes [i.e., at -0.1 to -0.4 vs. -0.5 to -0.9 V vs. the reversible hydrogen electrode (RHE), respectively].[2] To this day, the reasons for this potential-induced change in product selectivity remain poorly understood and a subject of open debate in the literature. In this regard, several publications have suggested that PdHx forms at the negative potentials at which the CO2RR takes place, and that this hydride acts as the active phase in the reduction of CO2 to formate.[3, 4] To elucidate this catalytic mechanism, we have investigated two different types of Pd catalysts: one consisting of dispersed Pd-nanoparticles supported on a carbon black, and a second one in the form of unsupported Pd nanoparticles tridimensionally interconnected into a network structure (i.e., a so called aerogel).[5] To track these materials’ potential-dependent PdHx-formation using X-ray absorption spectroscopy (XAS) at the Pd K-edge under CO2RR-conditions and link it to their partial current densities (pCDs) towards formate, we employed a newly designed spectroelectrochemical operando XAS flow cell. The latter enables spectral acquisition in a grazing incidence (GI) configuration allowing the use of thin layer electrodes (i.e., with a thickness < 1 μm) which in turn minimizes the accumulation of evolved gaseous bubbles along the CL-thickness, thus avoiding spectral artifacts related to the present of such bubbles. Moreover, the implementation of an ion-conductive membrane to separate the working- and counter-electrode compartments enables the accurate quantification of gaseous products via mass spectrometry and gas chromatography, as well as of liquid products by collecting aliquots of the electrolyte over time (which, in the case of formate, are subsequently analyzed through ion chromatography).Using this combination of spectroelectrochical and analytic techniques, we found that the two catalysts exhibit significantly distinct behaviors, as illustrated in Figure 1. Specifically, while for the C-supported Pd nanoparticles the stable pCD towards formate observed at -100 mV and -200mV vs. RHE is accompanied by a quick PdHx-formation (stabilizing at hydride stoichiometries of x ~ 0.6 vs. ~ 0.5, respectively), the unsupported Pd aerogel features a negligible formate- production capability at the same potentials, and the corresponding hydride phases only form gradually in the course of the potential holds and reach x-values of ~ 0.35 and x ~ 0.4, respectively. Moreover, the fact that for the C-supported Pd nanoparticles the higher pCD towards formate observed at -200 mV vs RHE corresponds to a hydride phase with a lower H-content compared that at -100 mV vs RHE indicates an indirect correlation between the formate- production rate and the nanoparticles H-content.In conclusion, these results provide valuable new insights into the important role of the time-dependent formation of PdHx on these materials’ CO2-to-formate selectivity. References Durst, J., et al., Electrochemical CO2 Reduction - A Critical View on Fundamentals, Materials and Applications. Chimia (Aarau), 2015. 69(12): p. 769-776.Diercks, J.S., et al., An Online Gas Chromatography Cell Setup for Accurate CO2-Electroreduction Product Quantification. Journal of The Electrochemical Society, 2021. 168(6).Min, X. and M.W. Kanan, Pd-catalyzed electrohydrogenation of carbon dioxide to formate: high mass activity at low overpotential and identification of the deactivation pathway. J Am Chem Soc, 2015. 137(14): p. 4701-8.Rahaman, M., A. Dutta, and P. Broekmann, Size-Dependent Activity of Palladium Nanoparticles: Efficient Conversion of CO2 into Formate at Low Overpotentials. ChemSusChem, 2017. 10(8): p. 1733-1741.Diercks, J.S., et al., Interplay between Surface-Adsorbed CO and Bulk Pd Hydride under CO2-Electroreduction Conditions. ACS Catalysis, 2022: p. 10727-10741. Figure 1

CO2 Hydrogenation through Electrochemical Hydrogen Activation in a Gas-Vapor Fed Reactor

An attractive concept in the chemical manufacturing industry is the adoption of a circular carbon economy, which can include continuous capture and conversion of CO2 into industrially relevant chemical feedstocks. This has driven considerable research interest in electrochemical CO2 reduction.1 Despite this popularity, major challenges remain even for the most advanced CO2 reduction reactors, including low conversion rates and energy efficiencies; moreover, in many cases, multiple carbon-containing products are generated, which add to costs for downstream separation.2 By contrast, thermochemical CO2 hydrogenation is well established and typically demonstrates higher energy efficiency and selectivity compared to electrochemical CO2 reduction.3,4 This notable contrast drives our interest in better understanding the physics that governs differences in reactivity between thermocatalytic and electrocatalytic CO2 reduction reactors. To address these questions, we are pursuing a unique approach that involves feeding humidified CO2 and H2, respectively, to the cathode and anode of an electrochemical membrane-electrode assembly (MEA). This presentation will cover initial work we have undertaken to design and validate this reactor for the study CO2 electro-reduction.The overall design of our reactor resembles a hydrogen fuel cell fed with humidified H2 and CO2. Thus, it was initially benchmarked through operation as an electrochemical hydrogen pump, wherein humidified Ar was fed to the cathode and humidified H2 was fed to the anode with Pt/C as the catalyst on each side of the membrane. Under these conditions, a cation exchange membrane (CEM) readily generated current densities in excess of 1 A/cm2 with monotonic decreases in polarization with increased temperature at fixed current. We then undertook analogous hydrogen pumping experiments using anion exchange membranes (AEM) that had been ion-exchanged with hydroxide, carbonate, and bicarbonate anions. We observed net proton transport between the anode and cathode chambers in each case, albeit with higher ionic resistance for AEMs in the bicarbonate form.We then undertook further studies to demonstrate the ability to reduce CO2 using H2 fed to the anode. This operating mode eliminates the need for a liquid anode feed, which dramatically reduces the driving force for CO2 crossover via bicarbonate formation. Moreover, the Pt/C anode catalyst is expected to oxidize hydrogen with minimal polarization, allowing the total cell polarization to be interpreted simply as the cathode potential on the RHE scale. CO2 reduction experiments were carried out using commercial Cu/C catalyst with online gas chromatography and NMR for product analysis of volatile and condensable products, respectively. Operation with a CEM yielded only H2(g) at the cathode, but initial experiments with an AEM in the carbonate/bicarbonate form gave high selectivity to ethanol at 70 oC.

Disentangling the Pitfalls of Rotating Disk Electrode-Based OER Stability Assessment: Bubble Blockage or Substrate Passivation?

Oxygen evolution reaction (OER) catalyst stability metrics derived from aqueous model systems (AMSs) prove valuable only if they are transferable to technical membrane electrode assembly (MEA) settings. Currently, there is consensus that stability data derived from ubiquitous rotating disk electrode (RDE)-based investigations substantially overestimate material degradation mainly due to the nonideal inertness of catalyst-backing electrode materials as well as bubble shielding of the catalyst by evolved oxygen. Despite the independently developed understanding of these two processes, their interplay and relative impact on intrinsic and operational material stability have not yet been established. Herein, we employ an inverted RDE-based approach coupled with online gas chromatographic quantification that exploits buoyancy and anode hydrophilicity existing under operating acidic OER conditions and excludes the influence of bubble retention on the surface of the catalyst. This approach thus allows us to dissect the degradation process occurring during the RDE-based OER stability studies. We demonstrate that the stability discrepancy between galvanostatic nanoparticle (NP)-based RDE and MEA data does not originate from the accumulation of bubbles in the catalyst layer during water oxidation but from the utilization of corrosion-prone substrate materials in the AMS. Moreover, we provide mechanistic insights into the degradation process and devise experimental measures to mitigate or circumvent RDE-related limitations when the technique is to be applied to an OER catalyst stability assessment. These findings should facilitate the transferability between AMS and MEA approaches and promote further development of the latter.

Physicochemical Analysis of Cu(II)-Driven Electrochemical CO2 Reduction and its Competition with Proton Reduction.

The reduction of CO2 has become a key role in reducing greenhouse gas emissions in efforts to search for long-term responses to climate change. We report a couple of CO2-reducing molecular catalysts based on earth-abundant copper complexes. These are [Cu(DPA)(PyNAP)] (1) and [Cu(DPA)(PyQl)] (2) (where, DPA=pyridine-2,6-dicarboxylate, PyNAP=2-(pyridin-2-yl)-1,8-naphthyridine, and PyQl=2-(pyridin-2-yl)quinoline). The copper metal-catalysed 2-electron reduction of CO2 to CO in the presence of 2-protons is challenging. These catalysts exhibit the production of CO gas in DMF/water mixtures, achieving an impressive Faradaic efficiency of 84 % and 72 % for complex 1 and 2 at -1.7 V vs. SCE, respectively, for selective CO2 reduction. The production of H2 due to 2H++2e- was also observed as a byproduct through the competitive proton reduction reaction. This was cross-verified by online gas and mass analysis. A comprehensive series of electrochemical experiments have substantiated the homogeneous behaviour exhibited by these molecular electrocatalysts. Our investigations confirmed the stability of the electrocatalysts under the electrocatalytic conditions. The mechanistic pathways were proposed to work with the EECC and ECEC (E: electrochemical and C: chemical) mechanisms. A CO2 insertion into an in-situ generated hydride from the Cu-center generates CO through the favourable path. This critical path kinetically favors excess Faradaic efficiency in 1 than 2, which agrees with the computational investigation.

Characteristics and Source Apportionment of Atmospheric Volatile Organic Compounds in Zhengzhou During O3 Campaign Period

An online gas chromatograph （GC5000） was used to monitor the volatile organic compounds （VOCs） in the atmospheric environment of Zhengzhou City during the ozone campaign period from May to September of 2022. The relationship between O3 and its precursors as well as meteorology was analyzed and the pollution characteristics of VOCs during the O3 exceeding and non-exceeding the standard days were compared and explored. Different VOC activity evaluation methods of OFP and L·OH were utilized to compare and analyze the key active components and species and the ratio analysis （RA） and positive matrix factorization （PMF） analysis models were used to study the apportionment contribution of VOCs. The results showed that the O3 pollution in June and September in Zhengzhou was mainly due to the adverse meteorological conditions of high temperature and low humidity, strong radiation, and low wind speed, superimposed by the prominent concentrations of local VOCs and NO2, resulting in frequently high and excessive O3 occurrences. The VOCs concentration in Zhengzhou during the campaign period was an average of （68.3 ± 18.4） μg·m-3, whereas it was 75.7 μg·m-3 during O3 exceeding standard days and 13.4 μg·m-3 during O3 non-exceeding days, respectively. Among the VOC species, the OVOCs was 31.6%, accounting for the highest mass fraction, followed by halogenated hydrocarbon, alkane, and aromatic hydrocarbon, and the major species were ethane, n-butane, dichloromethane, propane, isopentane, toluene, chloromethane, 1,2-dichloroethane, and acetylene. VOC diurnal variation indicated that the emission of VOC pollution sources in the morning, evening peak, and at night should be paid more attention. The contribution of VOCs to OFP during the campaign period was （130.5 ± 46.4） μg·m-3, and the L·OH was （6.5 ± 2.9） s-1, among which the top 15 species with high activity were primarily acetaldehyde, isoprene, ethylene, m/p-xylene, toluene, hexal, isopentane, propanal, propylene, trans-2-butene, etc. In particular, the contributions of acetaldehyde, isoprene, ethylene, and hexal species were prominent during the O3 exceeding days. Ratio analysis showed that the B/T ratio in Zhengzhou from May to September ranged from 0.05 to 5.3, with an average value of 1.1 ± 0.6, and the regional VOCs was mainly controlled by the aging air mass with possible long-distance transports. The analysis of the PMF model showed that the major pollution sources to VOC concentration in Zhengzhou were motor vehicle exhaust emission sources and industrial solvent and secondary conversion sources, contributing 25.6% and 25.8%, respectively. The contribution rates of solvent coating sources, oil and gas volatile sources, plant emission sources, industrial solvents, and secondary conversion sources during O3 exceeding days were 5.4%, 4.7%, 3.3%, and 0.7% higher than those during O3 non-exceeding days, respectively. The research showed that the management of VOCs and NOx pollution sources should be strengthened to reduce their contribution to the O3 generation when O3 exceeds the standard.

Investigating the oxidation characteristic of a hydro-processed bio-jet fuel: Experimental and modeling study

A rapid transition from conventional jet fuels to sustainable aviation fuels (SAFs) is imperative in order to reduce carbon emissions. Hydro-processed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK), as a type of SAF, exhibits broad applications. In this study, a new HEFA-SPK named ZH-HEFA was investigated. The fuel comprises 14% n-alkanes, 85% iso-alkanes and only 1% cycloalkanes by weight, with the majority of alkanes ranging from C9 to C17. Oxidation experiments of the fuel were conducted using an atmospheric pressure flow reactor at temperatures ranging from 550 K to 1075 K under three equivalence ratios (0.5, 1.0 and 1.5). Species mole fraction profiles were measured by an on-line gas chromatographic (GC). For comparison purposes, an experiment was also performed on RP-3, a conventional jet fuel commonly used in China, under the equivalence of 0.5. Compared to RP-3, ZH-HEFA exhibited significantly stronger low temperature reactivity and higher combustion conversion rates while demonstrating considerably lower yields of aromatics at high temperatures. The kinetic simulation of ZH-HEFA was achieved by proposing two surrogates and their corresponding kinetic models. Surrogate S-1 consisted solely of n-dodecane, while S-2 comprised 35% n-dodecane and 65% 2,6,10-trimethyl dodecane by weight. Both surrogate models were validated by the experimental data. S-1 exhibited a closer resemblance to the global oxidation characteristics of ZH-HEFA, whereas S-2 demonstrated improved accuracy in predicting the formation of small hydrocarbon intermediates during the fuel oxidation. Rate of production analysis revealed that the branched alkane component in S-2 possessed more pathways and greater capability than S-1 in generating C3 intermediates, which are important for the generation of aromatics. Furthermore, both models displayed good predictive performance for the auto-ignition properties of HEFA-SPK fuels.-

Novel assessment of molten salt oxidation for cation exchange resin treatment: Effective neutralization of sulfurous gas with Li2CO3-Na2CO3-K2CO3 system

The conventional thermal treatment of cation exchange resin substantially releases sulfurous gases, causing significant equipment corrosion and air pollution. In contrast, the Li2CO3-Na2CO3-K2CO3 as an alkaline molten system effectively neutralizes sulfur gas and mitigates waste gas production inherent in thermal oxidation methods. In the molten salt oxidation process, the volume concentration of SO2 was reduced by 81.7 % compared to that in the traditional thermal oxidation process, and this method reduces the generation of hazardous gases such as CO, CH4, and C2H6. The integration of online gas mass spectrometry and phase stability diagrams for carbonate and sulfur interception products demonstrate excellent thermodynamic stability during the molten salt oxidation (MSO) process. Moreover, a more accurate assessment of the acid gas neutralization capacity of the molten salt system is provided, and the acid gas neutralization capacity of the Li2CO3-Na2CO3-K2CO3 carbonate system can reach 82.58 % at 800 °C. The predominant contributors to acid gas neutralization are Na2CO3 and K2CO3, as evidenced by waste salt composition and ternary phase diagrams. The stable presence of Li2CO3 throughout the MSO process contributes to the lowering of the melting point of the carbonate system to 393 °C.

A high‐frequency greenhouse gas flux analysis tool: Insights from automated non‐steady‐state transparent soil chambers

AbstractNon‐steady‐state chambers are widely employed for quantifying soil emissions of CO2, CH4, and N2O. Automated non‐steady‐state (a‐NSS) soil chambers, when coupled with online gas analysers, offer the ability to capture high‐frequency measurements of greenhouse gas (GHG) fluxes. While these sampling systems provide valuable insights into GHG emissions, they present post‐measurement challenges, including the management of extensive datasets, intricate flux calculations, and considerations for temporal upscaling. In this study, a computationally efficient algorithm was developed to compute instantaneous fluxes and estimate diel flux patterns using continuous, high‐resolution data obtained from an a‐NSS sampling system. Applied to a 38‐day dataset, the algorithm captured concurrent field measurements of CO2, CH4, and N2O fluxes. The automated sampling system enables the acquisition of high‐frequency data, allowing the detection of episodic gas flux events. By using shape‐constrained additive models, a median percentage deviation (bias) of −1.031 and −4.340% was achieved for CO2 and N2O fluxes, respectively. Simpson's rule allowed for efficient upscale from instantaneous to diel flux values. As a result, the proposed algorithm can rapidly and simultaneously calculate CO2, CH4, and N2O fluxes, providing both instantaneous and diel values directly from raw, high‐temporal‐resolution data. These advancements significantly contribute to the field of GHG flux measurement, enhancing both the efficiency and accuracy of calculations for a‐NSS soil chambers and deepening our understanding of GHG emissions and their temporal dynamics.

Development, optimization and validation of automated volatile organic compound data analysis using an on-line thermal desorption gas chromatograph with dual detection and application to measurements in ambient air

Because of their major role in indoor and outdoor air pollution, even at trace levels, VOCs are of great interest, and their monitoring requires sensitive analytical instruments. Several techniques are commonly used, such as portable sensors, Proton Transfer Reaction Mass Spectrometry (PTR-MS) and Thermal Desorption Gas Chromatography (TD-GC). The latter is widely used off- and on-line with Flame Ionization Detectors (FID) or Mass Spectrometers (MS). Given the large number of molecules detected per chromatogram, the data generated by these monitoring techniques are usually checked and reprocessed manually. This process is extremely time consuming and could result in human error. The challenge is to provide reliable results as quickly as possible.In this study, the performances of an on-line TD-GC system with dual detection FID and MS were tested. The Method Detection Limits (MDL), linearities and accuracies of 60 VOCs (alkanes, aromatics, oxygenated and halogenated) were calculated both for FID and MS detectors. The MDLs and accuracies ranged from 0.006 to 0.618 ppbv and from 77 % to 100 % for FID, and from 0.018 to 0.760 ppbv and from 80 % to 100 % for MS. Both detectors showed good complementarity and allowed the development of two programs to facilitate data analysis. These algorithms were designed to autonomously select optimal results between FID and MS detectors, and were evaluated for outdoor and indoor measurement conditions. Measuring VOCs in field campaigns is challenging, and it is anticipated that these programs could be extended to other types of dual-detector systems or for the comparison of data from different calibrated instruments.

Thermochemical production of ammonia via a two-step metal nitride cycle - materials screening and the strontium-based system.

Ammonia synthesis via the catalytic Haber-Bosch process is characterized by its high pressures and low single-pass conversions, as well as by the energy-intensive production of the precursors H2 and N2 and their concomitant greenhouse gas emissions. Alternatively, thermochemical cycles based on metal nitrides stand as a promising pathway to green ammonia production because they can be conducted at moderate pressures without added catalysts and be further driven by concentrated solar energy as the source of high-temperature process heat. The ideal two-step cycle consists of the nitridation of a metal to form a metal nitride, followed by the hydrogenation of the metal nitride to synthetize NH3 and reform the metal. Here, we perform a combined theoretical and experimental screening of mono-metallic nitrides for several candidates, namely for Sr, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, Li, and Al. For the theoretical screening, Ellingham diagrams and chemical equilibrium compositions are examined with thermodynamic data derived from density function theory computations. For the experimental screening, thermogravimetric runs and mass balances supported by on-line gas analyses are performed for both steps of the cycle at ambient pressure and over the temperature ranges 100-1000 °C for nitridation and 100-500 °C for hydrogenation. The strontium-based cycle is selected as a reference for detailed examination and shown to synthetize NH3 at 1 bar by effecting the nitridation at 407 °C (at peak rate) and the hydrogenation at 339 °C (at peak rate). The co-formation of metal hydrides (SrH2) and metal imides (Sr2HN) are shown to help close the material cycle.

A modified capacitance tomography image reconstruction approach based on iterative shrinkage-thresholding algorithm combined with deep networks

Abstract Due to the ‘soft-field’ effect and the challenges posed by ill-posed and ill-conditioned inverse problems, it is difficult to obtain high quality images from an electrical capacitance tomography (ECT) system. To achieve both high-quality images and fast imaging speed with limited measurement data, an image reconstruction algorithm, which was initially proposed for compressive sensing, is adapted for ECT image reconstruction to optimize the ill-posed nature of its inverse problem. The proposed algorithm leverages deep learning networks inspired by the iterative shrinkage-thresholding algorithm (ISTA), thereby creating a model that is both mathematically interpretable and endowed with trainable parameters. Building upon this foundation, the conventional Landweber iteration is integrated with the ISTA-Net to refine the optimization process for ECT image reconstruction. In order to propose an effective model adapting to the actual multiphase flow characteristics and complex flow pattern changes, the training and test process is driven by a comprehensive dataset generated from dynamic simulations, rather than artificial samples of multiphase distributions. This numerical methodology simulates the dynamic measurement process of a virtual ECT sensor by coupling the gas–liquid two-phase flow field and the ECT electrostatic field. The results of the testing phase indicate that the proposed algorithm outperforms traditional ECT image reconstruction methods. Compared with the linear back projection algorithm, the average image error and gas fraction error have been reduced by 20.44% and 16.74%, respectively, while maintaining a computational speed comparable to that of the Landweber iteration. The accuracy of the new algorithm in reconstructing the two-phase interface and estimating the gas fraction has been validated by static experimental tests, showing its potential for practical application in online gas–liquid two-phase flow measurement scenarios.

Electrochemical CO2 Reduction on Silver – a Perspective through Electrochemical Impedance Spectroscopy

Anthropogenic carbon rise in the earth's atmosphere is the leading cause towards global warming. Electrochemical CO2 reduction (eCO2RR) is one of the most promising sustainable pathways for the utilization and recycling of anthropogenic carbon. The current challenge in eCO2RR is to make the process more energy efficient and to drive the selectivity toward the desired products. eCO2RR normally takes place in parallel with hydrogen evolution reaction (HER). Additionally, dependent on catalyst material and potential different C-products can be obtained. The mechanistic understanding of the interplay between different reactions is still limited, since the involved reactions are characterized by faster kinetics and/or different adsorbed species as well as mass transfer dependences than the other ones. Moreover, we have recently shown that under dynamic conditions eCO2RR product selectivity towards CO can be tuned1. In that study, we developed a simple model and identified key kinetic parameters which govern product selectivity under dynamic conditions. The model included only the electrochemical kinetics of two parallel reactions without consideration of adsorbed species or mass transport limitations. Therefore, some of the experimental observations could not be completely explained. In such complicated cases involving different physicochemical phenomena acting in parallel at different time scales, the use of electrochemical impedance spectroscopy (EIS) to analyse the system could shed light on the understanding of the process.In this contribution, we have developed a mathematical model which couples micro-kinetics with continuum transport. At first, the model was validated under steady-state conditions. The experiments have been performed under different conditions (mass transport and buffer concentrations) on silver rotating disk electrodes and the product distribution (H2 and CO) has been determined with the help of online gas chromatography. This model was then used to calculate EIS. Based on this approach, we present here a detailed interpretation of the EIS spectrum during eCO2RR and the features obtained at different applied electric potentials. Key insights are drawn about the role of charge and mass transport as well as adsorbed intermediates on the observed features.

A Comprehensive Online Analytical System Coupled with Standardized Data Analysis for the Electrochemical Reduction of CO2

The electrochemical reduction of CO2 (CO2RR) is a promising way to convert detrimental CO2 emissions into sustainable fuels and chemicals, and thus to achieve a circular carbon economy. 1 Depending on catalyst type and reaction conditions, different gaseous and liquid products can be obtained from the CO2RR, and their production rates vary with reaction time. It becomes thus imperative, for any catalytic performance analysis, to be able to assess the product distribution online during CO2RR. 2,3 However, while gaseous products are readily analyzed online by gas chromatography, liquid products are typically only assessed at the end of the reaction due to the lack of suitable automated liquid sampling and analysis methods. In addition, reaction parameters such as CO2 mass flow rates, temperatures and pressures are seldom recorded, causing the loss of significant information on catalysts, electrodes, and electrolyzers behavior.To overcome these issues, we assemble a comprehensive analytical system coupling online gas and liquid product analysis by gas and liquid chromatography leveraging a special automated liquid sampling valve with electrochemical protocols that assess CO2RR performance, electrolyzer cell resistance and electrode surface area. In addition, we record CO2 mass flow rates, electrolyzer temperatures, as well as gas and liquid flow pressures. 4 To rapidly and reproducibly handle the large and heterogeneous data volume obtained we implement a standardized data pipeline based on our own open-source software,5 which automatically parses the numerous different raw data files, composes a data set following FAIR practices,6 and post-processes and plots the data in a standardized way. We validate the analytical system by carrying out CO2RR at 200 mA/cm2 on Cu gas diffusion electrodes, following the changes in selectivity with reaction time for > 10 gaseous and liquid products, and recording mass flow rates, electrolyzer temperatures and pressures. The modular nature of our analytical system, combined with the standardized data pipeline, allows us to freely increase the number and type of sensors used with minimal impact on the data analysis time, as well as to multiplex our analysis to 8 parallel electrolyzer cells, paving the way for a much deeper and faster understanding of the function of CO2RR catalysts, electrodes, and electrolyzers.

Scanning Gas Diffusion Electrode Setup for Real-Time Analysis of Catalyst Layers.

The scanning gas diffusion electrode (S-GDE) half-cell is introduced as a new tool to improve the evaluation of electrodes used in electrochemical energy conversion technologies. It allows both fast screening and fundamental studies of real catalyst layers by applying coupled mass spectrometry techniques such as inductively coupled plasma mass spectrometry and online gas mass spectrometry. Hence, the proposed setup overcomes the limitations of aqueous model systems and full cell-level studies, bridging the gap between the two approaches. In this proof-of-concept work, standard fuel cell electrodes are investigated at elevated oxygen reduction reaction current densities, while dissolved Pt x+ ions in the electrolyte and gaseous CO2 in the outlet gas stream are detected to track platinum dissolution and carbon corrosion, respectively. Relevant current densities of up to 0.75 A cm-2 are demonstrated. The electrochemically active surface area, oxygen reduction reaction activity, and Pt dissolution rates are quantified and benchmarked to the values obtained in the conventional stationary GDE half-cell. Moreover, it is found that Pt dissolution is suppressed when O2 is purged into the catalyst layer. Overall, this work demonstrates the feasibility of fast fuel cell electrode screening obtaining, complementary to electrochemical, mass spectrometry data necessary in fundamental studies on structure/performance relationships under actual reaction conditions. While Pt/C, in relevance to its fuel cell application, is used in this study, the proposed setup can be applied in water electrolysis, CO2 conversion, metal-air batteries, and other neighbor technologies.

Design of a Rotating Disk Electrode setup operating under high pressure and temperature: Application to CO2 reduction on gold

We describe the design and development of a rotating disk electrode (RDE) cell capable of operating at pressures up to 200 bar and temperatures up to 200 °C. This setup enables electrochemical surface characterization through techniques such as voltammetry and impedance spectroscopy, under different mass transport regimes. Furthermore, evaluation of catalytic performance, including CO2 reduction, is possible as the system works in a semi-continuous mode interfaced with online gas sample measurements. As a proof of concept of the high-pressure cell designed, we examined the temperature-dependent changes in the cyclic voltammograms (CVs) of polycrystalline gold up to 150 °C and 50 bar. Additionally, online catalytic performance of CO2 reduction to CO on a rotating polycrystalline gold disk electrode was investigated under different pressure and temperature. Our results indicate a positive impact of temperature on the faradaic efficiency (FE) towards CO up to 50 °C, beyond which a rapid drop in performance was observed at atmospheric pressure. Conversely, increasing pressure positively affected CO2 solubility in the electrolyte, resulting in enhanced FE towards CO, reaching approximately 90 % at 6 bar compared to 40 % at atmospheric pressure. Notably, further increases in pressure did not significantly alter the FE, but led to higher current densities. Moreover, at pressures exceeding 6 bar, we observed a plateau in efficiency at temperatures higher than 50 °C. This observation suggests that increasing pressure can sustain CO2 electrolysis, validating the hypothesis that increasing CO2 solubility would suppress catalytic decay at higher temperatures. This study opens up promising avenues for future investigations in electrocatalysis, ranging from fundamental explorations of surface modifications induced by variations in temperature and pressure to the development of high-performance catalysts.