Low-temperature Gas Research Articles

Experimental study of SCR DeNOX efficiency at low exhaust gas temperatures

Experimental study of SCR DeNOX efficiency at low exhaust gas temperatures

Gasification of multi-layer porous fuels in low-temperature gas generator for flying vehicle

The paper is aimed at investigating the influence of porous fuel layering on the operating regimes and performance of a low-temperature gas generator for high-speed flying vehicles equipped with a ramjet engine. The gas generator consists of a propellant and a porous fuel arranged sequentially to generate hydrocarbon gases that cool the engine before burning in the combustion chamber. In this paper, using a novel numerical model, gasification of multi-layer solid porous fuels consisting of polymethylmethacrylate (PMMA) and polyethylene (PE) is studied for various volume contents and relative arrangements of fuel parts. It is shown that during the gasification of the multi-layer fuels, several gasification waves can simultaneously occur in the gas generator. The operating time of the gas generator depends on the relative sizes and relative location of the PMMA and PE layers, and an increase in the number of layers leads to a decrease in the influence of their relative arrangement on the process. Thus, during the gasification of two-component multi-layer solid porous fuel, the composition of this fuel, i.e., the relative sizes of the layers and their relative arrangement, can be the control parameter that allows one to choose the desired characteristics of the gasification process.

A porous three-dimensional Cu-MOF: Preparation and application in supercapacitors, low temperature hydrogen storage and gas separation

Due to its unique porosity, metal–organic frameworks (MOFs) have great application prospects in the fields of gas adsorption and separation. However, the synthesis of multi-functional MOFs is still a great challenge. Herein, a multi-functional Cu-MOF of {[Cu2(TPTA)(H2O)2]·2DMF·NMP·4H2O}n with a porosity of 62.0 % was designed and synthesized. The H2 adsorption amount of Cu-MOF is about 289.2 cm3 g−1 at 77 K and 1 bar. Meanwhile, the selectivity adsorption of Cu-MOF towards CO2 over CH4 (V:V = 0.5:0.5), CO2/N2 (V:V = 0.5:0.5) and CO2/H2 (V:V = 0.5:0.5) is 95.1, 139.2 and 147.5, respectively, which is 1.5 times higher than the previously reported Cu-MOFs. The Cu-MOF@NF//AC asymmetric supercapacitor demonstrates high specific capacitance (53.4 F g−1) and stability (90.3 % after 2000 cycles). Furthermore, this work presents a novel approach to design multifunctional materials with low temperature hydrogen storage, gas separation and energy storage properties.

Perovskite CsPbBr3 quantum dots enhanced In2O3 nanospheres for triethylamine detection at low temperature

In recent years, the vigorous industrial development of the country has brought about serious air pollution, and the development of low-temperature gas sensors with high response and short response/recovery time has become ideal for monitoring the industrial environment. This work demonstrates a composite gas sensor based on CsPbBr3 perovskite quantum dots (QDs) and In2O3 nanospheres for the detection of TEA gases at low temperatures. Compared with pure In2O3, the best responsive gas for the In2O3-CsPbBr3 QDs composite was triethylamine (TEA), with a response value of 52.92 at an optimal operating temperature of 60 °C. In addition, due to the sensitive optical properties of the CsPbBr3 QDs, UV irradiation of the In2O3-CsPbBr3 composites was performed, and the samples were found to have response values as high as 156.42. The In2O3-CsPbBr3 composite also has a short response recovery time (1/19 s), which is favorable for timely warning. The results of the gas-sensing experiments showed that the sensor has good sensitivity, reproducibility, and stability for triethylamine.

Structural and morphological properties of CeO2 films deposited by radio frequency magnetron sputtering for back-end-of-line integration

Cerium oxides have potential applications ranging from low-temperature gas sensing to photodetection. A back-end-of-line integration of the material into complementary metal-oxide-semiconductor device fabrication processes has many advantages but places limits on material deposition, most notably the thermal budget for deposition and annealing. Here, we investigate thin cerium oxide films deposited by radio frequency (RF) magnetron sputtering at substrate temperatures of 300°C and RF magnetron powers between 30 W and 70 W without any post-deposition annealing steps. Our investigation of the structural and morphological properties reveals a columnar texture of the thin films, and we find that the material is composed predominantly of CeO2 (111), with a large degree of crystallinity. We discuss implications for resistive gas sensing applications.

Composite photocatalysts g-C<SUB>3</SUB>N<SUB>4</SUB>/TiO<SUB>2</SUB> for hydrogen production and dye decomposition

The photocatalytic activity of the g-C3N4 /TiO2 composite samples in the processes of dye (methylene blue) decomposition and hydrogen evolution from an aqueous ethanol solution under the action of visible radiation (400 nm) has been studied. A new original method for the synthesis of the g-C3N4 /TiO2 composite by depositing g-C3N4 /TiO2 to TiO2 nanoparticles during sol-gel synthesis is proposed. The synthesized photocatalysts were characterized by X-ray diffraction, low-temperature gas adsorption, X-ray photoelectron spectroscopy, high-resolution transmission microscopy, and diffuse reflectance spectroscopy in the UV and visible regions. The maximum activity in the hydrogen evolution reaction was 1.3 mmol h–1, which exceeds the rate of hydrogen evolution on the unmodified g-C3N4 and TiO2 samples.

Studying the process of metals and non-metals transfer in a low-temperature gas flow over sulfide tailings materials

ABSTRACT A large number of publications have been devoted to the study of aerosol atmospheric transport, but the low-temperature transfer of metals and metalloids as a part of gas flow remains poorly understood. The present work is devoted to the study of gas stream composition using an approach based on the collection of nascent condensate upon cooling of the air flow formed over the surface of contaminated sites. A special laboratory unit was designed to collect the condensate followed by the study of its composition using atomic emission and mass spectrometry. The main novelty of this work consists of the application of the single-particle ICP‒MS technique to obtain qualitative information concerning the state of the elements in the condensates. Gold and silver are most likely present in the samples as nanoparticles; arsenic, selenium, tin and lead are present both as nanoparticles and as soluble forms; and barium and mercury are present only in soluble forms. The condensed phase contains As, Hg, Au, Ag, Pb and Sn at the ppb level, while the main elements of the tailings material (Fe, Ba, Cu, Zn and others) are present at the ppm level, which exceeds the background concentration.

Oxygen vacancy-enriched WO3 hierarchical tubes inherited from pine needle for the enhanced detection to ppb-level hydrazine at near room temperature

It is of great importance to develop low-temperature gas sensors for monitoring hydrazine (N2H4) with high toxicity and easy explosion. However, how to highly sense its ppb-level concentration remains challenging. For this purpose, biomorphic WO3 structure replicated by small-size nanoparticles was simply prepared though air calcinations of tungsten salt-immersed pine needle (PN) template. The mesoporous WO3-PN tubes with pore volume of 0.096 cc·g−1 had relatively large specific surface area (38 m2·g−1) for exposing more active sites, as well as rich oxygen vacancies (g = 2.005) and small band gap for promoting electron migration. With the assistance of W6+ Lewis acid catalytic sites, such unique multilevel structure facilitated the rapid transport and adsorption of basic N2H4 molecules, as well as their chemical reactions with high content of oxygen species (37.4 %) in sensing layer, thus first achieving the highly sensitive detection of ppb-level N2H4 gas at near room temperature. At 50 °C, WO3-PN sensor exhibited ultra-high response (S = 307), fast response time (Tres = 16 s) for 1 ppm N2H4, and low actual detection concentration (5 ppb). These key indicators were remarkably superior to reported semiconductor gas sensors. In addition, the enhanced low-temperature sensing mechanism of WO3-PN sensor was explored by means of analytical tests and DFT calculations.

Performance and mechanism investigation of Cu loading and S vacancy synergistic promotion of MoS2 catalyzed low-temperature water gas shift reaction: Experimental and theoretical calculations

In this paper, MoS2 with S vacancies and Cu loading (Cu/VS-MoS2) was synthesized and used for low-temperature water gas shift reactions (WGSR); the intrinsic reasons and reaction mechanisms for the high catalytic activity of Cu/VS-MoS2 were studied through DFT calculation. The material characterization fully confirms the successful construction of Cu loading and S vacancies on spherical cluster structures of Cu/VS-MoS2. The experimental results show that Cu/VS-MoS2 exhibits the highest CO conversion, up to 40.41%, which is 3.9 times, 1.8 times, and 1.5 times higher than MoS2, VS-MoS2, and Cu/MoS2, respectively. DFT calculations indicate that Cu/VS-MoS2 has high WGSR activity due to the superior electron transfer ability of the dual active sites, and the S vacancy is used to activate CO to generate CO2, while the Cu site activates H2O to produce hydrogen. The synergistic effect of S vacancies and Cu sites, while satisfying hydrogen production and carbon dioxide enrichment, greatly enhances the activity of MoS2. In addition, Cu/VS-MoS2 can more effectively break down the transfer barriers between surface electrons and CO, H2O molecules, allowing electrons to continuously transfer to CO and H2O using S vacancies and Cu atoms as mediators, reducing the energy barrier of the rate-determining step in association mechanism.

A comparative study of gas temperature determination in non-thermal atmospheric pressure plasma jet by spectral analysis and scattering technique for plasma-catalyst measurements

Comparison and validation of different methods for the measurements of plasma gas temperature were studied. The investigations depend on optical emission spectroscopy OES, laser scattering technique, and line-broadening mechanisms. The rotational temperature of the second positive system SPS (C3 ∏+ u - B3 ∏+ g) around 380 nm, second positive system SPS at 337.1 nm of nitrogen molecule (C3 ∏+ u - B3 ∏+ g), and first negative system FNS at 391.4 nm of nitrogen ion (B2Σu +→X2Σg +) were investigated. Moreover, Raman scattering spectra at 532 nm were used to measure the gas temperature in the plasma jet. Gas temperature from the emission line broadening method was also calculated. The role of non-thermal plasma in assisting NOx reduction over an Ag/Al2O3 catalyst at low temperatures using simulated diesel fuels (toluene) was confirmed. Importantly, a significant activity of both NOx and hydrocarbons oxidation was observed and obtained at low gas temperatures. It was found that there is a clear correlation between the gas temperature and the conversion efficiency of the catalyst under different operating conditions of the plasma reactor. The main objective of this investigation was to confirm the important role of the non-thermal plasma in catalyst activation at low gas temperatures compared to traditional thermal activation.

Experimental study on the preparation of desulfurizer for low temperature dry desulfurization by digesting CaO in urea solution

Calcium hydroxide (Ca(OH)2) with outstanding sulfur dioxide (SO2) adsorption properties was synthesized through the utilization of calcium oxide (CaO) with a urea solution via a digestion method. This innovative calcium-based desulfurizer aims to meet the needs of low-temperature dry flue gas desulfurization in the steel industry. Fixed-bed experiments were conducted to investigate the impact of different water-ash ratios, urea solution concentrations, and digestion time on the desulfurization efficiency and particle structure of the desulfurizers. Sample CAC-2–0.1 U exhibited outstanding desulfurization performance, achieving 100 % removal efficiency, a sulfur capacity of 34.64 mg/g, and a breakthrough time of 142.6 minutes under target flue gas conditions. The sample also displayed a high specific surface area of 22.10 m2/g and demonstrated adaptability under varying operating conditions. Characterization and reaction mechanisms of the desulfurizer were studied using XRD, SEM, BET, XPS, ICP-OES, and Materials Studio software. Experimental data was analyzed through pseudo-first-order and pseudo-second-order kinetic equations, and intra-particle diffusion model. The product's strong adsorption capacity for SO2 positions it as a highly promising adsorbent for controlling low-temperature flue gas emissions in the steel industry.

Thermal oxidation CuO nanowire gas sensor for ozone detection applications

In this study, cupric oxide nanowires (CuO NWs) on patterned interdigitated electrodes (PIEs) used as ozone (O3) gas sensors, were successfully fabricated using thermal oxidation and the microelectromechanical systems (MEMS) technique. After the thermal oxidation process, CuO NWs with different heights and densities were fabricated using a pure copper seed layer with a thickness ranging from 0.5 μm to 2 μm. In this experiment, a low temperature, low concentration, and repeatable CuO NWs gas sensor was fabricated, which can detect O3 gas at a low concentration of 50 ppb and low temperature of 100°C with a high sensor response (40%). The concentration response of this gas sensor shows an increasing linear trend, with an increase of O3 concentration in the range of 50 ppb - 300 ppb. Additionally, the results indicated that this CuO NWs gas sensor is more selective for O3 than CO, CO2, C2H5OH, C3H6O, NO2, or NH3. While CuO has been less studied in O3 detection compared with other semiconducting metal oxide materials, CuO NWs show potential applications in gas sensing devices for low-temperature and low-concentration O3 environmental monitoring.

Cationic conjugated polymer coupled non-conjugated segments for dually enhanced NIR-II fluorescence and lower-temperature photothermal-gas therapy

The lack of a simple design strategy to obtain ideal conjugated polymers (CPs) with high absorbance and fluorescence (FL) in the near-infrared-II (NIR-II; 1000–1700 nm) region still hampers the success of NIR-II light-triggered phototheranostics. Herein, novel phototheranostic nanoparticles (PPN-NO NPs) were successfully prepared by coloading a cationic NIR-II CPs (PBC-co-PBF-NMe3) and a NO donor (S-nitroso-N-acetylpenicillamine, SNAP) onto a 1:1 mixture of DSPE-PEG5000 and dimyristoylphosphatidylcholine (DMPC) for NIR-II FL and NIR-II photoacoustic (PA) imaging-guided low-temperature NIR-II photothermal therapy (PTT) and gas combination therapy for cancer treatment. A precise NIR-II FL dually enhanced design tactic was proposed herein by integrating flexible nonconjugated segments (C6) into the CPs backbone and incorporating quaternary ammonium salt cationic units into the CPs side chain, which considerably increased the radiative decay pathway, resulting in desirable NIR-II FL intensity and balanced NIR-II absorption and NIR PTT properties. The phototheranostic PPN-NO NPs exhibited distinguished NIR-II FL and PA imaging performance in tumor-bearing mice models. Furthermore, the low-temperature photothermal effect of PPN-NO NPs could initiate NO release upon 980 nm laser irradiation, efficiently suppressing tumor growth owing to the combination of low-temperature NIR-II PTT and NO gas therapy in vitro and in vivo.Graphical

Effect of Tectonic Deformation on the Pore System and Methane Adsorption of Anthracite Coal.

Tectonic deformation significantly alters the physical structure of coals, holding great importance to the coal mining industry and coalbed methane. In this study, eight anthracite coal samples with varying degrees of deformation were collected to investigate the effects of tectonic deformation on the pore system and CH4 adsorption of anthracite coals. In addition, low-temperature gas adsorption (N2 and CO2), Raman spectroscopy, and CH4 isothermal experiments were performed. The results revealed that coal samples with higher degrees of deformation exhibited larger ratios of D-band intensity to G-band intensity (I D/I G), indicating increased molecular defects induced by tectonic deformation. As the deformation degree of the coal samples increased, the mesopore volume increased from 0.00044 cm3/g (primary coal) to 0.0019 cm3/g (scaly coal). Conversely, the micropore volume tended to decrease with the increasing deformation degree of the coal samples. Moreover, the impact of deformation degree on the CH4 adsorption capacity of anthracite coals was complex. With the deformation degree increasing, the Langmuir volume initially decreased from 32.0 to 24.55 cm3/g and then rose to 30.14 cm3/g. This complexity arose from the differential effects of tectonic deformation on various pore types, where micropores and mesopores collectively determined the CH4 adsorption capacity of anthracite coals. This study analyzed the influence of tectonic deformation on the pore structure and CH4 adsorption capacity at the molecular level, providing valuable insights for evaluating the in situ CH4 content in anthracite coal seams.

Research on the Low-Temperature Oxygen Consumption and Low-Oxygen Gas Emission Law in Goaf of Ultrathick Coal Seams.

Low-oxygen (oxygen concentration below 18.5%) phenomena often occur in the top coal caving working face of ultrathick coal seams, posing a serious threat to the safety of workers. The characteristics of oxygen consumption and gas production at low-constant temperature and the corresponding functional group evolution of residual coal in goaf were studied by temperature-programmed and infrared spectrum experiments. The influence of different factors on the emission of low-oxygen gases was studied through numerical calculation. The results show that low-temperature oxygen consumption and gas production occurred when the coal was about 40 °C. When the temperature was constant, the oxygen consumption and gas production rate increased with the extension of time. In the early stage of coal oxidation, the aliphatic C-H components were attacked by oxygen molecules and reacted with them. The asymmetric methyl and methylene groups were more likely to oxidize and produce carbonyl compounds. With the increase of nitrogen injection, the overall width of the oxidation zone (oxygen concentration was defined as 10-18%) narrowed, and the range of the oxidation zone moved forward from the depth of the goaf. The oxygen concentration in the air return corner decreased gradually, and the low-oxygen area in the air return corner expanded gradually. The distance between the low-oxygen area of the working face and the air intake corner was gradually shortened. With the increase of air intake, the width of the oxidation zone increased and moved to the depth of goaf, and the degree of low oxygen in the air return corner increased. The research results are of great significance for the understanding and prevention of the low-oxygen phenomenon in ultrathick coal seams.

Formation of Methanol via Fischer-Tropsch Catalysis by Cosmic Iron Sulphide.

Chemical reactions in the gas phase of the interstellar medium face significant challenges due to its extreme conditions (i. e., low gas densities and temperatures), necessitating the presence of dust grains to facilitate the synthesis of molecules inaccessible in the gas phase. While interstellar grains are known to enhance encounter rates and dissipate energy from exothermic reactions, their potential as chemical catalysts remain less explored. Here, we present mechanistic insights into the Fischer-Tropsch-type methanol (FTT-CH3OH) synthesis by reactivity of CO with H2 and using cosmic FeS surfaces as heterogeneous catalysts. Periodic quantum chemical calculations were employed to characterize the potential energy surface of the reactions on the (011) and (001) FeS surfaces, considering different Fe coordination environments and S vacancies. Kinetic calculations were also conducted to assess catalytic capacity and allocate reaction processes within the astrochemical framework. Our findings demonstrate the feasibility of FeS-based astrocatalysis in the FTT-CH3OH synthesis. The reactions and their energetics were elucidated from a mechanistic standpoint. Kinetic analysis demonstrates the temperature dependency of the simulated processes, underscoring the compulsory need of energy sources considering the astrophysical scenario. Our results provide insights into the presence of CH3OH in diverse regions where current models struggle to explain its observational quantity.

Characteristics and mechanism of low-temperature NO adsorption by activated carbon

Activated carbon is widely used to purify flue gas in industries like steel and metallurgy, but its ability to adsorb NOx at medium to low flue gas temperatures is limited. This study conducted adsorption experiments in different atmospheres within −20 to 30 °C. As the temperature decreased from 30 °C to −20 °C, the NOx adsorption amount was increased by 4.61 times. Lowering temperature greatly promoted NOx adsorption. Temperature-programmed desorption experiments determined the amount of NOx adsorbed through physical adsorption and chemical adsorption. As the temperature decreased from 30 °C to −20 °C, the proportion of physically adsorbed NOx to total adsorption amount increased from 2.9 % to 45.5 %, and the proportion of physically adsorbed NO2 to total physical adsorption amount increased from 0 to71.6 %. Lowering the temperature benefited NO oxidation and NO2′s adsorption on activated carbon. Desorption curves of chemically adsorbed NOx indicated that a decrease in temperature does not affect the chemical adsorption pathways of NOx. Physical adsorption of NOx was studied by density functional theory calculations. NO2 has much stronger physical adsorption than NO and can physically adsorb near saturated carbon atoms, carbonyl groups, ether groups, hydroxyl groups, and lactone groups. At low temperatures, NO is first oxidized to NO2 on activated carbon and then NO2 is adsorbed through both physical and chemical pathways. Modifying the surface of activated carbon to increase hydroxyl, ether, and lactone groups can help enhance its performance of low-temperature NOx adsorption.

Aerodynamic performance optimization of a UAV's airfoil at low-Reynolds number and transonic flow under the Martian carbon dioxide atmosphere

Unmanned aerial vehicles (UAV) on Mars operate in a thin atmosphere of carbon dioxide, where the flow Reynolds number and local sound velocity are significantly reduced compared to the Earth's atmosphere because of low gas density and temperature. Therefore, a Mars UAV with a rotary-wing design can operate in a state of low-Reynolds number (Re = 1-5 × 104) and transonic flow (Matip = 0.7–1.2), where flow separation and shock waves occur simultaneously. The interaction between flow separation and shock waves not only makes the entire flow field more complex but also seriously affects the aerodynamic performance of the airfoil, thereby reducing the payload of UAVs, which previous aircraft designs based on the thick atmospheric environment of the Earth have not considered. Therefore, in this study, a numerical simulation method is used to conduct airfoil optimization research on a characteristic airfoil under low-Reynolds number transonic flow (Re = 33200, Ma = 0.85) conditions to acquire additional insight, improve aerodynamic performance of the airfoil, and enhance the payload. The results were compared with the optimization results of subsonic flow (Re = 19500, Ma = 0.50). The Hicks-Henne bump functions method was selected for airfoil parameterization, and non-dominated sorting genetic algorithms (NSGA)-Ⅱ were used for optimization. Through an analysis of the pressure coefficient (Cp), surface friction coefficient (Cf), and density gradient, the number and intensity of oblique shock waves on the upper and lower surfaces were observed to significantly affect the aerodynamic performance of airfoils under low-Reynolds number flow. The changes in flow separation and transition positions do not directly affect the aerodynamic performance but weaken the oblique shock wave intensity induced by the separation point or directly transform strong shock waves into weaker compression waves because of the absence of flow separation. The optimization results for both subsonic and transonic flow point to a thinner overall shape with a flatter surface with the drag greatly reduced due to the disappearance of shock waves on the lower surface, which significantly improves aerodynamic performance. Compared with the original airfoil, at Ma = 0.85, this design can increase the lift coefficient (Cl) by at least 124 % and lift drag ratio (Cl/Cd) by 177 %.

Effects of real gas models on the wave dynamics and refrigeration of gas wave rotor

The gas wave rotor was usually designed and performed on the ideal gas model. However, the real gas effect could not be ignored anymore under high-pressure ratio conditions. In this study, for the first time, a two-dimensional computational model of a double-opening gas wave refrigerator (GWR) using a multi-parameter Benedict–Webb–Rubin equation of state is established and the influence of the real gas effect on gas wave dynamics and energy transfer processes in the GWR with discontinuous boundary conditions is thoroughly investigated. The numerical results show that the wave dynamics of the ideal gas and the real gas are similar under different operating conditions, but compression waves and expansion waves in real gas obviously lag behind the ideal gas. In addition, the low-temperature real gas is completely discharged earlier than the ideal gas and the difference between them gradually increases as the pressure ratio gets higher, which benefits the GWR compact structure design and cost reduction. At the same time, the temperature of the real gas being discharged is lower than that of the ideal gas. Therefore, the refrigeration efficiency of the isentropic expansion of the real gas will be improved compared with the operation in ideal gas. The research results on the real gas effect reveal the mechanism of wave dynamics and energy transfer, providing support for the optimization design of GWR.

Low-temperature NO2 gas sensing by delafossite-structured AgFeO2 nanograins

Low-temperature NO2 gas sensing by delafossite-structured AgFeO2 nanograins