Ppm SO2 Research Articles

M-MnCeOX derived from MOF for low temperature selective catalytic reduction of NOX by NH3: Experiments and mechanisms

A series of M-MnCeOX catalysts using MOF (Metal-organic Framework) were prepared to apply for NH3-SCR (Selective Catalytic Reduction) of NOX. The effects of Mn/Ce molar ratio, calcination temperature and its activity including catalytic activity, H2O/SO2 resistance and stability were systematically investigated. The results showed that under the Mn/Ce molar ratio of 1 and calcination temperature of 400 ℃, the catalyst exhibited excellent catalytic activity, H2O/SO2 resistance, and stability. When the concentration of NO was 500 ppm, the gas spatiotemporal velocity (GHSV) was 36,000 h−1, and the reaction temperature was 100 ℃, the NO conversion efficiency of M-MnCeOX exceeded 90.0 %. Added 200 ppm SO2 and 3 vol% H2O simultaneously, the NO conversion efficiency was close to 80.0 %. By analyzing the physicochemical properties of the catalyst, M-MnCeOX had a large specific surface area, numerous acidic sites, and excellent redox properties. According to density functional theory (DFT), the NH3/NO adsorption energy of M-MnCeOX were −2.35 and −2.40 eV, exhibiting lower than a single MOF-derivative, promoting the adsorption of NH3 or NO. The reaction mechanism on the M-MnCeOX catalyst followed the E-R and L-H mechanisms by In situ DRIFTS.

Formation of Fe2(SO4)3-Fe2O3 interface induced by OCFGs electrostatic anchoring on AC surface: High efficiency NH3-SCR performance at low temperatures

Low-temperature activity and SO2 poisoning were the key factors limiting the application of NH3-SCR catalysts. In this study, Fe2(SO4)3/AC and Fe2(SO4)3/OAC catalysts were prepared by oxidation function modification and incipient wetness impregnation. In the temperature range of 100–250 ℃, the catalytic performance and SO2 resistance of Fe2(SO4)3/AC and Fe2(SO4)3/OAC catalysts were investigated, the denitrification efficiency increased from 28 % (Fe2(SO4)3/AC) to 80 % at 100 °C and reached 100 % at 170 °C, and 100 ppm SO2 was introduced at 250 ℃ for 24 h, the denitrification efficiency remains 100 % unchanged. The mechanism of activity enhancement was further explored by BET, XRD, ICP, TG, XPS, FT-IR, H2-TPR and NH3-TPD. The results showed that (NH4)2S2O8 modification enhanced the surface acidity, and the increase of surface oxygen-containing functional groups improved the redox performance. At the same time, due to electrostatic anchoring effects of oxygen-containing functional groups, Fe3+ and SO42- were adsorbed at different sites and promoted the binding of S to the carbon skeleton to form −C-S-C-. Thus, the interaction between OAC and Fe2(SO4)3 caused part of Fe2(SO4)3 to decompose into Fe2O3, and the formation of Fe2(SO4)3-Fe2O3 interface further enhanced the acidity and redox properties. More importantly, the decomposition temperature of NH4HSO4 was lower and the decomposition was more thorough on the Fe2(SO4)3/OAC than that of Fe2(SO4)3/AC. Finally, the possible mechanism of (NH4)2S2O8-modified Fe2(SO4)3/OAC catalyst to improve NH3-SCR performance was proposed, which is of great significance for the development of NH3-SCR catalyst with sulfur resistance at low temperatures.

Revealing the effect of O2, SO2 and H2O in supercritical CO2 on the corrosion behavior of 316 L steel at elevated temperature

Closed supercritical CO2 (sCO2) power systems require steels that can resist corrosion in high temperature CO2 containing different impurities at ppm levels. However, potential impurity effects on Fe-16Cr steels are not well understood. Herein we evaluated the corrosion behavior of 316 L steel in sCO2 containing 100 ppm O2, SO2 or H2O at 600 °C and 20 MPa. All investigated impurities enhanced Fe-oxide nodule formation, leading to higher carburization in underlying substrate. Presence of O2 caused transition of chromia scale into Fe-Cr spinel, because Cr supply from underlying substrate could not meet the consumption. Spallation occurred when 316 L was exposed with SO2 impurity, attributed to the formation of sulfides within and beneath the oxide scales. H2O impurity showed relatively low damage to protective chromia layer with localized aggravation. Corrosion mechanisms related to impurities were unraveled based on experimental results and thermodynamic analysis.

TiO2 modified limonite for selective catalytic reduction of NO from cement kiln flue gas with NH3

Limonite was used as a precursor and TiO2 as a modifier to synthesize TiO2/Limonite composites through the wet impregnation method. The influences of the TiO2 doping amount, the calcination temperature on the denitration efficiency and the structure and properties of composites were systematically studied. The results showed that the modified catalyst over the Ti/Fe mass ratio was 0.07 and the calcination temperature was 300°C exhibited excellent catalytic activity, good stability, and remarkable resistance to water and sulfur dioxide within reaction temperature of 100 ∼ 240°C. When NO initial concentration was 0.05 % and gas hourly space velocity (GHSV) was 36,000 h−1 and the reaction temperature was 130°C, the NO conversion efficiency reached 100 %, and the N2 selectivity was 99.6 %. When the catalyst was exposed to 10 %H2O at 150°C, it maintained a 100 % NO conversion efficiency. In the presence of 10 %H2O and 50 ppm SO2 at 200°C, the NO conversion efficiency remained at 100 %. The TiO2/Limonite catalyst possessed improved performance due to the introduction of the anatase TiO2, which led to more lattice defects, weak Lewis acid sites, and higher adsorbed oxygen mobility.

Effect of sulfation on the catalytic performance of Mn-Co composite oxide catalyst for the selective catalytic reduction of NOx by NH3

The effect of sulfation on the catalytic performance of Mn-Co composite oxide catalyst for the selective catalytic reduction of NOx by NH3 (NH3-SCR) has been investigated. Different concentrations of SO2 have been used to sulfate Mn-Co composite oxide catalyst. The catalyst sulfated with 30 ppm SO2 showed the widest activity temperature window, over which 80% NOx conversion was obtained in the temperature range of 80–350 °C. The sulfation leads to the appropriate redox property of Mn-Co composite oxide, thus improving the N2 selectivity. Meanwhile, the sulfation contributes to the generation of more Brønsted acid sites, which is crucial for the enhanced activity. In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) demonstrated that the adsorbed NH3 species on both Lewis acid and Brønsted acid sites, monodentate nitrite, bidentate nitrate and cis-nitrite species are the reactive intermediates in the NH3-SCR reaction. This study provides an idea for the regulating the activity temperature window of NH3-SCR catalyst to adapt to its practical application.

Insights into the influence mechanism of SO2 on the selenium capture by Fe/Al-MgO-based adsorbents: Experiment and DFT

The adsorption experiments and density functional theory (DFT) analysis revealed together the adsorption characteristics of composite adsorbents for selenium and the mechanism of SO2 influence. Adsorption experiments indicated that the optimal adsorption capacity for selenium occurred at 500 °C with a molar ratio of Mg/Fe/Al as 20:1:1 (MFA), yielding 9.30 mg/g, surpassing that of single or binary magnesium-based adsorbents. The presence of SO2 diminished the selenium removal capability of the ternary adsorbent, although maintaining a high adsorption capacity of 7.06 mg/g even at a concentration of 2000 ppm SO2. X-ray photoelectron spectroscopy (XPS) results showed selenium primarily existed as Se4+/Se0 species on the MFA surface. Sulfur appeared as MgSO4/MgSO3/MgS, which confirmed that sulfur-containing low-valent products was formed. Characteristic peaks of Se0 on pure MgO surfaces, providing substantial evidence of SO2-induced SeO2 reduction. Furthermore, DFT computations suggested that the doping of Fe/Al activated the adsorption activity of the MgO surface. At 500 °C, SeO2 exhibited enhanced chemisorption on the MFA surface, with an adsorption energy of −547.56 kJ/mol. Reaction rate constants and activation energies corroborated the propensity for redox reactions between SO2 and SeO2 to occur in the heterogeneous phase.

SO2-resistant hollow carbon spheres encapsulated Pt nanoparticles for benzene oxidation

In the catalytic combustion of volatile organic compounds (VOCs) using noble metal catalysts, resistance to SO2 poisoning poses a significant challenge. To tackle this problem, Pt nanoparticle catalysts encapsulated in hollow carbon spheres (Pt@HCS catalysts) are synthesized. The Pt@HCS catalyst exhibits excellent benzene conversion, achieving 100 % conversion at 165 °C under an air velocity of 20,000 mL/(g h). Compared to the conventional supported Pt/HCS catalyst, the Pt@HCS catalyst demonstrates a significantly improved resistance to SO2 poisoning. In the presence of 25 ppm SO2, the Pt@HCS catalyst is capable of maintaining a 100 % benzene conversion rate within 24 h, whereas the conversion rate of Pt/HCS drops substantially to approximately 52 %. It is confirmed that the hollow porous structure provided a larger specific surface area and more adsorption sites, thereby facilitating benzene oxidation. More importantly, in situ DRIFTS reveals that the adsorption and desorption processes of SO2, along with the generation of substances like SO32−, are strictly limited to the surface of the carbon shell, thereby preserving the integrity of the internal reaction environment. Multiple characterizations combined with density functional theory (DFT) have demonstrated a unique separation effect over Pt@HCS, whereby the hydroxyl groups on the carbon shell preferentially capture SO2 while allowing benzene molecules to enter the cavities of the catalyst. In this way, any internal ingress of SO2 and competition with benzene for Pt adsorption is effectively avoided. This study offers a potential solution to enhance the performance of noble metal catalysts in the presence of sulfur compounds.

Effect of SO2 on the soot oxidation activity of flame spray pyrolysis-made manganese oxide catalyst in gasoline model exhaust

AbstractThis study deals with the effect of SO2 on the soot oxidation activity of flame spray pyrolysis-prepared manganese oxide in gasoline model exhaust. The catalyst was exposed to 15 and 30 ppm SO2 at 250 °C and was characterized by N2 physisorption, SO2-TPD, O2-TPD, DRIFTS, XPS and PXRD. It was shown that the SO2 adsorption results in the formation of surface sulfate, while the uptake increased from 26 to 45 μmol/g with growing sulfur content of the model exhaust. The sulfur adsorption reduces the mobility and availability of oxygen on the catalyst thus inhibiting the oxygen transport from gas phase over the catalyst to the contact points of the soot. Consequently, the soot oxidation activity, investigated with tight contact blends of catalyst and soot, decreases with inclining amount of sulfate. Finally, the sulfate species were mostly removed by thermal treatment at 705 °C, which additionally provoked catalyst sintering. As a result, the catalytic performance of the de-sulfated catalyst was slightly lower compared to the sulfated sample.

Layer-tunable synthesis of tetragonal Pr-doped SnO2 nanoplates for enhanced sensitive SO2 sensor

Nowadays SnO2 is widely used in manufacturing gas sensors for the detection of toxic and harmful gases such as SO2. However, SnO2 sensor still has the drawbacks of long recovery/response time and low response value. In this experiment, layer-tunable synthesis of tetragonal Pr-doped SnO2 nanoplates are prepared by a feasible hydrothermal method. Observation at SEM reveals that the layer number increases and the interlayer spacing reduces with the increase of doping ratio of Pr (1, 3, 5 mol%). The gas sensing performance show that the three layer tetragonal structure of 1 mol% Pr-doped SnO2 sample with the extended interlayer spacing exhibits outstanding gas sensing performance to 5 ppm SO2 gas at 300℃, including excellent gas response (Ra/Rg = 2.4), fast gas adsorption and desorption equilibrium (15 s/16 s). This work reveals the significance of the layer number and interlayer spacing on the gas sensing characteristics, and the strategy of Pr dopant will promote the widespread application of SnO2 nanomaterials in SO2 gas sensors to figure out severe environmental problems.

High entropy oxide catalysts with SO2 resistance in RWGS reaction

Ubiquitous presence of SO2 usually shows adverse effects on industrial catalysis. Herein, a concept of engineering entropy to design SO2 resistance oxide catalysts is proposed. (Ni0.2Mg0.2Cu0.2Zn0.2Co0.2)Fe2O4 showed excellent performance (the CO2 conv. = 41.4%, CO selec. = 99.6% at 400°C) compared to the control samples in the reverse water–gas shift (RWGS). In addition, (Ni0.2Mg0.2Cu0.2Zn0.2Co0.2)Fe2O4 had the SO2-tolerant ability (the CO2 conv. = 38.5%, CO selec. = 99.2% at 400°C) after being poisoned with 1000 ppm SO2 at 400°C for 1 h. In sharp contrast, the control samples NiFe2O4, MgFe2O4, CuFe2O4 and CoFe2O4 lost their activity. O1S XPS indicated that (Ni0.2Mg0.2Cu0.2Zn0.2Co0.2)Fe2O4 had higher oxygen vacancy concentrations. SO2 resistance mechanism was studied by infrared spectroscopy, SO2-TPD, in situ S 2p XPS and the DFT results, confirming that the low SO2 adsorption energy of (Ni0.2Mg0.2Cu0.2Zn0.2Co0.2)Fe2O4, which was attributed to the lower Gibbs free energy. This work may inspire the rational design of SO2-resistant catalysts.

Rapid Solid‐State Gas Sensing Realized via Fast K+ Transport Kinetics in Earth Abundant Rock‐Silicates

Here we report on the discovery of a novel fast potassium super stoichiometric silicate, with fully earth‐abundant nominal chemical composition of K2+xMg1−x/2SiO4, which exhibits near superionic K+ conductivity, up to 5 × 10−5 S cm−1 at room temperature. Fast K+ conduction is attributed to a high Continuous Symmetry Measure value in K‐polyhedrons, coupled with a low packing ratio of Corner‐Sharing‐framework. This is the first time that such a high conductivity is measured by a rock‐silicate formed only by abundant metal ions. K2+xMg1−x/2SiO4 displays excellent stability under air and humidity, which renders it a very promising candidate for economical fabrication of electrochemical devices such as potentiometric gas sensors. We demonstrated this by fabricating a gas sensor for SO2 detection, as the first demonstration of type III potentiometric gas sensors using K+ conductors. At 500 °C and SO2 concentrations in the range of 0–10 ppm, the sensor exhibited high sensitivities (69–72 mV dec−1), robust signal output (220 mV for 2 ppm of SO2), fast response times (1–6 min), and excellent stability in ambient condition.

Metal-free β zeolite used as an efficient NH3-SCR catalyst can achieve complete immunity to SO2: Unique design strategy of sulfur-resistant catalyst

Sulfur oxides present in flue gas can deactivate metal oxide catalysts or metal cation exchange zeolite catalysts used in NH3-SCR, as the deposition of (NH4)2SO4/NH4HSO4 and metal sulfate can obstruct and damage active sites, respectively. The physical poisoning of the (NH4)2SO4/NH4HSO4 deposition can be prevented by selecting an appropriate reaction temperature range (reversible), while chemical poisoning caused by the sulfation of active sites is challenging to avoid and can permanently deactivate the catalyst (irreversible). This research addresses the issue of irreversible catalyst deactivation resulting from sulfur poisoning by employing metal-free β zeolite without redox sites, which effectively prevents redox site sulfation at its source and shields the catalyst from physical poisoning by operating at moderate to high temperatures. This metal-free β zeolite with an appropriate pore structure exhibited exceptional deNOx activity, N2 selectivity, stability, and sulfur resistance at 300 °C. The NO oxidation experiment and DFT analysis demonstrated that the specific pore structure of β zeolite functioned as a sub-nano reactor, facilitating the oxidation of NO to NO2, thereby triggering the subsequent series catalytic reaction of “fast” SCR. Even in an atmosphere with a high concentration of 300 ppm SO2, the β zeolite catalyst maintained over 80 % NOx conversion after 130 h. The slight reduction in activity was attributable to the inhibitory influence of SO2 on the collision reaction between NO and O2; however, SO2 did not have any poisonous impact on the catalyst. The unique design strategy found in present work provides valuable insights for the sulfur resistance of metal-free zeolites used in NH3-SCR process, and provides a new idea for the design of completely sulfur-resistant catalysts.

Trace SO2 capture within the engineered pore space using a highly stable SnF62--pillared MOF.

Developing reliable solid sorbents for efficient capture and removal of trace sulfur dioxide (SO2) under ambient conditions is critical for industrial desulfurization operations, but poses a great challenge. Herein, we focus on SNFSIX-Cu-TPA, a highly stable fluorinated MOF that utilizes SnF62- as pillars, for effectively capturing SO2 at extremely low pressures. The exceptional affinity of SNFSIX-Cu-TPA towards SO2 over CO2 and N2 was demonstrated through single-component isotherms and corroborated by computational simulations. At 298 K and 0.002 bar, this material displays a remarkable gas uptake of 2.22 mmol g-1. Among various anion fluorinated MOFs, SNFSIX-Cu-TPA shows the highest SO2/MF62- of 1.39 mmol mmol-1 and exhibits a low Qst of 58.81 kJ mol-1. Additionally, SNFSIX-Cu-TPA displays excellent potential for SO2/CO2 separation, as evidenced by its ideal adsorbed solution theory (IAST) selectivity of 148 at a molar fraction of SO2 of 0.01. Dynamic breakthrough curves were obtained to reveal the effective removal of trace SO2 from simulated flue gas (SO2/CO2/N2; v/v/v 0.2/10/89.8) with a high dynamic capacity of up to 1.52 mmol g-1. Furthermore, in situ TGA demonstrated the efficient and reversible capture of 500 ppm SO2 over 20 adsorption-desorption tests. This durable material presents a rare combination of exceptional SO2 capturing performance, good adsorption selectivity, and mild regeneration, thus making it a good candidate for a realistic desulfurization process.

Study on the SO2 adsorption performance of dual-layer activated carbon cloth cathode air filter for high-power fuel cell

The removal of SO2 contaminant from the cathode air is crucial for the improvement of the efficiency of high-power fuel cell. The SO2 adsorption behaviour of dual-layer activated carbon cloth (ACC) was investigated at 5–15 ppm SO2 and filtration velocities of 0.125–0.45 m/s. The adsorption amount increased following a power function with time. The equilibrium breakthrough rate declines from approx. 88% to 56% when the concentration drops from 20 ppm to 5 ppm at 0.26 m/s and reduces from approx. 81% to 59% as the filtration velocity decreases from 0.45 m/s to 0.125 m/s at 10 ppm of SO2. In comparison to the packed bed filter, the pressure drop per thickness of the ACC media was considerably lower, measuring less than 9 Pa/mm, which can effectively decrease the parasitic power of the air supply unit. To determine filter’s breakthrough time and adsorption amount for the real application condition, a prediction method coupling the Yoon-Nelson model and the adsorption amount prediction model has been developed. The model can predict the breakthrough time and the adsorption amount of the full-scale filter using low-cost performance test data from the ACC materials with less than 10% error.

Enhanced dual-catalytic elimination of NO and VOCs by bimetallic oxide (CuCe/MnCe/CoCe) modified WTiO2 catalysts: Boosting acid sites and rich oxygen vacancy

It remains challenging to remove nitrogen oxides (NOx), benzene (C6H6), and toluene (C7H8) simultaneously under conditions of low oxygen and high SO2 concentration. Herein, CuCe, MnCe, and CoCe doped WTiO2 catalysts were designed. The prepared CuCe-WTiO2 catalyst consistently maintained more than 85% NO, 92% C6H6, and 91% C7H8 removal in 260–420 °C under 3.33% O2 and 1000 ppm SO2. The adequate charge flow between the catalyst surface and the gas molecules was enhanced, promoting SO2 tolerance of CuCe-WTiO2. More NH3, NH4+, and -NH2 were adsorbed with acid sites on the CuCe-WTiO2 surface. The high concentration of adsorption centers and superior redox properties effectively improved the co-catalytic efficiency. The primary intermediates in the reduction processes via the Langmuir-Hinshelwood and Eley-Rideal mechanisms were NO2, bridged nitrite (NO2–), and monodentate nitrite (NO2–). The generation of reactive chemisorbed oxygen (Oα) becomes more accessible with the transfer of electrons from Ce4+ to adsorbed O2. C6H6 and C7H8 are progressively oxidized by Oα and eventually completely mineralized to CO2 and H2O. This study is anticipated to offer a new option for co-catalytic removal of NO, C6H6, and C7H8.

Robust Type III Potentiometric Sensors for SOx Realized Via Fast Solid-State Potassium Ion Conductors

Sulfur oxide gases (SOx) are among the most serious air pollutants that contribute to acid rain and have a significant impact on human health and the environment. The sensing and quantification of SOx is critical for industrial and environmental applications, such as monitoring air quality, controlling emissions from power plants and maritime vessels, as well as ensuring safety in industrial processes. However, conventional sensing methods are limited by prohibitive costs, complex hardware, and maintenance requirements. In this work, we present a novel potentiometric type III solid-state sensor for the sensing of SOx using fast and ambient stable potassium-ion (K+) conducting solid-state electrolytes (KSE). Several potentiometric sensors including (O2,Au|Ag|KSE|K2SO4|Pt|Au,SO2,O2), (O2,Au|Ag|KSE|K2SO4+LaNi0.6Fe0.4O3|Pt|Au,SO2,O2) and (O2,Au|Ag|KSE|LaNi0.6Fe0.4O3|Pt|Au,SO2,O2) were assembled and characterized by chronopotentiometry. This is the first demonstration of a type III potentiometric SOx sensor using solid-state K+ conductor, operational while both sensing and reference electrodes exposed to same gas mixture without the need for sealed and separated gas chambers. The sensors in this study, at 0-10 ppm SO2 concentration and temperature range of 300-500 ℃, exhibited high sensitivities (74-89 mV/dec), robust signal output (as high as 600 mV for 2 ppm of SO2), fast response times (as low as 2 minutes), and excellent stability in ambient condition. These sensors also demonstrated good selectivity towards SOx over other interfering gases such as CO2. The results of this study indicate that the proposed sensor has immense potential for technological applications such air quality monitoring in maritime applications. Figure 1

SO2-Tolerant Electrocatalytic Reduction of CO2 from Simulated Industrial Flue Gas

The electrochemical reduction of CO2 using copper-based electrocatalysts offers a route to produce high-value multicarbon (C2+) products from renewable electricity (Nat. Catal. 4, 952-958 (2021); Nature 614, 262-269 (2023)). To date, the efficient electrocatalytic conversion of CO2 to multicarbon products has only been possible when using impurity-free CO2 sources, such as from direct air capture. The generation of such high-grade CO2 streams is expensive, accounting for almost half of the total energy required for both capture and electroreduction processes (Nat. Catal. 4, 952-958 (2021)). Conversely, capturing CO2 from point sources, such as industrial flue gas, is more efficient due to the higher concentration of CO2 in the feed. However, trace amounts of sulfur dioxide (10 ~ 400 ppm SO2) inherently present in these streams will significantly degrade the CO2 conversion process. All previous attempts to convert CO2 with SO2 present in the feed have resulted in immediate catalyst poisoning and an irreversible loss of CO2 conversion activity.In this study, we designed a modified catalyst layer to react a stream of dilute CO2 containing 400 ppm SO2 to multicarbon products with high stability and performance metrics that match or exceed those achieved with pure CO2 streams. Driven by density function theory and COMSOL simulations, we designed an ionomer:copper:polytetrafluoroethylene (PTFE) (ICP) electrode that features both hydrophobic and highly-charged hydrophilic domains to limit water adsorption and promote CO2 over SO2 transport near the electrochemically active sites. This deactivates the SO2 poisoning mechanism, thus enabling stable and efficient CO2 conversion (see figure). Our approach achieved a sustained C2+ Faradaic efficiency (FE) of 50% for the initial 160 hours at 100 mA cm-2.In order to improve the overall C2+ current efficiency (jC2+) towards industrial scales, we applied our strategy in high-surface-area copper electrodes. We achieved CO2 conversion in the presence of 400 ppm SO2 with a C2+ FE of 76% at a current density of 700 mA cm-2, surpassing what can be achieved in existing integrated CO2 capture-electrolysis systems that use pure CO2. Overall, our approach provides a fully 140-fold increase in performance (FEC2+ × jC2+) compared to the best prior CO2 conversion systems with added SO2 (Nat. Nanotechnol. doi: 10.1038/s41565-022-01286-y (2023); J. Am. Chem. Soc. 141, 9902-9909 (2019)). These findings represent an important advancement in the field of CO2 conversion and highlight the potential of our strategy for industrial-scale applications. Figure 1

Chemiresistive detection of SO2 in SF6 decomposition products based on ZnO nanorod/MoS2 nanoflower heterojunctions: Experimental and first-principles investigations

Sulfur dioxide (SO2) is a typical gas in SF6 discharge decomposition components. The detection of SO2 can reflect the safe operation of SF6 gas insulation equipment. In this paper, the ZnO nanorod/MoS2 nanoflower (ZnO NR/MoS2 NF) heterojunction was prepared by hydrothermal and physical mixing methods for the ultra-sensitive detection of SO2. In the two test environments of the air and SF6, the response and recovery time of the ZnO NR/MoS2 NF heterojunction sensor to 30 ppm SO2 are 52 s/5 s (11 s/7 s), respectively, and the response value of the sensor are 46.12% (47.33%) at 250 °C. The sensor shows excellent selectivity, moisture resistance, and long-term stability. Furthermore, it has been demonstrated through first principles calculations that the ZnO/MoS2 heterogeneous composite exhibits superior adsorption performance for SO2 compared to ZnO and MoS2 alone. The sensor mechanism in the air is mainly described as the interaction between SO2 and oxygen adsorbed on the surface of the sensitive material. The sensing mechanism under SF6 background gas can be described as the competitive adsorption of SO2 molecules with lattice oxygen molecules on the surface of ZnO NR/MoS2 NF heterojunction, and the reaction of F2− adsorbed on the surface of ZnO/MoS2 heterojunction with SO2 molecules.

Influence of gas impurities (SO2 and NOX) in flue gas on the carbonation and hydration of cement compacts

Flue gas with a typical CO2 concentration of 10–20 % is found to be potentially utilized for accelerating the curing process of cement compacts. However, the competitive effect of acid gas impurities (i.e. SO2 and NOX) contained in flue gas on carbonation behaviors remains unclear. In this work, multi-component gases (500 ppm SO2, 500 ppm NO2, 10 % O2, and 74.9 % N2) with a CO2 concentration of 15 % are simulated to study the carbonation reactivity of cement compacts after 2 h of curing. The influence of subsequent water curing on strength and microstructure development over time is also further investigated. The experimental results show that after exposure to CO2, the highly soluble acidic SO2 and NOX gases can considerably reduce the pH of cement compacts, and thus mitigate the carbonation efficiency. The dissolved SO2 can potentially compete with CO2 for calcium-bearing ion combination, leading to a reduction of ∼30 % in compressive strength. However, this inferior performance can be compensated by the progressive hydration reaction in subsequent water curing. The findings from this study highlight the essential consideration of gas impurities in flue gas CO2 curing, in particular their impact at an early age. Additionally, there is a need to explore the durability characteristics and interactions of gas impurities during high-temperature curing.

Room temperature detection of sulfur dioxide using functionalized carbon nanotubes

The construction of a simple sensor structure sensitive to sulfur dioxide (SO2) based on multi-walled carbon nanotubes (MWCNTs) functionalized by nitric acid is described in this study. The functionalized MWCNTs were comparatively analyzed by X-ray diffraction, Raman, and FTIR spectroscopy methods, and their morphology was observed by scanning electron microscope (SEM). The sensitivity to 5 ppm SO2 gas is based on the change of resistance of functionalized MWCNTs. Tests on the fabricated sensor were performed at room temperature and defined that functionalized MWCNTs are sensitive to SO2 gas compared with the pristine MWCNTs.