Low-temperature Reaction Research Articles

Na2Ti3O7@RF@Ag Heterostructures as Efficient Substrates for SERS and Photocatalytic Applications.

A multi-step procedure was effectively employed to synthesize innovative three-dimensional (3D) heterostructures encompassing sodium titanate (Na2Ti3O7) nanowire cores, an intermediate resorcinol-formaldehyde (RF) layer, and outer silver (Ag) nanoparticle sheaths, referred to as Na2Ti3O7@RF@Ag heterostructures. Initially, a one-step hydrothermal technique facilitated the direct growth of single-crystal Na2Ti3O7 nanowires onto a flexible Ti foil. Subsequently, a two-step wet chemical process facilitated the sequential deposition of an RF layer and Ag nanoparticles onto the Na2Ti3O7 nanowires at a low reaction temperature. Optimal concentrations of silver nitrate and L-ascorbic acid can lead to the cultivation of Na2Ti3O7@RF@Ag heterostructures exhibiting heightened surface-enhanced Raman scattering (SERS), which is particularly beneficial for the detection of rhodamine B (RhB) molecules. This phenomenon can be ascribed to the distinctive geometry of the Na2Ti3O7@RF@Ag heterostructures, which offer an increased number of hot spots and surface-active sites, thereby showcasing notable SERS enhancement, commendable reproducibility, and enduring stability over the long term. Furthermore, the Na2Ti3O7@RF@Ag heterostructures demonstrate remarkable follow-up as first-order chemical kinetic and recyclable photocatalysts for the photodecomposition of an RhB solution under UV light irradiation. This result can be attributed to the enhanced inhibition of electron-hole pair recombination and increased surface-active sites.

Transition of characteristic explosion limits: From hydrogen to diethyl ether

In this work, the explosion limits of three different fuels: hydrogen (H2), propane (C3H8, C3), and diethyl ether (DEE, C2H5OC2H5, C4), are investigated based on detailed chemical kinetics. The results reveal that the explosion limit of H2O2 exhibits the typical Z-shape, while C3H8O2 exhibits a single-NTC response, and DEE-O2 displays a double-NTC response. Sensitivity analysis indicates that the appearance of the NTC response in both the C3 and DEE fuels is intricately linked to low-temperature reaction paths. Moreover, the extents of the NTC responses are comparable for these two fuels with similar low-temperature reaction paths, but operate under different temperature conditions. Specifically, the double-NTC response observed in DEE is attributed to its primary CH and CO bonds, generating C4 and C2 radicals. The oxygen addition and the subsequent pathways of these radicals dominate in distinct temperature ranges. In contrast, C3H8 only possesses the CH bond, resulting in a single-NTC response, as OH radicals are mainly released by C3 radicals through oxygen addition, isomerization, and decomposition reactions. The results of binary fuel mixtures with H2 addition indicate that the reactivity of H2 controls the low-pressure and high-temperature regime, while the C3 and DEE fuels dominate the high-pressure and low-temperature regime. Additionally, a triangular crossover regime is identified between these two regimes due to the switchover of the reactivity. Sensitivity analysis further reveals the transition of the dominating reactions related to different fuels at various pressure-temperature regimes. Finally, based on the explosion limits of the multi-component mixtures, a detailed explosion regime diagram is proposed for carbon-free fuel (H2), alkane fuel (C3H8), and oxygenated ether fuel (DEE). This new regime diagram provides valuable insights for the investigation and utilization of ether fuels and the mixture of different fuels.

A revised reaction kinetic mechanism for the oxidation of methyl formate

The combustion kinetics of methyl formate (MeFo), a promising oxygenated, highly knock-resistant e-fuel, is investigated in this work. The potential energy surfaces (PESs) of the low-temperature oxidation reactions of MeFo radicals were determined at the CCSD(T)-F12/cc-pVTZ-F12//B2PLYP-D3/cc-pVTZ level of theory and their rate coefficients were obtained with RRKM/master equation. The thermochemical properties of relevant intermediate species were calculated by using the G4 method. A chemical mechanism for the oxidation of MeFo was developed by adding fuel-specific reactions taken from a literature model into a well-validated base mechanism, and incorporating the newly calculated rate constants of elementary reactions and thermochemical properties of species. The fuel-specific mechanism was further revised in terms of reaction channels and rate coefficients for improved prediction accuracy. In particular, the O2 addition to hydroperoxy radicals (QOOH), the isomerization of peroxy hydroperoxy radicals (OOQOOH), the subsequent ketohydroperoxide (KET) decomposition, and the formally direct pathways of MeFo radicals (R) with O2 were added for the completeness of consumption pathways, in conjunction with the reaction channels of alkoxy radicals (RO) and hydroperoxides (ROOH). For good model prediction accuracy of ignition delay times, especially in the high-temperature range, the resulting mechanism was optimized by modifying the rate constants of several important H-atom abstraction reactions of MeFo within their uncertainty limits. The performance of the proposed mechanism is demonstrated through extensive validation against literature data obtained from different experimental configurations. Finally, the underlying reaction pathways of MeFo are explored by means of reaction flux analysis with the newly developed chemical mechanism.Novelty and significance statement: This work proposes a new reaction kinetic mechanism for the oxidation of methyl formate. Quantum chemistry calculation at high level of theory was performed to explore the low-temperature chemistry of MeFo. The reaction mechanism was improved by including missing reaction channels, incorporating theoretically calculated rate and thermochemical data, and modifying rate constants of sensitive reactions. The mechanism has been validated successfully against extensive data available in the literature covering a wide range of conditions and facilities. By using this new mechanism, reaction pathway analysis is performed to provide insights into the oxidation chemistry of MeFo.

Catalytic Hydrogenation Property of Methyl Benzoate to Benzyl Aldehyde over Manganese-Based Catalysts with Appropriate Oxygen Vacancies

The synthesis of benzaldehyde, a compound widely utilized in food, medicine, and cosmetics, was achieved through a one-step catalytic hydrogenation using the cost-effective raw material, methyl benzoate. This process aligns with the principles of atom economy and green production. Despite the development of numerous high-performance catalysts by scholars, the challenge remains in achieving lower reaction temperatures, ideally below 400 °C. In this study, a series of MnOx/γ-Al2O3 catalysts were meticulously prepared using the precipitation-impregnation method. These catalysts featured supports calcined at various temperatures and distinct manganese active components. Characterization techniques such as X-ray diffraction (XRD), N2 physical adsorption, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), and NH3 temperature-programmed desorption (NH3-TPD) were employed to analyze the structure and surface properties of the catalysts. Notably, the optimized reaction temperature was found to be 360 °C. The catalyst exhibited the most favorable performance when the calcination temperature of the support was 500 °C and the Mn/Al molar ratio reached 0.18. Under these conditions, the catalyst demonstrated the most suitable oxygen vacancy concentration, yielding impressive results: a conversion rate of 87.90% and a benzaldehyde selectivity of 86.1%. These achievements were attained at 360 °C, atmospheric pressure, a hydrogen to methyl benzoate molar ratio of 40:1, and a Gas Hourly Space Velocity (GHSV) of 800 h−1. This research underscores the potential for optimizing catalysts to enhance the efficiency and sustainability of benzaldehyde synthesis.

Selective Synthesis of Defect-Rich LaMnO3 by Low-Temperature Anion Cometathesis.

The synthesis of complex oxides at low temperatures brings forward aspects of chemistry not typically considered. This study focuses on perovskite LaMnO3, which is of interest for its correlated electronic behavior tied to the oxidation state and thus the spin configuration of manganese. Traditional equilibrium synthesis of these materials typically requires synthesis reaction temperatures in excess of 1000 °C, followed by subsequent annealing steps at lower temperatures and different p(O2) conditions to manipulate the oxygen content postsynthesis (e.g., LaMnO3+x). Double-ion exchange (metathesis) reactions have recently been shown to react at much lower temperatures (500-800 °C), highlighting a fundamental knowledge gap for how solids react at lower temperatures. Here, we revisit the metathesis reaction, LiMnO2 + LaOX, where X is a halide or mixture of halides, using in situ synchrotron X-ray diffraction. These experiments reveal low reaction onset temperatures (ca. 450-480 °C). The lowest reaction temperatures are achieved by a mixture of lanthanum oxyhalide precursors: 2 LiMnO2 + LaOCl + LaOBr. In all cases, the resulting products are the expected alkali halide salt and defective La1-ϵMn1-ϵO3, where ϵ = x/(3 + x). We observe a systematic variation in defect concentration, consistent with a rapid stoichiometric local equilibration of the precursors and the subsequent global thermodynamic equilibration with O2 (g), as revealed by computational thermodynamics. Together, these results reveal how the inclusion of additional elements (e.g., Li and a halide) leads to the local equilibrium, particularly at low reaction temperatures for solid-state chemistry.

Reversible Transition of Semiconducting PtSe2 and Metallic PtTe2 for Scalable All-2D Edge-Contacted FETs.

Two-dimensional (2D) transition metal dichalcogenide (TMD) layers are highly promising as field-effect transistor (FET) channels in the atomic-scale limit. However, accomplishing this superiority in scaled-up FETs remains challenging due to their van der Waals (vdW) bonding nature with respect to conventional metal electrodes. Herein, we report a scalable approach to fabricate centimeter-scale all-2D FET arrays of platinum diselenide (PtSe2) with in-plane platinum ditelluride (PtTe2) edge contacts, mitigating the aforementioned challenges. We realized a reversible transition between semiconducting PtSe2 and metallic PtTe2 via a low-temperature anion exchange reaction compatible with the back-end-of-line (BEOL) processes. All-2D PtSe2 FETs seamlessly edge-contacted with transited metallic PtTe2 exhibited significant performance improvements compared to those with surface-contacted gold electrodes, e.g., an increase of carrier mobility and on/off ratio by over an order of magnitude, achieving a maximum hole mobility of ∼50.30 cm2 V-1 s-1 at room temperature. This study opens up new opportunities toward atomically thin 2D-TMD-based circuitries with extraordinary functionalities.

Rapid synthesis of Cu-SSZ-39 and study of phosphorus poisoning in NH3-SCR

Cu-SSZ-39 has attracted great interest due to its excellent NH3-SCR activity and hydrothermal stability. However, impediments such as high synthesis costs, lengthy preparation duration, and the issue of phosphorus-induced deactivation have hampered its widespread commercialization. Herein, H2O2 was first introduced into the synthesis system dedicated to the rapid synthesis of SSZ-39, and the crystallization time was shortened to 3 d. Various characterization techniques were used to analyze deeply the structure–activity relationship of the resulting Cu-SSZ-39 catalysts before and after phosphorus poisoning. Our findings revealed a pronounced decline in acidic sites and active copper species as Cu-SSZ-39 underwent deeper phosphorus poisoning, leading to the formation of Cu-P species and a consequential reduction in the low-temperature activity of the catalyst. Surprisingly, hydrothermal treatment of the poisoned catalyst allowed the decomposition of Cu-P species to generate active Cu2+ species, alleviating the poisoning effect. It was also shown that phosphorus poisoning did not affect the low-temperature reaction mechanism of Cu-SSZ-39, which still followed the “L-H” reaction pathway. Finally, it was unexpectedly found that the anti-phosphorus poisoning performance of 0.9C-Cu-SSZ-39 significantly improved after mesopores were introduced.

(Best Presentation Award - 2nd Place) Investigating Low Temperature Reaction Mechanisms of Alloy Anodes for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are the battery of choice for most energy storage applications, including personal electronic devices and electric vehicles. However, poor low temperature performance, resulting from hindered solid state diffusion, slow desolvation kinetics, and dendrite formation, limits their use in nascent applications that require operation below -20 ºC, like electric aviation and space exploration. A small number of previous studies have shown that anode materials that electrochemically alloy with lithium ions can be cycled at temperatures as low as -40 ºC with significantly improved performance compared to graphite. Despite their improved low-temperature performance, reaction mechanisms and degradation behavior for these materials at low temperatures are poorly understood. This work aims to fill this gap in understanding by investigating the structural pathways during reactions of alloy anodes at low temperatures as well as characterizing their mechanical and electrochemical degradation. Electrode cross sectioning and scanning electron microscopy reveal that rapid capacity decay in antimony anodes at -40 ºC is a result of increased lithium trapping as well as particle fracture due to mechanical damage associated with volume change. We show that rapid capacity degradation of antimony at -40 ºC can be mitigated through the use of nanoscale particles. While nanoscale particles have been studied extensively at room temperature, little is known about they behave at low temperatures. Through SEM cross-sectioning and the galvanostatic intermittent titration technique (GITT), we show that the improvement in stability is likely due to faster kinetics related to the shorter diffusion length and increased mechanical stability resulting in less lithium trapping at low temperatures. Additionally, X-ray diffraction measurements were carried out as a function of temperature on micron- and nanosized antimony particles, as well as tin and graphite, to determine the composition and structure of lithiated phases formed at low temperatures. The results show that reduced temperatures alter phase transformation behavior in certain alloy materials. Overall, this work provides improved mechanistic understanding of alloy anodes at low temperatures, setting the stage for enhanced electrochemical performance.

Enhanced low-temperature H2-selective catalytic reduction performance and selectivity of Pt/ZSM-5–TiO2 washcoated monolithic catalysts for NOx reduction

Hydrogen-selective catalytic reduction (H2-SCR) is a promising technology for reducing nitrogen oxide (NOx) emissions at low temperatures, but the selectivity of this process is limited by the generation of N2O. To achieve enhanced denitrification (deNOx) performance, H2-SCR catalysts with mixed zeolite and TiO2 supports washcoated on monolithic cordierite were developed. The catalyst support, active metal type and content, and monolithic cordierite cell density significantly influenced the H2-SCR performance. The xPt/TiO2 catalysts (where x is the metal content, wt.%) achieved >90% NOx conversion 135–180 °C, whereas the xPd/TiO2 catalysts exhibited poor H2-SCR activity, with <30% NOx conversion. In contrast to 0.5Pt/TiO2, the 0.5Pt/zeolite catalysts achieved high NOx conversion at 140–150 °C (91% at 140 °C for 0.5Pt/ZSM-5 > 89% at 140 °C for 0.5Pt/BETA >85% at 150 °C for 0.5Pt/SSZ-13), suggesting that zeolite supports significantly promote H2-SCR activity at low reaction temperatures. For the 0.5Pt/ZSM-5 washcoated monolithic catalyst, increasing the cell density from 400 to 900 cpsi significantly improved the NOx conversion from 52% to 90% at 100 °C owing to the increased geometric surface area and open frontal area of monolithic cordierite. For catalyst with mixed supports (0.5Pt/yZSM-5zTiO2) changing the ZSM-5/TiO2 ratio (y:z) from 25:75 to 90:10 increased the low-temperature NOx conversion from 39% to 89% at 100 °C, indicating that the deNOx characteristics can be tuned. With NO as the reactant, the 0.5Pt/90Z10T catalyst produced the lowest N2O share (8–17%) within the temperature window of maximum NOx conversion, resulting in an increased N2 share (83–88%). Thus, the synergetic effect of mixed ZSM-5/TiO2 catalyst supports can enhance low-temperature NOx conversion and mitigate N2O formation.

Enhanced Low-Temperature Activity and Hydrothermal Stability of Ce-Mn Oxide-Modified Cu-SSZ-39 Catalysts for NH3-SCR of NOx

Cu-SSZ-39 zeolite with an AEI structure exhibits excellent hydrothermal stability and can be a potential alternative to Cu-SSZ-13 zeolite SCR catalysts for NOx removal in diesel vehicles. However, the inferior low-temperature performance of Cu-SSZ-39 leads to substantial NOx emissions during the cold-start period, impeding its practical application. In this study, Ce-Mn oxide-modified Cu-SSZ-39 catalysts (CeMnOx/Cu-SSZ-39) and references (CeO2/Cu-SSZ-39 and MnOx/Cu-SSZ-39) were prepared by the ion-exchange of Cu ions followed by impregnation of the oxide precursors, with the aim of enhancing the NH3-SCR performance at low temperatures. The modified catalysts exhibited improved low-temperature activity and hydrothermal stability compared to the unmodified counterpart. In particular, CeMnOx/Cu-SSZ-39 showed the highest activity among the three catalysts and achieved NOx conversions above 90% within the temperature range of 180 °C to 600 °C, even after undergoing hydrothermal aging at 800 °C. Experimental results indicated that the synergistic effect between Ce and Mn in CeMnOx improves the redox properties and acidity of the catalyst due to the presence of Ce3+, Mn4+, and abundant adsorbed oxygen species, which facilitate low-temperature SCR reactions. Furthermore, the interaction of CeMnOx with Cu-SSZ-39 stabilizes the zeolite framework and hinders the agglomeration of Cu species during the hydrothermal aging process, contributing to its exceptional hydrothermal stability. The kinetics and NO oxidation experiments demonstrated that CeMnOx provides access to fast SCR reaction pathways by oxidizing NO to NO2, resulting in a significant increase in low-temperature activity. This study provides novel guidelines for the design and preparation of Cu-SSZ-39 zeolite with outstanding SCR performance over a wide temperature range.

Fe/amorphous-Al2SiO5 composites fabricated by low-temperature solid-phase reaction densification achieve synergistically enhanced structural and soft magnetic properties

To date, an urgent problem for various metal-based soft magnetic composites (SMCs) is that it is difficult to simultaneously achieve high strength and optimum magnetic performance, which actually restricts their large-scale applications in many electromagnetic fields. In this work, we have tried to resolve this basic problem by proposing a new concept of low-temperature solid-phase reaction densification instead of conventional particle-deformation densification to fabricate high-performance metal-based SMCs. Specifically, fully-densified nanoscale amorphous Al2SiO5 coating layers are formed through a solid phase reaction at 500 °C between initially-prepared nano-sized amorphous SiO2 and amorphous Al2O3, and meanwhile coated in situ on the surface of deformed Fe to fabricate novelly-structured Fe/amorphous-Al2SiO5 SMCs. The low-temperature solid-phase reaction for fabrication of Fe/amorphous-Al2SiO5 SMCs can avoid negative effects of high processing temperature for conventional metal-based SMCs on their structure and magnetism resulting in their high strength, increased resistivity, low core loss and high saturation magnetic inductions. Thus, Fe/amorphous-Al2SiO5 SMCs show synergistically enhanced structural and soft magnetic properties, which exceed those of most conventional metal-based SMCs. This work also provides a special and useful insight into the design and applications of metal-based composites needing both functional and structural properties.

High shear reactor for glycerolysis—Interesterification palm stearin‐olein blend: Reaction kinetics and physical properties

AbstractStructured lipids containing high monoacylglycerol (MAG) and diacylglycerol (DAG) (SLs‐MDAG) were synthesized by chemical glycerolysis‐interesterification using sodium metasilicate as the catalyst in High Shear Reactor (HSR). The objective of this research was to investigate the effect of temperature on the glycerolysis‐interesterification kinetics at relatively low temperatures in an HSR and the physical product properties. The reaction was performed using immiscible and highly viscous reactants at various temperatures (80–120°C) and a mixing rate of 2000 rpm for 5 h. Results showed that the reaction rate constant exponentially increased as temperature increased. Triacylglycerol (TAG) conversion was 2.5 fold greater at 110 and 120°C compared to lower reaction temperatures (80 and 90°C). MAG and DAG increased by about 18.3% and 13.4%, respectively, as the reaction temperature increased from 80 to 120°C. The product's melting point, hardness, and color were also improved by increasing temperature. In summary, SLs‐MDAG could be produced at a relatively low temperature (110°C) using HSR. The glycerolysis‐interesterification kinetic displayed an exponential relationship, even though it did not precisely fit the Arrhenius model.

Heterogeneous Catalysts for Carbon Dioxide Methanation: A View on Catalytic Performance

CO2 methanation offers a promising route for converting CO2 into valuable chemicals and energy fuels at the same time as hydrogen is stored in methane, so the development of suitable catalysts is crucial. In this review, the performance of catalysts for CO2 methanation is presented and discussed, including noble metal-based catalysts and non-noble metal-based catalysts. Among the noble metal-based catalysts (Ru, Rh, and Pd), Ru-based catalysts show the best catalytic performance. In the non-noble metal catalysts, Ni-based catalysts are the best among Ni-, Co-, and Fe-based catalysts. The factors predominantly affecting catalytic performance are the dispersion of the active metal; the synergy of the active metal with support; and the addition of dopants. Further comprehensive investigations into (i) catalytic performance under industrial conditions, (ii) stability over a much longer period and (iii) activity enhancement at low reaction temperatures are anticipated to meet the industrial applications of CO2 methanation.

Low temperature reaction mechanism of NH3-SCR reaction on MoOx modified CePO4 catalyst: Combination study on experiments and DFT calculations

Developing CePO4-based NH3-SCR catalysts with high NOx conversion, N2 selectivity, and SO2 tolerance at low temperatures is challenging. Analyzing the atomic-level surface structure of these catalysts is particularly important. Hence, we conducted a combined computational and experimental study to design the surface structure of MoxCe1-xPO4 catalysts, corroborate the reaction performance and structural sensitivity, and investigate the relationship between active sites and structural performance at the atomic level. DFT calculations were used to systematically investigate the NH3 and NO adsorption capacity of the Mo-doped CePO4 solid solution structure model. The rationality of using the Mo-doped CePO4 solid solution structure as a catalyst was further supported by DFT calculation data and experimental results from BET, XRD, Raman, SEM, TEM, HR-TEM, NH3-TPD, H2-TPR, XPS and in situ DRIFTS. The source of the excellent intrinsic NH3-SCR activity of the Mo-doped CePO4 solid solution structure is disclosed. The role of the Mo dopant in the Mo-doped CePO4 solid solution as an SO2 trapping site to protect the catalytic active site from sulfation is discussed from a molecular perspective.

Automatic Potential Energy Surface Exploration by Accelerated Reactive Molecular Dynamics Simulations: From Pyrolysis to Oxidation Chemistry.

Automatic potential energy surface (PES) exploration is important to a better understanding of reaction mechanisms. Existing automatic PES mapping tools usually rely on predefined knowledge or computationally expensive on-the-fly quantum-chemical calculations. In this work, we have developed the PESmapping algorithm for discovering novel reaction pathways and automatically mapping out the PES using merely one starting species is present. The algorithm explores the unknown PES by iteratively spawning new reactive molecular dynamics (RMD) simulations for species that it has detected within previous RMD simulations. We have therefore extended the RMD simulation tool ChemTraYzer2.1 (Chemical Trajectory Analyzer, CTY) for this PESmapping algorithm. It can generate new seed species, automatically start replica simulations for new pathways, and stop the simulation when a reaction is found, reducing the computational cost of the algorithm. To explore PESs with low-temperature reactions, we applied the acceleration method collective variable (CV)-driven hyperdynamics. This involved the development of tailored CV templates, which are discussed in this study. We validate our approach for known pathways in various pyrolysis and oxidation systems: hydrocarbon isomerization and dissociation (C4H7 and C8H7 PES), mostly dominant at high temperatures and low-temperature oxidation of n-butane (C4H9O2 PES) and cyclohexane (C6H11O2 PES). As a result, in addition to new pathways showing up in the simulations, common isomerization and dissociation pathways were found very fast: for example, 44 reactions of butenyl radicals including major isomerizations and decompositions within about 30 min wall time and low-temperature chemistry such as the internal H-shift of RO2 → QO2H within 1 day wall time. Last, we applied PESmapping to the oxidation of the recently proposed biohybrid fuel 1,3-dioxane and validated that the tool could be used to discover new reaction pathways of larger molecules that are of practical use.

A reaction study for Al–Ni2O3 nano self-exothermic materials

Cast-infiltration has emerged as a prevalent technique for fabricating metal matrix composites. Studying Al–Ni2O3 nano self-exothermic materials proves valuable, given their potential to enhance metal matrix composites' casting defect resolution as nano self-exothermic materials. This study analyzes reaction characteristics, mechanisms, parameter-exothermic characteristic relationships, moderating methods, and their respective influences. Reaction products from Al–Ni2O3 nano self-exothermic materials include Al2O3, AlNix, and trace amounts of Al. The closer the powder's composition ratio aligns with equilibrium stoichiometry, the smaller the heat released during self-exothermic reactions; smaller powder particles result in larger self-exothermic reaction heat releases and lower reaction temperatures, with reactions ceasing when exceeding the critical size (l > 40 μm). Different reaction environments also impact reaction products, with comparatively lesser effects on reaction temperatures. By modulating powder parameters and reaction conditions, Al–Ni2O3 nano self-exothermic materials' reaction temperature can be adjusted between 609 °C and 900 °C. Correspondingly, the reaction exotherm ranges from 232 J/g to 1560 J/g, providing heat compensation for subsequent composite material casting.

Low temperature reaction kinetics inside an extended Laval nozzle: REMPI characterization and detection by broadband rotational spectroscopy.

Chirped-Pulse Fourier-Transform millimeter wave (CP-FTmmW) spectroscopy is a powerful method that enables detection of quantum state specific reactants and products in mixtures. We have successfully coupled this technique with a pulsed uniform Laval flow system to study photodissociation and reactions at low temperature, which we refer to as CPUF ("Chirped-Pulse/Uniform flow"). Detection by CPUF requires monitoring the free induction decay (FID) of the rotational coherence. However, the high collision frequency in high-density uniform supersonic flows can interfere with the FID and attenuate the signal. One way to overcome this is to sample the flow, but this can cause interference from shocks in the sampling region. This led us to develop an extended Laval nozzle that creates a uniform flow within the nozzle itself, after which the gas undergoes a shock-free secondary expansion to cold, low pressure conditions ideal for CP-FTmmW detection. Impact pressure measurements, commonly used to characterize Laval flows, cannot be used to monitor the flow within the nozzle. Therefore, we implemented a REMPI (resonance-enhanced multiphoton ionization) detection scheme that allows the interrogation of the conditions of the flow directly inside the extended nozzle, confirming the fluid dynamics simulations of the flow environment. We describe the development of the new 20K extended flow, along with its characterization using REMPI and computational fluid dynamics. Finally, we demonstrate its application to the first low temperature measurement of the reaction kinetics of HCO with O2 and obtain a rate coefficient at 20K of 6.66 ± 0.47 × 10-11cm3 molec-1s-1.

Performance assessment of an energetically self-sufficient system for hydrogen production from oilfield wastewater treated by supercritical water gasification

Oilfield wastewater with high moisture content can be efficiently treated by supercritical water gasification (SCWG) technology to produce hydrogen. This paper conducted a thermodynamic and environmental analysis of the oilfield wastewater SCWG system to provide optimization strategies. The waste heat utilization technology can enhance the heat integration of the system to reduce the exergy destruction and increase the H2 yield. Sensitivity analysis showed that a ratio of preheating water to emulsion 3 can promote water-sensitive reactions to produce H2 and save the H2 needed to maintain the energetically self-sufficient system. Low system pressures, high feedstock preheating temperatures, and low oxidation reactor temperatures can reduce system energy destruction to obtain high H2 yield and system efficiency. Meantime, the developed SCWG system has the potential to achieve natural enrichment of greenhouse gases after the H2 separation has been completed. The use of waste heat utilization technology and carbon capture and storage (CCS) technology is expected to increase system efficiency to 53.43 % and reduce global warming potential (GWP) of 5.52 kg CO2-eq/kg H2. This work would be of great value to the process design and optimization for the SCWG system of oilfield wastewater.

Low-temperature oxidation characteristics and reaction pathways of crude oil within tight shale during air injection

The investigation of low-temperature oxidation (LTO) of crude oil within tight shale holds significant importance due to its implications for subsequent oxidation reactions and enhanced oil recovery in the process of air injection. In this study, the tight shale sample underwent oxidation at various LTO temperatures, followed by an analysis of the resulting gas composition. Furthermore, the oxidized oil was separated from the tight shale and subjected to characterization using electron paramagnetic resonance, nuclear magnetic resonance, and negative ion electrospray Fourier transform-ion cyclotron resonance mass spectrometry techniques. The primary focus was on examining the distinct LTO reaction pathways observable across different temperature ranges. The findings demonstrated a correlation between LTO temperature and the concentration of free radicals, which predominantly resided on aromatic hydrocarbons, alkanes, and oxygen atoms. Additionally, the proton count of polycyclic aromatic hydrocarbons exhibited a continuous increase from 83 to 350 °C, suggesting intensified aromatization and condensation reactions involving aliphatic and aromatic compounds. With rising LTO temperature, the molecular structure of O2 compounds underwent significant transformations, characterized by increased condensation degree and a decrease in low carbon number molecular structures, while higher equivalent double bonds and carbon number molecular structures became more prevalent. The influence of cycle path 1 diminished at temperatures ranging from 83 to 150 °C and 250 to 350 °C, whereas the significance of cycle paths 2 and 3 increased, resulting in an overall escalation of the oxidation rate with temperature elevation. It was observed that the shale oil LTO process exhibited a negative temperature coefficient within the temperature range of 150-250 °C, emphasizing the criticality of overcoming the energy barrier in this region to achieve stable combustion. This comprehensive investigation provides valuable insights into the mechanisms underlying LTO in crude oil confined within tight shale.

Growth of epitaxial Bi0.5(Na1-xKx)0.5TiO3 films by hydrothermal reaction time and their characterization

The hydrothermally grown films can be used in various applications because of their relatively lower reaction temperature than the other growth methods. Bi0.5(Na1-xKx)0.5TiO3 films on SrTiO3 substrates are synthesized using the hydrothermal reaction to study its structural and piezoelectric response. The different morphological analysis of films by field emission scanning electron microscope shows the grains on films get through the dissolution-recrystallization process with Ostwald ripening. Also, the structural analyses are carried out using X-ray diffraction and transmission electron microscope which confirmed the formation of epitaxial films with their high crystallinity, and tetragonal symmetry under compressive strain. Through X-ray photoelectron spectroscopy, it was confirmed that the constituent elements and element ratios of BNKT vary according to the reaction time, and the piezoelectric and ferroelectric behaviors were confirmed through a piezoelectric force microscope and piezoelectric coefficient. A combination of the structural and piezoelectric measurements reveals that the reaction time affects the composition of our epitaxial film.