Low-pressure Synthesis Research Articles

Methanolation of Olefins: Low-Pressure Synthesis of Alcohols by the Formal Addition of Methanol to Olefins.

Methanolation of olefins is introduced as a new low-pressure synthetic pathway to C1 elongated alcohols. Formally, H3COH is added to the C=C bond in a 100% atom efficient manner. Mechanistically, the overall transformation occurs as a tandem reaction sequence by combining the dehydrogenation of methanol to syngas at a CO:H2 ratio of 1:2 with subsequent hydroformylation to the corresponding aldehyde and its final hydrogenation to the alcohol. The dehydrogenation and hydrogenation steps are catalysed by a Mn/pincer complex, while the hydroformylation is accomplished by a Rh/phosphine catalyst. Using 1-octene as prototypical substrate, a yield of 80% nonanol was achieved with a ratio of 93:7 of linear to branched alcohols and turnover numbers (TONRh) of more than 17 000 could be obtained in relation to the precious metal Rhodium. The integrated catalytic system provides direct access to alcohols from olefins and "green" methanol, avoiding the handling of pressurized CO and H2 and the use of specialized high-pressure equipment as the process conditions do not exceed 10 bar with partial pressures of syngas in the range of only 1-2 bar.

Experimental Verification of Low-Pressure Kinetics Model for Direct Synthesis of Dimethyl Carbonate Over CeO2 Catalyst

AbstractDimethyl carbonate (DMC) has emerged as a promising candidate for sustainable chemical processes due to its remarkable versatility and low toxicity. From a green chemistry perspective, the direct synthesis of DMC has been considered the most promising route, as water is the only byproduct generated in the reaction between CO2 and methanol. However, this synthetic route has faced significant thermodynamic limitations, even at elevated pressure conditions. Therefore, a two-part study explored low-pressure synthesis of DMC via the direct route, and a low-pressure kinetic model for the CeO2 catalyst was developed based on the results. Proposed Langmuir–Hinshelwood mechanisms were verified using experimental data generated in our labs. The investigation suggests that DMC formation in the direct synthetic route is a surface reaction of CO2 and methanol on the catalyst. The kinetic model predictions closely aligned with experimental data, demonstrating a 17% mean absolute percentage error and indicating a high level of predictability. Additionally, a rigorous assessment was conducted on CO2 fixations in DMC synthesis, quantifying CO2 capture and its conversion into stable or high-value products, formally designated as CO2 Fixation (CO2Fix). The CO2Fix analysis revealed that, at a conversion rate of 27%, the process can achieve a "net zero" state when operated at an approximate pressure of 30 bar, thereby supporting the viability of low-pressure synthesis. Increasing the conversion rate to levels exceeding 95% significantly enhances the CO2Fix metric, potentially surpassing 3.5 or higher.

Plant-wide modeling and techno-economic optimization of a low-pressure microwave-assisted ammonia synthesis process with adsorption separation

Ammonia production has traditionally been done by using the Haber-Bosch process, that operates at extremely high pressure (200–300 bar), has a large carbon footprint, and requires significant energy. For ammonia to be used as a hydrogen carrier, it is desired that it is produced by using modular technologies under benign conditions, yet the economics remain commercially viable. This paper investigates a novel technology for ammonia synthesis by using a microwave-assisted low-pressure reactor. Microwave reactors are compact and can be readily modularized and started/shutdown thus making them ideal to be integrated with the electric grid or with regional/local renewable-based electric generation facilities. For separation of unreacted reactants from the product ammonia, if the traditional condensation separation technology used in the high-pressure Haber-Bosch process is used, then the separation process needs to be operated under cryogenic condition thus adversely affecting the economics. A solid sorbent based separation technology is investigated in this paper. A kinetic model for the microwave-catalytic synthesis process is used. An isotherm model is developed for MgCl2–Si adsorbent and used for modeling the dynamic adsorption-desorption cycle. A plant-wide model with heat and mass integration is developed. An economic model is developed and used for economic optimization by using an equation-oriented approach. Since the adsorption-desorption process is dynamic, for techno-economic optimization, a reduced order model for the key performance measures of the adsorption-desorption process as a function of its input and decision variable is developed under cyclic steady-state conditions. For the optimized MW-assisted process, the levelized cost of ammonia is $772/mt as opposed to $808/mt for the conventional Haber-Bosch process for a hydrogen price of $2.07/kg. The MW-assisted process is found to be economically viable in the US market if the hydrogen price is below $4/kg.

Research on the Application of Superhard Coating Technology for Cutting Tools in Mechanical Processing

The superhard coating technology for cutting tools has important applications in the field of mechanical processing. This article introduces the development of superhard coating materials for cutting tools, including low-pressure gas-phase synthesis of diamond, cubic boron nitride, and physical vapor deposition (PVD) coating technology. The superhard coating of cutting tools is widely used in turning, milling, tapping, key component machining, high-speed steel drill bits and taps. Research has shown that coatings can reduce cutting forces and improve tool life, but attention should be paid to residual compressive stress. The future development direction includes researching new superhard material cutting tools and developing coating methods that are more wear-resistant and have high temperature hardness.

Mechanistic insights into the role of zinc oxide, zirconia and ceria supports in Cu-based catalysts for CO[formula omitted] hydrogenation to methanol

Copper-based catalysts enable the hydrogenation of CO2 to methanol (MeOH). Selective MeOH synthesis requires the interaction of copper with a metal oxide support to facilitate CO2 adsorption and hydrogenation. Here, we systematically appraise the role of ZnO, ZrO2 and CeO2 in Cu-based catalysts for low-pressure (1 bar) MeOH synthesis. During temperature-programmed desorption (TPD) of CO2, the bare ZnO, ZrO2, and CeO2 exhibited desorption events at both low (70–100 °C) and high (400–700 °C) temperatures, also observed when combining each support with copper. Investigations in a packed bed reactor showed suppressed CO by-production over Cu-ZrO2, leading to a 1.5-fold improvement as compared to Cu-ZnO. Upon Cu-CeO2, CO2 was prone to undergo reduction to CO and desorb, resulting in a MeOH yield 9 times lower than over Cu-ZrO2. Experiments aiming at intermittent operation with successive start-ups and shut-downs showed that the performance of Cu-ZrO2 catalyst remained stable, whilst Cu-ZnO deteriorated monotonically, ascribed to sintering driven by OH and H2O species. In situ infrared spectroscopy demonstrated that methanol synthesis over Cu-ZnO progresses via a single pathway with formate species, whilst parallel formate and bicarbonate pathways were demonstrated over Cu-ZrO2. Unlike Cu-ZnO, the formation of bicarbonate over Cu-ZrO2 allows surface OH species to participate in MeOH synthesis, which we link to the superior performance and stability of Cu-ZrO2.

Fe/Cu diatomic catalysts for electrochemical nitrate reduction to ammonia

Electrochemical conversion of nitrate to ammonia offers an efficient approach to reducing nitrate pollutants and a potential technology for low-temperature and low-pressure ammonia synthesis. However, the process is limited by multiple competing reactions and NO3− adsorption on cathode surfaces. Here, we report a Fe/Cu diatomic catalyst on holey nitrogen-doped graphene which exhibits high catalytic activities and selectivity for ammonia production. The catalyst enables a maximum ammonia Faradaic efficiency of 92.51% (−0.3 V(RHE)) and a high NH3 yield rate of 1.08 mmol h−1 mg−1 (at − 0.5 V(RHE)). Computational and theoretical analysis reveals that a relatively strong interaction between NO3− and Fe/Cu promotes the adsorption and discharge of NO3− anions. Nitrogen-oxygen bonds are also shown to be weakened due to the existence of hetero-atomic dual sites which lowers the overall reaction barriers. The dual-site and hetero-atom strategy in this work provides a flexible design for further catalyst development and expands the electrocatalytic techniques for nitrate reduction and ammonia synthesis.

Low-Pressure CVD Synthesis of Tetragonal Borophene Single-Crystalline Sheets with High Ambient Stability

Being a typical graphene-like two-dimensional (2D) material, borophene has received a lot of attention due to its low density, high electron mobility, large Young’s modulus, and good chemical stability. Compared with the corresponding bulk counterparts, 2D borophene has larger specific surface area, higher conductivity, and smaller work function, finding potential applications in high-speed transistors, optoelectronic detection, field emission (FE), and mechanical enforcement areas. In this paper, 2D tetragonal borophene sheets with high ambient stability have been successfully fabricated on the surface of 1 cm2 copper foil using a developed low-pressure chemical vapor deposition (LPCVD) method. The vapor–solid mechanism was used to comprehend the formation of the tetragonal borophene sheets. The electrical conductivity of individual borophene sheets ranged from 4 to 5 × 10–4 S/cm, and the band gap was about 2.1 eV, suggesting their narrow semiconductive nature. Also, the maximum FE current of individual borophene sheets was close to 1 μA, and their emission properties enhanced with the decreasing sheet thickness, comparable to many other nanomaterials with excellent FE performances. More interestingly, individual borophene sheets were found to retain good enough electrical transport and FE behaviors even if they experienced several days’ atmospheric conservations. Our research results suggest that the LPCVD-grown borophene may be a promising building block for constructing high-performance nanodevices with good ambient stability.

Revolutionizing CO2 capture: Molecular complexes of deep eutectic solvents with enhanced hydrogen bond accepting interaction for superior absorption performance

In this study, functionalized deep eutectic solvents (DESs) were synthesized to enhance the CO2 absorption characteristics, such as absorption capacity and reaction rate, compared to conventional alkanolamine-based absorbents. DES consists of a hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) and has the advantages of facile synthesis without complex molecular design as well as low vapor pressure and low synthesis cost. It is a liquid material formed by large networks of molecular architectures via static interactions, including hydrogen bonds. Hence, it is possible to capture CO2 physically via intermolecular vacancies, and chemical absorption is possible via functionalization by introducing suitable HBAs and HBDs that have functional groups that are reactive toward CO2. Herein, two amino acids, glycine (GLY) and proline (PRO), were used to prepare HBAs by converting them into amino acid salts. Upon conversion, the proton attached to the carboxyl group is detached and the potassium cation supports the loss of an electron charge. Hence intermolecular interactions are enhanced, and they are available for DES formation.Alkanolamines, such as monoethanolamine (MEA), diethanolamine (DEA), and Nmethyldiethanolamine (MDEA), were used as HBDs with these HBAs to functionalize DESs for enhancing the CO2 absorption capacity. Using FT-IR, DSC, and 13C NMR the characteristics of CO2 absorption by the new DESs were determined and compared with those of conventional absorbents. The relationship of equilibrium capacity and reaction rate with the order of amines and molecular free volume was evaluated to ascertain the effects of HBA and HBD on the absorption characteristics.

Low-Pressure Electrochemical Synthesis of Complex High-Pressure Superconducting Superhydrides.

There is great current interest in multicomponent superhydrides due to their unique quantum properties under pressure. A remarkable example is the ternary superhydride Li_{2}MgH_{16} computationally identified to have an unprecedented high superconducting critical temperature T_{c} of ∼470 K at 250GPa. However, the very high synthesis pressures required remains a significant hurdle for detailed study and potential applications. In this Letter, we evaluate the feasibility of synthesizing ternary Li-Mg superhydrides by the recently proposed pressure-potential (P^{2}) method that uniquely combines electrochemistry and applied pressure to control synthesis and stability. The results indicate that it is possible to synthesize Li-Mg superhydrides at modest pressures by applying suitable electrode potentials. Using pressure alone, no Li-Mg ternary hydrides are predicted to be thermodynamically stable, but in the presence of electrode potentials, both Li_{2}MgH_{16} and Li_{4}MgH_{24} can be stabilized at modest pressures. Three polymorphs are predicted as ground states of Li_{2}MgH_{16} below 300GPa, with transitions at 33 and 160GPa. The highest pressure phase is superconducting, while the two at lower pressures are not. Our findings point out the potentially important role of the P^{2} method in controlling phase stability of complex multicomponent superhydrides.

Reverse Boudouard reforming produces CO directly suitable for the production of methanol from CO2 and CH4

We report the development of a novel process for the production of CO from CO2 and CH4, with CO suitably pure for use in conventional low-pressure methanol synthesis processes over Cu-ZnO-Al2O3 catalysts. The experimentally achieved yield of 3.07 molCO molCH4−1 is substantially higher than the 2 molCO molCH4−1 that is produced, at best, by the dry reforming process. We demonstrate the production of 84-mol%-pure CO (the remainder being CO2) for the first time without any dilution gas or further gas separation required. The syngas prepared by the addition of hydrogen is directly suitable for methanol synthesis, with a stoichiometric number (S = (H2 − CO2)/(CO + CO2)) of 2.05 and a CO2 concentration ≤ 5 mol%, which is achieved in a single packed-bed reactor operated in a cyclic manner. Each cycle consists of two steps, with the CH4 reactant fed in the first step, and the CO2 reactant fed in the second step. After each step, the direction of the gas flow is reversed. Methane cracking produces solid carbon and gaseous H2 in the first step, which is then oxidised by the lattice oxygen of an oxygen storage material to H2O, while CO2 is reduced to CO by the uptake of oxygen by the oxygen storage material in the second step. This is followed by the further production of CO by gasification of the solid carbon by CO2 through the reverse Boudouard reaction. Hence, we refer to this novel process as “reverse Boudouard reforming”.

The Search for Efficient and Stable Metal-Organic Frameworks for Photocatalysis: Atmospheric Fixation of Nitrogen

Recent research targets the low-pressure synthesis of ammonia via a light-initiated catalytic process. Despite the importance of materials selection for photocatalysis, computational efforts to guide candidate materials’ nomination ahead of experiments are lacking. The purpose of this study is to employ computational screening, using density functional theory and molecular simulations, to select and evaluate metal–organic frameworks (MOFs) as nitrogen fixation photocatalysts and further deduce correlations for the prediction of MOFs’ electronic properties. First, MOFs with appropriate electronic and structural properties are identified. The top candidates have been examined from the perspective of adsorption, diffusion, and mechanical and chemical stability properties. Four MOFs, Fe2Cl2(BBTA), Fe2(mDOBDC), Zn2(mDOBDC), and Ni-BTP, have been selected based on their band edges, while only Fe2Cl2(BBTA) MOF exhibited a bandgap less than 3 eV. Fe2(mDOBDC) exhibited the highest shear modulus of approximately 31 GPa. In addition, a life cycle assessment of the four MOFs showed that Ni-BTP has the lowest environmental impact. A set of 48 MOFs’ combinations are proposed for heterojunction application to enhance charge carriers’ separation. Intriguingly, we demonstrated the predictability of MOF’s bandgap and edges from MOF’s organic linker bandgap and metal node type (oxidation state and corresponding electronic configuration) for MOF families.

An Ammonia–Hydrogen Energy Roadmap for Carbon Neutrality: Opportunity and Challenges in China

Abstract China has promised to reach the peak carbon dioxide emission (ca. 10 billion tons) by 2030 and carbon neutrality by 2060. To realize these goals, it is necessary to develop hydrogen energy and fuel cell techniques. However, the high cost and low intrinsic safety of high-pressure hydrogen storage limit their commercialization. NH3 is high in hydrogen content, easily liquefied at low pressure, and free of carbon, and the technology of NH3 synthesis has been commercialized nationwide. It is worth noting that the production of NH3 in China is about 56 million tons per year, accounting for 35% of worldwide production. Hence, with the well established infrastructure for NH3 synthesis and transportation and the demand for clean energy in China, it is feasible to develop a green and economical energy roadmap, viz., “Clean low-pressure NH3 synthesis → Safe and economical NH3 storage and transportation → Carbon-free efficient NH3-H2 utilization”, for low-carbon or even carbon-free energy production. Currently, the academic and industrial communities in China are striving to make technological breakthroughs in areas such as photocatalytic water splitting, electrocatalytic water splitting, mild-condition NH3 synthesis, low-temperature NH3 catalytic decomposition, and indirect or direct NH3 fuel cells, with significant progress. Taking full advantage of the NH3 synthesis industry and readjusting the industrial structure, it is viable to achieve energy saving and emission reduction in NH3 synthesis industry (440 million tons CO2 per year), as well as promote a new energy industry and ensure national energy security. Therefore, relevant academic and industrial communities should put effort on mastering the key technologies of “Ammonia-Hydrogen” energy conversion and utilization with complete self-dependent intellectual property. It is envisioned that through the establishment of “Renewable Energy-Ammonia-Hydrogen” circular economy, a green technology chain for hydrogen energy industry would pose as a promising pathway to achieve the 2030 and 2060 goals.

Electrochemical Ammonia: Power to Ammonia Ratio and Balance of Plant Requirements for Two Different Electrolysis Approaches

Electrochemical ammonia generation allows direct, low pressure synthesis of ammonia as an alternative to the established Haber-Bosch process. The increasing need to drive industry with renewable electricity central to decarbonisation and electrochemical ammonia synthesis offers a possible efficient and low emission route for this increasingly important chemical. It also provides a potential route for more distributed and small-scale ammonia synthesis with a reduced production footprint. Electrochemical ammonia synthesis is still early stage but has seen recent acceleration in fundamental understanding. In this work, two different ammonia electrolysis systems are considered. Balance of plant (BOP) requirements are presented and modelled to compare performance and determine trade-offs. The first option (water fed cell) uses direct ammonia synthesis from water and air. The second (hydrogen-fed cell), involves a two-step electrolysis approach firstly producing hydrogen followed by electrochemical ammonia generation. Results indicate that the water fed approach shows the most promise in achieving low energy demand for direct electrochemical ammonia generation. Breaking the reaction into two steps for the hydrogen fed approach introduces a source of inefficiency which is not overcome by reduced BOP energy demands, and will only be an attractive pathway for reactors which promise both high efficiency and increased ammonia formation rate compared to water fed cells. The most optimised scenario investigated here with 90% faradaic efficiency (FE) and 1.5 V cell potential (75% nitrogen utilisation) gives a power to ammonia value of 15 kWh/kg NH3 for a water fed cell. For the best hydrogen fed arrangement, the requirement is 19 kWh/kg NH3. This is achieved with 0.5 V cell potential and 75% utilisation of both hydrogen and nitrogen (90% FE). Modelling demonstrated that balance of plant requirements for electrochemical ammonia are significant. Electrochemical energy inputs dominate energy requirements at low FE, however in cases of high FE the BOP accounts for approximately 50% of the total energy demand, mostly from ammonia separation requirements. In the hydrogen fed cell arrangement, it was also demonstrated that recycle of unconverted hydrogen is essential for efficient operation, even in the case where this increases BOP energy inputs.

Low-pressure UV-initiated synthesis of cationic starch-based flocculant with high flocculation performance

A kind of starch-based flocculant (starch-graft-poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride], denoted St-g-PDMC-LPUV) has been synthesized by low-pressure ultraviolet initiation and was employed to remove humic acid (HA) for water purification. The physicochemical characteristics of starch and St-g-PDMC-LPUV were characterized by FT-IR, 1H NMR, XRD, TGA, SEM and BET to confirmed the successful grafting DMC onto starch. Effects of flocculant dosage, pH, the adding amount of Fe3O4, initial HA concentration and stirring speed were investigated systematically. The prepared St-g-PDMC-LPUV flocculant with non-toxic, biodegradability and environmental friendliness exhibited effective performance for removing HA from water in a wide pH range (5–10). The flocculation mechanism was attributed to the effective collision between function groups of the St-g-PDMC-LPUV flocculant and HA by charge neutralization, adsorption, bridging and patching.

Low-pressure flame synthesis of carbon-stabilized TiO2-II (srilankite) nanoparticles

Nanoparticulate (3–10 nm) TiO2 polymorphs, i.e., rutile, anatase, and srilankite (also known as TiO2-II or α-PbO2-type TiO2) phases are produced via low-pressure (e.g., 20 torr) flame synthesis at temperatures ranging from 1560K to 2650K, with burner flow velocities varying from 150 to 300 cm/s, using titanium tetra-isopropoxide (TTIP) as precursor. Interestingly, added carbon (i.e., ethylene) in the feed stream produces nanoparticles of the generally characteristic low-temperature high-pressure metastable srilankite phase. The as-synthesized nanopowder is composed of either rutile or srilankite phase, with composition dependent on particle residence time in the flow field. Under the same conditions, feed gas without carbon, e.g., hydrogen, yields anatase phase TiO2. Post heat treatment up to 773K in thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) highlights the thermal stability of the samples, while x-ray photoelectron spectroscopy (XPS) indicates the presence of carbon, with absences of Ti3+, Ti–C, and nitrogen. Microscopy reveals morphology on both the micrometer scale (scanning electron microscopy, SEM) and nanometer scale (transmission electron microscopy, TEM), while x-ray diffraction (XRD) and selected area electron diffraction (SAED) confirm polymorph variation under different synthesis conditions. CHN analysis determines that the synthesized srilankite contains a greater weight percentage of carbon than does anatase. Excess carbon doped into the lattice during low-pressure flame synthesis seems to be the key in stabilizing the high-pressure srilankite phase for such nanoparticles.

PtxCuy@TiO2 nanoparticles by low-pressure plasma synthesis

A new and original method is presented to synthesize Pt, Cu, and PtxCuy nanoparticles (NPs) anchored onto an inorganic nanopowder substrate (TiO2), based on the plasma degradation, within an Ar/NH3 radiofrequency plasma discharge, of solid organometallics (Cu and Pt acetylacetonate), mixed with TiO2. Both chemical and crystallographic characterizations confirm the formation of metastable alloyed Pt-Cu nanoparticles. The difference of Pt and Cu concentrations in NPs measured with a volume technique (X-ray diffraction) and a surface technique (X-ray photoelectron spectroscopy) suggests a Pt concentration gradient within NPs attributed to a difference in organometallics degradation kinetics.

Comparison of Si Nanoparticle types for use as a Potencial Drug Delivery System for Central Nervous System Diseases

Diseases affecting the central nervous system (CNS) are considered to be some of the most debilitating conditions worldwide. The range of standard therapies for disorders affecting CNS is largely limited for many patients. Nonetheless, nanoparticle-based drug delivery offers itself to be a promising strategy for effective drug delivery into the brain, addressing the frequently arising complications with blood-brain barrier crossing. This study compared the drug adsorption ability and the surface chemistry of two types of silicon nanoparticles (Si-NPs). Si- NPs were prepared using two methods: electrochemical etching of Si wafers (Si-E) and low-pressure plasma synthesis (Si-P). Silicon nanoparticles were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and nitrogen physisorption (method of Barrett, Joyner, and Halenda (BJH) and method of Brunauer, Emmett and Teller (BET)). The size and morphology were characterized by high-resolution transmission electron microscopy (HRTEM) linked with energy-dispersive X-ray spectroscopy (EDAX) and dynamic light scattering (DLS), respectively. The concentration of the drug substance that was captured by the silicon-based drug delivery system was determined by ultra high-performance liquid-chromatography-diode-array (UHPLC-DAD) method. Results of XPS showed that the Si-E are more oxidized than Si-P. The BET analysis showed us that the Si-E have more surface area, pore volume and grain size then the Si-P, and Si-P have a bigger pore size than Si-E. We also demonstrated by XRD that silicon nanoparticles prepared by both methods have a crystalline structure. The Si-P adsorption analysis of the model compound (ferulic acid) showed better adsorption ability than Si-E. The size of the Si-P (40- 120 nm) was also measured by HRTEM.

Pressureless and Low-Pressure Synthesis of Microporous Carbon Spheres Applied to CO2 Adsorption

In this work, low-pressure synthesis of carbon spheres from resorcinol and formaldehyde using an autoclave is presented. The influence of reaction time and process temperature as well as the effect of potassium oxalate, an activator, on the morphology and CO2 adsorption properties was studied. The properties of materials produced at pressureless (atmospheric) conditions were compared with those synthesized under higher pressures. The results of this work show that enhanced pressure treatment is not necessary to produce high-quality carbon spheres, and the morphology and porosity of the spheres produced without an activation step at pressureless conditions are not significantly different from those obtained at higher pressures. In addition, CO2 uptake was not affected by elevated pressure synthesis. It was also demonstrated that addition of the activator (potassium oxalate) had much more effect on key properties than the applied pressure treatment. The use of potassium oxalate as an activator caused non-uniform size distribution of spherical particles. Simultaneously higher values of surface area and total pore volumes were reached. A pressure treatment of the carbon materials in the autoclave significantly enhanced the CO2 uptake at 25 °C, but had no effect on it at 0 °C.

Investigation of the combustion of iron pentacarbonyl and the formation of key intermediates in iron oxide synthesis flames

The information of the gas phase kinetics are relevant for the development of detailed reaction mechanisms as well as for process design and control in flame synthesis. In this study, the decomposition of iron pentacarbonyl and the reaction pathways towards iron oxide clusters and particles in laminar H2/O2/Ar low-pressure synthesis flames are investigated. Gas-phase species are analyzed by photoionization and electron ionization mass spectrometry. The extraction of a representative sample from the particle-laden flow of a synthesis flame by an intrusive sampling technique for the analysis is challenging, because iron-intermediate species can condense easily. Cations can be extracted from the flame with a high efficient ion sampling technique that results in high sensitivity. Iron-containing cations provide evidence of the presence of key intermediates, e.g., Fe(OH)2, Fe(OH)3, Fe2O3, and larger Fe-O-clusters which are the dominant intermediates with respect to particle formation and need to be considered in future gas-phase reaction mechanisms.

Low oxygen pressure synthesis of NdNiO3-δ nanowires by electrospinning

Synthesis of RNiO3 (R = rare earth) nanowires can be interesting as building blocks with potential applications in optoelectronic devices. Here, we describe the synthesis and characterization of NdNiO3-δ (NNO) nanowires produced by electrospinning technique via polymeric precursor solution at relatively low temperature and oxygen pressure. These NNO nanowires were characterized by x-ray diffraction (XRD), x-ray photodetection spectroscopy (XPS), Field Emission Scanning Electron Microscopy (Fe-SEM), Magnetization (M(T)) and electrical resistance (R(T)) measurements. SEM images revealed a granular nanowire microstructure of NNO nanostructures, with a distribution of nanowire diameters ranging from 50 to 150 nm. The NNO nanowires also exhibit granular characteristics with an average grain diameter of 40 nm. The x-ray diffraction patterns of the NNO nanowires indicated that these samples exhibited a high degree of crystallinity and their Bragg reflections can be indexed to an orthorhombic-distorted (Pbnm symmetry) perovskite structure. The crystalline structure seems to be slightly texturized in some Bragg directions and with a slightly strained crystallite. M(T) and R(T) measurement as a function of temperature curves show that these NNO samples present a metal-insulator (MI) transition close to TMI ∼ 198 K, which is usually observed in NNO thin films and bulk samples. The nanostructured shape and these experimental observations can be promising in designing new electronic devices using this strongly correlated oxide.