Maximum Reaction Temperature Research Articles

Exploring strategies for valorizing wood processing waste: advancing sustainable, fully lignocellulosic biocomposites

This study presents the design and synthesis of bio-composites exhibiting high properties, wherein both the matrix and filler originate from wood biomass. Notably, no additional hardener compounds or treatments/modifications of the lignocellulosic filler were employed. Thermosetting materials were developed by homopolymerizing a bio-based aromatic epoxy monomer, the resorcinol diglycidyl ether (RDGE), with different percentages, from 1 wt% to 30 wt% of natural wood processing side-product, such as spruce bark powder (SB), which was used as such without additional treatments and modifications. The DSC analyses revealed enhanced reactivities with the bio-filler content, resulting in a reduced reaction temperature range and maximum reaction temperature. These findings provide evidence of the chemical interaction between the functional groups from spruce bark and the epoxides groups. The obtained fully based lignocellulosic materials show high E' values from 2.4 GPa to 2.5–3.5 GPa (glassy state) and from 64 MPa to 99–156 MPa in the rubbery region. The damping factor of the bio-composites with 1–10 wt% SB have shown an increase of the α transition temperature from 92 °C to 94–97 °C. The excellent filler/matrix interface and optimal adhesion between them were confirmed by SEM analysis.

Universal measuring cell and installation for determining dielectric parameters during the transition from a liquid oligomer to a solid polymer

This paper presents the design of a new installation and a universal measuring cell that allows determining the dielectric properties of materials in various states of aggregation.The data of dielectric permittivity studies for the initial components of the oligomeric binder, ED-20 epoxy oligomer and aminetype hardener triethylenetetramine (TETA), as well as the kinetics of its curing process, established by the change in dielectric permittivity, were obtained for the first time. It is also shown that the maximum temperature of the curing reaction of the ED20+TETA system can be determined from dielectric permittivity data.

Analyzing Solar Pyrolysis Process of Walnut Shells: Thermal Biomaterial Behavioral Outcomes

This paper presents a new experimental method for the thermal analysis of solar pyrolysis of walnut shells. The method consists of two types of thermal experiments: (A) the pyrolysis of walnut shells, and (B) the heating-cooling of the biochar obtained during experiment A. Nutshells are a waste product from the pecan nut industry. The state of Sonora, Mexico, produces large volumes of walnuts and their residue. Likewise, this region has a considerable solar resource. The motivation of this study is to obtain biochar - a bi-product of high commercial value used for soil enhancement - using solar energy and agro-industrial waste. In this experiment, biomass pyrolysis of 50g of nutshells was carried out inside a stainless-steel reactor heated with concentrated radiation from a solar simulator. Three different heat fluxes were used: 234, 482, and 725 W. The maximum reaction temperatures were: 382, 498, and 674 °C respectively. The composition of the pyrolysis gases (H2, CO, CO2, and CH4) was measured and the biochar obtained was characterized. Finally, the performance of the solar reactor allowed us to identify and differentiate between evaporation, pyrolysis of cellulosic material, and lignin degradation

Simulation study on the oxidation performance of low-concentration methane preheating direct current catalytic oxidation plant considering thermal radiation

In this study, the process of catalytic oxidation of methane considering radiative heat transfer was simulated using FLUENT computational software to study the effect of thermal radiation on the oxidation performance of the simulated device, and to investigate the extent to which radiative heat transfer affects the oxidation performance of the device under different operating conditions. The results show that the extent to which thermal radiation affects the oxidative performance of the equipment increases with increasing inlet temperature. When the intake temperature reaches 900K, its proportion is close to 45 %. At the same time, as the inlet gas temperature increases, the maximum reaction temperature of the oxidation unit is 1154 K, and the methane conversion rate reaches up to 89 %. The main factor affecting the oxidation performance of the unit at this time is radiation heat transfer. The extent to which thermal radiation affects the oxidative performance of the device diminishes with increasing inlet velocity. When the wind speed reaches 2 m/s, the proportion of radiative heat transfer is only 10 %, the maximum reaction temperature of the plant falls to 993 K, and the methane conversion rate drops to 68 %. At this time, the main factor affecting the oxidation performance of the plant is convective heat transfer. The influence of thermal radiation on oxidation performance gradually diminishes with an increase in intake velocity, and the proportion of radiative heat transfer decreases continuously. At methane concentrations above 1 %, the proportion of radiative heat transfer is less than 25 per cent, the maximum reaction temperature of the unit increases to 1087 K, and the methane conversion rises to 88 %. At this point, the main factor affecting the oxidation performance of the plant is convective heat transfer.

Effects of ZrO2 ceramics doped with varying content on the mechanical properties and energy release characteristics of W-Zr alloys

A W-Zr alloy doped with ceramic powder W54.5Zr35-xNi6.7Fe3.3Mo0.5 (ZrO2) x was prepared by powder metallurgy. The effects of the ceramic content on the dynamic and static compressive mechanical behavior and energy release properties of the alloy were studied. The results showed that the addition of ceramics enhanced the energy release characteristics of the W-Zr alloy, and made the alloy break more thoroughly and the fragment cloud distribute evenly. The reaction delay time was shorter and the energy release reaction was more complete. However, the maximum temperature of the alloy reaction decreased. In addition, the addition of ceramics improves the mechanical properties of the material, and its compressive strength is much higher than that of traditional W-Zr alloys.(ZrO2)1 exhibited good mechanical behavior and energy release characteristics. The aftereffect damage performance was further verified using a ballistic gun experiment. Ballistic gun test results showed that (ZrO2) 1 can penetrate A92124 aluminum targets with a thickness of 2 mm at a speed of 809.3 m s−1 and ignite post-target absorbent cotton, with both penetration and post-target damage capabilities.

Safe Operating Conditions of isoperiodic Homogeneous Semi-Batch Reaction Based on Parameter Uncertainties Analysis

Proper operating conditions have a significant impact on the process state of semi-batch reaction. However, various error and bias lead to the uncertainties of parameter, which affect process safety of the semi-batch reaction. In this work, the effect of dimensionless parameters dimensionless adiabatic temperature rise (), Westerterp number (Wt), , dimensionless activation energy (γ), volumetric heat capacity ratio (RH) and relative volume increase (ε) on the temperature of the isoperiodic homogeneous semi-batch reaction are investigated by local sensitivity analysis. The sensitivity of the dimensionless maximum temperature to global parameters is analyzed using the scatter plot method based on Monte-Carlo sampling. Parameter sensitivity results are further quantitatively calculated by the eFAST method. The results indicate that there is a strong linear relationship between the maximum reaction temperature and △τad,0, which exhibits the highest sensitivity index compared to the other parameters. The safety boundary diagram and adiabatic temperature diagram are constructed by considering parameter uncertainty and the effect of parameter uncertainty on the critical criteria is analyzed.

Microbial community assembly during aging of food waste-derived hydrochar: Key bacterial guilds mediate nutrient dynamics

Hydrochar aging may mitigate the adverse effects of direct hydrochar application on plant growth. However, little is known about the strategies for accelerating aging process and the microbiological mechanisms involved. This study explored the effects of three aging strategies, including the addition of straw and efficient-degrading microorganisms, on the aging processes of food waste-derived hydrochar, and identified the key microbial drivers. The bacterial and fungal sequencing was performed to estimate the species composition in hydrochar at different aging periods (i.e., day 1, 7, 14 and 35). The results showed that the addition of straw and microbial inoculum improved the maximum reaction temperature by 13%, and shortened the aging time by ∼30%. Three bacterial guilds, mainly including Bacillus-like species, were identified that showed significant correlations with the nitrogen and phosphorus dynamics during aging. This study demonstrates the feasibility of manipulating key microbial guilds artificially to achieve efficient harmless-treatment of hydrochar.

Evaluation of the activity of amine hardeners of epoxy resins

With the appearance of new epoxy resins and amines, which are widely used for hardening epoxy compositions using energy-saving technology (at "ordinary" temperatures), on the world market, the targeted selection of these materials to provide the desired technological and operational properties becomes relevant. In order to predictively choose amine hardeners for epoxy resins, their quantum-chemical calculations were performed using the semi-empirical parameterized 3 (PM3) method. The energy value of the highest occupied molecular orbital (HOMO) of amines and the absolute value of the energy gap || (the absolute difference in energies between the HOMO of amines and the lower vacant molecular orbital (LUMO) of epoxy resins) were used. The relationships between the absolute value of the energy gap || and the main technological parameters of the curing process of dian epoxy resin ED-20 with individual amines were established with pairwise correlation coefficients of not less than 0.977. The evaluation of the activity of modified polyamines and their mixtures in hardening epoxy resins is proposed to be carried out based on the maximum temperature of the exothermic reaction of interaction between the epoxy groups of resins and the amine groups of hardeners. The possibility of adjusting the temperature of the exothermic hardening reaction of epoxy compositions and their "viability" time by introducing epoxy-containing diluents with different values of the LUMO energy was shown.

Analysis of the Solar Pyrolysis of a Walnut Shell: Insights into the Thermal Behavior of Biomaterials

The state of Sonora, Mexico, stands as one of the leading producers of pecan nuts in the country, which are commercialized without shells, leaving behind this unused residue. Additionally, this region has abundant solar resources, as shown by its high levels of direct normal irradiance (DNI). This study contributes to research efforts aimed at achieving a synergy between concentrated solar energy technology and biomass pyrolysis processes, with the idea of using the advantages of organic waste to reduce greenhouse gas emissions and avoiding the combustion of conventional pyrolysis through the concentration of solar thermal energy. The objective of this study is to pioneer a new experimental analysis methodology in research on solar pyrolysis reactors. The two main features of this new methodology are, firstly, the comparison of temperature profiles during the heating of inert and reactive materials and, secondly, the analysis of heating rates. This facilitated a better interpretation of the observed phenomenon. The methodology encompasses two different thermal experiments: (A) the pyrolysis of pecan shells and (B) the heating–cooling process of the biochar produced in experiment (A). Additionally, an experiment involving the heating of volcanic stone is presented, which reveals the temperature profiles of an inert material and serves as a comparative reference with experiment (B). In this experimental study, 50 g of pecan shells were subjected to pyrolysis within a cylindrical stainless-steel reactor with a volume of 156 cm3, heated by concentrated radiation from a solar simulator. Three different heat fluxes were applied (234, 482, and 725 W), resulting in maximum reaction temperatures of 382, 498, and 674 °C, respectively. Pyrolysis gas analyses (H2, CO, CO2, and CH4) and characterization of the obtained biochar were conducted. The analysis of heating rates, both for biochar heating and biomass pyrolysis, facilitated the identification, differentiation, and interpretation of processes such as moisture evaporation, tar production endpoint, cellulosic material pyrolysis, and lignin degradation. This analysis proved to be a valuable tool as it revealed heating and cooling patterns that were not previously identified. The potential implications of this tool would be associated with improvements in the design and operation protocols of solar reactors.

Nitration of biodiesel by acetyl nitrate: Kinetic study and chemical safety parameters

The aim of this study was to synthesize a bio-sourced substitute to the 2-Ethyl Hexyl Nitrate (EHN) by nitrating a biodiesel. EHN is commonly used to improve the auto-ignition properties of diesel fuels. The biodiesel was obtained by trans-esterification of canola oil. The nitration reaction of biodiesel by acetyl nitrate was carried out in a reaction calorimeter RC1 with semi-batch mode to study its kinetic and exothermic behavior and acetyl nitrate as nitrating agent. The impact of the synthesis temperature on the thermal behavior and on the reaction medium composition was investigated. The final product was analyzed by using several analytical techniques such as iodine value, infrared spectrometry, GC–MS. Three nitrated products have been identified: Methyl-8-nitro oleate, Methyl-10-nitrate-9-nitrostearate and 10-acetoxy-methyl-9-nitrostearate, whose selectivity depends on the synthesis temperature. A chemical model for nitration is proposed and the thermal power profiles released by the reaction mixture are used to estimate the energy and chemical kinetic parameters. Safety parameters, maximum temperature of the synthesis reaction (MTSR) and TD24 were also determined. In addition, a Cooperative Fuel Research (CFR) engine was used to analyze the cetane number of diesel fuel mixed with our additive. The results showed an increase in cetane number by 6 points.

Beyond equilibrium ammonia synthesis in a membrane and heat exchange integrated microreactor: A modeling study

Ammonia (NH3) synthesis is modeled in a micro–structured membrane reactor (MR) comprising reaction, cooling and NH3 separation functions in the same volume. The proposed MR involves permeate and reaction channels segregated by layers of zirconia supported ZnCl2 immobilized molten–salt (IMS) membrane selective to NH3 transport. While H2 + N2 is fed to reaction channels washcoated with an iron–based catalyst, permeate channels host N2 as the sweep gas which also regulates reaction temperature. The in–situ cooled MR is modeled by considering mass, momentum and energy conservation in the fluid phases of the reaction and permeate channels, reaction in the catalyst layer and NH3 transport across the membrane, whose thermal stability limit of 623 K is set as the maximum reactor temperature. Upon N2 sweep dosing equal to 50 × the molar H2 + N2 input at H2/N2 = 3, 613 K, 50 bar and 1.5 × 103 m3 kgcat–1 s−1, MR can deliver ∼47 % N2 conversion which exceeds 40 and 13.5 % of the pertinent thermodynamic barrier and the membraneless case, respectively. Despite the exothermic heat release, co–current partitioning of the streams ensures operability below 623 K. Increasing space velocity and H2/N2 ratio, and decreasing inlet temperature and pressure inhibit reactor performance. Using molar sweep–to–reactive mixture ratios < 50 is penalized by the violation of the specified maximum temperature. Membrane integration can improve NH3 production by ∼3.5 times per unit amount of H2O consumed in its electrocatalytic conversion to H2.

Energy and exergy analysis of a novel solar-hydrogen production system with S–I thermochemical cycle

A novel hydrogen production system based on a sulfur-iodine (S–I) thermochemical water-splitting cycle driven by 100% solar energy is proposed in this paper. A solar power tower (SPT) with thermal energy storage (TES) is used to supply heat stably. Considering the large heat recovery potential in the S–I cycle, a supercritical carbon dioxide (S–CO2) Brayton cycle is used to improve the system performance. A complete thermodynamic model and detailed description of the energy and exergy flow from the sun to SPT, TES, S–I cycle, S–CO2 Brayton cycle and hydrogen is obtained. The system performance in the base case and actual weather conditions are obtained. The influence of major parameters on the system performance is investigated. The results show that the hydrogen production rate is 3.52 mol s−1 in the base case. Using the S–CO2 Brayton cycle, the overall energy and exergy efficiency can be increased from 10.6%, 11.1% to 30.5%, 32.4%, respectively. The solar part accounts for 48.2% of the total energy loss and 76.1% of the exergy destruction. In addition, increasing DNI, the maximum reaction temperature, the regeneration ratio of the S–CO2 Brayton cycle (RR) can improve the system performance, and the system efficiency is more sensitive to RR.

Effect of multilayered catalytic bed on temperature profiles and catalytic performance for Fischer–Tropsch synthesis over Co/Al2O3 catalyst in a multitubular fixed-bed reactor

Fischer-Tropsch synthesis (FTS) is a widely recognized process that catalytically converts syngas into higher hydrocarbons and oxygenates, which are ultimately upgraded into transportation fuels and chemicals. Effective temperature control and heat dissipation are crucial considerations due to the exothermic nature of the FT reaction. Underutilization of the catalytic bed is another challenge in fixed-bed reactors. The implementation of a multilayered catalytic bed, with the catalytic activity in an ascending order, has shown positive effects in addressing these issues. It mitigates adiabatic temperature rise, reduces the maximum reactor temperature, and minimizes catalyst deactivation at high temperatures. Moreover, this multilayered bed effectively addresses the underutilization issue by ensuring optimal utilization of the entire bed as the catalytic activity transitions from one layer to another during the reaction. Layers with a higher cobalt loading remain active until the completion of the reaction, resulting in minimal fluctuations in CO conversion. To achieve uniform temperature profiles, catalytic activities, and product distributions in all reactor tubes in a multitubular reactor, it is imperative to maintain consistent reaction conditions, utilize the same catalyst loading in all tubes, employ an appropriate heating system, and implement an efficient cooling system to dissipate the heat generated by the exothermic reaction. Furthermore, investigations into the properties of the used catalysts after the reaction indicate that catalyst deactivation primarily occurs due to the deposition of FT products on the catalyst surface and pores and blockage of active cobalt sites, and sintering of cobalt particles.

Combustion synthesis of Eu2O3 nanomaterials with tunable phase composition and morphology

Combustion reactions in europium nitrate – acetylacetone – 2-methoxyethanol solutions and gels were investigated to produce europium (III) oxide (Eu2O3) nanocrystalline materials and thin films. Thermal analyses of solutions indicated that the 2-methoxyethanol solvent also acts as a fuel in the absence of acetylacetone. Adding acetylacetone increases the overall heat of the reaction. Thermal analysis results revealed that the slow oxidation of unburned hydrocarbon residues follows the primary combustion reaction. Time-temperature profile measurements of the bulk combustion synthesis process in air and nitrogen atmospheres enabled the extraction of the maximum reaction temperature and the heating and cooling rates in the combustion zone. Several direct correlations exist between measured combustion parameters and the phase composition of the products. Combustion in air results in mixed-phase cubic and monoclinic nanocrystalline Eu2O3. Increasing the acetylacetone concentration in solutions increases the synthesis temperature and decreases the quantity of cubic Eu2O3. The reaction of solutions in a nitrogen atmosphere or diluted with Eu2O3 provides control of the product phase composition and reduces the quantity of the monoclinic phase. Transmission electron microscopy imaging shows that the Eu2O3 end products are highly porous aggregates of nanocrystalline particles. Electrospraying of reactive solutions onto different substrates followed by short annealing makes the preparation of Eu2O3 materials with diverse morphologies possible.

Preparation and structure analysis of aluminum oxide/water glass/polyurethane composite grouting material for mining

In order to achieve safer and more efficient coal mining, the utilization of water glass/polyurethane (WG/PU) composite grouting material has become widespread in treating fractured coal mining faces. The reaction temperature and mechanical properties of WG/PU are crucial considerations that significantly impact safety and reinforcement effectiveness. However, reducing the reaction temperature without compromising the material's mechanical properties poses a challenge with conventional modification methods. Therefore, this study presents the development of a novel hybrid grouting material, namely Al2O3-WG/PU, which incorporates thermally conductive aluminum oxide (Al2O3) into WG/PU. The response surface method was employed to investigate the effects of key factors such as modules, mass ratio, Al2O3 content, and plasticizer content on the reaction temperature and compressive strength. Additionally, the static and dynamic compression properties of Al2O3-WG/PU were measured and analyzed. The morphology, elemental distribution, chemical composition, and valence information of the composite materials were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the introduction of A2O3 and scientific formula design reduces the maximum reaction temperature of Al2O3-WG/PU by 14.9 °C (12.7%). Although the percentage reduction may not seem significant, it represents substantial progress in the field of coal mine grouting materials. Moreover, this modification method not only maintains the material's mechanical properties but also enhances its compressive strength by 13.84 MPa (27.3%). Based on the characterization results, this study proposes a mechanism for temperature reduction and strength enhancement. The hybrid composite materials produced from Al2O3 and WG/PU show lower reaction temperatures and improved mechanical properties, presenting a promising solution for improving the safety performance of coal grouting materials.

Thermal Risk Assessment of Sandmeyer Reaction from 5-Aminotetrazole (5-AT) to Hydronium Copper(II)-tris(5-nitrotetrazolate) trihydrate

5-NaNT was the raw key material of copper(I) 5-nitrotetrazolate (DBX-1) and tetraaminecis-bis(5-nitrotetrazolato) cobalt(III) perchlorate (BNCP), which was prepared from 5-AT by Sandmeyer reaction. This reaction was usually happened slightly blast due to release heat and nitrogen gas during whole procession. In order to enhance the safety of reaction, differential scanning calorimetry (DSC) was used to measure exothermal of reaction solution and intermediate, reaction calorimeter (RCle) was used to assess the thermal risk, adiabatic calorimeter (RAC) was used to estimate the stability of technological process and hydronium copper(II)-tris(5-nitrotetrazolate) trihydrate (Cu(H-NT)(NT)2(H2O)4) which was intermediate for 5-NaNT. The Td24 was 168h, the maximum temperature of the synthesis reaction (MTSR) was 17°C, adiabatic temperature rise was 43 K, the maximum heat accumulation was 9%, the specific heat release was 3654 kJ/kg. The result shown that dangerous chemical processes risk rank was 1, which mean that the risk of this reaction was relatively low. Matrix evaluation of thermal runaway reaction was level 1, it was that immediately cut off the feed raw material was useful if the cooling system out of service.

Thermal air oxidation of UO2: Joint effect of precursor's nature and particle size distribution

The rate and extent of the air oxidation of UO2 are of paramount importance due to its relevance in the management of spent nuclear fuel at dry storage facilities. In particular, the formation of U3O8 requires special interest because it could compromise the integrity of the fuel cladding. In an attempt to reproduce the behavior of used fuel (in which the presence of fission products and Pu will also influence the oxidation), unirradiated UO2 was studied in this work. UO2 oxidation is strongly dependent on physical parameters of the starting material, although some parameters are not fully-studied. In the present study, the nature of the UO2 starting material and the particle size distribution on thermal oxidation temperature were evaluated in detail. Since UO2 oxidation follows a complex kinetic mechanism comprising various crystalline phases, which composition and quantity change influenced by temperature and oxidant gas phase, oxidation conditions were set to favor the formation of U3O8, due to its practical importance, as well as to study the impact of the physico-chemical properties of raw material in UO2 oxidation. Various powdered sample substrates ranging from synthetic UO2 (prepared via ADU route) to grinded and sieved fragments of fresh UO2 pellets were oxidized in the same conditions. The average O/U atomic ratios of the samples were calculated by assuming total conversion to U3O8 from data of thermogravimetric analysis (TGA). Each weight variation curve was characterized and discussed in terms of the Oxidation Onset Temperature (OOT), the Maximum Reaction Temperature (MRT), and the Reaction Rate at the maximum reaction temperature (RRMRT). Scanning Electron Microscopy (SEM) was employed to evaluate the surface morphology. All thermally oxidized samples exhibit the presence of oxides with spallation. Surface morphology of starting materials confirms the different nature of the samples, while the oxidized substrates present the typical pop-corn-like particles. In order to accomplish a better description of UO2 oxidation, the results are discussed relative to the nature of different UO2 precursors, surface area and particle size. The nature of the starting materials affects the rate of U3O8 formation, being faster in synthetic powders than in powder coming from milled pellets. By comparing materials with the same origin, the effect of the width of the particle size distribution is proved for the first time, being the oxidation to U3O8 slower in the substrate with a wider distribution (labelled material P3). Since P3 is more similar to a real irradiated fuel pellet, from a mechanistic point of view, this work present valuable input to security studies of dry storage facilities for spent fuel.

Study on the Emission Characteristics in Renewable Energy Combustion under Different Working Conditions of Marine Two-Stroke Diesel Engine

In this paper, MAN 6S35ME-B9 two-stroke diesel engine is taken as the research object. By constructing a detailed combustion reaction mechanism including CH4, C4H10O, nitrides and other substances, CHEMKIN-PRO is used to simulate the same fuel mixing ratio and excess air coefficient. Under the condition of 1.5, the temperature, NO mole fraction and NH3 mole fraction in the reactor change and study the factors affecting the pollutant emission of marine diesel engine with the crank angle under different working conditions. The simulation shows that with the decrease of diesel engine speed, the maximum temperature of combustion reaction and the temperature at exhaust opening are obviously reduced. At the same time, mole fraction of NO and NH3 decreases with the decrease of rotational speed, and there is no nitride production in the combustion reaction at 25%.

Controlled preparation of core-shell SiC/graphene powders by combustion synthesis

High-purity SiC/graphene powders with the core-shell structure were controllably prepared by combustion synthesis from Mg/SiC powders in 0.5 MPa CO 2 atmosphere. The maximum reaction temperatures were much higher than 1000℃, greatly promoting the vapor reaction between Mg and CO 2 . The thickness of synthesized graphene can be well regulated in the range of 1-10 layers by changing the Mg/SiC mass ratio in the raw materials. The graphene layers were complete and uniformly coated on the surface of SiC particles. The interface between SiC and graphene was clear and well bonded without any interface separation or amorphous layer. Further, core-shell SiC/graphene powders synthesized in this work have great potential for application in the field of electromagnetic shielding, photocatalysis, etc. • Core-shell SiC/graphene powders were controllably prepared by combustion synthesis. • The thickness of graphene can be well regulated in the range of 1-10 layers. • A clear interface with the good interface bonding exists between SiC and graphene.

Molybdenum Oxide Precursors that Promote the Low-Temperature Formation of High-Surface-Area Cubic Molybdenum (Oxy)nitride.

Molybdenum nitrides and oxynitrides have been increasingly realized as (electro)catalysts for a variety of reactions. In this context, the cubic "γ-Mo2N", also known to contain oxygen in the bulk, is of particular interest. The γ phase is typically derived from ammonolysis of MoO3, and a high temperature is needed to fully react the stable MoO2 intermediate that often forms along the reaction pathway. In this study, ammonolysis of atypical bronze (HxMoO3) and peroxo (H2MoO5) precursors was undertaken to avoid the formation of this undesired intermediate with the aim of synthesizing "γ-Mo2N" at reduced temperatures and thus with a high surface area. It was found, using in situ powder diffraction, that, when the phase I bronze (x ≈ 0.3) served as the precursor, MoO2 formed as an intermediate and was retained in the reaction product until 700 °C. In contrast, ammonolysis of the phase III bronze (x ≈ 1.7) and of H2MoO5 circumvented the MoO2 intermediate. From these latter two precursors, "γ-Mo2N" was formed at the lowest maximum reaction temperatures reported in the literature, namely, 480 °C in the case of HxMoO3-III and 380 °C for H2MoO5. The resulting products displayed extremely high surface areas of 206 and 152 m2/g, respectively, presumably as a consequence of the low synthesis temperatures. While the HxMoO3-III precursor showed evidence of a topotactic transformation pathway, with morphological similarity between precursor and product phases, H2MoO5 transformed via amorphization. Electrochemical characterization showed moderate activity for the hydrogen evolution reaction (HER), which increased after exposure to reducing potentials and loosely scaled with the catalyst-specific surface area. This work points toward new low-temperature synthesis pathways for accessing molybdenum (oxy)nitrides with high surface areas.