High-temperature Reactor Research Articles

Blue‐Light Enhanced Iron Catalysed Hydrosilylation of Carboxamides and Carboxylic Esters at Ambient Conditions

AbstractWe report herein a blue‐light‐promoted iron‐catalyzed reduction of carboxamides and carboxylic esters. Conducting the reaction under hydrosilylation conditions and blue light (2×24 W, 450–460 nm) in the presence of an iron(0) based pre‐catalyst, Fe(CO)4(IMes), amines and alcohols were obtained, respectively, notably at ambient conditions, whereas using white light, higher reaction temperatures up to 100 °C were required. Preliminary mechanism studies highlighted the crucial role of blue light not only to generate the catalytic active species, but also in some steps of the catalytic cycle.

Congestion of steric and electronic factors in α-diimine nickel precatalysts for high-temperature ethylene polymerization in accessing direct PE elastomer

In α-diimine-nickel catalysts mediated ethylene polymerization, the synergistic impact of steric and electronic factors plays an instrumental role in fine-tuning catalytic activity, polymer molecular weights, microstructure, as well as mechanical and elastic properties. In this study, a new series of nonsymmetrical bis(arylimino)-acenaphthene-nickel complexes was prepared and investigated for ethylene polymerization. These complexes feature both bulky N-2,6-dibenzhydryl-3,4,5-fluorophenyl imine and smaller N-2,6-di(R)-4-(R1)phenyl imine units [Ni2Me (R, = Me, R1 = H), Ni2Et (R, = Et, R1 = H) and Ni2iPr (R, = iPr, R1 = H), Ni3Me (R, R1 = Me), Ni2Et,Me (R, = Et, R1 = Me)]. The incorporation of both steric congestion and strong electronic withdrawal groups into the catalyst structure resulted in significantly improved catalytic performance: high thermal stability and exceptional activity were observed at both ambient temperature (21.24 × 106 at 30 °C) and industrially relevant temperatures (1.65 × 106 at 100 °C). Polymer molecular weights and branching degree were tunable by adjusting the ligand structure and reaction conditions. This correlation extended to mechanical and elastic properties, demonstrating high tensile strength at low temperatures and good elastic recovery at high reaction temperatures, consistent with typical polyolefin elastomers.

Optimizing Mo2C-based catalytic system for efficient CO2 conversion and CO selectivity through carbon-nitrogen supporting and potassium promotion

Preparing highly active, stable, and selective catalysts for the reverse water gas shift (RWGS) reaction is challenging because of the aggregation of the active catalyst at high RWGS reaction temperatures and deactivation of the active sites. Herein, we present a comparative evaluation and optimization of a molybdenum carbide system using a carbon-nitrogen (CN) support and alkali promotion. Hydrothermally prepared MoO3 nanorods were carburized at 700 °C using H2:CO (4:1) to prepare unsupported Mo2C, while CN-supported Mo2C (Mo2C@CN) was prepared using Mo-based metal-organic framework (Mo-MOF) as a sacrificial template. The as-prepared Mo2C@CN catalytic system was found to be highly active in the RWGS reaction in comparison with the unsupported Mo2C, where CO2 conversion percentage was around 76 % at 700 °C, combined with high CO selectivity (87 %) and very reduced CH4 selectivity (2 %). The addition of potassium as a promoter enhanced CO selectivity (99 %). The active catalyst performance was stable during the catalysis process and for up to 100 h, which imposes the effect of the CN support in preventing the aggregation of Mo2C and keeping its active sites in direct contact with the reactant. This work presents an effective strategy for improving the active catalyst dispersion and reducibility in synergy with the promoter effect to optimize the RWGS reaction output.

Cr as a promoter for the In2O3-catalyzed hydrogenation of CO2 to methanol

The utility of Cr as a promoter for In2O3 catalysts in the hydrogenation of CO2 to methanol is investigated. Uniform precursors to binary CrOx-In2O3 and ternary NiO-CrOx-In2O3 catalysts are prepared by flame spray pyrolysis. For the CrOx-In2O3 samples, the highest methanol rate is obtained at a Cr content of 2 mol%, exceeding the methanol rate of In2O3 by 55 %. With increasing Cr content, the CO2 conversion rate does not increase, albeit the methanol selectivity decreases. Characterization of the samples supported by density functional theory calculations provides insight into the role of Cr. At low content, Cr is mainly doped into the lattice of In2O3, which leads to more oxygen vacancy (Ov) sites. The In2O3 surface sites close to Cr-oxide clusters present on the surface are also activated towards Ov formation, offsetting the decrease in Ov due to coverage of the In2O3 surface by Cr-oxide with increasing Cr content. Cr2O3 dispersed on the surface of the In2O3 particles suppresses sintering of In2O3 under reducing conditions, which is especially evident at a Cr content above 2 mol% and higher reaction temperatures. Introducing Ni to the CrOx-In2O3 catalysts results in a higher methanol formation rate compared to CrOx-In2O3. The methanol rate increases with the Ni content with the highest activity obtained at Ni and Cr contents of 22 mol% and 8 mol%, respectively. The optimum Ni(22)-Cr(8)-In2O3 catalyst displays twice the methanol rate of a Ni(22)-In2O3 reference. Ni and Cr play different promoting roles in achieving an increased and more stable rate of methanol formation compared to In2O3: Ni promotes the hydrogenation of formate and methoxy surface intermediates to methanol, while Cr results in more Ov sites and suppresses sintering of In2O3.

Development of a micro-infrared thermometry method for surface temperature distribution and variation of millimeter particle during high-temperature reaction

Temperature strongly affects the conversion efficiency, local reactivity, and particle stabilization of the reactions, particularly at high temperature. This study integrated infrared thermography with a high-temperature hot stage reactor to develop a methodology of continuous temperature measurement for a single particle reaction at high temperatures. The external optical transmission transmittance and temperature field core were corrected, and the relationship between the measured temperature (Tr) and true temperature (T0) was obtained by adjusting the sample emissivity. Sample temperature with known emissivity at elevated temperature was measured with 1% deviation. The instantaneous temperature measurement for the gasification process was carried out and the overall emissivities of coal particles were corrected. Temperature distribution and variation on the coal particle surface during the gasification process were further obtained and consistent with the previous research results. The proposed online temperature measurement method provides a new approach for gaining insights into particle reaction states.

Temperature Effects of Nuclear and Electronic Stopping Power on Si and C Radiation Damage in 3C-SiC.

Silicon carbide has been considered a material for use in the construction of advanced high-temperature nuclear reactors. However, one of the most important design issues for future reactors is the development of structural defects in SiC under a strong irradiation field at high temperatures. To understand how high temperatures affect radiation damage, SiC single crystals were irradiated at room temperature and after being heated to 800 °C with carbon and silicon ions of energies ranging between 0.5 and 21 MeV. The number of displaced atoms and the disorder parameters have been estimated by using the channeling Rutherford backscattering spectrometry. The experimentally determined depth profiles of induced defects at room temperature agree very well with theoretical calculations assuming its proportionality to the electronic and nuclear-stopping power values. On the other hand, a significant reduction in the number of crystal defects was observed for irradiations performed at high temperatures or for samples annealed after irradiation. Additionally, indications of saturation of the crystal defect concentration were observed for higher fluences and the irradiation of previously defected samples.

Roadmap of Graphite Moderator and Graphite-Matrix TRISO Fuel Management Options

Most high-temperature reactors use graphite as a moderator and structural material. This includes high-temperature gas-cooled reactors with helium cooling and TRi-structural ISOtropic (TRISO) fuel particles embedded in graphite, as well as fluoride salt–cooled high-temperature reactors with clean salt coolant and TRISO fuel particles embedded in graphite and thermal spectrum molten salt reactors with a graphite moderator and fuel dissolved in the salt. The largest volume radioactive waste stream from these reactors is the irradiated graphite. We describe herein a roadmap for management of these graphite wastes that contain radioactive 14C, tritium, and other radionuclides. There may be some graphite wastes with sufficiently low radioactivity levels that can be treated as nonradioactive waste and managed like other graphite waste. Management options for the graphite include (1) direct disposal, (2) recycled back to the reactor or other nuclear applications, and (3) oxidizing the graphite with release as an effluent or underground sequestration of the carbon dioxide. Cosequestration of this carbon dioxide with carbon dioxide from industrial, biological, and cement production processes can isotopically dilute the 14C before sequestration to eliminate the possibility of exceeding individual radiation exposure limits. We also describe options for processing graphite-matrix TRISO fuel, including separating the bulk graphite to reduce the volumes of used fuel for disposal or processing to recover fissile materials. The inventories of radioactive isotopes in different carbon wastes vary by many orders of magnitude; thus, there is no single economic option for the management of all graphite waste.

The efficient synthesis of Pregabalin with impurity control using a continuous flow system

This article developed a microreactor system for the continuous synthesis of Pregabalin. Due to the exceptional heat transfer and mixing capabilities exhibited by the system at the microscale, the Hofmann rearrangement reaction, traditionally requiring multiple sequential steps in batch reactors, can now be efficiently achieved in a consolidated single-step microreactor process. The reaction was executed at a comparatively elevated temperature range of 40–50 °C, and took 5–6 min to achieve the yield of over 90 %, which was a significant improvement compared to the conventional batch reactor method, requiring 7–8 h with a yield of 83 %. The microreactor system utilized its excellent mass and heat transfer performance to reduce the level of the key impurity to below 0.15 % at higher reaction temperatures, meeting the quality requirements for pharmaceutical production. Through experimental research, we determined the effects of reaction conditions like concentration, temperature, and residence time on the reaction rate, as well as key trace impurities.

An Unprecedented [BO2]-Based Deep-Ultraviolet Transparent Nonlinear Optical Crystal by Superhalogen Substitution.

Solid-state structures with the superhalogen [BO2]- have thus far only been observed with a few compounds whose syntheses require high reaction temperatures and complicated procedures, while their optical properties remain almost completely unexplored. Herein, we report a facile, energy-efficient synthesis of the first [BO2]-based deep-ultraviolet (deep-UV) transparent oxide K9[B4O5(OH)4]3(CO3)(BO2) ⋅ 7H2O (KBCOB). Detailed structural characterization and analysis confirm that KBCOB possesses a rare four-in-one three-dimensional quasi-honeycomb framework, with three π-conjugated anions ([BO2]-, [BO3]3-, and [CO3]2-) and one non-π-conjugated anion ([BO4]5-) in the one crystal. The evolution from the traditional halogenated nonlinear optical (NLO) analogues to KBCOB by superhalogen [BO2]- substitution confers deep-UV transparency (<190 nm), a large second-harmonic generation response (1.0×KH2PO4 @ 1064 nm), and a 15-fold increase in birefringence. This study affords a new route to the facile synthesis of functional [BO2]-based oxides, paving the way for the development of next-generation high-performing deep-UV NLO materials.

An Unprecedented [BO2]‐Based Deep‐Ultraviolet Transparent Nonlinear Optical Crystal by Superhalogen Substitution

AbstractSolid‐state structures with the superhalogen [BO2]− have thus far only been observed with a few compounds whose syntheses require high reaction temperatures and complicated procedures, while their optical properties remain almost completely unexplored. Herein, we report a facile, energy‐efficient synthesis of the first [BO2]‐based deep‐ultraviolet (deep‐UV) transparent oxide K9[B4O5(OH)4]3(CO3)(BO2) ⋅ 7H2O (KBCOB). Detailed structural characterization and analysis confirm that KBCOB possesses a rare four‐in‐one three‐dimensional quasi‐honeycomb framework, with three π‐conjugated anions ([BO2]−, [BO3]3−, and [CO3]2−) and one non‐π‐conjugated anion ([BO4]5−) in the one crystal. The evolution from the traditional halogenated nonlinear optical (NLO) analogues to KBCOB by superhalogen [BO2]− substitution confers deep‐UV transparency (&lt;190 nm), a large second‐harmonic generation response (1.0×KH2PO4 @ 1064 nm), and a 15‐fold increase in birefringence. This study affords a new route to the facile synthesis of functional [BO2]‐based oxides, paving the way for the development of next‐generation high‐performing deep‐UV NLO materials.

Startup and Multiphysics Analysis of a Compact kW-Class Thermal Spectrum Microreactor

Self-regulating compact nuclear microreactor concepts are being developed for use in space and at terrestrial remote sites. The current emphasis is on the development of high-assay low-enriched uranium–fueled reactors that rely on metal hydrides to achieve size, specific weight, and power parity with the legacy highly enriched uranium systems. In the case of terrestrial applications, metal hydride–moderated systems can also improve economic feasibility. The neutronic design of metal hydride–moderated high-temperature reactor cores is complicated by the need to optimize and synchronize delayed spatial and temporal reactivity feedback from outer reflectors. Zebra is a thermal spectrum proof-of-principle core designed for demonstrating the reactor dynamics of hydride-moderated spectrum reactors, which is studied in this work. The reactor, including the fuel, yttrium hydride moderator, heat pipes, central control rod, structural supports, and the beryllium reflector, weighs ~425 kg. The design shares several features common with nuclear criticality test geometries routinely used in National Criticality Experiments Research Center (NCERC) experiments such that a prototype of the reactor can be readily assembled and tested. Additional features, such as heat pipes and hydrogen barrier clads, were added to minimize the potential for large thermal gradients that in turn could induce hydrogen loss or structural deformation during extended periods of operation at ~1000 K. In this work, normal and off-normal state performance of the Zebra rector core was analyzed using MCNP and Abaqus-based Reactor Multiphysics (MARM) software. Up-to-date nuclear, thermal, and mechanical performance data were used to characterize the performance of the yttrium hydride moderator. Steady-state analyses established that at a postulated power between 20 and 50 kW(thermal), the reactor core is nearly isothermal irrespective of quality of conduction coupling between heat pipes and fuel plates. Additionally, heat pipe failure modes, including simultaneous failure of all heat pipes in a quadrant of a reactor, were examined to bound the maximum credible temperature spike in the reactor core for extreme off-normal operating conditions. Finally, we detail the startup design challenges for the hydride-moderated thermal core, and analyze load-following cases to achieve “self-regulation” using the Dynamic Analysis of Reactor Transients module of MARM. The reactor is self-regulating with a reactivity temperature coefficient of ~−1 pcm/K at the operating point based solely on nuclear cross-section feedback. It can be further strengthened using additional spectral shift neutron absorbers and incorporating design features that enhance core expansion. This work captures that hydride-moderated systems are feasible for various self-regulating applications once systematic checks are verified in order to achieve a well-engineered core design.

Experimental investigation on the origin of carbonaceous materials in the fault zone of the Wenchuan earthquake

Carbonaceous materials in seismic fault zones may considerably influence seismic fault slip; however, the formation mechanism of carbonaceous materials remains unclear. In this study, we proposed a novel hypothesis for the formation of carbonaceous materials in fault gouge. Thus, we conducted a CO2 hydrogenation experiment in a high-temperature reactor at a co-seismic temperature, with fault gouge formed during the Wenchuan earthquake as the catalyst. Our experimental results demonstrate that carbonaceous materials in fault zones are formed on the fault gouge during the chemical reaction process, suggesting that the carbonaceous materials are possibly generated from the catalytic hydrogenation of CO2, followed by thermal cracking of its products. The results of this study provide a theoretical basis for understanding fault behavior and earthquake physics.

Thermohydraulic Analysis of Coolant Entry Patterns in a High-Temperature Pebble Bed Reactor: Insights and Characterization

Thermohydraulic Analysis of Coolant Entry Patterns in a High-Temperature Pebble Bed Reactor: Insights and Characterization

Evaluation of nanocrystalline ZrC under gamma irradiation and high pressure

Zirconium carbide (ZrC) is known for its exceptional properties, positioning it as a leading ultrahigh-temperature ceramic for diverse applications such as coating, oxygen-gettering, and inert matrix utilization in advanced high-temperature reactor fuels. Its impressive resistance to fission product corrosion, superior fission product retention capabilities, and resilience against hydrogen corrosion further highlight its significance in these fuel systems. In this work, the structural properties of zirconium carbide crystals (particle size of 20 nm) irradiated with 60Co gamma source were investigated at absorption doses from 300 kGy up to 3000 kGy using X-ray diffraction (XRD). Furthermore, the crystallinity properties of the crystals under high-pressure conditions were examined using the Small-angle X-ray Scattering (SAXS)/Wide-angle X ray scattering (WAXS) Xeuss 3.0 system. A comparative analysis of theoretical calculations and experimental results was conducted. The crystalline size experienced a decrease, while the microhardness showed variation. ZrC was identified to possess an Face Centered Cubic (FCC) – B1 structure of transition metal carbides (TMCs), with specific atomic arrangements. Under high pressure conditions, ZrC exhibits a shift to higher two-theta angles with compression of all diffraction peaks, without the formation of new peaks, up to a pressure of 9.0 GPa.

Synergistic effect of Ru single atom and nanoparticle on photothermal methane dry reforming reaction

Dry reforming of methane is indeed an attractive pathway for converting greenhouse gases into syngas. However, owing to the strong-endothermic nature of this reaction, high reaction temperature is commonly involved which causes high energy consumption, catalytic deactivation by sintering of active species, and/or coke formation. Herein, a RuSA+NP/TiO2 composite catalyst consisting of uniformly dispersed Ru nanoparticles (RuNP) and Ru single atoms (RuSA) on TiO2 sheet is fabricated. This catalyst demonstrates remarkable syngas generation rates of 1380 mmol g-1h−1 for CO and 933 mmol g-1h−1 for H2 at 500 °C under light irradiation. It is concluded that the presence of Ru single atoms modulates the electronic structure of catalyst, reducing energy barrier in the DRM process. Additionally, the electron-deficient Ru nanoparticles provide effective sites for CH4 dissociation. Light irradiation is found to reduce the apparent activation energy (Ea) of DRM and enhance durability of catalyst by retarding coking process.

Optimized preparation of Ni-Febm bimetallic particles by ball milling NiSO4 and iron powder for efficient removal of triclosan

The excessive usage and emissions of triclosan (TCS) pose a serious threat to aquatic environments. Iron-based bimetallic particles (Pd/Fe, Ni/Fe, and Cu/Fe, etc.) were widely used for the degradation of chlorophenol pollutants. This study proposed a novel synthesis method for the preparation of Ni/Fe bimetallic particles (Ni-Febm) by ball milling microscale zero valent iron ZVI (mZVI) and NiSO4. Ball-milling conditions such as ball-milling time, ball-milling speed and ball-to-powder ratio were optimized to prepare high activity Ni-Febm bimetallic particles. During the ball-milling process, Ni2+ was reduced to Ni0 and formed a coupled structure with ZVI. The amount of Ni0 on ZVI significantly affected the activity of Ni-Febm bimetallic particles. The highest activity Ni-Febm bimetallic particles with Ni/Fe ratio of 0.03 were synthesized under optimized conditions, which could remove 86.56% of TCS (10 μM) in aerobic aqueous solution within 60 min. In addition, higher particle dosage, lower pH condition and higher reaction temperature were more conducive for TCS degradation. The higher corrosion current and lower electron transfer impedance of Ni-Febm bimetallic particles were the main reasons for its high activity. The hydrogen atom (•H) on the surface of Ni-Febm bimetallic particles was mainly contributed to the removal of TCS, as reductive transformation products of TCS were detected by LC-TOF-MS. Notably, a small amount of oxidation products were discovered. The total dechlorination rate of TCS was calculated to be 39.67%. After eight reaction cycles, the residual Ni-Febm bimetallic particles could still degrade 28.34% of TCS within 6 h. Low Ni2+ leaching during reaction indicated that Ni-Febm bimetallic particles did not pose potential environmental risks. The prepared environmental-friendly Ni-Febm bimetallic particles with high activity have great potential in the degradation of other chlorinated organic compounds in wastewater.

Thermodynamic and economic analysis of hierarchical gas–gas nuclear power plants and CHPs with high-temperature reactors and helium as the circulating medium

This paper presents the results of thermodynamic and economic analyses of innovative, gas–gas nuclear power plants and CHP plants with high-temperature gas-cooled reactors (HTGRs). In these power plants, two Joule cycles are performed in a hierarchical system. One is performed in the high-temperature range, the other in the low-temperature range. The reactor coolant is helium. It is also the circulating medium in the whole gas–gas system. The results of the thermodynamic and economic analyses presented in this paper cover a wide range of thermal capacities of HTGRs, from 100 to 3000 MW.

Catalytic reduction of U(Ⅵ) to U(Ⅳ) using hydrogen as the sole reducing agent

Using hydrogen gas as a sole reducing agent to catalyze the reduction of hexavalent uranium to prepare tetravalent uranium can avoid the problem of pollutant poisoning catalysts caused by hydrazine reducing agents. However, research using only hydrogen as the sole reducing agent is very scarce. Herein, catalyst has been developed for catalytic hydrogen reduction to prepare uranium(Ⅳ) and a systematic study of the influence of process parameters such as catalyst carrier particle size, temperature, pressure, and acidity on the catalytic hydrogen reduction process for the preparation of uranium(Ⅳ) is presented. The effect of catalyst carrier particle size is particularly pronounced due to the differing rates of molecular diffusion. Fine particle-sized catalyst carriers exhibit faster catalytic reaction kinetics. Temperature exhibits an unusual phenomenon in its impact on the reaction process. As temperature increases, the reaction rate decreases, and an upper limit reaction temperature is observed. Furthermore, at excessively high reaction temperatures, an anomalous occurrence of uranium(Ⅳ) formation followed by disappearance was observed. Through an analysis of the reaction mechanism, the underlying reasons for this abnormal phenomenon are elucidated. Additionally, this paper also reveals that reaction rates increase with increasing reaction pressure and decrease with decreasing raw material acidity. Process parameters such as reaction temperature, pressure, and acidity exhibit coupled effects on the reaction process. Different reaction upper limit temperatures are observed under varying pressures and raw material acidities.

Investigation into the photothermal catalytic CO2 decomposition over CeO2 with different morphologies: Behaviors of oxygen vacancies

CO2 is a viable renewable energy source, as global CO2 emissions are perennially increasing. The decomposition of CO2 to CO and O2 through high-temperature cracking of metal oxides via a two-step thermochemical cycle has been an effective strategy to reduce CO2 concentrations in the atmosphere. However, this thermochemical cycle requires a high reaction temperature (1273 K). Hence, in this study, we investigated photothermal CO2 decomposition over three CeO2 catalysts with different morphologies: porous CeO2 nanosheets (2D-CeO2), cubic-shaped CeO2 (C-CeO2), and octahedral CeO2 (O-CeO2). The photothermal synergistic effect eliminated the necessity of high temperatures, where light illumination increased the generation of oxygen vacancies and electron transfer to promote CO2 decomposition. The maximum rate of CO production by 2D-CeO2 at 250 °C was 69 μmol g-1h−1, which is significantly higher than those of O-CeO2 (47 μmol g-1h−1) and C-CeO2 (19 μmol g-1h−1). However, no activity was observed in dark conditions, even at 250 °C. In-situ DRIFTS, quasi in-situ EPR, XPS, and Ar-TPD experiments revealed that light irradiation promotes the production of oxygen vacancies on the catalyst surface and generates the intermediate CO2•− species, which cleave the C=O bonds and CO2 conversion, while temperature promotes the adsorption of CO2 on the catalyst surface and facilitates electron transfer. DFT calculations revealed the differences in oxygen vacancy formation and CO2 adsorption among various exposed crystal facets of CeO2. These findings provide new avenues for CO2 decomposition based on the adsorption and activation of CO2 on metal oxide surfaces and the low-temperature synergistic photothermal effect.

A new perspective on density and strength loss profiles at the surface of thermally oxidized nuclear graphite

Oxidation of graphite components could influence their designed life in a high-temperature nuclear reactor. The oxidized regions could potentially lower the allowed stress capacity. The American Society of Mechanical Engineers rules for the design and construction of graphite-moderated reactors recommend that subsurface regions that might become excessively damaged by oxidation during reactor operation be identified and excluded from geometry and stress calculations. Identification of oxidation-affected regions is possible, in principle, through complex modeling exercises of reactor behavior during hypothetical accident scenarios coupled with graphite oxidation models, but this procedure may not have the precision needed for informed decisions. This paper proposes an alternate method, based on interpretation of a series of well-designed oxidation experiments, which could augment the designer's tools. The procedure is illustrated by data on oxidation by air of several graphite grades (NBG-18, PCEA, IG-110, R4-650) that are corroborated with independent literature information, when available. The Wichner model for graphite oxidation used for this analysis provides conservative results that could be quickly implemented in the design process.