Gas-phase Reactions Research Articles

Reaction of SO3 with H2SO4 and its implications for aerosol particle formation in the gas phase and at the air–water interface

Abstract. The reactions between SO3 and atmospheric acids are indispensable in improving the formation of aerosol particles. However, relative to those of SO3 with organic acids, the reaction of SO3 with inorganic acids has not received much attention. Here, we explore the atmospheric reaction between SO3 and H2SO4, a typical inorganic acid, in the gas phase and at the air–water interface using quantum chemical (QC) calculations and Born–Oppenheimer molecular dynamics simulations. We also report the effect of H2S2O7, the product of the reaction between SO3 and H2SO4, on new particle formation (NPF) in various environments using the Atmospheric Cluster Dynamics Code (ACDC) kinetic model and QC calculations. The present findings show that the gas-phase reactions of SO3 + H2SO4 without and with water molecules are both low-energy-barrier processes. With the involvement of interfacial water molecules, H2O induced the formation of the S2O72-⋯H3O+ ion pair, HSO4- mediated the formation of the HSO4-⋯H3O+ ion pair, and the deprotonation of H2S2O7 was observed and proceeded on the picosecond timescale. The present findings suggest the potential contribution of the SO3–H2SO4 reaction to NPF and aerosol particle growth, showing that (i) although H2S2O7 is easily hydrolyzed with water to form H2SO4, it can directly participate in H2SO4–NH3-based cluster formation and can present a more obvious enhancement effect on SA–A-based cluster formation, and (ii) the formed interfacial S2O72- can attract candidate species from the gas phase to the water surface and, thus, accelerate particle growth.

Investigation of unexpected silane ions caused by gas-phase reactions in Orbitrap gas chromatography-mass spectrometry.

The mass spectra of compounds containing dimethyl (phenyl)silyl group (-SiMe2Ph) sometimes exhibit unusual ion peaks when measured using Orbitrap gas chromatography-mass spectrometry (GC-MS). This would complicate the mass spectra and may limit the matching of spectral data with preexisting resources for compound annotation. These peaks were identified as products from reactions with residual water. A series of dimethyl (phenyl)silyl compounds were dissolved in methanol and investigated using Orbitrap GC-MS. Certain ions reacted with residual water in the C-trap. The reaction was confirmed using accurate mass and elemental composition analysis via MS studies, and the active center of the reaction was determined using density functional theory (DFT) calculations. Two types of gas-phase reactions between gaseous water and cations from a series of silanes were identified. DFT calculations indicate that silicon (Si) acts as the active center for these gas-phase water reactions. Compounds with multiple Si atoms generate a larger number of additional ions, which would complicate the mass spectra. The mass spectra of vinylsilanes and alkylsilanes with -SiMe2Ph indicate that the conjugated group linked to -SiMe2Ph can affect the water adduction process. Silane ions could react with residual water in the C-trap of an Orbitrap mass spectrometer. The mass spectra of these compounds may exhibit unexplained peaks arising from gas-phase reactions. Although these reactions may decrease spectral matching scores for compound annotation, they offer opportunities for systematic investigations into the mechanistic and kinetic aspects of high-energy ion reactivity.

Effectiveness of Noble Gas Addition for Plasma Synthesis of Ammonia in a Dielectric Barrier Discharge Reactor

Non-thermal plasma driven ammonia synthesis has great potential for future industrial applications due to its low theoretical energy requirements. To achieve technological advancement and environmental sustainability, it is crucial to boost the energy yield in plasma-assisted ammonia synthesis. Therefore, optimizing energy transfer and utilization are key strategies for enhancing energy efficiency. In this study, dielectric barrier discharge driven by a nanosecond pulsed power supply is used to enhance plasma-assisted ammonia synthesis by controlling the energy transfer through the addition of noble gases. It was found that the addition of noble gases changed the plasma characteristics, significantly improved the uniformity of the discharge, and achieved a high energy yield for ammonia synthesis. The effects of additive amounts of argon (Ar) and helium (He), as well as the pulse parameters including the pulse voltage, pulse repetition frequency, pulse width, and pulse rise time on the energy yield of ammonia synthesis are discussed. The inclusion of noble gases expanded the pathway for gas-phase reactions, with the active components of critical reactions examined through optical emission spectra. This analysis revealed an increased presence of both N2+ and N2* particles in the reaction’s rate-limiting step, attributed to the addition of noble gases. Finally, a zero-dimensional (0D) plasma chemical kinetic model was established to investigate the influence of Ar addition on the reaction mechanism of ammonia synthesis.

Retrofit and application of pulverized coal burners with LNG and oxygen ignition in utility boiler under ultra-low load operation

An oxygen-rich and low NOx burner integrated with liquefied natural gas (LNG) was proposed to address unstable combustion and high NOx emissions from a 330 MW subcritical boiler under ultra-low load operation in China. To assess the effectiveness of the retrofit, Chemkin and Fluent softwares were utilized to construct a new NOx model and calculate NOx generation, based on the combustion of pulverized coal gas and LNG. Further, an eddy dissipation concept (EDC) model, which can reflect detailed chemical reactions, was applied to calculate gas-phase reactions in the furnace. The results showed that when performing the deep peak shaving after the retrofit, the combustion in the furnace was stable under 50% or more load, and NOx emission level at the furnace outlet was lower than 350 mg/m3 (6% O2 content, dry basis). Under 25% load, the oxygen-rich burner integrated with LNG was applied, and the pulverized coal flow entered the furnace in a state of high-intensity combustion, which effectively promoted the stability of combustion in the furnace. The reductive combustion state with reductive free radicals generated by LNG decomposition inhibited NOx formation. Consequently, NOx emissions from the furnace outlet decreased from 380 mg/m3 to 316 mg/m3.

On the nature of Con±/0 clusters reacting with water and oxygen

Bulk cobalt does not react with water at room temperature, but cobalt nanometals could yield corrosion at ambient conditions. Insights into the cobalt cluster reactions with water and oxygen enable us to better understand the interface reactivity of such nanometals. Here we report a comprehensive study on the gas-phase reactions of Con±/0 clusters with water and oxygen. All these Con±/0 clusters were found to react with oxygen, but only anionic cobalt clusters give rise to water dissociation whereas the cationic and neutral ones are limited to water adsorption. We elucidate the influences of charge states, bonding modes and dehydrogenation mechanism of water on typical cobalt clusters. It is unveiled that the additional electron of anionic Con– clusters is not beneficial to H2O adsorption, but allows for thermodynamics- and kinetics-favourable H atom transfer and dehydrogenation reactions. Apart from the charge effect, size effect and spin effect play a subtle role in the reaction process. The synergy of multiple metal sites in Con– clusters reduces the energy barrier of the rate-limiting step enabling hydrogen release. This finding of water dissociation on cobalt clusters put forward new connotations on the activity series of metals, providing new insights into the corrosion mechanism of cobalt nanometals.

Bio-aromatics synthesis via catalytic pyrolysis of cellulose with lithium-ion battery cathodes and modified HZSM-5 coupled in-situ plasma mode

This work proposed a novel method based on in-situ plasma mode to synthetize bio-aromatics from cellulose co-pyrolyzed with lithium-ion battery cathodes and tandem catalyzed by modified HZSM-5. Ni and Ti modified HZSM-5 were compared in the catalytic pyrolysis of cellulose without cathode conditions, and then cellulose was co-pyrolyzed with cathodes (LCO, LMO and LNCM). The results showed that modified-zeolites improved the upgrading of pyrolysis products, producing more refined bio-oils, and Ti-modified version was superior, while cellulose co-pyrolyzed with cathodes decreased the residual char and catalyst deposits to increase refined bio-oil. When using LNCM, the refined bio-oil yield reached 38.80%, attributing to the catalytic effect of cathodes, enhanced thermal conductivity, and micro lithium-ion battery effect. The application of cathodes and modified zeolites enhanced the conversion of furans, greatly elevating the MAHs selectivity; herein, Ni-modified version increased PAHs. After using LNCM, the selectivity of MAHs reached 77.67% (mainly C8 hydrocarbons), C10 and above hydrocarbons were suppressed, which was possibly attributed to enhanced gas-phase reactions. Abundant free radical reactions and higher cracking capability enabled coking to initially occur inside, and using LNCM decreased the catalyst coke content by approximately 80%. Co-pyrolysis with cathodes caused the surface coke to transform from filament-like to amorphous.

Gas-Phase Reactivity of Quinoline-Based Singlet Oxenium Cations.

Isomeric quinolyloxenium cations were generated in the gas phase in an ion trap mass spectrometer to explore their reactions. The structures of some products were identified via collision-activated dissociation experiments involving model compounds to demonstrate that they have the expected heavy atom connectivity. The lack of radical reactions suggests that the cations have closed-shell singlet electronic ground states. Calculations (CASPT2/CASSCF(16,14)/cc-pVTZ//CASSCF(16,14)/cc-pVTZ) predict that their closed-shell singlet (1A') ground states are lower in energy by ca. 25 kcal mol-1 than their lowest-lying excited states. All cations are reactive toward dimethyl disulfide, dimethyl sulfide, and allyl iodide and most toward water and moderately reactive toward cyclohexane, reflecting their strongly electrophilic nature. They form adducts with nucleophiles in exothermic reactions (ca. 50 kcal mol-1 for dimethyl sulfide) that can fragment or be stabilized via IR emission. Most water adducts spontaneously isomerize to lower-energy tautomers. The nucleophiles preferentially add to those carbon atoms in the benzene ring that have the greatest positive charge (but not the carbonyl carbon). The cations react with cyclohexane via hydride abstraction by the oxygen atom. This is the only reaction that initially involves the oxygen atom and hence reflects the formally positively charged, monovalent oxygen atom in these cations.

Kinetics of the Gas-Phase Reactions of syn- and anti-CH3CHOO Criegee Intermediate Conformers with SO2 as a Function of Temperature and Pressure.

Kinetics of reactions between SO2 and CH3CHOO Criegee intermediate conformers have been measured at temperatures between 242 and 353 K and pressures between 10 and 600 Torr using laser flash photolysis of CH3CHI2/O2/N2/SO2 gas mixtures coupled with time-resolved broadband UV absorption spectroscopy. The kinetics of syn-CH3CHOO + SO2 are pressure-dependent and exhibit a negative temperature dependence, with the observed pressure dependence reconciling apparent discrepancies between previous measurements performed at ∼298 K. Results indicate a rate coefficient of (4.80 ± 0.46) × 10-11 cm3 s-1 for the reaction of syn-CH3CHOO with SO2 at 298 K and 760 Torr. In contrast to the behavior of the syn-conformer, the kinetics of anti-CH3CHOO + SO2 display no significant dependence on temperature or pressure over the ranges investigated, with a mean rate coefficient of (1.18 ± 0.21) × 10-10 cm3 s-1 over all conditions studied in this work. Results indicate that the reaction of syn-CH3CHOO with SO2 competes with unimolecular decomposition and reaction with water vapor in areas with high SO2 concentration and low humidity, particularly at lower temperatures.

Numerical investigation on the effect of gas-phase dynamics on graphene growth in chemical vapor deposition

Chemical vapor deposition (CVD) is a crucial technique to prepare high-quality graphene because of its controllability. In the research, we perform a systematic computational fluid dynamics numerical investigation on the effect of gas-phase reaction dynamics on the graphene growth in a horizontal tube CVD reactor. The research results indicate that the gas-phase chemical reactions in the CVD reactor are in a nonequilibrium state, as evidenced by the comparison of species mole fraction distributions during the CVD process and under chemical equilibrium conditions. The effect of gas-phase reaction dynamics on the deposition rate of graphene under different conditions is studied, and our research shows that the main causes of change in graphene growth rates under different conditions are gas-phase reaction dynamics and active species transport. The results of numerical simulation agree well with the experimental phenomena. The research results also indicate that, for methane, the main limiting factor of graphene growth is the surface kinetic reaction rate. Conversely, for active species, the main limiting factor of graphene growth is species transport. Our research suggests that the growth rate of graphene can be regulated from the perspective of the gas reaction mechanism. This method has theoretical guiding significance and can be extended to the preparation of large-area graphene.

Exploring Gas-Phase Chemical Reactions in NH3/B2H6 Systems for Chemical Vapor Deposition Using Reactive Molecular Dynamics.

Hexagonal boron nitride (hBN) has attracted significant attention as a two-dimensional (2D) material due to its unique structure and properties. In this paper, we investigated the gas-phase reactions between B2H6 and NH3 and the reaction pathways potentially leading to the synthesis of hBN by using ReaxFF-based reactive molecular dynamics (MD) simulations. From the hundreds of chemical reaction pathways observed in these MD simulations, we extracted a highly reduced chemical kinetic model to describe the gas-phase mixture evolution in chemical vapor deposition of hBN using B2H6 and NH3 as precursors. The intent is to integrate this chemical model into future computational fluid dynamics (CFD) simulations of actual hBN deposition testing and production reactors to provide enhanced insights for experimental synthesis processes and reactor optimization. The chemical model of this study will serve as a stepping stone for large-scale simulations.

Low temperature vaporisation of Cr from fluoride flux reacted at 1350 °C with Al–Cr–Fe powder: Thermochemical analysis of gas phase reactions and nano-strand formation

The submerged arc welding (SAW) process is complex because multi-phase reactions occur simultaneously across a large temperature interval from 2500 °C in the arc cavity, down to the weld pool liquidus temperare at the slag-weld pool interface. This complexity hinders research on specific process metallurgy aspects, such as gas formation from the oxy-fluoride slag. The main objective of this work is to illustrate a low temperature experimental technique as an accurate reaction simulation experiment of SAW flux oxy-fluoride slag behaviour in terms of gas formation and metal powder assimilation reaction mechanisms as observed in the SAW process. The oxy-fluoride slag behaviour was confirmed by identification and analyses of nano-strand formation in the reacted slag formed from the reaction of welding flux with Al-Fe-Cr metal powders at 1350 °C. The observed nano-strand formation agrees with similar observations in SAW post-weld slags used to confirm of oxy-fluoride vaporisation and re-condensation. Element distribution from energy dispersive X-ray spectroscopy (EDS) maps and thermochemical calculations were used to gain insights into the reactions in nano-strand formation. The nano-strands contained chromium patches and spots of less than 1 μm in scale, confirming that added Cr metal powder assimilated via the gas phase. Cr-fluoride formed part of the oxy-fluoride slag and likely formed Cr-fluoride gas. Cr was recovered via re-condensation of Cr vapour formed from the reaction of Cr-fluoride with Al gas. This work presents an accurate low temperature simulation method of gas formation and metal powder assimilation reactions in oxy-fluoride slags as in the SAW process.

Organosulfate produced from consumption of SO3 speeds up sulfuric acid–dimethylamine atmospheric nucleation

Abstract. Although sulfuric acid (SA) and dimethylamine (DMA)-driven nucleation mainly dominates the new particle formation (NPF) process in the atmosphere, seeking the involvement of other gaseous species remains crucial for a better understanding of the NPF. Organosulfate has been detected in the gas phase and abundantly in atmospheric fine particles. However, its molecular formation mechanism and its impact on the NPF are still much less understood. Here, we explored the gas-phase reaction of glycolic acid (GA) with SO3 and evaluated the enhancing potential of its products on the SA–DMA-driven NPF using a combination of quantum chemical calculations and kinetics modeling. We found that the considerable concentration of glycolic acid sulfate (GAS) is thermodynamically accessible from the reaction of GA with SO3, efficiently catalyzed by SA or H2O molecules. The produced GAS can form stable clusters with SA and DMA and speeds up the nucleation rate of the SA–DMA system obviously. Notably, the enhancement by GAS in the SA–DMA-based particle formation rate can be up to ∼ 800 times in the region where the concentration of SA is about 104 molec. cm−3. Supported by observations of atmospheric NPF events at Mt. Tai in China, our proposed ternary GAS–SA–DMA nucleation mechanism further indicates that the organosulfates produced from the consumption of SO3 may play an important role in the unexpected high NPF rates observed in areas with relatively low concentrations of SA. The presented reaction and nucleation mechanisms provide a new feasible source of organosulfates in atmospheric new particles. Based on our findings, the impact of organosulfates on the atmospheric NPF in multiple regions around the world was estimated and discussed.

Atmospheric chemistry of trifluorodicarbonyls initiated by Cl atoms: Reactivity trends, mechanism, and acid formation yields

Rate coefficients of the gas-phase reactions of Cl atoms with a series of fluorinated diketones (FDKs): CF3C(O)CH2C(O)CH3 (TFP), CF3C(O)CH2C(O)CH2CH3 (TFH) and CF3C(O)CH2C(O)CH(CH3)2 (TFMH), have been measured at (298 ± 2) K and under atmospheric pressure. The experiments were performed using the relative-rate method with a GC-FID detection system. From different determinations and references used, the following rate coefficients were obtained (in cm3/(molecule·sec)): k4(TFP + Cl) = (1.75 ± 0.21) × 10−10, k5(TFH + Cl) = (2.05 ± 0.23) × 10−10, k6(TFMH + Cl) = (2.71 ± 0.34) × 10−10. Reactivity trends of FDKs were discussed and Free Energy Relationships analysis was developed. The expression lgkOH = 1.68 lgkCl + 5.71 was obtained for the reactivity of the studied FDKs together with similar unsaturated VOCs with Cl and OH radicals Additionally, acetic acid (CH3C(O)OH) and trifluoroacetic acid (CF3C(O)OH) were positively identified and quantified as degradation products using in situ FTIR spectroscopy. According to the identified products, atmospheric chemical mechanisms were proposed. The atmospheric implications of the studied reactions were assessed by the estimation of the tropospheric lifetimes of TFP, TFH, and TFMH concerning their reaction with Cl atoms to be 48, 41, and 31 hours, respectively. The relatively short residence in the atmosphere of the fluorocarbons studied will have a local/regional impact with restricted transport. Global warming potential (GWP(20yr)) calculated for the studied fluoro diketones were 0.014, 0.003 and 0.001 for TFP, TFH and TFMH, respectively with a negligible contribution to the greenhouse effect.

Unexpected high yield of acrolein underlies the importance of the hydrogen-abstraction mechanism in photooxidation of allyl methyl sulfide (AMS).

This work explores theoretically the gas phase oxidation of allyl methyl sulfide (AMS, H2CCHCH2SCH3) initiated by •OH radicals, focusing on the H-abstraction pathway at the M06-2X-D3/aug-cc-pVTZ and MN15/aug-cc-pVTZ levels of theory (m06Tz and mn15Tz). The formation of a prereactive complex (PRC) is involved in H-abstraction processes with two potential directions of approach for the OH radical, denoted as “α” and “β”. The PRCs, demonstrate increased reactivity, primarily due to the interaction between the sulfur atoms and the hydroxyl hydrogen. A scheme for the H-abstraction mechanism that supports the experimentally identified products and predicts the formation of some S-containing low volatility products is proposed. The comparison of the potential energy surface (PES) between the double bond addition and H-abstraction paths in the AMS molecule shows that at the m06Tz level of theory, the H-abstraction on C3 and the addition to C1 have nearly the same profile of energy, while at the mn15Tz level, the minimum energy channel is the addition to C1. The theoretical rate coefficient for each reaction channel was calculated, considering the formation of a PRC prior to reaching the transition state of each channel and assuming thermal equilibrium between reactants and the PRC. The rate constants were calculated in a multi-TS/multi-conformer way at the SVECV-f12/m06Tz and SVECV-f12/mn15Tz levels of theory. The SVECV-f12 method is consistent in its predictions in both systems and exhibits only minor deviations from the experimental rate constants. Despite some specific differences due to the DFT method supporting the SVECV-f12 calculations, both methodologies predict a significant H-abstraction contribution in the AMS + OH gas phase reaction, which explains the high formation yield for acrolein determined experimentally.

Kinetics of the reaction of OH radical with ethylfluoroacetate, ethyl 4,4,4-trifluorobutyrate, and butylfluoroacetate

Kinetics of the gas-phase reactions of •OH radicals with a series of fluoroesters were studied for the first time at 298 ± 3 K and atmospheric pressure. Relative rate coefficients were determined by in situ FTIR spectroscopy in nitrogen and GC-FID in air to monitor the decay of reactants and references. The following coefficient values (in 10−12 cm3/(molecule•sec)) were obtained for ethyl fluoroacetate (EFA), ethyl 4,4,4-trifluorobutyrate (ETB), and butyl fluoroacetate (BFA), respectively: k1 (EFA + OH) = 1.15 ± 0.25 by FTIR and 1.34 ± 0.23 by GC-FID; k2 (ETB + OH) = 1.61 ± 0.36 by FTIR and 2.02 ± 0.30 by GC-FID; k3 (BFA + OH) = 2.24 ± 0.37 by FTIR. Reactivity trends were developed and correlated with the number of CH3 and F substituents in the fluoroester, and structure-activity relationships (SARs) calculations were performed. In addition, the tropospheric lifetimes of EFA, ETB, and BFA upon degradation by OH radicals were calculated to be 9, 6, and 5 days, respectively, indicating that these fluorinated compounds could have a possible regional effect from the emission source. Relatively small photochemical ozone creation potentials of 9, 7, and 19 were estimated for EFA, ETB, and BFA, respectively. The Global Warming Potentials (GWPs) for EFA, ETB, and BFA were calculated for different time horizons. For a 20-year time horizon, the GWPs were 1.393, 0.063, and 0.062, respectively. In the case of a 100-year time horizon, the GWPs were 0.379, 0.017, and 0.017, and for a 500-year time horizon, the GWPs were 0.108, 0.005, and 0.005 for EFA, ETB, and BFA.

Sustainable method for disposing of ceramic-coated battery separator via carbon dioxide-assisted thermochemical process

The increasing demand for energy storage systems is driven by variability in renewable energy sources and the substantial energy requirements of electric vehicles. However, the typical 3–10-year lifespan of lithium-ion batteries raises concern about their disposal. The environmental challenges associated with conventional disposal and recycling methods (landfilling, incineration, and pyrometallurgical/hydrometallurgical processes) include the release of microplastics and air pollutants, such as volatile organic compounds, from plastic components. To address these issues, we propose a thermochemical process for managing plastic waste from discarded batteries, focusing on a separator from lithium-ion batteries as a model feedstock. Using carbon dioxide (CO2) as a reaction medium enhances the sustainability of thermochemical processes. Specifically, co-feeding CO2 at elevated temperatures (≥500°C) improves syngas and C1–2-hydrocarbon production while reducing liquid pyrolysates. These reactions result from the partial oxidation of volatiles via gas-phase reactions with CO2. Incorporation of CO2 to optimize the conversion of battery separators into syngas represents an advancement toward the environmentally sound and efficient disposal of battery waste while yielding value-added products.

Experimental and ReaxFF MD study on the release characteristics of gaseous nitrogen during pressurized bituminous coal gasification

Coal gasification is the leading technology of clean coal technology such as Integrated Gasification Combined Cycle (IGCC). The release pattern of gaseous nitrogen during coal gasification is crucial for clean coal technology. This paper investigated the gaseous nitrogen emission characteristics of pressurized gasification through experiments and molecular dynamics studies. The experimental results show that the elevated temperatures promoted the release of NO and accelerated the conversion of nitrogen-containing precursors (HCN, NH3). However, high pressure weakened the effect of temperature and resulted in the decreased emissions of HCN, NH3, and NO. Because high pressure facilitated the conversion of fuel nitrogen to nitrogen. The emissions of HCN and NH3 decreased as the CO2 blending ratio increased, while NO emissions increased. The observed difference was primarily attributed to the amounts of free radicals and was also related to gas-phase reactions involving H2O and CO2. Furthermore, as the primary nitrogen-containing structure in bituminous coal, the pyrrole was used in Reactive force field molecular dynamics (ReaxFF MD) to study the release of gas-phase nitrogen during gasification process. The simulation results show that both temperature and pressure promote the migration of pyrrole nitrogen and also provided the main nitrogen migration paths during gasification which can be used to (indirectly) confirm the experimental analysis. The O2/N2/CO2 gasification system supplied additional O and OH radicals to enhance NO emissions, while H2O directly participated in reaction paths such as CN, NCO → NHi or provided H radicals to increase NH3 emissions.

Heavily boron-doped polycrystalline diamond films: Microstructure, chemical composition investigation and plasma in-situ diagnostics

The introduction of boron brings excellent electrical conductivity to diamond films, but also induces uncontrollability of the doping process. Therefore, it is crucial to the monitor of the growth and doping processes. In this work, to establish the correlation between the gas-phase chemical reactions and the microstructure characteristics of heavily boron-doped diamond (BDD) films, the plasma reactions in the chemical vapor deposition (CVD) process of BDD films were in-situ diagnosed and monitored using optical emission spectroscopy (OES), and the effect of different B/C ratios (from 10,000 to 60,000 ppm) on the microstructure, chemical composition were investigated comprehensively. As the B/C ratio increases, the insufficient gas-phase excitation and the “hydrogen abstraction” reaction of BH species lead to a massive loss of H species in the gas-phase of plasma, which is unfavorable for the diamond growth, weakens the etching on sp2 carbon, induces the development of defects and seriously damages the diamond films quality. The in-situ diagnostics and monitoring of the plasma state can realize the optimization of the growth and doping process for heavily doped polycrystalline BDD films, which is highly significant for its preparation and application.

Mechanocatalytic Synthesis of Ammonia: State of the Catalyst During Reaction and Deactivation Pathway.

Ammonia synthesis holds significant importance for both agricultural fertilizer production and emerging green energy applications. Here, we present a comprehensive characterization of a catalyst for mechanochemical ammonia synthesis, based on Cs-promoted Fe. The study sheds light on the catalyst's dynamic evolution under reaction conditions and the origin of deactivation. Initially, elemental Cs converts to CsH, followed by partial CsOH formation due to trace oxygen impurities on the surface of the Fe metal and the equipment. Concurrently, the mechanical milling process comminutes Fe, exposing fresh metallic Fe surfaces. This comminution correlates with an induction period observed during ammonia formation. Critical to the study, degradation of active Cs promoter species (CsH and CsNH2) into inactive CsOH emerged as the primary deactivation mechanism. By increasing the Cs content from 2.2 mol % to 4.2 mol %, we achieved stable, continuous ammonia synthesis for nearly 90 hours, showcasing one of the longest-running mechanocatalytic gas phase reactions. Studies of the temperature dependence of the reaction revealed negligible bulk temperature influence in the range of -10 °C to 100 °C, highlighting the dominance of mechanical action over bulk thermal effects. This study offers insights into the complex interplay between mechanical processing, reactive species, and deactivation mechanisms in mechanocatalytic ammonia synthesis.

Mechanocatalytic Synthesis of Ammonia: State of the Catalyst During Reaction and Deactivation Pathway

AbstractAmmonia synthesis holds significant importance for both agricultural fertilizer production and emerging green energy applications. Here, we present a comprehensive characterization of a catalyst for mechanochemical ammonia synthesis, based on Cs‐promoted Fe. The study sheds light on the catalyst‘s dynamic evolution under reaction conditions and the origin of deactivation. Initially, elemental Cs converts to CsH, followed by partial CsOH formation due to trace oxygen impurities on the surface of the Fe metal and the equipment. Concurrently, the mechanical milling process comminutes Fe, exposing fresh metallic Fe surfaces. This comminution correlates with an induction period observed during ammonia formation. Critical to the study, degradation of active Cs promoter species (CsH and CsNH2) into inactive CsOH emerged as the primary deactivation mechanism. By increasing the Cs content from 2.2 mol % to 4.2 mol %, we achieved stable, continuous ammonia synthesis for nearly 90 hours, showcasing one of the longest‐running mechanocatalytic gas phase reactions. Studies of the temperature dependence of the reaction revealed negligible bulk temperature influence in the range of −10 °C to 100 °C, highlighting the dominance of mechanical action over bulk thermal effects. This study offers insights into the complex interplay between mechanical processing, reactive species, and deactivation mechanisms in mechanocatalytic ammonia synthesis.