Atm N2 Research Articles

Volatile N,N′-dialkyl-β-dialdiminate complexes of magnesium and zinc as possible chemical vapor deposition precursors

A series of volatile magnesium(II) and zinc(II) bis(β-dialdiminato) complexes (of stoichiometry M[RN(CH)3NR]2 where R = methyl, ethyl, isopropyl, or tert-butyl) have been prepared and investigated as potential precursors for the chemical vapor deposition of thin films. Several of the compounds have been characterized crystallographically; the metal centers adopt pseudo-tetrahedral geometries with the two ligands forming six-membered rings with the metal center. All eight compounds sublime cleanly both in vacuum and under 1 atm of N2, and the most volatile compounds (those having N-methyl substituents) have vapor pressures of 1 Torr at 88 (Mg) and 90 °C (Zn). In general, metal complexes of N,N′-dialkyl-β-dialdiminate ligands are more volatile than their corresponding N,N′-dialkyl-β-diketiminate and N,N-dialkylamidinate analogues.

Novel high nitrogen austenitic stainless steels: From high-throughput screening to experimental validation and properties relationship

The quest for affordable and price-stable alternatives for nickel as the main austenitizing alloying element is pushing the stainless steel industries to develop new types of Ni-lean austenitic stainless steels. This work focuses on the challenges of designing austenitic stainless steels with appreciable nitrogen content using computational methods, which can still be produced at 1 atm N2 pressure and thermomechanically processed without excessive cracking or N2 degassing. CALPHAD-based computational tools enabled the identification of promising alloys by high-throughput screening from more than 2000 candidates based on predefined criteria considering composition (Ni-poor, N-rich), phase stability (austenite), degassing (far from N2 loss from liquid or solid phase), cost (Ni-lean), and pitting resistance equivalent number (PREN > AISI 201 stainless steel). The resulting alloys exhibited an austenitic microstructure with dispersed micrometric and nanometric aluminum nitrides (AlN) precipitates. Even with the occurrence of appreciable AIN precipitates, hot rolling was performed without cracking, resulting in equiaxed austenitic grains. The mechanical properties of the developed alloys exceeded those of AISI 201 stainless steel in terms of hardness, yield strength, and ultimate tensile strength, with values of 304 HV, 534 MPa, and 953 MPa, respectively, yet with considerable ductility (∼40% elongation). Even in the presence of AlN that pick up some of the nitrogen from solid solution, the corrosion resistance of the developed alloy was superior to the AISI 201 stainless steel. This research provides valuable insights for developing and processing high-nitrogen austenitic stainless steels to compete with 201 and 304 stainless steels in terms of mechanical properties and corrosion resistance.

Glycerol carbonate synthesis via Zn(OBu)2/AlCl2(OBu) initiated-glycerolysis of urea

Glycerol carbonate (4-hydroxymethyl-1,3-dioxolane-2-one) was efficiently synthesized from glycerolysis of urea initiated by Zn(OBu)2/Al(OBu)Cl2. The zinc-aluminum complex mixture was prepared from zinc chloride (ZnCl2) and aluminum tri-sec-butylate (Al(OBu)3. The complex successfully initiated the urea glycerolysis in 1 : 1 ​mol ratio of glycerol to urea to produce glycerol carbonate up to 85% and selectivity up to 97% at 150 ​°C and 1 ​atm of N2 for 4 ​h in the absence of solvents. Isocyanate was observed as a key intermediate in this reaction. A kinetic study showed the reaction likely followed pseudo first-order kinetics with estimated activation energy (Ea) of 38 ​kJ/mol. Density-functional theory calculations with MN15-L functional described the formation of glycerol carbonate as spontaneous with the Gibbs free energy of −28.41 ​kJ ​mol−1.

Easy fabrication method of Li4SiO4-K2CO3 based pellets for CO2 capture at high temperature

This study focuses on a novel fabrication method of K2CO3-Li4SiO4 based sorbents for CO2 capture from hot flue gas of gas turbines. The developed pellets were produced by sintering K2CO3-Li4SiO4 powders at 550 °C using viscous polyalphaolefins as pore formers. This mild calcination temperature was selected as the optimal condition for the development of a suitable porosity preventing powder degradation which typically occurs at higher temperatures. The sorption/desorption performance was tested by thermogravimetric analysis conducted at 580 °C under 0.04 atm of CO2 and 620 °C under 1 atm of N2, respectively. Results showed that the use of 20 wt% K2CO3 represents the optimal content to achieve a stable formation of molten eutectic K2CO3-Li2CO3 mixture during CO2 chemisorption, while avoiding K2CO3 crystals phase segregation during multiple sorption cycles. In addition, the use of 30 wt% olefin allowed the development of resistant and porous pellets of tuneable dimension and shape with a stable sorption capacity up to 130 mgCO2/g obtained over 25 multiple cycles of 30 min each. The present research lays the groundwork for the adoption of a novel pelletizing technique to produce innovative sorbents with enhanced CO2 capture and cycling capabilities, manufactured via a simple and more sustainable approach.

Low-temperature trapping of N2 reduction reaction intermediates in nitrogenase MoFe protein-CdS quantum dot complexes.

The biological reduction of N2 to ammonia requires the ATP-dependent, sequential delivery of electrons from the Fe protein to the MoFe protein of nitrogenase. It has been demonstrated that CdS nanocrystals can replace the Fe protein to deliver photoexcited electrons to the MoFe protein. Herein, light-activated electron delivery within the CdS:MoFe protein complex was achieved in the frozen state, revealing that all the electron paramagnetic resonance (EPR) active E-state intermediates in the catalytic cycle can be trapped and characterized by EPR spectroscopy. Prior to illumination, the CdS:MoFe protein complex EPR spectrum was composed of a S = 3/2 rhombic signal (g = 4.33, 3.63, and 2.01) consistent with the FeMo-cofactor in the resting state, E0. Illumination for sequential 1-h periods at 233K under 1 atm of N2 led to a cumulative attenuation of E0 by 75%. This coincided with the appearance of S = 3/2 and S = 1/2 signals assigned to two-electron (E2) and four-electron (E4) reduced states of the FeMo-cofactor, together with additional S = 1/2 signals consistent with the formation of E6 and E8 states. Simulations of EPR spectra allowed quantification of the different E-state populations, along with mapping of these populations onto the Lowe-Thorneley kinetic scheme. The outcome of this work demonstrates that the photochemical delivery of electrons to the MoFe protein can be used to populate all of the EPR active E-state intermediates of the nitrogenase MoFe protein cycle.

Removal of gaseous benzene by a fixed-bed system packed with a highly porous metal-organic framework (MOF-199) coated glass beads

The utility of nanomaterial adsorbents is often limited by their physical features, especially fine particle size. For example, a large bed-pressure drop is accompnied inevitably, if fine-particle sorbents are used in a packed bed system. To learn more about the effect of adsorbent morphology on uptake performance, we examined the adsorption efficiency of metal-organic framework 199 (MOF-199) in the pristine (fine powder) form and after its binding on to glass beads as an inert support. Most importantly, we investigated the effect of such coatings on adsorption of gaseous benzene (0.1–10 Pa) in a dry N2 stream, particularly as a function of the amount of MOF-199 loaded on glass beads (MOF-199@GB) (i.e., 0,% 1%, 3%, 10%, and 20%, w/w) at near-ambient conditions (298 K and 1 atm). A 1% MOF-199 load gave optimal performance against a 0.1 Pa benzene vapor stream in 1 atm of N2, with a two-to five-fold improvement (e.g., in terms of 10% breakthrough volume [BTV] (46 L atm [g.MOF-199)−1], partition coefficient at 100% BTV (3 mol [kg.MOF-199]−1 Pa-1), and adsorption capacity at 100% BTV (20 mg [g.MOF-199]−1 (areal capacity: 8.8 × 10−7 mol m−2) compared with those of 3%, 10%, and 20% loading. The relative performance of benzene adsorption was closely associated with the content of MOF-199@GB (e.g., 1% > 3% > 10% > 20%) and the surface availability (m2 [g.MOF-199]−1) such as 291 > 221 > 198 > 181, respectively. This study offers new insights into the strategies needed to expand the utility of finely powdered MOFs in various environmental applications.

The feasibility and temporal storability of gas phase standards of volatile organic compounds prepared through liquid phase vaporization in polyester aluminum bags at room temperature

Currently, the presence of many classes of volatile organic compounds (VOCs) in indoor air is well recognized. There is an impetus to accurately quantify airborne VOCs for the proper assessment of their human health risks. VOC standards prepared in a solvent are often vaporized in N2 gas-filled sampling bags for external calibration as the use of grab sampling bags is a common practice for the collection of real ambient air samples. Such practices can nontheless be subject to many sources of biases in their calibration (e.g., VOC chemical reaction with the solvent, adsorption on the bag interior surface, or leakage). The main goal of this work is to measure the temporal stability of 11 VOC targets (benzene, toluene, o-xylene, styrene, propionaldehyde, n-butyraldehyde, isovaleraldehyde, valeraldehyde, acrylonitrile, isoprene, and methyl ethyl ketone) selected in this research over 24 h which started 10 min after the injection and vaporization of liquid-phase standards (all prepared in methanol solvent) into polyester aluminum (PEA) bags containing 1 atm N2. Although all tested VOCs showed gradual decreases of their concentrations (e.g., >17% in 24 h), the aromatic hydrocarbon VOCs (namely BTXS) yielded the best relative recoveries (e.g., decreases of 11%–30% in 24 h) and relative errors (e.g., relative standard error (RSE) = 2.14–3.59%) in 5 replicate tests. A good linear relationship was established between the 24 h VOC relative recovery and molecular weight (R2 > 0.81). The results of this study offers valuable clues to properly reduce the bias in the calibration of gas-phase VOC standards when calibrating the system through the vaporization of liquid-phase VOC standards prepared in a solvent.

Insertion products in the reaction of carbonyl oxide Criegee intermediates with acids: Chloro(hydroperoxy)methane formation from reaction of CH2OO with HCl and DCl

The reactions of carbonyl oxide Criegee intermediates with acids proceed predominantly by an insertion mechanism. We characterise the products from one of the simplest reactions of carbonyl oxides with inorganic acids, CH2OO + hydrogen chloride, which occurs via a 1,2-insertion in the H–Cl bond. Reactions of both HCl and DCl isotopologues yield product signal at the mass of the insertion product chloro(hydroperoxy)methane and a dissociative ionisation peak at the mass of the protonated (or deuteronated) Criegee intermediate. The isotopic composition of the insertion product has been measured for reaction mixtures where both HCl isotopologues are present, and the H/D ratio of the product is consistently higher (by a factor of 1.6 ± 0.3) than that of the reactants. This isotope selectivity in the products has smaller uncertainty than the ratio of measured rate coefficients and suggests a normal (k H > k D) kinetic isotope effect in the reaction. Theoretical kinetics calculations predict a small normal kinetic isotope effect for the overall reaction (k H / k D = 1.35 at 20 Torr N2 and k H / k D = 1.2 at 1 atm N2) but predict a substantial inverse kinetic isotope effect (k D > k H) for the stabilisation fraction, in disagreement with the experimental observation.

The stability of Cl-, Br-, and I-passivated Si(100)-(2 × 1) in ambient environments for atomically-precise pattern preservation

Atomic precision advanced manufacturing (APAM) leverages the highly reactive nature of Si dangling bonds relative to H- or Cl-passivated Si to selectively adsorb precursor molecules into lithographically defined areas with sub-nanometer resolution. Due to the high reactivity of dangling bonds, this process is confined to ultra-high vacuum (UHV) environments, which currently limits its commercialization and broad-based appeal. In this work, we explore the use of halogen adatoms to preserve APAM-derived lithographic patterns outside of UHV to enable facile transfer into real-world commercial processes. Specifically, we examine the stability of H-, Cl-, Br-, and I-passivated Si(100) in inert N2 and ambient environments. Characterization with scanning tunneling microscopy and x-ray photoelectron spectroscopy (XPS) confirmed that each of the fully passivated surfaces were resistant to oxidation in 1 atm of N2 for up to 44 h. Varying levels of surface degradation and contamination were observed upon exposure to the laboratory ambient environment. Characterization by ex situ XPS after ambient exposures ranging from 15 min to 8 h indicated the Br– and I–passivated Si surfaces were highly resistant to degradation, while Cl–passivated Si showed signs of oxidation within minutes of ambient exposure. As a proof-of-principle demonstration of pattern preservation, a H–passivated Si sample patterned and passivated with independent Cl, Br, I, and bare Si regions was shown to maintain its integrity in all but the bare Si region post-exposure to an N2 environment. The successful demonstration of the preservation of APAM patterns outside of UHV environments opens new possibilities for transporting atomically-precise devices outside of UHV for integrating with non-UHV processes, such as other chemistries and commercial semiconductor device processes.

In Situ TEM Study of Rh Particle Sintering for Three-Way Catalysts in High Temperatures

One of the main factors in the deterioration of automobile three-way catalysts is the sintering of platinum group metals (PGMs). In this study, we used in situ tunneling electron microscopy (TEM) to examine the sintering of Rh particles as the temperature increases. Two types of environmental conditions were tested, namely, vacuum atmosphere with heating up to 1050 °C, and N2 with/without 1% O2 at 1 atm and up to 1000 °C. Under vacuum, Rh particles appeared to be immersed in ZrO2. In contrast, at 1 atm N2 with or without 1% O2, the sintered Rh particles appeared spherical and not immersed in ZrO2. The latter trend of Rh sintering resembles the actual engine-aged catalyst observed ex situ in this study. In the N2 atmosphere, the sintering of support material (ZrO2 or Y-ZrO2) was first observed by in situ TEM, followed by Rh particle sintering. The Rh particle size was slightly smaller on Y-ZrO2 compared to that on ZrO2. To better understand these experimental results, density functional theory was used to calculate the systems’ junction energies, assuming three layers of Rh(111) 4 × 4 structures joined to the support material (ZrO2 and Y-ZrO2). The calculated energies were consistent with the in situ TEM observations in the N2 atmosphere.

Kinetics of CO2 fixation by Sulfurovum lithotrophicum 42BKTT: Medium optimization and tolerance of CO2 toxicity

CO2 toxicity, ionic strength, and specific culture media components, such as thiosulfate have been reported to influence the growth of CO2-fixing autotrophic bacteria. In this study, a chemostat culture was used to determine the kinetics of CO2 fixation by S. lithotrophicum 42BKTT. The medium composition was determined to be capable of reaching a steady state at a high concentration of thiosulfate, an energy source, without growth inhibition by the excessively high ionic strength and thiosulfate itself. CO2 was supplied by saturating the medium with a 1 atm CO2 gas or a gaseous mixture of 0.8 atm N2 and 0.2 atm CO2. The Monod equation successfully described the kinetics of CO2 fixation; the maximum specific growth rate was 0.33 h−1 regardless of CO2 pressure while the Monod constant was 0.0379 g Na2S2O3/L and 0.196 g Na2S2O3/L under 0.2 atm and 1.0 atm CO2, respectively. We found that when nutrients, including thiosulfate, were supplied sufficiently, the CO2 fixation rate at 1 atm CO2 was only slightly lower than that at 0.2 atm CO2 (e.g. only by 4.7 % for 3.0 g Na2S2O3/L). Therefore, the CO2 fixation by S. lithotrophicum 42BKTT is not subject to CO2 toxicity at least up to 1.0 atm CO2.

Effect of sintering on morphology and magnetic properties of Fe-Co nano-rods prepared by wet chemical route

Ferromagnetic Fe-Co oxide nano-rods with high coercivity have been synthesized using wet chemical method. Samples were sintered in hydrogen and nitrogen atmosphere at different temperatures. Structural and morphological studies were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) and transmission electron microscopy (TEM) analysis. The magnetic properties of the particles were measured by a vibrating sample magnetometer (VSM) with a varying magnetic field. XRD pattern demonstrates the presence of pure α-Fe phase in the samples sintered in H2 atmosphere while the presence of Co substituted oxide phases in the samples sintered in N2 atmosphere. SEM micrograph of samples sintered in N2 demonstrates the growth of plate like morphology; such growth was not observed when the samples were sintered in H2atmosphere. Non homogeneous growth of nano-rods was obtained when sintered in N2 atm at 550 ºC whereas homogeneous growth was obtained when sintered in N2 atm at 900 ºC. VSM measurement gives the higher amount of coercivity in the samples sintered in N2 which could be attributed to the rod shape of oxide phase which has high L/D ratio and helps in increasing the anisotropy and hence the coercivity. The higher amount of magnetization value than as prepared samples was observed in samples sintered in H2 atmosphere.

Reduced Contact Resistance in GaN Using Selective Area Si Ion Implantation

We report selective area n-type doping using ion implantation of Si into semi-insulating, C-doped GaN samples activated using both conventional rapid thermal annealing (RTA) and 30 atm N2 overpressure annealing. Implanted regions were tested for Si activation using Circular Transmission Line Measurements (CTLM), while linear and circular photoconductive switches (PCSS) in the unimplanted regions were used as a test vehicle to separate implanted Si dopant activation from leakage paths generated by N vacancy formation due to damage and decomposition during annealing. We observed that at an optimal temperature around 1060 °C, a low contact resistivity of $1\times 10^{-6}\,\,\Omega $ -cm2 was obtained while preserving the breakdown of the unimplanted regions.

Comprehensive study of high pressure annealing on the ferroelectric properties of Hf0.5Zr0.5O2 thin films

Thin films of ferroelectric materials are potential candidates to be implemented in the unfolding of a new paradigm in high-density memory devices. As the thickness of these films reaches the sub-10 nm level, the interface properties between the electrode and ferroelectric material undergo significant changes that play a crucial role in governing the ferroelectric behavior. The present state-of-the-art approach presents a detailed investigation of different high pressure annealing (HPA) conditions through simulation studies. The simulation studies were performed using Landau–Khalatnikov equations, with Landau’s parameters calculated using the least regression method as described in the Method S1. The extracted coefficients were used to determine various relationships (free energy, ferroelectric potential and negative capacitance) with which to observe the impact of HPA on the negative capacitance (NC) effect on account of the majority ferroelectric phase. To verify the simulation results, pulse transient switching measurements were conducted using Pt/Ti/TiN/Hf0.5Zr0.5O2/TiN-based metal-ferroelectric-metal (MFM) devices to study the coercive field, interfacial capacitance and load resistance behavior. The results suggest that the non-ferroelectric portion (t-phase) coexists with the ferroelectric (o-phase) within the thin layer of the MFM capacitor adjacent to TiN electrode, which undergoes a phase transformation from the t-phase to the o-phase when exposed to different HPA conditions as well as electric field cycling during PS measurements. The simulation and experimental results confirm that the 550 °C at 50 atm N2 environment provides the best possibility of achieving the highest ferroelectric characteristics with the lowest proportion of the non-ferroelectric phase and thus the maximum NC effect as well.

The retrograde adsorption phenomenon at the onset of breakthrough and its quantitation: An experimental case study for gaseous toluene on activated carbon surface

The adsorption dynamics of common solid sorbents against various pollutant species are yet poorly understood with respect to the retrograde phenomenon in which the relationship between breakthrough vs. pulled volume is characterized by an early unusual trend (initial increase followed by a decrease to a minimum) and by a normal trend of finally increasing to 100% (or equilibrium). If such trend is expressed in terms of the partition coefficient (PC), a reversed trend of adsorption processes becomes more evident. Retrograde has been previously observed in the initial breakthrough (<10%) isotherms in continuous flow gas-phase adsorption processes. However, retrograde has been neglected/overlooked and not discussed at all in the main stream literature even when it is explicitly observed from isotherm datasets. To properly describe the various aspects of such process, a stop-flow technique was developed to measure the adsorption isotherm of a model volatile organic compound (i.e., toluene in this study) onto a commercial low-cost sorbent (activated carbon: AC). Accordingly, a 10% breakthrough volume of 762 L atm g−1 (corresponding adsorption capacity of 142 mg g−1) was determined (at an inlet stream 5 Pa of toluene in 1 atm of N2 and 5 mg of AC). This automated method was effective to generate a detailed breakthrough profile at high stream-flow rates (or high space velocities) to specifically detect the retrograde phenomenon at the breakthrough onset. This study offers a practical approach towards establishing an in-depth monitoring protocol for the rare retrograde phenomenon.

Two-step catalytic hydrogenation of methanol to hydrocarbons conversion

Abstract The continuous two-step catalytic hydrogenation of methanol to hydrocarbons (MTH) was investigated for improving the distribution of liquid hydrocarbon products using HZSM-5 zeolite and consecutively with two supported Co catalysts, Co/Al2O3 and Co/SBA-15. The sequential catalytic system was employed to enhance the selectivity of long chain hydrocarbons. The catalysts were characterized by BET, XRD, XRF, NH3-TPD, and SEM techniques. The catalytic performance of prepared catalysts was performed at 300 oC in a fixed-bed reactor with the constant flow rate of methanol under 1 atm of N2. The liquid hydrocarbons were analyzed by GC-MS. The aromatic and light hydrocarbon products were produced by the HZSM-5 and Co-based catalysts. According to the analysis result, the aromatic hydrocarbon products of the catalysts modified by two-step of catalytic reaction have been significantly increased. The results indicated that the series of HZSM-5 and two supported Co catalysts system led to produce high yield of aromatic hydrocarbon products in the catalytic performance of methanol to hydrocarbon process comparing with only the single HZSM-5 catalyst.

Improvement of HZSM-5 catalytic performance by rice husk ash addition for methanol to hydrocarbons process

Abstract The catalytic conversion of methanol to hydrocarbons (MTH) of gasoline has been studied over the modification of HZSM-5 zeolite catalysts, which were prepared by different ratios of rice husk ash (RHA) addition. The catalysts were characterized by BET, XRD, XRF, NH3-TPD, FT-IR and SEM techniques. The dehydration of methanol over prepared catalysts was carried out in a fixed-bed reactor at 300 oC with a constant flow rate of methanol under 1 atm of N2. The liquid hydrocarbons product was analyzed by GC-MS. The analysis showed that the major product provided by RHA-HZSM-5 catalysts was aromatic hydrocarbon-rich. According to the experimental results, the methanol conversion to hydrocarbons has been found to be a function of RHA ratio. The aromatic product selectivity was increased but that of the acidity of catalyst was decreased with the increase of RHA ratio. The study indicated that the hydrocarbon product distribution of the catalysts treated by RHA significantly depended on the acidity of catalyst.

A comparison of figure of merit (FOM) for various materials in adsorptive removal of benzene under ambient temperature and pressure

To effectively remove gaseous pollutants from air using sorbents, a thorough knowledge of the actual sorption performance is needed at ambient conditions rather than at unrealistically high-pressure conditions, as is commonly presented in the literature. To this end, the sorbent capacities of gaseous benzene were evaluated at a constant sorbent bed inlet pressure (50 ppm or ~5 Pa) in 1 atm of N2, room temperature (298 K), a fixed flow rate (50 mL min−1), and equal outlet sampling intervals (5 min). The benzene adsorption patterns were investigated against six sorbent types in a total of 17 different forms: 1- zeolite in five forms: beads (ZB), ground to 212 µm (ZG212), beads ground to 300 µm (ZG300), coarsely ground/washed zeolite (ZWc), and coarsely ground/washed/thermally treated zeolite (ZTc), 2- activated carbon in two forms: 212 µm (ACd212) and granular (ACdg), 3- Carbopack-X (CX), 4- Tenax TA (TA), 5- used black tea leaves of 150 or 300 µm in three forms: dry (TD150/TD300), wet (TW150/TW300), and wet dust (TWd), and 6- used ground coffee in either dry (CD) or wet forms (CW). Accordingly, the largest adsorption capacities at 5 Pa (e.g., >10 mg g−1) were observed for ACd212 (79.1) and ACdg (73.6). Moderate values (e.g., 5 < < 10 mg g−1) were obtained for ZG212 (7.98), CX (6.79), ZG300 (5.70), and ZB (5.58), while the remainder were far lower at < 5 mg g−1 (e.g., tea leaves, ground coffee, TA, ZWc, and ZTc). The experimental benzene capacities of the tested sorbents were further assessed by the Langmuir, Henry's law, Freundlich, Dubinin-Radushkevich, and Elovich isotherm models. The linearized Langmuir adsorption isotherms of ACd212, ACdg, and CX showed the presence of more than one adsorption site (i.e., retrograde at the lowest pressures and two others at higher pressures). However, TA, zeolite, tea leaves, and ground coffee exhibited a type-V isotherm, wherein the sorption capacity continued to increase with loaded volume (i.e., multilayer adsorption). Thus, ACd212 has the best figure-of-merit based on a high 10% breakthrough volume (BTV) and low cost for real-world applications.

Microstructural evolution of amorphous Si2BC3N nanopowders upon heating at high temperatures: High pressures reverse the nucleation order of SiC andBN(C)

AbstractAmorphous Si2BC3N nanopowders (NPs) were heated at 1000‐1700°C temperatures for 30 minutes in 1 atm N2. The changes in phases, chemical bonds, and microstructures were investigated byXRD,XPS,NMR,TEM, and first‐principles calculation. Increases in heating temperatures lead to the nucleation and growth of SiC andBN(C) grains, along with partial transformation of SiC4units from amorphous to β/α‐SiC, and collapse of B–C–N bonds. SiC nucleates prior toBN(C) at 1 atm, while it goes in the opposite order at high pressures (≥1GPa). High pressures also shift the initial temperatures of crystallization of amorphous Si2BC3NNPs from 1400°C (1 atm) to 1150°C (5 GPa).

One-pot synthesis of secondary amine via photoalkylation of nitroarenes with benzyl alcohol over Pd/monolayer H1.07Ti1.73O4·H2O nanosheets

The photoalkylation of nitroarenes with benzyl alcohols in one pot at room temperature and 1 atm N2 was achieved over the Pd/H1.07Ti1.73O4·H2O nanosheets. The sample shows efficient photocatalytic activity with high conversion of nitrobenzene (99%) and selectivity of secondary amine (85%). This flexible photocatalytic system is also applicable to other nitroarenes with high efficiency. Results of in situ FTIR, DRS, and in situ ESR revealed that the benzyl alcohol and nitrobenzene molecules can bind with the surface Lewis and Brønsted acid sites in the catalyst via the HO⋯Ti and NO2⋯HOTi species. The formation of surface coordination species results in not only the activation of reactant molecules via surface electron transfer, but also the expanded visible light absorption of the catalyst. Moreover, in situ ESR suggested that the surface coordination can also facilitate the formation of oxygen vacancies in catalysts, which can greatly promote the exposure of Lewis sites and enhance the activation of reactant molecules. Finally, a possible hydrogen transfer strategy over the sample is proposed on a molecular level.