Determination of a Safe Distance for Atomic Hydrogen Depositions in Hot-Wire Chemical Vapour Deposition by Means of CFD Heat Transfer Simulations

A heat transfer study was conducted,in the framework of Computational Fluid Dynamics(CFD),on a Hot-Wire Chemical Vapour Deposition(HWCVD)reactor chamber to determine a safe deposition distance for atomic hydrogen produced by HWCVD.The objective of this study was to show the feasibility of using heat transfer simulations in determining a safe deposition distance for deposition of this kind.All CFD simulations were set-up and solved within the framework of the CFD packages of OpenFOAM namely;snappyHexMesh for mesh generation,buoyantSimpleFoam and rhoSimpleFoam as the solvers and paraView as the post-processing tool.Using a standard set of deposition parameters for the production of atomic hydrogen by HWCVD,plots of the gas temperature in the deposition region were produced.From these plots,we were able to determine a safe deposition distance in the HWCVD reactor to be in the range between 3 and 4 cm from the filament.

Conjugate addition‐enantioselective protonation to forge tertiary stereocentresαto azaarenes via cooperative hydrogen atom transfer and chiral hydrogen‐bonding catalysis

Cooperative hydrogen atom transfer and chiral hydrogen‐bonding catalysis as a new platform for the asymmetric synthesis of azaarene derivatives is reported.By using a tetrabutylammonium decatungstate as the photocatalyst and a chiral phosphoric acid as the hydrogen‐bonding catalyst,transformations of a variety of commercially available hydrocarbons and silanes with diverseα‐branched 2‐vinylazaarenes could efficiently experience a tandem radical conjugate addition and enantioselective protonation process,providing a convenient and fully atom economical approach to access a range of valuable enantioenrichedα‐tertiary azaarenes in high yields with good to excellent enantioselectivities(up to 93%ee).Through the direct use of tert‐butyl methylcarbamate as the feedstock,this method enables a highly practical and concise synthesis of the enantiomerically pure medicinal molecule pheniramine(Avil).

Balancing electron transfer and intermediate adsorption ability of metallic Ni-Fe-RE-P bifunctional catalysts via 4f-2p-3d electron interaction for enhanced water splitting

Balancing electron transfer and intermediate adsorption ability of bifunctional catalysts via tailoring electronic structures is crucial for green hydrogen production,while it still remains challenging due to lacking efficient strategies.Herein,one efficient and universal strategy is developed to greatly regulate electronic structures of the metallic Ni-Fe-P catalysts via in-situ introducing the rare earth(RE)atoms(Ni-Fe-RE-P,RE=La,Ce,Pr,and Nd).Accordingly,the as-prepared optimal Ni-Fe-Ce-P/CC self-supported bifunctional electrodes exhibited superior electrocatalytic activity and excellent stability with the low overpotentials of 247 and 331 mV at 100 mA cm^(-2) for HER and OER,respectively.In the assembled electrolyzer,the Ni-Fe-Ce-P/CC as bifunctional electrodes displayed low operation potential of 1.49 V to achieve a current density of 10 mA cm^(-2),and the catalytic performance can be maintained for 100 h.Experimental results combined with density functional theory(DFT)calculation reveal that Ce doping leads to electron decentralization and crystal structure distortion,which can tailor the band structures and d-band center of Ni-Fe-P,further increasing conductivity and optimizing intermediate adsorption energy.Our work not only proposes a valuable strategy to regulate the electron transfer and intermediate adsorption of electrocatalysts via RE atoms doping,but also provides a deep under-standing of regulation mechanism of metallic electrocatalysts for enhanced water splitting.

Rationally construction of atomic-precise interfacial charge transfer channel and strong build-in electric field in nanocluster-based Zscheme heterojunctions with enhanced photocatalytic hydrogen production

The lack of effective charge transfer driving force and channel limits the electron directional migration in nanoclusters(NC)-based heterostructures,resulting in poor photocatalytic performance.Herein,a Z-scheme NC-based heterojunction(Pt1Ag28-BTT/CoP,BTT=1,3,5-benzenetrithiol)with strong internal electric field is constructed via interfacial Co-S bond,which exhibits an absolutely superiority in photocatalytic performance with 24.89 mmol·h^(−1)·g−1 H_(2)production rate,25.77%apparent quantum yield at 420 nm,and~100%activity retention in stability,compared with Pt1Ag28-BDT/CoP(BDT=1,3-benzenedithiol),Ag29-BDT/CoP,and CoP.The enhanced catalytic performance is contributed by the dual modulation strategy of inner core and outer shell of NC,wherein,the center Pt single atom doping regulates the band structure of NC to match well with CoP,builds internal electric field,and then drives photogenerated electrons steering;the accurate surface S modification promotes the formation of Co-S atomic-precise interface channel for further high-efficient Z-scheme charge directional migration.This work opens a new avenue for designing NC-based heterojunction with matchable band structure and valid interfacial charge transfer.

Photocatalytic[3+2]Cycloaddition of Alkyl/aryl Iodides and Internal Alkynes by Merging Halogen and Hydrogen Atom Transfer

Comprehensive Summary A visible light photocatalytic[3+2]cycloaddition of alkynes with readily accessible organic iodides as the C3 synthon is developed herein.By merging halogen atom transfer(XAT)and hydrogen atom transfer(HAT),alkyl/aryl iodides serve as a formal diradical precursor and add across C-C triple bonds to deliver a number of functionalized cyclopentanes in moderate to high yields with exceptional regio-and diastereoselectivity.A reductive radical-polar crossover mechanism,involving the cascade XAT,radical addition,1,5-HAT,polar effect-promoted 5-endo annulation,single electron transfer(SET)reduction,and protonation,may account for this unprecedented dehalogenative[3+2]cycloaddition.This work not only expands the repertoire of the traditional RATC methodology,but also provides a robust platform for the expedient assembly of cyclopentanes,a valuable structural motif in the realms of medicinal chemistry and material sciences.

Recent advances in FeCl_(3)-photocatalyzed organic reactions via hydrogen-atom transfer

In recent years,FeCl_(3)-photocatalyzed direct C–H/Si–H bond functionalization reactions have attracted huge attention.In those transformations,chlorine radical(Cl·)could be generated from FeCl_(3)via a ligandto-metal charge transfer(LMCT)/homolysis process under light irradiation.The resulting chlorine radical subsequently acts as a hydrogen atom transfer(HAT)agent to abstract the hydrogen atom of aliphatic C–H,O–H,or Si–H bonds to give the corresponding C/Si/O-centered radicals for various organic transformations.In this review,we summarized the recent advances in the application of FeCl_(3)as a HAT photocatalyst for the C/Si–H functionalization to construct C–C,C–N,C–Si,C–S,C–B,and C-P bonds.

Ionization Process of Atoms by Intense Femtosecond Chirped Laser Pulses

We numerically investigate the ionization mechanism in a real hydrogen atom under intense fem to second chirped laser pulses. The central carrier frequency of the pulses is chosen to be 6.2 eV (λ = 200 nm), which corresponds to the fourth-harmonic of the Ti:Sapphire laser. Our simulation of the laser-atom interaction consists on numerically solving the three-dimensional time-dependent Schrodinger equation with a spectral method. The unperturbed wave functions and electronic energies of the atomic system were found by using an L2 discretization technique based on the expansion of the wave functions on B-spline functions. The presented results of kinetic energy spectra of the emitted electrons show the sensitivity of the ionization process to the chirp parameter. Particular attention is paid to the important role of the excited bound states involved in the ionization paths.

Cu single atoms embedded on hollow g-C_(3)N_(4)nanospheres with enhanced charge transfer and separation for efficient photocatalysis

Establishing an effective charge transfer mechanism in carbon nitride(g-C_(3)N_(4))to enhance its photocatalytic activity remains a limiting nuisance.Herein,the combination design of a single Cu atom with hollow g-C_(3)N_(4)nanospheres(Cu-N_(3)structure)has been proven to offer significant opportunities for this crucial challenge.Moreover,this structure endows two pathways for charge transfer in the reaction,namely,the N atoms in the three-dimensional planar structure are only bonded with a single Cu atom,and charge transfer occurs between the plane and the layered structure due to the bending of the interlayered g-C_(3)N_(4)hollow nanospheres.Notably,Cu-N_(3)and hollow nanosphere structures have been certified to greatly enhance the efficiency of photogenerated carrier separation and transfer between the layers and planes by ultrafast spectral analysis.As a result,this catalyst possesses unparalleled photocatalytic efficiency.Specifically,the hydrogen production rate up to 2040μmol h^(−1) g^(−1),which is 51 times that of pure C_(3)N_(4)under visible light conditions.The photocatalytic degradation performance of tetracycline and oxidation performance of benzene is also expressed,with a degradation rate of 100%,a conversion of 97.3%and a selectivity of 99.9%.This work focuses on the structure-activity relationship to provide the possibilities for the development of potential photocatalytic materials.

Quasi-continuous synthesis of cobalt single atom catalysts for transfer hydrogenation of quinoline

Improving the transfer hydrogenation of N-heteroarenes is of key importance for various industrial pro-cesses and remains a challenge so far.We reported here a microcapsule-pyrolysis strategy to quasi-continuous synthesis S,N co-doped carbon supported Co single atom catalysts(Co/SNC),which was used for transfer hydrogenation of quinoline with formic acid as the hydrogen donor.Given the unique ge-ometric and electronic properties of the Co single atoms,the excellent catalytic activity,selectivity and stability were observed.Benefiting from the quasi-continuous synthesis method,the as-obtained cata-lysts provide a reference for the large-scale preparation of single atom catalysts without amplification ef-fect.Highly catalytic performances and quasi-continuous preparation process,demonstrating a new and promising approach to rational design of atomically dispersed catalysts with maximum atomic efficiency in industrial.

Decatungstate as a direct hydrogen atom transfer photocatalyst for synthesis of trifluromethylthioesters from aldehydes

We have developed a versatile,mild protocol for trifluoromethylthiolation reactions of aldehydes with catalysis by a decatungstate hydrogen atom transfer photocatalyst under redox-neutral conditions.The protocol is highly selective,operationally simple,and compatible with a wide array of sensitive functional groups.It can be used for late-stage functionalization of bioactive molecules,which makes it convenient for drug discovery.

Determining the contribution of Mo single atoms components in MoO_(2)nanocatalyst in transfer hydrogenation

Nanocatalysts are likely to contain undetected single-atom components,which may have been ignored but have significant effect in catalytic reactions.Herein,we report a catalyst composed of Mo single atoms(SAs)and MoO_(2)nanoparticles(NPs)(MoSAs-MoO_(2)@NC),which is an exact model to understand how the SAs contribute to the nanocatalyst.Both experimental results and the density functional theory calculations reveal that Mo SAs on nitrogen-doped carbon provides the reaction zone for nitro reduction,while MoO_(2)is the active site for decomposing hydrazine hydrate to produce H*.Thanks to the synergy between Mo SAs and MoO_(2)NPs,this catalyst exhibits noble metal-like catalytic activity(100%conversion at 4 min)for the dechlorination-proof transfer hydrogenation.Additionally,the hydrogen migration on the catalyst is verified by the electrochemical tests in the absence of a hydrogen source.This work provides a model for further study on the coexistence of single atoms in nanoparticle catalysts.

Photoinduced and palladium-catalyzed hydrogen atom transfer triggered 1,2-difunctionalization of 1,3-dienes with hydroxamides

The discovery of novel catalysis modes to generate a significant increase in structural complexity from readily available reactants is a fundamental goal in modern organic synthesis.Here,we report a photoinduced palladium-catalyzed hydrogen atom transfer triggered 1,2-difunctionalization of conjugated dienes.Without the employment of exogeneous photosensitizers and external oxidants,the cascade reaction realized the integration of remote functionalization of various C(sp^(3))-H bonds and selective difunctionalization of 1,3-dienes with 100% atom efficiency,allowing for the synthesis of structurally diverse amides with up to 90% yields.Given the prevalence of amides in pharmaceuticals and natural products,the current protocol has provided an efficient means to access highly functionalized amides from readily available carboxylic acid derivatives and 1,3-dienes.

Exact quantum calculations on the collinear hydrogen atom transfer reaction——I. Study on oscillations of the reaction probabilities of Cl+HCl

1-D quantum calculations of reaction probabilities have been carried out for the col- linear reaction Cl+HCl (v≤3)→ClH (v＇≤3)+Cl using hyperspherical coordinates. An LEPS po- tential energy surface with a shallow well depth of -3.22 KJ/mol has been used in the calculations. The state-to-state reaction probabilities have been calculated. According to the results obtained we found that the diagonal (v=v＇) reaction probabilities dominate over the off-diagonal (vv＇) reaction probabilities and the largest off-diagonal reaction probabilities are smaller than 0.1. The reaction probabilities show oscillation as a function of energy. Dynamic resonances strengthen for the potential energy surface with a well.

果蔬食品体外抗氧化方法研究进展

食用果蔬食品可以有效降低多种疾病的发生率,抗氧化能力是重要原因。抗氧化物质清除自由基的机制主要有氢原子转移(HAT)和单电子转移(SET)2种。本文具体介绍了ORAC法、TRAP法、PCL化学发光法、β-胡萝卜素亚油酸体系、LDL低密度脂蛋白氧化方法、福林酚法、ABTS清除自由法、DPPH清除自由基法、FRAP法。并结合实例介绍果蔬食品体外抗氧化方法研究进展,对抗氧化方法的标准化进行了展望。

质子化双氧/硫杂卟啉内氢原子迁移反应的理论研究

在确定各反应体系反应物、产物稳定构象的基础上,采用B3LYP/6-31G**方法在Gaussian03程序下,对质子化的双氧/硫杂卟啉的内氢迁移(IHAT)反应进行研究,寻找并优化相应的过渡态,比较其迁移反应速率的差异.计算结果表明,质子化双氧/硫杂卟啉的构象稳定性仍然是由芳香性、空间位阻、静电作用共同决定的.质子化后的双取代体系的内氢迁移反应速率大小差异显著,内环取代对IHAT反应速率的影响主要来源于电子效应,而非构象变化;且双取代对体系IHAT反应速率的影响要远大于单取代.

茶黄素抗氧化化学机制研究

采用DPPH自由基清除法、ABTS自由基清除法、Cu^(2+)还原能力评价法3种化学模型,测定茶黄素的体外抗氧化能力(以Trolox作为阳性对照),并进一步探讨其化学机制。结果表明:在3种化学模型中,茶黄素(及Trolox)的抗氧化能力表现出良好的剂量相关性;茶黄素的IC_(50)值均低于阳性对照Trolox。茶黄素在上述3种化学模型中,抗氧化活性分别相当于Trolox的2.57,3.13,3.74倍。作为一种天然的抗氧化剂,茶黄素抗氧化的化学机制涉及氢原子转移(HAT)和电子转移(ET)。通过HAT机制,茶黄素可能转化为稳定的邻苯醌式产物。

卟啉内氢迁移反应氟取代基效应的理论研究

采用B3LYP/6-31G**的方法在Gaussian03程序下对卟吩(PH2)、m-四氟卟啉(m-TFPH2)、β-八氟卟啉(β-OFPH2)和m-四氟,β-八氟卟啉(12FPH2)的结构进行几何优化,并进行振动分析.计算并讨论了PH2、m-TFPH2、β-OFPH2和12FPH2在内氢迁移反应中的反应物、产物、中间体、过渡态及二级鞍点的结构与能量.通过对结构和能量的比较,发现各物质内氢迁移反应均以异步历程进行,可见取代基对卟啉内氢迁移反应的历程选择没有影响.但取代基会影响同步历程和异步历程之间的速率差异.另外,氟取代基使得内氢迁移反应的异步历程的正负反应速率有所减小,起决定性作用的是取代基的电子效应,这些与化学直观也是相一致的.

氧/硫杂卟啉内氢迁移反应的理论研究

采用B3LYP/6-31G**方法在Gaussian03程序下,对氧杂卟啉(OPH),硫杂卟啉(SPH)的结构和能量进行优化,并寻找与内氢迁移反应相关的过渡态构型.计算结果表明,由于分子内氢键的存在,氧或硫杂化均会使卟吩内氢迁移正负反应速率明显降低.

一氯乙酸/FeCl_2·4H_2O催化合成聚苯乙烯遥爪预聚物

以一氯乙酸为引发剂 ,以FeCl2 ·4H2 O为新型催化剂 ,对苯乙烯进行了原子转移自由基聚合(ATRP) ,制得了含端羧基和端基氯的聚苯乙烯遥爪预聚物 ,并对聚苯乙烯与丙烯酸丁酯的嵌段共聚进行了研究 .结果表明 :利用ATRP技术可一步合成含端羧基和端基氯的聚苯乙烯遥爪预聚物 ,并可有效控制预聚物的相对分子质量及其相对分子质量分布 (1.3～ 1.6 ) ,预聚物的数均相对分子质量随单体转化率的提高而线性增加 ,ln([M ]0 / [M ])与时间呈线性关系 .表明该催化引发聚合反应具有活性可控聚合的特征 .

卟吩内氢迁移反应的理论研究

用B3LYP/6 3 1G 方法计算卟吩内氢迁移反应中的反应物、产物、中间体、过渡态及其二级鞍点的结构与能量 .结果表明 ,分步反应历程的几率较大 ,与实验的预测一致 .