Orientation and Structure of Ionic Liquid Cation at Air/[bmim][BF4] Aqueous Solution Interface

The watermiscible room temperature ionic liquid 1butyl3methylimidazolium tetrafluorob orate （[bmim] [BF4]） is a model system for studying the interactions between ionic liquid and water molecules. In this work the orientational structure of the low concentrated aqueous solution of [bmim] [BF4] at the air/liquid interface was investigated by sum frequency gener ation vibrational spectroscopy. It has been found that at very low concentrations, the butyl chain exhibited a significant gauche defect, indicating a disordered conformation; and the cation ring oriented with a fairly small tilting angle at the surface. When the concentration increased, the cation ring tended to lie flat at the surface, and the gauche defects of the butyl chain decreased due to the intermolecular chainchain interactions and the consequent more ordered interfacial molecular arrangement. Additionally, the antisymmetric stretching mode in the PPP and SPS spectra exhibited a peak shift, showing that there exists more than one kind of orientation or chemical environment for the butyl CH3 group. These results may shed new light on understanding the surface behavior of watermiscible ionic liquids as well as the imidazolium based surfactants.     

Laser-induced Fluorescence Spectroscopy of CoS： Identification of a New Excited State Arising from the Ground State

Laser-induced fluorescence excitation spectra and dispersed fluorescence spectra of cobalt sulfide （COS） have been recorded in the energy range of 22400-24400 cm-1 （corresponding to 446-409 nm）. A new electronic transition progression with six vibronic bands, stemming from the X4AT/2 state of CoS, was identified and assigned to be [24.0014AT/2-X4A7/2. The new observed 4A state most probably originates from the core[10a2][47r3][lla2][153][57r3] electronic configuration. Strong perturbations are found to extensively exist in the transition bands of this new state. The rotational constants and lifetimes of these bands have been determined.     

Theoretical insights into the mechanism of photocatalytic reduction of CO2 over semiconductor catalysts

Photocatalytic reduction of CO₂ is one important approach to alleviate greenhouse gas emission and energy crisis, which has gained huge attention in the past decades. However, the lack of understanding complex reaction mechanism impedes new catalysts design. It is also very difficult to understand the mechanism by using only experimental approaches. For this concern, theoretical calculations can effectively supplement the experimental deficiency and thus play an important role. Recently theoretical calculations have been performed on adsorption, migration and reduction of CO₂ molecule on the photocatalyst surface, leading to useful information that have contributed greatly to this field. This review summarizes recent advances in first-principles calculations about CO₂ photoreduction over various semiconductor photocatalysts like metal oxides, sulfides and g-C₃N₄. The methods, models, adsorption and reaction pathways have been discussed in detail. The perspective about future investigation on the photocatalytic reduction of CO₂ using first principles calculations is also presented.     

热稳定单原子催化剂的理性构筑:从原子级结构到实际应用

80%以上的工业生产过程涉及催化,如化工生产、能源转换、制药和废物处理等等.催化剂的使用显著提高了生产效率,降低了生产成本,为国民经济、地球环境和人类文明的可持续发展做出了很大贡献.为了满足日益增长的生产需求和最大的经济效益,开发高效、稳定、低成本的新型催化剂已成为当务之急.金属中心负载在载体上的负载型金属催化剂因其较好的催化活性和相对较低的金属用量而受到广泛关注.研究发现,负载型结构可增强传热和传质并增加活性金属中心的分散度,从而影响催化性能.此外,负载金属的颗粒尺寸对催化剂的性能有很大影响.迄今为止,科学家们一直在通过减小金属颗粒尺寸和提高原子利用效率来提高催化剂的活性.原子级尺寸的颗粒通常表现出与大尺寸颗粒显着不同的物理和化学性质,而当活性位点的尺寸缩小到单个原子时,单原子催化剂的概念应运而生.对于单原子催化剂,金属原子中心通过配位被载体中的缺陷锚定,从而调整金属原子的电子云分布.这种配位调整使得单原子催化剂拥有与传统催化剂不同的性能.作为催化领域的新前沿,单原子催化剂已经在许多催化反应中表现出前所未有的活性和选择性.然而,许多报道的单原子催化剂在高温环境或长期催化应用中容易受到奥斯特瓦尔德熟化过程的影响,从而导致催化剂烧结和失活.而烧结的原因在于金属原子和载体之间较弱的相互作用.失活催化剂的再生和回收将大大增加工业生产的时间和经济成本.因此,开发具有优异热稳定性的单原子催化剂以满足工业需求是十分必要的.本综述首先总结了近年来关于热稳定型单原子催化剂合成方法的基础研究,并从原子尺度上分析了这些方法所构建的金属中心的结构形态和配位环境.此外,结合近些年的研究中新的表征技术与理论计算手段解释了热稳定性的来源.重点讨论了热稳定单原子催化剂的实际催化应用.分析了热稳定单原子催化剂在热催化应用中的独特作用机理、并尝试为确定催化过程中真正的活性中心以及通过原子级调控手段进行高活性热稳定单原子催化剂的合成提供理论指导.最后总结了热稳定单原子催化剂发展的主要问题,并简要分析了单原子催化领域的研究挑战和发展前景.     

Unraveling the Mechanism for the Sharp‐Tip Enhanced Electrocatalytic Carbon Dioxide Reduction: The Kinetics Decide

The electrocatalytic reduction reaction of carbon dioxide can be significantly enhanced by the use of a sharp‐tip electrode. However, the experimentally observed rate enhancement is many orders of magnitudes smaller than what would be expected from an energetic point of view. The kinetics of this tip‐enhanced reaction are shown to play a decisive role, and a novel reaction‐diffusion kinetic model is proposed. The experimentally observed sharp‐tip enhanced reaction and the maximal producing rate of carbon monoxide under different electrode potentials are well‐reproduced. Moreover, the optimal performance shows a strong dependence on the interaction between CO₂ and the local electric field, on the adsorption rate of CO₂, but not on the reaction barrier. Two new strategies to further enhance the reaction rate have also been proposed. The findings highlight the importance of kinetics in modeling electrocatalytic reactions.     

Precisely installing gold nanoparticles at the core/shell interface of micellar assemblies of triblock copolymers

Two reduction-cleavable ABA triblock copolymers possessing two disulfide linkages, PMMA-ss-PMEO₃MA-ss-PMMA and PDEA-ss-PEO-ss-PDEA were synthesized via facile substitution reactions from homopolymer precursors, where PMMA, PMEO₃MA, PDEA, and PEO represent poly(methyl methacrylate), poly(tri(ethylene glycol) monomethyl ether methacrylate, poly(2-(diethylamino)ethyl methacrylate), and poly(ethylene oxide), respectively. Spherical micelles were obtained through supramolecular self-assembly of these two triblock copolymers in aqueous solutions. The resultant micelles with abundant disulfide bonds could serve as soft templates and precisely accommodate gold nanoparticles in the core/shell interface as a result of the formation of Au-S bonds.     

Characterization of the low-temperature oxidation chemistry of an unsaturated aldehyde 2-butenal in a Jet-stirred reactor

Unsaturated aldehydes such as butenal are essential intermediates in the combustion of various alkenes and oxygenated biofuels. 2-Butenal is a typical intermediate included in the core mechanism, containing a C=C double bond adjacent to an aldehyde group. In the present work, the oxidation of 2-butenal is studied in a jet-stirred reactor (JSR) at atmospheric pressure under temperature ranging from 500 to 850 K. The synchrotron vacuum ultraviolet photoionization mass spectrometry is employed to identify the key intermediates. A kinetic model for 2-butenal oxidation is developed and validated against the experimental datasets. Fuel flux and sensitivity analyses are performed to clarify reactions governing the reactivity of 2-butenal. OH addition to the C=C double bond is essential for fuel reactivity at the initial stage. A combination of experimental observations and kinetic simulations is used to illuminate the Waddington mechanism initiated by OH addition. The resonance-stabilized feature of fuel radicals facilitates their interactions with HO₂ radicals, which replenishes a large amount of OH radicals and contributes to the formation of CO₂.     

New insights into the oxidation chemistry of pyrrole,an N-containing biomass tar component

Pyrrole, the smallest molecule with a nitrogen atom in the heterocycle ring, is an important tar component from coal and nitrogen-rich biomass devolatilization. Understanding the combustion chemistry of pyrrole can help to elucidate the pollutant formation chemistry from fuel nitrogen, thus enabling cleaner biomass energy utilization technologies. Experimental measurements were performed in a jet stirred reactor coupled with time of flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet beam as photon ionization source, and gas chromatography-mass spectrometry to provide comprehensive measurements of 31 species including nine C₄ and C₅ N-containing compounds. Based on the evidence from the experiments and aiming to improve the kinetic model performance, possible formation routes are proposed with OH addition as the entrance reaction. Reaction rate coefficients for the OH addition channel as well as those for key H-atom abstraction reactions (H, OH, CH_3, and HO₂) were calculated by quantum chemical methods and updated in the model. The updated model can qualitatively predict the identified C₄ N-containing species and perform reasonably well for a large set of experimental data considered for validation, overall improving the performance of the previous model. The influence of the investigated reactions on the predictions of fuel reactivity and pollutant formation motivates further investigations of N-containing fuel chemistry.     

Oxidation of ethyl methyl ether: Jet-stirred reactor experiments and kinetic modeling

Larger ethers such as diethyl ether (DEE) and di-n-propyl ether (DPE) have different oxidation behavior (double-NTC behavior) compared to the simplest dimethyl ether (DME). Such phenomena are interpreted with different reactions and processes in different ether kinetic models, which also predict different formation pathways of oxidation intermediates such as acids. To gain further insights into the oxidation kinetics of linear ethers, ethyl methyl ether (EME), which has a nonsymmetrical structure, was studied in this work. Oxidation experiments of 1% of EME were performed in a jet-stirred reactor at 1 atm, a residence time of 2 s, an equivalence ratio of 1, and over a temperature range of 375–850 K. The intermediates were analyzed with photoionization molecular-beam mass spectrometry. To explain the oxidation behavior of EME, a detailed kinetic model was also constructed. The oxidation of EME spans a wider temperature range than DME, but no obvious double-NTC behavior was observed as DEE. Based on the model analysis and profiles of critical intermediates such as ketohydroperoxides (KHPs) and CH₃O₂H, the low-temperature oxidation behavior of EME was explained by the chain-branching reactions of the fuel itself and the oxidation intermediates. Abundant species such as aldehydes, acids, esters, and fuel-specific dione species were detected and could be well reproduced by the current model. In particular, acids are produced by the decomposition of KHPs and subsequent reactions of the intermediate CH₃CHO. Esters and dione species are mainly formed via fuel-related pathways.     

On the low-temperature chemistry of 1,3-butadiene

In this paper, species versus temperature profiles were measured during the oxidation of 1,3-butadiene in a jet-stirred reactor (JSR) at 1 atm, at different equivalence ratios (φ = 0.5, 1.0 and 2.0), in the temperature range 600 – 1020 K. Both synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography (GC) methods were used to analyze the species. The experimental results show that a large proportion of the products are aldehydes (formaldehyde, acetaldehyde, acrolein, etc.) and ketenes (ketene, methyl-ketene), with acrolein being one of the major products. Moreover, furan, 1,3-cyclopentadiene and benzene are also present as intermediates in significant amounts. The reaction pathways leading to the formation of these species are discussed in detail. A new detailed mechanism, NUIGMech1.3, was developed to simulate these new data as well as other experimental data available in the literature. The validation results indicate that quantum calculations are also needed to explore the formation of some important species formed in the oxidation of 1,3-butadiene. Overall, the new 1,3-butadiene mechanism agrees well with various experimental data in the low- to high-temperature regimes and at different pressures. Flux and sensitivity analyses show that 1,3-butadiene shares some common reaction chemistry pathways with 1- and 2-butene via Ḣ atom and HȮ₂ radical addition to the C = C double bond in 1,3-butadiene, reactions which are important for both systems. The low temperature chemistry of 1,3-butadiene is mainly controlled by the reaction pathways of ȮH radical addition to the C = C double bond of the fuel molecule. The 1-buten-4-ol-3-yl radicals so formed subsequently add to O₂ and react via the Waddington mechanism, which is important in accurately simulating the oxidation and auto-ignition of 1,3-butadiene at engine relevant conditions.