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Photocatalysis via direct solar‐to‐chemical energy conversion is an intriguing approach for alleviating the pressure of high energy consumption caused by social development. However, photocatalytic efficiency is greatly restricted by unsatisfactory light‐harvesting capacity, high carrier recombination rates, and sluggish reaction kinetics. Indeed, vacancy engineering is an attractive strategy to regulate photocatalytic reaction performance to maximize the utilization and storage of solar energy. In this review, we summarize recent progress about the important roles of vacancy defects on solar‐driven photocatalytic applications. The current advanced characterization techniques, especially for in situ/operando techniques, are first presented for elucidating the structure‐performance relationships of defective semiconductors in photocatalysis. Subsequently, the crucial roles of vacancies in enhancing photocatalytic performance are highlighted from three important processes: light absorption, carrier separation and migration, and surface reaction. Finally, based on the above understanding, perspectives and opportunities about defective materials are considered for various photocatalytic applications. [ABSTRACT FROM AUTHOR]

H 2 /O 2 chemistries are of great crucial for all hydrocarbon and syngas oxidations. Recent study showed that presence of residual H-atom in shock tubes may heavily influences experimental determination of ignition delay times in H 2 /O 2 mixtures. Although numerous studies of hydrogen ignition delay times were reported, none of them discussed the residual H-atom in their studies which may impact the accuracy of their measurements. In this study, a systematic measurement related to the ignition delay times were conducted for H 2 /O 2 mixtures diluted with argon over the temperatures from 850 K to 1500 K, the pressures from 1.2 to 16.0 atm, and the equivalence ratios of 0.5, 1.0 and 2.0. Special attentions were paid to eliminate the influence of residual H-atom on ignition delay time and the calculation showed that the residual H-atom in current shock tube shows no obvious effect on ignition delay time, which guarantees the present data more convincing. The measurements showed that the hydrogen mixtures have different global activation energies under different pressures. Thus, correlations were derived under different pressures based on all experimental data, which fit fairly well with the experimental data. A couple of detailed kinetic models from literature were validated against the present experimental results. The result shows that the mechanism of Kéromnès-2013 yields the best agreement with data from shock tube experiments at various pressures up to 16 atm, while Davis-2005, GRI 3.0, SanDiego-2011 and Li-2004 mechanisms present significant poor predictions at higher pressures. This investigation is contrary to the previous studies. Reaction pathway and sensitivity analysis indicated that reaction R10: H + O 2 (+M) <=> HO 2 (+M) is of significant important pressure-dependent reaction in controlling of hydrogen oxidation. It is inferred that significant differences of their rate constants among various mechanisms induce the difference of performance on hydrogen ignition predictions. [ABSTRACT FROM AUTHOR]

A new, reduced reaction mechanism for DME combustion in internal combustion engines is proposed. The new mechanism is based on a detailed DME mechanism suitable for low to high temperature ranges. The reduced model consists of 29 species and 66 reactions and contains a detailed H 2 /CO mechanism and reduced C1–C2 chemistry. The reduced mechanism inherits the major reaction pathways of the detailed mechanism, which ensures its predictive capability when coupled into CFD simulations. The performance of the reduced mechanism was compared to simulation results of the detailed mechanism, ignition delay times from a shock tube and a rapid compression machine, and DME engine combustion data. Overall, the reduced mechanism shows a good balance between accuracy and computational efficiency necessary for use in combustion system design applications. [ABSTRACT FROM AUTHOR]

Ignition delay times of 1-butene were measured behind reflected shock wave at the pressures of 1.2, 4.0, 16.0 atm, in temperature range of 1000–1700 K and equivalence ratios of 0.5, 1.0 and 2.0. Results show that ignition delay times exhibit the typical Arrhenius dependence on temperature, pressure, equivalence ratio and fuel concentration. A correlation was deduced from the experimental data. Comparison was made between the correlation and the previous data, and good agreement was achieved. Three widely used models, NUIG Aramco Mech 1.3 (Metcalfe et al., 2013), USC Mech 2.0 (Wang et al.) and LLNL C4 (Marinov et al., 1998) model, were used to predict the ignition delay times and comparison was made with the experimental data. None of these models can well reproduce the experimental data of 1-butene especially at lower temperature. Besides, comparative studies and qualitative analysis between C4 hydrocarbons and 1-alkenes with respect to the effect of C C bond and the carbon chain length were made at same argon–oxygen dilution ratios ( D ). Sensitivity analysis was made to identify the key reactions that control the ignition of 1-butene, and modifications for improving the model performance were recommended. [ABSTRACT FROM AUTHOR]

The effects of hydrogen on ignition characteristics of dimethyl ether (DME) with air under engine-relevant conditions were studied by CHEMKIN package coupled with chemical kinetic models. Firstly, four recently developed DME models were used to validate the measured ignition delay times from previous literature. The validation results showed that NUIG Mech_56.54 agrees the literature data best and thus was chosen to conduct the following simulations and chemical kinetic analysis of ignition behaviors of DME/H 2 mixture at low temperature. Subsequently, simulations of auto-ignition of DME/H 2 /air using NUIG Mech_56.54 were made under various hydrogen blending ratios (0, 50%, 80%, 90%, 95%, 98% and 100%). It was found that hydrogen retarded the ignition timing of DME at engine-relevant conditions and this effect was non-linear with the increase of hydrogen blending ratio. The inhibition and non-linear effect was chemically interpreted by radical mole fraction analysis. Finally, reaction pathway and sensitivity analysis were made to gain further insight on ignition chemistries of DME/H 2 blends under engine-relevant conditions. [ABSTRACT FROM AUTHOR]

Abstract: Using a high-pressure shock tube facility, the ignition delay times of stoichiometric C2H6/H2/O2 diluted in argon were obtained behind reflected shock wave at elevated pressures (p = 1.2, 4.0 and 16.0 atm) with ethane blending ratios from 0 to 100%. The measured ignition delay times were compared to the previous correlations, and the results show that the ignition delay times of ethane from different studies exhibit an obvious difference. Meanwhile, numerical studies were conducted with three generally accepted kinetic mechanisms and the results show that only NUIG Aramco Mech 1.3 agrees well with the measurements under all test conditions. Sensitivity analysis was made to interpret the poor prediction of the other two mechanisms. Furthermore, the effect of ethane blending ratio on the ignition delay times of the mixtures was analyzed and the results show that ethane blending ratio gives a non-linear effect on the auto-ignition of hydrogen. Finally, chemical interpretations on this non-linear effect were made from the reaction pathway analysis and normalized H radical consumption analysis. [Copyright &y& Elsevier]

Abstract: Ignition delay times of dimethyl ether (DME)/hydrogen/oxygen/argon mixtures (hydrogen blending ratio ranging from 0% to 100%) were measured behind reflected shock waves at pressures of 1.2–10atm, temperature range of 900–1700K, and for the lean (ϕ =0.5), stoichiometric (ϕ =1.0) and rich (ϕ =2.0) mixtures. For more understanding the effect of initial parameters, correlations of ignition delay times for the lean mixtures were obtained on the basis of the measured data (X H2 ⩽95%) through multiple linear regression. Ignition delay times of the DME/H2 mixtures demonstrate three ignition regimes. For X H2 ⩽80%, the ignition is dominated by the DME chemistry and ignition delay times show a typical Arrhenius dependence on temperature and pressure. For 80%⩽ X H2 ⩽98%, the ignition is dominated by the combined chemistries of DME and hydrogen, and ignition delay times at higher pressures give higher ignition activation energy. However, for X H2 ⩾98%, the transition in activation energy for the mixture was found as decreasing the temperature, indicating that the ignition is dominated by the hydrogen chemistry. Simulations were made using two available models and different results were presented. Thus, sensitivity analysis was performed to illustrate the causes of different simulation results of the two models. Subsequently, chemically interpreting on the effect of hydrogen blending ratio on ignition delay times was made using small radical mole fraction and reaction pathway analysis. Finally, high-pressure simulations were performed, serving as a starting point for the future work. [Copyright &y& Elsevier]

Abstract: n-Butanal is a key stable intermediate during the combustion of n-butanol, and as such strongly affects its chemical kinetics. In this study, ignition delay times of n-butanal/oxygen diluted with argon were measured behind reflected shock waves in the temperature range of 1100–1650K, at pressures of 1.3, 5 and 10atm, and equivalence ratios of 0.5, 1.0 and 2.0. An n-butanal sub-model was developed on the basis of literature review, and exhibits fairly good agreement with the experimental results under all test conditions. Reaction pathway and sensitivity analysis were conducted to gain an insight into the controlling reaction pathways and reaction steps. [Copyright &y& Elsevier]

Abstract: Experimental and numerical study on laminar burning velocity of H2/CO/N2/CO2/air mixtures was conducted by using a constant volume bomb and Chemkin package. Good agreement between experimental measurements and numerical calculations by using USCII Mech is achieved. Diffusional-thermal instability is enhanced but hydrodynamic instability is insensitive to the increase of hydrogen fraction in fuel mixtures. For mixtures with different hydrogen fractions, the adiabatic flame temperature is not the dominant influencing factor while high thermal diffusivity of hydrogen obviously enhances the laminar burning velocity. Laminar burning velocities increase with increasing hydrogen fraction and equivalence ratio (0.4–1.0). This is mainly due to the high reactivity of H2 leading to high production rate of H and OH radicals. Reactions R3 and R2 play the dominant role in the production of H radical for mixtures with high hydrogen fraction, and reaction R31 plays the dominant role for mixtures with low hydrogen fraction. [Copyright &y& Elsevier]

• NiCoP/NF is prepared by two steps, reduction and phosphidation. • Cobalt doping significantly enhances the charge polarization of Ni and P. • 4-NiCoP/NF shows the highest hydrogen evolution rates. • Chemical kinetics for catalysts are determined. Ammonia borane (NH 3 BH 3) is being widely used as a hydrogen (H 2) storage material. Hydrogen storage content of NH 3 BH 3 is suitable to produce H 2 at room temperature in the presence of an efficient catalyst. Herein, cobalt doped nickel phosphide catalyst is developed to improve NH 3 BH 3 hydrolysis by two steps. In first step, cobalt doped nickel hydroxide nanosheets are developed on the surface of nickel foam (NF) by immersing the NF in different concentrations of cobalt nitrate solution. In second step, self-supported cobalt doped nickel phosphide on NF is prepared by phosphidation at 300 °C. The partial positive charge of Ni and partial negative charge of P produce the charged polarization at the surface of NF. The catalyst optimization shows that 4-NiCoP/NF (0.01 M concentration of cobalt nitrate solution) produces the highest H 2 production among all prepared samples. Same procedure is adopted to produce FeNiP/NF to determine the authenticity of the method. The reaction kinetics are calculated for both 4-NiCoP/NF and 4-FeNiP/NF best catalysts. The energy of activations 58.95 kJ·mol−1 for NiCoP/NF and 60.26 kJ·mol−1 NiFeP/NF are calculated via Arrhenius Equation. High activation energy of NiFeP/NF reveals that NiCoP/NF is better for H 2 production. The on/off characteristics of the catalyst is unique for H 2 evolution. [ABSTRACT FROM AUTHOR]

High-energy-density (HED) fuels have drawn substantial attention for volume-limited aerospace vehicles because they can provide high propulsion energy. Herein, we report a route for synthesis of HED fuel pentacyclo[5.3.0.02,5.03,9.04,8]decane (PCD) with strained structure by photoinduced intramolecular [2 + 2] cycloaddition of dicyclopentadiene (DCPD). The reaction conditions, like photosensitizer, solvent, concentration, temperature and light intensity, were optimized for achieving the best photochemical performance, with the high DCPD conversion of 95.89% and high PCD selectivity of 62.08%. The triplet quenching and phosphorescence quenching results show that DCPD cycloaddition proceeds under the photosensitizer photoexcitation, triplet-triplet energy transfer, cyclization and relaxation. Moreover, a reaction kinetic model is established with the reaction rate constant being correlated with light intensity, with the pseudo reaction kinetics parameters and reaction rate equations obtained. As a caged fuel, PCD possesses both high density (1.066 g/cm3) and high volumetric neat heat of combustion (44.43 MJ/L), which is very promising to blend with current high density liquid fuels to obtain high-performance fuels for practical application. • PCD is synthesized by a one-step photoinduced intramolecular [2 + 2] cycloaddition. • The triplet sensitization mechanism was proposed. • A reaction kinetic model correlated with light intensity is established. • PCD exhibits both high density and high volumetric neat heat of combustion. • PCD is a promising high-energy additive for practical application. [ABSTRACT FROM AUTHOR]

Abstract: Ignition delay times of n- and i-propanol mixtures in argon-diluted oxygen were measured behind reflected shocks. Experimental conditions are: temperatures from 1100 and 1500K, pressures from 1.2 to 16.0atm, fuel concentrations of 0.5%, 0.75%, 1.0%, and equivalence ratios of 0.5, 1.0 and 2.0. A detailed kinetic model consisting of 238 species and 1448 reactions was developed to simulate the ignition of the two propanol isomers, with the computed ignition delay times agreeing well with the present measured results as well as the literature data at other conditions. Further validation of the kinetic mechanism was conducted by comparing the simulated results with measured JSR data and laminar flame speeds, and reasonable agreements were achieved for all test conditions. Moreover, reaction pathway analysis indicated that n-propanol mainly produces ethenol, ethene and propene, while i-propanol primarily produces acetone and propene. Finally, sensitivity analysis demonstrated that some fuel-species reactions can be found in the most important reactions for both propanols, and these are mainly the H-abstraction reactions. [Copyright &y& Elsevier]

Abstract: Measurements on ignition delay times of propane/hydrogen mixtures in argon diluted oxygen were conducted for hydrogen fractions in the fuel mixtures from 0 to 100%, pressures of 1.2, 4.0 and 10 atm, and temperatures from 1000 to 1600 K using the shock-tube. Results show that for less than 70%, ignition delay time shows a strong Arrhenius temperature dependence and it decreases with the increase of pressure, while for larger than 90%, there is a crossover pressure dependence of the ignition delay time with increasing temperature. Numerical studies were made using the selected kinetic mechanisms and results show that the predicted ignition delay time gives a reasonable agreement with the measurements. Both measurements and predictions show that for less than 70%, the ignition delay time is only moderately decreased with the increase of , indicating that hydrogen addition has weak effect on ignition enhancement. Sensitivity analysis reveals the key reactions that control the simulation of ignition delay time. Kinetic study is made to interpret the ignition delay time dependence on pressure and . [Copyright &y& Elsevier]

In current aircraft designs, jet fuel serves a dual role as a coolant to satisfy the cooling requirements and as a propellant to provide propulsion power, especially in high-performance aircraft. Importantly, thermal oxidative stability is one of the key issues for jet fuels that serve as coolants since the formation of deposits during heat exchange will directly influence the operational safety of the aircraft. This review summarizes the research progress on the thermal oxidation and deposition of jet fuel during autoxidation, with particular emphasis on the research performed over the past few decades. The precise concept of thermal oxidative stability is first introduced. Then, the oxidation and deposition mechanisms of jet fuel and the corresponding reaction kinetics during thermal stress are comprehensively summarized. After that, different evaluation techniques (oxidation and deposition), as well as the factors influencing the thermal oxidative stability of jet fuel (chemical and physical factors), are presented in detail. Finally, the corresponding improvement methods for delaying fuel oxidation and mitigating deposition are proposed. This review will be beneficial for the design of jet fuel with high thermal oxidative stability and the further development of high-performance aircraft. [ABSTRACT FROM AUTHOR]