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Solar‐driven conversion of renewable biomass resources into high‐density hydrocarbon fuels can effectively realize biomass valorization and renewable energy conversion. In this work, an efficient self‐sensitized [2 + 2] photocycloaddition process is explored to develop highly strained fuel with high yield using norbornene and biomass‐derived cyclohexenone as feedstocks. The enhancement mechanism is revealed by phosphorescent measurement and theoretical calculation, and a reasonable reaction path for self‐sensitized [2 + 2] co‐cycloaddition is proposed. When using methanol as solvent, the apparent activation energy of co‐cycloaddition is 21.37 W/mol, which is lower than that of self‐cycloaddition (31.57 W/mol). Importantly, the jet‐fuel‐range highly strained fuel has high density (0.986 g/cm3) and high volumetric net heat of combustion (41.14 MJ/L), which are 5.34% and 4.39% higher than those of JP‐10, respectively. This work proposes a green and effective pathway for the preparation of high‐performance hydrocarbon fuel with polycyclic‐asymmetric structure. [ABSTRACT FROM AUTHOR]

The conversion of biomass is a favorable alternative to the fossil energy route to solve the energy crisis and environmental pollution. As one of the most versatile platform compounds, 5‐hydroxymethylfural (HMF) can be transformed to various value‐added chemicals via electrolysis combining with renewable energy. Here, the recent advances in electrochemical oxidation of HMF, from reaction mechanism to reactor design are reviewed. First, the reaction mechanism and pathway are summarized systematically. Second, the parameters easy to be ignored are emphasized and discussed. Then, the electrocatalysts are reviewed comprehensively for different products and the reactors are introduced. Finally, future efforts on exploring reaction mechanism, electrocatalysts, and reactor are prospected. This review provides a deeper understanding of mechanism for electrochemical oxidation of HMF, the design of electrocatalyst and reactor, which is expected to promote the economical and efficient electrochemical conversion of biomass for industrial applications. [ABSTRACT FROM AUTHOR]

The excessive dependence on fossil fuels contributes to the majority of CO2 emissions, influencing on the climate change. One promising alternative to fossil fuels is green hydrogen, which can be produced through water electrolysis from renewable electricity. However, the variety and complexity of hydrogen evolution electrocatalysts currently studied increases the difficulty in the integration of catalytic theory, catalyst design and preparation, and characterization methods. Herein, this review first highlights design principles for hydrogen evolution reaction (HER) electrocatalysts, presenting the thermodynamics, kinetics, and related electronic and structural descriptors for HER. Second, the reasonable design, preparation, mechanistic understanding, and performance enhancement of electrocatalysts are deeply discussed based on intrinsic and extrinsic effects. Third, recent advancements in the electrocatalytic water splitting technology are further discussed briefly. Finally, the challenges and perspectives of the development of highly efficient hydrogen evolution electrocatalysts for water splitting are proposed. [ABSTRACT FROM AUTHOR]

• Introduce the mechanism of LHF steam reforming (SR), defines the main problems faced by the current reactions and catalysts. • Systematically summarize recent progress in the development of catalysts for SR of LHFs. • The applications of LHF SR are highlighted, including hydrogen production, fuel cell, and engine thermal management. • The enhancement technologies for LHF SR process are described. • The challenges and perspectives of SR of LHF are discussed and proposed. Liquid hydrocarbon fuels (LHFs) possessing the features of high energy density, large content of hydrogen volume and convenient storage and transportation have received great attention in hydrogen production, fuel cell, and national defense weapon application. However, the efficiency of LHF conversion is still far from satisfying at present, especially suffering from low conversion of the reaction and quick deactivation of the catalyst. The synthesis of robust and low-price catalysts is crucial for LHF conversion. Recently, significant progress has been achieved in regulating the composition, structure, and active site of catalyst and understanding the structure–activity relationship. At first, this review discusses the mechanism of LHF steam reforming (SR), defines the main problems faced by the current reactions and catalysts to guide the design and development of high-performance catalysts. Then, recent progress in the development of catalysts for SR of LHFs is systematically summarized, including gasoline, kerosene, diesel, tar and sulfur containing hydrocarbon fuel. Thereafter, the relevant applications of LHF SR are highlighted, including hydrogen production, fuel cell, and engine thermal management. Finally, several enhancement technologies for SR process are described, including plasma reforming, chemical looping reforming, adsorption enhanced reforming and reaction separation coupling reforming technology. The advantage and disadvantage of various technologies are explained, and the enhanced conversion of LHF is expected to be realized through the construction of high-efficient catalysts coupling of enhancement technology and unique reactor. We hope that this review can provide the relevant guidance and new ideas for the technological development of hydrogen production, fuel cell, and engineering thermal management via SR of LHFs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Review on NBD and NBE dimerization for the synthesis of high density fuels. • Typical metal-based catalysts and the key results have been summarized. • Dimerization mechanism on typical coordination catalysts has been illustrated. • The relationship between dimer structure and fuel properties has been discussed. High-density hydrocarbon fuels are essential for air craft to increase payload and expand flight distance. This review will summarize the synthesis of high-density hydrocarbon molecules through catalytic dimerization of norbornadiene and norbornene in the past few decades, which can be used as new fuels or high-energy additives for conventional fuels. Dimerization of norbornadiene including relationship between structural dimers and investigation on metal based homogeneous catalysts and heterogeneous catalysts as well as description of possible mechanisms are firstly introduced. Then synthesis of multi-cyclic compounds from norbornene is illustrated with a focus on efficient and greener routes. After that, physicochemical properties of partial norbornadiene and norbornene dimers and influence of the composition on fuel performance are reviewed. Finally, we will propose the problems in synthesis of high-energy-density fuel through dimerization of norbornene and norbornadiene. This review will be helpful to explore new approaches to synthesize more valuable high-density hydrocarbon fuels and predict possible directions of synthesizing new multi-cyclic hydrocarbon compounds with norbornadiene and norbornene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Relationship between fuel molecular structure and pyrolysis performance was investigated. • Pyrolysis conversion of the fuels is highly associated with their C + H atom numbers. • The heat sink of the fuels is closely correlated with n H/C 6.9 × n H+C 3.8. High-energy-density endothermic hydrocarbon fuels (HDEHFs) are the ideal on-board coolants for the thermal management of advanced aircrafts. However, the pyrolysis performace of high-energy-density (HED) fuels with different molecular structures remains ambiguous. Herein, we investigated the pyrolysis performance of five HED fuels with different cyclic structures, i.e., bicyclohexyl (BCH), perhydrofluorene (PHF), decahydronaphthalene (DHN), exo -tetrahydrodicyclopentadiene (exo -THD) and cyclopropyl-tetrahydrodicyclopentadiene (CTHD), to reveal the molecular structure-reactivity relationship. The pyrolysis conversion (650 °C, 4 MPa) of the tested fuels is in the order of CTHD > PHF > BCH > DHN > exo -THD, which is highly associated with their C + H atom numbers, n H+C (except for CTHD with high-tension ring). With the analysis of product distribution as well as DFT calculation, the decomposition reaction pathways of the fuels were proposed. The heat sink of the fuels follows the order of BCH > PHF > DHN > exo -THD > CTHD, which is closely correlated with n H/C 6.9 × n H+C 3.8. Meanwhile, the fitting results between molecular structures and physicochemical properties of the fuels were also demonstrated. This study could provide a guidance on the design and development of HDEHFs fuels for the high-performance aerospace vehicles with long flight distance and hypersonic speed. [ABSTRACT FROM AUTHOR]

• Thermal cracking of Al NPs-containing nanofluid was proceeded successfully. • Al NPs can improve the energy density, thermal conductivity, ignition and combustion performance of fuel. • Al NPs slightly inhibit the cracking of the three fuels in the order of DHN > MCH > JP-10. • 0.5 wt% Al NPs reduce the conversion of JP-10, DHN and MCH by 3.0%, 18.8% and 14.1%, respectively. • The coke deposition produced during the cracking process shows a tendency of increasing with Al NPs. Endothermic hydrocarbon fuels containing energetic nanoparticles, which combine high-energy–density and endothermic capability, are promising for improving the flight performance of hypersonic vehicles. Here, the feasibility of nanofluid fuels as energetic endothermic fuel is studied. Aluminum nanoparticles (Al NPs)-containing nanofluid fuels were prepared by dispersing 0.1 wt% and 0.5 wt% Al NPs into JP-10, decahydronaphthalene (DHN) and methylcyclohexane (MCH), respectively. Characterizations of nanofluid fuels confirm the addition of Al NPs improves the density and combustion performance of the hydrocarbon fuels. The cracking performance of three fuels with Al NPs added is slightly inhibited in the order of DHN > MCH > JP-10. Cracking conversion (and heat sink) of JP-10, DHN and MCH containing 0.5 wt% Al NPs decrease by 3.0 %, 18.8 % and 14.1 % (and 0.04, 0.09 and 0.05 MJ/kg), respectively. JP-10 is the least affected by Al NPs. Meanwhile, Al NPs are observed to slightly increase the amount of coking during cracking, and the non-uniformly dispersed Al can be found in the coke deposition. This work indicates the potential application of energetic nanofluids to serve as endothermic fuels, and provides the method for the further development of high-energy–density endothermic fuels. [ABSTRACT FROM AUTHOR]

The exploration to increase the fuel energy density is stimulated by the payload and cruising range concerns in aerospace industry. The high-density fuels are always rationally designed for the advanced volume-limited aircrafts to fulfill more complicated missions. Alkyl adamantanes gradually become a prospective class of high-energy-density fuels. Herein, in this work, we reported an approach to synthesize asymmetric cyclopentyl adamantane via AlCl 3 -catalyzed alkylation of adamantane and cyclopentene with an attractive combination of a high density of 0.990 g/mL as well as a low freezing point of −30 °C. The obtained 1-cyclopentyl-adamantane was well designed with the cyclic substituent (enhance the density) and asymmetric structure (lower the freezing temperature). Subsequently, the comprehensive fuel performance of cyclopentyl adamantane, i.e. , density, freezing point, low-temperature viscosity, heating value, and combustion properties were evaluated. It was shown that both density and combustion properties of cycloalkyl adamantane were superior to the typical high-density JP-10 fuel. In addition, the properties of binary fuel mixture (1-cyclopentyl-adamantane and JP-10) demonstrated that cyclopentyl adamantane could be used as a promising blendstock with conventional jet fuel to enhance the energy density and promote the combustion performance of the final fuel blends. [Display omitted] • Asymmetric cycloalkyl adamantane was synthesized via alkylation. • Cyclopentyl adamantane owned higher density than reported adamantanes and JP-10. • Relationships between molecular structure and properties were discovered. • Cyclopentyl adamantane was a novel hydrocarbon fuel for aerospace propulsion. [ABSTRACT FROM AUTHOR]

Biofuels are important alternative for fossil-based fuel but they have either relatively low density or high freezing point and viscosity. Here we reported a simple and efficient route to synthesis biofuel with density comparable to widely used JP-10 fuel as well as good low-temperature properties. Substituted diphenyl methane was synthesized by acid catalytic alkylation of lignin-derived phenols (phenol, anisole, guaiacol) with benzyl ether or benzyl alcohols, and MMT-K10 exhibits better activity than HPW, Amberlyst-15, and Al-MCM-41, due to the modest acid strength and open lamellar structure. High selectivity along with good-to-excellent conversion was obtained under optimized conditions regardless of different reactant used. Then the alkylated product was subjected to hydrogenation with the presence of Pd/C and HZSM-5, and interestingly, intramolecular cyclization reaction occurred to produce a large amount of perhydrofluorene as well as dicyclohexylmethane. Subsequently, biofuel with density as high as 0.93 g/mL and freezing point as low as −40.0 °C was obtained, which surpasses the state-of-art of biofuel reported. [ABSTRACT FROM AUTHOR]

• Four sesquiterpene-based renewable biofuels were synthesized. • Cyclopropanation enhances energy density and hydrogenation maintains good low-temperature characters. • As-prepared biofuels possess density of 0.925–0.965 g/mL and volumetric energy is up to 41.51 MJ/L. • The minimum ignition temperature and ignition delay time of biofuels are shortened by 46–108 °C and 27.0–71.4%, respectively, compared with JP-10 fuel. Considering the global carbon emissions and ambition of carbon neutrality, renewable fuels synthesized from biomass have great application prospects. Herein we adopted hydrogenation and cyclopropanation to synthesize four biofuels using α-cedrene and longifolene as feedstocks. Specifically, the modified Simmons-Smith method was used to synthesize cyclopropanated biofuels with a yield greater than 80% under the optimized conditions. The as-prepared biofuels possess the density of 0.925–0.965 g/mL, and the volumetric energy of 39.45–41.51 MJ/L. Additionally, the minimum ignition temperature and ignition delay time of the synthesized biofuels are shortened by 46–108 °C and 27.0–71.4%, respectively, compared with the widely used JP-10 fuel. The synthesized sesquiterpene-based biofuels have good potential to as alternative of high energy density fossil fuels like JP-10. [ABSTRACT FROM AUTHOR]

• 1. Core-shell nAl@MOF are prepared as bifunctional energetic particles for nanofluid fuels. • 2. Core-shell nAl@MOF have higher combustion rate and combustion efficiency than nAl. • 3. Thermal decomposition process of nAl@MOF particles can be divided into three stages. • 4. Energetic solid particles can significantly reduce the ignition delay time of nanofluid fuels. • 5. Ignition and combustion are enhanced by regulating the interfacial reaction and microexplosions. With the continuous development of advanced fuel and engine technology, the boundary between liquid and solid fuel is more and more blurred, so the development of new solid-liquid two-phase fuels has become a major opportunity and challenge. Herein, two kinds of nAl@MOF energetic particles (nAl@Zn-MOF and nAl@Co-MOF) were fabricated by an in-situ electrostatic self-assembly method. The thermal property, ignition and combustion performances of nAl@MOF are characterized by TG-DSC, CO 2 laser ignition and constant-volume combustion experiments. The results show that the initial exothermic temperature of nAl@Zn-MOF and nAl@Co-MOF are reduced by about 60 and 110 °C, respectively, compared with nAl (579.6 °C). Moreover, nAl@MOF has a lower ignition delay time, higher peak pressure, and faster pressurization rate than nAl, especially nAl@Zn-MOF-1 and nAl@Co-MOF-1. The combustion process of nAl@MOF is proposed, which can be obviously enhanced by regulating the interfacial reaction and the generation of microexplosions. In the ignition experiment of nanofluid fuel, nAl@MOF energetic particles exhibit the bifunction characteristics, which can simultaneously improve the ignition and combustion performances of solid-phase nAl particles and liquid-phase hydrocarbon fuel. This work provides a new strategy for advanced aerospace fuel by introducing MOF shells to construct bifunctional energetic particles with enhanced ignition and combustion properties. [ABSTRACT FROM AUTHOR]

• The oxidation stability and deposition propensity of C10 hydrocarbon fuels were investigated. • The oxidation stability follows the order of n- decane > exo -THDCPD > trans- decalin > cis- decalin > tetralin. • The deposition propensity follows the order of trans- decalin > exo- THDCPD > n- decane > cis- decalin > tetralin. • The oxidation stability is highly associated with molecular-structure-dependent C–H bond dissociation enthalpy. • The deposition propensity is associated with the stability of oxidation intermediates. Thermal oxidation stability is a key issue for jet fuel when serving as a coolant in aircraft. However, the deposition propensity and mechanism of hydrocarbons with different molecule structures remain ambiguous. In this study, the oxidation stability and deposition propensity of C10 hydrocarbon fuels, i.e. , tetralin, cis- / trans- decalin, exo -tetrahydrodicyclopentadiene (exo- THDCPD), and n- decane, were determined. The oxidation stability of hydrocarbons follows the order of n- decane > exo- THDCPD > trans- decalin > cis- decalin > tetralin, which is highly associated with the molecular-structure-dependent C–H bond dissociation enthalpy. Differently, the deposition propensity follows the order of trans- decalin > exo- THDCPD > n- decane > cis- decalin > tetralin, which can be associated with the stability of oxidation intermediates, especially the hydroperoxides. The more stable the intermediates are, the fewer deposits will be produced. These results demonstrate the relationship between thermal oxidation stability and hydrocarbon molecular structure, which is helpful for a better understanding of jet fuel deposition mechanism. [ABSTRACT FROM AUTHOR]