Sustainable Energy & Fuels最新文献

In this work, a new route was developed for the synthesis of jet fuel range C₁₆ and C₁₁ paraffins with cellulose, the most abundant biomass. In the first step, cellulose was selectively converted to 5-methylfurfural (MFA) by a cascade hydrolysis/isomerization/dehydration/chlorination reaction in a toluene/NaCl aqueous solution biphasic system, followed by the hydrodechlorination over Pd/C catalyst at room temperature. After being decarbonylated, the MFA was converted to 2-methylfuran (2-MF). Among the investigated catalysts, Pd/C exhibited the highest activity for this reaction, which can be rationalized by the higher activity of Pd for the decarbonylation. Subsequently, tris(5-methylfuran-2-yl)methane (TMFM) was obtained by the solvent-free hydroxyalkylation/alkylation (HAA) reaction of MFA and 2-MF over a series of acidic resins. Among them, Nafion resin exhibited the highest activity, which can be rationalized by the high acid strength of this catalyst. Finally, the TMFM as obtained was hydrodeoxygenated to jet fuel range C₁₆ and C₁₁ paraffins under the co-catalysis of Ni/hydroxyapatite (Ni/HAP) and H-ZSM-5.

It is acknowledged that hydrogen evolution reaction (HER) in basic media is mainly limited by H₂O molecule dissociation. To overcome this problem, in this study, intermetallic MnNi₃ phase separated from nanoporous (np) Ni was rapidly synthesized and proved to be a cost-effective HER catalyst. Interestingly, the as-prepared MnNi₃/np-Ni-9h has integrated and dense nanosheets, showing a huge surface area for electrocatalysis. It only demands HER overpotentials of 107, 234 and 337 mV to achieve current densities of 10, 50 and 100 mA cm⁻², respectively. It also possesses long-term durability for 650 h, indicating that the self-dissociated MnNi₃ phase is ultra-stable even under the action of violent H₂ bubbles. Furthermore, the MnNi₃/np-Ni-9h‖RuO₂ couple needs only 1.90 V to reach a high current density of 1 A cm⁻² at the industrial conditions (6 M KOH, 60 °C). Meanwhile, the simulated cell could steadily produce hydrogen for over 190 h with merely 6% voltage loss, reconfirming the superior catalytic activity and robustness of the MnNi₃/np-Ni-9h electrode. From a theoretical perspective, H₂O molecule is preferred to be adsorbed on the Mn site and subsequently is beneficial to be dissociated into *OH–*H co-adsorption. Correspondingly, the rate-determining step (RDS) of alkaline HER on MnNi₃ can be changed into the third step (*OH–*H → *H) and energy barrier can be reduced to 0.56 eV when *OH and *H are neither far nor near. This work offers a guide to facilely fabricate cost-effective HER catalysts that are suitable for industrial hydrogen production.

In this work, a rational design of an efficient electrocatalyst containing metal–nitrogen–carbon linkage (M–N–C) has been demonstrated for the oxygen reduction reaction (ORR) in a neutral medium. M–N–C composite materials comprising transition metals are the most competitive catalysts for the ORR and have drawn extensive research interest due to their enhanced activity and low-cost. Herein, a facile electrochemical synthetic strategy is designed for the fabrication of free-standing electrocatalysts [abbreviated as TC-GO (GO-ZIF-67) and TC-GO (GO-ZIF67-Fe)] containing graphene oxide as a base layer and a composite layer consisting of GO and ZIF-67 (with and without Fe) on a Toray carbon (TC) electrode and demonstrated their application for the ORR at a neutral pH. The fabricated electrocatalysts display a large electrochemically active surface area (2.37 cm²) and good electrical conductivity and possess ideal structural and compositional features required for the ORR when compared with its parent material (ZIF-67). This work highlights the efficiency of the electrochemical method in preparing the freestanding films of a composite material consisting of GO and ZIF on a TC electrode rather than the usually followed chemical methods of synthesizing ZIF or its composites followed by high temperature pyrolysis. Such processes generally are energy intensive and affect the structural stability of the framework that also needs to be drop-cast onto the electrode surface. The electrochemically prepared composite material displays good electrochemical activity towards the ORR (E_onset = 0.654 V vs. RHE and E_1/2 = 0.361 V vs. RHE) at neutral pH. Thus, the proposed strategy has the potential to serve as a platform for designing non-precious, highly electroactive catalysts under neutral conditions with desirable activity towards the ORR which can be used in energy conversion technologies including fuel cells.

Batteries and hydrogen energy devices are considered the most critical technologies for achieving zero carbon dioxide emissions. However, they still suffer from several limitations, including low efficiency, short cycling life, low storage, and poor safety. With their strong mechanical strength (flexibility), chemical inertness, large surface area, remarkable thermal stability, and excellent electrical and high ion conductivity, graphene can overcome some of the issues associated with batteries and hydrogen energy devices. The properties of various two-dimensional (2D) materials make them potential candidates for a wide range of applications (batteries and hydrogen energy devices), thereby gaining considerable interest. Similarly, graphene has the potential for efficient hydrogen production and storage because of its large surface area and adjustable porosity. Graphene/2D composite materials are promising electrodes for lithium batteries, hydrogen storage, and production applications. This review provides a comprehensive overview of graphene/2D composite materials for lithium batteries and hydrogen storage and production applications.

The combination of micromix and diluted combustion technologies is an effective way to realize stable H₂ flames with low NO_x emission, and the dynamic modes and turbulent flame structures with corrected OH-PLIF (1 kHz) images for a hydrogen micromix burner were experimentally studied in this work under different steam dilution ratios (D) and equivalence ratios (φ). Two types of flames, anchored and lifted, are found for different inlet conditions (dilution ratios (D) and equivalence ratios (φ)). When the flame tends to lift, the flame shape and location of the peak OH signal have obvious change over time and the results show that the flame stability reduces. Besides, the flame surface density (FSD) has small values distributed around the flame root, making the flame more unstable. When the flame is lifted, the distribution of FSD becomes wider (not mainly in the shear layer zone (SLZ)) and a large part of FSD is distributed in the flame root. In general, dynamic mode decomposition (DMD) analysis results show that the anchored flame has a lower flame frequency than that of the lifted flame in the same mode.

Hydrothermal liquefaction (HTL) is a promising technique for the conversion of wet biomasses into a complex biocrude. In this study, biocrudes from 10 different feedstocks of Spirulina, Miscanthus, sewage sludge and their mixtures were investigated in a mixture design. Furthermore, the effects of temperature (250–350 °C), reaction time (5–31 min), and solid loading (5–25 wt%) were investigated using a central composite design. Analysis of the biocrudes was performed using gas chromatography coupled to mass spectrometry (GC-MS). The software PARADISe was applied to deconvolute chromatographic peaks and tentatively identify 152 compounds, including small carboxylic acids, fatty acids, hydrocarbons, alcohols, carbonyls, amino acids, carbohydrates, oxygenated aromatics and nitrogen-containing compounds. Principal component analysis (PCA) separated the samples corresponding to feedstock in PC1 and PC2, whereas PC3 separated samples based on their process conditions. Partial Least Squares (PLS-R), random forest, lasso, ridge, and gradient boosting regressors were applied to develop predictive models and their performance was compared. The models were evaluated according to the coefficient of determination (R²), root mean square error (RMSE), and bias values. This work highlights the differences in biocrudes from HTL of feedstocks of varying biochemical composition and presents new knowledge of the effect of biochemical composition and process conditions on different compound classes found in the biocrude. The results thus provide valuable information for the optimization of biocrude production via HTL.

Pyrolysis has become one of the most attractive options for converting carbonaceous biomass into bio-oil or biochar. This study explores a novel solar pyrolysis process intended to produce both bio-oil and biochar, thereby improving carbon efficiency. Aspen Plus and SolarPILOT were used to model a 10 MW biomass pyrolysis plant thermally sustained by hot particles from a falling-particle solar tower receiver. A yearly analysis was carried out for three configurations to estimate the annual production of oil and biochar. The results showed that the hybrid plant, combining solar receiver and biochar backup combustor, leads to the lowest cost of bio-oil (18.7 € per GJ, or 0.29 € per kg) and a carbon efficiency of 83%. Whereas, the plant fully sustained by solar power achieves a carbon efficiency of 90%; however, it results in a significantly higher cost of bio-oil (21.8 € per GJ, or 0.34 € per kg) due to the larger size of particle storage and a lower capacity factor of the pyrolysis plant. In comparison, a conventional pyrolysis plant with no biochar production yielded the most expensive option in terms of the cost of produced bio-oil (27.5 € per GJ) and features the lowest carbon efficiency (74%). Sensitivity analysis shows that the pyrolyzer Capex, operational cost, biochar market price, plant availability and discount rate significantly affect bio-oil production cost.

A crystalline perylene–porphyrin based covalent organic framework is synthesized via Schiff base [2 + 2] type condensation between 4,4′,4′′,4′′′-(perylene-2,5,8,11-tetrayl) tetrabenzaldehyde (PETA) and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (PAM) under solvothermal conditions. The porphyrin and perylene units occupy the vertex of a three-dimensional triclinic crystal in an alternate manner. PETA-PAM-COF exhibits permanent microporosity, a reasonably high surface area (about 1400 m² g⁻¹), and promising chemical stability. A conducting perylene bridged channel is created by AA stacking. PETA-PAM-COF has been utilized for the metal-free hydrogen evolution reaction with a low charge-transfer resistance (R_ct) value of 62.22 Ω and a Tafel slope of 122 mV dec⁻¹, demonstrating its potential for practical utilization. PETA-PAM COF showed a current density of 10 mA cm⁻² at an overpotential of 261 mV. Remarkable HER activities are demonstrated by the PETA-PAM-COF catalyst as indicated by its faradaic efficiency (96%) and durability (which retained 93% of its original current density after 1000 cycles). We anticipate that the imine-based COF will not only enhance the structural variety but also the electrochemical behavior of these classes of materials.

The discovery of graphdiyne (GDY) represents a significant advancement in the field of carbon allotropes, and has garnered widespread attention for its potential applications in hydrogen production. Lamellar graphdiyne (GDY) synthesized via the ball milling method serves as a good carrier for preparing a composite photocatalyst. Modified with flower-ball CoSe particles, the GDY/CoSe ohmic junction composite photocatalyst has been reasonably designed. The GDY/CoSe-15 photocatalyst (15 wt% CoSe) exhibited stable photocatalytic H₂ evolution activity. It was capable of achieving a rate of 2.54 mmol h⁻¹ g⁻¹, which was 8.7 and 6.1 times higher than the respective rates of GDY (0.29 mmol h⁻¹ g⁻¹) and CoSe (0.42 mmol h⁻¹ g⁻¹). The experimental findings and density functional theory (DFT) calculations indicate that the GDY/CoSe photocatalyst demonstrates exceptional light absorption capacity and effectively separates photogenerated carriers. Furthermore, the CoSe cocatalyst has the potential to function as an electron acceptor, facilitating the efficient transfer and transportation of photogenerated electrons; as a result, this enhances the efficiency of photocatalytic hydrogen production.

Expanding the use of sustainable fuels in hard to decarbonise transport vehicles utilising heavy-duty engines is urgently required to reduce greenhouse gas emissions from sectors reliant on these engines. As biofuel production turns to alternative sources of biomass with a differing chemical composition to fossil fuel, it is increasingly important to understand how chemical functional groups which may be present in biomass influence the process of combustion. Biofuels are more homogeneous in chemical composition than fossil diesel or gasoline, which are a variety of compounds with a common range of boiling points. As the transport industry progresses in replacing fossil volumes with renewable liquid fuels it also moves towards fuels which are more homogeneous in chemical composition and therefore reactivity. Esters and carbon–carbon double bonds are two common functional groups found in biodiesel and many other classes of bioderived molecules. When adjacent to each other in a specific conformation, they are classed as a Michael acceptor functional group which has a unique reactivity with free radicals separate to either the ester or alkene alone and may play a key role in the low temperature reactions preceding auto-ignition in the combustion process. In this study, the combustion and emissions characteristics of a series of saturated and unsaturated fatty acid esters were tested as single component test fuels, to observe how the inclusion of a Michael acceptor group in esters influences reactivity in a heavy-duty compression ignition engine. Under constant injection duration and timing conditions, it was found that the inclusion of the Michael acceptor in methyl non-2-enoate reduced the duration of ignition delay and increased the IMEP relative to methyl nonanoate and methyl non-3-enoate. Conversely, the inclusion of the Michael acceptor in C₈ and C₁₀ ethyl esters resulted in a longer duration of ignition delay and similar observed IMEPs.