As the candidates for large-scale hydrogen storage, liquid organic hydrogen carriers (LOHCs) exhibit evident advantages in hydrogen storage density and convenience of storage and transportation. ...Among them, NECZ (N-ethylcarbazole)/12H-NECZ (dodecahydro-N-ethylcarbazole) is considered as a typical system with the lower hydrogenation/dehydrogenation temperature. However, the low dehydrogenation efficiency restrict its commercial applications. In this work, the single-layer Ti3C2Tx MXene was employed as the support to load the Pt nanoparticles for the 12H-NECZ dehydrogenation reaction. The effect of transition metals, loading amounts and morphologies of catalysts were analyzed. It was found that the 3 wt% Pt/S–Ti3C2Tx catalyst exhibited the best catalytic performance with 100% conversion, 91.55% selectivity of NECZ and 5.62 wt% hydrogen release amount at 453 K, 101.325 kPa for 7 h. The product distributions and kinetics analysis suggested that the elementary reaction from 4H-NECZ to NECZ was the rate-limiting step. The selectivity of NECZ is sensitive to the dehydrogenation temperature. Combined with the XRD, SEM, HRTEM, XPS, BET and FT-IR results, it could be indicated that the special two-dimension structure of S–Ti3C2Tx and electronic effect between Pt and S–Ti3C2Tx enhanced the dehydrogenation efficiency of 12H-NECZ. The measurements of cyclic dehydrogenation indicated that the Pt/S–Ti3C2Tx catalyst exhibited good stability after 42 h. This work brought a new strategy for the design of efficient catalysts using two-dimensional materials in the applications of the liquid organic storage hydrogen technology.
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•The effect of active metals, loading amounts and morphologies of catalysts were analyzed.•The 3 wt% Pt/S–Ti3C2Tx catalyst exhibited the best catalytic performance.•The special structure and electronic effect enhanced the dehydrogenation efficiency.•The selectivity of NECZ was enhanced with the increase of temperature.•The elementary reaction from 4H-NECZ to NECZ was the rate-limiting step.
•Techno-economic modeling of future hydrogen supply chains with spatial resolution.•Spatially-resolved infrastructure design for hydrogen transport.•Large-scale seasonal storage for renewable ...hydrogen production.•Implementation of different technologies for hydrogen storage and transportation.•Evaluation of optimization potential for hydrogen distribution.
Hydrogen could play a key role in future energy systems by enabling the storage of excess electricity from renewable power sources, like solar and wind, and fueling emission-free fuel cell electric vehicles. Nevertheless, the temporal and spatial gap between the fluctuating production in electrolysis plants and the demand at fueling stations necessitates the construction of infrastructures. Different technologies are available for storing and transporting hydrogen in its gaseous or liquid states, or even via liquid organic hydrogen carriers. To select and compare these different infrastructure options on a nationwide scale in Germany for an energy system 2050, we carried out an infrastructure assessment with spatial resolution to analyze the resulting costs and CO2 emissions, as well as the primary energy demand. To do so, methods for designing a spatially-resolved infrastructure are presented. In particular, the setup of a transmission pipeline with gaseous trailer distribution has not been well represented and investigated in the literature so far. The results show that salt caverns, as well as transmission pipelines, are key technologies for future hydrogen infrastructure systems. The distribution should be handled for low penetration of fuel cell vehicles rates with gaseous compressed trailers and replaced by distribution pipelines in areas with high fueling station densities. This ensures the cost-effective supply during the transition to higher fuel cell vehicle fleets.
This work contributes to the characterization of the liquid organic hydrogen carrier (LOHC) system diphenylmethane/dicyclohexylmethane by the experimental determination and molecular simulation of ...the thermophysical properties of the dehydrogenated and fully hydrogenated compounds in a process-relevant temperature range of up to 623 K. Liquid density, liquid viscosity, surface tension and liquid self-diffusion coefficient data measured by vibrating-tube densimeters, surface light scattering, rotational viscometry and NMR spectroscopy are correlated and compared with available literature data which are mostly restricted to temperatures below 473 K. Furthermore, it is demonstrated that an L-OPLS force field (FF) modified in the present study outperforms commonly used FFs from literature in predicting the thermophysical properties of both substances by equilibrium molecular dynamics simulations.
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•A new force field for the LOHC system DPM/DCM was developed and validated.•Thermophysical properties of DPM and DCM were measured and simulated up to 623 K.•DPM shows a higher surface tension, density and self-diffusion coefficient.•DCM shows a higher dynamic viscosity especially at low temperatures.•At high temperature, the viscosities of DPM and DCM converge.
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•Novel analysis of integrated solar based hydrogen fueled stand-alone energy system.•A system with and without integrated LOHC storage are compared.•Integration of a LOHC based ...hydrogen storage is energetically beneficial.•LOHC improves energy and exergy efficiencies and reduces irreversibilities.•High capital investment costs make the solution economically not attractive.
The integration of energy storage technologies into renewable energy systems has gained increasing attention for continuous supply of the renewable-based enegy. Among different storage alternatives, the use of a Liquid Organic Hydrogen Carrier (LOHC) has a significant potential as a reversible energy carrier for short and long-term energy storage. In this study, the technical and economic performance of an stand-alone renewable energy systems using a LOHC for energy storage have been evaluated by exergy-based methods in addition to simple energy and economic analysis. The analysis of the LOHC-free system was also included to determine the effect of LOHC on the system performance. The system containing phovoltaic (PV) panels, an electrolyzer, a micro gas turbine and hydrogenation/dehydrogenation LOHC units was designed to meet the power, heating and cooling requirement of a residential building. The system modelling and performance evaluation were made by using TRNSYS and EES softwares. Results show that the LOHC-containing system has higher energy and exergy efficiencies and exergoeconomic performance than the LOHC-free system while the latter is economically more feasible than the former due to its low capital investment cost.
Rise in population and industrialisation has significantly impacted the fossil fuel reserves at global scale which has given rise to alarming emission levels in the environment. To address these ...issues, hydrogen is a favourable alternative owing to its high calorific value, high flame speeds, shorter flame quenching distance and clean burning nature. The present review provides a comprehensive coverage of different hydrogen production methods, hydrogen storage techniques and application of hydrogen in CI engines. Comparative assessment studies illustrated that thermal based hydrogen production methods have higher environmental impact than all other methods but are commercially mature, cost competitive than other hydrogen production routes. Storage techniques of hydrogen includes compression, liquification, cryo-compression, physical and chemical based storage methods. Compression based technology for hydrogen storage offers the advantages of being commercially mature, faster filling and release compared to other technologies offering higher volumetric and gravimetric density than compression-based methods at impractical operating conditions. CI engine studies of hydrogen as dual fuel suggested better performance attributes (high BTE and lower BSFC), lower emissions (such as CO, CO2, HC, smoke with slight increment in NOx emissions) and improved combustion (high HRR, in-cylinder temperature & pressure) owing to high flame speed, wider flammability limits, small quenching zone and high diffusivity of hydrogen.
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•H2 production and storage technologies analysed and compared.•H2 utilisation in CI engines extensively explored and analysed.•Role of world governments in green hydrogen implementation discussed.
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•Reversible hydrogenation-dehydrogenation of polycyclic hydrocarbons was studied.•Activation energies and pre-exponents of both processes were determined.•Correlations of reaction ...rates with the structure and condensation extent were found.
The reversible reactions of hydrogenation-dehydrogenation of polycyclic aromatic hydrocarbons with a different extent of condensation (naphthalene, anthracene, biphenyl, meta- and para-terphenyl isomers) were studied in comparison with benzene on a 3%Pt/C catalyst. Hydrogenation of naphthalene and anthracene was carried out at T = 280 °C, P = 90 atm, whereas the reaction of benzene, biphenyl and terphenyl isomers was performed at T = 180 °C, P = 70 atm in an autoclave. Dehydrogenation of the corresponding polycyclic naphthenes (cyclohexane, decalin, perhydroanthracene, bicyclohexyl, ortho, meta, and para-isomers of perhydroterphenyl) was carried out in the temperature range of 280 to 340 °C in a flow setup at the volume hourly space velocity of 1 h−1 and atmospheric pressure. Correlation dependences of the reaction rates of hydrogenation-dehydrogenation of the studied substrates on their structure and extent of condensation were found.
Two-dimensional Mo2C (2D-Mo2C) is reported for the first time as an effective promoter of a Pt/Al2O3 catalyst for both the hydrogenation and dehydrogenation of the liquid organic hydrogen carrier ...(LOHC) pair, dibenzyltoluene (DBT) and perhydro-dibenzyltoluene (H18-DBT), respectively. Addition of 6.2 wt% 2D-Mo2C to a Pt/Al2O3 catalyst resulted in a significant increase in both the degree of hydrogenation and dehydrogenation compared to the unpromoted catalyst. An analysis of the initial (120 min) perhydro-DBT dehydrogenation kinetics in the temperature range of 270–330 °C, resulted in a reduction in apparent activation energy from 119.5 ± 3.8 kJ/mol for the Pt/Al2O3 catalyst to 110.4 ± 5.6 kJ/mol for the 6.2 wt% 2D-Mo2C/Pt/Al2O3 catalyst. The 6.2 wt% 2D-Mo2C/Pt/Al2O3 catalyst was also more stable than the unpromoted catalyst over several consecutive cycles of hydrogenation and dehydrogenation. Catalyst characterization showed that addition of 2D-Mo2C resulted in an increase in particle size and electron density of the Pt, which enhanced both the hydrogenation and dehydrogenation reactions, despite the fact that the 2D-Mo2C alone was inactive for both reactions.
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•H2 storage and release from LOHC enhanced by 2D-Mo2C.•2D-Mo2C increased particle size and electron density of the Pt.•Results in reduction in dehydrogenation activation energy.•2D-Mo2C/Pt/Al2O3 catalyst also more stable than Pt/Al2O3.
Hydrogen production using formic acid (FA) as renewable carrier has been investigated in a fixed bed reactor packed with a commercial Pd/AC catalyst. For the first time, both FA disappearance and ...evolved gas flow rate have been monitored upon space-time, enabling the elucidation of the FA reaction pathway and the development of a kinetic model that accounts for catalyst deactivation. Nearly complete FA conversion and a production of 10 mL min−1 of hydrogen gas were achieved under the following operating conditions: CFA,0 = 1 M, T = 45 ºC and τ = 66.7 gCAT h L−1. The reaction was found not to be controlled the mass transfer limitations. The kinetic model reveals a first order with respect to FA concentration, with FA disappearing through dehydrogenation into hydrogen and CO2 (Ea = 53.6 kJ mol−1) as well as sorption onto the catalyst surface without reaction (Ea = 36.7 kJ mol−1). The catalyst deactivation is attributed to the accumulation of reaction species, including FA/HCOO- (reversibly sorbed) and CO2 (irreversibly chemisorbed), on the Pd active sites and the progressive decrease in the Pd2+/Pd0 ratio.
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•Continuous production of CO-free H2 from FA decomposition over Pd/AC catalysts.•FA undergoes dehydrogenation and accumulates on the catalyst surface.•Kinetic equation is first order with respect to FA concentration and catalyst activity.•Slow but irreversible deactivation due to the reduction of Pd2+ into Pd0.
Understanding of the critical atomistic steps during the dehydrogenation process of liquid organic hydrogen carriers (LOHCs) is important to the design of cost-efficient, high-performance LOHC ...catalysts. Based on the density functional theory (DFT) we studied the thermodynamics and kinetics of the complete dehydrogenation path of perhydro-N-ethylcarbazole (12H-NEC) on Ru(0001) surface, involving the adsorption of 12H-NEC, the discharge of H ions onto Ru surface, and the desorption of H2 and hydrogen-lean NEC. It was found that the bonding of nH-NEC is significantly strengthened for n≤4 because of the flat aromatic ring. Although the whole dehydrogenation process is endothermic, the release of H from nH-NEC, with H adsorbed onto the Ru surface, was found to be exothermic. The desorption of flat, hydrogen-lean NEC, which costs ∼255 kJ/mol, was identified as the most energy demanding step. In addition, the effect of surface morphology on adsorption was studied based on an amorphous surface model. Overall, the results imply more efficient dehydrogenation could be achieved from relatively weak bonding of NEC to catalysts, either through engineering catalyst surface (such as surface defects or smaller catalyst particles) or different catalyst materials. Our calculations also revealed possible dealkylation at elevated temperatures.
•Full paths of dehydrogenation of 12H-NEC on Ru(0001) surface explored.•Energetically and kinetically critical steps for dehydrogenation identified.•Relationship between bonding strength of nH-NEC on Ru and structures discussed.
