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•Effective catalysts for dehydrogenation processes of perhydro-dibenzyl toluene (DBT) are suggested.•Doping M atoms onto Pt/M/Pt(111) (M = Pd, Cu, or Ni) can effectively tune the ...dehydrogenation of DBT over the catalyst.•D-band centers and reaction energies of the rate-determining step are correlated with hydrogen adsorption energies on DBT.•H-adsorption strength on DBT is an effective catalytic descriptor for dehydrogenation activity.•Tensile and compressive strain applied to Pt/M/Pt (M = Pd, Cu, or Ni) decrease and increase reaction energies, respectively.
Designing effective dehydrogenation catalysts for liquid organic hydrogen carriers is essential to the release and transport of hydrogen. The hydrogen release of perhydro-dibenzyltoluene using Pt-based subsurface alloys (Pt/M/Pt(111), where M = Pd, Cu, or Ni) and the effect of the applied biaxial strain on dehydrogenation performance of Pt/M/Pt(111) were systematically investigated. The doping of M atoms onto Pt/M/Pt(111) and strained Pt/M/Pt(111) could effectively tune the electronic properties of the Pt atoms, thus eventually affecting the hydrogen adsorption strength. The rate-determining step (RDS) of the dehydrogenation process on surfaces of Pt(111), Pt/M/Pt(111), strained Pt(111), and strained Pt/M/Pt(111) was identical: the first step of dehydrogenation in the middle ring of perhydro-dibenzyltoluene. The doping of the M atoms and application of tensile strain promoted dehydrogenation. Furthermore, it was revealed that d-band centers and reaction energies of the RDS correlated with the hydrogen adsorption energy, suggesting that hydrogen adsorption strength is a practical descriptor of dehydrogenation activity.
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•Well-dispersed Pt particles were prepared on highly reducible CeO2-SiO2 support.•High oxygen vacancy surface concentration was obtained over Pt/CeO2-SiO2.•Pt particles prepared over ...the rich oxygen vacancy surface were significantly stable.•CeO2 was significantly reduced under MCH dehydrogenation conditions.•Pt/CeO2-SiO2 showed excellent catalytic activity for MCH dehydrogenation.
A highly reducible CeO2 surface was prepared on a SiO2 support to investigate the effect of redox properties of CeO2 on the catalytic activity of Pt/CeO2-SiO2 for MCH dehydrogenation. Characterization of the Pt/CeO2-SiO2 catalyst revealed a significantly higher Pt dispersion than Pt/micro-sized CeO2 and Pt/SiO2. The well-dispersed Pt particles averaging 1.1 nm in size (Pt/CeO2-SiO2) were primarily attributed to the high surface concentration of oxygen vacancies, which provided abundant defect sites that stabilized the Pt particles from sintering. Hydrogen released from MCH dehydrogenation was approximately 5–6 times greater with high selectivity towards toluene products for Pt/CeO2-SiO2 compared to its counterparts. The excellent catalytic activity of Pt/CeO2-SiO2 was attributed to the presence of rich oxygen vacancies on the CeO2 surface, which was significantly reduced under MCH dehydrogenation conditions, resulting in faster toluene desorption.
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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•Four Pt bead catalysts were synthesized using two distinct methods, both with and without potassium.•Catalyst synthesis methods impact the Pt electronic structure by altering the ...size and distribution of Pt sites.•The K promotor plays a pivotal role in modifying the Pt electronic state to enhance catalytic activity.•An egg-shell structured, K-PtE/θ-Al2O3 catalyst exhibits superior activity for LOHC dehydrogenation.
Alumina-supported Pt bead catalysts with uniform (PtU/θ-Al2O3) or egg-shell (PtE/θ-Al2O3) structure and their corresponding potassium-doped counterparts (K-PtU/θ-Al2O3, K-PtE/θ-Al2O3) were synthesized to elucidate the influence of structure-induced active metal distribution and promotor on the dehydrogenation of liquid organic hydrogen carriers (LOHCs). Characterizations of the catalysts confirmed that different synthetic methods led to distinct Pt distributions on the Al2O3 surface. PtE/θ-Al2O3 and K-PtE/θ-Al2O3 had an average size of 1 nm with narrow Pt distributions while PtU/θ-Al2O3 and K-PtU/θ-Al2O3 exhibited bimodal distributions in Pt particle size (<0.2 nm and <0.8 nm), which also influenced the oxidation states. Introducing the promotor (K) facilitated electron transfer into Pt, which resulted in a more metallic state. When applied to the dehydrogenation of two different LOHCs, including methylcyclohexane and perhydro-monobenzyltoluene, K-PtE/θ-Al2O3 exhibited superior catalytic activity and durability compared to other catalysts. The improved activity of K-PtE/θ-Al2O3 was primarily attributed to the combined electronic influences of the catalyst bulk structure and promotor.
•Microwave enhances the specific surface area and pore volume of the catalyst carrier.•The interactions between carrier and active metals are improved by microwave heating.•Microwave applications for ...dehydrogenation reactions improve energy use efficiency.•Hot spots in the catalyst bed encourage higher reaction rates.
Liquid organic hydrogen carriers (LOHC) can store acceptable amounts of hydrogen at ambient temperature and pressure for long periods of time, usually with a storage capacity of 6–8 wt%, and are considered as high-density hydrogen storage materials. Catalytic dehydrogenation of LOHCs is currently a research hot topic. The unique "inside-out" heating mechanism of microwaves is more conducive to the catalysis of LOHC than conventional heating. In this paper, the application of microwaves in catalyst preparation and reaction process were reviewed. Furthermore, three representative LOHC materials were selected for the enhanced dehydrogenation via microwave action. This paper summarizes the enhancement of microwave heating on the LOHC catalytic process and puts forward the prospect for the future, which should further increase the advantages of microwaves in terms of energy utilization efficiency, using numerical simulations to predict the microwave action and explain the mechanism.
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Ni nanoparticles (≈ 8 nm) have been prepared at about 15 wt% loading strongly grafted on N-doped graphitic carbon matrix Ni@(N)C by pyrolysis of Ni(OAc)2 adsorbed on chitosan. Ni@(N)C was used as ...catalyst for H2 storage/release on N-ethylcarbazole (EC). Ni@(N)C exhibits higher H2 storage capacity than analogous Ni nanoparticles (NPs) supported on silica. The addition of minute amounts (18 ppm) of Pt increases significantly the H2 storage/release activity of Ni@(N)C due to effect of Pt promoting H spill over the Ni NPs. There is no linear correlation between Pt concentration and hydrogenation/dehydrogenation activity of Ni@(N)C, the lowest Pt loading (18 ppm) resulting in the most efficient Pt/Ni@(N)C for hydrogenation-dehydrogenation of EC. This fact was attributed to the presence of small Pt clusters or single atoms, while higher concentration would correspond to a less-efficient larger cluster regime. The most efficient Pt/Ni@(N)C-18 catalyst was used for four consecutive hydrogenation/dehydrogenation cycles, exhibiting some fatigue in the H2 storage/release of the same EC batch that was attributed to the increase in the product mixture complexity upon cycling, with the formation of some intermediates that undergo more difficult hydrogenation/dehydrogenation reaction as well as partial catalyst deactivation. After four cycles, (Pt)Ni@(N)C exhibits in the fifth use a H2 storage capacity of 5.2 wt%, somewhat lower than the 5.8 wt% H2 capacity of the fresh sample, while no changes in the XRD, TEM and XPS characterization of the five-times used catalyst compared to the fresh material is observed.
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•Ni nanoparticles on N-doped graphitic carbon (Ni@(N)C) were obtained by chitosan pyrolysis.•Ni@(N)C were used for hydrogenation/dehydrogenation of N-ethylcarbazole (EC).•Pt at ppm levels (0.0018 wt%) increases significantly the activity of Ni@C.•Pt doped Ni@(N)C is able to store 5.8 wt% H2 that is the maximum EC storage capacity.•The Pt-Ni@(N)C were stable and reusable in four hydrogenation/dehydrogenation cycles.
Pt supported on ordered mesoporous silica (KIT-6) catalyst was examined for the dehydrogenation of homocyclic liquid organic hydrogen carriers (LOHCs, 1: MCH, 2: hydrogenated biphenyl-based eutectic ...mixture (H-BPDM)) conditions. The longer pore-residence time of the MCH molecules in the 3D bicontinuous pore structure of the Pt/KIT-6 catalyst strongly affected the catalytic activity because a higher MCH concentration was achieved in the vicinity of the Pt active sites. Pt/KIT-6 catalyst exhibited a higher surface area, pore volume, and Pt dispersion with narrower particle size distribution (average Pt particle size: ~1.3 nm). Therefore, higher LOHC conversion with faster hydrogen production occurred, with a higher hydrogen selectivity over Pt/KIT-6 compared with Pt/SiO2 and Pt/Al2O3. Long-term experiment results indicated that the Pt/KIT-6 catalytic activity was stable over the reaction time than that of the other catalysts. No significant structural collapse occurred in KIT-6 during the dehydrogenation. Carbon coking was observed for all three samples.
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•Pt was supported on order mesoporous silica with a 3-D pore structure (KIT-6).•Pt/KIT-6 exhibited excellent LOHC dehydrogenation activity and high H2 selectivity.•Pt/Al2O3 and Pt/SiO2 revealed formation of partially dehydrogenated products.•Pt was confined in the KIT-6 mesopores showing narrow particle size distribution.•Longer pore-residence time was achieved attributed to the 3-D structure of KIT-6.
A new set of compounds based on N- and S-heterocycles were investigated through Density Functional Theory (DFT) for their use as liquid organic hydrogen carriers (LOHCs). The hydrogenated forms of ...these compounds could release hydrogen within the most important technical requirements in mobile and stationary applications. In this work, the potential of the 1H-pyrrole/tetrahydro-1H-pyrrole and thiophene/tetrahydrothiophene pairs as possible leader structures to synthesize more sustainable LOHCs from costless oil-refining and oil-hydrotreating by-products is shown. According to DFT-M06-HF results, the 3-allyl-1H-pyrrole/3-allyl-tetrahydro-1H-pyrrole pair presented an adequate theoretical hydrogen storage capacity (3.6 %wt H) and a high theoretical dehydrogenation equilibrium yields (% εd = 67.8%) at 453 K. Therefore, this pair is recommended for hydrogen storage stationary applications. On the other hand, the 2-(thiophen-2-yl)-1H-pyrrole/2-(2,3-dihydrothiophen-2-yl)tetrahydropyrrole pair proved to be suitable for both mobile and stationary applications; the storage capacity of this pair was 3.9 %wt H and the theoretical dehydrogenation equilibrium yields at 453 K (% εd = 28.1%) was considered moderate.
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•DFT calculations for hydrogenation/dehydrogenation of heterocycles was examined.•Thermodynamic calculations with M06HF are consistent with those of the G3(MP2) one.•The thermodynamic parameters for reactions of N- and S-heteroclycles are discussed.•Pyrrole and thiophene could be key structures for the development of new LOHCs.•It is the first report on the potentiality of allyl- and thienyl-pyrrole as LOHCs.
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•DFT calculations propose B and N substituted bicyclohexyl as a novel LOHC.•Formation energies confirm the feasibility of synthesizing the novel material.•BN-bicyclohexyl exhibits ...significantly enhanced dehydrogenation efficiency.•Electronegativity difference between B and N facilitates the formation of H2 bonding.•The Pd catalyst further enhances the potential of BN-bicyclohexyl as a LOHC.
Hydrogen is considered as an environmentally friendly energy resource to replace fossil fuels. This study aims to enhance the dehydrogenation efficiency of liquid organic hydrogen carrier (LOHC) materials by investigating the dehydrogenation and hydrogenation mechanisms through hetero atom (B and N) substitution of bicyclohexyl, as well as by applying the high-efficiency catalysts, palladium and ruthenium. To achieve this, BN-bicyclohexyl, a novel material based on bicyclohexyl, was proposed using density functional theory (DFT) calculations, and the synthesis of the new material was evaluated through enthalpy and free energy calculations. Mulliken charge analysis showed that the B and N atoms substituted in bicyclohexyl can induce dihydrogen bonding, resulting in efficient dehydrogenation at the substitution site. The dehydrogenation efficiency of BN-bicyclohexyl (1.53 eV in activation energy) surpasses that of bicyclohexyl (2.77 eV) on the Pd(111) surface. However, on the Ru(001) surface, BN-bicyclohexyl exhibits a slightly lower hydrogenation efficiency than bicyclohexyl, with an increase of 0.39 eV in activation energy. This trend highlights BN as a promising candidate for enhancing the capability of LOHCs. Notably, the dehydrogenation efficiency of BN-bicyclohexyl is significantly higher than that of bicyclohexyl, which go beyond slightly lower hydrogenation efficiency than bicyclohexyl.
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