Methylcyclohexane (MCH), one of the liquid organic hydrogen carriers (LOHCs), offers a convenient way to store, transport, and supply hydrogen. Some features of MCH such as its liquid state at ...ambient temperature and pressure, large hydrogen storage capacity, its well-known catalytic endothermic dehydrogenation reaction and ease at which its dehydrogenated counterpart (toluene) can be hydrogenated back to MCH and make it one of the serious contenders for the development of hydrogen storage and transportation system of the future. In addition to advances on catalysts for MCH dehydrogenation and inorganic membrane for selective and efficient separation of hydrogen, there are increasing research interests on catalytic membrane reactors (CMR) that combine a catalyst and hydrogen separation membrane together in a compact system for improved efficiency because of the shift of the equilibrium dehydrogenation reaction forwarded by the continuous removal of hydrogen from the reaction mixture. Development of efficient CMRs can serve as an important step toward commercially viable hydrogen production systems. The recently demonstrated commercial MCH-TOL based hydrogen storage plant, international transportation network and compact hydrogen producing plants by Chiyoda and some other companies serves as initial successful steps toward the development of full-fledged operation of manufacturing, transportation and storage of zero carbon emission hydrogen in the future. There have been initiatives by industries in the development of compact on-board dehydrogenation plants to fuel hydrogen-powered locomotives. This review mainly focuses on recent advances in different technical aspects of catalytic dehydrogenation of MCH and some significant achievements in the commercial development of MCH-TOL based hydrogen storage, transportation and supply systems, along with the challenges and future prospects.
•Liquid organic hydrogen carriers are potential candidates for hydrogen storage.•A chromatographic method for separation of partially hydrogenated LOHC is presented.•The method is successfully scaled ...up to the semi-preparative scale.•Recovery method of desired product from eluent is presented.
Liquid organic hydrogen carriers (LOHC) are an interesting option for hydrogen storage and transportation. This concept is based on reversible hydrogenation and dehydrogenation of a carrier compound for uptake and release of hydrogen respectively. Among others, dibenzyltoluene is a potential LOHC due to its reasonable hydrogen storage capacity (6.2ma-%) and high thermal stability. However, a huge number of stable intermediates with different degrees of hydrogenation are observed in a partially hydrogenated reaction mixture of dibenzyltoluene. For the process development and studies of the dibenzyltoluene reaction mechanism, it is crucial to determine physico-chemical properties of its various partially hydrogenated fractions, which requires their isolation from the reaction mixture. In this work, a reversed-phase high performance liquid chromatography (RP-HPLC) method for the separation and purification of partially hydrogenated mixtures of dibenzyltoluene is presented. The method was developed and validated at analytical scale and successfully scaled up to semi-preparative scale. The mixture was separated into four fractions according to their degree of hydrogenations using phenylhexyl silica stationary phase and a mobile phase consisting of acetone/water (96/4, v/v). Fractions with purity above 98% and yield higher than 90% were obtained in a semi-preparative column with an internal diameter of 50mm.
Reversible hydrogenation of nitriles to amines has been proposed as a method of hydrogen storage. Several research groups have demonstrated that acceptorless dehydrogenation of amines can be ...performed. Furthermore, the reactions were performed with homogeneous catalysts at moderate temperatures of only about 110 °C. This is highly beneficial in terms of efficiency. However, all reported works have been performed in nitrogen atmospheres. The research question to be evaluated in this study is whether it is possible to carry out the reaction at moderate conditions without any inert gas. Reaction thermodynamics, including the calculation of the reaction equilibria with the superimposed phase equilibria, has been analyzed to answer this question. The main conclusion in this regard is that the thermodynamic driving force for dehydrogenation of amines at 110 °C is too low to reach reasonable conversions. The addition of nitrogen dilutes hydrogen, decreasing its partial pressure. This way, near‐vacuum conditions are simulated regarding hydrogen. This shifts equilibrium toward the products. However, a technical hydrogen storage process requires the release of pure hydrogen. A possibility to enable hydrogen release at moderate temperatures and provide pure hydrogen could be the application of electrochemical compression. This technic selectively withdraws hydrogen, making high conversions thermodynamically feasible.
Dehydrogenation of amines to nitriles has been proposed as a method of hydrogen storage. Catalytically the reaction can be performed at low temperatures, but thermodynamics set strict limits. It is shown that conversion at 100 °C is only possible in the presence of a large excess of inert gas. Hence, other methods are needed for technical hydrogen storage.
We have studied the dehydrogenation of the liquid organic hydrogen carrier (LOHC) dicyclohexylmethane (DCHM) to diphenylmethane (DPM) and its side reactions on a Pd(111) single crystal surface. The ...adsorption and thermal evolution of both DPM and DCHM was measured in situ in ultrahigh vacuum (UHV) using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (HR-XPS). We found that after deposition at 170 K, the hydrogen-lean DPM undergoes C-H bond scission at the methylene bridge at 200 K and, starting at 360 K, complete dehydrogenation of the phenyl rings occurs. Above 600 K, atomic carbon incorporates into the Pd bulk. For the hydrogen-rich DCHM, the first stable dehydrogenation intermediate, a double π-allylic species, forms already at 190 K. Until 340 K, further dehydrogenation of the phenyl rings and of the methylene bridge occurs, yielding the same intermediate that is formed upon heating of DPM to this temperature, that is, DPM dehydrogenated at the methylene bridge. The onset for the complete dehydrogenation of this intermediate occurs at a much higher temperature than after adsorption of DPM. This behavior is mainly attributed to coadsorbed hydrogen from DCHM dehydrogenation. The results are discussed in comparison to our previous study of DPM and DCHM on Pt(111) revealing strong material dependencies.
Graphical Abstract
Liquid organic hydrogen carriers (LOHCs) have great potential as a hydrogen storage medium needed for a future sustainable energy system. Dehydrogenation of LOHCs requires a catalyst, such as ...supported Pd nanoparticles. Under reaction conditions, hydrogen and carbon may diffuse into the bulk of supported Pd catalyst particles and affect their activity and selectivity. The detailed understanding of this process is critical for the use of LOHCs in future hydrogen storage technologies. In this work, we studied these processes in-situ on a Pd model catalyst using high-energy grazing incidence X-ray diffraction. Pd nanoparticles were evaporated in ultra-high vacuum on a polished α-Al
2
O
3
(0001) substrate. The particles, with an initial average size of ~ 3.4 nm, were investigated at elevated temperature during their interaction with H
2
and methylcyclohexane (MCH) representing a model LOHC. The interaction with H
2
was studied in-situ at partial pressures up to 1 bar and temperatures between 300 and 500 K. At 300 K, the Pd nanoparticles (NPs) show a transition from α-PdH to β-PdH as a function of the H
2
pressure. The transition occurs gradually, which is attributed to the heterogeneity of the NP system. The hydrogen uptake in β-PdH
x
at 300 K and 1 bar is estimated to be X
H
~ 0.37 ± 0.03 indicating that the miscibility gap is narrowed for the nanoparticular system. With increasing temperature, X
H
decreases until no β-PdH phase is formed anymore at 500 K. At the same temperature, we studied the interaction of the Pd/sapphire model catalyst with MCH, both in the presence and in the absence of H
2
. In the absence of H
2
, carbon is formed and diffuses into the bulk yielding PdC
x
with a C concentration of around x ~ 0.05 ± 0.01. In the presence of H
2
in the gas phase, bulk carbon formation in the Pd/sapphire model catalyst is completely suppressed. These results show that Pd nanoparticles act as an adequate catalyst for the dehydrogenation of MCH.
Graphical Abstract
Supported Ru catalysts have been often employed for hydrogen charge into liquid organic hydrogen carrier molecules (monobenzyltoluene in this work), and their catalytic performance largely depends ...upon physicochemical properties of the support materials. We prepared supported Ru catalysts on SiO
2
-ZrO
2
with different Si/(Si+Zr) ratios ranging from 0 to 30mol% by loading Ru
3
(CO)
12
onto Si,Zr-mixed metal hydroxide and subsequent thermolysis. The textural properties, Ru particle size, and hydrogenation activity of Ru/SiO
2
-ZrO
2
catalysts show a volcano-shaped dependence on the content of Si added, where the maximum is achieved at the Si/(Si+Zr) ratio of 5 mol%. Up to this Si content the incorporation of Si into ZrO
2
improves thermal stability and decreases the particle size of tetragonal ZrO
2
, resulting in a positive contribution to hydrogen storage efficiency. However, the further addition of Si increases surface heterogeneity and charge imbalance, and hence induces a decrease in the density of surface OH group reacting with Ru
3
(CO)
12
, which explains the lowered activity. Therefore, the addition of up to 5 mol% Si into ZrO
2
is effective in enhancing the hydrogenation performance of Ru/ZrO
2
owing to the improved textural properties and smaller Ru particles.
Ultrahigh vacuum (UHV) surface science techniques are used to study the heterogeneous catalytic dehydrogenation of a liquid organic hydrogen carrier in its liquid state close to the conditions of ...real catalysis. For this purpose, perhydrocarbazole (PH), otherwise volatile under UHV, is covalently linked as functional group to an imidazolium cation, forming a non‐volatile ionic liquid (IL). The catalysed dehydrogenation of the PH unit as a function of temperature is investigated for a Pt foil covered by a macroscopically thick PH‐IL film and for Pd particles suspended in the PH‐IL film, and for PH‐IL on Au as inert support. X‐ray photoelectron spectroscopy and thermal desorption spectroscopy allows us to follow in situ the catalysed transition of perhydrocarbazole to carbazole at technical reaction temperatures. The data demonstrate the crucial role of the Pt and Pd catalysts in order to shift the dehydrogenation temperature below the critical temperature of thermal decomposition.
This is no joke: Catalysis in the liquid state is probed in vacuum. Vacuum surface science techniques such as X‐ray photoelectron spectroscopy and thermal desorption spectroscopy probe in situ the dehydrogenation of the liquid organic hydrogen carrier (LOHC) perhydrocarbazole close to equilibrium reaction conditions of real heterogeneous catalysis. The otherwise volatile LOHC is linked to an imidazolium cation, forming a non‐volatile LOHC ionic liquid.
A pair of 2-(n-methylcyclohexyl)methylpiperidine (H12-MBP) and its full dehydrogenation product (H0-MBP) has recently been considered as a potential liquid organic hydrogen carrier with 6.15 wt% H2 ...storage capacity. In the discovery of an active and stable catalyst for H2 discharge from H12-MBP at lower temperatures, a mesoporous Pd-Al2O3 catalyst (MPdA) was synthesized by a one-pot solvent deficient precipitation (SDP). In the present work, the sensitivity and effectiveness of the SDP method are examined by varying the calcination temperature and time in the preparation of the MPdA catalyst. The characterization revealed that the final properties of the MPdA catalyst greatly rely on both the calcination temperature and time. The MPdA catalyst showed better dehydrogenation activity for calcination at 600 °C than at other temperatures, because of Pd particles of smaller size with higher dispersion. Although the MPdA catalysts calcined at 600 °C for different periods of time have similar size and dispersion of Pd particles, the dehydrogenation efficiency was superior as the calcination time became shorter (e.g., 1 h), which originated from the better arrangement of Pd particles over a higher surface area. These MPdA catalysts, irrespective of the calcination time, displayed a remarkable stability in the dehydrogenation of H12-MBP owing to the protection of Pd particles by the Al2O3 layer.
Chiyoda have been continuing the technology development employing liquid organic hydrogen carrier (LOHC) as large-scale storage and transportation technology for hydrogen since 2002. Chiyoda ...succeeded the development of the dehydrogenation catalyst through the fundamental research for around ten years. After completing the establishment of the system technology through a pilot plant demonstration in 2014, Chiyoda has been preparing to participate in a project by NEDO to demonstrate an international hydrogen supply chain in large-scale, and in 2020, the project was successfully completed between Brunei Darussalam in Southeast Asia and the Kawasaki waterfront area in Japan for 5,000 km. “SPERA Hydrogen®” System has been shift to commercialization phase due to completion of the International Hydrogen Supply Chain Demonstration including whole process. This paper introduces outline and the features of the SPERA hydrogen system, and the international hydrogen supply chain demonstration funded by NEDO.
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