Liquid Organic Hydrides Research Articles

Ni-Cu High-Loaded Sol-Gel Catalysts for Dehydrogenation of Liquid Organic Hydrides: Insights into Structural Features and Relationship with Catalytic Activity.

The heightened interest in liquid organic hydrogen carriers encourages the development of catalysts suitable for multicycle use. To ensure high catalytic activity and selectivity, the structure–reactivity relationship must be extensively investigated. In this study, high-loaded Ni–Cu catalysts were considered for the dehydrogenation of methylcyclohexane. The highest conversion of 85% and toluene selectivity of 70% were achieved at 325 °C in a fixed-bed reactor using a catalyst with a Cu/Ni atomic ratio of 0.23. To shed light on the relationship between the structural features and catalytic performance, the catalysts were thoroughly studied using a wide range of advanced physicochemical tools. The activity and selectivity of the proposed catalysts are related to the uniformity of Cu distribution and its interaction with Ni via the formation of metallic solid solutions. The method of introduction of copper in the catalyst plays a crucial role in the effectiveness of the interaction between the two metals.

Experimental Investigation of Isobaric specific heat capacity (Cp) of 9-ethylcarbazole in liquid and solid state

Liquid organic hydrides, e.g. 9-ethylcarbazole, are potentially interesting hydrogen storage materials because of their reversible hydrogen sorption properties. In this study, the isobaric specific heat capacity of 9- ethylcarbazole in solid and liquid phases was investigated using adiabatic calorimeter. The experimental setup consisting of two basic components adiabatic calorimeter and pressure unit was developed. To calibrate the apparatus the specific heat of the water was measured. The experimental data points were obtained at 0.1 MPa to 0.88 MPa pressure range and 353 K to 480 K temperature range. The specific heat dependence on pressure and temperature was presented. The increase in specific heat of 9-ethylcarbazole was observed with increasing pressure and temperature for solid phase, while for liquid phase decrease in trend was observed for increasing pressure. Keywords: 9-ethylcarbazole, Adiabatic Calorimeter, Specific Heat, Nitrogen Gas Cylinder

Palladium Supported on Carbon Nanotubes as a High-Performance Catalyst for the Dehydrogenation of Dodecahydro-N-ethylcarbazole

Hydrogen storage in the form of liquid organic hydrides, especially N-ethylcarbazole, has been regarded as a promising technology for substituting traditional fossil fuels owing to its unique merits such as high volumetric, gravimetric hydrogen capacity and safe transportation. However, unsatisfactory dehydrogenation has impeded the widespread application of N-ethylcarbazole as ideal hydrogen storage materials in hydrogen energy. Therefore, designing catalysts with outstanding performance is of importance to address this problem. In the present work, for the first time, we have synthesized Pd nanoparticles immobilized on carbon nanotubes (Pd/CNTs) with different palladium loading through an alcohol reduction technique. A series of characterization technologies, such as X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES), X-ray photoelectron spectroscopy (XPS) and transmission electron spectroscopy (TEM) were adopted to systematically explore the structure, composition, surface properties and morphology of the catalysts. The results reveal that the Pd NPs with a mean diameter of 2.6 ± 0.6 nm could be dispersed uniformly on the surface of CNTs. Furthermore, Pd/CNTs with different Pd contents were applied in the hydrogen release of dodecahydro-N-ethylcarbazole. Among all of the catalysts tested, 3.0 wt% Pd/CNTs exhibited excellent catalytic performance with the conversion of 99.6% producing 5.8 wt% hydrogen at 533 K, low activation energy of 43.8 ± 0.2 kJ/mol and a high recycling stability (>96.4% conversion at 5th reuse).

Application of microwave synthesized Ag-Rh nanoparticles in cyclohexane dehydrogenation for enhanced H2 delivery

The catalytic dehydrogenation of liquid organic hydrides (LOH) is a promising route to deliver H2 for various mobile and stationary applications. However, an efficient and low-cost dehydrogenation catalyst, as an alternative to Pt, is a key for the success of LOH-based H2 supply. In a quest for such catalysts, we synthesized stable Ag-Rh bimetallic nanoparticles (BNP) supported on activated carbon cloth (ACC) and Y2O3 using the microwave-assisted polyol technique. The performance of these catalysts during dehydrogenation of LOH viz., cyclohexane, was evaluated at 300 °C using an advanced spray-pulse reactor system. The Ag:Rh ratio was optimized to maximize the cyclohexane conversion and H2 evolution. The effect of Ag:Rh ratio, catalyst support, and synthesis method was investigated, too. The most stable H2 evolution performance was exhibited by microwave-synthesized 1:4 Ag-Rh/Y2O3 catalyst with the cyclohexane conversion, dehydrogenation rate and H2 evolution rate of 35.8%, 17.2 mmol/gMet/min and 400 mmol/gMet/min, respectively. Finally, the performance of catalysts used in this study was compared with the Pt-based catalysts.

Kinetics on NiZn Bimetallic Catalysts for Hydrogen Evolution via Selective Dehydrogenation of Methylcyclohexane to Toluene

Liquid organic chemical hydrides are effective hydrogen storage media for easy and safe transport. The chemical couple of methylcyclohexane (MCH) and toluene (TOL) has been considered one of the feasible cycles for a hydrogen carrier, but the selective dehydrogenation of MCH to TOL has been reported using only Pt-based noble metal catalysts. This study reports MCH dehydrogenation to TOL using supported NiZn as a selective, non-noble-metal catalyst. A combined experimental and computational study was conducted to provide insight into the site requirements and reaction mechanism for MCH dehydrogenation to TOL, which were compared with those for cyclohexane (CH) dehydrogenation to benzene (BZ). The kinetic measurements carried out at 300–360 °C showed an almost zero order with respect to MCH pressure in the high-pressure region (≥10 kPa) and nearly a positive half order with respective to H2 pressure (≤40 kPa). These kinetic data for the dehydrogenation reaction paradoxically indicate that hydrogenation of a...

Heat storage by the dehydrogenation of methylcyclohexane – Experimental studies for the design of a microstructured membrane reactor

The concept of hydrogen storage via liquid organic hydrides in cycles of hydrogenation and dehydrogenation with preferably low amount of reaction enthalpy is well known under the abbreviation LOHC, Liquid Organic Hydrogen Carrier. However, our study addresses the dehydrogenation of methylcyclohexane in a prototype microstructured membrane reactor, which is mainly devoted to the heat storage in a so-called LORC, a Liquid Organic Reaction Cycle. While using the same cycles of hydrogenation and dehydrogenation, heat shall be stored on the contrary by high reaction enthalpy in the LORC. A novel planar membrane module with an integrated catalytic fixed-bed has been developed. It is equipped with structured supports to reduce the mechanical stress on the Pd-membrane foil. Experiments investigating the membrane separation performance were conducted with operational parameters up to 400 °C and 13 bar. The ability of shifting equilibrium conditions to product side and pure H2 recovery was shown. Catalyst deactivation and regeneration was tested in order to analyze stability of the Pd-membrane. An experimental parameter study was performed to obtain a future optimized design of a large-scale prototype reactor.

Liquid organic and inorganic chemical hydrides for high-capacity hydrogen storage

In this review, we survey the research progress in catalytic hydrogen generation from, and the regeneration of, diverse liquid-phase chemical hydrogen storage materials, including both organic and inorganic chemical hydrides.

有機ハイドライドによる水素貯蔵・輸送・供給

有機ハイドライドによる水素貯蔵・輸送・供給

Catalyst development for the dehydrogenation of MCH in a microstructured membrane reactor—For heat storage by a Liquid Organic Reaction Cycle

Liquid organic hydrides can act as energy storage from renewable sources in a cycle of hydrogenation and dehydrogenation. In this work, a feasibility study for heat storage by methylcyclohexane dehydrogenation as a system component in a Liquid Organic Reaction Cycle (LORC) is presented. The endothermic dehydrogenation of methylcyclohexane was investigated in a microstructured reactor, in order to supply reaction heat efficiently. The integration of a membrane into the microstructured reactor for in-situ pure hydrogen removal is intended in further studies.In order to obtain an efficient microstructured membrane reactor, basic catalyst studies were performed. For this purpose different catalysts were prepared and applied to the microstructured reactor. A catalyst containing Pt as active metal and Al2O3 as porous support was selected as the most active catalyst and it was further characterized by BET, H2 chemisorption, SEM, EPMA and ICP-OES. The different catalysts deactivated rapidly by coke formation at the entrance of the microstructured reactor. Carbon black was analyzed on the catalyst surface by Raman spectroscopy. The addition of H2 or a higher pressure level in the reaction zone delayed the deactivation rate considerably. Therefore, the utilization of a microstructured membrane reactor is beneficial; it provides conditions to reduce coke formation like a higher reaction pressure and continuous H2 partial pressure in the catalyst zone if sweep gas is absent on the permeate side of the membrane.

Non-noble Ni–Cu/ACC bimetallic catalyst for dehydrogenation of liquid organic hydrides for hydrogen storage

The effect of Cu on dehydrogenation activity of Ni has been observed when dehydrogenation of methyl cyclohexane (MCH) was carried out by using bimetallic Ni–Cu supported on activated carbon cloth (ACC) catalysts with various Ni to Cu ratios and constant total metal content of about 10 wt%. The dehydrogenation of MCH was studied for delivery of clean hydrogen to hydrogen fueling station. Catalysts have been synthesized by adsorption method and characterized by atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Among all combinations of this study 8 wt% Ni + 2 wt% Cu/ACC was found to show strong synergetic effect. This catalyst exhibited relatively high H2 evolution rate 39.4 mmol/gmet/min during the dehydrogenation of MCH. At the same time methane evolution rate was relatively low which indicated insignificant side reaction of hydrogenolysis. The study reveals that presence of specific amount of Cu enhances the dehydrogenation activity of Ni and suppresses the hydrogenolysis activity for the same. The Ni–Cu/ACC catalyst may be a potential non-noble metal catalyst for dehydrogenation reaction.

Hydrogen storage in liquid organic hydride: Selectivity of MCH dehydrogenation over monometallic and bimetallic Pt catalysts

Hydrogen storage for mobile and stationary applications is an expanding research topic. One of the more promising storage techniques relies on the reversibility, high selectivity, and high hydrogen density of liquid organic hydrides, in particular methylcyclohexane (MCH). Catalyst evaluation for MCH dehydrogenation to toluene is based on three catalytic parameters: activity, selectivity, and stability. Current catalysts, optimized for catalytic reforming, do not meet the targeted aromatic selectivity (+99%) for MCH dehydrogenation. Therefore, a range of Pt catalysts was prepared and compared with commercially available catalysts in a fixed-bed reactor under operating conditions suitable for mobile and stationary applications. The best overall performance was realized by a particular monometallic Pt catalyst. This catalyst showed superior activity, selectivity, and stability compared with other prepared and commercial catalysts. As an effort to further enhance the aromatic selectivity, this study identified the main side-reactions associated with MCH dehydrogenation, the effect of operating parameters on by-product yields, and the effect of catalyst deactivation on long-term selectivity.

Carbon supports for the catalytic dehydrogenation of liquid organic hydrides as hydrogen storage and delivery system

The use of liquid organic hydrides as hydrogen carriers is a promising storage and delivery system due to the advantages of using liquid-based infrastructures and its economic feasibility compared to other conventional systems. The reversible dehydrogenation/hydrogenation of liquid organic hydrides is a key point for the development of highly performance reactors. In this study different carbon materials have been investigated as platinum supports, including carbon nanofibers, carbon black, carbon xerogel, activated carbon and ordered mesoporous carbon. To individuate the effect of the carbon support on the catalytic activity, platinum particles were synthesized by a microemulsion procedure. The analysis of the hydrogen evolution curves indicate that the support BET surface area plays a very important role on the initial catalytic activity, obtaining a maximum rate of 220 mmol gPt−1 min−1 when using an ordered mesoporous carbon with a surface area of 930 m2 g−1. Nevertheless, the analysis of catalytic activity at prolonged duration indicates a better behavior toward deactivation for supports characterized by wide pores and low graphitization degree like carbon black or carbon xerogel, despite their lower initial dehydrogenation rate (100–140 mmol gPt−1 min−1). The ultimate use in the dehydrogenation reactor as well as the operation conditions will define the best catalyst structure from the point of view of the carbon support.

The short-channel function of hollow carbon nanoparticles as support in the dehydrogenation of cyclohexane

The structure function of hollow carbon nanoparticles (HCNP) as support of Pt particles in the dehydrogenation of cyclohexane was studied. The catalysts and supports were characterized by the XRD, TEM, TG-MS and N2 adsorption/desorption technologies. The results indicated that the short-channel of HCNP can improve the activity and stability of Pt/HCNP, which was confirmed and explained by the temperature programmed desorption (TPD) experiments. The extent of coke deposited on HCNP was much less than that on MCNT, which can be attributed to fast diffusion and quick removal of benzene from active sites through the short path of HCNP. The HCNP with short channel is very important for improving catalyst performance in the storage system of liquid organic hydrides.

Comparative Study of Catalytic Hydrogenation of 9-Ethylcarbazole for Hydrogen Storage over Noble Metal Surfaces

The use of liquid organic hydrides (LOH) as a chemical hydrogen store to supply hydrogen gas for a polymer electrolyte membrane fuel cell (PEFC) is explored. In the present work, hydrogenation of 9-ethylcarbazole is particularly investigated in the liquid phase over different unsupported noble metal powders. The kinetics obtained from the hydrogenation of the substrate over these catalytic systems are modeled, and the derived fundamental rate constants are systematically compared. It is found that the differences in activity and product distribution of the reaction over different metal surfaces depend critically on the electronic structures of the metals. From the prospective application of 9-ethyl-carbazole, an effective catalyst should be able to convert the substrate to the fully hydrogenated cis product without forming any kinetically stable intermediates. Ruthenium is the most active catalyst among all the metals studied for this reaction. However, this catalyst suffers from relatively low selectivity with the accumulation of large quantities of partially hydrogenated intermediates due to weak adsorption and poor surface diffusion of the intermediates for further hydrogenation.

Hydrogen Storage in Liquid Organic Hydride: Producing Hydrogen Catalytically from Methylcyclohexane

Hydrogen storage for stationary and mobile applications is an expanding research topic. One of the more promising hydrogen storage techniques relies on the reversibility and high selectivity of liquid organic hydrides, in particular, methylcyclohexane (MCH). The use of liquid organic hydrides in hydrogen storage also provides high gravimetric and volumetric hydrogen density, low potential risk, and low capital investment because it is largely compatible with the current transport infrastructure. Despite its technical, economical, and environmental advantages, the concept of hydrogen storage in liquid organic carriers has not been commercially established because of technical limitations related to the amount of energy required to extract the hydrogen from liquid organic hydride and the insufficient stability of the dehydrogenation catalyst. This paper provides a review for the effort that has been directed toward the development of this concept over the past few decades and mainly focuses on the catalytic...

Hydrogen delivery through liquid organic hydrides: Considerations for a potential technology

Carrying hydrogen in chemically bounded form as cycloalkanes and recovery of hydrogen via a subsequent dehydrogenation reaction is a potential option for hydrogen transport and delivery. We have earlier reported a novel method for transportation and delivery of hydrogen through liquid organic hydrides (LOH) such as cycloalkanes. The candidate cycloalkanes including cyclohexane, methylcyclohexane, decalin etc. contains 6 to 8 wt% hydrogen with volume basis capacity of hydrogen storage of 60–62 kg/m3. In view of several advantages of the system such as transportation by present infrastructure of lorries, no specific temperature pressure requirement and recyclable reactants/products, the LOH definitely pose for a potential technology for hydrogen delivery. A considerable development is reported in this field regarding various aspects of the catalytic dehydrogenation of the cycloalkanes for activity, selectivity and stability. We have earlier reported an account of development in chemical hydrides. This article reports a state-of-art in LOH as hydrogen carrier related to dehydrogenation catalysts, supports, reactors, kinetics, thermodynamic aspects, potential demand of technology in field, patent literature etc.

A feasibility analysis of hydrogen delivery system using liquid organic hydrides

The paper discusses the techno-economic feasibility of a hydrogen storage and delivery system using liquid organic hydrides (LOH). Wherein, LOH (particularly cycloalkanes) are used for transporting the hydrogen in chemical bonded form at ambient temperature and pressure. The hydrogen is delivered through a catalytic dehydrogenation process. The aromatics formed in the process are used for carrying more hydrogen by a subsequent hydrogenation reaction. Cost economics were performed on a system which produces 10 kg/h of hydrogen using methylcyclohexane as a carrier. With proprietary catalysts we have demonstrated the possibility of hydrogen storage of 6.8 wt% and 60 kg/m 3 of hydrogen on volume basis. The energy balance calculation reveals the ratio of energy transported to energy consumed is about 3.9. Moreover, total carbon footprint calculation for the process of hydrogen delivery including transportation of LOH is also reported. The process can facilitate a saving of 345 tons/year of carbon dioxide emissions per delivery station by replacing gasoline with hydrogen for passenger cars. There is an immense techno-economic potential for the process.

Kinetics of 9-ethylcarbazole hydrogenation over Raney-Ni catalyst for hydrogen storage

Hydrogen storage in form of liquid organic hydrides, e.g. 9-ethylcarbazole, is a relatively novel method. In the present work, the hydrogenation kinetics of 9-ethylcarbazole over Raney-Ni catalyst was studied by investigating the influences of the reaction temperature, pressure and catalyst concentration on the mass transfer-reaction processes. The results show that the kinetics of reaction is controlled by the chemical process on the catalyst surfaces. The hydrogenation reaction followed first-order kinetics with an apparent activation energy of 65.17 KJ/mol. The apparent kinetics model of the hydrogenation was established.

Hydrogenation of 9-ethylcarbazole as a prototype of a liquid hydrogen carrier

Liquid organic hydrides, e.g. 9-ethylcarbazole, are potentially interesting hydrogen storage materials because of their reversible hydrogen sorption properties. In the present work, hydrogenation reaction of 9-ethylcarbazole in the molten form was investigated over a wide variety of noble metal and nickel supported catalysts. The catalytic activity of 8.2 × 10 −6 mol-ethylcarbazole/g of metal/s and selectivity of 98% towards a fully hydrogen loaded product were recorded over 5 wt% ruthenium on alumina which was prepared by mild chemical reduction of ruthenium salt. Using this catalyst the theoretical capacity of hydrogen uptake (5.7 wt%) was obtained and the rate of the reaction and activation energy were estimated. Due to its potential high hydrogen storage capacity, this system could be a promising on-board storage candidate for mobile applications. The structures of reaction products and intermediates were identified using 2D NMR techniques. These structures were also predicted to be thermodynamically stable using density functional theory (DFT), matching well with the experimental observations.

Ni/Al 2O 3 catalysts and their activity in dehydrogenation of methylcyclohexane for hydrogen production

Previous results on different catalysts revealed that methylcyclohexane underwent selective dehydrogenation to form toluene and hydrogen. This reaction system is a useful prototype model for similar systems in the chemical process and petroleum refining industries, such as hydrotreating for aromatics reduction, desulfurization, denitrogenation, reforming for aromatics reduction, dehydrocyclization, and fuel processing of liquid hydrocarbons in the generation of hydrogen feed for fuel cells. Dehydrogenation of methylcyclohexane to toluene is a method for hydrogen storage in the form of liquid organic hydrides. The efficiency of the dehydrogenation reactions and the quantity of products depend on the catalyst used. In the case of the dehydrogenation of methylcyclohexane to toluene, a metallic function, usually platinum is required as the catalyst. Although, there were some different catalysts used by former researchers, there was almost no investigation about the use of the nickel catalysts for this reaction. From the economical point of view, more efficient catalysts and reaction engineering methods should be developed for these reactions. In this work dehydrogenation of methylcyclohexane was performed in a fixed-bed catalytic reactor in the temperature range of 653–713 K on prepared Ni/Al 2O 3 catalysts having 5, 10, 15 and 20 wt.% Ni content. The inlet flowrates of methylcyclohexane and hydrogen to the reactor were changed by keeping one of them constant in order to investigate their effects on this reaction.