Integration of hydrogenation and dehydrogenation based on dibenzyltoluene as liquid organic hydrogen energy carrier

The heat transfer oil dibenzyltoluene (DBT) offered an intriguing approach for the scattered storage of renewable excess energy as a novel Liquid Organic Hydrogen Carrier (LOHC). The integration of hydrogenation and dehydrogenation in H0-DBT/H18-DBT pairs demonstrated that the feasibility of hydrogenation and dehydrogenation reaction conducted in one reactor with the same catalyst, which would be proposed to simplify the hydrogen storage process. The optimal reaction temperature based on the inhibition of ring opening and cracking was investigated combined with the ¹H NMR analysis. Meanwhile, the ideal catalyst 3 wt% Pt/Al₂O₃ for high hydrogen storage efficiency was screened out. Cycle tests of hydrogenation and dehydrogenation integration reaction had shown that the hydrogen storage efficiency was 84.6% after five cycle tests. The integration of hydrogenation and dehydrogenation reaction based on DBT exhibited the ideal thermal stability, which demonstrated its potential as a reversible H₂ carrier.     

Connected evaluation of polymer electrolyte membrane fuel cell with dehydrogenation reactor of liquid organic hydrogen carrier

Recently, hydrogen energy technologies attract attention as power systems. To develop hydrogen energy systems, hydrogen storage methods with high storage density and good safety are required. Liquid organic hydrogen carrier (LOHC) is one of the novel hydrogen storage technologies. LOHC has advantages of high storage density, good safety, and easy handling. In this study, a polymer electrolyte membrane fuel cell (PEMFC) stack is operated with hydrogen released from LOHC to evaluate the feasibility of the connected operation of the PEMFC stack and LOHC dehydrogenation reactor. Dibenzyltoluene (H0-DBT) is used as a LOHC material, and the dehydrogenation of perhydro dibenzyltoluene (H18-DBT) is conducted at 240–300 °C. Released hydrogen is purified by adsorbent of activated carbon to remove impurities. However, 100–1400 ppm of methane is observed after the purification, and the PEMFC stack power is reduced from 39.4 W to 39.0 W during the operation by hydrogen dilution and physical adsorption of methane. Then, to evaluate the irreversible damage, pure hydrogen was supplied to the PEMFC stack. The stack power is recovered to 39.4 W. It is concluded that the connected operation of the LOHC dehydrogenation reactor and PEMFC stack is feasible, and the activated carbon adsorbent can be a cost-effective purification method for LOHC.     

Benzyltoluene/dibenzyltoluene-based mixtures as suitable liquid organic hydrogen carrier systems for low temperature applications

In this contribution we propose mixtures of the two LOHC systems benzyltoluene (H0-BT)/perhydro benzyltoluene (H12-BT) and dibenzyltoluene (H0-DBT)/perhydro dibenzyltoluene (H18-DBT) as promising hydrogen storage media for technical applications at temperatures below ambient. The mixing of the two LOHC systems provides the advantage of a reduced viscosity of the hydrogen-rich system, for example a 20 wt% addition of H12-BT to H18-DBT reduces the viscosity at 10 °C by 80%. Interestingly, it is also found that the dehydrogenation of such mixture provides a hydrogen release productivity that is 12–16% higher compared to pure H18-DBT dehydrogenation under otherwise identical conditions. This enhanced rate is attributed to a combination of reduced hydrogen partial pressure in the reactor (due to the higher H12-BT vapor pressure), preferred H12-BT dehydrogenation (due to faster H12-BT diffusion) and effective transfer hydrogenation between the two LOHC systems.     

Pt/CeO2 catalyst synthesized by combustion method for dehydrogenation of perhydro-dibenzyltoluene as liquid organic hydrogen carrier: Effect of pore size and metal dispersion

Liquid organic hydrogen carrier (LOHC) is a chemical hydrogen storage method that stores hydrogen in the form of liquid organics. Dibenzyltoluene (DBT) is a promising LOHC material due to its high storage density, low ignitability, and low cost. In this study, Pt/Al₂O₃ and Pt/CeO₂ catalysts are synthesized using a combustion nanocatalyst synthesis method called the glycine nitrate process (GNP) to obtain high catalytic activity for the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT). Pt/CeO₂ exhibits much faster dehydrogenation than Pt/Al₂O₃, 80.5%/2.5 h versus 3.5%/2.5 h. To investigate the causes of the difference in the dehydrogenation rates, microstructural characterization by N₂ physisorption, CO chemisorption and transmission electron microscopy analysis are conducted, and the catalytic activities are evaluated at various liquid hourly space velocities (LHSVs). The differences in dehydrogenation can be attributed to the mass transport of liquid H18-DBT into the catalyst pores being slow due to the small pores in Pt/Al₂O₃, which is a rarely addressed issue for other LOHC materials. This is because many LOHC materials are dehydrogenated at the gas phase, which has higher diffusivity than that of the liquid phase. Pt/CeO₂ synthesized by the GNP is also compared with a commercial Pt/Al₂O₃ catalyst. The commercial Pt/Al₂O₃ catalyst shows a dehydrogenation of 17.8%/2.5 h, which is much slower than that of Pt/CeO₂ synthesized by the GNP, at 80.5%/2.5 h.     

Enhancing selectivity and reducing cost for dehydrogenation of dodecahydro-N-ethylcarbazole by supporting platinum on titanium dioxide

N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NECZ/12H-NECZ) was a promising system for hydrogen storage applications. 1.0 wt% Pt/TiO₂ was regarded as the optimal loading in Pt/TiO₂ catalyst applied in the 12H-NECZ dehydrogenation reaction. The hydrogen release amount, selectivity to NECZ and TOF of 12H-NECZ dehydrogenation are 5.75 wt %, 98% and 229.73 min⁻¹ at 453 K. Compared with the commercial 5.0 wt% Pd and Pt-based catalysts, it exhibited very high activity, selectivity and stability for 12H-NECZ dehydrogenation with low Pt loading. Combined with the XRD, XPS, HRTEM, TPR analysis, it was indicated that the enhanced catalytic performance was due to the SMSI (strong metal-supporting interaction) between Pt and TiO₂ support, which accelerated the rate-limiting step and enhanced the whole dehydrogenation reaction. This work may be beneficial for the commercial application of Pt/TiO₂ catalysts in the Liquid Organic Hydrogen Carrier (LOHC) system.     

Analysis of reaction mixtures of perhydro-dibenzyltoluene using two-dimensional gas chromatography and single quadrupole gas chromatography

Energy storage via liquid organic hydrogen carrier (LOHC) systems has gained significant attention in recent times. A dibenzyltoluene (DBT) based LOHC offers excellent properties which largely solve today's hydrogen storage challenges. Understanding the course of the dehydrogenation reaction is important for catalyst and process optimization. Therefore, reliable and exact methods to determine the degree of hydrogenation (doh) are important. We here present other possible techniques, namely: comprehensive two-dimensional gas chromatography coupled with time of flight mass spectrometry (2D-GC-TOF-MS) and single quadrupole-mass spectrometry gas chromatogram system (GC-SQ-MS). The 2D-GC-TOF-MS results indicate that isomer fractions lose three molecules of hydrogen, as follows: H18-DBT, H12-DBT, H6-DBT and H0-DBT, and the doh decreases with an increase in dehydrogenation temperature. ¹H NMR and GC-SQ-MS were employed as additional analytical techniques. The GC-SQ-MS was also used to analyse decomposition products that result from thermal cracking of reaction mixture molecules.     

Combined dynamic operation of PEM fuel cell and continuous dehydrogenation of perhydro-dibenzyltoluene

Hydrogen storage in liquid organic hydrogen carriers (LOHC) such as the substance system dibenzyltoluene/perhydro-dibenzyltoluene (H0/H18-DBT) offers a promising alternative to conventional methods. In this contribution, we describe the successful demonstration of the dynamic combined operation of a continuously operated LOHC reactor and a PEM (polymer exchange membrane) fuel cell. The fuel cell was operated stable with fluctuating hydrogen release from dehydrogenation of H18-DBT over a total period of 4.5 h, reaching electrical stack powers of 6.6 kW. The contamination with hydrocarbons contained in the hydrogen after activated carbon filtering did not result in any detectable impairment or degradation of the fuel cell. The proposed pressure control algorithm based on a proportional integral (PI) controller proved to be a robust and easy-to-implement approach to enable the dynamic combined operation of LOHC dehydrogenation and PEM fuel cell.     

Purity of hydrogen released from the Liquid Organic Hydrogen Carrier compound perhydro dibenzyltoluene by catalytic dehydrogenation

While Liquid Organic Hydrogen Carrier (LOHC) systems offer a very promising way of infrastructure-compatible storage and transport of hydrogen, the hydrogen quality released from charged LOHC compounds by catalytic dehydrogenation has been a surprisingly rarely discussed topic to date. This contribution deals, therefore, with a detailed analysis of the hydrogen purity released from the hydrogen-rich Liquid Organic Hydrogen Carrier compound perhydro dibenzyltoluene (H18-DBT). We demonstrate, that high purity hydrogen (>99.999%) with carbon monoxide levels below 0.2 ppmv can be obtained from the dehydrogenation of H18-DBT if the applied H18-DBT had been carefully pre-dried and pre-purified prior to the dehydrogenation experiment. Indeed, the largest part of relevant impurities to comply with the hydrogen quality standard for fuel cells in road vehicles (ISO 14687-2) was found to originate from water and oxygenate impurities present in the applied, technical LOHC qualities.     

Experimental determination of the hydrogenation/dehydrogenation - Equilibrium of the LOHC system H0/H18-dibenzyltoluene

Liquid organic hydrogen carrier (LOHC) systems store hydrogen through a catalyst-promoted exothermal hydrogenation reaction and release hydrogen through an endothermal catalytic dehydrogenation reaction. At a given pressure and temperature the amount of releasable hydrogen depends on the reaction equilibrium of the hydrogenation/dehydrogenation reaction. Thus, the equilibrium composition of a given LOHC system is one of the key parameters for the reactor and process design of hydrogen storage and release units. Currently, LOHC equilibrium data are calculated on the basis of calorimetric data of selected, pure hydrogen-lean and hydrogen-rich LOHC compounds. Yet, real reaction systems comprise a variety of isomers, their respective partially hydrogenated species as well as by-products formed during multiple hydrogenation/dehydrogenation cycles. Therefore, our study focuses on an empirical approach to describe the temperature and pressure dependency of the hydrogenation equilibrium of the LOHC system H0/H18-DBT under real life experimental conditions. Because reliable measurements of the degree of hydrogenation (DoH) play a vital role in this context, we describe in this contribution two novel methods of DoH determination for LOHC systems based on ¹³C NMR and GC-FID measurements.     

Hydrogenation of liquid organic hydrogen carrier systems using multicomponent gas mixtures

The cost of industrial hydrogen production and logistics, and the purity of hydrogen produced from different technologies are two critical aspects for the success of a future hydrogen economy. Here, we present a way to charge the Liquid Organic Hydrogen Carrier (LOHC) dibenzyltoluene (H0-DBT) with industrially relevant, CO₂- and CO-containing gas mixtures. As only hydrogen binds to the hydrogen-lean carrier molecule, this process step extracts hydrogen from the gas mixture and binds it selectively to the carrier. Pd on alumina has been identified as the most promising catalyst system for successfully hydrogenating H0-DBT using model gas mixtures resembling the compositions produced in methane reforming and in industrial coke production (up to 50% CO₂ and 7% CO). Up to 80% of the hydrogen present in the feedstock mixture could be extracted during the LOHC hydrogenation process. 99.5% of the reacting hydrogen was selectively bound to the H0-DBT LOHC compound. The purity of hydrogen released from the resulting perhydro dibenzyltoluene previously charged with the hydrogen-rich gas mixture proved to be up to 99.99 mol%.     

Dehydrogenation properties of two phases of LiNH2BH3

Lithium amidoborane (LiNH₂BH₃) is known as one of the most prospective hydrogen storage materials. In this paper, the differences between two allotropes (α-LiNH₂BH₃ and β-LiNH₂BH₃) of LiNH₂BH₃ in the dehydrogenation properties was reported for the first time. A series of mixtures of α-LiNH₂BH₃/β-LiNH₂BH₃ with different mass ratios were prepared by ball milling for different time and the contents of two phases in samples were determined with Rietveld's method. The thermal decomposition behaviors of samples were investigated by DSC. It shows that the initial dehydrogenation temperature of samples decreases with the content of α-LiNH₂BH₃ phase increasing. The initial dehydrogenation temperature of α-LiNH₂BH₃ is about 61 °C, which is approximately 15 °C lower than that of β-LiNH₂BH₃. Dehydrogenation kinetic analysis shows that α-LiNH₂BH₃ has the lower activation energy (157 kJ mol⁻¹) and higher rate (k = 1.422 × 10¹ min⁻¹) than that of β-LiNH₂BH₃ (272 kJ mol⁻¹ and 1.023 × 10⁻¹ min⁻¹, respectively). It is suggested that α-LiNH₂BH₃ is more supportive for hydrogen desorption. It gives a critical clue on exploring the dehydrogenation mechanism of lithium amidoborane. Moreover, the significant decrease of desorption temperature will shine a light on on-board hydrogen storage systems.     

Thermodynamics analysis of hydrogen storage based on compressed gaseous hydrogen,liquid hydrogen and cryo-compressed hydrogen

Safe, reliable, and economic hydrogen storage is a bottleneck for large-scale hydrogen utilization. In this paper, hydrogen storage methods based on the ambient temperature compressed gaseous hydrogen (CGH₂), liquid hydrogen (LH₂) and cryo-compressed hydrogen (CcH₂) are analyzed. There exists the optimal states, defined by temperature and pressure, for hydrogen storage in CcH₂ method. The ratio of the hydrogen density obtained to the electrical energy consumed exhibits a maximum value at the pressures above 15 MPa. The electrical energy consumed consists of compression and cooling down processes from 0.1 MPa at 300 K to the optimal states. The recommended parameters for hydrogen storage are at 35–110 K and 5–70 MPa regardless of ortho-to parahydrogen conversion. The corresponding hydrogen density at the optimal states range from 60.0 to 71.5 kg m⁻³ and the ratio of the hydrogen density obtained to the electrical energy consumed ranges from 1.50 to 2.30 kg m⁻³ kW⁻¹. While the ortho-to para-hydrogen conversion is considered, the optimal states move to a slightly higher temperatures comparing to calculations without ortho-to para-hydrogen conversion.     

A small pilot reactor containing active MgTi–based hydrides at low operational temperatures

This study was investigated to utilize innovatively oil-free diaphragm pump to forcibly desorb the hydrogen from the small pilot MgH₂–TiH₂ based hydride reactor below the theoretical temperature of 278 °C. Active MgH₂-0.1TiH₂ composites were prepared using ball milling. Their hydrogenation performances at 25–300 °C were measured under a constant H₂ flow mode using a modified Sieverts apparatus. The dehydrogenation rates at 250–350 °C with or without diaphragm pump were investigated to examine whether the pilot reactors could be integrated with a proton exchange membrane fuel cell (PEMFC) for power generation. At a H₂ flow rate of 25 ml min⁻¹ g⁻¹, the reactors exhibited excellent hydrogenation, achieving gravimetric hydrogen storage capacities of 2.9–5.2 wt% (excluding the weight of the reactors) at 25–300 °C after 22 min. All hydrided MgTi–based reactors could be dehydrogenated at 250 °C at an average rate of 5 ml min⁻¹ g⁻¹ under vacuum. This is the first demonstration of Mg-based reactors that were hydrogenated at 100 °C and dehydrogenated at 250 °C to power a small PEMFC, yielding a measured conversion efficiency of 18%.     

High active pd@mil-101 catalyst for dehydrogenation of liquid organic hydrogen carrier

Highly dispersed Pd nanoparticles immobilized in MIL-101 (Pd@MIL-101) were prepared and used for the catalytic dehydrogenation of Liquid organic hydrogen carriers (LOHC). The as-synthesized catalysts were characterized and it was found that 3 wt% of Pd@MIL-101 embodied smaller and highly dispersed Pd NPs. The catalytic activities of as-synthesized catalysts were investigated by the dehydrogenation of a representative LOHC compound, perhydro-N-propylcarbazole (12H-NPCZ). The results indicated that 3 wt% Pd@MIL-101 catalyst exhibited good catalytic activity and good reusability for the dehydrogenation of 12H-NPCZ, which is superior to that of commercial 5 wt% Pd/Al₂O₃ catalyst. This study demonstrates that Pd@MIL-101 is a promising dehydrogenation catalyst for the application of LOHC technology.     

A solid oxide fuel cell operating on liquid organic hydrogen carrier-based hydrogen – A kinetic model of the hydrogen release unit and system performance

In this paper, a kinetic model for the catalytic dehydrogenation of perhydro dibenzyltoluene (H18-DBT), a well-established Liquid Organic Hydrogen Carrier (LOHC) compound, is presented. Kinetic parameters for hydrogen release at a Pt on alumina catalyst in a temperature range between 260 °C and 310 °C are presented. A Solid Oxide Fuel Cell (SOFC) system model was coupled to the hydrogen release from H18-DBT in order to validate the full sequence of LOHC-bound hydrogen-to-electric power. A system layout is described and investigated according to its transient operating behavior and its efficiency. We demonstrate that the maximum efficiency of LOHC-bound hydrogen-to-electricity is 45% at full load, avoiding any critical conditions for the system components.     

Evaluation of catalyst activity for release of hydrogen from liquid organic hydrogen carriers

This contribution investigate the effect of parameters for production of hydrogen by catalytic dehydrogenation of perhydrodibenzyltoluene (H18-DBT). The sensitivity of the dehydrogenation reaction to temperature (290–320 °C) is justified by an increase in degree of dehydrogenation (DoD) from 40 to 90% when using 1 wt % Pt/Al₂O₃ catalyst. However, the increase in temperature increases the hydrogen production rate and decreases the hydrogen purity by increasing the formation of by-products. In addition, the DoD of 96% is obtained when 2 wt % Pt/Al₂O₃ is used at 320 °C. The DoD obtained for Pd, Pt, and Pt–Pd catalysts is 11, 82 and 6%, respectively. Therefore, Pd is not a metal of choice for dehydrogenation of H18-DBT, in both monometallic and bimetallic system. The ab-initio density functional theory (DFT) calculations are consistent with this observation. Furthermore, dehydrogenation of H18-DBT followed 1st order reaction kinetics and the activation energies for 1 wt % Pt/Al₂O₃, 1 wt % Pd/Al₂O₃ and 1:1 wt % Pt–Pd/Al₂O₃ catalysts are: 205, 84 and 66 kJ/mol, respectively.     

Catalytically activated stainless steel plates for the dehydrogenation of perhydro dibenzyltoluene

Hydrogen storage and transport via Liquid Organic Hydrogen Carriers (LOHC) is gaining increasing attention. In this study, we present catalytically activated stainless steel plates as a promising alternative to the commonly used pellet catalysts for the dehydrogenation of perhydro dibenzyltoluene (H18-DBT). These plate catalysts promise better heat transport to the active sites. For improved performance, we modified our Pt/alumina plate catalysts by using i) platinum sulfite impregnation and ii) post-treatment with (NH₄)₂SO₄. Post-treatment with (NH₄)₂SO₄ resulted in a less active catalyst with lower formation of high-boiling side products compared to the S-free plate catalyst. Catalysts prepared with platinum sulfite showed both >35% higher activities and 90% reduction in high-boiler formation compared to the S-free plate catalysts. Our findings pave the way for the development of catalytically activated heat transfer plates that would allow the incorporation of LOHC dehydrogenation units into the geometry of future high temperature fuel cell stacks.     

Highly dispersed cobalt nanoparticles onto nitrogen-doped carbon nanosheets for efficient hydrogen generation via catalytic hydrolysis of sodium borohydride

Porous carbon nanostructures are promising supports for stabilizing the highly dispersed metal nanoparticles and facilitating the mass transfer during the reaction, which are critical to achieve the high efficiency of hydrogen generation from sodium borohydride dehydrogenation. Herein, the catalytically active porous architectures are simply prepared by using 2-methylimidazole and melamine as reactive sources. The structural and compositional characterizations reveal the coexistence of metallic cobalt and N-doped carbon in porous architectures. Electron microscopy observations indicate that the synthesized products are smartly constructed from the carbon nanosheets with densely dispersed Co nanoparticles. Due to the notable structural features, the prepared Co@NC-600 sample presents the highly efficient activity for catalytic hydrolysis of NaBH₄ with a hydrogen generation rate of 2574 mL min⁻¹ g_cat⁻¹ and an activation energy of 47.6 kJ mol⁻¹. The catalytically active metallic Co and suitable support-effect of N-doped carbon are responsible for catalytic dehydrogenation.     

Ruthenium supported on nitrogen-doped porous carbon for catalytic hydrogen generation from NH3BH3 hydrolysis

In this paper, ruthenium supported on nitrogen-doped porous carbon (Ru/NPC) catalyst is synthesized by a simple method of in situ reduction using ammonia borane (AB) as reducing agent. The composition and structure of Ru/NPC catalyst are systematically characterized. This catalyst can efficiently catalyze the hydrolysis of AB. The hydrogen production reaction is completed within about 90 s at a temperature of 298 K and the maximum rate of hydrogen production is 3276 ml·s⁻¹·g⁻¹ with a reduced activation energy of 24.95 kJ·mol⁻¹. The turnover frequency (TOF) for hydrogen production is about 813 mol_H2·mol_Ru⁻¹·min⁻¹. Moreover, this catalyst can be recycled with a well-maintained performance. After five cycles, the maximum rate of hydrogen generation is maintained at 2206 ml·s⁻¹·g⁻¹, corresponding to 67.3% of the initial catalytic activity. Our results suggest that Ru/NPC prepared by in situ reduction is a highly efficient catalyst for hydrolytic dehydrogenation of AB.     

Natural liquid organic hydrogen carrier with low dehydrogenation energy: A first principles study

Liquid organic hydrogen carriers (LOHCs) represent a promising approach for hydrogen storage due to their favorable properties including stability and compatibility with the existing infrastructure. However, fossil-based LOHC molecules are not green or sustainable. Here we examined the possibility of using norbelladine and trisphaeridine, two representative structures of Amaryllidaceae alkaloids, as the LOHCs from the sustainable and renewable sources of natural products. Our first principles thermodynamics calculations reveal low reversibility for the reaction of norbelladine to/from perhydro-norbelladine because of the existence of stabler isomers of perhydro-norbelladine. On the other hand, trisphaeridine is found promising due to its high hydrogen storage capacity (~5.9 wt%) and favorable energetics. Dehydrogenation of perhydro-trisphaeridine has an average standard enthalpy change of ~54 kJ/mol-H₂, similar to that of perhydro-N-ethylcarbazole, a typical LOHC known for its low dehydrogenation enthalpy. This work is a first exploration of Amaryllidaceae alkaloids for hydrogen storage and the results demonstrate, more generally, the potential of bio-based molecules as a new sustainable resource for future large-scale hydrogen storage.