Addressing the urgent need to reduce global CO2 emissions, there is a growing emphasis on transitioning from the current fossil fuel-dependent energy system to an environmentally sustainable ...hydrogen-based economy, devoid of carbon emissions. However, the inherent challenges in the conventional storage and transportation of elemental hydrogen have impeded progress. To overcome this hurdle and achieve a seamless transition to a cost-effective hydrogen storage solution, researchers propose the use of liquid organic hydrogen carriers (LOHCs). These carriers involve chemically binding elemental hydrogen within hydrogen-deficient organic molecules, allowing for efficient storage and retrieval of hydrogen under low pressure conditions. An attractive feature of LOHCs is their compatibility with existing infrastructure such as storage tanks, ships, and fueling stations, facilitating a smoother transition. This contribution delves into the crucial role of various catalyst materials in enhancing the hydrogenation activity of various LOHCs such as benzene, toluene, N-ethylcarbazole (NEC) and dibenzyltoluene (DBT). Through the exploration of catalytic aspects, this review investigates the effect of noble metal, transition metal, and multimetallic catalysts, providing valuable insights into their design and optimization. These efforts aim to achieve efficient and sustainable hydrogen storage within the LOHC framework. The findings presented in this study aim to contribute to the development of economically viable solutions for hydrogen storage and utilization, thereby aiding the seamless transition toward a hydrogen-based energy economy.
The roles of catalyst materials in enhancing the hydrogenation activity of various LOHCs such as toluene, benzene, N-ethlycarbazole and dibenzyltoluene are studied. By investigating various catalytic aspects, it offers valuable insights into the design and optimization of catalysts for efficient hydrogen storage within the LOHC framework. Display omitted
Methylcyclohexane (MCH) is considered as one of the most promising liquid organic hydrogen carriers (LOHCs) in terms of hydrogen storage and delivery. However, the dehydrogenation process of MCH is ...relatively difficult, which requires catalyst having high activity and stability. In this work, a catalyst of Pt/Al2O3 by doping Ga2O3 was prepared and tested in the dehydrogenation of MCH, resulting in both high activity and stability. After 176 h of the reaction, the conversion of MCH is no significant decrease, and the toluene (TOL) selectivity was greater than 99%. The characterization results of the catalyst evidenced that the excellent performance of the catalyst is due to the introduction of Ga2O3, which prevents the growth of Pt species and results more positively charged Pt species. These Pt species can weaken the strength of the adsorption between Pt and dehydrogenation products, making dehydrogenation products more easily to be desorbed, which achieving high activity and stability. The catalyst shows great potential for industrial application in the future. This work provides theoretical guidance for designing highly stable dehydrogenation catalysts.
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•A highly stable Pt-Ga2O3/Al2O3 with good activity has been prepared for dehydrogenation of methylcyclohexane.•The introduction of Ga2O3 prevents the growth of Pt species and results more positively charged Pt species.•These Pt species weaken the strength of the adsorption between Pt and products, achieving high activity and stability.
Transition to renewable energy systems is essential to achieve the climate change mitigation targets. However, the timing and the regions of the production and consumption of the renewable energy do ...not always match, and different energy storage technologies are needed to secure the uninterrupted energy supply. Liquid organic hydrogen carriers (LOHCs) offer a flexible media for the storage and transportation of renewable energy. These “liquid hydrogen batteries” are reversibly hydrogenated and dehydrogenated using catalysts at elevated temperatures. Commercial LOHC concepts are already available. Another flexible route to store energy is through “circular” hydrogen carriers, such as methanol and methane produced from atmospheric carbon dioxide (CO2). These fuels have a long history as fossil fuels. In this review, the chemistry and state-of-the-art of LOHCs are explored and discussed against defined criteria with comparison made to existing energy storage systems. The LOHCs and “circular” hydrogen carriers were found to be particularly promising hydrogen storage systems.
•Solutions are needed for storing and transporting the renewable energy.•Hydrogen storage options are reviewed and discussed.•Some end-use sectors are more demanding than the others.•Liquid organic hydrogen carriers are promising hydrogen storages.•The “circular” methanol and hydrocarbons or are also promising hydrogen storages.
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.
•N-doped carbon exhibits a porous nanosheet structure accompanied by abundant anchoring sites.•3 wt% Pd/Ni@NC-10 exhibits the highest catalytic performance with 6.48 wt% hydrogen release amount.•The ...defective structure due to N doping and the Ni sites, improves the dispersion of Pd NPs.•The doping of N, Ni synergistically optimized the electronic structure of Pd.•Pd/Ni@NC-10 shows good structural stability, durability and recyclability.
Liquid organic hydrogen carriers (LOHCs) are considered as promising candidates for large-scale hydrogen storage, which offers significant advantages in terms of hydrogen storage density, ease of storage and transportation. NPhCZ (N-phenylcarbazole)/18H-NPhCZ (perhydro-N-phenylcarbazole) is proposed as a typical system with high hydrogen storage capacity. However, low dehydrogenation activity and selectivity of catalysts restrict the cyclic efficiency of hydrogen storage. In this study, the efficient catalysts are designed by the immobilization of ultrafine, highly dispersed Pd nanoparticles onto Ni, N co-doped carbon materials through wet chemical reduction. The Pd/Ni@NC-10 catalyst exhibits the highest catalytic performance with 100 % conversion, 81.9 % selectivity of NPhCZ and 6.48 wt% hydrogen release amount. Combined with XRD, HRTEM, Raman, XPS, H2-TPR, N2 physisorption characterization methods and DFT calculations, it is found that the doped Ni, N species could synergistically increase the dispersion of loaded Pd nanoparticles, as well as regulate the electronic state around Pd, which in turn accelerates the rate of the rate-limiting step. The evident interaction between Pd nanoparticles and Ni, N co-doped carbon brings the enhancement of dehydrogenation efficiency. Besides, the spent catalysts are measured by XRD, TEM, XPS and evaluated for the dehydrogenation reaction, indicating that Pd/Ni@NC-10 shows good structural stability, durability and recyclability. It provides practical guidance for the design of LOHCs dehydrogenation catalysts.
The dehydrogenation steps of dodecahydro-N-ethylcarbazole over Pt/Al2O3 are quite sensitive to the Pt particle size. Large Pt particle can greatly enhance the reaction rates in ...octahydro-N-ethylcarbazole → tetrahydro-N-ethylcarbazole and tetrahydro-N-ethylcarbazole → N-ethylcarbazole steps. The high performance of large Pt particle in dehydrogenation can be ascribed to its highly exposed (111) crystal face. The optimized catalyst Pt5.0/γ-Al2O3 with Pt average size of 4.63 nm demonstrated exceptional performance in dodecahydro-N-ethylcarbazole dehydrogenation at 180 ℃ and 101 kPa, and the dodecahydro-N-ethylcarbazole conversion of 100%, N-ethylcarbazole selectivity of 96.44% and dehydrogenation efficiency of 98.73% can be achieved.
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•Pt/Al2O3 catalysts for dehydrogenation of dodecahydro-N-ethylcarbazole were developed.•The relationship between dehydrogenation performance and Pt structure was revealed.•Dehydrogenation of dodecahydro-N-ethylcarbazole are sensitive to the Pt particle size.•The Pt5.0/γ-Al2O3 with Pt average size of 4.63 nm exhibits best performance.
The use of dodecahydro-N-ethylcarbazole in hydrogen storage for liquid organic hydrogen carrier systems holds potential for achieving large-scale application. In order to investigate the relationship between dodecahydro-N-ethylcarbazole dehydrogenation performance and Pt particles size, a series of monometallic Pt/Al2O3 catalysts with different Pt particles size from 0.70 nm to 5.12 nm were controlled synthesized by a simple impregnation method. The obtained catalysts are systematically characterized via XRD, 27Al MAS NMR, SEM-EDS, TEM, N2-adsorption, CO-IR, H2-TPR and NH3-TPD analyses, which provide essential micro-structure of these catalysts. The dehydrogenation of dodecahydro-N-ethylcarbazole over Pt/Al2O3 is a typical consecutive reaction, which follows a reaction sequence of dodecahydro-N-ethylcarbazole → octahydro-N-ethylcarbazole → tetrahydro-N-ethylcarbazole → N-ethylcarbazole. These dehydrogenation steps are quite sensitive to the Pt particle size. Large Pt particle can greatly enhance the reaction rates in octahydro-N-ethylcarbazole → tetrahydro-N-ethylcarbazole and tetrahydro-N-ethylcarbazole → N-ethylcarbazole steps. However, these two steps are difficult to take place in small Pt particles. The high performance of large Pt particle in dehydrogenation can be ascribed to its highly exposed (111) crystal face. The optimized catalyst Pt5.0/γ-Al2O3 with Pt average size of 4.63 nm demonstrated exceptional performance in dodecahydro-N-ethylcarbazole dehydrogenation at 180 °C and 101 kPa, and the dodecahydro-N-ethylcarbazole conversion of 100 %, N-ethylcarbazole selectivity of 96.44 % and dehydrogenation efficiency of 98.73 % can be achieved. These results provide valuable insights for the development of efficient metal-based catalysts for liquid organic hydrogen carriers hydrogen storage system.
The repercussions of the burning of fossil fuels on the global air quality index need to be countered with implementable green alternatives such as the hydrogen economy. High energy density, ...abundance, and the eco-friendly oxidation product of hydrogen make it an ideal fossil fuel replacement. However, the quest for safe, inexpensive, and compact storage material for hydrogen remains the prime concern. The scientific community is mainly looking for two major characteristics, i.e., high hydrogen storage capacity and the onboard reversibility of the host at operable thermodynamic conditions. Since the past decade, a tremendous amount of research has been undertaken toward such material development and exploring their stable hydrogen storage characteristics. In this extensive review, we report the significant material advancements made in this decade toward the methodical and sustainable hydrogen economy. Hydrogen weight percentage (wt%), reversibility, stability, onboard feasibility, and the heat-pressure response of these prospective hydrogen storage hosts have been thoroughly discussed.
•Hydrogen is a green-energy source and the best replacement for fossil fuels.•Reversible hydrogen storage materials with high sorption is highlighted.•Newly developed porous and low-dimensional materials store hydrogen reversibly.•Metal functionalization enhances the hydrogen storage capacity of materials.•Scope of advancement in the thermodynamic stability of hosts is discussed.
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.
The cost of storing and transporting hydrogen have been one of the main challenges for the realization of the hydrogen economy. Liquid organic hydrogen carriers (LOHC) are a promising novel solution ...to tackle these challenges. In this paper we compare the LOHC concept to compressed gas truck delivery and on-site production of hydrogen via water electrolysis. As a case study we consider transportation of by-product hydrogen from chlor-alkali and chlorate plants to a single industrial customer, which was considered to have the greatest potential for the LOHC technology to enter the markets. The results show that the LOHC delivery chain could significantly improve the economics of long distance road transport. For economic feasibility, the most critical parameters identified are the heat supply method for releasing hydrogen at the end-user site and the investment costs for LOHC reactors.
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•Techno-economic model for point-to-point large scale road transport of hydrogen.•The LOHC concept can decrease long-distance delivery costs significantly.•Heat supply method for dehydrogenation and heat integration are key.•Utilization of waste heat can reduce costs by 40%.
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