Fast Dehydrogenation Research Articles

Bridging oxygen mediated alkaline Fenton catalysis in LDHs for water purification

In this study, we fabricate a non-redox layered double hydroxides (CuFe-LDHs) catalyst to realize Fenton catalysis under alkaline conditions. The electronic structure of bridging oxygen atoms (OB) is optimized via hybridizing with Cu2+ and Fe3+ for fast dehydrogenation and recombination of hydrogen peroxide (H2O2) without the influence of -OH. Experimental results confirm that the moderate p-band center of OB and the strong interlayer force enhance H2O2 activation from thermodynamic and kinetic perspectives, respectively. The required free energy of the rate-determining step decreases from 1.78 eV to 1.06 eV. The CuFe-LDHs/H2O2 system demonstrates extraordinary treatment performance for alkaline organic wastewater. The continuous flow reactor experiment achieves long-term stability (up to 12 h), confirming the potential of CuFe-LDHs in practical applications. This study enriches the H2O2 activation mechanism over nonmetallic sites and provides the theoretical and feasible basis for the practical application of heterogeneous Fenton reactions.

Producing Hydrogen with Less Energy in Ammonia Electrolyzer Stack Using Pt-Ir Catalyst Dual-Layer Electrode

Electrochemical ammonia decomposition has recently been regarded as a possible future technology for CO2-free hydrogen production. Pt-based catalysts have already known for having excellent activity in ammonia oxidation reactions (AOR) due to the fast dehydrogenation step enabled by the moderate adsorption strengths of nitrogen species [1]. Among them, the incorporation of Ir into Pt notably decreases the activation energy required for ammonia oxidation on Pt, lowing onset potential in alkaline media [2]. Besides, the electrolysis of ammonia has a less energy consumption than water electrolysis because of the lower operating voltage at the Anode [3]. In this study, we fabricated dual-layer electrode containing Pt-Ir catalyst, enhancing the AOR catalytic activity and showing long-term stability. The ammonia electrolysis single-cell with an anion exchange membrane (AEM) was successfully operating and then scaled up to a large area stack cell. We observed that this electrolyzer stack cell produced high-purity hydrogen using less energy than water electrolysis.AcknowledgementsThis research was supported by National R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (NRF-2021K1A4A8A01079455). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) [No. 2021R1A5A1028138].Reference[1] J. Liu, Z. Liu, Adv. Funct. Mater 2022, 32, 2110702[2] A. Estejab, G. G. Botte, Comput. Theor. Chem 2016, 1091, 31-40[3] J. Gwak, M. Choun, ChemSusChem 2016, 9, 403–408

Mechanistic Pathways for the Dehydrogenation of Alkanes on Pt(111) and Ru(0001) Surfaces

AbstractThe dehydrogenation of alkanes is a critical process to enable olefin upcycling in a circular economy. A suitable selective catalyst is required in order to avoid demanding reaction conditions and ensure the activation of the C−H bond rather than breaking the C−C bond, which is the weaker of the two. Herein, using periodic density functional theory, we have investigated the dehydrogenation of n‐pentane (as a model compound) on Pt and Ru surface catalysts. The results show that the first dehydrogenation occurs through the dissociative adsorption of the C−H bond, resulting in pentyl and H intermediates on the metal surfaces. A successive dehydrogenation creates pentene via a hydride di‐σ state, leaving the abstracted hydrogen atoms on the metal surfaces. In agreement with recent experiments, Pt and Ru catalysts show a similar reactivity trend: pentane dehydrogenation yields pent‐1‐ene and pent‐2‐ene. The simulations reveal that the 1st C−H dissociation is the rate‐determining step, whereas the double‐bonded alkenes (pent‐1‐ene and pent‐2‐ene) are formed due to fast successive dehydrogenation processes. Pt favors the formation of pent‐1‐ene, whereas Ru favors the formation of pent‐2‐ene.

Experimental investigations on a coupled metal hydride based thermal energy storage system

Thermal energy storage using coupled metal hydride reactors is attractive because it offers several advantages such as one-time hydrogen loading, high thermal storage density, compactness and possibility of simultaneous heating and cooling. This study presents experimental investigations on a coupled metal hydride based thermal energy storage system. Based on compatibility criteria of hydrides described in this work, LaNi4.25Al0.75 for thermal energy storage and La0.75Ce0.25Ni5 for hydrogen storage were chosen. The study employed two novel cartridge type coupled reactors with enhanced heat transfer surfaces. The effects of heat source and ambient temperatures on the system performance were investigated. The study reveals that coupled hydride systems with suitable pairs of hydrides can deliver high energy storage capacities at good thermal efficiencies. The heat output of 227.7 kJ was achieved with a heat transfer rate of 130.7 W at 55.7 % efficiency. The hydrogen storage alloy exhibited good compatibility with the energy storage alloy with fast hydrogenation and dehydrogenation. It also produced a cooling effect of 171.8 kJ while desorbing hydrogen.

Anchoring PdAu nanoclusters inside aminated metal-organic framework for fast dehydrogenation of formic acid

Liquid sunshine formic acid (FA), which is obtainable through CO2 hydrogenation with green H2 or biomass processing, is regarded as a prospective liquid organic hydrogen carrier (LOHC) owing to its high volumetric capacity (53 g H2 L−1), stability, and renewability. The search for effective catalysts to produce H2 from additive-free FA under ambient conditions is necessary but remains a challenge. Herein, highly dispersed and ultrafine PdAu nanoclusters (NCs) (1.2 nm) anchored by the aminated metal–organic framework (NH2-MIL-101) were successfully fabricated using a facile wet-chemical method and employed as a superior catalyst for formic acid dehydrogenation (FAD). The resulting PdAu/NH2-MIL-101 catalyst demonstrates 100 % H2 selectivity and superior performance with a turnover frequency value reaching 2921.0 h−1 at 323 K without any additive. Under similar conditions, this value is higher than the majority of published MOF-based FAD heterogeneous catalysts. The superior performance of PdAu/NH2-MIL-101 originates from a synergistic combination of the promoting effect of amino groups, the effective electronic coupling of Pd and Au, and the strong metal-support interaction between PdAu NCs and NH2-MIL-101, which promote the formation of reactive PdAu NCs and thus greatly improve catalytic performance. This work may provide important inspiration for developing highly efficient catalysts and strongly promote FA as a promising LOHC for chemical H2 storage.

Fast and Durable Dehydrogenation of Formic Acid over Pd–Cr(OH)3 Nanoclusters Immobilized on Amino-Modified Reduced Graphene Oxide

Formic acid, attractive as a renewable and safe liquid organic hydrogen carrier (LOHC), can be obtained by biomass conversion and CO2 hydrogenation with green hydrogen. The efficient and durable catalysts for formic acid dehydrogenation (FAD) are beneficial in the industry. Herein, Cr(OH)3-promoted Pd nanoclusters (NCs) (i.e., 1.6 nm) immobilized on amino-modified reduced graphene oxide (NH2-rGO) were successfully prepared through a simple wet-chemical approach. The obtained Pd–Cr(OH)3/NH2-rGO catalyst exhibits excellent catalytic activity and 100% hydrogen selectivity for CO-free FAD, giving a high turnover frequency of 2519.5 h–1 at 323 K, outperforming most reported Pd-based heterogeneous catalysts. Especially, the catalyst possesses robust durability toward FAD with no significant decline in activity and aggregation of metal NCs even after 10 cycles. The superior performance of the catalyst may be ascribed to the well-distributed Pd–Cr(OH)3 NCs, the strong electronic coupling of Pd with Cr(OH)3, the synergetic interaction of Pd–Cr(OH)3 with NH2-rGO, and the promotion effect of amino group. The reaction mechanism of FAD was explored based on the isotope experiments. This work provides insights into designing an effective and durable heterogeneous catalyst for dehydrogenation of LOHC.

Enhanced catalysis of Pd/Al2O3-SiO2 for perhydro-N-propylcarbazole dehydrogenation: Effect of Al/Si ratio on acidity and Pd particle size

Catalysts played a vital role in fast dehydrogenation of Liquid Organic Hydrogen Carriers (LOHCs) for the large-scale application of LOHCs technology. A series of 1 wt% Pd/AlSiO catalysts with different Al/Si molar ratios were prepared by impregnation method to dehydrogenate perhydro-N-propylcarbazole as an important LOHC candidate. It is found that Al/Si molar ratios have a dramatic influence on specific surface area, support acidity, metal reduction degree, and particle size. 100% dehydrogenation of perhydro-N-propylcarbazole can be realized in 360 min catalyzed by Pd/AlSiO catalyst with Al/Si molar ratio of 2:1, which also showed perfect cycle stability in five times of perhydro-N-propylcarbazole dehydrogenation. The high activity of the Pd/AlSiO-2/1 catalyst was attributed to its high specific surface area, medium acidity, and small particle size (4.9 nm). Modification of the carrier is an effective strategy to improve the catalytic dehydrogenation activity.

Synthesizing active and durable cubic ceria catalysts (

Dehydrogenation is considered as one of the most important industrial applications for renewable energy. Cubic ceria-based catalysts are known to display promising dehydrogenation performances in this area. Large particle size (>20 nm) and less surface defects, however, hinder further application of ceria materials. Herein, an alternative strategy involving lactic acid (LA) assisted hydrothermal method was developed to synthesize active, selective and durable cubic ceria of <6 nm for dehydrogenation reactions. Detailed studies of growth mechanism revealed that, the carboxyl and hydroxyl groups in LA molecule synergistically manipulate the morphological evolution of ceria precursors. Carboxyl groups determine the cubic shape and particle size, while hydroxyl groups promote compositional transformation of ceria precursors into CeO2 phases. Moreover, enhanced oxygen vacancies (Vö) on the surface of CeO2 were obtained owing to continuous removal of O species under reductive atmosphere. Cubic CeO2 catalysts synthesized by the LA-assisted method, immobilized with bimetallic PtCo clusters, exhibit a record high activity (TOF: 29,241 h−1) and Vö-dependent synergism for dehydrogenation of bio-derived polyols at 200 °C. We also found that quenching Vö defects at air atmosphere causes activity loss of PtCo/CeO2 catalysts. To regenerate Vö defects, a simple strategy was developed by irradiating deactivated catalysts using hernia lamp. The outcome of this work will provide new insights into manufacturing durable catalyst materials for aqueous phase dehydrogenation applications.

Synergistic Strategy for the Fast Dehydrogenation of Liquid Organic Hydrogen Carriers over a Pd/MoO3 Catalyst

Synergistic Strategy for the Fast Dehydrogenation of Liquid Organic Hydrogen Carriers over a Pd/MoO₃ Catalyst

Acceptorless Dehydrogenation of Methanol to Carbon Monoxide and Hydrogen using Molecular Catalysts.

The acceptorless dehydrogenation of methanol to carbon monoxide and hydrogen was investigated using homogeneous molecular complexes. Complexes of ruthenium and manganese comprising the MACHO ligand framework showed promising activities for this reaction. The molecular ruthenium complex [RuH(CO)(BH4)(HN(C2H4PPh2)2)] (Ru‐MACHO‐BH) achieved up to 3150 turnovers for carbon monoxide and 9230 turnovers for hydrogen formation at 150 °C reaching pressures up to 12 bar when the decomposition was carried out in a closed vessel. Control experiments affirmed that the metal complex mediates the initial fast dehydrogenation of methanol to formaldehyde and methyl formate followed by subsequent slow decarbonylation. Depending on the catalyst and reaction conditions, the CO/H2 ratio in the gas mixture thus varies over a broad range from almost pure hydrogen to the stoichiometric limit of 1:2.

Acceptorless Dehydrogenation of Methanol to Carbon Monoxide and Hydrogen using Molecular Catalysts

AbstractThe acceptorless dehydrogenation of methanol to carbon monoxide and hydrogen was investigated using homogeneous molecular complexes. Complexes of ruthenium and manganese comprising the MACHO ligand framework showed promising activities for this reaction. The molecular ruthenium complex [RuH(CO)(BH4)(HN(C2H4PPh2)2)] (Ru‐MACHO‐BH) achieved up to 3150 turnovers for carbon monoxide and 9230 turnovers for hydrogen formation at 150 °C reaching pressures up to 12 bar when the decomposition was carried out in a closed vessel. Control experiments affirmed that the metal complex mediates the initial fast dehydrogenation of methanol to formaldehyde and methyl formate followed by subsequent slow decarbonylation. Depending on the catalyst and reaction conditions, the CO/H2 ratio in the gas mixture thus varies over a broad range from almost pure hydrogen to the stoichiometric limit of 1:2.

In-situ nitrogen and Cr2O3 co-doped MOF-derived porous carbon supported palladium nanoparticles: A highly effective catalyst towards formic acid dehydrogenation

Fast and high selective dehydrogenation of formic acid (FA) is regarded as one of the most promising pathways to obtain the clean energy carrier: hydrogen. In this work, a nitrogen and Cr2O3 co-doped hierarchical carbon material has been successfully synthesized by in-situ pyrolysis of NH2-MIL-101(Cr) in one step, followed by boiling in hot NaOH solution for surface etching. The activated carbon material is used to anchor the ultrafine Pd nanoparticles (2.18 nm) for formic acid dehydrogenation (FAD). As a result, the 5 wt% Pd@Cr2O3-NPCB-850 exhibits an excellent catalytic activity towards FAD: the turnover frequency (TOF) value is as high as 11 241 h−1 at 333 K, and the selectivity of H2 is up to 100%. The excellent catalytic performance is mainly attributed to the existence of N species and Cr2O3, which plays an important role of electron transfer and anti-aggregation. Our studies open a new methodology for convenient and fast syntheses of nitrogen and metal oxide co-doped activated carbon material, which also provides potential access for producing more highly effective catalysts for other catalytic reactions.

Ultrafine RhNi Nanocatalysts Confined in Hollow Mesoporous Carbons for a Highly Efficient Hydrogen Production from Ammonia Borane.

Ammonia borane (AB) has received growing research interest as one of the most promising hydrogen-storage carrier materials. However, fast dehydrogenation of AB is still limited by sluggish catalytic kinetics over current catalysts. Herein, highly uniform and ultrafine bimetallic RhNi alloy nanoclusters encapsulated within nitrogen-functionalized hollow mesoporous carbons (defined as RhNi@NHMCs) are developed as highly active, durable, and selective nanocatalysts for fast hydrolysis of AB under mild conditions. Remarkable activity with a high turnover frequency (TOF) of 1294 molH2 molRh-1 min-1 and low activation energy (Ea) of 18.6 kJ mol-1 is observed at room temperature, surpassing the previous Rh-based catalysts. The detailed mechanism studies reveal that when catalyzed by RhNi@NHMCs, a covalently stable O-H bond by H2O first cleaves in electropositive H* and further attacks B-H bond of AB to stoichiometrically produce 3 equiv of H2, whose catalytic kinetics is restricted by the oxidation cleavage of the O-H bond. Compositional and structural features of RhNi@NHMCs result in synergic electronic, functional, and support add-in advantages, kinetically accelerating the cleavage of the attacked H2O (O-H bond) and remarkably promoting the catalytic hydrolysis of AB accordingly. This present work represents a new and effective strategy for exploring high-performance supported metal-based alloy nanoclusters for (electro)catalysis.

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.

Immobilization of palladium silver nanoparticles on NH2-functional metal-organic framework for fast dehydrogenation of formic acid

Selective dehydrogenation of formic acid is regarded as a universal strategy for providing a clean energy carrier (hydrogen, H2) to reduce the dependence on fossil fuel. In this work, ultrafine PdAg nanoparticles (NPs) are successfully immobilized on NH2-functionalized metal–organic framework MIL-101(Cr) by a facile wet-reduction method. By virtue of amine group, the size of obtained PdAg NPs can be controlled into 2.2 nm, which are monodispersed on NH2-MIL-101(Cr) surface. In addition, the resulting Pd0.8Ag0.2 NPs/NH2-MIL-101(Cr) catalyst systems demonstrate excellent catalytic activity for formic acid decomposition in mild condition, the turn over frequency (TOF) value can achieve as high as 1475 h−1 at 323 K, which is comparable to most of the reported noble metal heterogeneous catalysts for this catalytic reaction under similar conditions. The excellent catalytic kinetics is mainly attributed to the ultrafine size and high dispersion of PdAg NPs. Also, the amine group from NH2-MIL-101(Cr) support facilitates the OH bond dissociation of formic acid and improves the kinetics of formic acid decomposition.

A YH3 promoted palladium catalyst for reversible hydrogen storage of N-ethylcarbazole

N-ethylcarbazole (NEC) is a promising liquid organic hydrogen carrier, while sluggish kinetics of hydrogen absorption and desorption restrict its application. To overcome that, a YH3 promoted palladium catalyst Pd/Al2O3-YH3 is developed in this work by taking advantage of the fast reversible hydrogenation and dehydrogenation kinetics of YH3. With the Pd/Al2O3-YH3, NEC can reversibly store 5.5 wt% hydrogen in 4 h below 473 K. The performance is the best compared to that of all the reported catalysts for both hydrogen absorption and desorption. Moreover, there are no gaseous impurities produced and no performance decay during three hydrogen storage cycles. The excellent performance derives from the intrinsic high catalytic activity of Pd/Al2O3 and the promoting effect of YH3 by providing a new hydrogen transfer path, making NEC more attractive for practical application.

Highly active, robust and reusable micro-/mesoporous TiN/Si3N4 nanocomposite-based catalysts for clean energy: Understanding the key role of TiN nanoclusters and amorphous Si3N4 matrix in the performance of the catalyst system

Herein, we developed a precursor approach toward the design of a titanium nitride (TiN)/silicon nitride (Si3N4) nanocomposite with an activated carbon monolith as a support matrix forming a highly micro-/mesoporous component to be used as a Pt support for the catalytic hydrolysis of sodium borohydride (NaBH4) as a model reaction. The experimental data demonstrated that the amorphous Si3N4 matrix, the strong Pt-TiN nanocluster interaction and the synergistic effects between the three components contributed to the improved performance of the catalyst system. Thus, the use of this TiN/Si3N4 nanocomposite allowed to significantly reducing the noble metal loading (only ∼1 wt% of Pt) for the complete and fast dehydrogenation of NaBH4 under alkaline conditions at 80 °C. Additionally, the catalytic system displayed an excellent robustness and durability to offer reusability without collapsing and performance decrease under the harsh conditions imposed by the reaction.

Fast hydrogenation and dehydrogenation of Pd-Mg bimetal capped Ti nanoparticles layer deposited on Si substrate

This work reports on the hydrogenation and dehydrogenation abilities of the Pd-Mg bimetal capped Ti nanoparticles (NPs) layer on Si substrate, which were prepared by the Radio Frequency magnetron sputtering system (RF sputtering). Samples were prepared by varying the deposition rate and annealing conditions, then characterized using the FE-SEM, XRD, and XPS to investigate the optimum material structure for better sensing performance. The fabricated devices show resistivity changing in the hydrogenation state and a complete reversible dehydrogenation at room temperature (RT = ∼ 25 °C). The fabricated device showed a detection range of 1,000–10,000 ppm and fast hydrogenation/dehydrogenation time of 3/3 s for 10,000 ppm (1 vol%) at RT along with good selectivity. This Pd-Mg bimetal capped Ti nanoparticles (Pd-Mg/TiNPs) layer on silicon (Si) substrate can be a potential sensing device for its application in low temperature environments where fast hydrogenation/dehydrogenation processes are required.

An amine-functionalized mesoporous silica-supported PdIr catalyst: boosting room-temperature hydrogen generation from formic acid

PdIr/SBA-15-NH2 nanocomposites were synthesized via a facile surface functionalization and co-reduction method and used as a superior catalyst for complete and fast dehydrogenation of formic acid at room temperature.

General Synthesis and Optical Properties of N-Aryl-N′-Silyldiazenes

While organo-substituted diazenes (R1–N═N–R2 with R = alkyl, aryl) are a well-studied class of compounds, much less is known about their heavier group 14 analogues, notably because of their perceived instability. We report herein a general oxidative protocol to prepare various N-aryl-N′-silyldiazenes by a fast and mild dehydrogenation of the corresponding silylhydrazines using di-tert-butylazodicarboxylate as an oxidant. The optical properties of these stable blue to purple silyldiazenes were also studied by UV/visible absorption spectroscopy and supported by TD-DFT calculations.