Dehydrogenation Behavior Research Articles

Investigation of the Effect of the Third Cation M (M = Mg, Al, Mn, and Fe) on the Properties and Catalytic Behavior in Ethane Oxidative Dehydrogenation of M-NiNbO Mixed Oxides

Investigation of the Effect of the Third Cation M (M = Mg, Al, Mn, and Fe) on the Properties and Catalytic Behavior in Ethane Oxidative Dehydrogenation of M-NiNbO Mixed Oxides

Hydrogenation and dehydrogenation behaviors of tantalum under different conditions

The hydrogenation behaviors of tantalum metal and the dehydrogenation behaviors of tantalum hydride powder have been studied in this paper. The results of hydrogenation show that the tantalum ingot is easy to form a barrier layer on its surface during hydrogenation, which can be broken by increasing the pressure of hydrogen and using hydrogenation-dehydrogenation-hydrogenation (H-De-H) process at the same time. Finally, tantalum hydride powder with hydrogen content of 0.427 wt % was obtained. The dehydrogenation results show that TaH0.1 and Ta phases begin to appear at 500 °C under vacuum condition, and complete dehydrogenation can be achieved at 600 °C for 1 h. Under the condition of hydrogen atmosphere, the presence of H2 has an inhibitory effect on the dehydrogenation reaction, and it is most obvious when the temperature is 700 °C.

Effect of Ball Milling Conditions on the Microstructure and Dehydrogenation Behavior of TiH2 Powder

This study investigated the effects of revolution speed and ball size in planetary milling on the microstructure and dehydrogenation behavior of TiH2 powder. The particle size analysis showed that the large particles present in the raw powder were effectively refined as the revolution speed increased, and when milled at 500 rpm, the median particle size was 1.47 m. Milling with a mixture of balls of two or three sizes was more effective in refining the raw powder than milling with balls of a single size. A mixture of 3-mm and 5-mm-diameter balls was the optimal condition for particle refinement, and the measured median particle size was 0.71 m. The dependence of particle size on revolution speed and ball size was explained by changes in input energy and the number of contact points of the balls. In the milled powder, the endothermic peak measured using differential thermal analysis was observed at a relatively low temperature. This finding was interpreted as the activation of a dehydrogenation reaction, mainly due to the increase in the specific surface area and the concentration of lattice defects.

Unprecedented selectivity behavior in the direct dehydrogenation of n-butane to n-butenes with similar active Pt nanoparticle size: unveiling structural and electronic characteristics of supported monometallic catalysts.

In this work, supported Pt monometallic catalysts were prepared using oxide and carbon supports by conventional impregnation methods. Similar Pt metallic nanoparticle sizes (mean sizes about 1.8-2 nm) have been obtained using different Pt precursor loadings (0.3 to 5 wt%). For comparison, catalysts with larger nanoparticle sizes were prepared using the liquid phase reduction method. Characterization results indicate different electronic and structural characteristics for the Pt nanoparticles, comparing nanoparticles with similar and different sizes, implying that both the Pt loading and the preparation method affect the formation of different metallic phases. We used the direct dehydrogenation of n-butane to n-butenes reaction as a test reaction to study the catalytic behavior of the Pt nanoparticles obtained at different Pt atomic concentrations. Surprisingly, Pt catalysts with the lowest metallic loading show the highest selectivities to olefins. Besides, Pt catalysts supported on carbon materials showed higher selectivity to butenes than those supported on oxide materials, this was attributed to a higher electron density in the Pt active sites. Likewise, at low Pt loadings, the CNP-supported Pt nanoparticles could be confined at the defect in the nanotube structure as crystalline agglomerates of atoms with few layers or monolayers with very few surface adatom or stepped adatom nanostructures or simply as a group of atoms, thus creating active Pt sites that favor the dehydrogenation reaction over secondary reactions.

Magnesium nickel hydride monocrystalline nanoparticles for reversible hydrogen storage

Although Mg-based hydrides are extensively considered as a prospective material for solid-state hydrogen storage and clean energy carriers, their high operating temperature and slow kinetics are the main challenges for practical application. Here, a Mg–Ni based hydride, Mg2NiH4 nanoparticles (∼100 nm), with dual modification strategies of nanosizing and alloying is successfully prepared via a gas-solid preparation process. It is demonstrated that Mg2NiH4 nanoparticles form a unique chain-like structure by oriented stacking and exhibit impressive hydrogen storage performance: it starts to release H2 at ∼170 °C and completes below 230 °C with a saturated capacity of 3.32 wt% and desorbs 3.14 wt% H2 within 1800 s at 200 °C. The systematic characterizations of Mg2NiH4 nanoparticles at different states reveal the dehydrogenation behavior and demonstrate the excellent structural and hydrogen storage stabilities during the de/hydrogenated process. This research is believed to provide new insights for optimizing the kinetic performance of metal hydrides and novel perspectives for designing highly active and stable hydrogen storage alloys.

Investigation on Nonisothermal Dehydrogenation Behavior of Mg–Ni–La–H Materials Prepared by Mechanochemical Reaction

Mg10NixLa–H alloys are synthesized by mechanochemical reaction starting with Mg–Ni–La multiphase polycrystalline alloys prepared by resistance melting furnace. The nonisothermal hydrogen desorption behaviors are investigated herein. All prepared samples are characterized by scanning electron microscopy, X‐ray diffraction, fully automatic fast surface and porosity analysis meter Brunauer–Emmett–Teller (BET), differential scanning calorimetry, and thermogravimetric analyzer to get information of phase compositions, microstructure, BET surface area, and dehydrogenation properties. The results demonstrate that Mg10NixLa–H exhibits enhanced nonisothermal hydrogen desorption behavior owing to the synergistic effects among hydrides. The main peak dehydrogenation temperatures for Mg10Ni5La–H, Mg10Ni10La–H, and Mg10Ni15La–H alloys are 375.3, 374.4, and 359.7 °C at 5 °C min−1, respectively. And the apparent activation energy for Mg10Ni5La–H, Mg10Ni10La–H, and Mg10Ni15La–H is 111.7, 275.5, and 184.7 kJ mol−1, respectively. However, the actual hydrogen release capacities of Mg10Ni5La–H, Mg10Ni10La–H, and Mg10Ni15La–H are about 5.09, 3.98, and 4.49 wt%, respectively. Mg10Ni15La–H exhibits the lowest onset dehydrogenation temperature due to its reduced particle size and uniformly distributed hydride phase. The modification of Mg‐based hydrogen storage materials by combining mechanochemical reaction and multiple microalloying is essential for further improvement of thermal properties.

Zn2TiO4 synthesized via solid-state method and its effects on dehydrogenation properties of LiAlH4

Lithium alanate (LiAlH4) has high gravimetric capacity but its practical application is still severely constrained by poor reversibility and sluggish kinetics. In this study, the dehydrogenation behaviour of LiAlH4 was modified with the inclusion of Zn2TiO4. The initial temperature for the dehydrogenation of LiAlH4 was downshifted to 111 °C (first dehydrogenation) and 151 °C (second dehydrogenation) with the inclusion of 10 wt% Zn2TiO4. The as-milled LiAlH4 released only 0.1 wt% H2 while the LiAlH4–10 wt% Zn2TiO4 sample released 3.6 wt% H2 in 60 min at 90 °C which is 36 times faster than undoped LiAlH4. The dehydrogenation activation energies for the first two dehydrogenation process was also reduced by 24.1 and 21.0% than as-milled LiAlH4. The X-ray diffraction analysis revealed that the Zn2TiO4 reacts with LiAlH4 and the formed Al–Ti and Ti–Zn during the dehydrogenation leading to the superior dehydrogenation behaviour of LiAlH4.

Effective attempt towards enhancing hydrogen storage performance of LPSO phase contained high-capacity Mg-based alloy by Indium

To explore more possibilities for hydrogen economy, Mg-based alloys containing long period stacking ordered (LPSO) phase for solid-state hydrogen storage deserve attention. In this paper, indium (In) element is adopted to alter the de/hydrogenation abilities of Mg–Y–Zn alloys. The relationship between microstructural features and hydrogen storage behaviors of Mg95Y3Zn2-xInx (x = 0, 1 and 2 at.%) alloys are discussed in detail. Indium element can modify the morphology of LPSO phase and more Mg interfaces are obtained. LPSO phase cannot be generated when Zn is completely replaced by In element; instead α-Mg grains and eutectic phase (Mg + MgYIn) the constitute the In2 alloy. Element In benefits the activation process of the alloys in this paper, which helps the alloy particles to be hydrogenated quickly in the first hydrogenation. Specifically, 1 at.% In substitution for Zn accelerates dehydrogenation and the dehydrogenation temperature reduces by 11 °C. The benefits of In element for dehydrogenation behaviors mainly come from increased Mg grain boundaries, larger MgH2 lattice constants with weaker Mg–H bonds, uniformly distributed nanoscale YH2/YH3 phase.

Highly active bimetallic MOF derivatives for improving the dehydrogenation performance of LiAlH4

LiAlH4 is considered an effective hydrogen storage material due to its high hydrogen storage capacity and relative abundance of aluminum. However, LiAlH4 presents disadvantages such as slow kinetics, high dehydrogenation temperature, and poor reversibility. To improve these shortcomings of LiAlH4, we designed and prepared Ni-Ti bimetallic metal-organic framework derivatives with stable structures and high dispersion of metal species, which named as Ni-Ti-NC. A series of tests show that the composite components and circular disk-like structure of Ni-Ti-NC can improve the dehydrogenation behavior of LiAlH4. Benefiting from the addition of Ni-Ti-NC, the initial decomposition temperature of LiAlH4 significantly decreased to 59.5 ℃, and about 6.11 wt% of hydrogen was rapidly released within 25 min at 200 ℃. Meanwhile, the activation energies of the two-step hydrogen evolution reaction decreased to 64.18 kJ·mol−1 and 73.99 kJ·mol−1, respectively. Furthermore, compared with only 0.09 wt% hydrogen absorption of pure LiAlH4 at 30 bar hydrogen pressure and 300 ℃ constant temperature, doping Ni-Ti-NC promoted the hydrogen absorption capacity of LiAlH4 to nearly 0.64 wt% under the same conditions. In addition, the structure and chemical changes of LiAlH4 after the addition of Ni-Ti-NC were investigated in detail. The reasons why Ni-Ti-NC improved the hydrogen storage performance of LiAlH4 were comprehensively analyzed, which helped us design efficient catalysts for solid hydrogen storage materials.

Unraveling the Lattice O Assisted Internal Selective Catalytic Reduction Mechanism on High N2 Selectivity of CuOx/PtCu Catalysts in NH3-SCO

Supported Pt catalysts suffer from low reaction selectivity (<65% at 100% conversion) in the selective catalytic oxidation of ammonia (NH3-SCO) because of their intrinsic over-oxidation tendencies. Herein, a strategy based on facilitating byproduct NOx reduction to N2 is demonstrated at CuOx/PtCu catalysts, aiming to tackle the low selectivity challenge. This PtCu alloy sample with a CuOx-rich surface displays an N2 selectivity of 95%, while its turnover frequencies are the highest among reported supported Pt-based catalysts. The enhanced reaction activities and N2 selectivities are primarily attributed to the Pt-Cuδ+ dual-site synergies at the CuOx/PtCu interface, in which dual sites exhibit distinct NH3 adsorption, activation, and dehydrogenation behaviors. The Olat assisted internal selective catalytic reduction mechanism at CuOx/PtCu with N2O22– as the central intermediates is proposed. Density functional theory calculation and temperature-programmed surface reaction measurements show that the N–O bond in N2O22– tends to break simultaneously with the assistance of Ov in CuOx followed by the easy transition from N2O22– to N2, which serve as the origin of the high selectivity.

Dehydrogenation behavior and mechanism of LiAlH4 adding nano-CeO2 with different morphologies

Dehydrogenation behavior and mechanism of LiAlH4 adding nano-CeO2 with different morphologies

Enhancement of ethylene production by alkali metal doping of MoVSb mixed oxide catalyst for ethane oxidative dehydrogenation

Hydrothermally prepared Mo-V-Sb mixed oxides doped with alkali metal cations (Li+, Na+, K+, Rb+, or Cs+) show a significantly improved catalytic behavior in the oxidative dehydrogenation of ethane (ODH) compared to conventional alkali metal-free MoVSbO catalysts. Initial selectivity to ethylene above 95 % was held up to 20 % of ethane conversion for all alkali metal promoted MoVSbO catalysts, as well as lower ethylene overoxidation at higher ethane conversion, with differences depending on the alkali metal employed. Thus, from Li to K, the enhanced catalytic performance follows a bottom-up trend as increasing the size of the cation. An intermediate behavior is observed though for the catalyst doped with Cs cations, with the highest atomic radius. The K-doped MoVSbO catalyst is the least prone to both ethane total oxidation and ethylene overoxidation, which enables up to 90 % selectivity to ethylene at ethane conversion higher than 65 %.

Boosting the Dehydrogenation Properties of LiAlH4 by Addition of TiSiO4

Given its significant gravimetric hydrogen capacity advantage, lithium alanate (LiAlH4) is regarded as a suitable material for solid-state hydrogen storage. Nevertheless, its outrageous decomposition temperature and slow sorption kinetics hinder its application as a solid-state hydrogen storage material. This research's objective is to investigate how the addition of titanium silicate (TiSiO4) altered the dehydrogenation behavior of LiAlH4. The LiAlH4-10 wt% TiSiO4 composite dehydrogenation temperatures were lowered to 92 °C (first-step reaction) and 128 °C (second-step reaction). According to dehydrogenation kinetic analysis, the TiSiO4-added LiAlH4 composite was able to liberate more hydrogen (about 6.0 wt%) than the undoped LiAlH4 composite (less than 1.0 wt%) at 90 °C for 2 h. After the addition of TiSiO4, the activation energies for hydrogen to liberate from LiAlH4 were lowered. Based on the Kissinger equation, the activation energies for hydrogen liberation for the two-step dehydrogenation of post-milled LiAlH4 were 103 and 115 kJ/mol, respectively. After milling LiAlH4 with 10 wt% TiSiO4, the activation energies were reduced to 68 and 77 kJ/mol, respectively. Additionally, the scanning electron microscopy images demonstrated that the LiAlH4 particles shrank and barely aggregated when 10 wt% of TiSiO4 was added. According to the X-ray diffraction results, TiSiO4 had a significant effect by lowering the decomposition temperature and increasing the rate of dehydrogenation of LiAlH4 via the new active species of AlTi and Si-containing that formed during the heating process.

Experimental and theoretical investigations into propane dehydrogenation over MIL-101(Cr/Al) derived catalysts

Propane dehydrogenation is commonly operated at temperatures exceeding 600 °C due to thermodynamic requirements. However, high temperature accelerates the deactivation of catalysts because of the coke deposition. Therefore, it is quite necessary to develop catalysts with high catalytic activity and improved anti-coking ability. To this end, an Al-doped Cr2O3 catalyst derived from MIL-101(Cr/Al) is prepared in this work. The preparation conditions, including the carbonization temperature of MIL-101 and the proportion of Cr/Al, are optimized via experimental studies. Meanwhile, the adsorption and dehydrogenation behaviors of propane on the catalyst are investigated using Density Functional Theory (DFT) methods. Findings indicate that the optimum carbonization temperature and Cr/Al proportion are 900 °C and 6:4, respectively. Under the reaction condition of P = 0.1 MPa, T = 580 °C and GHSV = 800 h−1, the propane conversion and propylene selectivity on the Cr6/Al4 catalyst are 19.5% and 92.0%, respectively. The activity stability of the Al-doped Cr2O3 is elongated significantly due to the lower desorption energy of propene and higher energy barrier for the coke formation on the catalyst. In sum, the present work completed via experiments and DFT calculations will lead to a better understanding of the Al-doped Cr2O3 catalyst and guide the rational design of anti-coking catalysts for propane dehydrogenation.

Tuning dehydrogenation behavior of formic acid on boosting cell performance of formic acid fuel cell at elevated temperatures

In high-temperature formic acid fuel cell (HT-FAFC), the dehydrogenation behavior of formic acid plays a significant role in boosting cell output performance by leading to a favorable and powerful hydrogen oxidation reaction (HOR) on the anode side instead of the direct formic acid oxidation reaction (dFAOR). The formic acid dehydrogenation mechanism of HT-FAFC at 200 °C is investigated by regulating concentration and flow rate. As a competitive path of dehydrogenation, unfavorable dehydration occurs simultaneously accompany by carbon monoxide (CO) release. It is found that high formic acid concentration is conducive to the dehydrogenation to produce more hydrogen, however, the reduction of water vapor content may promote the dehydration reaction and result in the inhibition of dehydrogenation. As the non-preferable alternative, the dehydration-caused total CO release remains under CO maximum tolerance (3%) of Pt catalyst at 200 °C which is unlikely to affect the power output of HT-FAFC. The permeation of formic acid can be considered as a barrier when the high concentration exceeds 12 mol L−1 or the flow rate exceeds 1 mL min−1. These findings may deepen understanding of formic acid consuming behavior of HT-FAFC anode, which helps to formulate strategies to improve cell performance in general.

Microwave-assisted reduction of Ti species in MgH2-TiO2 composite and its effect on hydrogen storage

The goal of this work is to shed light on the significant dehydrogenation behavior of MgH2-TiO2 composite exposed to microwave irradiation, and the changes in chemical state of titanium species that occur as a result. It is discovered that the reduced titanium oxide (TiO2-x) formed during ball milling can significantly absorb microwave radiation and act as “hot spots”, such that the MgH2 with 25 wt% TiO2 sample is nearly completed dehydrogenated at a constant temperature of 220 °C in a microwave field. Upon full dehydrogenation, the microwave irradiated sample significantly absorbs 1.25 wt% H2 within 600 sec and 4.25 wt% H2 within 10 h at 25 °C under 1 bar of hydrogen. Characterization results of these samples show that microwave irradiation assists the uniform dispersal of defective TiO2-x species around Mg/MgH2 particles and further promotes the reduction of Ti4+ to lower valence states, for better electron transfer between Mg2+ and H-. HRTEM images as well reveal that part of Mg grain size falls around 10 nm, which is believed to significantly enhance the hydrogen sorption as observed. Our findings show that the synergistic effects of microwave irradiation and heat may advance MgH2 further to practical applications.

Cobalt phosphide with porous multishelled hollow structure design realizing promoted ammonia borane dehydrogenation: Elucidating roles of architectural and electronic effect

Exploring advanced non-noble metal-based catalysts for H2 release from chemical hydrogen storage materials is of paramount importance to boost hydrogen economy. Rationally tailoring over architecture and electronic state promises high-efficiency catalysis. Herein we present, for the first time, delicate engineer of cobalt phosphide with a unique porous, multishelled, and hollow architecture (multishelled Co-P) for dramatically promoting ammonia borane (AB) dehydrogenation. Featuring hollow porous structure and complex nanoconfined interior space, multishelled Co-P possesses abundant accessible active sites and facile mass transfer. Importantly, theoretical calculations decipher that P incorporation in Co-P can modulate electronic structure of Co sites to give promoted H2O adsorption and favorable H2O dissociation kinetics (rate-determining step), thereby facilitating AB dehydrogenation. This study provides a fundamental understanding of correlation between electronic state of Co-P and AB dehydrogenation behavior, and highlights that decent architectural engineering coupled with electronic modulation is an effective protocol to construct advanced catalytic systems.

Study on high hydrogen yield for large-scale hydrogen fuel storage and transportation based on liquid organic hydrogen carrier reactor

Large-scale hydrogen fuel storage and transportation are one of the main bottlenecks in the hydrogen-supported future energy system. In this study, a symmetrical two-dimension model of large-scale liquid organic hydrogen carrier reactor using N-ethylcarbazole (NEC) hydrogen carrier as a case is developed to explore the dehydrogenation behavior. The influences of operating parameters including heating temperature, thermal conductivity, and LOHC mass flow rate and geometry parameter reactor length on the dehydrogenation are investigated for performance optimization. The flow field distribution of N-ethyl-tetrahydro-carbazole (4H-NEC) intermediate product shows that the peak position of 4H-NEC mass fraction is turning point of the competition between the reactions of N-ethyl-dodecahydro-carbazole(12H-NEC) to 4H-NEC and 4H-NEC to 0H-NEC. It is significant to obtain large conversion of 12H-NEC to 4H-NEC within the tube pass as short as possible. In comparison, the dehydrogenation reaction of 4H-NEC to 0H-NEC with the slow kinetics is the rate-determining step of whole dehydrogenation process. Based on the dehydrogenation mechanism, the optimal operating and geometry parameters are suggested to be 520 K for operating temperature, 83 W/(m∙K) for thermal conductivity, 24 mL/min for 12H-NEC mass flow rate, and 3 m for reactor length. In such case, the proposed reactor could achieve high hydrogen yield of 90.58% and fast reaction kinetics of 1.43 h for reaction duration in large scale.

Elucidating the Critical Role of Ruthenium Single Atom Sites in Water Dissociation and Dehydrogenation Behaviors for Robust Hydrazine Oxidation‐Boosted Alkaline Hydrogen Evolution

AbstractHydrazine oxidation (HzOR)‐assisted overall water splitting (OWS) provides a unique approach to energy‐efficient hydrogen production (HER). However, there are still major challenges in the design of bifunctional catalysts and gain deep insight into the mechanism of both water dissociation and dehydrogenation kinetics triggered by the same active species during HzOR‐assisted OWS. Here, ruthenium single atoms (Ru SAs) anchored onto sulphur‐vacancies of tungsten disulphide (WS2) are prepared by a sulfidation and facile galvanostatic deposition strategy. The WS2/Ru SAs act as a bifunctional catalyst and outperforms commercial platinum (Pt) catalysts for both HzOR and HER. Ultralow potentials of −74 and −32.1 mV at 10 mA cm−2 are achieved for HzOR and HER, respectively. Two‐electrode electrolyzer using WS2/Ru SAs as both anode and cathode reaches 10 mA cm−2 with cell voltage of only 15.4 mV, which is far below that of most electrocatalysts including commercial Pt. Density functional theory calculations unravel the critical role of Ru SAs in WS2, where the sluggish dissociation of water in HER can be promoted on Ru sites, and the sulfur sites of WS2 exhibit a more thermoneutral behavior for hydrogen intermediate adsorption. Moreover, Ru sites are also active centers for stepwise hydrazine dehydrogenation during HzOR.

Green dehydrogenation of dimethylamine borane catalyzed by cheaply copper(0) nanocatalysts without any stabilizer at nearly room temperature.

In this work, the findings of the work on the green dehydrogenation behavior of molten dimethylamine borane (DMAB) catalyzed by the precatalyst copper(II) acetylacetonate (Cu(acac)2) in solvent-free medium (green) at near room temperature (nRT, 30.0+0.1°C) were reported. Herein, a complete study has been presented, which includes the following steps: (i) synthesis and catalytic activity of Cu(0) NCats in solvent-free medium, (ii) determination of activation energy for Cu(0) NCats catalyzed green dehydrogenation of DMAB, (iii) demonstration of catalytic lifetime of Cu(0) NCats, (iv) test of isolability and reusability of Cu(0) NCats, (v) poisoning experiments using carbon disulfide on a per-active-copper-atom basis, (vii) characterization of Cu(0) NCats by UV-vis, XRD, XPS and TEM/HRTEM/TEM-EDX spectroscopies. In addition, ATR-FTIR and 11B NMR techniques were use to characterize the cyclic aminoborane product obtained as a result of dehydrogenation of dimethylamine-borane.