Complete Dehydrogenation Research Articles

Light‐Induced Nonoxidative Coupling of Methane Using Stable Solid Solutions

AbstractAchieving efficient and direct conversion of methane under mild conditions is of great significance for innovations in the chemical industry. However, the efficiency and lifetime of most catalysts remain too far from practical requirements, since it is difficult to break the first C−H bond of methane as well as to suppress the following complete dehydrogenation (or overoxidation) and the resulting carbonaceous deposition (or CO2). Here, we report that wurtzite GaN:ZnO solid solutions exhibit unique and unprecedented photocatalytic performances for the nonoxidative coupling of methane at room temperature, exclusively generating ethane with nearly stoichiometric H2. High conversion rate (>330 μmol g−1 h−1), long‐term stability (>70 h), and superior coke‐resistance were achieved. At 293 K, the methane conversion exceeds 7 %, comparable to the equilibrium conversion of thermal catalysis at 910 K. Mechanistic studies revealed that the N‐ZnGa‐ON units and the absence of acid sites on the surface played crucial roles in reactivity and coke resistance, respectively.

The catalytic activity of PtnCum (n= 1-3, m= 0-2) clusters for methanol dehydrogenation to CO.

A large number of experiments show that PtCu catalyst has a good catalytic effect on methanol decomposition. Therefore, density functional theory (DFT) was used to further study the dehydrogenation of methanol catalyzed by PtnCum (n= 1-3, m= 0-2). The energy diagrams of O-adsorption path and H-adsorption path were drawn. By calculation, the Pt is the active site of the whole reaction process, and the barrier energy of the rate-determining step is 11.09kcalmol-1 by Pt2Cu, which is lower than that of Pt3 and PtCu2. However, the complete dehydrogenation product of methanol, CO, is easier to dissociate from PtCu2 clusters than from Pt3 and Pt2Cu clusters. Therefore, Cu doping can improve the catalytic activity and anti-CO toxicity of Pt to a certain extent.

Reaction Pathway for Coke-Free Methane Steam Reforming on a Ni/CeO2 Catalyst: Active Sites and the Role of Metal-Support Interactions.

Methane steam reforming (MSR) plays a key role in the production of syngas and hydrogen from natural gas. The increasing interest in the use of hydrogen for fuel cell applications demands development of catalysts with high activity at reduced operating temperatures. Ni-based catalysts are promising systems because of their high activity and low cost, but coke formation generally poses a severe problem. Studies of ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) indicate that CH4/H2O gas mixtures react with Ni/CeO2(111) surfaces to form OH, CHx, and CHxO at 300 K. All of these species are easy to form and desorb at temperatures below 700 K when the rate of the MSR process is accelerated. Density functional theory (DFT) modeling of the reaction over ceria-supported small Ni nanoparticles predicts relatively low activation barriers between 0.3 and 0.7 eV for complete dehydrogenation of methane to carbon and the barrierless activation of water at interfacial Ni sites. Hydroxyls resulting from water activation allow for CO formation via a COH intermediate with a barrier of about 0.9 eV, which is much lower than that through a pathway involving lattice oxygen from ceria. Neither methane nor water activation is a rate-determining step, and the OH-assisted CO formation through the COH intermediate constitutes a low-barrier pathway that prevents carbon accumulation. The interactions between Ni and the ceria support and the low metal loading are crucial for the reaction to proceed in a coke-free and efficient way. These results pave the way for further advances in the design of stable and highly active Ni-based catalysts for hydrogen production.

The mechanism of the water dissociation and dehydrogenation of glycerol on Au (111) and PdAu alloy catalyst surfaces

Hydrogen is an energy carrier found from renewable sources such as biomass, geothermal, solar, or wind. Water splitting and dehydrogenation of glycerol is a sustainable process of H2 production from renewables because water is abundant, and the glycerol is formed from the biomass-derived compounds. However, finding a suitable and best catalyst for these processes is challenging. Thus, this paper proposed a theoretical study to find the mechanism of the dissociation of water and dehydrogenation of glycerol using Au metal and PdAu alloy catalysts using the density functional theory (DFT) method. Four PdAu alloys have been constructed with different atomic compositions ranging from 1 to 3 of Pd metal to Au metal. The result showed strong adsorption on the Pd1Au3 catalyst surface, and the water splitting is best on the Pd3Au1 catalyst surface. Simultaneously, the glycerol adsorption on catalyst surfaces is tested before proceeding for the complete dehydrogenation mechanism of glycerol. Strong adsorption was found at the Pd1Au3 catalyst compared to other catalyst surfaces on the glycerol adsorption. The dehydrogenation mechanism was found toward a downhill reaction and removed eight hydrogens from the glycerol compared to Au metal, referring to easy dehydrogenation of glycerol using the alloy PdAu. The final species that adsorbed on the Pd1Au3 surface is the carbon monoxide will be turned later into carbon dioxide.

Synergistic effect of metal components of the low-loaded Pt-Ni-Cr/C catalyst in the bicyclohexyl dehydrogenation reaction

The problem of hydrogen storage in liquid organic hydrogen carriers is not only the choice of an appropriate organic substrate, but the development of a selective and active catalyst containing as low as possible noble metals. A synergistic effect of increasing conversion and selectivity in bicyclohexyl dehydrogenation to biphenyl on trimetallic Pt-Ni-Cr/C catalysts with an extremely low Pt loading (0.1 wt %), compared with bimetallic Ni-Cr/C and Pt/Ni/C systems, due to the supporting of platinum on nickel-chromium nanoparticles was established for the first time. The TOF values (mmol (H2)/gPt min) for hydrogen evolution under conditions of the reaction of bicyclohexyl dehydrogenation (320 °C, 0.1 MPa) on Pt supported onto a Ni-Cr/С composite exceed by two orders of magnitude the values found for the two-component catalysts. The maximum amount of the evolved hydrogen correlates to the selectivity of the complete dehydrogenation of bicyclohexyl into biphenyl on the Pt-Ni-Cr/C catalyst. The formation of a Ni-Cr solid substitution solution in a Ni-Cr composite deposited on a carbon carrier is shown by magnetometry, XRD, and TEM methods.

Catalytic Hydrogenation and Dehydrogenation Reactions of N-alkyl-bis(carbazole)-Based Hydrogen Storage Materials

Recently, there have been numerous efforts to develop hydrogen-rich organic materials because hydrogen energy is emerging as a renewable energy source. In this regard, we designed and prepared four new materials based on N-alkyl-bis(carbazole), 9,9′-(2-methylpropane-1,3-diyl)bis(9H-carbazole) (MBC), 9,9′-(2-ethylpropane-1,3-diyl)bis(9H-carbazole) (EBC), 9,9′-(2-propylpropane-1,3-diyl)bis(9H-carbazole) (PBC), and 9,9′-(2-butylpropane-1,3-diyl)bis(9H-carbazole) (BBC), to investigate their hydrogen adsorption/hydrogen desorption reactivity depending on the length of the alkyl chain. The gravimetric densities of MBC, EBC, PBC, and BBC were 5.86, 5.76, 5.49, and 5.31 H2 wt %, respectively, again depending on the alkyl chain length. All materials showed complete hydrogenation reactions under ruthenium on an alumina catalyst at 190 °C, and complete reverse reactions and dehydrogenation reactions were observed under palladium on an alumina catalyst at <280 °C. At this temperature, all the prepared compounds were thermally stable, and no decomposition was observed.

Supported ultrafine NiPt–MoOxnanocomposites as highly efficient catalysts for complete dehydrogenation of hydrazine borane

A NiPt–MoOx/NH2–N-rGO nanocomposite is developed at room temperature, and it has a high dehydrogenation efficiency for hydrazine borane at 323 K.

Molecular bending as a vital step toward transforming planar PAHs to fullerenes and tubular structures

Context. Polycyclic aromatic hydrocarbons (PAHs) and fullerenes are the largest molecules found in the interstellar medium (ISM). They are abundant and widespread in various astronomical environments. However, the detailed connection between these two species is unknown; in particular, no quantum chemical studies have been performed. Aims. In this work, we investigate a vital step in transforming planar PAHs to fullerenes, that is, the tubulation processes of PAHs. Methods. We used density functional theory for this study. The molecular structures and vibrational frequencies were calculated using the hybrid density functional B3LYP method. To better describe intermolecular forces, we considered Grimme’s dispersion correction in the calculations for this work. Intrinsic reaction coordinate calculations were also performed to confirm that the transition state structures are connected to their corresponding local potential energy surface minima. Results. As expected, we find that it is easier to bend a molecule as it gets longer, whereas it is harder to bend the molecule if it gets “wider” (i.e., with more rows of benzene rings). The change of multiplicity slightly alters the bending energies, while (a complete) dehydrogenation alleviates the bending barrier significantly and facilitates the formation of pentagons, which may act as an indispensable step in the formation of fullerenes in the ISM.

CH4 dissociation on the Pd/Cu(111) surface alloy: A DFT study

AbstractThe periodic four-layered model of the pure Cu(111) surface has been considered, and the effect of doping with palladium on CH4dissociation has been investigated. The most stable adsorption geometries of CHxspecies (x= 1–4) and H atom on the PdCu(111) and pure Cu(111) surfaces have been obtained. Their computed adsorption energy results on the pure Cu(111) surface have been compared with the previously reported studies. Then, transition state geometries of CH4dehydrogenation steps on both surfaces were calculated by the climbing image nudged elastic band method. Finally, the relative energy diagram for CH4complete dehydrogenation has been represented. The results show that the PdCu(111) surface is more favorable than the Cu(111) surface in terms of the activation energies. The addition of Pd atoms to the Cu(111) surface significantly improves the catalytic activity. This knowledge can enable an efficient catalyst design at a lower cost using different strategies.

Controllable H2 Generation by Formic Acid Decomposition on a Novel Pd/Templated Carbon Catalyst

A novel Pd/templated carbon catalyst (Pd/TC) was developed, characterized, and tested in the dehydrogenation of formic acid (FA) under mild conditions, with the possibility to control the H2 generation rate, in the absence or presence of HCOONa (SF), by adjusting the Pd:FA and/or FA:SF ratios. The characterization results of the templated carbon obtained by the chemical vapor deposition of acetylene on NaY zeolite revealed different structural and morphological properties compared to other C-based supports. Therefore, it was expected to induce a different catalytic behavior for the Pd/TC catalyst. Indeed, the TC-supported Pd catalyst exhibited superior activity in the decomposition of FA, even at room temperature, with turnover frequencies (TOFs) of up to 143.7 and 218.8 h−1 at 60 °C. The H2 generation rate increased with an increasing temperature, while the H2 yield increased with a decreasing FA concentration. Constant generation of gaseous flow (H2 + CO2) was achieved for 11 days, by the complete dehydrogenation of FA at room temperature using a 2 M FA solution and Pd:FA = 1:2100. The presence of SF in the reaction medium significantly enhanced the H2 generation rate (535 h−1 for FA:SF = 3:1 and 60 °C).

Complete Dehydrogenation of Hydrazine Borane on Manganese Oxide Nanorod-Supported Ni@Ir Core-Shell Nanoparticles.

Hydrazine borane (HB; N2H4BH3) has been considered to be one of the most promising solid chemical hydrogen storage materials owing to its high hydrogen capacity and stability under ambient conditions. Despite that, the high purity of hydrogen production from the complete dehydrogenation of HB stands as a major problem that needs to be solved for the convenient use of HB in on-demand hydrogen production systems. In this study, we describe the development of a new catalytic material comprised of bimetallic Ni@Ir core-shell nanoparticles (NPs) supported on OMS-2-type manganese oxide octahedral molecular sieve nanorods (Ni@Ir/OMS-2), which can reproducibly be prepared by following a synthesis protocol including (i) the oleylamine-mediated preparation of colloidal Ni@Ir NPs and (ii) wet impregnation of these ex situ synthesized Ni@Ir NPs onto the OMS-2 surface. The characterization of Ni@Ir/OMS-2 has been done by using various spectroscopic and visualization techniques, and their results have revealed the formation of well-dispersed Ni@Ir core-shell NPs on the surface of OMS-2. The catalytic employment of Ni@Ir/OMS-2 in the dehydrogenation of HB showed that Ni0.22@Ir0.78/OMS-2 exhibited high dehydrogenation selectivity (>99%) at complete conversion with a turnover frequency (TOF) value of 2590 h-1 at 323 K, which is the highest activity value among all reported catalysts for the complete dehydrogenation of HB. Furthermore, the Ni0.22@Ir0.78/OMS-2 catalyst enables facile recovery and high stability against agglomeration and leaching, which make it a reusable catalyst in the complete dehydrogenation of HB. The studies reported herein also include the collection of wealthy kinetic data to determine the activation parameters for Ni0.22@Ir0.78/OMS-2-catalyzed dehydrogenation of HB.

Theoretical study of CH4 adsorption and dissociation on W-Cu(1 0 0) surface

First principle density functional theory calculations (DFT GGA-PW91) have been employed to study the activity of W-doped Cu(1 0 0) surface for methane dissociation. We studied methane site preference for CH4, CH3, CH2, CH, C and H species at a coverage of a 0.25 monolayer. From the calculated adsorption energies, we found that W-doping stabilizes better all species. The top tungsten site is the most stable for methane, methyl and hydrogen. However, the methyn and carbon atoms prefer the fourfold hollow site, while methylene prefer bridge site. In addition, the electronic structure analysis of methane and surface showed a weak chemical interaction. Furthermore, methane complete dehydrogenation mechanism have been investigated in terms of the thermodynamics and kinetics. The results revealed that the W-Cu(1 0 0) is more reactive surface for methane dissociation, thermodynamically and kinetically, rather than others Cu-based catalysts.

Tunable Thiolate Coordination Networks on Metal Surfaces

AbstractThiolate coordination networks (TCNs) were synthesized on metal surfaces using benzenehexathiol (BHT) and analyzed by cryogenic scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS) as well as density functional theory. Upon adsorption, the deprotonation of the thiol groups occurred on the metal surface with the formation of metal‐sulfur coordination bonds. Increasing the surface temperature triggered the complete dehydrogenation of BHT and promoted the formation of TCNs. On Ag(111), the TCN of [Ag3(C6S6)]n was achieved and showed good thermal stability. On Cu(111), two TCNs ([Cu6(C6S6)]n and [Cu8(C6S6)]n,) were identified. Interestingly, the construction of the two TCNs on Cu(111) can be precisely controlled by adjusting the temperature of the surface during deposition and thermal annealing. Our results reveal the significant influence of the metal surface on the formation of coordination networks.

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.

On the Catalytic Activity of [RuH2(PPh3)3(CO)] (PPh3=triphenylphosphine) in Ruthenium‐Catalysed Generation of Hydrogen from Alcohols: a Combined Experimental and DFT study

AbstractUsing density functional theory calculations (at the B97‐D2//BP86 level) and measurements of kinetic isotope effects, we explored the mechanism of [RuH2(PPh3)3(CO)] (22) in catalytic acceptor‐less dehydrogenation of methanol to formaldehyde. 22 is found to exhibit a similar activity as the previously studied [RuH2(H2)(PPh3)3] (1 b) complex. On the computed pathway, η2→η1 slippage of Ru‐bound formaldehyde prior to decoordination is indicated to be rate‐limiting, consistent with the low kH/kD KIE of 1.3 measured for this reaction. We also explored computationally the possibility of achieving complete dehydrogenation of methanol (into CO2 and H2), through subsequent decarbonylation of formaldehyde and water‐gas shift reaction of the resulting carbonyl complex. Complete pathways of this kind are traced for 22 and for [RuH2(PPh3)2(CO)2]. An alternative mechanism, involving a gem‐diol intermediate (obtained upon attack of OH− to coordinated formaldehyde), has also been investigated. All these pathways turned out to be unfavourable kinetically, in keeping with the lack of CO2 evolution experimentally observed in this system. Our calculations show that the reactions are hampered by the low electrophilicities of the CO and HCHO ligands, making OH− uptake unfavourable. Consequently, the subsequent intermediates are too high‐lying on the reaction profiles, thus leading to high kinetic barriers and preventing full dehydrogenation of methanol to occur by this kind of mechanism.

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.

Enhanced H2 production from dehydrogenation of sodium borohydride over the ternary Co0.97Pt0.03/CeO x nanocomposite grown on CGO catalytic support.

The development of low-cost materials for the 100% dehydrogenation of metal hydrides is highly essential to vitalize the chemical hydride-based hydrogen economy. In this context, the ternary Co–Ce–Pt nanocomposite immobilized on functionalized catalytic support CGO is synthesized by the one step chemical reduction approach and has been directly employed for the ethanolysis of sodium borohydride. The co-operative effect of CGO and the synergy between metallic nanoparticles is investigated to determine the highest rate of hydrogen (H2) production. The maximum hydrogen generation rate (HGR) of 41.53 L (min gM)−1 is achieved with the Co0.97Pt0.03/CeOx/CGO nanohybrid from the alkaline ethanolysis of sodium borohydride (SB). In addition, the resultant nanohybrid exhibited a relatively low activation energy of 21.42 kJ mol−1 for the ethanolysis of SB. This enhanced catalytic activity may be attributed to the intermetallic charge transport among metallic Pt, Co/Co3O4, and CeOx counterparts. Moreover, the catalytic support CGO provides mesoporous functionalized surface and its intercalated GO layers promote charge transport. These results indicate that the resultant catalytic system described here for the dehydrogenation of SB can offer a portable and low-cost H2 supply for various fuel cell applications.

Cr2O3-modified NiFe nanoparticles as a noble-metal-free catalyst for complete dehydrogenation of hydrazine in aqueous solution

The development of highly active, stable, and inexpensive catalysts for efficient and complete dehydrogenation of hydrazine is highly attractive but still very challenging. Herein, Cr2O3-modified NiFe (NiFe-Cr2O3) nanopartciles (NPs) have been designed as the heterogeneous catalyst. Both the catalytic activity and hydrogen selectivity of Ni0.9Fe0.1-Cr2O3 NPs were improved remarkably as compared with those of their mono-metallic counterparts. The prepared Ni0.9Fe0.1-Cr2O3 catalyst exhibited an outstanding catalytic activity to release 3.0 equiv. (H2 + N2) from hydrazine in only 8.5 min at 70 °C, providing a turnover frequency (TOF) value of 893.5 h−1 based on surface metal atoms. Systematic studies indicated that the small size and high surface area of Ni0.9Fe0.1-Cr2O3 as well as the strong synergistic electronic effect between Cr2O3 and NiFe NPs resulted in the excellent activity of Ni0.9Fe0.1-Cr2O3 catalyst. Such a highly rapid, long term durability, and low cost catalyst may encourage greatly the practical application of hydrous hydrazine as a chemical hydrogen storage material.

N-Substituted Auxiliaries for Aerobic Dehydrogenation of Tetrahydro-isoquinoline: A Theory-Guided Photo-Catalytic Design

Visible-light mediated aerobic dehydrogenation of N-heterocyclic compounds is a reaction with enormous potential for application. Herein, we report the first complete aerobic dehydrogenation pathway to large-scale production of isoquinolines. The discovery of this visible light photoredox reaction was enabled through the combination of mathematical simulations and real-time quantitative mass spectrometry screening. The theoretical calculations showed that hyper-conjugation, the main underlying factor hindering the aerobic oxidation of tetrahydroisoquinolines, is relieved both by π- and σ-donating substituents. This mechanistic insight provided a novel photocatalytic route based on N-substituted auxiliaries that facilitated the conversion of tetrahydroisoquinolines into the corresponding isoquinolines in just three simple steps (yield 71.7% in bulk-solution phase), using unmodified Ru(bpy)3Cl2 photocatalyst, sun energy, atmospheric O2, and at ambient temperature.