H2 Reaction Research Articles

A new global potential energy surface for the BH2 molecule and dynamics studies of the B(2p2P) + H2 reaction

A new global potential energy surface (PES) for the ground state of the BH2 system was constructed using permutation invariant polynomial neural network. In ab initio calculation, the AVQZ basis set and multi-reference configuration interaction method was used. The topographic features of the new PES were discussed in detail. To further clarify the accuracy of PES, the dynamics studies of the B(2p2P) + H2 reaction were carried out using time-dependent wave packet method. The dynamics properties such as reaction probabilities, integral cross sections, differential cross sections (DCSs) and rate constants were reported. The DCSs indicated that the “complex-forming” reaction mechanism plays a dominant role at low collision energies and the forward abstraction mechanism dominates the reaction at high collision energies.

Unravelling the atmospheric and climate implications of hydrogen leakage

In recent years, hydrogen is adopted as a clean source of energy to combat emissions and climate change resulting from fossil fuels. All along the value chain of hydrogen economy, leakage of hydrogen is possible which is expected to have profound impacts on air quality and climate. In the present study, quantum chemistry calculations are employed to understand the atmospheric oxidation mechanism of H2 by OH and O3. The results reveal that oxidation of H2 by both the OH and O3 are both possible and the reaction of H2 with O3 is thermodynamically favoured over its reaction with OH radical. The O3 initiated reaction of H2 is around 80 kcal/mol more exothermic than that of the OH initiated reaction. The O3 initiated reactions of H2 has longer lifetime in the atmosphere when compared to OH initiated reactions. This shows that in addition to undergoing OH radical initiated reaction, where ozone is formed as a product, the H2 can also undergo oxidation by O3 leading to the tropospheric ozone loss processes. Depending upon the background atmospheric concentration, either the OH radical generation is suppressed and methane is formed or the H2 can undergo oxidation with O3. The global warming potential (GWP) weighted emissions for hydrogen leakage incidents reported in the literature is obtained. The emissions are maximum from the hydrogen leakage in transportation and power sectors and minimum in the pipeline leakage. Taken together the atmospheric oxidation potential of H2 by OH radical and O3 oxidation and its GWP weighted emissions, it is clear from the study that the atmospheric and climate implications of H2 leakage is relatively less. The present study is based on molecular level and a rigorous model accounting the atmospheric composition is required for better understanding of the atmospheric and climate implications.

Pd and carbon quantum dots co-decorated TiO2 nanosheets for enhanced photocatalytic H2 production and reaction mechanism

TiO2-based composites are promising photocatalysts for efficient generation of the clean energy, H2, from water splitting. Herein, series of Pd nanoparticles and carbon quantum dots (CQDs) co-decorated TiO2 nanosheets (NSs), Pd-CQDs/TiO2, were designed by overall considering taking advantages of the three components: highly active TiO2 NSs, highly conductive CQDs and electron sink of Pd. Series of photocatalytic experiments were performed and the photocatalytic reaction mechanism was explored. The Pd-0.5CQDs/TiO2 exhibited an excellent photocatalytic hydrogen evolution rate (HER), which is 901.5, 41.8 and 1.7 times higher than those of the bare TiO2, 0.5CQDs/TiO2 and Pd/TiO2, respectively. The synergistic effect of the CQDs and Pd was found responsible for the enhanced photocatalytic activity of the Pd-0.5CQDs/TiO2. Besides, the CQDs was found facilitating complete conversion of Pd2+ to metallic Pd on the surface of TiO2 NSs, which may offer a new thought for design of other composite materials.

New diabatic potential energy surfaces of KH2 system constructed using neural network method

New diabatic potential energy surfaces (PESs) for the KH2 system, related to both ground and first excited states, were constructed using only adiabatic electronic energies. The elements of the diabatic potential energy matrix were determined using neural network (NN) method. Prior to calculation, the symmetry constraints of the coupling term were incorporated into the NN code. A comprehensive comparison was undertaken between the topographic characteristics of the newly constructed diabatic PESs and those previously developed using the molecular properties method. To validate the accuracy of the new diabatic PESs, the dynamics calculations of K(4p2P) + H2 (v 0 = 1, j 0 = 0) reaction were performed based on both new and old diabatic PESs with same parameters. The results indicate that the values based on the new diabatic PESs generally agree well with those from the old ones. In addition, compared with the previous diabatic PESs, the new diabatic PESs can accurately describe the geometric phase effect.

Continuous Unsteady-State De-NOx System via Tandem Water-Gas Shift, NH3 Synthesis, and NH3-SCR under Periodic Lean/Rich Conditions.

The development of urea-free and platinum group metal (PGM)-free catalytic systems for automotive emission control is a challenging task. Herein, we report a new de-NOx system using cyclic feeds of rich and lean gas mixtures with PGM-free catalysts. Initial catalyst screening tests showed that Cu/CeO2 with 5 wt % Cu loading was the most suitable for the water-gas shift reaction (WGS, CO + H2O → CO2 + H2), followed by the selective NH3 synthesis by the NO + H2 reaction. The unsteady-state system under alternating feeds of rich (0.1% NO + 0.5% CO + 1% H2O) and lean (0.1% NO + 2% O2 + 1% H2O) gas mixtures over a mixture of Cu/CeO2 and Cr-exchanged mordenite (CrMOR) showed higher NOx conversion than the steady-state (0.1% NO + 0.35% CO + 0.6% O2 + 1% H2O) reaction between 200 and 500 °C. The de-NOx mechanism under periodical rich/lean conditions was studied by operando infrared (IR) experiments. In the rich period, the WGS reaction on the Cu/CeO2 catalyst yield H2, which reduces NO to NH3 on the Cu/CeO2 catalyst. NH3 is then captured by the Brønsted acid sites of CrMOR. In the subsequent lean period, the adsorbed NH3 acts as a reductant for the selective catalytic reduction of NOx catalyzed by the Cr sites of CrMOR. This study demonstrates a new urea-free and PGM-free catalytic system that can provide an alternative de-NOx technology for automotive catalysis under periodic rich/lean conditions.

Geometric Phase Effects in the H + H2+ Reaction on the Lowest Triplet Ground State.

To our knowledge, this is the first time geometric phase (GP) effects in the H + H2+ reaction on its lowest triplet ground state with collision energies lower than 1.85 eV have been studied using the quantum wave packet method and vector potential approach. We obtained the total reaction probabilities including and not including GP (NGP) effects for J ≤ 4. Visible GP effects could be seen at the lower energy regime but are tiny at the higher one. Moreover, they are more obvious in the product rovibrational state-resolved reaction probabilities, and the relative resonance magnitudes between GP and NGP results change with product rotational state values alternatively. The main reasons are the interferences between the one- and two-transition-state (1-TS and 2-TS) reaction paths, in that at the lower energy regime, the reaction probabilities from the 2-TS pathway show peaks of comparable probabilities compared with that of the 1-TS pathway. In addition, the "out-of-phase" trend observed in the H + H2 reaction does not exist rigorously in this system. Importantly, the visible GP effects exist in this H3+ system, which makes it a very useful candidate reaction for nonadiabatic investigations in both theory and experiment.

P-doped Mn0.5Cd0.5S coupled with cobalt porphyrin as co-catalyst for the photocatalytic water splitting without using sacrificial agents

Photocatalytic water splitting over semiconductors is an important approach to solve the energy demand of human beings. Most photocatalytic H2 generation reactions are conducted in the presence of sacrificial agent. However, the use of sacrificial reagents increases the cost of hydrogen generation. Realizing photocatalytic water splitting for hydrogen production without the addition of sacrificial agents is a major challenge for photocatalysts. The porphyrin MTCPPOMe and P doped MnxCd1-xS make a significant contribution in facilitating the MnxCd1-xS photocatalytic pure water splitting to H2 reaction. Herein, a novel MTCPPOMe/P-MnxCd1-xS (M = 2H, Fe, Co, Ni) composite catalyst which can efficiently split pure water without using sacrificial agents is developed. As a result, the H2 generation rate of CoTCPPOMe/P-Mn0.5Cd0.5S is as high as 2.10 μmol h−1, which is 9.1 and 4.2 times higher than that of Mn0.5Cd0.5S (MCS) and P-Mn0.5Cd0.5S (P-MCS), respectively. P doped MnxCd1-xS inhibits the recombination of photogenerated carriers, and introduction of MTCPPOMe as co-catalyst enhances the reduction capacity. In summary, an efficient and economical photocatalystis prepared for pure water splitting to prepare hydrogen.

Synergistic Activation of Nitrite and Thiocarbonyl Compounds Affords NO and Sulfane Sulfur via (Per)thionitrite (SNO- /SSNO- ).

(Per)thionitrite (SNO- /SSNO- ) intermediates play vital roles in modulating nitric oxide (NO) and hydrogen sulfide (H2 S) dependent bio-signalling processes. Whilst the previous preparations of such intermediates involved reactive H2 S/HS- or sulfane sulfur (S0 ) species, the present report reveals that relatively stable thiocarbonyl compounds (such as carbon disulfide (CS2 ), thiocarbamate, thioacetic acid, and thioacetate) react with nitrite anion to yield SNO- /SSNO- . For instance, the reaction of CS2 and nitrite anion (NO2 - ) under ambient condition affords CO2 and SNO- /SSNO- . A detailed investigation involving UV/Vis, FTIR, HRMS, and multinuclear NMR studies confirm the formation of SNO- /SSNO- , which are proposed to form through an initial nucleophilic attack by nitrite anion followed by a transnitrosation step. Notably, reactions of CS2 and nitrite in the presence of thiol RSH show the formation of organic polysulfides R-Sn -R, thereby illustrating that the thiocarbonyls are capable of influencing the pool of bioavailable sulfane sulfurs. Furthermore, the availability of both NO2 - and thiocarbonyl motifs in the biological context hints at their synergistic metal-free activations leading to the generation of NO gas and various reactive sulfur species via SNO- /SSNO- .

Significant non-adiabatic effects of the K(4s2S) + H2 reaction

The non-adiabatic dynamical calculations of the K(4s2S) + H2(v 0 = 1, 2, j 0 = 0) reaction are carried out using the time-dependent wave packet method. The non-adiabatic dynamics results, such as reaction probabilities and integral cross sections, are calculated and compared with previous adiabatic values. The adiabatic values are several tens of times larger than those of the non-adiabatic results. The non-adiabatic effect becomes stronger with the increase in the number of excited vibrational states. In addition, the excitation of the vibrational states of H2 can increase the reaction probability of the reaction channel. However, the KH product is still barely formed through the K(4s2S) + H2 reaction, even if the H2 molecule is excited to a high vibrational excited state, which also leads to the opposite conclusion from the adiabatic results. The forward-biased differential cross sections indicate that a direct stripping mechanism plays a dominant role in the reaction.

A multi-criteria optimization and decision-making framework of green DME reactor configurations with a focus on high productivity and low CO2 emission rate

The combination of a conventional Dimethyl Ether (DME) reactor with hydrogen perm-selective membrane and effluent recycling creates innovative membrane reactor (MR) configurations that can efficiently improve thermodynamic limits plus low kinetic rates. In the present article, two eco-friendly configurations were applied to the DME conventional reactor (CR) to boost the DME production rate, yield, and selectivity. These configurations comprise two concentric pipes in which in the 1st configuration the fresh synthesis gas is fed to the inner tube side, hydrogen permeates through the reaction zone, and finally the effluent is recycled back to the outer tube, while in the 2nd one, the effluent of outer tube recycled to the inner pipe. The comprehensive 1-D heterogeneous model has an excellent agreement with industrial data. Also, the simulation results reveal that the higher temperature profile in the 2nd configuration is the consequence of more intensification in the reaction zone by H2 injection and proper heat removal which leads to around 9.5 %, 8.22 %, and 10 % increases in the DME production rate, selectivity, and yield compared to CR, respectively. Enjoying reaction output recycling and H2 permeation, the reaction rate of CO and CO2 hydrogenation plus methanol dehydration enhances significantly in the 2nd scheme.According to Euclidean Distance, the optimization results show that the MODE algorithm has a better performance compared to NSGA-II to obtain optimal Pareto Front and also more rapid respect to lower computational time. The LINMAP approach provides a minimum deviation index among all three decision-making algorithms. Employing optimal operation conditions leads to an enhancement of 17 %, 47 %, and 36 % in DME production rate, selectivity, and yield compared to CR. This eco-friendly configuration prevents the emission of 22000 tons of per year CO2 to the atmosphere.

Construction of highly efficient CuS/CdS nanostructure for enhanced solar H2 evolution

The fabrication of efficient photocatalytic system for enhanced production of hydrogen is exceptionally thought-provoking.To address this issue herein we fabricated the CuS/CdS heterostructures by ultrasonication for photocatalytic H2 production. The structural integrity of the produced heterostructure is confirmed by the aid of analytical tools such as X-ray diffraction studies (XRD), Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV–vis DRS), scanning electron microscopy (SEM), High-Resolution Transmission Electron Microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The fabricated CuS/CdS sample exhibited the highest H2 production rate (824 μmol/g) than CuS (67 μmol/g) and CdS (135 μmol/g) under simulated solar illumination. The hydrogen output is noticeably enhanced due to improved absorption of visible light and competent charge carrier partition. It was confirmed by UV–vis diffuse reflectivity and photoluminescence spectra (PL) as charge carrier parting was effective as absorption of visible light was enhanced. A plausible photocatalytic H2 reaction mechanism has been elucidated from increased charge carrier division and visible light absorptivity. This work depicts a new approach for greatly resourceful nano architecture for energy-related applications.

Educational problems in electrochemical thermodynamics

This article reviews educational problems of electrochemical thermodynamics required as introduction to any electrochemistry-related course. Specifically, the most important, electromotive force (EMF) equation, – is generally derived from Guggenheim’s formulation of electrochemical potential. For this aim the more general equation for equilibrium between phases is introduced. Special attention is given to the measurement of electrode potential. Potential drop across metal|metal contacts, usually displayed in potential profiles of electrochemical cells, can be excluded from them. The conclusion is based on Lord Kelvin’s formulation of the case, when metals are in contact, as “metallic zero”. Concerning absolute potentials, for the cases when the electrode material does not participate in electrochemical reaction, it can be calculated from the Gibbs free energy of the corresponding chemical reaction occurring in solution. Accordingly, the absolute hydrogen electrode potential is determined by thermodynamics of H+/H2 reaction.

Configurationally Nonselective Aquation of a Mononuclear Ru(II) Chloro Complex to Aquo Complex Isomers with Distinctive Aspects in Photoisomerization, Redox, and Catalytic Water Oxidation.

distal-[Ru(EtOtpy)(pynp)Cl]+ (d-EtO1Cl) (EtOtpy = 4'-ethoxy-2,2':6',2″-terpyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine), and distal/proximal-[Ru(EtOtpy)(pynp)OH2]2+ (d/p-EtO1H2O) complexes were newly synthesized to investigate the synergistic influence of the geometric configuration coupled with substituent introduction of an ethoxy (EtO) group on the physicochemical properties and reactions of the Ru(II) complexes. Configurationally nonselective aquation of d-EtO1Cl was uniquely observed to form d/p-EtO1H2O isomers in water, in contrast to configurationally selective aquation of distal-[Ru(tpy)(pynp)Cl]+ (d-1Cl, tpy = 2,2':6',2″-terpyridine) without the EtO group [Yamazaki, H. . J. Am. Chem. Soc. 2011, 133, 8846-8849].The kinetic profiles of the aquation reactions of d-EtO1Cl were well analyzed using a sequential reversible reaction model assuming the reversible interconversion between d/p-EtO1H2O isomers via d-EtO1Cl. The observed equilibrium constant (Kiso) of isomerization between p/d-EtO1H2O was calculated from the kinetic analysis as Kiso = 0.45, which is consistent with the final concentration ratio (1:0.43) of p/d-EtO1H2O generated in the aquation reaction of d-EtO1Cl. The irreversible photoisomerization from d-EtO1H2O to p-EtO1H2O was observed in water with an internal quantum yield (Φ) of 0.44% at 520 nm. Electrochemical measurements showed that d-EtO1H2O undergoes a 2-step oxidation reaction of 1H+-coupled 1e- processes of RuII-OH2/RuIII-OH and RuIII-OH/RuIV═O at pH 1.3-9.7, whereas p-EtO1H2O undergoes a 1-step oxidation reaction of a 2H+-coupled 2e- process of RuII-OH2/RuIV═O in the pH range of 1.8-11.5. Any redox potential of d/p-EtO1H2O isomers was decreased by the electro-donating EtO substitution, compared with distal/proximal-[Ru(tpy)(pynp)OH2]2+ (d/p-1H2O). The turnover frequency (kO2 = 1.7 × 10-2 s-1) of d-EtO1H2O for water oxidation catalysis is higher than that (3.5 × 10-4 s-1) of p-EtO1H2O by a factor of 48.6. The kO2 value (1.7 × 10-2 s-1) for d-EtO1H2O is 4.5-fold higher than those of d-1H2O (3.8 × 10-3 s-1). The higher kO2 value of d-EtO1H2O compared with d-1H2O could be explained by the fast oxidation rate from RuIV═O to RuV═O involved in the rate-determining step due to the electron-donating EtO group.

Effect of secondary phases on the selectivity of CO2 reduction properties of Mg-based alloy

It is a great challenge to achieve adsorption and desorption of H2 on magnesium-based metal materials under room temperature and ambient pressure. To address this problem, we proposed a strategy to tailing the secondary phases in Mg alloy to directly drive catalytic reactions, and utilizing ambient sunlight-driven solar energy to convert heat energy to promote the adsorption and reaction of H2 and CO2 gas. Thus, the magnesium-based materials can convert CO2 into CO and CH4 under sunlight. Here we report a magnesium-based material LiAlSiO4/Mg, where MgO/Mg interface and Li4SiO4 particles play different roles in production CO or CH4 under varied solar energy. The large amount of MgO reduced the adsorption of H2 on Mg, while the existence of Li4SiO4 enhanced the production rate of CO. This work explores the functional applications of main-group alloys and paves the way towards ambient sunlight-driven adsorption and use of hydrogen.

Development of a Simple Electroless Method for Depositing Metallic Pt-Pd Nanoparticles over Wire Gauge Support for Removal of Hydrogen in a Nuclear Reactor.

Electroless noble metal deposition on the conducting substrate is widely used to obtain the desired film or coating on the substrate of interest. Wire-gauge-based Pt/Pd/Pt-Pd (individually, sequentially, and simultaneously deposited) catalysts have been developed using formaldehyde and sodium formate as reducing agents. Various surface pretreatment methods like SnCl2 + PdCl2 seeding, oxalic acid etching, and HCl activation (etching) have been employed to obtain the desired noble metal coating. Minimum time duration was observed for simultaneously deposited catalysts using formaldehyde as a reducing agent. Prepared catalysts were characterized for noble metal deposition, coating kinetics, surface morphology, and binding energy. The catalyst was found to be active for H2 and O2 recombination reactions for hydrogen mitigation applications in nuclear reactors.

Co-reactant confined and vertically ordered silica nanochannel regulated electrochemiluminescence for homogeneous detection of miRNA

Electrochemiluminescence (ECL) arises from the collisional annihilation between the electro-excited luminophore and co-reactant. Most ECL-based bioassays require extensive free co-reactants that collide with luminophores randomly. Herein, the N,N-dimethylaniline (DMA) group was electro-grafted on the ITO electrode surface as the bottom co-reactant layer, and the vertically ordered mesoporous silica film (VMSF) was prepared as the upper layer to regulate the accessibility of Ru(bpy)32+. Thus, the dual-layer functionalized VMSF/N-ITO was newly built for the controllable ECL study. Relevant conditions, including the DMA electro-grafting, VMSF thickness, buffer concentration and pH value, were discussed to improve the ECL efficiency. Based on the VMSF/N-ITO platform, a homogeneous ECL bioassay was developed for miRNA-21 detection. The target nucleotide sequence induced the hybridization chain reaction (HCR) of probes H1 and H2 to absorb free Ru(bpy)32+ as much as possible. Residual Ru(bpy)32+ permeated the VMSF nanochannels to collide with the DMA co-reactant in producing an ECL response. There was a linear relationship between ∆ECL intensity and logarithmic concentration of miRNA-21 in the 1 fM ∼ 100 pM range, and the detection limit was 0.25 fM. The developed approach was probes immobilization-free, highly sensitive, and anti-interference, opening a new avenue for ECL-based bioassays.

Superiority of BNCT Treatment Planning Metrics Achieved Using Novel vs. Reference (BPA-F) Pharmaceuticals in Head and Neck Locations

Several novel boron delivery compounds currently under investigation by our group have demonstrated formulation, biodistribution, and dose response benefits in small animal models [1]. In this study we analyze the potential clinical impact of these compounds for boron neutron capture therapy (BNCT) in human patients. Pharmacokinetic models were used to estimate the tumor and normal tissue boron concentrations after continuous infusion of the novel compounds and BPA-F. Patient model segmentation, material assignment, and alignment of one or more treatment beams were exported from a commercial treatment planning system (TPS) to a novel dose calculation tool. This information was used to generate a voxelized model that incorporated the source, beam shaping assembly, collimator, and patient materials so that the full albedo effect was included in each dose calculation. Physical dose from 10B(n,α), 14N(n,p), 1H(n,n') interactions plus gamma rays from 1H(n,γ) and other reactions within the patient and treatment equipment were calculated by Monte Carlo transport of particles originating in a pre-generated phase space at the cover surface. RBE and CBE weighting factors are applied to combine these four physical dose volumes into an equivalent dose volume, and these five dose volumes were passed back to the TPS for evaluation. Tumor dose was increased by up to 2.6x for the novel compounds while normal tissue doses were constant or slightly reduced in comparison to BPA-F plans. Alternatively, for identical tumor dose the normal tissue doses and treatment time were reduced by up to 2.6x. In addition, in some cases it was possible to generate a single beam treatment plan using the new compounds that delivered higher tumor dose and lower normal tissues doses than a multiple beam plan using BPA-F. This study demonstrates both dosimetric and practical benefits of the new compounds in comparison to BPA-F, including the potential to deliver treatment using fewer beam directions and correspondingly easier treatment setups and higher patient throughput. The potential of these compounds to extend the range of clinical indications for BNCT is also discussed. These results motivate upcoming experimental testing of the key assumptions involved in their calculation.

Hydrogen from industrial aluminium scraps: Hydrolysis under various conditions, modelling of pH behaviour and analysis of reaction by-product

The study explores the feasibility of utilizing aluminium scrap waste from the construction industry for hydrogen production via hydrolysis. Specifically, the study involves a primary analysis of aluminium scrap waste and the impact of various reaction parameters, such as NaOH molarity, reaction temperature, amount of Al scrap, solvent quantity, and the reaction vessel insulation, and their effects on the reaction rate, H2 yield, and by-product formation. The pH of the reaction solution was continuously monitored to determine the reaction mechanism, while the structure of the by-product was analysed at two stages: after removal and drying, and after removal and washing. Our findings indicate that increasing the reaction temperature has the most significant influence on the reaction kinetics. Insulating the reaction vessel ensured self-promoted hydrogen production due to the heat generated from the exothermic reaction inside the vessel, resulting in an approximate temperature increase of 5 °C for all tested reaction solution molarities compared to non-insulated conditions. The pH measurements were conducted in two different ways. The first one involved immersing a pH probe directly into an open reaction container. The second approach utilized a closed reaction container under isothermal conditions, where both the pH and H2 yield were measured simultaneously. In addition, the obtained data was compared between the measured pH values and the predictions generated by models utilizing the measured H2 evolution in order to forecast the pH behaviour. The modelling results recognize and suggest the existence of separate reaction phases or zones, each characterized by distinct influences on the pH level.

Academic Stress in the Psychological Well-being of Higher Education Students

Academic Stress in the Psychological Well-being of Higher Education Students

Non-adiabatic dynamical studies of the Rb(52P) + H2(X1[formula omitted]) → RbH(X1Σ+) + H(2s) reaction based on new diabatic potential energy surfaces

The reaction of Rb(52P) atom with H2 molecule is studied using time-dependent wave packet method based on the newly reported diabatic potential energy surfaces. The dynamics properties such as reaction probabilities, integral cross sections, differential cross sections (DCSs) and so on are calculated at state-to-state level of theory. In addition, the effect of vibrational excitation of reactant is considered in the calculations. The results indicate that the vibrational excitation of reactant can significantly increase the reaction probability and the RbH molecule is hardly formed when the reactant H2 molecule is in the ground state. The vibrational excitation of H2 molecule promotes the reaction more effectively than translational energy. The forward biased DCSs indicate that the stripping mechanism dominates the reaction.