Kinetic Evidence Research Articles

Theoretical Kinetic Studies on Thermal Decomposition of Glycerol Trinitrate and Trimethylolethane Trinitrate in the Gas and Liquid Phases.

Glycerol trinitrate (NG) and trimethylolethane trinitrate (TMETN), as typical nitrate esters, are important energetic plasticizers in solid propellants. With the aid of high-precision quantum chemical calculations, the Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation theory and the transition state theory have been employed to investigate the decomposition kinetics of NG and TMETN in the gas phase (over the temperature range of 300-1000 K and pressure range of 0.01-100 atm) and liquid phase (using water as the solvent). The continuum solvation model based on solute electron density (SMD) was used to describe the solvent effect. The thermal decomposition mechanism is closely relevant to the combustion properties of energetic materials. The results show that the RO-NO2 dissociation channel overwhelmingly favors other reaction pathways, including HONO elimination for the decomposition of NG and TMETN in both the gas phase and liquid phase. At 500 K and 1 atm, the rate coefficient of gas phase decomposition of TMETN is 5 times higher than that of NG. Nevertheless, the liquid phase decomposition of TMETN is a factor of 5835 slower than that of NG at 500 K. The solvation effect caused by vapor pressure and solubility can be used to justify such contradictions. Our calculations provide detailed mechanistic evidence for the initial kinetics of nitrate ester decomposition in both the gas phase and liquid phase, which is particularly valuable for understanding the multiphase decomposition behavior and building detailed kinetic models for nitrate ester.

Practical Strategy for Arsenic(III) Electroanalysis without Modifier in Natural Water: Triggered by Iron Group Ions in Solution

Significant progress has been made in nanomaterial-modified electrodes for highly efficient electroanalysis of arsenic(III) (As(III)). However, the modifiers prepared using some physical methods may easily fall off, and active sites are not uniform, causing the potential instability of the modified electrode. This work first reports a promising practical strategy without any modifiers via utilizing only soluble Fe3+ as a trigger to detect trace-level As(III) in natural water. This method reaches an actual detection limit of 1 ppb on bare glassy carbon electrodes and a sensitivity of 0.296 μA ppb-1 with excellent stability. Kinetic simulations and experimental evidence confirm the codeposition mechanism that Fe3+ is preferentially deposited as Fe0, which are active sites to adsorb As(III) and H+ on the electrode surface. This facilitates the formation of AsH3, which could further react with Fe2+ to produce more As0 and Fe0. Meanwhile, the produced Fe0 can also accelerate the efficient enrichment of As0. Remarkably, the proposed sensing mechanism is a general rule for the electroanalysis of As(III) that is triggered by iron group ions (Fe2+, Fe3+, Co2+, and Ni2+). The interference analysis of coexisting ions (Cu2+, Zn2+, Al3+, Hg2+, Cd2+, Pb2+, SO42-, NO3-, Cl-, and F-) indicates that only Cu2+, Pb2+, and F- showed inhibitory effects on As(III) due to the competition of active sites. Surprisingly, adding iron power effectively eliminates the interference of Cu2+ in natural water, achieving a higher sensitivity for 1-15 ppb As(III) (0.487 μA ppb-1). This study provides effective solutions to overcome the potential instability of modified electrodes and offers a practical sensing platform for analyzing other heavy-metal anions.

Transition State Stabilization by SCF2 -H⋅⋅⋅O Bifurcated Hydrogen Bond.

The difluoromethylthio group (SCF2 H), which is generally considered a highly lipophilic weak hydrogen bonding donor, has attracted special interest from the pharmaceutical and agrochemical industry. Remarkably, there have been relatively few literature investigations of SCF2 H hydrogen bonding interactions. Here, we report the determination of the hydrogen bond acidity parameter A of the SCF2 H in the most popularly used electrophilic difluoromethylthiolating reagent. We present kinetic and computational evidence of the RSCF2 -H⋅⋅⋅O2 bifurcated hydrogen bond for stabilizing the SCF2 H-transferring transition state, which could cause a reversal of apparent electrophilic reactivity of difluoromethylthiolating and trifluoromethylthiolating reagents. Solvent effects on the RSCF2 -H⋅⋅⋅O2 bifurcated hydrogen bonds will also be discussed.

Ultrastructural and kinetic evidence support that thick filaments slide through the Z-disc.

How myofilaments operate at short mammalian skeletal muscle lengths is unknown. A common assumption is that thick (myosin-containing) filaments get compressed at the Z-disc. We provide ultrastructural evidence of sarcomeres contracting down to 0.44 µm-approximately a quarter of thick filament resting length-in long-lasting contractions while apparently keeping a regular, parallel thick filament arrangement. Sarcomeres produced force at such extremely short lengths. Furthermore, sarcomeres adopted a bimodal length distribution with both modes below lengths where sarcomeres are expected to generate force in classic force-length measurements. Mammalian fibres did not restore resting length but remained short after deactivation, as previously reported for amphibian fibres, and showed increased forces during passive re-elongation. These findings are incompatible with viscoelastic thick filament compression but agree with predictions of a model incorporating thick filament sliding through the Z-disc. This more coherent picture of mechanical mammalian skeletal fibre functioning opens new perspectives on muscle physiology.

Kinetic and molecular evidence for DON transformation in the deep vadose zone: Important implications for soil nitrogen budgeting and groundwater nitrate management

The neglect of dissolved organic nitrogen (DON), especially with regard to its transformation in the deep vadose zone, can result in high uncertainty surrounding estimated nitrogen (N) leaching losses to groundwater. This study provided kinetic and molecular evidence for DON transformation in the deep vadose zone by focusing on a typical agricultural area in Eastern China. DON was as important as inorganic N for N stocks, and 28.04% ∼ 71.94% of DON was sealed in the deep vadose zones (i.e., > 1 m depth). Soil N mineralization rates gradually decreased as incubation proceeded, and aerobic condition was more favorable for soil N mineralization. Both shallow and deep vadose zones could be potential hotspots for N mineralization, and the trend of N mineralization rate varying with soil depth was site-specific. Fourier-transform ion cyclotron resonance mass spectrometry data revealed that DON was dominated by lipids before incubation, whereas lignins were dominant after incubation was complete. Lignin-like compounds were not intrinsically recalcitrant, instead persisting in soil due to concurrent removal, transformation, and formation. DON transformation occurred along the entire soil profile regardless of redox conditions, potentially having different microbe-mediated pathways. These findings emphasize the implications of considering DON transformation in the deep vadose zone for soil N budgeting and groundwater nitrate management.

Hypercrosslinked waste polymers as adsorbents for O2/N2 separation

Waste polymer materials offer a lot of promise for recycling or enhancement in terms of the environment. HCPs (hypercrosslinked polymers) are an excellent contender for recycling polymers in environmental applications. We employed waste-expanded polystyrene and waste polycarbonate as precursors to make HCPs adsorbents for O2/N2 adsorption. Characterization analysis were performed to determine the adsorbents' morphology and structure. The fine adsorbent was waste-expended polystyrene which had been synthesized at 45 °C for 12 h and had a surface area of 802.84 (m2/g), an average pore diameter of 2.86 nm, and a micropore volume of roughly 184.46 (cm3/g). The Sips isotherm and Elovich kinetic models provided the best agreement (R2 = 0.9994), according to experimental data. At 5 °C and 10 bar, the fine adsorbent had the highest O2 and N2 adsorption, with 12.78 and 7.67 (mmol/g), respectively. Eventually, the kinetic evidence demonstrated that the process physically occurred. Over nine cycles, the sorbent's ability for adsorption decreased by about 5%, indicating a high degree of reusability for air separation. The method described in this study can be considered a promising approach to air separation and purification by eco-friendly hypercrosslinked polymers.

Kinetics and the Mechanism of Reduction of Hexacholoroiridate (IV) by Carcinogenic Nicotine as an Alkaloid in Aqueous Solutions with the Determination of Ionization Constant of Nicotine

Background: Nicotine (NIC) is a lipid-soluble alkaloid found predominantly in tobacco products, including cigarettes, cigars, and oral tobacco products such as snuff and chewing tobacco. Since nicotine substrate is the major constituent of tobacco smoke, it may cause negatively impacted problems for human healthcare, which keeps many users hooked. Method: A spectrophotometric technique has been applied to investigate the kinetics of reductoin hexachloroiridate (IV) as an inert one-equivalent oxidant by carcinogenic nicotine (NIC) in aqueous perchlorate solutions. Results: First-order in [IrCl6]2- and fractional-first-order concerning the nicotine concentration has been revealed. Kinetic evidence for forming a 1:1 intermediate complex between the NIC and [IrCl6]2- before the rate-determining step was confirmed. Conclusion: The ionization constants of nicotine were evaluated from the kinetic data and are 8.57x10-4 and 4.57 x 10-4 moldm-3 at an ionic strength of 0.5 moldm-3 and 30°C and 40°C, respectively. The activation parameters have been deduced from the kinetic results of the temperature dependence of rate constants. A plausible reaction mechanism for the redox reaction is suggested and discussed. Nicotinic acid (Vitamin B3) was formed as an oxidation product of nicotine oxidation.

Kinetics of Bovine leukemia virus aspartic protease reveals its dimerization and conformational change

The retropepsin (PR) of the Bovine leukemia virus (BLV) plays, as in other retroviruses, a crucial role in the transition from the non-infective viral particle to the infective virion by processing the polyprotein Gag. PR is expressed as an immature precursor associated with Gag, after an occasional −1 ribosomal frameshifting event. Self-hydrolysis of PR at specific N- and C-terminal sites releases the monomer that dimerizes giving rise to the active protease. We designed a strategy to express BLV PR in E. coli as a fusion protein with maltose binding protein, with a six-histidine tag at its N-terminal end, and bearing a tobacco etch virus protease hydrolysis site. This allowed us to obtain soluble and mature recombinant PR in relatively good yields, with exactly the same amino acid composition as the native protein. As PR presents relative promiscuity for the hydrolysis sites we designed four fluorogenic peptide substrates based on Förster resonance energy transfer (FRET) in order to characterize the activity of the recombinant enzyme. These substrates opened the way to perform kinetic studies, allowing us to characterize the dimer-monomer equilibrium. Furthermore, we obtained kinetic evidence for the existence of a conformational change that enables the interaction with the substrate. These results constitute a starting point for the elucidation of the kinetic properties of BLV-PR, and may be relevant not only to improve the chemical warfare against this virus but also to better understand other viral PRs.

Charting the Atomic C Interaction with Transition Metal Surfaces.

Carbon interaction with transition metal (TM) surfaces is a relevant topic in heterogeneous catalysis, either for its poisoning capability, for the recently attributed promoter role when incorporated in the subsurface, or for the formation of early TM carbides, which are increasingly used in catalysis. Herein, we present a high-throughput systematic study, adjoining thermodynamic plus kinetic evidence obtained by extensive density functional calculations on surface models (324 diffusion barriers located on 81 TM surfaces in total), which provides a navigation map of these interactions in a holistic fashion. Correlation between previously proposed electronic descriptors and ad/absorption energies has been tested, with the d-band center being found the most suitable one, although machine learning protocols also underscore the importance of the surface energy and the site coordination number. Descriptors have also been tested for diffusion barriers, with ad/absorption energies and the difference in energy between minima being the most appropriate ones. Furthermore, multivariable, polynomial, and random forest regressions show that both thermodynamic and kinetic data are better described when using a combination of different descriptors. Therefore, looking for a single perfect descriptor may not be the best quest, while combining different ones may be a better path to follow.

Radiofrequency Plasma‐Assisted Pulsed Laser Deposited Pt/TiOxNy Coatings on Multi‐Walled Carbon Nanotubes as Gas Diffusion Electrodes for the Oxygen Reduction Reaction

AbstractThis study reports on the fabrication and characterization of novel multilayered electrocatalyst nanostructures for the oxygen reduction reaction (ORR). Thin titanium oxynitride (TiOxNy) coatings are deposited on a forest of multi‐walled carbon nanotubes (MWCNTs), directly grown on a stainless‐steel mesh, by capacitively coupled radiofrequency plasma‐assisted pulsed laser deposition (RF‐PAPLD) in a N2 environment. The resulting high‐surface‐area binder‐free electrode is further coated with a low quantity of well‐dispersed Pt nanoparticles (NPs) by PLD in an inert atmosphere. High‐speed imaging of the laser‐induced plasma expansion provided evidence of a higher kinetics of the expanding plume at higher RF plasma powers, changing the morphology of the TiOxNy coatings. X‐ray photoelectron spectroscopy demonstrated that the coatings are homogeneous throughout their thickness, where the TiN, TiON, and TiO bonds exist in all samples. The oxygen content of the coating increases with the RF plasma power. Both TiOxNy/MWCNT and Pt/TiOxNy/MWCNT nanostructures are tested in a gas diffusion electrode setup to evaluate their activity in the ORR. The results showed the superior activity of the Pt/TiOxNy‐0.03 Torr‐30 W/MWCNT, reaching the highest current density of 180 mA cm−2, while the commercial Pt/C electrode with the same Pt loading yielded 105 mA cm−2 at the potential of 0.5 V.

Evidence for interface-rate limited densification kinetics at Al2O3-GdAlO3 interfaces characterized by in situ ultrahigh temperature transmission electron microscopy

The sintering behavior of single Al2O3 particles resting on GdAlO3 is characterized using in situ transmission electron microscopy imaging. In bicrystal experiments, particles with lower Al2O3-GdAlO3 phase boundary energies shrink via Ostwald ripening with no evidence of densification that would result from an atomic flux along the interface. Particles with higher Al2O3-GdAlO3 phase boundary energies undergo intermittent rigid body motion associated with an interfacial flux mediated by interfacial line defects, e.g. disconnections. Long incubation periods elapse between these comparatively rapid rigid body motion events. The interfacial diffusivity during each event agrees with the magnitude of interfacial diffusion obtained from independent measurements of interfacial diffusivity. The results from the model experiments suggest that capillarity driven interfacial strain mediation, e.g. densification during sintering, is interface rate limited at the driving forces investigated.

The chlorophenoxy herbicide MCPA: A mechanistic basis for the observed differences in toxicological profile in humans and rats versus dogs.

1. Metabolism data for MCPA in rat, dog and human shows a single oral dose is quantitatively and rapidly absorbed with evidence of non-linear kinetics at >100 mg/kg bw. The extent of metabolism is low and consistent between rat and human, with substantially higher metabolic conversion in dog. Parent accounts for 50-67% dose in rat, ∼40% in human and 2-27% in dog. No dog specific metabolite is apparent. 2. In rat and human, MCPA and metabolites are rapidly eliminated in urine (65-70% within 24 hours) but in dog, excretion is via urine and faeces (20-30% within 24 hours), with renal excretion saturating between 5 and 100 mg.kg bw. 3. The species difference in excretion is reflected in pharmacokinetics. Terminal half-life is similar in rat and human (15-17 hour) but higher in dog (47 hour). Modelling shows species differences in single dose kinetics profoundly affect systemic exposure following repeat dosing. 4. The difference in renal excretion and systemic exposure of MCPA between dogs and rats has been attributed to species differences in active transporters (OAT1/OAT3). A new in vitro flux study in renal proximal tubules supports this hypothesis with net secretion in rat and human of a similar magnitude but significantly less in dog.

Deinococcus radiodurans RecOR Proteins Stimulate RecA Filament Formation on SSB‐Bound Single‐stranded DNA

Deinococcus radioduransis a radiation resistant organism with the ability to survive hundreds of DNA double‐strand breaks. The compacity to withstand such a detrimental type of DNA break stems from the efficiency of the DNA repair machinery of this organism. D. radioduransrecombination mediator proteins RecO and RecR have been shown to be required for radiation resistance in this organism. In E. colithe RecOR proteins have been reported to stimulate RecA filament nucleation onto SSB‐bound single‐stranded DNA (ssDNA) through displacement of the SSB protein. However, how D. radioduransRecO and RecR proteins work to mediate RecA filament formation is not well understand. In this study, we further elucidate the biochemical mechanism of RecOR function; the kinetic evidence demonstrates that D. radiodurans RecOR alter the rate of ATP hydrolysis by the RecA protein when bound to ssDNA regardless of the presence of SSB protein. This effect has not been previously described for other homologous recombination systems. We believe that D. radioduransRecOR functions to stimulate RecA nucleation to ssDNA directly and independently of SSB protein. Potential mechanisms for this kinetic stimulation will be discussed.

Intriguing Chloride: Involvement of Chloride Ions in Proton Transfers.

The proton transfer from carbon to a chloride ion and the proton transfer to a molecule of water promoted by chloride ions in the acid-catalyzed formation of hydroxamic acids from aldehydes and substituted nitrosobenzenes in mixed solvents have been proposed based on experimental and theoretical investigations. The formation of uncommon contact ion pairs consisting of the nitrosocarbinolic cation intermediate and a chloride anion, followed by the proton transfer from a C-H moiety of the cation intermediate, has been proposed. The influence of chloride on the proton transfer to a water molecule of the solvent-separated nitrosocarbinolic-cation–chloride ion pair was investigated too. The insights are based on the obtained kinetic and other evidence with regard to (1) influences of chloride anions on the observed reaction rates and primary kinetic isotope effects (PKIE) in the reaction; (2) the observed variation of the PKIE-s and rates of the reaction when perchlorate anions are present along with the chloride ions; and (3) the consideration of a model of the nitrosocarbinolic-cation-intermediate—chloride ion pair and transition structure for the proposed proton transfers based on the ab initio calculations.

Transient and gradient analyses of depolarization criteria. Valuable tools in chloride‐induced rebar corrosion monitoring

AbstractThe aim of this study is to elucidate suitable methods of corrosion monitoring for chloride‐induced rebar corrosion in cracked concrete. Depolarization gradients and transients provide evidence for the electrode kinetics at the steel–concrete interface and the geometry of the macrocell. In the present study, a set of cracked, short‐term chloride‐exposed, reinforced concrete specimens is investigated in terms of their corrosion activity. Primarily, the depolarization behavior was observed by short‐term high‐frequency measurements, allowing for cost‐effective measurement campaigns and robust results. All measurement intervals are split apart via a gradient analysis to enable a congruent, numerical transient analysis. Since the geometry of macrocells in rebar corrosion follows the model of a series of ohmic resistances with a parallel connection of a diffusion‐controlled capacitor and an ohmic resistance, the transient of each depolarization curve with unit time in seconds provides evidence for the present electrode kinetics and macrocell geometry. According to the time, which is consumed until a certain state of depolarization is reached, transient modeling can be used to predict corrosion activity as a function of chloride ingress.

A Night-Time Edge Site Intermediate in the Cyanobacterial Circadian Clock Identified by EPR Spectroscopy.

As the only circadian oscillator that can be reconstituted in vitro with its constituent proteins KaiA, KaiB, and KaiC using ATP as an energy source, the cyanobacterial circadian oscillator serves as a model system for detailed mechanistic studies of day-night transitions of circadian clocks in general. The day-to-night transition occurs when KaiB forms a night-time complex with KaiC to sequester KaiA, the latter of which interacts with KaiC during the day to promote KaiC autophosphorylation. However, how KaiB forms the complex with KaiC remains poorly understood, despite the available structures of KaiB bound to hexameric KaiC. It has been postulated that KaiB-KaiC binding is regulated by inter-KaiB cooperativity. Here, using spin labeling continuous-wave electron paramagnetic resonance spectroscopy, we identified and quantified two subpopulations of KaiC-bound KaiB, corresponding to the "bulk" and "edge" KaiBC sites in stoichiometric and substoichiometric KaiBiC6 complexes (i = 1-5). We provide kinetic evidence to support the intermediacy of the "edge" KaiBC sites as bridges and nucleation sites between free KaiB and the "bulk" KaiBC sites. Furthermore, we show that the relative abundance of "edge" and "bulk" sites is dependent on both KaiC phosphostate and KaiA, supporting the notion of phosphorylation-state controlled inter-KaiB cooperativity. Finally, we demonstrate that the interconversion between the two subpopulations of KaiC-bound KaiB is intimately linked to the KaiC phosphorylation cycle. These findings enrich our mechanistic understanding of the cyanobacterial clock and demonstrate the utility of EPR in elucidating circadian clock mechanisms.

Kinetic evidence for methanol trimer assisted proton transfer: Transient absorption study on excited triplet state of 4-hydroxy-4′-nitrobiphenyl

Hydroxyaromatic compounds have a wide range of applications in catalytic synthesis and biological processes due to their enhanced acidity upon photo-excitation. Most hydroxyaromatic compounds with a medium excited state acidity are unable to deprotonate in non-aqueous solvents such as alcohol due to their short-lived excited singlet states. The nitro group in 4-hydroxy-4′-nitrobiphenyl (NO2-Bp-OH) increases the spin-orbit coupling between excited singlet states and the triplet state, resulting in ultrafast intersystem crossing and the formation of the long-lived lowest excited triplet state (T1) with a high yield. Using transient absorption spectroscopy and kinetic analysis, we discover that, despite its moderate acidity, the T1 state of NO2-Bp-OH (3NO2-Bp-OH) is able to transfer proton to methanol. Following the formation of the hydrogen-boned complex between 3NO2-Bp-OH and three methanol molecules in a consecutive process, proton transfer occurs very fast. This finding suggests that the long lifetime of the photoacid excited state allows for the formation of alcohol oligomer with sufficient basicity to induce photoacid deprotonation.

High-Pressure Operation of Proton-Conducting Electrolyzers for High-Temperature Water Splitting

In this work, we present our progress on high-temperature water splitting (HTWS) and hydrogen production at elevated pressure using proton-conducting ceramics. The electrochemical performance of the proton-conducting electrolyzer unit-cell stack is analyzed at 550 °C and pressures up to 12 bar.Proton-conducting ceramics are a promising new class of electrochemical cells due to their high proton conductivity at intermediate temperatures in comparison to more-conventional solid-oxide or molten-carbonate counterparts. Materials exploration continues for fabricating proton conducting cells to achieve better electrochemical performance during operation. Recently, lower ohmic resistance and degradation rates have been observed using the highly proton-conductive and chemically stable perovskite BaCe0.4 Zr0.4 Y0.1 Yb0.1 O3−δ (BCZYYb4411). In this study we work with a composite of Ni–BZCYYb4411 as the fuel electrode (cathode), BCZYYb4411 as the electrolyte and BCFZY as the steam electrode (anode). The cathode and electrolyte layers of the membrane-electrode assemblies used in this study are synthetized using the solid-state reactive sintering (SSRS) method. SSRS is an attractive MEA-fabrication method, as it greatly reduces the number of costly and time-consuming high-temperature sintering processes. During SSRS, single-phase protonic-ceramic perovskite is formed from parent oxides during high-temperature co-sintering of the anode-electrolyte layers. This is in contrast to more-traditional processing, in which the desired phase is first formed in powder form through calcination of parent oxides, while MEA formation is executed in follow-on high-temperature sintering steps.The cathode support is formed by dry-pressing to produce a 57-mm-dia x 1.5-mm-thick disc. The electrolyte (~ 10 mm) layer is deposited using an ultrasonic spray atomizer. The process control and narrow particle size distribution delivered by the ultrasonic atomizer consistently produces a high-density electrolyte, while minimizing thickness. We are now extending the use of ultrasonic spray deposition to other critical components such as the air-steam electrode and interfacial layers.As shown in Figure 1a, the protonic-ceramic membrane-electrode assembly (MEA) is bonded to a composite ceramic frame and assembled into a sealed cell stack with metallic interconnects, current collectors, sealing gaskets and end plates. The stack is placed in a preloaded spring-based mechanical compression system that axially compresses the electrolyzer stack while avoiding any direct compression of the MEA. The assembly is placed in a sealed vessel (Figure 1b); anode and cathode gas pressures are balanced across the MEA, and with the surrounding inert vessel gas (N2). Downstream back-pressure regulators maintain electrolyzer and vessel pressures to minimize the risk of cell fracture.Despite the challenges associated with high pressure operation, this technology is key to address some of the main issues associated with proton conducting ceramics. Higher pressure operation should lead to higher efficiencies by decreasing the electron hole concentration in the electrolyte usually associated with the electron leakage problem. Also, electrode activity can be enhanced at higher pressures, enabling higher currents at lower driving voltages. Figure 1c shows an increased electrolyzer performance of almost 50% when the operating pressure is raised to 12.5 bar. This is evidence of the better kinetics and lower power required to electrolyze at higher pressures.In parallel, the high-pressure protonic-ceramic electrolyzer delivers a pure, dry, pressurized hydrogen product stream that does not require downstream separation processes. Pressurized operation reduces downstream compression needs. Elevated-pressure operation is also beneficial for the synthesis of electrofuels, where green hydrogen is transformed into higher-value chemical. These chemistries often require high temperatures and pressures to achieve meaningful production rates. Ammonia serves as an example, the second-most-produced global chemical that contributes nearly 1.5% of global annual CO2 emissions. We are currently integrating our high-pressure electrolysis operation with ruthenium-based catalysts for electrochemical ammonia synthesis. In this talk, our progress in electrochemical energy storage with proton-conducting ceramics will be reviewed. Figure 1

DFT and kinetic evidences of the preferential CO oxidation pattern of manganese dioxide catalysts in hydrogen stream (PROX)

The oxidation functionality of Mn(IV) sites has been assessed by density functional theory (DFT) analysis of adsorption and activation energies of CO, H2 and O2 on a model Mn4O8 cluster. DFT calculations indicate that Mn(IV) atoms prompt an easy CO conversion to CO2 via a reaction path involving both catalyst and gas-phase oxygen species, while much greater energy barriers hinder H2 oxidation. Accordingly, a MnCeOx catalyst (Mnat/Ceat, 5) with large exposure of Mn(IV) sites shows a remarkable CO oxidation performance at T ≥ 293 K and no H2 oxidation activity below 393 K. Empiric kinetics disclose that the catalyst-oxygen abstraction step determines both CO and H2 oxidation rate, although different activation energies favor the preferential oxidation (PROX) pattern of the studied catalyst (353–423 K). Conversion-selectivity of 100%, high stability during 72 h reaction time and moderate inhibiting effects of water and CO2 feeding reveal the potential of MnO2 materials as efficient, low-cost and robust PROX catalysts.

Synthesis, Structure, and Ammonia Oxidation Catalytic Activity of Ru-NH3 Complexes Containing Multidentate Polypyridyl Ligands.

Ammonia (electro)oxidation with molecular catalysts is a rapidly developing topic with wide practical applications ahead. We report here the catalytic ammonia oxidation reaction (AOR) activity using [Ru(tda-κ-N3O)(py)2], 2, (tda2- is 2,2':6',2''-terpyridine-6,6''-dicarboxylate; py is pyridine) as a catalyst precursor. Furthermore, we also describe the rich chemistry associated with the reaction of Ru-tda and Ru-tPa (tPa-4 is 2,2':6',2''-terpyridine-6,6''-diphosphonate) complexes with NH3 and N2H4 using [RuII(tda-κ-N3O)(dmso)Cl] (dmso is dimethyl sulfoxide) and [RuII(tPa-κ-N3O)(py)2], 8, as synthetic intermediates, respectively. All the new complexes obtained here were characterized spectroscopically by means of UV-vis and NMR. In addition, a crystal X-ray diffraction analysis was performed for complexes trans-[RuII(tda-κ-N3)(py)2(NH3)], 4, trans-[RuII(tda-κ-N3)(N-NH2)(py)2], 5, cis-[RuII(tda-κ-N3)(py)(NH3)2], 6 (30%), and cis-[RuII(tda-k-N3)(dmso)(NH3)2], 7 (70%). The AOR activity associated with 2 and 8 as catalyst precursors was studied in organic and aqueous media. For 2, turnover numbers of 7.5 were achieved under bulk electrolysis conditions at an Eapp = 1.4 V versus normal hydrogen electrode in acetonitrile. A catalytic cycle is proposed based on electrochemical and kinetic evidence.