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The catalytic properties of bifunctional ZSM-5@t-ZrO2 catalyst for methanol thiolation were revealed by using methanol and H2S as probe molecules. Taking the ZSM-5/t-ZrO2 physically-blended catalyst, pure ZSM-5 and t-ZrO2 as control catalysts, we investigated the characteristics of adsorption and transformation of different reaction molecules on or over different catalysts by combination of in-situ diffuse reflectance Fourier transform infrared spectroscopy (Drifts) and a variety of techniques including XRD, XPS, XRF, FT-IR, N2 adsorption-desorption, CO2/NH3-TPD, and DSC. The results showed that the synergistic effect of acid sites between ZSM-5 phase and t-ZrO2 phase in the bifunctional catalyst enhanced the adsorption and dissociation of methanol molecules, while the base sites in t-ZrO2 phase were mainly responsible for the adsorption and dissociation of H2S molecules. Due to the small specific surface area of pure t-ZrO2 catalyst, precursor species for sulfur deposition and carbon deposition were easily formed. Presulfurization could improve the initial activity of methanol thiolation and shorten the induction period. The dissociation of H2S at the base sites was the rate-determining step of the bimolecular reaction, and the appropriate increase of base sites in the bifunctional components could construct the matching formation rate of sulfhydryl and methoxy groups. At the same time, the special composite structure and meso-microporous system of ZSM-5@t-ZrO2 could effectively reduce the formation rate of carbon and sulfur deposits.

The cognition of active sites in the Ni-based catalysts plays a vital role and remains a huge challenge in improving catalytic performance of low temperature CO2 dry reforming of methane (LTDRM). In this work, typical catalysts of SiO2 and γ-Al2O3 supported Ni and Ni-Ce were designed and prepared. Importantly, the difference in the chemical speciations of active sites on the Ni-based catalysts is revealed by advanced characterizations and further estimates respective catalytic performance for LTDRM. Results show that larger [ Ni n 0 ] particles mixed with [Ni-O-Sin]) species on the Ni/SiO2(R) make CH4 excessive decomposition, leading to poor activity and stability. Once the Ce species is doped, however, superior activity (59.0% CH4 and 59.8% CO2 conversions), stability and high H2/CO ratio (0.96) at 600 °C can be achieved on the Ni-Ce/SiO2(R), in comparison with other catalysts and even reported studies. The improved performance can be ascribed to the formation of integral ( [ Ni n 0 ] -[CeIII-□-CeIII]) species on the Ni-Ce/SiO2(R) catalyst, containing highly dispersed [ Ni n 0 ] particles and rich oxygen vacancies, which can synergistically establish a new stable balance between gasification of carbon species and CO2 dissociation. With respect to Ni-Ce/γ-Al2O3(R), the Ni and Ce precursors are easily captured by extra-framework Aln-OH groups and further form stable isolated ( [ Ni n 0 ] -[Ni-O-Aln]) and [CeIII-O-Aln] species. In such a case, both of them preferentially accelerate CO2 adsorption and dissociation, causing more carbon deposition due to the disproportionation of superfluous CO product. This deep distinguishment of chemical speciations of active sites can guide us to further develop new efficient Ni-based catalysts for LTDRM in the future.

In this work, we have performed density functional theory (DFT) calculations to investigate the methanol electro-oxidation reaction (MOR) catalyzed by the Pt, PtCu alloy and Cu. The complex reaction networks, including the intermediate dehydrogenation, water dissociation and anti-poison reaction steps, are systematically investigated to explore the mechanisms. At the standard condition of pH = 0 and zero potential, for Cu, most dehydrogenation steps along the favorable pathway are endergonic, making it less active in MOR. For the Pt and PtCu alloy, their dehydrogenation steps are mainly exergonic, but the formed CO intermediate binds too tightly on Pt, that can accumulate on active sites to poison the electro-catalyst. The CO can be consumed by the thermodynamic reaction with OH*, which comes from water dissociation. DFT calculation shows alloying the Pt with Cu could not only reduce the free energy barrier for binding between CO* and OH*, but also assist the water dissociation to produce more OH* for that anti-poison reaction. That makes the PtCu alloy more active than the pure Pt electrode in experiment. The results reveal the importance of anti-poison reaction and water dissociation in MOR, which could be applied to the rational design of more active alloy electro-catalysts in future.

The photo-catalyzed oxidation process of Brown HT dye was studied in the aqueous solution of the dye, using an irradiation source (ultraviolet rays UV) with the use of manganese oxide (MnO) and nickel oxide (NiO) catalysts, where the effect of increasing the weight of the catalyst in the range of 0.05–0.8 g was studied using a fixed concentration of dye 20 ppm, The best weight gave the highest dissociation rate of the dye 0.1 g from MnO and 0.075 g from NiO, and at the best weight the effect of many factors on it was studied, including pH, change of initial dye concentration, and temperature. The effect of changing the pH in the range (2–10) was studied, and the best pH gave the highest rate of dissociation of the dye at pH = 2 in the presence of MnO and pH = 4 in the presence NiO when using UV as an irradiation source. The effect of changing the initial concentration of the dye in the range of 10–50 ppm was studied, as the higher the concentration, the lower the dissociation rate. Accordingly, there is an inverse relationship between the initial concentration and the dissociation rate. The effect of changing the temperature in the range (298–323) K was studied. It was found that the higher the temperature, the greater the dissociation rate. Accordingly, the relationship is direct between temperature and reaction speed, and the activation energy for each reaction was calculated using the Arrhenius equation.

Synthesis of dimethylmethylphenylsiloxane rubbers with terminal hydroxyl groups by copolymerization of cyclosiloxanes can be accompanied by formation of low molecular weight compounds, impurities, which are difficultly removed (due to target product affinity) and can lead to rubber opalescence. Identification of the impurities (the content of each impurity ≥ 10 –4 wt.% in 1 μ l of the sample) can be carried out using a sensitive gas chromatography-mass spectrometric method. The method allows separation of the analyzed mixture into individual components on a capillary column. These components enter a mass analyzer and undergo electron ionization which leads to their dissociation into pairs «cation – neutral fragment». Only positively charged ions are observed in the mass spectra, which provides the possibility of predicting the structure of the analyzed siloxane impurities. Rearrangement of linear and cyclic molecules occurring upon mass spectrometric fragmentation result in their transformation into cyclic and bicyclic cations. The structure of the cations formed under ionization conditions depends on the number of silanol bonds and their location in the molecule. To prove the presence of compounds with hydroxyl groups in the composition of impurities and to demonstrate the effect of electron ionization on the fragmentation of compounds with silanol bonds, a sample of oligomethylsiloxane with terminal trimethylsiloxy groups was synthesized in a similar way using the copolymerization method. Compounds with silanol bonds present in the composition of the impurities appear as chromatographic asymmetric peaks with ascending and descending gently sloping zones. Those compounds are rearranged either when passing through a chromatographic column due to sorption-desorption and enter the detector in a modified form or drift through the column and undergo rearrangements already under conditions of electron ionization. The impurities contained linear and cyclic methylsiloxanes with silanol and phenyl bonds. The chromato-mass spectrometric method provide a reliable control of the composition and content of undesirable impurities which cause rubber opalescence.

Identifying optimal Ru size in NH3 synthesis can improve reaction activity and maximize the utilization of Ru to reduce catalyst cost. However, previous researches are focused on large Ru particle size (≥ 2 nm) while that below 2 nm in NH3 synthesis is unclear. Here we synthesized a series of Rux/BaCeO3 with different Ru sizes (x=1.1–3.0 nm) through size-controlled Ru colloid. With the decrease of Ru size, NH3 synthesis rate over Ru1.1/BaCeO3 increases to 19.4 mmol gcat−1 h−1 at 400°C and 1 MPa, which is 5.7 times that of Ru3.0/BaCeO3 and superior to most of Ru-based catalysts previously reported. It reveals that the reduction of Ru size enhances the generation of Ce3+ and oxygen vacancies in BaCeO3, which can donate electron to Ru centers and promote N2 dissociation. Moreover, the small Ru size enhances hydrogen spillover from Ru to BaCeO3 to alleviate hydrogen poisoning, resulting in efficient NH3 synthesis.

The magnetic bistability of spin-crossover (SCO) materials is highly appealing for applications as molecular switches and information storage. However, switching of the spin state around room temperature remains challenging. In this work, we reported the successful manipulation of the spin states of two iron(II) complexes (1-Fe and 2-Fe) based on pyridylacylhydrazone ligands in manifold ways. Both complexes are stabilized in the low-spin (LS) state at room temperature because of the strong ligand-field strength imposed by the ligands. 2-Fe shows thermoinduced SCO above room temperature with a very large and reproducible hysteresis (>50 K), while 1-Fe remains in the LS state up to 400 K. Acidity-driven spin-state switching of the two complexes was achieved at room temperature as a result of the complex dissociation and release of iron(II) in its high-spin (HS) state. Recovery of the complex is feasible upon further alkalization treatment in the case of 1-Fe, allowing bidirectional modulation of the spin state of the metal center. Light-driven one-way switching from LS to HS is also achieved by virtue of E-to-Z isomerization at the C═N double bond, which results in dissociation of the complex because of the poor binding affinity in the Z configuration.

Electrocatalytic nitrate reduction to ammonia is of great interest in terms of energy conservation and environmental protection. However, the development of abundant metal-free electrocatalysts with high activity, selectivity, and stability is still a big challenge. Herein, polymeric graphitic carbon nitride (g-C3N4) with controllable numbers of nitrogen vacancies is reported to exhibit high Faradaic efficiency (89.96%), selectivity (69.78%), and stability toward nitrate-to-ammonia conversion. 15N isotope labeling experiments prove the produced ammonia originating from nitrate reduction. The combined results of ex situ and in situ characterizations unveil the reaction pathway based on the captured critical intermediates. Density functional theory calculations reveal that nitrogen vacancies could introduce a new electron state at the Fermi level and promote the adsorption, activation, and dissociation of nitrate. An appropriate content of nitrogen vacancies is beneficial for modulating the adsorption energies of reaction intermediates (*NO, *NOH, *NH2, etc.), facilitating the enhancement in ammonia selectivity and Faradaic efficiency.

In this study, a series of Co nanoparticles (NPs) with different sizes and Co single-atom catalysts (SACs) with different cobalt-nitrogen coordination numbers (Co-N2, Co-N3, and Co-N4) were synthesized and applied to the synthesis of ammonia catalyzed by plasma at low temperatures and atmospheric pressures. Under the same reaction conditions, the yield of nitrogen obtained from the reduction to ammonia over a series of Co NP catalysts varies with the Co particle size. The smaller the size of the Co NPs, the greater the number of exposed active centers, and the catalytic activity is higher. Among the Co SACs, the best catalyst was Co-N2 with two coordinated nitrogen atoms, and the ammonia yield was 181 mg·h-1·gcat-1. The experimental and theoretical calculations were consistent in that a low Co-N coordination number was beneficial to the adsorption and dissociation of N2, thereby enhancing the reduction activity of N2 and promoting the increase of ammonia production.

Ligand substitution at the metal center is common in catalysis and signal transduction of metalloproteins. Understanding the effects of particular ligands, as well as the polypeptide surrounding, is critical for uncovering mechanisms of these biological processes and exploiting them in the design of bioinspired catalysts and molecular devices. A series of switchable K79G/M80X/F82C (X = Met, His, or Lys) variants of cytochrome (cyt) c was employed to directly compare the stability of differently ligated proteins and activation barriers for Met, His, and Lys replacement at the ferric heme iron. Studies of these variants and their nonswitchable counterparts K79G/M80X have revealed stability trends Met < Lys < His and Lys < His < Met for the protein FeIII-X and FeII-X species, respectively. The differences in the hydrogen-bonding interactions in folded proteins and in solvation of unbound X in the unfolded proteins explain these trends. Calculations of free energy of ligand dissociation in small heme model complexes reveal that the ease of the FeIII-X bond breaking increases in the series amine < imidazole < thioether, mirroring trends in hardness of these ligands. Experimental rate constants for X dissociation in differently ligated cyt c variants are consistent with this sequence, but the differences between Met and His dissociation rates are attenuated because the former process is limited by the heme crevice opening. Analyses of activation parameters and comparisons to those for the Lys-to-Met ligand switch in the alkaline transition suggest that ligand dissociation is entropically driven in all the variants and accompanied by Lys protonation at neutral pH. The described thiolate redox-linked switches have offered a wealth of new information about interactions of different protein-derived ligands with the heme iron in cyt c model proteins, and we anticipate that the strategy of employing these switches could benefit studies of other redox metalloproteins and model complexes.

Selective hydrogenation of nitroarene to aniline is a key reaction for the manufacture of fine chemicals, pharmaceuticals, and dyes. In this study, N-doped carbon nanotubes (NCNTs) are prepared by the pyrolysis of chitosan-CNTs composite. The outside diameter of CNTs, concentration of chitosan, pyrolysis temperature and heating rate are tuned to improve the catalytic performance. The catalyst of CS/CNTs-800 doped with 0.33% pyrrolic N and 0.30% graphitic N exhibits good activity and high selectivity for the hydrogenation of nitroarenes. The kinetics data reveal that the hydrogenation reaction is zero-order for 4-nitrophenol and first-order dependence to H2 pressure, and H2 dissociation on the active sites is the rate-determining step. On CS/CNTs-800, the nitro groups of 12 different substrates can be selectively reduced with the protection of the other reducible groups. Nonpolar H radicals are found to be formed on CS/CNTs-800 for efficient hydrogenation. In addition, the catalyst showed good stability.

In an effort to probe the impacts of speciation on spin-state switching, the synthesis and unique solution-phase magnetic properties of [((TIPSC≡C)3tren)Fe(OTf)2] (1) are described. Analysis of the single-crystal X-ray diffraction data shows that the tris(iminoalkyne) ligand coordinates to the iron(II) center through all four nitrogen atoms, while the other two coordination sites are filled by the oxygen atoms from triflate anions. Solid-state variable-temperature (VT) magnetic studies show that 1 remains high-spin (HS) at all temperatures. In the presence of moderately strong coordinating solvents, solvent replaces the two bound triflate counteranions, as observed by 19F NMR spectroscopy and supported by conductivity measurements. VT solution measurements show 1 to be in the HS state when this solvent is oxygen-donating but low-spin (LS) with a nitrogen-donating solvent. In the noncoordinating solvent dichloromethane, both triflates are bound to the iron(II) center at room temperature, but upon cooling, 1 undergoes a coordination change, resulting in the loss of one triflate, as shown by 19F NMR. With the moderately coordinating solvent acetone, triflate dissociation upon cooling results in a spin-switching species with a T1/2 value of 171 K, characterized via 19F NMR, Evans' method, and solution magnetometry measurements. Solution magnetic measurements collected in structurally similar cyclopentanone suggest that the spin-state switching event is exclusive to the acetone environment, suggesting the influence of both the local coordination environment and aggregation. Additionally, a comparison of the solvodoynamic diameters via dynamic light scattering suggests that aggregation of 1 is significantly different in (CH3)2CO and (CD3)2CO, leading to the observation of spin-switching behavior in the former and fully HS behavior in the latter. This study highlights the sensitivity of solution magnetic properties to solvent choice.

The research established the regularities for the separation of phenylalanine aqueous salt solutions by electrodialysis. It also determined the conditions for the effective and selective isolation of the target component by selecting a membrane with the desired properties. The composition of the model solution simulating industrial water in the technology of microbiological synthesis included an aromatic amino acid, phenylalanine (0.05 M), and sodium chloride (0.01 M). Experimental membranes with different mass fractions of sulfonated cation-exchange resin were used. Heterogeneous ion-exchange membranes were obtained by hot rolling of a homogenised mixture of a crushed ion-exchanger and polyethylene. The transport characteristics and features of the transfer of components of different nature through the experimental membranes were studied in a galvanostatic mode using a seven-section electrodialyser which was horizontally oriented. It was established that the content of the ion exchanger in the membrane influences the features of the transport of mineral salt and amino acid ions, the value of the separation factor, and the degree of solutions demineralization. It was shown that the change in the content of the sulfonated cation-exchanger in the membranes from 45 to 70 wt.% during the electrodialysis of a mixed solution of an amino acid and a mineral salt makes it possible to increase the rate of mass transfer of a mineral ion by 1.5 times. For all experimental membranes, the separation factor dependences are characterised by extrema corresponding to the interval exceeding the limiting diffusion current ilim by 2-3 times. The maximum separation efficiency was set for a cation exchange membrane with a 70% content of resin. It was found that when the limiting diffusion current was exceeded by a factor of 2 while the content of resin in the membrane increased, the separation factor increased by 1.5 times. Additionally, the degree of demineralization of the solution for the membrane with the maximum content of the ion exchanger was 40-60%. The possibility of almost complete demineralization of the solution for the membrane with a content of resin of 70 wt.% was established when the maximum current was exceeded by 6 times. The study revealed the role of electroconvection in the increase in the loss of the target product of the amino acid with overlimiting current modes of electrodialysis. It was shown that the main reason for the increase in the transfer of amino acids through the sulphonated cation-exchange membrane in intense current modes is the electroconvective mixing of the solution at the interface, which negatively affects the process of water dissociation and destroys the barrier effect of the near-membrane layers of the solution with a high pH value. The research established the possibility of deep demineralization of phenylalanine aqueous salt solution with a loss of the target product of no more than 0.2% using a membrane with a mass fraction of a sulfonated cation-exchange resin of 70 wt.% in intense current modes.

Supported bimetallic catalysts of (Co + Pd)/SiO2 system were studied in carbon monoxide hydrogenation. Comparative analysis showed that depending on precursor treatment mode the catalysts ranged in different rows of activity in CO conversion and selectivity to methane. Samples of best performance were obtained after pretreatment in Ar flow. Highly selective catalysts were synthesized by reduction at 450 °C determining low metal dispersion, high extent of alloying, and agglomeration. A low H2,100C/COstrong adsorbed gas ratio was ascribed to a great amount of bimetallic particles and concerned with a diminished number of sites for multiply bonded CO species. Metal dispersion was low due to large Co particles, which enhanced CO dissociation and hydrogenation to CH4. In presence of bimetallic particles the reaction CO + 3H2 = CH4 + H2O was hampered. A decreased H2O formation influenced the WGS reaction. Catalyst samples activated at higher temperatures had better selectivity. During the process, formation of bidentate carbonate species was registered. It was supposed that palladium impeded creation of the latter species and following decomposition to CO2. Active catalyst samples were prepared by reduction at 300 °C leading to higher unreduced cobalt quota and metal dispersion, and decreased alloy particle formation. Higher H2,100C/COstrong ratio values were assigned to pure Co and Pd particle segregation, i.e. availability of sites for multiply bonded CO species favoring a higher activity in CO dissociation and further hydrogenation. A higher amount of CO species on these samples was conducive to CH4 formation, but also to CO2 production. The latter reaction was facilitated by unreduced cobalt.

Yttrocene derivatives [Cp*2Y(MMe4)] (Cp* = C5Me5; M = Al, Ga) and Cp*2Y[Me3Al{B(NDippCH)2}] (Dipp = C6H3iPr2-2,6) deprotonate benzene at elevated temperatures via the release of methane. The formation of [Cp*2Y(Me2MPh2)] (M = Al, Ga), Cp*2Y(MPh4) (M = Al, Ga), Cp*2Y[Me2AlPh{B(NDippCH)2}], and Cp*2Y[AlPh3{B(NDippCH)2}] can be controlled via the temperature applied. The activation temperature and formation of the coordinatively unsaturated "reactive" [Cp*2YMe] strongly depend on the coordination strength of the displaceable Lewis acids [AlMe3]2, GaMe3, and [Me2Al{B(NDippCH)2}]2. Hence, [Cp*2Y(AlMe4)] requires temperatures above 100 °C to metalate benzene, while Cp*2Y[AlMe3{B(NDippCH)2}] undergoes C-H-bond activation even at ambient temperatures. A kinetic deuterium isotope effect was observed for the reactions in C6D6 solutions. Distinct differences in the stabilities of the bulky Group 13 anions ([Me2MPh2]-, [MPh4]-, [Me3Al{B(NDippCH)2}]-, [Me2AlPh{B(NDippCH)2}]-, and [AlPh3{B(NDippCH)2}]-) are assessed by detailed studies of the coordination chemistry with tetrahydrofuran (THF) and by variable-temperature 1H NMR spectroscopy. Thus, increased steric bulk or a reduced Lewis acidity of the Group 13 metal center promote temperature-sensitive dissociation of trivalent Group 13 alkyl entities. Consequently, compound Cp*2Y[AlPh3{B(NDippCH)2}] was found to engage in a dissociation equilibrium with [Cp*2YPh] and AlPh2{B(NDippCH)2} in a C6D6 solution at ambient temperature. The reaction of Cp*2Y[AlPh3{B(NDippCH)2}] with THF results in the concomitant formation of monometallic Cp*2YPh(THF) and the solvent-separated ion pair [Cp*2Y(THF)2][AlPh3{B(NDippCH)2}].

We present a strategy of self-nanocavity confinement for substantially boosting the superior electrochemical hydrogen peroxide (H2O2) selectivity for conductive metal-organic framework (MOF) materials. By using operando synchrotron radiation X-ray adsorption fine structure and Fourier transform infrared spectroscopy analyses, the dissociation of key *OOH intermediates during the oxygen reduction reaction (ORR) is effectively suppressed over the self-nanocavity-confined X-Ni MOF (X = F, Cl, Br, or I) catalysts, contributing to a favorable two-electron ORR pathway for highly efficient H2O2 production. As a result, the as-prepared Br-confined Ni MOF catalyst significantly promotes H2O2 selectivity up to 90% in an alkaline solution, evidently outperforming the pristine Ni MOF catalyst (40%). Moreover, a maximal faradic efficiency of 86% with a high cumulative H2O2 yield rate of 596 mmol gcatalyst-1 h-1 for electrochemical H2O2 generation is achieved by the Br-confined Ni MOF catalyst.

Background Chitosan (CS) is the most abundant cationic biopolymer on earth. However, the ionic conductivity performance of CS polymer electrolyte is relatively poor, restricting the application in energy storage devices. Methods Subject to carboxylation at pH of 6. 8, and 10, CS turns into CCS6, CCS8, and CCS10 respectively with the DC of 100.9%, 20.0%, and 17.8%, respectively. Significant findings From the Arrhenius plot, the activation energy of CS, CCS6, CCS8, and CCS10 electrolytes is estimated as 11.7, 2.5, 2.6, and 2.6 kJ/mol respectively. As for supercapacitor performance, CCS6 remains 57.2% capacitance but the others remain 0% with decreasing temperature from 25 °C to -7 °C. At -7 °C, only CCS6 supercapacitor shows relaxation peak in loss tangent versus frequency plot around 2 × 105 Hz according to dissociated ion pairs, being attributable to the existence of bound water. Three water states are examined by Differential Scanning Calorimetry (DSC) and Raman, verifying that CCS6 possesses high bound water proportion of 24.7%. With the highest DC, CCS6 possesses the almost equivalent amine and carboxyl groups in one glucosamine unit to play an important role to enhance dissociation, defer the breakpoints of ionic conductivity, and remain certain proportion of bound water for promising capacity at low temperature.

In article, we have been reported the study of a concentration effect of sodium chloride (NaCl) salt on benzoic acid solubility and its dissociation in water at 298 K temperature. At this temperature the benzoic acid solubility into water and their dissociation value for six samples in range of 0.00, 0.05, 0.10, 0.30, 0.40 and 0.50 M. Each of these different ionic strength or concentration of sodium chloride is analyzed by titrimetrically against of 0.05 M sodium hydroxide (NaOH) basic solution. The pH of each solution is measured well by using of calibrated pH-meter. Observation reveals that the value of pH of benzoic acid into water at applying temperature is may inversely related with concentration of NaCl. Graphically, the value of ionic strength (I) of that benzoic acid is plotted versus with dissociation constant (Kc) of acid into water at specific 298 K temperature. The value of benzoic acid dissociation constant for given each six concentration of NaCl is found to be -4.169, -4.045, -3.993, -3.885, -3.848 and -3.788, respectively.

We present measurements of isoprene-derived organic nitrates (ISOP-NITs) generated in the reaction of isoprene with the nitrate radical (NO3) in a 1 m3 Teflon reaction chamber. Detection of ISOP-NITs is achieved via their thermal dissociation to nitrogen dioxide (NO2), which is monitored by cavity ring-down spectroscopy (TD-CRDS). Using thermal dissociation inlets (TDIs) made of quartz, the temperature-dependent dissociation profiles (thermograms) of ISOP-NITs measured in the presence of ozone (O3) are broad (350 to 700 K), which contrasts the narrower profiles previously observed for, for example, isopropyl nitrate (iPN) or peroxy acetyl nitrate (PAN) under the same conditions. The shape of the thermograms varied with the TDI's surface-to-volume ratio and with material of the inlet walls, providing clear evidence that ozone and quartz surfaces catalyse the dissociation of unsaturated organic nitrates leading to formation of NO2 at temperatures well below 475 K, impeding the separate detection of alkyl nitrates (ANs) and peroxy nitrates (PNs). The use of a TDI consisting of a non-reactive material suppresses the conversion of isoprene-derived ANs at 473 K, thus allowing selective detection of PNs. The potential for interference by the thermolysis of nitric acid (HNO3), nitrous acid (HONO) and O3 is assessed.

Transition metal sulfides have become some of the most promising non-precious metal catalysts due to their high specific surface area, unique electronic structure, and rich phase and property modulation methods. However, defects such as high overpotential and slow reaction kinetics hinder their implementation in electrocatalytic applications. Herein, graphene-coated sponge nickel (SNG) supported Ni9S8 nanowires were doped with N to adjust the electronic structure and thus improve the electrocatalytic hydrogen evolution performance of the N-Ni9S8@SNG core/branch electrode. The N-Ni9S8@SNG electrode exhibits excellent hydrogen evolution performance, with an overpotential of 98 mV at 10 mA cm−2 and long-cycle stability with no significant attenuation of the overpotential after testing at 10 mA cm−2 for 10 h. The results of photoelectron spectroscopy and density functional theory calculations showed that, due to the higher electronegativity of the nitrogen site, the electron density of the surrounding Ni and S atoms is changed, thereby promoting the dissociation of H2O and the adsorption/desorption of hydrogen. The N-Ni9S8@SNG electrode exhibits excellent hydrogen evolution performance with an overpotential of 98 mV at 10 mA cm−2 and long-cycle stability. The results of photoelectron spectroscopy and density functional theory calculations showed that, due to the higher electronegativity of the nitrogen site, the electron density of the surrounding Ni and S atoms is changed, thereby promoting the dissociation of H2O and the adsorption/desorption of hydrogen.

Threshold collision-induced dissociation (TCID) of the thorium monocarbonyl cation, ThCO+, with xenon is performed using a guided ion beam tandem mass spectrometer. The only product observed is Th+ resulting from loss of the CO ligand. Analysis of the kinetic energy-dependent cross sections for this CID reaction yields the first experimental determination of the bond dissociation energy (BDE) of Th+-CO at 0 K as 0.94 ± 0.06 eV. Calculated BDEs at the CCSD(T) level of theory with cc-pVXZ (X = T and Q) basis sets and a complete basis set (CBS) extrapolation are in good agreement with the experimental result. The Feller-Peterson-Dixon composite coupled-cluster methodology was also applied on both ThCO+ and ThCO, with contributions up to CCSDT(Q) and a four-component treatment of spin-orbit coupling effects. The final 0 K Th+-CO BDE of 0.94 ± 0.04 eV is in excellent agreement with the current experimental result. The ionization energy of ThCO, as well as the atomization energies and heats of formation for both ThCO and ThCO+, is reported at this same level of theory. Complete potential energy profiles of both quartet and doublet spin are also constructed to elucidate the mechanism for the formation and interconversion of different isomers of [Th,O,C]+. Chemical bonding patterns in low-lying states of ThCO+ and potential energy curves for ThCO+ dissociation are also investigated.

Results are presented from investigating the structure of maleic acid, processes of gas-phase protonation, and acid–base equilibria with the participation of maleic acid in water–ethanol and water–dimethylsulfoxide solutions. The рK values of maleic acid dissociation in water–ethanol and water–dimethylsulfoxide solvents are determined. It is established that the рK values grow along with the content of the nonaqueous component in a water–organic mixture. Analysis of the solvation contributions from all reagents participating in the acid dissociation of maleic acid in water–ethanol and water–dimethylsulfoxide solvents reveals that the main contribution to the increase in рK1 and рK2 comes from the desolvation of anions.

The adsorption of thiophenic compounds over Ti0.9Ce0.1O2, an oxidatively regenerable sulfur adsorbent, was studied by XPS, DRIFT, and TPD-MS. Effect of the oxidative pretreatment on thiophene adsorption over Ti0.9Ce0.1O2 adsorbent, the adsorption site for thiophenic compound, and the role of surface Ce and Ti cations in the adsorptive desulfurization (ADS) were investigated. The results suggest that the surface oxygen plays an essential role in ADS and is a major active site for chemical adsorption of the thiophenic compounds. The surface Ce and Ti were further oxidized by the surface oxygen in the oxidative pretreatment, and then reduced during the adsorption of thiophenic compounds. This phenomenon is attributed to an electron transfer from the adsorbates to the surface Ce and Ti. It appears that the role of the surface Ce and Ti can accept electrons from adsorbate, and also contributes to producing the active oxygen to oxidize the sulfur atom of thiophenic compounds. An oxidative pretreatment, including oxidative regeneration, activates the surface oxygen to forms active oxygen species and oxidizes the surface Ce and Ti. Based on the results obtained, a possible mechanism was proposed for the chemical adsorption, dissociation and surface reaction of thiophene on Ti0.9Ce0.1O2 mixed metal oxide adsorbent.

Direct synthesis of hydrogen peroxide from hydrogen and oxide (DSHP) is considered as a green pathway for H2O2 production because of the simple reaction route and 100% theoretical atom efficiency. Here, 1.5 wt% Pd and 0.5 wt% Au were loaded on HZSM-5 nanosheets through sequential isovolumetric impregnation. TEM images and CO-TPD curves showed that Pd nanosheets were successfully synthesized between HZSM-5 nanosheets under zeolite confinement effect, and Au particles were loaded on the edge of Pd nanosheets and formed a structure that Pd nanosheets with edge decorated by Au nanoparticles (Au–Pd/ZN). The results showed that the selectivity for H2O2 could be reached around 60% in a 30 min reaction and the initial H2O2 productivity could reach 338.5 mmol gcat−1 h−1 on the Au–Pd/ZN catalyst. The enhanced selectivity and productivity could be related with high content of terrace sites and Au particles on the step sites of bimetallic nanosheets, in which both the terrace sites and the step sites replaced by Au particles showed higher dissociation activation energy for breaking the O–O bond than traditional step sites on Pd particles, inhibited the by-product reactions (2H2O2→2H2O​ + O2, 2H2 + O2→2H2O).

The vaporization of lithium pivalate (CH3)3CCOOLi (LiPiv) was studied by the Knudsen effusion method with the mass spectral analysis of the gas phase. The saturated vapor consisted of polynuclear molecules (LiPiv)n, dominated by (LiPiv)2 and (LiPiv)4 molecules. The absolute values of the partial pressures of these molecules and their dependence on temperature were calculated. The standard enthalpies of sublimation of the main components of the saturated vapor were determined to be $${{\Delta }_{s}}H_{{298}}^{^\circ }$$ (LiPiv)2 = 174.2 ± 6.6 kJ/mol and $${{\Delta }_{s}}H_{{298}}^{^\circ }$$ (LiPiv)4 = 195.7 ± 4.5 kJ/mol. The enthalpies of dissociation of the dimeric molecules into the monomeric molecules and of the tetrameric molecules into the dimeric molecules were calculated by the second and third laws of thermodynamics; the average values of these enthalpies are $${{\Delta }_{D}}H_{{298}}^{^\circ }$$ (LiPiv)2 = 175.8 ± 13.5 kJ/mol and $${{\Delta }_{D}}H_{{298}}^{^\circ }$$ (LiPiv)4 = 155.2 ± 10.0 kJ/mol. The standard enthalpies of formation of LiPiv in the condensed and gas phase were estimated from the known thermodynamic characteristics of lithium acetate and radicals of acetic and pivalic acids: $${{\Delta }_{f}}H_{{298.15}}^{^\circ }$$ (LiPivsolid) ≤ –804 kJ/mol, $${{\Delta }_{f}}H_{{298.15}}^{^\circ }$$ (LiPivgas) ≤ –627 kJ/kmol, $${{\Delta }_{f}}H_{{298.15}}^{^\circ }$$ ((LiPiv)2(gas)) ≤ –1430 kJ/mol, and $${{\Delta }_{f}}H_{{298.15}}^{^\circ }$$ ((LiPiv)4(gas)) ≤ –3017 kJ/mol.

Despite many efforts, there is no versatile way to realize reversible cross-linking for most polymers. Inspired by the abstraction of hydrogen and the iniferter polymerization of benzophenone (BP), we report a versatile approach for building dynamic covalent networks for polymers containing C–H bonds. Under ultraviolet irradiation, BP can effectively abstract the hydrogen from polymers to form dormant diarylsemipinacol (DASP) groups on the polymer chains. Then, the dormant DASP-based linkages can be homolytically cleaved upon heating, after which they generate carbon-centered aliphatic radicals and DASP-based radicals. Therefore, the cross-linked polymer network can rearrange its topology through the dissociation and association of DASP-based linkages, which endow polymer networks with remodeling and self-healing abilities. Given that most commercially available polymers contain aliphatic C–H bonds, this provides a general method for forming thermal reversible cross-linked networks.

We report the first example of the fabrication of pure, single-chain Janus particles (SCJPs). The SCJPs were prepared by double-cross-linking an A-b-B diblock copolymer in a common solvent. Inevitably, the double-cross-linking led to a mixture containing not only SCJPs but also multichain particles and irregular single-chain particles. Under well-controlled conditions, the SCJPs in the mixture self-assemble with high exclusivity to form regularly structured macroscopic assemblies (MAs) with a crystal-like appearance that precipitate from the suspension. Pure SCJPs that are uniform in size, shape and Janus structure were efficiently prepared by collection and dissociation of the MAs. Block copolymers with different structural parameters were successfully used for the exclusive self-assembly (ESA), and pure SCJPs with varied structural parameters were produced, confirming the reliability of the ESA method.

Herein, we report an example of self-driven morphological transition and the unique dissociation behavior of polymeric assemblies. Polymeric nanogels were introduced into the shell of polymeric assemblies and used as a powerful platform to endow the assemblies with unique properties and behaviors. It is exhibited that the nanogel can host an intrananogel cross-linking reaction and thus contracts automatically to change the geometrical packing parameters of the building blocks, driving morphological transitions of the assemblies; the transitions are self-driven without any external stimuli. Additionally, when the nanogels in the shell expand, the assemblies dissociate into small fragments even when the core is in a frozen state; in existing studies, polymeric assemblies with a frozen core cannot dissociate, except the core becomes dynamic under the stimuli. Both the self-driven morphological transition and the dissociation behavior are unique and have never been reported before.

Polymerizing electron-deficient arenes in a controlled, chain-growth fashion remains a significant challenge despite a decade of research on catalyst-transfer polycondensation. The prevailing hypothesis is that the chain-growth mechanism stalls at a strongly associated metal-polymer π-complex, preventing catalyst turnover. To evaluate this hypothesis, we performed mechanistic studies using thiazole derivatives and identified approaches to improve their chain-growth polymerization. These studies revealed a surprisingly high barrier for chain-walking toward the reactive C-X bond. In addition, a competitive pathway involving chain-transfer to monomer was identified. This pathway is facilitated by ancillary ligand dissociation and N-coordination to the incoming monomer. We found that this chain-transfer pathway can be attenuated by using a rigid ancillary ligand, leading to an improved polymerization. Combined, these studies provide mechanistic insight into the challenges associated with electron-deficient monomers as well as ways to improve their living, chain-growth polymerization. Our mechanistic studies also revealed an unexpected radical anion-mediated oligomerization in the absence of catalyst, as well as a surprising oxidative addition into the thiazole C-S bond in a model system.

Previously prepared Mn(II)- and quinol-containing magnetic resonance imaging (MRI) contrast agent sensors for H2O2 relied on linear polydentate ligands to keep the redox-activatable quinols in close proximity to the manganese. Although these provide positive T1-weighted relaxivity responses to H2O2 that result from oxidation of the quinol groups to p-quinones, these reactions weaken the binding affinity of the ligands, promoting dissociation of Mn(II) from the contrast agent in aqueous solution. Here, we report a new ligand, 1,8-bis(2,5-dihydroxybenzyl)-1,4,8,11-tetraazacyclotetradecane, that consists of two quinols covalently tethered to a cyclam macrocycle. The macrocycle provides stronger thermodynamic and kinetic barriers for metal-ion dissociation in both the reduced and oxidized forms of the ligand. The Mn(II) complex reacts with H2O2 to produce a more highly aquated Mn(II) species that exhibits a 130% greater r1, quadrupling the percentile response of our next best sensor. With a large excess of H2O2, there is a noticeable induction period before quinol oxidation and r1 enhancement occurs. Further investigation reveals that, under such conditions, catalase activity initially outcompetes ligand oxidation, with the latter occurring only after most of the H2O2 has been depleted.

Refluxing Mo(CO)6 in the presence of the phosphine-functionalized α-diimine ligand Ph2PPrDI allowed for substitution and formation of the dicarbonyl complex, (Ph2PPrDI)Mo(CO)2. Oxidation with I2 followed by heating resulted in further CO dissociation and isolation of the corresponding diiodide complex, (Ph2PPrDI)MoI2. Reduction of this complex under a N2 atmosphere afforded the corresponding bis(dinitrogen) complex, (Ph2PPrDI)Mo(N2)2. The solid-state structures of all three compounds were found to feature a tetradentate chelate and cis-monodentate ligands. Notably, the addition of CO2 to (Ph2PPrDI)Mo(N2)2 is proposed to result in head-to-tail CO2 coupling to generate the corresponding metallacycle and ultimately a mixture of (Ph2PPrDI)Mo(CO)2 and the bis(oxo) dimer, [(κ3-Ph2PPrDI)Mo(O)(μ-O)]2. Computational studies have been performed to gain insight into the reaction and evaluate the importance of cis-coordination sites for selective head-to-tail CO2 reductive coupling, CO deinsertion, disproportionation, and stepwise CO2 deinsertion.

Hydrogen evolution reaction (HER) usually has sluggish kinetics in alkaline solutions due to the difficulty in the formation of binding protons. Herein we report an electrocatalyst by sulfur atoms doping into the oxygen vacancies (V O ) of inverse spinel NiFe 2 O 4 (S-NiFe 2 O 4 ) to create active sites with enhanced electron transfer capability. Our results indicated this electrocatalyst has an ultralow overpotential of 61 mV at the current density of 10 mA cm -2 and long-term stability of 60 h at 1.0 A cm -2 in 1.0 M KOH media . After coupled with V O , the high electroactive S atoms facilitate binding with protons. In-situ Raman spectroscopy revealed that S sites absorb hydrogen adatom (H*) and in-situ form S-H*, that favor the production of hydrogen and boosts HER in the alkaline solution. DFT calculations further verified lowered energy barrier of the H 2 O dissociation induced by the S introduction, which is the key factor for this remarkable HER performance. Both experimental and theoretical investigations confirmed S atoms are active sites of the S-NiFe 2 O 4 . This work provides an facile and powerful solution in designing novel electrocatalysts to accelerate water splitting via vacancies filling strategy.

Solid-state structures find a self-assembled tetrameric nickel cage with carboxylate linkages, [Ni(N2S'O)I(CH3CN)]4 ([Ni-I]40), resulting from sulfur acetylation by sodium iodoacetate of an [NiN2S]22+ dimer in acetonitrile. Various synthetic routes to the tetramer, best described from XRD as a molecular square, were discovered to generate the hexacoordinate nickel units ligated by N2Sthioether, iodide, and two carboxylate oxygens, one of which is the bridge from the adjacent nickel unit in [Ni-I]40. Removal of the four iodides by silver ion precipitation yields an analogous species but with an additional vacant coordination site, [Ni-Solv]+, a cation but with coordinated solvent molecules. This also recrystallizes as the tetramer [Ni-Solv]44+. In solution, dissociation into the (presumed) monomer occurs, with coordinating solvents occupying the vacant site [Ni(N2S'O)I(solv)]0, ([Ni-I]0). Hydrodynamic radii determined from 1H DOSY NMR data suggest that monomeric units are present as well in CD2Cl2. Evans method magnetism values are consistent with triplet spin states in polar solvents; however, in CD2Cl2 solutions no paramagnetism is evident. The abilities of [Ni-I]40 and [Ni-Solv]44+ to serve as sources of electrocatalysts, or precatalysts, for the hydrogen evolution reaction (HER) were explored. Cyclic voltammetry responses and bulk coulometry with gas chromatographic analysis demonstrated that a stronger acid, trifluoroacetic acid, as a proton source resulted in H2 production from both electroprecatalysts; however, electrocatalysis developed primarily from uncharacterized deposits on the electrode. With acetic acid as a proton source, the major contribution to the HER is from homogeneous electrocatalysis. Overpotentials of 490 mV were obtained for both the solution-phase [Ni-I]0 and [Ni-Solv]+. While the electrocatalyst derived from [Ni-Solv]+ has a substantially higher TOF (102 s-1) than [Ni-I]0 (19 s-1), it has a shorter catalytically active lifespan (4 h) in comparison to [Ni-I]0 (>18 h).

Electrochemical reduction of CO2 to chemicals and fuels is an interesting and attractive way to mitigate greenhouse gas emissions and energy shortages. In this work, we report the use of atomic In catalysts for CO2 electroreduction to CO. The atomic In catalysts were anchored on N-doped carbon (InA/NC) through pyrolysis of In-based metal-organic frameworks (MOFs) and dicyandiamide. It was discovered that InA/NC had outstanding performance for selective CO production in the mixed electrolyte of ionic liquid/MeCN. It is different from those common In-based materials, in which formate/formic acid is formed as the main product. The faradaic efficiency (FE) of CO and total current density were 97.2% and 39.4 mA cm-2, respectively, with a turnover frequency (TOF) of ∼40 000 h-1. It is one of the highest TOF for CO production to date for all of the catalysts reported. In addition, the catalyst had remarkable stability. Detailed study indicated that InA/NC had higher double-layer capacitance, larger CO2 adsorption capacity, and lower interfacial charge transfer resistance, leading to high activity for CO2 reduction. Control experiments and theoretical calculations showed that the In-N site of InA/NC is not only beneficial for dissociation of COOH* to form CO but also hinders formate formation, leading to high selectivity toward CO instead of formate.

A series of halogenated organogold(III) complexes cis-[(L)Au(ArF)(Cl)(X)] (L = phosphine ligand, ArF = 2,2′,3,3′,5,5′,6,6′-octafluoro-[1,1′-biphenyl]-4-yl, and X = Cl, Br, I) were prepared, and the...

Electrocatalytic nitrogen fixation under ambient conditions represents an energy-saving sustainable alternative strategy to the energy-consuming traditional Haber–Bosch process toward ammonia synthesis. However, the traditional electrocatalysts for nitrogen reduction reaction (NRR) often suffer low selectivity and low activity. From quantum-mechanical calculations, we obtain a benefit clue that the Ni atom adsorbed by the first hydrogen ion in the catalyst exhibits selectivity for the adsorption of N2 and other H atoms, and it preferentially adsorbs N2 molecules. Thus, we propose an interfacial engineering strategy to simultaneously accelerate selectivity and activity using metal/metal hydroxide. The remarkable activity of metal/metal hydroxide originates from its synergized water dissociation and unique hydrogenation pathway of metal hydride. The priority absorption of the N2 suppresses the competitive hydrogen evolution reaction and accelerates the kinetics to generate ∗N2H: ∗H + N2 → ∗N2H, which a is rate-limiting step for NH3 synthesis. Using Ni/NiFe–OH as prototypes, here we show that selectivity and catalytic activity are simultaneously enhanced, surprisingly, in simple inorganic hybrid and confers exceptionally Faradaic efficiency of 23.34% and NH3 yield 19.74 μg h−1 cm−2 at −0.15 V versus reversible hydrogen electrode (RHE) in 0.5 M KOH electrolyte under ambient conditions. The long-term durability is also excellent. This work provides a possibility for the rational design of efficient electrocatalysts for N2 electrochemical reduction with a large-scale production.

Acid treated kaolinites (KA) were successively loaded with Zr and Fe, Ni or Co component to control the product distribution and upgrade the tar quality in coal pyrolysis. The structure of the resultant catalysts was characterized and their catalytic performance in the pyrolysis of demineralized low-rank coal and benzyl phenyl ether (BPE), a model compound containing Cal-O bridge bond, were investigated. Results show that the introducing of Zr into the KA can enlarge the hysteresis loop due to the stacking of ZrO2 particles. The acidities, especially the strong ones, increase as the Zr content is below 8 wt% (KA-8Z). When adding Fe, Ni or Co metals into the KA-8Z, the number of Bronsted acid sites obviously decreases, but Lewis acid sites increase. The maximum BPE conversion of 94.0% occurs for the KA-8Z, further metal-loaded sample promotes the cleavage of Cal-O bond in BPE and the formation of active H radicals from CH3OH, leading to the increase of BPE conversion. Besides, remarkable enhancement of target monomeric aromatics is observed for the Fe, Ni and Co-loaded samples. Compared with the pyrolysis without catalyst, the tar yield as well as pitch content decrease over the KA-8Z and its metal-modified catalysts. Wherein, Ni-KA-8Z has the highest activity for tar upgrading, leading to the largest increase in the contents of light oil and phenol oil. In-situ pyrolysis by time-of-flight mass spectrometry reveals the enhanced dissociation of weak covalent bonds linked in the coal skeleton over the KA-8Z and Fe, Ni and Co-modified catalysts, resulting in a decrease in the peak temperature for product release. A marked increase in phenols and diphenols confirms a promoted dissociation of ether bond in coal.

A series of BaCeO3 modified with different rare earth elements (La, Y, Pr) were synthesized by co-precipitation and calcination and the effect of rare earth elements for catalytic ammonia synthesis under mild conditions was studied. The ammonia synthesis performance tests show that 2.5% Ru/BaCe0.9La0.1O3–δ catalyst (All the percentages of Ru in this article are in mass fraction) exhibits the highest ammonia synthesis rate (34 mmol/(g·h)) at 3 MPa, 450 °C, and no sign of deactivation after 100 h of reaction. H2-TPR and XPS analyses indicate that the introduction of La increases the amount of oxygen vacancies of the catalyst, which is beneficial to increasing the electron density of Ru surface. HRTEM analysis shows that the Ru particle size is reduced greatly after La is introduced, which facilitates the catalyst generating more B5-type sites (active sites of Ru species for N N dissociation). CO2-TPD analysis indicates that BaCe0.9La0.1O3–δ has stronger basicity, which promotes electrons transfer from support to Ru. This work provides an effective method for design and synthesis of Ru-based multi-element composite perovskite oxide catalysts.

The concept of alkynophilicity is revisited with group 13 MX3 metal salts (M = In, Ga, Al, B; X = Cl, OTf) using M06-2X/6-31+G(d,p) calculations. This study aims at answering why some of these salts show reactivity toward enynes that is similar to that observed with late-transition-metal complexes, notably Au(I) species, and why some of them are inactive. For this purpose, the mechanism of the skeletal reorganization of 1,6-enynes into 1-vinylcyclopentenes has been computed, including monomeric ("standard") and dimeric (superelectrophilic) activation. Those results are confronted with deactivation pathways based on the dissociation of the M-X bond. The role of the X ligand in the stabilization of the intermediate nonclassical carbocation is revealed, and the whole features required to make a good π-Lewis acid are discussed.

X-ray diffraction, IR spectroscopy, and thermogravimetry and analyses of the composition of platinum carbonyl destruction products showed that oligomeric platinum carbonyl [Pt(CO)2]n is unstable in the air at room temperature and quickly decomposes with the loss of CO ligands due to their removal from the complex as a result of CO dissociation and CO ligand oxidation by atmospheric oxygen. The destruction processes of platinum carbonyl [Pt(CO)2]n and the composition of destruction products were described.

The role of silver species in the H2-assisted NH3 selective catalytic reduction of NOx (H2-NH3-SCR) over Ag/Al2O3 catalysts was investigated by operando spectroscopy (DRIFTS-MS and DR-UV–Vis) and Density Functional Theory (DFT) calculation. UV–Vis analysis showed that several kinds of silver species were present on the Ag/Al2O3, including dispersed silver cations, partially oxidized silver clusters, metallic silver clusters, and silver nanoparticles. Operando DRIFTS-MS experiments showed that the reduction of NOx was dependent on the formation rate of nitrates, which was closely related to the silver content, H2 concentration, and reaction temperature. Notably, operando DR-UV–Vis experiments unambiguously confirmed that the metallic silver clusters were the active sites for nitrates formation, and the reduction of silver nitrates was much slower than NO oxidation. DFT calculations further revealed that reducing silver nitrates required higher energy barriers than NO oxidation, while H2 dissociation could occur on metallic silver clusters with a moderate energy barrier. In conclusion, metallic silver clusters contributed to the formation of nitrates and H2 dissociation, and the reduction of silver nitrates was the rate-determining step in the overall H2-NH3-SCR reaction.

Nitrate produced from industrial and agricultural processes has imbalanced the global nitrogen cycle. Electrocatalytic reduction is a sustainable route to remediate nitrate while generating products such as ammonia or N2. Here we report the surface-area normalized activity of platinum-ruthenium (PtxRuy/C) catalysts of different compositions (x = 48–100%) for electrocatalytic nitrate reduction, chosen based on screening using a computational activity volcano plot. The PtxRuy/C alloys are more active than Pt/C, with Pt78Ru22/C six times more active than Pt/C at 0.1 V vs. RHE, and ammonia faradaic efficiencies of 93–98%. Density functional theory calculations predict maximum activity at 25 at% Ru, consistent with experiments. This maximum is due to a transition from nitrate dissociation as the rate determining step to a new rate-determining step at higher Ru content. This study demonstrates how electrocatalyst performance is tunable by changing the adsorption strength of reacting species through alloying.

In this work, vapor–liquid and vapor–solid equilibrium pressure and enthalpies of amine hydrochlorides were determined using a thermogravimetric method. Ferrocene was used as the reference compound to determine the calibration constant k. Then, ammonium bromide, ammonium chloride and benzoic acid were used for testing the k-ferrocene. Experimental vapor–solid equilibrium pressure of methylamine hydrochloride obtained in this study showed good agreement with recent literature data. For the other substances investigated, ethanolamine hydrochloride, pyridine hydrochloride, and trimethylamine hydrochloride, no reliable equilibrium data is available in the open literature. Among these substances, ethanolamine hydrochloride was found to be the less volatile, followed by methylamine, trimethylamine, and pyridine hydrochloride. Regarding the equilibrium enthalpies found in this work, all salts have shown a similar value. This can be explained by the similar reaction (dissociation) that takes place for these substances.

Author(s): Liu, J; He, N; Zhang, Z; Yang, J; Jiang, X; Zhang, Z; Su, J; Shu, M; Si, R; Xiong, G; Xie, HB; Vile, G | Abstract: We report herein the preparation, characterization, and catalytic performance of a series of heterogeneous catalysts featuring highly dispersed zinc sites on zeolitic SSZ-13 and ZSM-5 frameworks. The materials are evaluated in the CO2-assisted oxidative ethane dehydrogenation, a very important reaction for the synthesis of platform chemicals. In particular, we find that Zn2.92/SSZ-13 exhibits high reactivity in the conversion of C2H6 and CO2 and high ethene selectivity. In line with the experimental results, we show that the selective character of the catalyst is due to the characteristic compositional structure of the support and its topology that can effectively confine CO2 molecules. An in-depth molecular analysis via operando studies and DFT calculations shows that the rate-limiting step of the reaction with CO2 is the second C-H bond dissociation to give C2H4. The addition of CO2 effectively reduces the energy barrier of this step, favoring desorption of C2H4 while limiting byproduct formation. Overall, this work demonstrates the breakthrough potential of catalysts made of highly dispersed zinc species on zeolites in relevant transformations.

The ternary Pd complexes [(phen)Pd(H)]+ (1-Pd) and [(phen)Pd(CH3)]+ (5-Pd) (where phen = 1,10-phenanthroline) both react with hexane in a linear ion trap mass spectrometer, forming the C–H activation product [(phen)Pd(C6H11)]+ (3-Pd) and releasing H2 and CH4, respectively. Density functional theory (DFT) calculations agree well with the experiments in predicting low barriers for these reactions proceeding via a metathesis mechanism. Species 3-Pd undergoes extensive fragmentation, or "cracking", of the hydrocarbon chain when sufficient energy is supplied via collision-induced dissociation (CID), resulting in the extrusion of a mixture of alkenes, methane, and hydrogen. DFT calculations show that Pd "chain-walking" from α (terminal carbon) to β and from β to γ positions can proceed with barriers sufficiently below those required for chain "cracking". The fragmentation reactions can be made catalytic if 1-Pd and 5-Pd produced by CID of 3-Pd are allowed to react with hexane again. Ni complexes largely mirrored the chemistry observed for Pd. Both 1-Ni and 5-Ni reacted with hexane, forming 3-Ni, which fragmented under CID conditions in a fashion similar to 3-Pd. In contrast, only 5-Pt reacted with hexane to form 3-Pt, which fragmented predominantly via sequential losses of H2.

Electrocatalytic hydrogen evolution under alkaline media holds great promising in hydrogen energy production. Transition-metal sulfides (TMSs) are attractive for electrocatalytic alkaline hydrogen evolution, yet their catalytic performance is unsatisfactory owing to the sluggish water dissociation kinetics. Herein, a Mn/N co-doping strategy is proposed to regulate the water dissociation kinetics of Co9S8 nanowires array grown on nickel foam thus improve the activity of hydrogen evolution reaction (HER). The optimal Mn/N co-doping Co9S8 (Mn–N–Co9S8) catalyst achieves low overpotentials of 102 and 238 mV at 10 and 100 mA cm−2 in the 1 M KOH solution, respectively, remarkably higher than the single-doping Mn–Co9S8 and N–Co9S8 as well as superior to many reported Co9S8-based HER electrocatalysts. Density functional theory (DFT) calculation results confirm that the water dissociation barrier of the Mn–N–Co9S8 is reduced significantly owing to the synergistic co-doping of Mn and N, which accounts for the enhanced alkaline HER performance. This study offers an effective strategy to enhance the alkaline HER activity of TMSs by accelerating water dissociation kinetic via the cation and anion co-doping strategy.