Showing papers on "Oxidation state published in 2020"
TL;DR: It is reported that catalysts with nanocavities can confine carbon intermediates formed in situ, which in turn covers the local catalyst surface and thereby stabilizes Cu+ species, which leads to the marked C2+ selectivity at large conversion rate.
Abstract: Selective and efficient catalytic conversion of carbon dioxide (CO2) into value-added fuels and feedstocks provides an ideal avenue to high-density renewable energy storage. An impediment to enabling deep CO2 reduction to oxygenates and hydrocarbons (e.g., C2+ compounds) is the difficulty of coupling carbon-carbon bonds efficiently. Copper in the +1 oxidation state has been thought to be active for catalyzing C2+ formation, whereas it is prone to being reduced to Cu0 at cathodic potentials. Here we report that catalysts with nanocavities can confine carbon intermediates formed in situ, which in turn covers the local catalyst surface and thereby stabilizes Cu+ species. Experimental measurements on multihollow cuprous oxide catalyst exhibit a C2+ Faradaic efficiency of 75.2 ± 2.7% at a C2+ partial current density of 267 ± 13 mA cm-2 and a large C2+-to-C1 ratio of ∼7.2. Operando Raman spectra, in conjunction with X-ray absorption studies, confirm that Cu+ species in the as-designed catalyst are well retained during CO2 reduction, which leads to the marked C2+ selectivity at a large conversion rate.
289 citations
TL;DR: In situ SEIRAS results show the coexistence of COatop and CObridge as the reaction intermediates during CO2 reduction and the selectivity of CO2-to-ethylene conversion is further enhanced in the CV-treated Cu electrode.
Abstract: Understanding the role of the oxidation state of the Cu surface and surface-adsorbed intermediate species in electrochemical CO2 reduction is crucial for the development of selective CO2-to-fuel electrocatalysts. In this study, the electrochemical CO2 reduction mechanism over the Cu catalysts with various oxidation states was studied by using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), in situ soft X-ray absorption spectroscopy (Cu L-edge), and online gas chromatography measurements. The atop-adsorbed CO (COatop) intermediate is obtained on the electrodeposited Cu surface which primarily has the oxidation state of Cu(I). COatop is further reduced, followed by the formation of C1 product such as CH4. The residual bridge-adsorbed CO (CObridge) is formed on the as-prepared Cu surface with Cu(0) which inhibits hydrocarbon formation. In contrast, the CV-treated Cu electrode prepared by oxidizing the as-prepared Cu surface contains different amounts of Cu(I) and Cu(0) states. The major theme of this work is that in situ SEIRAS results show the coexistence of COatop and CObridge as the reaction intermediates during CO2 reduction and that the selectivity of CO2-to-ethylene conversion is further enhanced in the CV-treated Cu electrode. The Cu catalysts modulated by the electrochemical method exhibit different oxidation states and reaction intermediates as well as electrocatalytic properties.
254 citations
TL;DR: This work reports the first direct observation for the charge transfer and bond evolution of single-atom Pt/C 3 N 4 catalyst in photocatalytic water splitting using synchronous illumination X-ray photoelectron spectroscopy (SI-XPS).
Abstract: Single-atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single-atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single-atom Pt/C3 N4 catalyst in photocatalytic water splitting by synchronous illumination X-ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt-N bond cleavage to form a Pt0 species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum-decorated C3 N4 catalyst. As expected, H2 production activity (14.7 mmol h-1 g-1 ) was enhanced significantly with the single-atom Pt/C3 N4 catalyst as compared to metallic Pt-C3 N4 (0.74 mmol h-1 g-1 ).
207 citations
TL;DR: Control experiments and theoretical calculations demonstrate that the superior ORR catalytic performance of Cu1-SA/NC(meso)-7 catalyst is attributed to the atomically dispersed Cu1+ sites in catalyzing the reaction and the advantage of the introduced mesoporous structure in enhancing the mass transport.
Abstract: Herein, we report efficient single copper atom catalysts that consist of dense atomic Cu sites dispersed on a three-dimensional carbon matrix with highly enhanced mesoporous structures and improved...
160 citations
TL;DR: An X-ray crystallography and spectroscopy study at room temperature using anX-ray free electron laser to collect a “molecular movie” of the structural and oxidation state change steps leading to the insertion of this new oxygen bridge, in the 50 µs to 200 ms time scales after photon absorption, which triggers the S2 → S3 state transition.
Abstract: In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the room-temperature structures of PS II in the four (semi)stable S-states, S1, S2, S3, and S0, showing that a water molecule is inserted during the S2 → S3 transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O2 formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S2 → S3 transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QA and QB, are observed. At the donor site, tyrosine YZ and His190 H-bonded to it move by 50 µs after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of OX(H) at the open coordination site of Mn1. This water, possibly a ligand of Ca, could be supplied via a "water wheel"-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (τ of ∼350 µs) during the S2 → S3 transition mirrors the appearance of OX electron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.
118 citations
TL;DR: An overview of the last 10 years for aluminum (i) and gallium(i) stabilized by β-diketiminate ligands that have been widely explored in bond breaking and forming species is presented.
Abstract: Over the past few decades, β-diketiminate ligands have been widely used in coordination chemistry and are capable of stabilizing various metal complexes in multiple oxidation states. Recently, the chemistry of aluminum and gallium in their +1 oxidation state has rapidly emerged. NacNacM(i) (M = Al, Ga; NacNac = β-diketiminate ligand) shows a two coordinate metal center comparable with singlet carbene-like species. The metal center also possesses a formally vacant p-orbital. In this article we present an overview of the last 10 years for aluminum(i) and gallium(i) stabilized by β-diketiminate ligands that have been widely explored in bond breaking and forming species.
78 citations
TL;DR: It is revealed that CO2 can be captured and reduced into *CO on the Cut 0 site, owing to its zero oxidation state, and may open a new avenue for CO2 reduction into high-value fuels and chemicals.
Abstract: The mixing of charge states of metal copper catalysts may lead to a much improved reactivity and selectivity toward multicarbon products for CO2 reduction. Here, an electrocatalyst model composed of copper clusters supported on graphitic carbon nitride (g-C3 N4 ) is proposed; the connecting Cu atoms with g-C3 N4 can be oxidized to Cux + due to substantial charge transfer from Cu to N atoms, while others stay as Cu0 . It is revealed that CO2 can be captured and reduced into *CO on the Cut 0 site, owing to its zero oxidation state. More importantly, C-C coupling reaction of two *CHO species on the Cut 0 -Cub x + atomic interface can occur with a rather low kinetic barrier of 0.57 eV, leading to the formation of the final C2 product, namely, C2 H5 OH. During the whole process, the limiting potential is just 0.68 V. These findings may open a new avenue for CO2 reduction into high-value fuels and chemicals.
77 citations
TL;DR: In this article, the authors increased the concentration of interfacial sites with rich defects in a 3D hierarchical nanostructured NiO-Co3O4 electrocatalyst and investigated its catalytic performance for HMF electro-oxidation.
Abstract: Ni-based electrocatalysts with strong redox abilities are active for the electrochemical oxidation of 5-hydroxymethylfurfural (HMF). Interface engineering is an efficient way to modulate the electronic structure, tune the intermediate adsorption, and expose more active sites. Herein, we increased the concentration of interfacial sites with rich defects in a 3D hierarchical nanostructured NiO-Co3O4 electrocatalyst and investigated its catalytic performance for HMF electro-oxidation. The interface effect created abundant cation vacancies, modulated the electronic properties of Co and Ni atoms, and raised the oxidation state of Ni species. The NiO-Co3O4 catalysts show superb HMF oxidation activities with a low onset potential of 1.28 VRHE. Meanwhile, in-situ surface-selective vibrational spectroscopy of sum-frequency generation was performed to study the reaction pathway during the oxidation process on the electrocatalysts. The current study offers an efficient way to create cation vacancies and proves the decisive role of cation vacancies in catalyzing the HMF electro-oxidation.
65 citations
TL;DR: FexMo1-xS2/PS system can effectively remove various persistent organic pollutants and works well in a real water environment and can efficiently activate peroxymonosulfate, sulfite and H2O2, suggesting its potential practical applications under various circumstances.
65 citations
TL;DR: A paramagnetic beryllium radical cation, [(CAAC)2Be]+● [CAAC = cyclic (al-kyl)(amino)carbene] (2), prepared by oxidation of a zero-valent berylla complex with TEMPO (2, 2, 6, 6-tetramethylpiperidine-1-oxyl).
Abstract: The alkaline-earth elements (Be, Mg, Ca, Sr, and Ba) strongly favor the formation of diamagnetic compounds in the +2 oxidation state. Herein we report a paramagnetic beryllium radical cation, [(CAA...
61 citations
TL;DR: This work reports a molecular iron(II) system that captures this design concept in a homogeneous setting through the use of a redox non-innocent terpyridine-based pentapyridine ligand (tpyPY2Me) and provides a starting point for the design of systems that exploit metal-ligand cooperativity for electrocatalysis where the electrochemical potential of redoxNon-inn Innocent ligands can be tuned through secondary metal-dependent interactions.
Abstract: Biological and heterogeneous catalysts for the electrochemical CO2 reduction reaction (CO2RR) often exhibit a high degree of electronic delocalization that serves to minimize overpotential and maximize selectivity over the hydrogen evolution reaction (HER). Here, we report a molecular iron(II) system that captures this design concept in a homogeneous setting through the use of a redox non-innocent terpyridine-based pentapyridine ligand (tpyPY2Me). As a result of strong metal-ligand exchange coupling between the Fe(II) center and ligand, [Fe(tpyPY2Me)]2+ exhibits redox behavior at potentials 640 mV more positive than the isostructural [Zn(tpyPY2Me)]2+ analog containing the redox-inactive Zn(II) ion. This shift in redox potential is attributed to the requirement for both an open-shell metal ion and a redox non-innocent ligand. The metal-ligand cooperativity in [Fe(tpyPY2Me)]2+ drives the electrochemical reduction of CO2 to CO at low overpotentials with high selectivity for CO2RR (>90%) and turnover frequencies of 100 000 s-1 with no degradation over 20 h. The decrease in the thermodynamic barrier engendered by this coupling also enables homogeneous CO2 reduction catalysis in water without compromising selectivity or rates. Synthesis of the two-electron reduction product, [Fe(tpyPY2Me)]0, and characterization by X-ray crystallography, Mossbauer spectroscopy, X-ray absorption spectroscopy (XAS), variable temperature NMR, and density functional theory (DFT) calculations, support assignment of an open-shell singlet electronic structure that maintains a formal Fe(II) oxidation state with a doubly reduced ligand system. This work provides a starting point for the design of systems that exploit metal-ligand cooperativity for electrocatalysis where the electrochemical potential of redox non-innocent ligands can be tuned through secondary metal-dependent interactions.
TL;DR: A scalable approach to achieving a spatially partial substitution of S into NiMoO4 is presented and the increase in active components in a true Ni3+ oxidation state as a result of optimizing the coordination environment greatly improved urea oxidation activity.
TL;DR: Electrochemical operando Raman spectroscopy is established for investigation of the atomic structure and oxidation state of a non-crystalline, hydrated, and phosphate-containing Co oxide material (CoCat), which is an electrocatalyst for the oxygen evolution reaction (OER) at neutral pH and is structurally similar to LiCoO2 of batteries.
Abstract: Transition metal oxides are of high interest in both energy storage (batteries) and production of non-fossil fuels by (photo)electrocatalysis. Their functionally crucial charge (oxidation state) changes and electrocatalytic properties are best investigated under electrochemical operation conditions. We established operando Raman spectroscopy for investigation of the atomic structure and oxidation state of a non-crystalline, hydrated, and phosphate-containing Co oxide material (CoCat), which is an electrocatalyst for the oxygen evolution reaction (OER) at neutral pH and is structurally similar to LiCoO2 of batteries. Raman spectra were collected at various sub-catalytic and catalytic electric potentials. 2H labeling suggests Co oxidation coupled to Co—OH deprotonation at catalytic potentials. 18O labeling supports O—O bond formation starting from terminally coordinated oxygen species. Two broad bands around 877 cm−1 and 1077 cm−1 are assigned to CoCat-internal H2PO4-. Raman peaks corresponding to terminal oxide (Co=O) or reactive oxygen species were not detectable; 1000–1200 cm−1 bands were instead assigned to two-phonon Raman scattering. At an increasingly positive potential, the intensity of the Raman bands decreased, which is unexpected and explained by self-absorption relating to CoCat electrochromism. A red-shift of the Co—O Raman bands with increasing potentials was described by four Gaussian bands of potential-dependent amplitudes. By linear combination of Raman band amplitudes, we can follow individually the Co(2+/3+) and Co(3+/4+) redox transitions, whereas previously published x-ray absorption spectroscopy analysis could determine only the averaged Co oxidation state. Our results show how electrochemical operando Raman spectroscopy can be employed as a potent analytical tool in mechanistic investigations on OER catalysis.
TL;DR: This report reports the third example of a molecular complex of terbium(IV) which was isolated and characterized by EPR, UV-vis spectroscopy, SQUID magnetometry, and cyclic voltammetry, and provides key information for the isolation of stable lanthanide( IV) ions.
Abstract: The synthesis of lanthanides other than cerium in the oxidation state +IV has remained a desirable but unmet target until recently, when two examples of TbIV with saturated coordination spheres were isolated. Here we report the third example of an isolated molecular complex of terbium(IV), where the supporting siloxide ligands do not saturate the coordination sphere. The fully characterized six-coordinate complex [TbIV (OSiPh3 )4 (MeCN)2 ], 2-TbPh , shows high stability and the labile MeCN ligands can be replaced by phosphinoxide ligands. Computational studies suggest that the stability is due to a strong π(O-Tb) interaction which is stronger than in the previously reported TbIV complexes. Cyclic-voltammetry experiments demonstrate that non-binding counterions contribute to the stability of TbIV in solution by destabilizing the +III oxidation state, while alkali ions promote TbIV /TbIII electron transfer.
Adria Airways1, University of Barcelona2, Jiangsu University3, University of Electronic Science and Technology of China4, Southern University of Science and Technology5, Polytechnic University of Catalonia6, Spanish National Research Council7, Heilongjiang University8, Institute of Science and Technology Austria9
TL;DR: In this article, a new electrocatalyst by incorporating phosphorous into a palladium-tin alloy and demonstrating a significant performance improvement toward ethanol oxidation reaction (EOR) was proposed.
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TL;DR: In this article, X-ray spectroscopy and in situ micro-reactors were used to reveal the variation in the complex electronic structure of redox-active copper catalysts during fabrication and electrocatalytic reactions.
Abstract: Redox-active copper catalysts with accurately prepared oxidation states (Cu0, Cu+ and Cu2+) and high selectivity to C2 hydrocarbon formation, from electrocatalytic cathodic reduction of CO2, were fabricated and characterized. The electrochemically prepared copper-redox electro-cathodes yield higher activity for the production of hydrocarbons at lower oxidation state. By combining advanced X-ray spectroscopy and in situ micro-reactors it was possible to unambiguously reveal the variation in the complex electronic structure that the catalysts undergo at different stages (i.e. during fabrication and electrocatalytic reactions). It was found that the surface, sub-surface and bulk properties of the electrochemically prepared catalysts are dominated by the formation of copper carbonates on the surface of cupric-like oxides, which prompts catalyst deactivation by restraining effective charge transport. Furthermore, the formation of reduced or partially-reduced copper catalysts yields the key dissociative proton-consuming reactive adsorption of CO2 to produce CO; allowing the subsequent hydrogenation into C2 and C1 products by dimerization and protonation. These results yield valuable information on the variations in the electronic structure that redox-active copper catalysts undergo in the course of the electrochemical reaction, which, under extreme conditions are mediated by thermodynamics but, critically, kinetics dominate near the oxide/metal phase transitions.
TL;DR: In this paper, an electrochemical nitrogen oxidation reaction (NOR) approach is developed to produce nitrate catalyzed by ZnFex Co2-x O4 spinel oxides.
Abstract: Nitrates are widely used as fertilizer and oxidizing agents. Commercial nitrate production from nitrogen involves high-temperature-high-pressure multi-step processes. Therefore, an alternative nitrate production method under ambient environment is of importance. Herein, an electrochemical nitrogen oxidation reaction (NOR) approach is developed to produce nitrate catalyzed by ZnFex Co2-x O4 spinel oxides. Theoretical and experimental results show Fe aids the formation of the first N-O bond on the *N site, while high oxidation state Co assists in stabilizing the absorbed OH- for the generation of the second and third N-O bonds. Owing to the concerted catalysis, the ZnFe0.4 Co1.6 O4 oxide demonstrates the highest nitrate production rate of 130±12 μmol h-1 gMO-1 at an applied potential of 1.6 V versus the reversible hydrogen electrode (RHE).
TL;DR: In this paper, the Fe nanoparticles (Fe2O3) on the rutile TiO2 were partially transformed to the thermally stable FeTiO3 phases with its lower oxidation state (Fe 2+) below 700 °C.
Abstract: Prototype FeOx/TiO2 was applied for dehydrogenation of ethane to ethylene and successive CO2 activation to CO for further chemical looping (CL) application. The Fe(5)/TiO2 exhibited a facile redox cyclic activity with an insignificant coke formation and comparable CO2 activation through reduction-oxidation reaction cycles. During the oxidative dehydrogenation of chemical looping (CL-ODH), the Fe nanoparticles (Fe2O3) on the rutile TiO2 were partially transformed to the thermally stable FeTiO3 phases with its lower oxidation state (Fe2+) below 700 °C. However, the formations of Fe2TiO5 phases were found to be less active than the smaller sizes of iron oxides (Fe3+). The thermally stable iron phases with their reversible redox natures between FeTiO3 and Fe2O3 phases were responsible for a stable reduction-oxidation activity. The robust preservation of the partially reduced surface Fe2+ sites with the copresence of the larger Fe2O3 hematite crystallites on the TiO2 was responsible for improving the redox activity and stability.
TL;DR: The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under as mentioned in this paper, and this understanding is crucial for the design of electrocatalyst design.
Abstract: The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under
TL;DR: In this article, bare chromia nanoparticles (Cr2O3 NPs) and chromia supported on reduced graphene oxide and graphene oxide (GO) hybrids were synthesized, followed by characterization by means of FESEM, Raman spectroscopy, TGA, XRD, TEM/HRTEM, XPS and N2 sorptiometry.
Abstract: Herein, bare chromia nanoparticles (Cr2O3 NPs) and chromia supported on reduced graphene oxide (rGO) and graphene oxide (GO) hybrids were synthesized, followed by characterization by means of FESEM, Raman spectroscopy, TGA, XRD, TEM/HRTEM, XPS and N2 sorptiometry. The investigated bare Cr2O3 and the hybrids (Cr2O3/rGO and Cr2O3/GO) were employed as catalysts for low-temperature CO oxidation. Compared with the other catalysts, the results revealed efficient catalytic activity using Cr2O3/GO, which was attributed to its higher surface area together with the mixed oxidation state of chromium (Cr3+ and Cr>3+). These are important oxidation sites that facilitate the electron mobility essential for CO oxidation. Moreover, the presence of carbon vacancy defects and functional groups facilitate the stabilizing of Cr2O3 NPs on its surface, forming a thermally stable hybrid material, which assists the CO oxidation process. The Cr2O3/GO hybrid is a promising low-cost and efficient catalyst for CO oxidation at low temperatures. The higher activity of graphene oxide supported Cr2O3 NPs can provide an efficient and cost-effective solution to a prominent environmental problem.
TL;DR: IUPAC’s “ionic approximation” is a useful tool to reliably classify nitrosyl metal complexes in an orbital‐centered approach.
Abstract: Nitrosyl-metal bonding relies on the two interactions between the pair of N-O-π* and two of the metal's d orbitals. These (back)bonds are largely covalent, which makes their allocation in the course of an oxidation-state determination ambiguous. However, apart from M-N-O-angle or net-charge considerations, IUPAC's "ionic approximation" is a useful tool to reliably classify nitrosyl metal complexes in an orbital-centered approach.
TL;DR: In this paper, the authors found that IrO2 NP (nanoparticles) of around 7nm are found to activate CH4 at a temperature as low as −110°C when Raman bands of surface species at 1328 and 1581 cm−1 are observed, accompanied by the partial reduction of IrO 2.
TL;DR: It is demonstrated that cation-intercalation and H2SO4 environment alter the Ti3C2Tx surface chemistry.
Abstract: Intercalation in Ti3C2Tx MXene is essential for a diverse set of applications such as water purification, desalination, electrochemical energy storage, and sensing. The interlayer spacing between the Ti3C2Tx nanosheets can be controlled by cation intercalation; however, the impact of intercalation on the Ti3C2Tx MXene chemical and electronic structures is not well understood. Herein, we characterized the electronic structure of pristine, Li-, Na-, K-, and Mg-intercalated Ti3C2Tx MXenes dispersed initially in water and 10 mM sulfuric acid (H2SO4) using X-ray absorption spectroscopy (XAS). The cation intercalation is found to dramatically influence the chemical environment of Ti atoms. The Ti oxidation of the MXene increases progressively upon intercalation of cations of larger sizes after drying in air, while interestingly a low Ti oxidation is observed for all intercalated MXenes after dispersion in diluted H2SO4. In situ XAS at the Ti L-edge was conducted during electrochemical oxidation to probe the changes in the Ti oxidation state in the presence of different cations in H2SO4 aqueous electrolyte. By applying the sensitivity of the Ti L-edge to probe the oxidation state of Ti atoms, we demonstrate that cation-intercalation and H2SO4 environment significantly alter the Ti3C2Tx surface chemistry.
TL;DR: In this article, a nanocrystalline high entropy oxide with near-equimolar composition consisting of 5 transition metal cations and one alkali cation (Co,Cu,Mg,Na,Ni,Zn)O was synthesised by a reverse co-precipitation (RCP) process and characterised by standard methods of X-ray diffraction (for crystallite size and phases), electron microscopy (for particle morphology and size distribution) and Fourier transform infra-red spectroscopy, for bond identification and bond lengths).
Abstract: A nanocrystalline high entropy oxide with near-equimolar composition consisting of 5 transition metal cations and one alkali cation (Co,Cu,Mg,Na,Ni,Zn)O was synthesised by a reverse co-precipitation (RCP) process and characterised by standard methods of X-ray diffraction (for crystallite size and phases), electron microscopy (for particle morphology and size distribution) and Fourier transform infra-red spectroscopy (for bond identification and bond lengths). Charge compensation in the lattice by the formation of Co3+ and/or Ni3+ (in order to offset the +1 oxidation state of Na) and the creation of oxygen vacancies was quantified from X-ray photoelectron spectroscopy and Raman spectroscopy and further studied using vibrating sample magnetometry (VSM). The influence of different transition metals in being able to accommodate the larger and aliovalent sodium ion in a single phase-pure rocksalt lattice was investigated and the criteria for element selection in such multicomponent systems for single-phase formation examined. Presence of multivalency/non-stoichiometry to accommodate a different-sized cation and maintaining electroneutrality were identified as the critical criteria for single-phase formation in multicomponent systems and further confirmed through synthesis of various lower combination systems (by systematic removal of one transition metal cation) and by addition of bivalent Ca as well as cations of higher valencies. These criteria would aid in designing the compositions of high entropy oxides with aliovalent substitutions.
TL;DR: In this article, a new perovskite oxide, La1.15MnO3+δ with excess La, for a lowered average oxidation state of Mn cations and abundant oxygen vacancies, which can be active sites for peroxymonosulfate activation.
TL;DR: This work systematically compares IUPAC, EOS, and LOBA across a series of complexes where OS assignment is challenging, and introduces a clarity index for LOBA OS assignments that provides an indication of whether or not its predictions are close to the ionic-covalent boundary.
Abstract: The oxidation state (OS) of metals and ligands in inorganic complexes may be defined by carefully curated rules, such as from IUPAC, or by computational procedures such as the effective oxidation state (EOS) or localized orbital bonding analysis (LOBA). Such definitions typically agree for systems with simple ionic bonding and innocent ligands but may disagree as the boundary between ionic and covalent bonds is approached, or as the role of ligand noninnocence becomes nontrivial, or high oxidation states of metals are supported by heavy dative bonding, and so on. This work systematically compares IUPAC, EOS, and LOBA across a series of complexes where OS assignment is challenging. These systems include high-valent transition metal oxides, transition metal complexes with noninnocent ligands such as dithiolate and nitrosyl, metal sulfur dioxide adducts, and two transition metal carbene complexes. The differences in OS assignment by the three methods are carefully discussed, demonstrating the synergy between EOS and LOBA. In addition, a clarity index for LOBA OS assignments is introduced that provides an indication of whether or not its predictions are close to the ionic-covalent boundary.
TL;DR: An iron metal–organic framework, Fe-BTTri, is reported that binds O2 in a manner similar to hemoglobin and therefore results in highly selective O2 binding, with the highest reported O2/N2 selectivity for any iron-based framework.
Abstract: Bio-inspired motifs for gas binding and small molecule activation can be used to design more selective adsorbents for gas separation applications. Here, we report an iron metal-organic framework, Fe-BTTri (Fe3[(Fe4Cl)3(BTTri)8]2·18CH3OH, H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), that binds O2 in a manner similar to hemoglobin and therefore results in highly selective O2 binding. As confirmed by gas adsorption studies and Mossbauer and infrared spectroscopy data, the exposed iron sites in the framework reversibly adsorb substantial amounts of O2 at low temperatures by converting between high-spin, square-pyramidal Fe(ii) centers in the activated material to low-spin, octahedral Fe(iii)-superoxide sites upon gas binding. This change in both oxidation state and spin state observed in Fe-BTTri leads to selective and readily reversible O2 binding, with the highest reported O2/N2 selectivity for any iron-based framework.
TL;DR: The Inorganic Crystal Structural Database (ICSD) strongly evidences the relevance of NgBs in the solid state structures of xenon derivatives and the ability of Xe compounds to participate in π,σ-hole interactions has been studied using different types of electron donors (Lewis bases and anions) and the molecular electrostatic potential (MEP) surfaces.
Abstract: A noble gas bond (also known in the literature as aerogen bond) can be defined as the attractive interaction between any element of group-18 acting as a Lewis acid and any electron rich atom of group of atoms, thus following the IUPAC recommendation available for similar π,σ-hole interactions involving elements of groups 17 (halogens) and 16 (chalcogens). A significant difference between noble gas bonding (NgB) and halogen (HaB) or chalcogen (ChB) bonding is that whilst the former is scarcely found in the literature, HaB and ChB are very common and their applications in important fields like catalysis, biochemistry or crystal engineering have exponentially grown in the last decade. This article combines theory and experiment to highlight the importance of non-covalent NgBs in the solid state of several xenon fluorides [XeFn]m+ were the central oxidation state of Xe varies from +2 to +6 and the number of fluorine atoms varies from n = 2 to 6. The compounds with an odd number of fluorine atoms (n = 3 and 5) are cationic (m = 1). The Inorganic Crystal Structural Database (ICSD) strongly evidences the relevance of NgBs in the solid state structures of xenon derivatives. The ability of Xe compounds to participate in π,σ-hole interactions has been studied using different types of electron donors (Lewis bases and anions) using DFT calculations (PBE1PBE-D3/def2-TZVP) and the molecular electrostatic potential (MEP) surfaces.
TL;DR: K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions is reported and the presence of three distinct Cl species in the materials is demonstrated and how these species evolve during reaction is demonstrated.
Abstract: The replacement of HgCl2/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl−, Au–Cl, and C–Cl and how these species evolve during reaction Direct evidence of Au–S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles This stability was clear during gas switching experiments, where exposure to C2H2 alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst
TL;DR: In this article, a new synthetic method to prepare a composite of metal oxide nanoparticles and zeolite (Fe-ZSM-5) in hot compressed water was described.