Variable Oxidation States Research Articles

Augmented gravimetric and volumetric capacitive performance of rare earth metal oxide (Eu2O3) incorporated polypyrrole for supercapacitor applications

We report a facile in situ synthesis approach to incorporate rare earth metal oxide (Eu2O3) into the polypyrrole matrix and evaluate its electrochemical performance as supercapacitor electrode material. Polypyrrole, having good conductivity, higher chemical and thermal stability proves to be a very interesting electrode material. Eu2O3 further augments the capacitance of the material owing to its variable oxidation states. Also, owed to the higher stability, it provides additional support to the polymer backbone imparting extra thermal and cyclic stability to the hybrid composite so formed. The PPy/Eu2O3-32 composite exhibits a volumetric capacitance of 535Fcm−3 at the current density of 1Ag−1. This material also exhibits an improved energy density of 13.5WhL−1 and a maximum power density of 4597.25WL−1. Further, a good rate capability (18% loss of specific capacitance from 1 to 10Ag−1) and high coulombic efficiency (99.8% at 10Ag−1) proves integration of Eu2O3 with PPy to be an effective way to eliminate the drawbacks of PPy in pristine form.

Design and synthesis of some novel 7-substituted thiosemicarbazinyl-quinolines via Ullmann coupling reaction and examination of their antimicrobial activities

The present work demonstrates functionalization of 4,7-dichloro quinoline via a modified Ullmann coupling reaction concept of varying oxidation state and reaction conditions. Based on these conditions, novel 2-(4-morpholino quinolin-7-yl)-N-substituted phenyl hydrazinyl carbothioamide derivatives have been synthesized. Structures of the final synthesized compounds including intermediates were confirmed by IR, 1H NMR and 13C NMR spectral studies. Examination of biological profiles was carried out against various strains of micro-organisms. SAR and HOMO–LUMO calculations were carried out for judicious design.

Non-classical behaviour of higher valence dopants in chromium (III) oxide by a Cr vacancy compensation mechanism

Modification of metal oxides with dopants that have a stable oxidation in their parent oxides which is higher than the host system is expected to introduce extra electrons into the material to improve carrier mobility. This is essential for applications in catalysis, SOFCs and solar energy materials. Density functional theory calculations are used to investigate the change in electronic and geometric structure of chromium (III) oxide by higher valence dopants, namely; Ce, Ti, V and Zr. For single metal doping, we find that the dopants with variable oxidation states, Ce, Ti and V, adopt a valence state of +3, while Zr dopant has a +4 oxidation state and reduces a neighbouring Cr cation. Chromium vacancy formation is greatly enhanced for all dopants, and favoured over oxygen vacancy formation. The Cr vacancies generate holes which oxidise Ce, Ti and V from +3 to +4, while also oxidising lattice oxygen sites. For Zr doping, the generated holes oxidise the reduced Cr2+ cation back to Cr3+ and also two lattice oxygen atoms. Three metal atoms in the bulk lattice facilitate spontaneous Cr vacancy from charge compensation. A non-classical compensation mechanism is observed for Ce, Ti and V; all three metals are oxidised from +3 to +4, which explains experimental observations that these metals have a +4 oxidation state in Cr2O3. Charge compensation of the three Zr metals proceeds by a classical higher valence doping mechanism; the three dopants reduce three Cr cations, which are subsequently charge compensated by a Cr vacancy oxidising three Cr2+ to Cr3+. The compensated structures are the correct ground state electronic structure for these doped systems, and used as a platform to investigate cation/anion vacancy formation. Unlike the single metal doped bulks, preference is now given for oxygen vacancy formation over Cr vacancy formation, indicating that the dopants increase the reducibility of Cr2O3 with Ce doping showing the strongest enhancement. The importance of the correct ground state in determining the formation of defects is emphasised.

(Invited) First Principles Studies of Nitrogen Electrochemistry and the Electrocatalytic Properties of Ultrathin (hydroxy)Oxide Films

Advances in the theoretical understanding of interfacial electrochemistry have, over the past decade, permitted the extension of periodic Density Functional Theory studies, which have traditionally been applied to probe chemistry at gas/solid interfaces, to electrochemical systems where potential-dependent structural and chemical phase transformations occur at liquid/solid interfaces. Indeed, such techniques have been employed to study a surprisingly wide class of electrochemical processes, ranging from electrocatalysis to corrosion. In this talk, we will discuss how these strategies can be applied to predict the detailed, atomic-scale properties of monolayer (hydroxy)oxide base metal films on precious metal and precious metal alloy substrates as a function of applied potential. We will describe the analysis of Moire patterns, variable oxidation states, and three-phase boundaries of these films, and we will demonstrate how these results may be used to predict the shape and oxidation states of supported two-dimensional nanoislands as a function of electrochemical conditions. We will next discuss how the three-phase boundaries may promote hydrogen evolution rates in alkaline environments, and we will close with some perspectives on the possibilities for electrocatalyst design offered by these systems. If time permits, we will also discuss a new approach, based on a combination of DFT and kinetic Monte Carlo simulations, that permits direct simulation of polarization curves as a function of sweep rate and that rigorously predicts intrinsic reaction pathways for both electroreduction of nitrates and NO in acidic environments.

Selective synthesis of 2, 5-furandicarboxylic acid by oxidation of 5-hydroxymethylfurfural over MnFe2O4 catalyst

Development of green catalytic processes using biobased feedstock for valuable chemicals such as 5-hydroxymethylfurfural (HMF) is hotly pursued. 2, 5-Furandicarboxylic acid (FDCA), a bio-based alternative to terephthalic acid was efficiently synthesized by oxidation of HMF using MnFe2O4 spinel structured magnetic nanoparticles (MNPs) and tert-butyl hydroperoxide as an oxidant. MnFe2O4 catalyst showed the highest activity and selectivity and gave 85% yield of FDCA at 100°C in 5h. The higher activity of MnFe2O4 catalyst is due to the variable oxidation state of manganese. The combination of MnFe2O4 catalyst and TBHP oxidant requires less time and energy compared to other reported processes of FDCA synthesis. Also, many reported methods have used a homogeneous base for FDCA synthesis which is totally avoided in the current process. The concentration profiles of reactants and products were established and kinetics determined. The effects of various reaction parameters were studied to validate kinetic model. The catalyst was easily recycled due to its magnetic property and showed good catalytic activity up to four cycles. All metal ferrites were characterized by different analytical techniques. The catalyst maintained its fidelity.

Zircon Trace Element Constraints on the Evolution of the Paleoproterozoic Birimian Granitoids of the West African Craton (Ghana)

The Paleoproterozoic Birimian granitoids of the West African Craton (WAC) in the northwestern part of Ghana, have been studied for their zircon trace elements concentrations to infer the source characteristics, origin, and magmatic evolution. The zircons in the granitoids have Th/U ratios ranging from 0.03 to 1.55, and display depleted light rare earth elements (LREE) and enriched heavy rare earth elements (HREE) contents, characterized by pronounced positive to negative anomalies of Eu (Eu/Eu*=0.14–0.98 and 1.01–6.06, respectively) and Ce (Ce/Ce*=0.08–0.98 and 1.02–116, respectively), which may imply that they were derived from both magmatic and hydrothermal sources. The geochemical plots of U/Yb vs. Y and Hf, the positive correlation between Hf and the other high field strength elements (HFSE) and high rare earth elements (REE) contents, with enrichment in Ce and depletion in Eu, indicate that the granitoids possibly formed from partial melting of the crust. The trace elements characteristics (i.e., wide range of Hf, Ce/Ce*, Th/U and Zr/Hf values) of the zircons suggest that crystallization of the magma occurred under variable oxidation states, which spanned over a longer period, implying that our data corroborate interpretations from studies of whole-rock geochemistry and geochronology on the granitoids of northwestern Ghana. This further indicates that the evolution of the Birimian granitoids in this part of the WAC occurred earlier than what had been reported in the literature.

Fairly improved pseudocapacitance of PTP/PANI/TiO2 nanohybrid composite electrode material for supercapacitor applications

A ternary composite of PTP/PANI/TiO2 was synthesized using in situ oxidative polymerization. Material design involves the blending of the two polymers namely polyaniline and polythiophene and further incorporating TiO2 particles in the blended polymer matrix. TiO2 being transition metal oxide possesses variable oxidation states leading to excellent pseudocapacitive properties, owing to the synergy of the inorganic filler (TiO2). PTP/PANI/TiO2 ternary composite exhibits improved capacitive performance as compared to its constituents in pristine form. This ternary composite exhibits the maximum specific capacitance of 265 F g−1 as measured by galvanostatic charging-discharging (GCD) at 1 A g−1. Further, the hybrid composite was also characterized to possess an energy density of 9.09 Wh kg−1 at 1 A g−1 and a power density of 3770 W kg−1 at a current density of 10 A g−1.

Highly Stable Nanocarbon Catalysts for Bifunctional Oxygen Reduction and Evolution Reactions in Alkaline Media

Bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play predominant role in improving electrochemical performance of reversible fuel cell (RFC) and metal-air batteries (MRB).1-3 In addition, the cost of these electrocatalysts largely determine economic feasibility and market penetration of these renewable energy technologies. Although precious metals such as Pt, Ru and Ir have been used as bifunctional electrocatalysts, their high cost and poor long-term stability has restricted the commercial feasibility of these devices. On the other hand, transition metal oxides (such as carbon supported MnO2) including perovskite oxides (such as carbon supported BSCF, PBCO, SNCF) have appreciable catalytic activity, they suffer from poor surface area, electronic conductivity and carbon support corrosion in high potential of OER regime. Nanocarbon-based catalysts have many advantages over others due to their low cost, excellent electrical conductivity, high surface area, and easy functionalization. However, they typically cannot withstand the highly oxidative OER environment. In our recent works, we found that the electrochemical stability of carbon is highly depended on their morphology, structure and surrounding electronic environment. For instance, amorphous carbon black was found to be highly unstable, whereas highly graphitized carbon nanotubes were very stable during accelerated stress test (AST). Subsequently, in a parallel effort we found that the presence of transition metals (Fe, Co, Ni, Mn) and their alloys can significantly improve the stability of the as synthesized transition metal derived and nitrogen (N) doped graphene tubes. As a result, we were successful to synthesize ultralarge sized N doped graphene tubes (N-GTs) (>500 nm) decorated with FeCoNi alloy particles as a highly active and stable bifunctional electrocatalyst (N-GT(FeCoNi)). To present our more recent work, I will also show some electrochemical and related physical characterization highlighting tremendous increase in the stability and corrosion resistant as a result of the incorporation of multivalent Mn cation with variable oxidation states as the fourth dopant transition metal in the resulting highly graphitized N co-doped nanocarbon structure. The cost effective, easily scalable, and environmentally benign synthesis method along with impressive overall bifunctional performance favors the novel nanocarbon, i.e., graphene tubes’ application as a practical bifunctional electrocatalyst for alkaline membrane fuel cells and metal air batteries.

Recent developments in the nanostructured materials functionalized with ruthenium complexes for targeted drug delivery to tumors.

In recent years, the field of metal-based drugs has been dominated by other existing precious metal drugs, and many researchers have focused their attention on the synthesis of various ruthenium (Ru) complexes due to their potential medical and pharmaceutical applications. The beneficial properties of Ru, which make it a highly promising therapeutic agent, include its variable oxidation states, low toxicity, high selectivity for diseased cells, ligand exchange properties, and the ability to mimic iron binding to biomolecules. In addition, Ru complexes have favorable adsorption properties, along with excellent photochemical and photophysical properties, which make them promising tools for photodynamic therapy. At present, nanostructured materials functionalized with Ru complexes have become an efficient way to administer Ru-based anticancer drugs for cancer treatment. In this review, the recent developments in the nanostructured materials functionalized with Ru complexes for targeted drug delivery to tumors are discussed. In addition, information on “traditional” (ie, non-nanostructured) Ru-based cancer therapies is included in a precise manner.

IRIDIUM CHEMISTRY AND ITS CATALYTIC APPLICATIONS: A BRIEF

Iridium is very important element among the all transition metals with highest reported oxidation state i.e. +9 in gas phase existing species IrO4+. Instead of its less reactivity, it forms number of compounds having oxidation states between -3 to +9. It is second known densest element after osmium. Till now its toxicity and environmental impact is not much more reported and thus it may be use as green element in various fields of its application. Reason behinds it’s less toxicity and environmental impact may be due to its less reactivity and solubility. Corrosion and heat resistant properties of Iridium makes it much more useful element for alloying purpose. Iridium is the member of platinum family and used as catalyst due to its variable oxidation states. Iridium(III) complexes show great catalytic activity in both the acidic and basic medium for various organic as well as inorganic chemical transformations. Catalyst may be defined as the substance which can increases the rate of reaction of a specific chemical reaction without changing its own composition. Iridium is only one reported catalyst which is able to capture the sunlight and convert it into the chemical energy. Thus, it may be used in artificial photosynthesis process to solve our future food problem. Instead of these advantage, Iridium chemistry and its catalytic activity is not much reviewed till date, therefore, present review includes a brief introduction about chemistry and catalytic application of Iridium, which proof itself a boon for beginners to start their research career in the field of Iridium chemistry.

Studies on dielectric dispersion, relaxation kinetics and a.c. conductivity of Na2O[sbnd]CuO[sbnd]SiO2 glasses mixed with Bi2O3-Influence of redox behavior of copper ions

Na2OCuOSiO2 glasses mixed with different concentrations Bi2O3 (ranging from 0 to 20.0 mol%) were prepared. Various dielectric parameters viz., dielectric constant, ε′, loss tan δ, electric moduli, M, electrical impedance, Z, and also a.c. conductivity, σac(ω), in the frequency region 100 Hz to 1 MHz and in the temperature region 200 K‒400 K were measured as a function of Bi2O3 concentration. The obtained results were analyzed on the basis of space charge and dipolar polarization models. All the dielectric parameters exhibited decreasing trend with increase of Bi2O3 concentration. Our earlier spectroscopic studies of the same glass system indicated that there is a gradual reduction of Cu2+ ions into Cu+ ions with increase of Bi2O3 content in the glass network and these monovalent copper ions were found to participate in the network forming and form linkages with silicate structural units. The gradual increase in the degree of polymerization of the glass network is found to be the reason for the decrease of dielectric parameters. The variation of dielectric loss tanδ and electric moduli with frequency exhibited dipolar relaxation effects. The relaxation intensity is found to decrease, whereas the activation energy for the dipoles and the dielectric relaxation time are found to increase with increase in the concentration of Bi2O3. The observed relaxation effects are attributed to the complexes of divalent copper ions and Bi3+ ions. The variation of a.c. conductivity as a function Bi2O3 content exhibited a decrease (∼three orders of magnitude) with increase of Bi2O3 from 0 mol% to 20.0 mol%. The change of a.c. conductivity is explained in the light of varying oxidation states of copper ions using quantum mechanical tunneling model. The overall, analysis of these results indicated a gradual increase in the insulating character of the studied glass material with increase in the concentration of Bi2O3.

South-to-north pyroxenite–peridotite source variation correlated with an OIB-type to arc-type enrichment of magmas from the Payenia backarc of the Andean Southern Volcanic Zone (SVZ)

New high-precision minor element analysis of the most magnesian olivine cores (Fo85–88) in fifteen high-MgO (Mg#66–74) alkali basalts or trachybasalts from the Quaternary backarc volcanic province, Payenia, of the Andean Southern Volcanic Zone in Argentina displays a clear north-to-south decrease in Mn/Feol. This is interpreted as the transition from mainly peridotite-derived melts in the north to mainly pyroxenite-derived melts in the south. The peridotite–pyroxenite source variation correlates with a transition of rock compositions from arc-type to OIB-type trace element signatures, where samples from the central part of the province are intermediate. The southernmost rocks have, e.g., relatively low La/Nb, Th/Nb and Th/La ratios as well as high Nb/U, Ce/Pb, Ba/Th and Eu/Eu* = 1.08. The northern samples are characterized by the opposite and have Eu/Eu* down to 0.86. Several incompatible trace element ratios in the rocks correlate with Mn/Feol and also reflect mixing of two geochemically distinct mantle sources. The peridotite melt end-member carries an arc signature that cannot solely be explained by fluid enrichment since these melts have relatively low Eu/Eu*, Ba/Th and high Th/La ratios, which suggest a component of upper continental crust (UCC) in the metasomatizing agent of the northern mantle. However, the addition to the mantle source of crustal materials or varying oxidation state cannot explain the variation in Mn and Mn/Fe of the melts and olivines along Payenia. Instead, the correlation between Mn/Feol and whole-rock (wr) trace element compositions is evidence of two-component mixing of melts derived from peridotite mantle source enriched by slab fluids and UCC melts and a pyroxenite mantle source with an EM1-type trace element signature. Very low Ca/Fe ratios (~1.1) in the olivines of the peridotite melt component and lower calculated partition coefficients for Ca in olivine for these samples are suggested to be caused by higher H2O contents in the magmas derived from subduction zone enriched mantle. Well-correlated Mn/Fe ratios in the wr and primitive olivines demonstrate that the Mn/Fewr of these basalts that only fractionated olivine and chromite reflects the Mn/Fe of the primitive melts and can be used as a proxy for the amount of pyroxenite melt in the magmas. Using Mn/Fewr for a large dataset of primitive Payenia rocks, we show that decreasing Mn/Fewr is correlated with decreasing Mn and increasing Zn/Mn as expected for pyroxenite melts.

Effect of Variable Oxidation States of Vanadium on the Structural, Optical, and Dielectric Properties of B2O3-Li2O-ZnO-V2O5 Glasses.

In the present study, the effect of variable vanadium oxidation states on the structural, optical, and dielectric properties of vanadium oxide containing lithium borate glasses has been investigated. Electron paramagnetic resonance studies indicate that vanadium in these glasses is mostly in the V4+ state, having a tetragonal symmetry. As the glass composition of V2O5 increases, tetragonality also increases at the cost of octahedral symmetry. The photoluminescence (PL) spectra of these glasses are dominated by zinc oxide transition, whereas the peaks pertaining to the vanadyl group are not visible in the PL spectra. The optical absorption spectra show a single wide absorption band, which is attributed to V4+ ions in these glasses. The ac conductivity of the glasses increases with an increase in vanadium content. The highest electrical conductivity observed is ∼10-5 S cm-1 at 250 °C for the glass with 2.5 mol % V2O5. Electrical conductivity is dominated by electron conduction, as indicated by the activation energy calculation.

4 - Vacant Heme Catalyzes NO Yield from Nitrosopersulfide

When nitrosothiols react with excess hydrogen sulfide, H 2 S, they form several intermediates including nitrosopersulfide. The stability and importance of this species has been debated. While some data suggest nitrosopersulfidecan be a relatively stable source of NO activity, others suggest that the species degrades too quickly. In our hands, the species is relatively stable in isolation. The prevalence of iron-containing proteins throughout the human body adds importance to determining the interaction of ferrous- and ferric-iron containing proteins with nitrosopersulfide. Studying these interactions can also provide information about the potential in vivo stability and spontaneous reactivity of this species. We have used time-resolved electron paramagnetic resonance and UV-Vis absorption spectroscopy to study the reactions of nitrosopersulfide with heme proteins. We find that in the absence of heme proteins, nitrosopersulfide is relatively stable. Iron-nitrosyl hemoglobin is formed when nitrosopersulfide is reacted with unliganded hemoglobin of varying oxidation states, suggesting NO formation from nitrosopersulfide. However, iron-nitrosyl hemoglobin yields from the reaction of ferriheme and nitrosopersulfide is greater than that of ferrous heme and nitrosopersulfide. Little to no nitrosyl hemoglobin or methemoglobin is formed when nitrosopersulfide - is reacted with liganded ferrous heme. Although these data confirm the release of NO, they suggest a vacant heme is necessary to facilitate a direct heme-nitrosopersulfide reaction to form substantial NO. These data also suggest that the ferric iron in methemoglobin potentiates nitrosopersulfidereactivity. These results could potentially impact NO and sulfide bioavailability and reactivity. Supported by NIH grant HL058091

Measurement Techniques for the Study of Thin Film Heterogeneous Water Oxidation Electrocatalysts

Heterogeneous electrocatalysts for the oxygen evolution reaction (OER) are complicated materials with dynamic structures. They can exhibit potential-induced phase transitions, potential-dependent electronic properties, variable oxidation and protonation states, and disordered local/surface phases. These properties make understanding the OER, and ultimately designing higher efficiency catalysts, challenging. We report a series of procedures and measurement techniques that we have adopted or developed to assess each of the above challenges in understanding materials for the OER. These include the targeted synthesis of hydrated oxyhydroxide phases, the assessment and elimination of electrolyte impurities, the use of a quartz crystal microbalance to monitor film loading and dissolution, and the use of an in situ conductivity measurement to understand the flow of electrons from the catalyst active sites to the conductive support electrode. We end with a recipe for the synthesis and characterization of a “stand...

First Principles Studies of the Structural and Electrocatalytic Properties of Ultrathin (OXY)Hydroxide FILMS on Precious Metal Substrates

Advances in the theoretical understanding of interfacial electrochemistry have, over the past decade, permitted the extension of periodic Density Functional Theory studies, which have traditionally been applied to probe chemistry at gas/solid interfaces, to electrochemical systems where potential-dependent structural and chemical phase transformations occur at liquid/solid interfaces. Indeed, such techniques have been employed to study a surprisingly wide class of electrochemical processes, ranging from electrocatalysis to corrosion. In this talk, we will discuss how these strategies can be applied to predict the detailed, atomic-scale properties of monolayer (oxy)hydroxide base metal films on precious metal and precious metal alloy substrates as a function of applied potential in alkaline solutions. We will describe the analysis of Moire patterns, variable oxidation states, and three-phase boundaries of these films, and we will demonstrate how these results may be used to predict the shape and oxidation states of supported two-dimensional nanoislands as a function of electrochemical conditions. We will close with some perspectives on the possibilities for alkaline electrocatalyst design offered by these systems.

Unsymmetric (μ-oxido)/(μ-pyrazolato) and Symmetric (μ-pyrazolato)2 Bridged Diosmium Frameworks: Electronic Structure and Magnetic Properties.

The present article deals with the structurally characterized unsymmetric oxido/pyrazolato-bridged [(bpy)2Os(III)(μ-oxido)(μ-pz)Os(III)(bpy)2](ClO4)3 ([1](ClO4)3) and symmetric dipyrazolato-bridged [(bpy)2Os(II)(μ-pz)2Os(II)(bpy)2](ClO4)2 ([2](ClO4)2) (pz = pyrazolato, bpy = 2,2'-bipyridine) complexes with the Os···Os separations of 3.484 and 4.172 Å, respectively. The anti-ferromagnetically coupled Os(III) centers [E(S = 1)-E(BS(1,1) S = 0) = 322.504 cm(-1)] in 1(3+) and diamagnetic (S = 0) 2(2+) exhibit well-resolved (1)H NMR resonances. [1](ClO4)3 shows temperature- and magnetic field-dependent paramagnetism at low magnetic field and diamagnetism at high magnetic field. 1(3+) and 2(2+) display successive metal-based oxidation processes involving the intermediate mixed-valent states and isovalent congeners: Os(IV)Os(IV) (1(5+))→Os(III)Os(IV) (1(4+))⇌Os(III)Os(III) (1(3+))⇌Os(III)Os(II) (1(2+)) and Os(III)Os(III) (2(4+))→Os(II)Os(III) (2(3+))⇌Os(II)Os(II) (2(2+)) as well as bpy-centered reductions. The effect of π donor O(2-) and σ/π-donating pz(-) in 1(3+) and 2(2+), respectively, leads to varying oxidation state of the metal ions in the isolated complexes: Os(III)Os(III) versus Os(II)Os(II). UV-visible-near-IR-electron paramagnetic resonance spectro-electrochemistry and density functional theory (DFT)/time-dependent DFT calculations collectively reveal overlapping of the metal- and ligand (pz, O, bpy)-based frontier orbitals in the delocalized mixed-valent states in 1(4+) and 1(2+) with comproportionation constant (Kc) value > 1 × 10(14) as well as in isovalent 1(3+), resulting in mixed metal/ligand to metal/ligand near-IR transitions in all the three states. The mixed-valent Os(II)Os(III) state in 2(3+) exhibits high Kc value of 1 × 10(22) corresponding to a strong electrochemical coupling situation. However, closeness of the bandwidth (Δν1/2, 4861 cm(-1)) of broad and weak intervalence charge transfer transition of 2(3+) at 1360 nm (ε/M(-1) cm(-1): 490) with the calculated Δν1/2 of 4121 cm(-1) based on the Hush formula as well as spin-density distributions of Os1: 0.811/0.799, Os2: 0.045/0042, and pz: 0.162/0.173 in meso and rac diastereomeric forms, respectively, attribute its localized class II state.

Dissociative adsorption of methane on the Cu and Zn doped (111) surface of CeO2

The development of economical heterogeneous catalysts for the activation of methane is a major challenge for the chemical industry. Screening potential candidates becomes more feasible using rational catalyst design to understand the activity of potential catalysts for CH4 activation. The focus of the present paper is the use of density functional theory to examine and elucidate the properties of doped CeO2. We dope with Cu and Zn transition metals having variable oxidation state (Cu), and a single oxidation state (Zn), and study the activation of methane. Zn is a divalent dopant and Cu can have a +1 or +2 oxidation state. Both Cu and Zn dopants have an oxidation state of +2 after incorporation into the CeO2 (111) surface; however a Hubbard +U correction (+U=7) on the Cu 3d states is required to maintain this oxidation state when the surface interacts with adsorbed species. Dissociation of methane is found to occur locally at the dopant cations, and is thermodynamically and kinetically more favorable on Zn-doped CeO2 than Cu-doped CeO2. The origins of this lie with the Zn(II) dopant moving towards a square pyramidal geometry in the sub surface layer which facilitates the formation of two-coordinated surface oxygen atoms, that are more beneficial for methane activation on a reducible oxide surface. These findings can aid in rational experimental catalyst design for further exploration in methane activation processes.

Rh chemistry through the eyes of theory

We discuss the properties of Rh and its compounds from a theoretical chemistry perspective. Like its neighbors in the platinum metal group, this element exhibits a remarkable spectrum of catalytic activity both as an elemental metal and as the central ion of transition metal complexes. This property is reflected in a comparatively weak chemical bond dominated by d–p interactions, varying oxidation states and a highly flexible coordination shell. In turn, theoretical methods and their generalization as empirical concepts have to be able to deal with a multitude of binding situations and the strong electron–electron interaction within the Rh valence orbitals. Whereas density functional theory has greatly enhanced the computational accessibility of Rh compounds, quantitative models of catalytic cycles require a more explicit treatment of static electron correlation, such as integrated density functional‐coupled cluster schemes. WIREs Comput Mol Sci 2016, 6:311–320. doi: 10.1002/wcms.1250This article is categorized under: Structure and Mechanism > Molecular Structures Structure and Mechanism > Reaction Mechanisms and Catalysis

Effect of transition metal impregnation on oxidative regeneration of activated carbon by catalytic wet air oxidation

Impregnation of a commercial activated carbon (AC) with transition metals was investigated to extend its reuse as phenol adsorbent after regeneration by catalytic wet air oxidation (CWAO). Iron and copper catalysts were prepared with varied metal dispersions and oxidation states by using different heat treatments. The main feature of the iron catalysts was to reduce the phenol oligomerization due to oxidative coupling, while the copper catalyst was prone to leaching promoting homogeneous reaction. However their regeneration efficiency was not significantly improved with respect to the starting AC due to an increased adverse effect of CWAO itself on their adsorptive properties.