Theory of surface chemistry and reactivity of reducible oxides

Metal-support interactions in metal oxide-supported atomic, cluster, and nanoparticle catalysis

Supported metal catalysts are essential to a plethora of processes in the chemical industry. The overall performance of these catalysts depends strongly on the interaction of adsorbates at the atomic level, which can be manipulated and controlled by the different constituents of the active material (i.e., support and active metal). The description of catalyst activity and the relationship between active constituent and the support, or metal-support interactions (MSI), in heterogeneous (thermo)catalysts is a complex phenomenon with multivariate (dependent and independent) contributions that are difficult to disentangle, both experimentally and theoretically. So-called "strong metal-support interactions" have been reported for several decades and summarized in excellent review articles. However, in recent years, there has been a proliferation of new findings related to atomically dispersed metal sites, metal oxide defects, and, for example, the generation and evolution of MSI under reaction conditions, which has led to the designation of (sub)classifications of MSI deserving to be critically and systematically evaluated. These include dynamic restructuring under alternating redox and reaction conditions, adsorbate-induced MSI, and evidence of strong interactions in oxide-supported metal oxide catalysts. Here, we review recent literature on MSI in oxide-supported metal particles to provide an up-to-date understanding of the underlying physicochemical principles that dominate the observed effects in supported metal atomic, cluster, and nanoparticle catalysts. Critical evaluation of different subclassifications of MSI is provided, along with discussions on the formation mechanisms, theoretical and characterization advances, and tuning strategies to manipulate catalytic reaction performance. We also provide a perspective on the future of the field, and we discuss the analysis of different MSI effects on catalysis quantitatively.

Understanding the Electronic and Structural Effects in ORR Intermediate Binding on Anion-Substituted Zirconia Surfaces

For oxygen reduction reaction (ORR), the surface adsorption energies of O and OH* intermediates are key descriptors for catalytic activity. In this work, we investigate anion-substituted zirconia catalyst surfaces and determine that adsorption energies of O and OH* intermediates is governed by both structural and electronic effects. When the adsorption energies are not influenced by the structural effects of the catalyst surface, they exhibit a linear correlation with integrated crystal orbital Hamiltonian population (ICOHP) of the adsorbate-surface bond. The influence of structural effects, due to the re-optimisation slab geometry after adsorption of intermediate species, leads to stronger adsorption of intermediates. Our calculations show that there is a change in the bond order to accommodate the incoming adsorbate species which leads to stronger adsorption when both structural and electronic effects influence the adsorption phenomena. The insights into the catalyst-adsorbate interactions can guide the design of future ORR catalysts.

Interfacial Electron Potential Well Facilitates the Design of Cobalt Phosphide Heterojunctions for Hydrogen Evolution

The interfacial electron modulation of electrocatalysts is an effective way to realize efficient hydrogen production, which is of great importance for future renewable energy systems. However, systematic theory-guided design of catalysts in heterojunction coupling is lacking. In this work, a multi-level theoretical calculation is performed to screen optimal candidates to form a heterojunction with CoP (101) surface for electrocatalytic hydrogen production. To overcome the weak adsorption of H+ on CoP (101), rational design of electrons potential well at the heterojunction interface can effectively enhance the hydrogen adsorption. All p-type cobalt-based phosphides are considered potential candidates at the beginning. After screening for conductivity, stability, interface matching screening, and ΔGH* evaluation, the CoP/Co2P-H system is identified to be able to display optimal hydrogen production performance. To verify the theoretical design, CoP, CoP/Co2P-H, and CoP/Co2P-O are synthesized and the electrochemical analysis is carried out. The hydrogen evolution reaction (HER) performance is consistent with the prediction. This work utilizes the electron potential well effect and multi-level screening calculations to design highly efficient heterojunction catalysts, which can provide useful theoretical guidance for the rational design of heterojunction-type catalysts.

Surface Chemistry of Biologically Active Reducible Oxide Nanozymes

Reducible metal oxide nanozymes (rNZs) are a subject of intense recent interest due to their catalytic nature, ease of synthesis, and complex surface character. Such materials contain surface sites which facilitate enzyme-mimetic reactions via substrate coordination and redox cycling. Further, these surface reactive sites are shown to be highly sensitive to stresses within the nanomaterial lattice, the physicochemical environment, and to processing conditions occurring as part of their syntheses. When administered in vivo, a complex protein corona binds to the surface, redefining its biological identity and subsequent interactions within the biological system. Catalytic activities of rNZs each deliver a differing impact on protein corona formation, its composition, and in turn, their recognition, and internalization by host cells. Improving the understanding of the precise principles that dominate rNZ surface-biomolecule adsorption raises the question of whether designer rNZs can be engineered to prevent corona formation, or indeed to produce "custom" protein coronas applied either in vitro, and preadministration, or formed immediately upon their exposure to body fluids. Here, fundamental surface chemistry processes and their implications in rNZ material performance are considered. In particular, material structures which inform component adsorption from the application environment, including substrates for enzyme-mimetic reactions are discussed.

Operando CO Infrared Spectroscopy and On-Line Mass Spectrometry for Studying the Active Phase of IrO2 in the Catalytic CO Oxidation Reaction

We combine operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with on-line mass spectrometry (MS) to study the correlation between the oxidation state of titania-supported IrO2 catalysts (IrO2@TiO2) and their catalytic activity in the prototypical CO oxidation reaction. Here, the stretching vibration of adsorbed COad serves as the probe. DRIFTS provides information on both surface and gas phase species. Partially reduced IrO2 is shown to be significantly more active than its fully oxidized counterpart, with onset and full conversion temperatures being about 50 °C lower for reduced IrO2. By operando DRIFTS, this increase in activity is traced to a partially reduced state of the catalysts, as evidenced by a broad IR band of adsorbed CO reaching from 2080 to 1800 cm−1.

Spinel structure of activated carbon supported MFe2O4 composites as an economic and efficient electrocatalyst for oxygen reduction reaction in neutral media

For more sustainability and marketing of microbial fuel cells (MFCs) in wastewater treatment, the sluggish kinetics of cathode oxygen reduction reaction (ORR) and platinum scarcity (with its high cost) should be swept away. So, this work aimed to synthesize metal ferrite (MFe2O4; M = Mn, Cu, and Ni) -based activated carbon composites as inexpensive ORR cathode catalysts. The composites were synthesized using a facile modified co-precipitation approach with low-thermal treatment and labeled as MnFe2O4/AC, CuFe2O4/AC, and NiFe2O4/AC. The as-synthesized catalysts are physicochemically characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared microscopy (FTIR), Barrett-Joyner-Halenda (BJH), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and electron spin resonance (ESR). The electrochemical catalytic performance toward ORR was studied in a phosphate buffer solution (PBS) at neutral media via cyclic voltammetry (CV) and linear sweep voltammetry (LSV). MnFe2O4/AC has the highest onset potential (Eonset) value of − 0.223 V compared to CuFe2O4/AC (− 0.280 V) and NiFe2O4/AC (− 0.270 V). MnFe2O4/AC also has the highest kinetic current density (jK) and lowest Tafel slope (− 5 mA cm−2 and − 330 mV dec−1) compared to CuFe2O4/AC (− 3.05 mA cm−2 and − 577 mV dec−1) and NiFe2O4/AC (− 2.67 mA cm−2 and − 414 mV dec−1). The ORR catalyzed by MnFe2O4/AC at pH = 7 proceeds via a 4e− -kinetic pathway. The ESR is in good agreement with the electrochemical analysis due to the highest ∆Hppvalue for MnFe2O4/AC compared to CuFe2O4/AC and NiFe2O4/AC. Thus, MnFe2O4/AC is suggested as a promising alternative to Pt- electrocatalyst cathode for MFCs at neutral conditions.

Graphical Abstract

A novel non-enzymatic sensor for prostate cancer biomarker sensing based on electrocatalytic oxidation of sarcosine at nanostructured NiMn2O4 impregnated carbon paste electrode

This work addresses the electrocatalytic activity of a binary metal oxide catalyst of NiMn₂O₄ for electroxidation of sarcosine, the well-known prostate cancer biomarker. The nanocatalyst described was prepared via hydrothermal synthesis route, followed by calcination at 800 °C. Field emission scanning electron microscopy and X-ray diffraction were applied to obtain information about the material morphology and structure. A carbon paste electrode modified with nano-NiMn₂O₄ showed unique catalytic activity in sarcosine electroxidation which led to a significant rise in oxidation current (about four times) in comparison with the blank electrode. However, the carbon paste electrodes containing single oxides of NiO and Mn₂O₃ exhibited no considerable enhancement in sarcosine signal. The cyclic voltammetry results indicated that the Mn³⁺/Mn⁴⁺ couple was responsible for sarcosine oxidation, and NiO may enhance the content of Mn⁴⁺species in NiMn₂O₄ material. The carbon paste-based NiMn₂O₄ electrode was applied in the sensitive determination of sarcosine in the concentration range of 0.01-5.0 μM with the relative standard deviation of 3.49% (n = 5). The detection limit and quantification limit of the probe were determined to be 3.8 and 12 nM, respectively. The remarkable sensitivity and high selectivity of the method approved the sensor applicability in measurement of sarcosine content in urine samples.

Dielectric Properties and Spectral Characteristics of Photocatalytic Constant of TiO2 Nanoparticles Doped with Cobalt

Dielectric properties and spectral dependence of the photocatalytic constant of Co doped P25 Degussa powder were studied. Doping of TiO₂ matrix with cobalt was achieved by precipitation method using of Tris(diethylditiocarbamate)Co(III) precursor (CoDtc–Co[(C₂H₅)₂NCS₂]₃). Five different Co contents with nominal Co/Ti atomic ratios of 0.005, 0.01, 0.02, 0.05 and 0.10 were chosen. Along with TiO₂:Co samples, a few samples of nanopowders prepared by Sol-Gel method were also studied. As it follows from XPS and NMR studies, there is a concentration limit (TiO₂:0.1Co) where cobalt atoms can be uniformly distributed across the TiO₂ matrix before metallic clusters start to form. It was also shown that CoTiO₃ phases are formed during annealing at high temperatures. From the temperature dependence of the dielectric constant it can be concluded that the relaxation processes still take place even at temperatures below 400 °C and that oxygen defect Ti–O octahedron reorientation take place at higher temperatures. The spectral dependency of the photocatalytic constant reveals the presence of some electronic states inside the energy gap of TiO₂ for all nanopowdered samples.

Double-network cross-linked aerogel with rigid and super-elastic conversion: simple formation, unique properties, and strong sorption of organic contaminants

Novel adsorbents with high adsorption capacity, broad-spectrum adsorption performance, and good reusability are needed for the treatment of diverse and complex contaminants in water. In this work, we used in situ hydrothermal reaction to fabricate graphene oxide (GO) and poly(vinyl alcohol) (PVA) based aerogels (GP_XA, X represented the volume of PVA) through the cross-linking network that meets the above requirement. After adding Ca²⁺, GP₁₆A (with 16 mL PVA) had surprisingly rigid and super-elastic conversion that is dependent on water stimulus. The strong adsorption of methylene blue (MB) on GP₁₆A illustrated that it had excellent dye removal ability. The adsorption capacity of GP₁₆A to MB was 698.38 mg g^-1 and it remained 85.62% after repeated adsorption-desorption cycles. The adsorption was controlled by multiple mechanisms including electrostatic interaction, π-π interaction, and hydrogen bond. In addition, hydrophobically modified GP₁₆A (GP₁₆A-MTMS) effectively absorbed common oils and organic solvents. Repeated absorption of GP₁₆A-MTMS was re-activated by squeezing operation. This study provides an alternative technique for preparing aerogel materials with high recyclability, dimensional stability, and solvent resistance, and for dealing organic contaminants in water.

Machine learned features from density of states for accurate adsorption energy prediction

Materials databases generated by high-throughput computational screening, typically using density functional theory (DFT), have become valuable resources for discovering new heterogeneous catalysts, though the computational cost associated with generating them presents a crucial roadblock. Hence there is a significant demand for developing descriptors or features, in lieu of DFT, to accurately predict catalytic properties, such as adsorption energies. Here, we demonstrate an approach to predict energies using a convolutional neural network-based machine learning model to automatically obtain key features from the electronic density of states (DOS). The model, DOSnet, is evaluated for a diverse set of adsorbates and surfaces, yielding a mean absolute error on the order of 0.1 eV. In addition, DOSnet can provide physically meaningful predictions and insights by predicting responses to external perturbations to the electronic structure without additional DFT calculations, paving the way for the accelerated discovery of materials and catalysts by exploration of the electronic space.

Computational catalysis would strongly benefit from general descriptors applicable for predicting adsorption energetics. Here the authors propose a machine-learning approach for adsorption energy predictions based on learning the relevant descriptors in a surface atom's density of states as part of the training.

Hydrogen in Nanocatalysis

Hydrogen is ubiquitous in catalysis. It is involved in many important reactions such as water splitting, N₂ reduction, CO₂ reduction, and alkane activation. In this Perspective, we focus on the hydrogen atom and follow its electron as it interacts with a catalyst or behaves as part of a catalyst from a computational point of view. We present recent examples in both nanocluster and solid catalysts to elucidate the parameters governing the strength of the hydrogen-surface interactions based on site geometry and electronic structure. We further show the interesting behavior of hydride in nanometal and oxides for catalysis. The key take-home messages are: (1) the in-the-middle electronegativity and small size of hydrogen give it great versatility in interacting with active sites on nanoparticles and solid surfaces; (2) the strength of hydrogen binding to an active site on a surface is an important descriptor of the chemical and catalytic properties of the surface; (3) the energetics of the hydrogen binding is closely related to the electronic structure of the catalyst; (4) hydrides in nanoclusters and oxides and on surfaces offer unique reactivity for reduction reactions.

Absolute energy level positions in tin- and lead-based halide perovskites

Metal halide perovskites are promising materials for future optoelectronic applications. One intriguing property, important for many applications, is the tunability of the band gap via compositional engineering. While experimental reports on changes in absorption or photoluminescence show rather good agreement for different compounds, the physical origins of these changes, namely the variations in valence and conduction band positions, are not well characterized. Here, we determine ionization energy and electron affinity values of all primary tin- and lead-based perovskites using photoelectron spectroscopy data, supported by first-principles calculations and a tight-binding analysis. We demonstrate energy level variations are primarily determined by the relative positions of the atomic energy levels of metal cations and halide anions and secondarily influenced by the cation-anion interaction strength. These results mark a significant step towards understanding the electronic structure of this material class and provides the basis for rational design rules regarding the energetics in perovskite optoelectronics.

The band gap of metal halide perovskites can be tuned by changing composition, but the underlying mechanism is not well understood. Here the authors determine, by experiments and theoretical analysis, the energy levels of all primary tin- and lead-based perovskites, relating them to the levels of the composing ions.

Correlations between Density-Based Bond Orders and Orbital-Based Bond Energies for Chemical Bonding Analysis

Quantum chemistry-based codes and methods provide valuable computational tools to estimate reaction energetics and elucidate reaction mechanisms. Electronic structure methods allow directly studying the chemical transformations in molecular systems involving breaking and making of chemical bonds and the associated changes in the electronic structure. The link between the electronic structure and chemical bonding can be provided through the crystal orbital Hamilton population (COHP) analysis that allows quantifying the bond strength by computing Hamilton-weighted populations of localized atomic orbitals. Another important parameter reflecting the nature and strength of a chemical bond is the bond order that can be assessed by the density derived electrostatic and chemical (DDEC6) method which relies on an electron and spin density-partitioning scheme. Herein, we describe a linear correlation that can be established between the DDEC6-derived bond orders and the bond strengths computed with the COHP formalism. We demonstrate that within defined boundaries, the COHP-derived bond strengths can be consistently compared among each other and linked to the DDEC6-derived bond orders independent of the used model. The validity of these correlations and the effective model independence of the electronic descriptors are demonstrated for a variety of gas-phase chemical systems, featuring different types of chemical bonds. Furthermore, the applicability of the derived correlations to the description of complex reaction paths in periodic systems is demonstrated by considering the zeolite-catalyzed Diels-Alder cycloaddition reaction between 2,5-dimethylfuran and ethylene.

New Bonding Model of Radical Adsorbate on Lattice Oxygen of Perovskites

A new model of bonding between radical adsorbates and lattice oxygens is proposed that considers both the adsorbate-oxygen bonding and the weakening of the metal-oxygen bonds. Density functional calculations of SrMO₃ perovskites for M being 3d, 4d, and 5d transition metals are used to correlate the bulk electronic structure with the surface-oxygen reactivity. Occupation of the metal-oxygen antibonding states, examined via the crystal orbital Hamilton population (COHP), is found to be a useful bulk descriptor that correlates with the vacancy formation energy of the lattice oxygen and its hydrogen adsorption energy. Analysis of density-of-states and COHP indicates that H adsorption energy is a combined result of formation of the O-H bond and the weakening of the surface metal-oxygen bond due to occupation of the metal-oxygen antibonding states by the electron from H. This insight will be useful in understanding the trends in surface reactivity of perovskites and transition-metal oxides in general.

Electronic Structure Analysis of the Diels-Alder Cycloaddition Catalyzed by Alkali-Exchanged Faujasites

The Diels-Alder cycloaddition (DAC) reaction is a commonly employed reaction for the formation of C-C bonds. DAC catalysis can be achieved by using Lewis acids and via reactant confinement in aqueous nanocages. Low-silica alkali-exchanged faujasite catalysts combine these two factors in one material. They can be used in the tandem DAC/dehydration reaction of biomass-derived 2,5-dimethylfuran (DMF) with ethylene toward p-xylene, in which the DAC reaction step initiates the overall reaction cycle. In this work, we performed periodic density functional theory (DFT) calculations on the DAC reaction between DMF and C2H4 in low-silica alkali(M)-exchanged faujasites (MY; Si/Al = 2.4; M = Li+, Na+, K+, Rb+, Cs+). The aim was to investigate how confinement of reactants in MY catalysts changed their electronic structure and the DAC-reactivity trend among the evaluated MY zeolites. The conventional high-silica alkali-exchanged isolated site model (MFAU; Si/Al = 47) served as a reference. The results show that confinement leads to initial-state (IS) destabilization and transition-state (TS) stabilization. Among the tested MY, most significant IS destabilization is found in RbY. Only antibonding orbital interactions between the reactants/reactive complex and cations were found, indicating that TS stabilization arises from ionic interactions. Additionally, in RbY the geometry of the transition state is geometrically most similar to that of the initial and final state. RbY also exhibits an optimal combination of the confinement-effects, resulting in having the lowest computed DAC-activation energy. The overall effect is a DAC-reactivity trend inversion in MY as compared to the trend found in MFAU where the activation energy correlates with the Lewis acidity of the exchangeable cations.

Mechanism of heterogeneous catalytic oxidation of organic compounds to carboxylic acids

The results of studies on the mechanism of heterogeneous catalytic oxidation of organic compounds of different chemical structure to carboxylic acids are analyzed and generalized. The concept developed by Academician G.K.Boreskov, according to which the direction of the reaction is governed by the structure and bond energy of surface intermediates, was confirmed taking the title processes as examples. Quantitative criteria of the bond energies of surface compounds of oxidizable reactants, reaction products and oxygen that determine the selective course of the reaction are presented.

The bibliography includes 195 references.

Constrained-Orbital Density Functional Theory. Computational Method and Applications to Surface Chemical Processes

We present a method for performing density-functional theory (DFT) calculations in which one or more Kohn-Sham orbitals are constrained to be localized on individual atoms. This constrained-orbital DFT (CO-DFT) approach can be used to tackle two prevalent shortcomings of DFT: the lack of transparency with regard to the governing electronic structure in large (planewave based) DFT calculations and the limitations of semilocal DFT in describing systems with localized electrons or a large degree of static correlation. CO-DFT helps to address the first of these issues by decomposing complex orbital transformations occurring during elementary chemical processes into simpler and more intuitive transformations. The second issue is addressed by using the CO-DFT method to generate configuration states for multiconfiguration Kohn-Sham calculations. We demonstrate both of these applications for elementary reaction steps involved in the oxygen evolution reaction.

LOBSTER: A tool to extract chemical bonding from plane-wave based DFT

The computer program LOBSTER (Local Orbital Basis Suite Towards Electronic-Structure Reconstruction) enables chemical-bonding analysis based on periodic plane-wave (PAW) density-functional theory (DFT) output and is applicable to a wide range of first-principles simulations in solid-state and materials chemistry. LOBSTER incorporates analytic projection routines described previously in this very journal [J. Comput. Chem. 2013, 34, 2557] and offers improved functionality. It calculates, among others, atom-projected densities of states (pDOS), projected crystal orbital Hamilton population (pCOHP) curves, and the recently introduced bond-weighted distribution function (BWDF). The software is offered free-of-charge for non-commercial research. © 2016 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

Hydrothermal synthesis of bi-functional nanostructured manganese tungstate catalysts for selective oxidation

The mechanism of C-H activation in selective oxidation reactions of short-chain alkane molecules over transition metal oxides is critically affected by the balance of acid-base and redox sites at the surface of the catalyst. Using the example of manganese tungstate we discuss how the relative abundance of these sites can be controlled via synthetic techniques. Phase-pure catalysts composed of the thermodynamic stable monoclinic MnWO4 phase have been prepared using hydrothermal synthesis. Variation of the initial pH value resulted in rod-shaped nano-crystalline MnWO4 catalysts composed of particles with varying aspect ratio. The synthesis products have been analysed using transmission electron microscopy, X-ray diffraction, infrared, and photoelectron spectroscopy. In situ Raman spectroscopy was used to investigate the dissolution-re-crystallization processes occurring under hydrothermal conditions. Ethanol oxidation was applied to probe the surface functionalities in terms of acid-base and redox properties. Changes in the aspect ratio of the primary catalyst particles are reflected in the product distribution induced by altering the fraction of acid-base and redox sites exposed at the surface of the catalysts in agreement with the proposed mechanism of particle growth by re-crystallization during ageing under hydrothermal conditions.

Insights into the synergistic role of metal–lattice oxygen site pairs in four-centered C–H bond activation of methane: the case of CuO

Of the three mechanisms for activation of methane on copper and copper oxide surfaces, the under-coordinated Cu–O site pair mediated mechanism on CuO surfaces has the lowest activation energy barriers.

The effect of lanthanum(III) and cerium(III) ions between layers of manganese oxide on water oxidation

Manganese oxide structure with lanthanum(III) or cerium(III) ions between the layers was synthesized by a simple method. The ratio of Mn to Ce or La in samples was 0.00, 0.04, 0.08, 0.16, 0.32, 0.5, 0.82, or 1.62. The compounds were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction studies, and atomic absorption spectroscopy. The compounds show efficient catalytic activity of water oxidation in the presence of cerium(IV) ammonium nitrate with a turnover frequency of 1.6 mmol O2/mol Mn.s. In contrast to the water-oxidizing complex in Photosystem II, calcium(II) has no specific role to enhance the water-oxidizing activity of the layered manganese oxides and other cations can be replaced without any significant decrease in water-oxidizing activities of these layered Mn oxides. Based on this and previously reported results from oxygen evolution in the presence of H 2 (18) O, we discuss the mechanism and the important factors influencing the water-oxidizing activities of the manganese oxides.

Structure Sensitivity of the Oxygen Evolution Reaction Catalyzed by Cobalt(II,III) Oxide

Quantum chemical calculations and simulated kinetics were used to examine the structure sensitivity of the oxygen evolution reaction on several surface terminations of Co3O4. Active sites consisting of two adjacent Co(IV) cations connected by bridging oxos were identified on both the (001) and (311) surfaces. Formation of the O-O bond proceeds on these sites by nucleophilic attack of water on a bridging oxo. It was found that the relative turnover frequencies for the different sites are highly dependent on the overpotential, with the dual-Co site on the (311) surface being most active at medium overpotentials (0.46-0.77 V), where O-O bond formation by water addition is rate limiting. A similar dual-Co site on the (001) surface is most active at low overpotentials (<0.46 V), where O2 release is rate limiting, and a single-Co site on the (110) surface is most active at overpotentials that are high enough (>0.77 V) to form a significant concentration of highly reactive terminal Co(V)═O species. Two overpotential-dependent Sabatier relationships were identified based on the Brønsted basicity and redox potential of the active site, explaining the change in the active site with overpotential. The (311) dual-Co site that is most active in the medium overpotential range is consistent with recent experimental observations suggesting that a defect site is responsible for the observed oxygen evolution activity and that a modest concentration of superoxo intermediates is present on the surface. Importantly, we find that it is essential to consider the kinetics of the water addition and O2 release steps rather than only the thermodynamics.

Structure and electronic properties of MoVO type mixed-metal oxides – a combined view by experiment and theory

The current state of experimental and theoretical work on structure and reactivity of MoVO type mixed-metal oxides is critically reviewed.