Chapter 3 - The Oxide Chemistry of Molybdenum
About: This article is published in Studies in Inorganic Chemistry.The article was published on 1994-01-01. It has received 19 citations till now. The article focuses on the topics: Molybdenum & Oxide.
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31 Oct 1956
TL;DR: In this article, a mass spectometric analysis of the vapor in thermodynamic equilibrium with powdered molybdenum trioxide, as sampled from a Knudsen effusion cell, has shown that the vapor phase consists of Mo3O9, Mo4O12 and Mo5O15 molecules.
Abstract: Mass spectometric analysis of the vapor in thermodynamic equilibrium with powdered molybdenum trioxide, as sampled from a Knudsen effusion cell, has shown that the vapor phase consists predominantly of Mo3O9, Mo4O12 and Mo5O15 molecules. Utilizing the Clausius‐Clapeyron equation, individual heats of sublimation have been determined to be 80.5±1.5, 93.6±1.6 and 105.6±3.5 kcal/mole respectively at 850° K. The heats of formation and third law entropies have been evaluated for each of these molecules.
112 citations
TL;DR: In this article, the role of 2-aminopyridine (2ampy) in the formation of the different solids under hydrothermal conditions is discussed, and the structures of these materials were established by single-crystal and powder X-ray diffraction techniques.
Abstract: The hydrothermal reaction of an aqueous ammonium heptamolybdate solution with first-row transition metal salts in the presence of 2-aminopyridine at around 180 °C and under autogenous pressure yields several molybdates, such as the 1D chains in (C5N2H7)4Mo8O26 (1), zero-dimensional (C5N2H7)6Mo7O24·3H2O (2), and the first synthesis of Lindgrenite [Cu3Mo2O8(OH)2 (3)] The structures of these materials were established by single-crystal and powder X-ray diffraction techniques. The crystal structures of wolframite-based MnMoO4 (4) and ZnMoO4 (5) were established by powder X-ray diffraction. The role of 2-aminopyridine (2-ampy) in the formation of the different solids under hydrothermal conditions is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
81 citations
TL;DR: In this article, a chemical etching method has been developed for restructuring these thermally processed catalysts using a 0.1 M NaOH etchant, where the surface steps, ledges, and terraces are created.
Abstract: Crystalline catalysts of orthorhombic MoO3 have been prepared via a vapor phase deposition method, and their crystallographic structure has been affirmed by XRD and FTIR investigations. A chemical etching method has been developed for restructuring these thermally processed catalysts. Using a 0.1 M NaOH etchant, {001} and {100} plane areas of the catalysts can be significantly increased while surface steps, ledges, and terraces are created. Moreover, alternate crystal plane combinations of either {100} and {010} or the {001} and {010} are observed on crystal edges and rectangular etch pits in the basal planes {010}. Both materials chemistry of MoO3 and etching mechanisms have been studied on the basis of the surface morphological evolution of etching patterns of the catalysts. Technological merits and the processing parameters of this new method have also been identified. Following the findings of the current work, it is believed that the chemically carved surface structures may be crucial for certain MoO...
72 citations
TL;DR: In this article, a review of the benefits and methods for interlayer modification of layered transition metal oxides, which include the presence of structural water, solvent cointercalation and exchange, cation exchange, polymers, and small molecules, exfoliation, and exfoliated heterostructures, is presented.
Abstract: Layered transition metal oxides are some of the most important materials for high energy and power density electrochemical energy storage, such as batteries and electrochemical capacitors. These oxides can efficiently store charge via intercalation of ions into the interlayer vacant sites of the bulk material. The interlayer can be tuned to modify the electrochemical environment of the intercalating species to allow improved interfacial charge transfer and/or solid-state diffusion. The ability to fine-tune the solid-state environment for energy storage is highly beneficial for the design of layered oxides for specific mechanisms, including multivalent ion intercalation. This review focuses on the benefits as well as the methods for interlayer modification of layered oxides, which include the presence of structural water, solvent cointercalation and exchange, cation exchange, polymers, and small molecules, exfoliation, and exfoliated heterostructures. These methods are an important design tool for further development of layered oxides for electrochemical energy storage applications.
66 citations
TL;DR: In this article, the structural aspects of the crystallographic shear planes and the resulting thermoelectric properties of transition metal oxides with adaptive structures have been investigated with respect to their thermal properties.
Abstract: Thermoelectric devices can help to tackle future challenges in the energy sector through the conversion of waste heat directly into usable electric energy. For a wide applicability low-cost materials with reasonable thermoelectric performances and cost-efficient preparation techniques are required. In this context metal oxides are an interesting class of materials because of their inherent high-temperature stability and relative high sustainability. Their thermoelectric performance, however, needs to be improved for wide application. Compounds with adaptive structures are a very interesting class of materials. A slight reduction of early transition metal oxides generates electrons as charge carriers and crystallographic shear planes as structure motif. The crystallographic shear planes lead to a reduction of intrinsic thermal conductivity. At the same time, the electronic transport properties can be tuned by the degree of reduction. So far only a few transition metal oxides with adaptive structures have been investigated with respect to their thermoelectric properties, leaving much room for improvement. This review gives an overview of thermoelectric oxides, highlights the structural aspects of the crystallographic shear planes and the resulting thermoelectric properties.
50 citations
References
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TL;DR: In this paper, a detailed overview of metal oxides in relation to their behavior in batteries is presented, covering electrochemical, conductivity, ion diffusivity, spectroscopic, and other physico-chemical data.
Abstract: Due to their rather low molecular weight and their favorable electrochemical and solid‐state properties, first row transition metal oxides seem to be specially attractive as cathode materials in electrochemical energy storage systems. Therefore, we undertook a detailed overview, covering electrochemical, conductivity, ion diffusivity, spectroscopic, and other physico‐chemical data on metal oxides in relation to their behavior in batteries. Metal oxide‐based primary batteries have achieved a high technological level and yield energy densities of up to 300 Wh kg−1 or 880 Wh l−1. Oxide‐based secondary batteries, on the other hand, typically yield less than 100 Wh kg−1. Based on the present review, V, Cr, Mn, and Co oxides seem to be the most promising solid‐state cathode materials for future high performance secondary batteries.
182 citations
166 citations
TL;DR: In this paper, the stable phase at STP was solved and refined by a combination of three-dimensional Patterson and Fourier series and by the method of least squares, and the final agreement factor between measured and calculated structure factors is 0.0574.
Abstract: Paramagnetic alpha‐MnMoO4, the stable phase at STP, is monoclinic with lattice constants a=10.469±0.005, b=9.516±0.005, c=7.143±0.005 A, and β=106°17′±6′, and space group C2/m. The crystal structure has been solved and refined by a combination of three‐dimensional Patterson and Fourier series and by the method of least squares. 1873 independent integrated intensities were measured by PEXRAD; the final agreement factor between measured and calculated structure factors is 0.0574. Two crystallographically independent Mn atoms are surrounded by highly distorted oxygen octahedra; the Mn–O distance varies between 2.091±0.006 and 2.252±0.003 A, with average length 2.164 A. Two crystallographically independent Mo atoms are surrounded by slightly distorted oxygen tetrahedra, with Mo–O distances ranging from 1.724±0.005 to 1.851±0.004 A, the average being 1.761 A. The thermal vibrations are significantly anisotropic. An analysis is given of various current methods for estimating the standard deviation in the measur...
166 citations
159 citations
TL;DR: In this paper, the electrochromic optical absorption of mixed-oxide WO3/MoO3 amorphous films occurs at higher energy than either pure oxide alone and the systematics of the energy shifts as a function of MoO3 concentration and coloration density is determined.
Abstract: The electrochromic optical absorption of mixed‐oxide WO3/MoO3 amorphous films occurs at higher energy than either pure oxide alone. The systematics of the energy shifts as a function of MoO3 concentration and coloration density is determined. The data is explained by the intervalency charge‐transfer model if we assume that electrons trapped at Mo6+ ions lie 0.73 eV deeper than electrons on W6+ ions. Measurements of electron diffusion in mixed oxides support this hypothesis. The maximum absorption peak of mixed oxides is 2.15 eV compared with 1.4 eV for WO3. This is close to the peak in eye sensitivity, thereby leading to improved electrochromic display devices.
153 citations