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.

POLYMERIC GASEOUS SPECIES IN THE SUBLIMATION OF MOLYBDENUM TRIOXIDE. Period covered: To June 30, 1956. Technical Report No. 2 on THERMODYNAMICS OF REFRACTORY MATERIALS AS DETERMINED WITH A MASS SPECTROMETER

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)

Influence of 2-Aminopyridine on the Formation of Molybdates under Hydrothermal Conditions

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...

Chemical etching of molybdenum trioxide : a new tailor-made synthesis of moo3 catalysts

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.

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Tuning the interlayer of transition metal oxides for electrochemical energy storage

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.

A.K. Cheetham

Papers

Chapter 3 - The Oxide Chemistry of Molybdenum