Polymeric Gaseous Species in the Sublimation of Molybdenum Trioxide

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.

Mechanism of Selective Oxidation and Ammoxidation of Propene on Bismuth Molybdates from DFT Calculations on Model Clusters

“…[12][13][14] Its sixring structure has been suggested as the lowest-energy structure. 12,14 The Bi 4 O 6 cluster in the adamantane-type cage structure has been proposed as a neutral species present in the gas phase, [15][16][17][18] and the cationic species Bi 4 O 6 + has been recently detected from the laser vaporization experiment from a bismuth rod with an expansion gas seeded with oxygen. 19 There have been many recent experiments on the reaction of these massselected gas-phase metal oxide clusters with small molecules such as ammonia, ethene, and propene as a model study of the heterogeneous catalysis.…”

The formation and stability of molybdenum–antimony and tungsten–antimony ternary oxides Sb2MO6, Sb2M2O9, Sb2Mo3O12 and Sb4MO9 in the gas phase (M = Mo, W). Quantum chemical and mass spectrometric studies

“…The obtained samples were characterised using X-ray diffraction (XRD) techniques. Comparison of the XRD patterns of the synthesised samples with the literature data confirms the crystal structures of the obtained Sb 2 MoO 6 and Sb 2 Mo 3 O 12 compounds. Vaporisation of the two Sb 2 MoO 6 and Sb 2 Mo 3 O 12 solid oxides using a conventional Knudsen cell was studied at 840 and 893 K, respectively.…”

“…The Gibbs free energy of the isomer transition, Δ i G 0 T (QC), is theoretically calculated to be 1. (6). All the calculated enthalpies of formation for the ternary oxides, Δ f H 0 T , were converted into the standard enthalpies of formation, Δ f H 0 298 , using eqn (6) and the calculated a, b and c coefficients of the c 0 p,T function.…”

“…The gas phase of the pure molybdenum, tungsten and antimony oxides has been the subject of several mass spectrometric studies. [4][5][6][7][8] It has been shown that the molybdenum and tungsten oxides, MoO 3 and WO 3 , evaporate congruently without decomposition as the gas phase contains monomer and oligomer molecules (MO 3 ) x , (M = Mo, W; x = 1-5). 4,6 The antimony oxide, Sb 2 O 3 , also evaporates congruently and the gas phase primarily contains antimony oxide in the dimeric form, Sb 4 O 6 .…”

“…[4][5][6][7][8] It has been shown that the molybdenum and tungsten oxides, MoO 3 and WO 3 , evaporate congruently without decomposition as the gas phase contains monomer and oligomer molecules (MO 3 ) x , (M = Mo, W; x = 1-5). 4,6 The antimony oxide, Sb 2 O 3 , also evaporates congruently and the gas phase primarily contains antimony oxide in the dimeric form, Sb 4 O 6 . In the present article, we report the results of mass spectrometric and theoretical investigations of the formation and stability of the gaseous ternary molybdenumantimony and tungsten-antimony oxides Sb 2 MO 6 , Sb 2 M 2 O 9 , Sb 4 MO 9 , (M = Mo, W) and Sb 2 Mo 3 O 12 (Scheme 1).…”