A New Catalyst for the Selective Oxidation of Butane and Propane This work was funded by BP (original) (raw)
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Catalysis Today, 2001
Syntheses of Mo-V-Sb-Nb-O bulk materials, which are candidate catalyst systems for the selective oxidation of propane to acrolein and acrylic acid, were made using soluble precursor materials. The products were characterized by X-ray powder diffraction and Raman spectroscopic studies. The objectives of this work were to explore the utility of liquid phase automated synthesis for the preparation of bulk mixed metal oxides, and the identification of the oxide phases present in the system. This is the first published study of the phase composition for these materials. After calcination of these bulk oxides under flowing nitrogen at 600 • C, and using stoichiometric ratios of Mo-V-Sb-Nb 1:1:0.4:0.4) and Mo-V-Sb-Nb (3.3:1:0.4:0.4) it was demonstrated that a mixture of phases were obtained for the syntheses. X-ray powder diffraction studies distinguished SbVO 4 , Mo 6 V 9 O 40 , MoO 3 , and a niobium-stabilized defect phase of a vanadium-rich molybdate, Mo 0.61-0.77 V 0.31-0.19 Nb 0.08-0.04 O x , as the major phases present. Complementary data were provided by the Raman spectroscopic studies, which illustrated the heterogeneity of the phases present in the mixture. Raman also indicated bands attributable to the presence of phases containing terminal M=O bonds as well as M-O-M polycrystalline phases. Previous studies on this system have identified SbVO 4 and niobium-stabilized vanadium molybdate species as the active phases necessary for the selective oxidation of alkanes. (V.V. Guliants).
Journal of Catalysis, 2003
A highly active and selective catalyst for light alkane oxidation that is composed of a pyridine salt of niobium-exchanged molybdo(vanado)phosphoric acid (NbPMo 11 (V)pyr) is characterized using TGA-DSC, 31 P MAS NMR, and in situ powder XRD, XAS, and XPS. The presence of both niobium and pyridinium species strongly influences structural and redox properties of the polyoxometalate. Activation of the catalyst by heating to 420 • C in an inert atmosphere removes all of the organic species present in the solid, and structural rearrangement of the starting heteropolyanion occurs at 420 • C as evidenced by 31 P NMR and EXAFS. XRD shows that activated NbPMo 11 Vpyr consisted of a mostly amorphous molybdenum oxide phase, the formation of which is strongly related to the composition of the catalyst. The presence of niobium as an exchange cation (NbO) 3+ or a framework atom PMo 11 NbO 40 4− in the Keggin unit is verified by EXAFS for NbPMo 11 Vpyr and (VO)PMo 11 Nbpyr, respectively. During activation of either catalyst, niobyl species migrate and most likely coordinate to molybdenum oxide octahedra. Comparison of near-edge electronic spectra (XANES) for as-made NbPMo 11 Vpyr and after activation that removes the pyridinium ions suggests reduction of Mo 6+ to Mo 5+ and Nb 5+ to Nb 4+. Under hydrocarbon-rich reaction mixtures molybdenum and niobium remain in their reduced state.
MoVO-based catalysts for the oxidation of ethane to ethylene and acetic acid
Applied Catalysis A-general, 2006
The influence of niobium and/or palladium in MoV 0.4 O x on both solid state chemistry and catalytic properties in the oxidation of ethane to acetic acid and ethylene is examined. Catalysts without molybdenum (VNb 031 Pd 3e-4 O x ) are also studied for comparison. The structural properties of the precursors and of the catalysts obtained by calcination of precursors at 350 and 400°C are studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. These properties depend on the presence or absence of niobium, and to a lesser extent, of palladium. Nb-free precursors and catalysts are heterogeneous mixtures of crystalline oxides, among which hexagonal and orthorhombic MoO 3 . The presence of Pd favors the instability of both precursors and catalysts. The catalysts are poorly active (conversion < 4%), but they are mainly selective to acetic acid (S AA max = 61-73 mol%) and to CO x (S COx max = 30-72 mol%). The Nb-containing precursors without or with Pd are more stable, and the catalysts are made up of nanocrystalline particles of V,Nb-doped Mo 5 O 14 and of V x Mo 1-x O 3-x/2 . They are active (conversion < 15%) and very selective to ethylene and acetic acid (S tot = 90-96 mol%). The surface being enriched with vanadium in most cases, the discussion deals with the relative role of Nb and Pd and their possible location in the identified oxides. Because no M1 and/or M2 oxides could be identified, synergistic effects between nanocrystals of (VMoNb) 5 O 14 and V x Mo 1-x O 3-0.5x are proposed to account for the high catalytic performance of the multicomponent MoVNb(Pd)oxides.
Catalysis in Industry, 2010
The replacement of expensive propylene by propane, which requires the development of catalysts for the direct oxidation of propane into acrylonitrile, is an important and insufficiently studied problem. Mul ticomponent Mo m V n Te k Nb x oxide systems are promising in one stage ammoxidation of propane to acryloni trile. Despite considerable attention of various authors to the preparation methods for these catalysts, the reproducibility of their physicochemical and catalytic properties is low. To optimize the technology of catalyst synthesis, we studied the effect of drying method (evaporation or spray drying) for the aqueous suspension of the initial compounds on the formation of the Mo 1 V 0.3 Te 0.23 (Nb 0.12 ) oxide catalyst. It is shown that the method of drying determines the chemical and phase composition of solid catalyst precursors and the phase composition of the final catalyst in high temperature treatment. The use of spray drying provides the required physicochemical characteristics of the catalyst (the specific surface area and the phase composition) that determine the high activity and selectivity in the selective conversion of propane. These catalysts contain two crystalline phases: orthorhombic M1 and hexagonal M2 in an optimal ratio of 3 : 1.
Effect of Mo on the Active Sites of VPO Catalysts upon the Selective Oxidation of n-Butane
Journal of Catalysis, 1999
The effect of the addition of Mo to VPO formulations on the physicochemical and catalytic properties of VPO solids was studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Laser Raman spectroscopy (LRS), temperature-programmed reduction, and a flow reactor system. The addition of Mo to the oxides increases the activity and selectivity of the VPO catalysts. The promoting effect is a function of both the Mo loading and the way such cation was added to the VPO matrix. The best catalyst was obtained when 1% Mo was impregnated on the VOHPO 4 · 0.5H 2 O phase. At 400 • C 36% of molar yield to maleic anhydride was obtained in this catalyst against 12% of the unpromoted catalysts and only 3% of the solids where Mo was added during the phosphatation step. The impregnated 1%
Microporous and Mesoporous Materials, 2010
The preparation of Keggin-type phosphovanadomolybdic acid H4PMo11VO40 (PMo11V) supported on a hexagonal mesoporous silicate (HMS) material was performed via three different methods: dry impregnation, wet impregnation and mechanical mixing. The state of the heteropolyacid (HPA) on the siliceous surface and the integrity of the support were characterized by several physico-chemical techniques: elemental analysis, X-ray diffraction, transmission and diffuse reflectance (DR)
Unsupported and SiO 2 supported GePt bimetallic catalysts were prepared by depositing Ge on to Pt underpotentially. Surface-sensitive cyclic voltammetry of Pt black indicated that Ge covered ca. 40-45% of the Pt surface, whereas XPS showed just ∼96% Pt and ∼4% Ge (normalized to Pt + Ge = 100%). Highresolution Ge map of GePt black obtained by Energy Filtered TEM (EFTEM) showed Ge scattered in the near-surface regions. Both catalysts were tested in hexane (nH) transformation reactions between 543 and 603 K and 60 to 480 Torr H 2 pressure (with 10 Torr nH), and compared with the parent Pt catalysts. GePt/SiO 2 catalyst was also tested with methylcyclopentane (MCP). Adding Ge to Pt/SiO 2 lowered the activity; the opposite effect was observed with GePt black. The selectivities of saturated products on bimetallic catalysts decreased, while those of hydrogenolysis products, benzene and hexenes increased in nH transformations over supported catalyst. The reverse effects were observed over the black samples where addition of Ge prevented accumulation of adventitious carbon. Ring opening was the main reaction with MCP, together with some fragments, benzene and unsaturated hydrocarbons. Ring opening of MCP became more selective with decreasing temperature and increasing hydrogen pressure. Ge on GePt black blocked contiguous Pt sites favoring the formation of coke precursors. The different catalytic behavior of GePt/SiO 2 indicated somewhat different Pt-Ge interaction(s).