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Sökning: WFRF:(Burrington J. D.)

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1.
  • Grasselli, Robert K., et al. (författare)
  • Active centers, catalytic behavior, symbiosis and redox properties of MoV(Nb,Ta)TeO ammoxidation catalysts
  • 2006
  • Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 38:1-3, s. 7-16
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective as well as waste forming active centers were defined for MoVNbTeO and MoVTaTeO catalysts in the ammoxidation of propane to acrylonitrile and all catalytic functionalities were assigned to specific elements at the respective active centers. Symbiosis between M1 and M2 phases of these catalysts was observed, with phase cooperation being more extensive in the Nb than Ta containing compositions. The difference in catalytic effectiveness arises most likely because contact and surface area exposure of the two respective, cooperating phase pairs are not equal. The M1 phase of the catalysts is reducible by propane and ammonia in the absence of dioxygen and is regenerable to its original, fully oxidized state by dioxygen (air). No structural collapse is observed even after 120 C3H8 + NH3 reduction pulses. The so induced reduction of the catalyst extends up to 70 layers deep. The product distribution over the first few pulses is very similar to that under catalytic conditions, supporting the concept that lattice oxygen is involved in the catalytic ammoxidation process. Therefore, the ammoxidation of paraffins is a redox process, as is of course the well-known olefin ammoxidation process.
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3.
  • Grasselli, R. K., et al. (författare)
  • Inhibition of propylene oxidation to acrylic acid by amorphous overlayers on MoV(Nb)TeO based M2 catalysts
  • 2008
  • Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1011-372X .- 1572-879X. ; 126:3-4, s. 231-240
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the most effective catalysts for the selective oxidation of propane to acrylic acid (AA) and ammoxidation to acrylonitrile (AN) is the MoV(Nb,Ta)(Te,Sb)O system, comprised of two phases, with M1 the major catalyst and M2 the co-catalyst in symbiosis with M1, converting intermediately formed propylene to the respective desired end products. An improvement in either phase should enhance the overall desired yields of a combined M1/M2 conglomerate. The current study concentrates on the M2 phase (variously substituted and/or doped) where depending on composition and preparation technique crystalline materials or crystalline materials with amorphous overlayers are obtained. Crystalline M2 catalysts without amorphous overlayers are vastly superior to those encumbered with overlayers. In a comparative study the former give a maximum AN yield of *45% in propylene ammoxidation, the latter *24%. In the selective oxidation of propylene to acrylic acid, the difference in performance between the two types of catalysts becomes enormous: The crystalline M2 catalyst gives a maximum AA yield of *34% while the Te–molybdate overlayered M2 a meager *3%. Doping of crystalline M2 phase with P significantly enhances AA yields over the base and should be seriously considered in future attempts to improve M1/M2 propane/propylene catalyst systems.
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