Title of article :
Structure, properties and roles of the different constituents in Pt/WOx/ZrO2 catalysts
Author/Authors :
Punnoose، نويسنده , , A and Seehra، نويسنده , , M.S and Wender، نويسنده , , I، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2001
Pages :
15
From page :
33
To page :
47
Abstract :
Six samples of platinum-promoted tungstated zirconia catalysts (Pt0.5/WOx/ZrO2) with W loadings between 6.5 and 12.5 wt.% are investigated using X-ray diffraction (XRD) and magnetic susceptibility measurements (4 to 350 K). Studies are also carried out on some of these samples after annealing them in air at temperatures up to 1000 °C. In the as-prepared samples, the absence of any lines due to WO3, irrespective of W loading, suggests the highly dispersed state of WO3. However, the dispersed WO3 appears to be necessary to stabilize the tetragonal phase of zirconia (t-ZrO2). Ex-situ XRD studies show that on heating the samples to 1000 °C, the fraction of m-ZrO2 (monoclinic) increases, with the simultaneous appearance of crystalline m-WO3. This leads us to infer that the dispersed WOx species are associated with t-ZrO2 only. By comparing the magnitude and the temperature variations of the magnetic susceptibility χ of the samples with those of Pt, α-PtO2, Pt3O4, WO3 and ZrO2, we infer that Pt in the as-prepared catalysts is primarily in the oxidized form, α-PtO2 and/or Pt3O4, relative magnitudes of the two oxides being dependent on the preparation procedures, thermal treatments and aging. The oxides are converted to Pt in reducing atmosphere.
Keywords :
Tungstated zirconia , XRD , Magnetic measurements , Solid acid catalysts , Platinum species
Journal title :
Fuel Processing Technology
Serial Year :
2001
Journal title :
Fuel Processing Technology
Record number :
1506424
Link To Document :
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