Ž . Fuel Processing Technology 74 2001 33–47 www.elsevier.comrlocaterfuproc Structure, properties and roles of the different constituents in PtrWO rZrO catalysts x 2 A. Punnoose a , M.S. Seehra a, ) , I. Wender b a Department of Physics, Eberly College of Arts and Sciences, West Virginia UniÕersity, P.O. Box 6315, Morgantown, WV 26506-6315, USA b Chemical and Petroleum Engineering Department, UniÕersity of Pittsburgh, Pittsburgh, PA 15261, USA Received 1 February 2001; accepted 1 June 2001 Abstract Ž . Six samples of platinum-promoted tungstated zirconia catalysts Pt rWO rZrO with W 0.5 x 2 Ž . loadings between 6.5 and 12.5 wt.% are investigated using X-ray diffraction XRD and magnetic Ž . 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 8C. In the as-prepared samples, the absence of any lines due to WO , irrespective of W loading, suggests the highly dispersed state of WO . 3 3 However, the dispersed WO appears to be necessary to stabilize the tetragonal phase of zirconia 3 Ž . t-ZrO . Ex-situ XRD studies show that on heating the samples to 1000 8C, the fraction of 2 Ž . m-ZrO monoclinic increases, with the simultaneous appearance of crystalline m-WO . This 2 3 leads us to infer that the dispersed WO species are associated with t-ZrO only. By comparing x 2 the magnitude and the temperature variations of the magnetic susceptibility x of the samples with those of Pt, a-PtO , Pt O , WO and ZrO , we infer that Pt in the as-prepared catalysts is 2 3 4 3 2 primarily in the oxidized form, a-PtO andror Pt O , relative magnitudes of the two oxides being 2 3 4 dependent on the preparation procedures, thermal treatments and aging. The oxides are converted to Pt in reducing atmosphere. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Solid acid catalysts; Tungstated zirconia; Platinum species; XRD; Magnetic measurements ) Corresponding author. Tel.: q 1-304-293-3422; fax: q 1-304-293-5732. Ž . E-mail address: mseehra@wvu.edu M.S. Seehra . 0378-3820r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0378-3820 01 00217-X