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Title: Studies of Cluster Evolution During Reduction of Pt/Alumina Catalysts

Authors:
 [1];  [2];  [2];  [1]
  1. ORNL
  2. UOP LLC
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Temperature Materials Lab. (HTML)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1361273
DOE Contract Number:
AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Journal Volume: 13; Journal Issue: S02; Conference: Microscopy and Microanalysis, Ft. Lauderdale, FL, USA, 20070805, 20070809
Country of Publication:
United States
Language:
English

Citation Formats

Blom, Douglas Allen, Bradley, Steven, Sinkler, Wharton, and Allard Jr, Lawrence Frederick. Studies of Cluster Evolution During Reduction of Pt/Alumina Catalysts. United States: N. p., 2007. Web. doi:10.1017/S1431927607077641.
Blom, Douglas Allen, Bradley, Steven, Sinkler, Wharton, & Allard Jr, Lawrence Frederick. Studies of Cluster Evolution During Reduction of Pt/Alumina Catalysts. United States. doi:10.1017/S1431927607077641.
Blom, Douglas Allen, Bradley, Steven, Sinkler, Wharton, and Allard Jr, Lawrence Frederick. Mon . "Studies of Cluster Evolution During Reduction of Pt/Alumina Catalysts". United States. doi:10.1017/S1431927607077641.
@article{osti_1361273,
title = {Studies of Cluster Evolution During Reduction of Pt/Alumina Catalysts},
author = {Blom, Douglas Allen and Bradley, Steven and Sinkler, Wharton and Allard Jr, Lawrence Frederick},
abstractNote = {},
doi = {10.1017/S1431927607077641},
journal = {},
number = S02,
volume = 13,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
Other availability
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  • The effect of Cl on the activity of Pt/Al{sub 2}O{sub 3} catalysts for methane oxidation has been studied by H{sub 2} and CO chemisorption, O{sub 2} isotopic exchange, kinetic studies and EXAFS spectroscopy. Catalysts containing 1.5% pt/Al{sub 2}O{sub 3} were prepared by incipient wetness from H{sub 2}PtCl{sub 6} and Pt(NH{sub 3}){sub 4}(NO{sub 3}){sub 2} precursors. Both reduced catalysts have similar dispersion (0.8) as determined by H{sub 2} chemisorption. At low methane concentration (0.3 vol.% CH{sub 4}, 16 vol.% O{sub 2}) the Cl-free catalyst was about 20 times more active during complete methane oxidation than the Cl-containing catalyst. Both CO chemisorptionmore » and oxygen exchange were observed on the Cl-free catalyst, whereas they were not detected on the Cl-containing catalyst. On the Cl-free catalyst, only Pt-Pt and Pt-O bonds were detected from the EXAFS results, while on the Cl-containing catalyst additional Pt-Cl bonds were present. The effect of chlorine on activity strongly depended on the reactant concentration. Exposure of the Cl-free catalyst to higher concentrations of methane (3 vol.% CH{sub 4}) reduced the activity to a level similar to that of the Cl-containing catalyst. Addition of HCl to the Cl-free catalyst rendered the activity identical to the catalyst prepared from Cl-containing precursors. A model is proposed to explain the mechanism of chloride poisoning, which appears to be site blocking.« less
  • In order to improve the upgrading of naphtha to high octane gasoline, the dehydrocyclization of n-octane, n-propylcyclopentane and isooctanes at atmospheric (482/sup 0/C) and 400 psig (500/sup 0/C) pressure has been compared using acidic and neutral Pt/Al/sub 2/O/sub 3/ and Pt-Sn/Al/sub 2/O/sub 3/ catalysts. Data for conversions, and product distribution (ethyl benzene, xylene isomers, total aromatics) are presented and are similar to those predicted by cyclohexane formation from n-octane rather than by n-propyl cyclopentane formation. Although less active than the Pt catalyst, the Pt-Sn catalyst gave lower alkane: aromatic ratios at 400 psig. Tin improves both dehydrocyclization activity and ageingmore » rate of Pt catalysts. Radiotracer studies of these systems are in progress.« less
  • This report concerns one of six groups of Pt/Sn loaded catalysts, prepared according to selected protocols, which incorporated a range of Sn loadings (0.4 to 1.5%), with Pt maintained at 1%. The X-ray fluorescence and absorption spectra of these preparations were recorded, for both the calcined and reduced states, at the CHESS facility. The near-edge and extended-edge spectra, at the Pt L{sub III} and Sn K-edges, were analyzed to ascertain the states of the metallic constituents. Spectra of the pure metals, of an alloy (Pt/Sn 1:1), and of their oxides were used for calibration. Specifically, for catalysts prepared by anmore » acetone-complexation method, on low area nonporous alumina (110 m{sup 2}/g), the location of the maximum slope for the catalysts (near edge, Sn) is close to that of SnO/SnO{sub 2}, definitely not near the alloy. The radial distribution peak (calcined or reduced) corresponds to Sn-O, as in SnO/SnO{sub 2}, with a minor adjacent peak which could be Sn-Cl. While SnO/SnO{sub 2} have strong Sn-Sn peaks, the catalysts show a very small peak of somewhat variable location. CONCLUSION: The data indicate that these catalysts incorporate no alloys of Pt/Sn, the Sn is in total oxygen environment, and is highly dispersed even on the low area support.« less
  • The introduction of a Pt-Re bimetallic reforming catalyst in the late 1960's had an immediate impact and revolutionized the reforming technology, much as the introduction of the Pt-Al{sub 2}O{sub 3} catalyst had done about twenty-five years earlier. Following the initial introduction of the catalyst, probably the most popular view to explain its greater stability was that of alloy formation. More detailed studies of this bimetallic catalyst system led to data that was viewed, on the one hand, to support alloy formation and, on the other hand, to support metallic Pt and ionic Re as well as to indicate that catalystmore » preparation and pretreatment may play an important role in determining the chemical state of the metals. While not nearly as widely utilized at Pt-Re in commercial operation, Pt-Sn supported bimetallic catalysts have also received widespread attention. This note describes some conflicting catalyst characterization data for Pt-Sn supported catalysts and the presentation will relate the characterization data and the alkane dehydrocyclization/alkyl cyclopentane hydrogenolysis selectivity of Pt-alumina and Pt-Sn-alumina catalysts.« less
  • Alumina reforming catalysts containing 1% plat and 1% iradium were prepared by coimpregnation of aluminium oxides with aqueous solutions of Pt and Ir chlorides. The prepared catalysts were thermally treated with hydrogen and/or oxygen up to 800/sup 0/C. The results of x-ray diffraction and transmission electron microscopy studies of the treated catalysts were reported and compared to previously reported hydrogen chemisorption measurements. It was concluded that oxygen treatment at 300/sup 0/C and above resulted in segregation of the Pt and Ir. Oxygen treatment at 500/sup 0/C resulted in decreased size of Pt or Pt-rich crystallites and increased size of themore » Ir and Ir-rich crystallites. Oxygen treatment above 600/sup 0/C resulted in metallic Pt and iridium oxide. Prolonged hydrogen treatment at high temperatures resulted in formation of large, homogeneous, bimetallic crystallites.« less