An ISS and Angle-Resolved XPS determination of the surface structures of real and planar model oxidic hydrodesulfurization catalysts /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1989.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | The super surface sensitive technique Ion Scattering Spectroscopy (ISS) has been used along with X-ray Photoelectron Spectroscopy (XPS), and Angle-Resolved XPS (ARXPS), a special variation of XPS with increased surface sensitivity, to determine the effects of promoter loadings and calcination temperatures upon the outer surface of the oxidic Co-Mo /Υ-AI2O3 and Ni-W/Υ-AI2O3 hydrodesulfurization catalysts. Powder catalyst models were prepared with a constant amount of the active metal (Mo or W) and varying amounts of promoter metal (Co or Ni). Catalysts were calcined at 450 and 750°C. XPS and ISS were used to analyze the lab-prepared powders; commercial catalysts were also analyzed. The results were used to formulate a model of the oxidic catalyst's surface structure. Planar catalysts were also prepared with a constant amount of the active metal and varying amounts of promoter metal; these models were calcined at 200 and 500°C. ISS and ARXPS were to examine the outer surfaces of the planar catalysts. The data from the planar models was compared to that from the powder models and correlations were made. ISS and ARXPS "depth profiles" were compared. Results indicate that the outer surface of these catalysts are highly dependent upon the number of metals atoms per squared nanometer. This was formulated in a Surface Saturation Limit (SSL) model. This SSL model finds that the Υ-alumina support can only accommodate around 4(1/2) metal atoms/nm^2 before overloading occurs. ISS clearly shows the effect of the overloading. For normal loadings and calcination temperatures, the promoter location differed between the two systems: Co was found to reside just beneath the Mo-rich outer layer, while Ni was on and beneath the outer surface along with the W. Moreover, for the Co-Mo system, a maximum Mo:Co ratio of 2:1 was found to be the limit for positive dispersion of Mo on the outer surface. No such enhancement effect was found for the Ni-W system. A higher calcination temperature resulted in the migration of the promoter metal into the support and a higher dispersion of the active metal on the surface. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xx, 213 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |