Characterization of active sites and the effect of reduction and metal promoters on iron 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: | Infrared spectroscopy has been used as the principal method of characterizing the adsorption sites of iron-based catalysts. Nitric oxide and carbon monoxide were used as probe molecules to observe the effects of reduction and metal promoters (i.e., potassium and copper) on iron adsorption sites. The resulting frequencies of the adsorbed molecules were correlated with the types of sites on the surface, and the nature of probe interaction with the surface. Temperature-programmed reduction (TPR) and x-ray photoelectron spectroscopy (XPS) were complementary methods used to establish the extent of reduction and the valence state of iron after calcination and reduction treatments. Calcination (300°C) of silica-supported iron catalysts generates Fe[^2+] sites, whether or not the catalyst is heat-treated in vacuum or cooled in oxygen. High-temperature (730°C) heat-treatment in vacuum forms a surface-reduced phase which generates cationic sites similar to those found on silica-influenced Fe3O4, in addition to non-interacting iron oxide. Reduction generates Fe[^0] sites, but overall reduction is incomplete. NO adsorption on metallic iron occurs associatively and dissociatively, oxidizing Fe[^0]. Subsequent NO adsorption generates bands associated with dinitrosyl species and a bent mononitrosyl species on low-coordination sites. CO adsorbs on calcined, unpromoted catalysts and reacts with surface oxygen to form carbonates. On reduced catalysts, CO adsorbs as a monocarbonyl on Fe[^0] sites and also dissociatively adsorbs, inhibiting NO adsorption on metallic iron, and blocking NO adsorption on high-coordination oxide sites. CO dissociation appears to be dependent on CO pressure and is inhibited by the presence of copper. Copper increases the extent of iron reduction in hydrogen. The amount of metal dispersion increases with copper content. Bulk reduction is about the same as that of the unpromoted silica-supported catalyst. Copper modifies NO adsorption on calcined and reduced catalysts. Potassium provides electron density to iron nitrosyl species associated with Fe[^2+] sites, causing frequency decreases from those which occur on the unpromoted catalyst. Potassium inhibits the formation of Fe[^0] sites on the surface, but does not inhibit bulk reduction. Potassium decreases the extent of NO adsorption, poisoning high-coordination sites, but permitting NO adsorption on low-coordination sites. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xvi, 231 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |