Silica-alumina-supported Mo oxide catalysts: Genesis and demise of Bronsted-Lewis acidity
- Univ. of Louisville, KY (United States)
Diffuse reflectance FTIR spectroscopy of chemisorbed pyridine was used to investigate the influence of catalyst composition and treatment on the content of Bronsted and Lewis acidity. This investigation included oxidic and reduced Mo oxide catalysts containing 2, 4, 8, and 12 wt% MoO{sub 3}. The supports were seven silica-aluminas of composition between 0 and 100 wt% SiO{sub 2}. The IR spectra were collected at 200{degrees}C under helium flow, and the areas under the 1545 and 1450 cm{sup -1} absorbance bands were related to the concentration of Bronsted and Lewis acid sites, respectively. The results indicate that the ratio of Bronsted to Lewis acid concentration (B/L) increases with SiO{sub 2} content in the support and reaches a maximum for SiO{sub 2}:Al{sub 2}O{sub 3} = 75:25 wt%. For Al{sub 2}O{sub 3} and alumina-rich supports B/L increases continuously with MoO{sub 3} loading because of the generation of new Bronsted acid sites and decrease of Lewis acid sites. For silica-rich supports, the B/L has a maximum at 2 wt% MoO{sub 3} and then decreases slightly as MoO{sub 3} loading is increased. The SiO{sub 2} support with MoO{sub 3} loading up to 12 wt% does not contain any Bronsted acidity in water-free environment. Upon reduction of the supported catalyst at 500{degrees}C in hydrogen, the B/L ratio decreases irrespective of SiO{sub 2} content and MoO{sub 3} loading. A structural model that includes tetrahedral surface species of Mo oxide explains the results. 59 refs., 11 figs., 4 tabs.
- OSTI ID:
- 75806
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 151; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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