Abstract
Concentrations of Brønsted and Lewis acid sites on sulfated-zirconia catalysts were determined using the31P MAS NMR spectra of adsorbed trimethylphospine. A sample that had been calcined and exposed to air for a long period exhibited only Brønsted acidity; however, treatment of the sample at progressively higher temperatures resulted in the development of at least three types of Lewis acidity, along with a decrease in the concentration of Brønsted acid sites. In a related study the activity of these catalysts for the alkylation of isobutane with 2-butene was determined. The aged catalyst was inactive, but activation of the material at 100°C resulted in the most active catalyst. Thermal treatment at higher temperatures resulted in a loss in activity which paralleled the decrease in the Brønsted acid sites. These results are consistent with a model in which strong Brønsted acidity is a result of the interaction between bisulfate groups and adjacent Lewis acid sites.
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Lunsford, J.H., Sang, H., Campbell, S.M. et al. An NMR study of acid sites on sulfated-zirconia catalysts using trimethylphosphine as a probe. Catal Lett 27, 305–314 (1994). https://doi.org/10.1007/BF00813917
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DOI: https://doi.org/10.1007/BF00813917