Propane and propylene adsorption effects over MoOx-based catalysts induced by low levels of alkali doping
✍ Scribed by Rick B Watson; Umit S Ozkan
- Publisher
- Elsevier Science
- Year
- 2003
- Tongue
- English
- Weight
- 468 KB
- Volume
- 194
- Category
- Article
- ISSN
- 1381-1169
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✦ Synopsis
The induced effects of low-level alkali promotion are studied in order to obtain a better understanding of the way the MoO x activity, altered by the presence of potassium, relates to the adsorption and reactivity of propane and propylene under various conditions. Non-steady-state and steady-state isotopic transient kinetic analyses (SSITKAs) show changes in lattice-oxygen mobility caused by the presence of potassium. Differential scanning calorimetry was used to determine the heat effects associated with propylene adsorption. The heat associated with the reversible and irreversible adsorption of propylene decreases with the addition of potassium. This information further corroborates the relationship between potassium addition and the decreased reactivity for propylene as elucidated in reaction experiments. Electron spin resonance was used to investigate changes in Mo(V) species upon contact with propane under different conditions as a probe for the electronic properties of the supported MoO x species. ESR experiments indicate that it may be possible that potassium stabilizes the MoO x domains in a more "reduced" state, Mo(V). Together with in situ-DRIFTS experiments, it is found that potassium cannot only affect the transformation of propylene over MoO x catalysts, but also change the interaction of the catalyst with propane, altering propane activation steps.