Rick B. Watson

Propane and propylene adsorption effects over MoOx-based catalysts induced by low levels of alkali doping

Abstract The induced effects of low-level alkali promotion are studied in order to obtain a better understanding of the way the MoOx 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 MoOx species. ESR experiments indicate that it may be possible that potassium stabilizes the MoOx 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 MoOx catalysts, but also change the interaction of the catalyst with propane, altering propane activation steps.

Oxidative dehydrogenation of propane over alkali-Mo catalysts supported on sol-gel silica-titania mixed oxides

A group of novel molybdena catalysts for propane oxidative dehydrogenation (ODH) is presented. These catalysts, which were prepared using a sol-gel/co-precipitation technique, were supported on silica-titania mixed oxides and promoted by alkali metals (Li, Na, K, Cs). While reaction results show no specific trend with the type of alkali promoter, comparisons indicate that promotion with potassium gives a superior catalyst. Propylene yields around 30% were obtained with K/Mo catalysts at 550°C, in dilute feed stream experiments. Differences in reaction performance are found to be closely related to surface acidity, oxidation-reduction behavior, and dispersion of the active components.