THE INFLUENCE OF MOLYBDENUM AND TUNGSTEN ON THE CRM-OXIDE CATALYST REACTIVITY IN PROPANE ACTIVATION: A QUANTUM MECHANICS CALCULATION

Abstract

A quantum chemical calculation for the activation of propane across CrM-oxide (M = Cr, Mo, and W) catalysts in the dehydrogenation of propane into propylene was studied. The calculation was carried out via the use of the PM3 semi-empirical approach. In this study, the reactivity of the catalyst was examined through the use of reactivity parameters such as C-H bond abstraction activation energy (Ea), energy bandgap (Egap), and its adsorption energy (Eads) during the dehydrogenation of propane. This study further identifies the effects of introducing promoters such as molybdenum (Mo) and tungsten (W) on chromium (III) oxide catalysts were evaluated. The findings show that W increases the catalyst's binding energy for the isopropyl species, while Mo slightly reduces it. The structures' energy band gaps indicate that W reduces stability, while the presence of Mo increases stability. The study of the propane activation mechanism across the surface of CrM-oxides (M = Cr, Mo, and W) identifies O-Cr pair sites were found to be a thermodynamically feasible route for the activation of H-C1 with a lesser energy demand on the unmodified-surface. The modification of the surface using tungsten (W) was found to have speed up the rate of propane activation on the H-C1 bond across W-O pair sites. This finding was due to the lower activation energy shown for the route. However, this study confirms that tungsten's introduction promotes propane activation, while molybdenum slightly reduces the activation rate. Thus, tungsten would be more promising for promoting propane activation rate, while molybdenum is a potential promoter for enhancing propane dehydrogenation's catalyst stability.

Keywords

• propane activation
• dehydrogenation
• semi-empirical calculation
• chromium oxide
• lewis acidity
• adsorption energy