The Quantum Mechanics Calculation of Molybdenum and Tungsten Influence on the CrM-oxide Catalyst Acidity

Abstract

Semi-empirical calculations were employed to understand the effects of introducing promoters such as molybdenum (Mo) and tungsten (W) on chromium (III) oxide catalyst for the dehydrogenation of propane into propylene. For this purpose, we investigated CrM-oxide (M = Cr, Mo, and W) catalysts. In this study, the Lewis acidity of the catalyst was examined using Lewis acidity parameters (Ac), including ammonia and pyridine adsorption energy. The results obtained from this study of overall acidity across all sites of the catalysts studied reveal Mo-modified catalyst as the one with the least acidity while the W-modified catalyst was found to have shown the highest acidity signifies that the introduction of Mo would reduce acidity while W accelerates it. The finding, therefore, confirms tungsten (W) to be more influential and would be more promising when compared to molybdenum (Mo) due to the better avenue that is offered by W for the promotion of electron exchange and its higher acidity(s). The suitability of some molecular descriptors for acidity prediction as a potential alternative to the current use of adsorption energies of the probes was also reported.