Combining computational and experimental studies to gain mechanistic insights for n-butane isomerisation with a model microporous catalyst†

Microporous solid acid catalysts are widely used in industrial hydrocarbon transformations in both the fuels and petrochemical industries. The specific choice of microporous framework often dictates the acidic properties of the system, such as acid site strength and concentration. In this work we have explored the influence of acid site concentration on butane isomerisation activity and the mechanistic pathway by controlling the quantity of magnesium doped into an aluminophosphate, keeping the acid site strength and framework topology constant. By combining experimental kinetic studies, and theoretical mechanistic studies, we conclude that isobutane formation, from n-butane, predominantly proceeds through a bimolecular pathway. Specifically, the activity of the system is strongly linked to the presence of alkenes, and herein the precise mechanistic roles of the alkenes are explored.