Fluorination modulates the interaction of water with MgO catalysts during propylene glycol dehydrogenation

Abstract

The influence of water on catalytic reactions and catalysts is an unavoidable point of concern in biomass valorization. In this study, we develop a fluorine-modified magnesium oxide catalyst (MgO-F) and explored the role of fluorine in the dehydrogenation of propylene glycol to hydroxyacetone in the presence of water. MgO-F is a mixed phase of magnesium oxide, magnesium fluoride, and oxyfluoride structure, resulting in changes to its electronic properties and consequently to its acidity and alkalinity. Detailed kinetics suggested that fluorine accelerates the dehydrogenation reaction rate while increasing the selectivity to allyl alcohol and propanol in absence of water. Increasing water pressure lowers the apparent barriers but hardly alters the reaction order of propylene glycol on MgO-F catalyst. In contrast, the MgO catalyst exhibits lower reaction orders and increased activation barriers under similar conditions. Further kinetic isotope effect (KIE) studies showed that the water actively participates in the reaction on MgO catalyst, whereas on the MgO-F catalyst negligible effects were observed. This weaker interaction with water led to improved stability and reduced kinetic sensitivity towards water. These results demonstrate the ability of fluorine to tailor the interaction of water molecules with metal oxide surfaces, which ultimately modifies the activity, selectivity, and stability of the catalyst.