Catalyst instability and deactivation are particularly problematic with nanoscale materials, and thus research in improving catalyst stability and activity remains prevalent to this day. Solid base metal oxide catalysts such as MgO offer utility in a wide variety of applications from pharmaceuticals to fuels. The (111) facet of MgO, as compared to its counterpart facets, has shown enhanced and unique properties highlighting the significance of surface exposed facets. However, MgO(111) suffers from deactivation in water. To tackle this problem, we studied the evolution of MgO(111) surfaces when exposed to deuterated hydration (D2O) during the condensation reaction of 2-pentanone. This reaction has industrial and sustainable relevance as methyl ketones can be biomass-derived and converted into both dimer and trimer products which can be used as precursors for biofuels. Catalyst screening showed that the MgO(111) surfaces were more active towards ketone condensation than MgO(100) surfaces. Because the (111) facet is higher in surface energy compared to its naturally forming (100) facet, computational modeling suggested that the high surface energy (111) facet is stabilized by hydroxyls thereby reducing the energy barrier for 2-pentanone condensation via surface mediated proton transfer. Vapor-phase D2O hydration studies showed an increase in hydroxyls on MgO(111) after 3 minutes and a retainment of surface area and activity; however, after 1 hour, the deuteroxide formation resulted in a reduction of surface area and activity by 30%. After 24 hours of vapor-phase D2O hydration, the deuteroxide formation slowed down and surface area and activity remained stable. It was speculated that after deuterated hydration, the MgO(111) hydroxylated surface may be responsible for the condensation of 2-pentanone. Despite a reduction in surface area and activity, after thermal regeneration of the 24-hour sample, the catalyst restored 86% of the surface area and 94% of the activity.

Catalytic activity and water stability of the MgO(111) surface for 2-pentanone condensation

ACS Spring 2022

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