Determining the active catalytic palladium species under hydrodeoxygenation conditions

Abstract

The molecular, homogeneous catalyst 2,6-bis(4-isopropyl-2-oxazolinyl)pyridine palladium(II) was examined for the ability to perform selective hydrodeoxygenation of benzyl alcohol. Reaction conditions and substrate were chosen to mimic conditions used to depolymerize lignin biomass and subsequently convert the lignin-derived monomers into useful biofuels. The molecular catalyst exhibited moderate catalytic activity in methanol solvent with complete selectivity towards hydrodeoxygenation (HDO) of benzyl alcohol under mild conditions, including room temperature. At elevated temperatures, the molecular catalyst decomposed into solid particles. These particles were characterized with XPS and contained metallic palladium, which also exhibited catalytic HDO activity. The particles also achieved complete selectivity towards hydrodeoxygenation over aromatic ring hydrogenation, but only at temperatures above 200 °C. Recycling the solid particle catalysts over multiple reaction cycles, led to the leaching of the catalytically active species back into solution and the eventual deactivation of the solid particles.