Lattice Expansion and Electronic Reconfiguration of MnCu Oxide Catalysts for Enhanced Transfer Hydrogenation of Levulinate

Abstract

Lattice-strained metal oxides often display enhanced catalytic activity and selectivity on activation of C–H, C═C, C═O, and O–H bonds in bio-oxygenates. However, limited experimental studies have been conducted on the structure sensitivity for tandem reactions, particularly on complicated surface redox chemical chain reactions over strained oxide materials. In this work, we employed transfer hydrogenation of levulinate as a representative example to illustrate how lattice strain affects tandem oxidation (dehydrogenation, C–H/O–H bond cleavage) and reduction (hydrogenation, C═O bond saturation) reactions. The key finding is that lattice strain at MnOx–CuOx boundaries within bimetallic MnCu oxides leads to a highly unsymmetrical strain across the interface and lattice distortion. Such unique behaviors further induce the Jahn–Teller effect for electronic reconfiguration and field split for Mn 3d orbitals. Thus, tandem H2 generation and hydrogenation of levulinate to valerolactone can occur much more efficiently with a fivefold enhancement over monometallic oxide catalysts. Detailed characterization of fresh and sintered catalyst samples further demonstrated the critical role of expansion of the Mn–O facet and phase segregation in facilitated chemical chain reactions. The design principles discussed in this work could be potentially applied for other non-noble oxide catalysts in energy and environmental fields.