Aligning H2 Activation with Functional-Group Polarity: K+-Promoted Switchable Hydrogenation on Pd/TiO2

Le résumé fourni par la source

Rationally aligning H2 activation modes with the polarity of substrate functional groups is central to chemoselective heterogeneous hydrogenation but remains poorly understood. Here we show that K+ doping of Pd/TiO2 (Pd/KTiOx) enables concerted control of H2 dissociation and C═O activation, resulting in a switchable hydrogenation chemoselectivity. Pristine Pd/TiO2 selectively hydrogenates the C═C bond of maleic anhydride to succinic anhydride with 99% selectivity, whereas Pd/KTiOx hydrogenates both C═C and C═O bonds to γ-butyrolactone with 99% selectivity. On both catalysts, H2 undergoes homolytic cleavage on Pd nanoparticles to generate H· species responsible for C═C hydrogenation. Introduction of K+ at the Pd-TiO2 interface strengthens K-O electrostatic interactions and increases the electron density on Pd, which together lower the barrier for heterolytic H2 cleavage at Pd-O sites and generate polarized Hδ--Hδ+ pairs. These heterolytic hydrogen species preferentially activate polar C═O bonds, thus redirecting the hydrogenation pathway. This work establishes alkali-metal promotion as a strategy to tune the balance between homolytic and heterolytic H2 activation and, in turn, to control functional-group-dependent hydrogenation selectivity in heterogeneous catalysis.

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