Abstract
Precisely controlling the spatial intimacy of multiple active sites at sub-nanoscale in heterogeneous catalysts can improve their selectivity and activity. Herein, we realize a highly selective nitrile-to-secondary imine transformation through a cascaded hydrogenation and condensation process by Pt1/CoBOx comprising the binary active sites of the single-dispersed Pt and interfacial Lewis acidic B. Atomic Pt sites with large inter-distances (>nanometers) only activate hydrogen for nitrile hydrogenation, but inhibit condensation. Both adjacent B…B on CoBOx and neighbouring Pt…B pairs with close intimacy of ~0.45 nm can satisfy the spatial prerequisites for condensation. Mechanism investigations demonstrate the energetically favorable pathway occurred on adjacent Lewis acidic B sites through the nitrile adsorption (acid-base interaction), hydrogenation via hydrogen spillover from Pt to B sites and sequential condensation. Strong intermolecular tension and steric hindrance of secondary imines on active sites lead to their effective desorption and thereby a high chemoselectivity of secondary imines.
Highlights
Controlling the spatial intimacy of multiple active sites at sub-nanoscale in heterogeneous catalysts can improve their selectivity and activity
Hydrogenation of several nitrile molecules can simultaneously occur on the surface of a metal nanoparticle, which is beneficial for the condensation process to give secondary imines
In the Pt1/CoBOx catalyst, three spatial configurations of binary active sites of single-dispersed Pt site and interfacial Lewis acidic B site are illustrated in Fig. 1d: Pt...Pt with a large inter-distance over nanometers; neighboring Pt...B and adjacent B...B site with a distance of ~0.45 nm
Summary
Controlling the spatial intimacy of multiple active sites at sub-nanoscale in heterogeneous catalysts can improve their selectivity and activity. We realize a highly selective nitrile-to-secondary imine transformation through a cascaded hydrogenation and condensation process by Pt1/CoBOx comprising the binary active sites of the single-dispersed Pt and interfacial Lewis acidic B. In the Pt1/CoBOx catalyst, three spatial configurations of binary active sites of single-dispersed Pt site and interfacial Lewis acidic B site are illustrated in Fig. 1d: Pt...Pt with a large inter-distance over nanometers; neighboring Pt...B and adjacent B...B site with a distance of ~0.45 nm. The efficient hydrogenation of the absorbed nitriles on adjacent Lewis acidic B sites through hydrogen spillover from Pt to B and thereby subsequent condensation (Step 3) are the energetically favorable pathways Such a catalyst with the spatially organized single-dispersed Pt and Lewis acidic B binary active-sites can yield a >99.9% selectivity and 864 h−1 TOF of benzonitrile hydrogenation to corresponding secondary imines
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