Understanding the interfacial changes of PtCo3O4 catalysts during the dehydrogenation of ammonia borane

Abstract

The redox properties of oxides are critical in catalysis and can be modified at the interface between oxides and metals; as a consequence, working catalysts can be reconstructed. Herein, the influence of metal-support interactions on the interface between Pt and Co3O4 was disclosed during the batch ammonia borane decomposition. Co3O4 with and without decorating Pt were compared, and tested against Pt on a non-reducible oxide (PtAl2O3). The kinetic profiles were analysed using kinetic models, and both fresh and used samples were characterised using XRD, XPS, XAS, HR-TEM, CO adsorption by IR, and in situ ATR-IR. The combined study revealed an enhanced reaction rate for PtCo3O4 and its reconstruction under reaction conditions due to metal-support interaction, and disclosed the nature of the stable active sites formed under reaction conditions. Indeed, during the reaction, metallic Pt re-distributed, and the H-spillover to the support reduced the surface of Co3O4, leading to Pt clusters on Co(II)-enriched Co3O4. Atomic-scale insights on the surface redox properties of the catalysts were then obtained through DFT, and the modification of PtCo3O4 was attributed to the facile reduction of octahedral Co(III) ions at the metal/oxide interface, and rationalised as a consequence of charge transfer from Pt to Co3O4.