Direct environmental TEM observation of silicon diffusion-induced strong metal-silica interaction for boosting CO2 hydrogenation

For the high-temperature catalytic reaction, revealing the interface of catalyst—support and its evolution under reactive conditions is of crucial importance for understanding the reaction mechanism. However, much less is known about the atomic-scale interface of the hard-to-reduce silica-metal compared to that of reducible oxide systems. Here we reported the general behaviors of SiO2 migration onto various metal (Pt, Co, Rh, Pd, Ru, and Ni) nanocrystals supported on silica. Typically, the Pt/SiO2 catalytic system, which boosted the CO2 hydrogenation to CO, exhibited the reduction of Si0 at the Pt-SiO2 interface under H2 and further Si diffusion into the near surface of Pt nanoparticles, which was unveiled by in-situ environmental transmission electron microscopy coupled with spectroscopies. This reconstructed interface with Si diffused into Pt increased the sinter resistance of catalyst and thus improved the catalytic stability. The morphology of metal nanoparticles with SiO2 overlayer were dynamically evolved under reducing, vacuum, and oxidizing atmospheres, with a thicker SiO2 layer under oxidizing condition. The theoretical calculations revealed the mechanism that the Si-Pt surface provided synergistic sites for the activation of CO2/H2 to produce CO with lower energy barriers, consequently boosting the high-temperature reverse water-gas shift reaction. These findings deepen the understanding toward the interface structure of inert oxide supported catalysts.