Facet-dependent adsorbate-mediated strong metal-support interaction in Ni/TiO₂

Despite the growing significance of adsorbate-mediated strong metal-support interaction (A-SMSI) in various catalytic processes, a comprehensive mechanistic understanding of its formation and effective strategies for its precise modulation remain elusive. Herein, by constructing three well-defined model Ni/TiO₂ catalysts with distinct exposed facets, we directly visualize a facet-dependent A-SMSI behavior in CO₂ hydrogenation via in situ environmental transmission electron microscopy (ETEM) at the atomic level. The in situ results reveal distinct formation behaviors of TiO_2-x overlayers: complete, partial, and no encapsulation of Ni nanoparticles (NPs) on the {100}, {101}, and {001} TiO₂ facets, respectively. Complementary in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray absorption spectroscopy (XAS) experiments and density functional theory (DFT) calculations further reveal a dual induction mechanism, where adsorbates both participate in TiO_2-x formation and stabilize the encapsulating overlayer. Moreover, TiO_2-x transfers electrons to Ni and stabilizes COOH^* intermediates that dehydroxylate to form CO. Guided by these mechanistic insights, facet-dependent A-SMSI enables remarkable selectivity modulation, yielding CH₄ selectivity exceeding 88% on Ni/TiO₂-{001} and CO selectivity over 83% on Ni/TiO₂-{100}. These findings advance the fundamental understanding of A-SMSI and offer a rational framework for designing oxide-supported catalysts with tailored interfacial properties.