Designing CeTiO_x-based composite encapsulation overlayer on platinum for enhanced methanol steam reforming

Methanol steam reforming (MSR) is a key reaction for sustainable hydrogen production, yet its efficiency is often limited by sluggish elementary steps and unfavorable selectivity on conventional supported metal catalysts. Herein, we report a Pt-5CeTiO_x catalyst featuring a rationally designed composite CeTiO_x encapsulation overlayer on Pt nanocluster, constructed under mild reduction conditions. Quasi in situ X-ray photoelectron spectroscopy reveals that the composite overlayer originates from the cooperative migration of highly mobile Ti³⁺ and Ce³⁺ species from the reduced CeTiO_x support along the oxygen-vacancies (OVs) pathway, leading to a well-defined multilayer structure. In this structure, Pt is preferentially coordinated with an inner CeO_x-rich layer, while an outer TiO_2-x layer acts as a protective shell that suppresses Ce³⁺ reoxidation and stabilizes the encapsulated interface. The resulting inverse Ce³⁺-OVs-(Pt⁰-Pt^δ+) configuration effectively tailors the electronic structure of Pt, thereby promoting the kinetically relevant *CH₂O → *CHO conversion, while abundant Ce³⁺-OVs sites within the composite CeTiO_x overlayer serve as highly efficient water dissociation centers. As a consequence, the Pt-5CeTiO_x catalyst exhibits a 1.56-fold enhancement in intrinsic MSR activity and over 80% suppression of CO selectivity relative to catalysts featuring single-component TiO_2-x encapsulation overlayers. Furthermore, temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR), and in situ diffuse-reflectance infrared spectroscopy (DRIFTS) measurements enable experimental identification of key surface intermediates and intrinsic reactivities of individual elementary steps, showing excellent agreement with density functional theory calculations. Overall, our study presents a strategy that enables the transition of encapsulation overlayers from single-component to rationally designed composite architectures, thereby accelerating catalytic reactions.