Thermal Migratory Alloying in Vacuum‐Stabilized Porous Silica Nanoreactor

ABSTRACT High‐temperature nanocrystal (NC) transformations in porous silica ( p SiO 2 ) are typically limited by densification, pore collapse, and sintering. We show that HVA‐enabled opens a distinct thermal window at 1000°Cwhere unusually preserved p SiO 2 confines metal species to gain sufficient mobility for NC‐alloying. Continuous removal of volatile SiO x and condensates suppresses viscous flow, enabling nanoscopic migratory solid‐state reactions inside intact p SiO 2 . Migration pathways are metal‐dependent: noble metals (Rh, Pd, Pt, Ru) diffuse inward to form concentric alloy NC, whereas non‐noble metals such as Fe, Co, and Ni proceed through transient silicide formation that drives outward NC migration, yielding an eccentric configuration via a melt–migrate–freeze mechanism. The resulting nanoreactors are compositionally tunable, thermally robust, and solution‐dispersible. Confinement‐programmed architectures generate catalytic microenvironments that tune activity and chemoselectivity across multiple hydrogenation reactions. HVA strategy converts migration from a high‐temperature failure mode into a controllable synthetic handle for designing functional confined alloys.