In situ Observation of Porosity Formation in Porous Single-crystalline TiO2 Monolith for Enhanced and Stable Catalytic CO Oxidation

Introducing pores in single crystals creates a new type of porous materials that incorporate porosity and structural coherence. Herein, we use in situ transmission electron microscopy to disclose the porosity formation by converting KTiOPO4 (KTP) single crystals into porous single-crystalline (PSC) TiO2 monoliths in a solid-solid transformation. The isolated crystalline nuclei of TiO2 clusters with identical lattice orientation on KTP surface moves TiO2/KTP interface toward mother phase for growing PSC TiO2 monoliths. The relative density in PSC TiO2 monoliths dominates porosity while the macroscopic dimensions remain unchanged in the transformation. The single-crystalline nature of porous architecture stabilizes oxygen vacancy to activate lattice oxygen while the three-dimensional percolation enhances species diffusion. PSC TiO2 monoliths with deposited Pt clusters show enhanced and stable catalytic CO oxidation in air at similar to 75 degrees C for 200 hours of operation.