A facile route to cage-like mesoporous silica coated ZSM-5 combined with Pt immobilization

Abstract

Uniform core–shell composites with cage-like mesoporous silica (CmesoSiO₂) shells and zeolite HZSM-5 cores have been synthesized by a facile acid-catalyzed sol–gel coating process. The mesoporous silica shells are uniform and coated on the anisotropic HZSM-5 crystal faces, and the shell-thicknesses can be tuned from 25 to 70 nm. The core–shell composites possess a high surface area (∼862 m² g⁻¹) and pore volume (∼0.66 cm³ g⁻¹), large pore sizes (3.2–8.2 nm) and unchanged zeolite micropore properties. The silica shells are composed of cage-like mesopores and entrances (ranging from 3.2 to 8.2 nm) as well as a plenty of micropores. Pt nanocatalysts with an average particle size of ∼3.2 nm have been successfully encapsulated into the micropores and partial mesopores of the cage-like silica shells. The catalytic oxidation of toluene shows that the Pt/HZ@CmesoSiO₂ composite presents an equivalent activity for toluene combustion at the light-off temperature of ∼195 °C (T_50%) relative to the mixture catalyst (198 °C of T_50%), but more excellent catalytic durability without activity loss (193 °C of T_50%) after a 100 h test.