Surface‐Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal Nanocatalysts

Abstract

Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general “encapsulation and etching” strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface‐protected etching process, both yolk–shell and core–satellite type nanoreactors are synthesized and their utilization in liquid‐ and gas‐phase catalysis is demonstrated. The thermal and chemical stability of the metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework.

A double-shelled yolk-like structure as an ideal magnetic support of tiny gold nanoparticles for nitrophenol reduction

“…The as-prepared yolk-shell SiO 2 @Fe 3 O 4 /C composites were rst mixed with 40 mL of anhydrous toluene and 0.8 mL of APTES and heated to 120 C for 12 h to functionalize the composites with amino groups. The amino modied microspheres were washed with ethanol and dispersed in deionized water.…”

A review on plasmonic metal⿿TiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system

“…This unique structure of the photocatalyst provides more advantages like: (i) the encapsulation of Ag nanoparticles was advantageous since this process increased its stability during calcination and subsequent photocatalysis. Further, encapsulation effectively avoids the Ag nanoparticles from moving together and coagulating [183][184][185]. (ii) The in situ growth of the Ag nanoparticles on the surface of porous silica bead leads to uniform distribution of the Ag nanoparticles inside the TiO 2 matrix.…”

Nanocatalysis I: Synthesis of Metal and Bimetallic Nanoparticles and Porous Oxides and Their Catalytic Reaction Studies

“…The shells overgrown on the surface of core nanoparticles become porous during the calcinations by removing organic surfactants. Recently, an alternative strategy was developed to control the porosity of the shells systematically by a surface-protected etching process [24,26]. The coated oxide shells resulted in porous layers by removing organic capping ligands in the shells by an appropriate etching agent.…”