Silica Encapsulation Strategy for Protection and Controllable Synthesis of Nanocatalysts

ConspectusNanocatalysts have shown remarkable potential for various catalytic reactions due to their high specific surface area. But the inherently high surface energy of these nanocatalysts promotes spontaneous growth, leading to their instability under harsh catalytic conditions. Additionally, high-temperature treatment is an important way to prepare nanocatalysts because it can enhance atomic diffusion and generate a wide range of nanocatalysts. Unfortunately, many nanocatalysts suffer from inevitable aggregation and fusion during the high-temperature treatment procedure and thus face challenges in controlling their sizes and morphologies. In recent decades, significant progress has been achieved in synthesizing silica with a controllable thickness and mesoporous structures. The construction of silica on nanocatalysts as a protective shell, including core@shell, yolk@shell, or reverse bubble-ball structures, proves to be an effective strategy to prevent aggregation under harsh catalytic conditions. Furthermore, the subsequent etching of the silica shell, similar to protection/deprotection procedures in organic synthesis, enables the successful synthesis of nanocatalysts with controllable size and morphology under high-temperature conditions.In this Account, we provide an overview of the key role of silica in protecting and controllably synthesizing nanocatalysts, focusing on the optimization of their sizes, phases, and morphologies for improved catalytic performance and broader applications. First, we highlight the design principles of yolk@shell and reverse-bumpy-ball nanoreactors. These nanoreactors incorporate single or multiple nanoparticles effectively and impart enhanced properties to the synthesized nanocatalysts. Furthermore, we discuss recent advancements in silica encapsulation strategies that facilitate the fabrication of diverse nanocatalysts with tunable sizes and superior catalytic capabilities even under high-temperature conditions. The materials synthesized by these strategies include noble metal-based alloys and intermetallic compounds, non-noble-metal-based interstitial compounds, sulfides, oxides, and carbon-based materials. By examining the protective effects of silica and underscoring its critical role, we shed light on the potential as well as the challenges associated with employing silica encapsulation techniques in the design of high-performance nanocatalysts. We hope that this Account serves as an informative resource for researchers interested in the controllable synthesis of nanocatalysts; meanwhile, it can inspire the development of novel nanocatalysts through the utilization of encapsulation strategies.