Au nanoparticle-embedded SiO2-Au@SiO2 catalysts with improved catalytic activity, enhanced stability to metal sintering and excellent recyclability

Synthesizing a precious metal catalyst with high performance and excellent recyclability is always an important issue in catalysis. Here, we report a synthetic strategy for preparing gold nanoparticle (Au NP)-embedded SiO2 particles for use as recyclable nanocatalysts. Au NP-embedded SiO2 (SiO2-Au@SiO2) particles were synthesized by applying a Au NP decoration on the surface of the SiO2 particles and additional SiO2 coating through a sol-gel reaction. In order to improve molecule accessibility, catalyst stability and catalytic performance, post-treatments such as calcination and/or etching with water or ammonia were carried out. A systematic study of the physical property changes of the resulting SiO2-Au@SiO2 samples with variations of each synthetic step revealed that the parameters that are very important for determining the catalytic performance, namely Au NP stability, porosity and capping agents on the Au surface, are strongly influenced by each post-treatment step. In particular, calcination followed by etching with ammonia enables the production of a highly active SiO2-Au@SiO2 catalyst with highly dispersed Au NPs in the silica layer, a surfactant-free Au surface and an improved porosity of the silica layer, which displays significantly enhanced catalytic performance and excellent recyclability as compared to SiO2-Au and as-synthesized SiO2-Au@SiO2.