Gold nanoparticle stabilization within tailored cubic mesoporous silica: Optimizing alcohol oxidation activity

Abstract

Stabilizing gold nanoparticles (AuNPs) within a desired size range is critical to realize their promising catalytic performance in many important reactions. Herein, we investigate the anti-sintering properties of cubic mesoporous silica (FDU-12) as a function of pore entrance size. Simple adjustments to the type of organic template and reaction temperature enable the successful synthesis of FDU-12 with controllable entrance sizes (< 3, 3–5 and 7 nm). Excellent anti-sintering properties are observed for FDU-12 with a sub-5-nm entrance size (3–5 nm) over a wide loading concentration (1.0–8.3 wt%) and the AuNPs can be stabilized within a 4.5–5.0-nm range after calcination at 550 °C in air for 5 h. Smaller entrance size (< 3 nm) prevents ingress of 3-nm AuNPs to the mesopores and results in low loading capacity and sintering. Conversely, FDU-12 possessing a larger entrance size (7 nm) shows promising anti-sintering properties at high loading concentrations, although catalytic performance is significantly lost at lower concentrations (e.g. 2.1 wt%, 14.2 ± 5.5 nm). Different anti-sintering mechanisms are proposed for each of the different FDU-12 entrance sizes. Additionally, catalytic data indicates that the obtained 4.5-nm AuNPs supported on FDU-12 with a sub-5-nm entrance size exhibit excellent mass-specific activity (1544 mmol gAu–1 h–1) and selectivity (> 99%) at 230 °C for the gas-phase selective oxidation of cyclohexanol.