Au/MnOx/3DOM SiO2: Highly active catalysts for toluene oxidation

• 3DOM SiO2 with ordered mesoporous walls is synthesized via the PMMA-templating route.
• zMnOx/3DOM SiO2 is prepared using the incipient wetness impregnation method.
• yAu/zMnOx/3DOM SiO2 is prepared via the PVA-protected reduction route.
• 0.93Au/11.2MnOx/3DOM SiO2 performs well in the oxidation of toluene.
• Oads content, reducibility, and noble metal–oxide interaction govern the catalytic activity.

Three-dimensionally ordered macro-/mesoporous silica (3DOM SiO2)-supported manganese oxide and gold nanocatalysts (yAu/zMnOx/3DOM SiO2, y = 0–0.95 wt%; z = 2.7–15.4 wt% (weight percentage of Mn2O3)) were prepared using the polymethyl methacrylate-templating, incipient wetness impregnation, and polyvinyl alcohol-protected reduction methods, respectively. It is shown that the yAu/zMnOx/3DOM SiO2 samples displayed a high-quality 3DOM architecture with macropores (180–200 nm in diameter) and mesopores (4–6 nm in diameter) and a surface area of 220–318 m2/g. MnOx nanoparticles (NPs) with a size of 18.7–25.7 nm were dispersed on the surface of 3DOM SiO2, and Au NPs with a size of 3.6–3.8 nm were uniformly dispersed on the surface of zMnOx/3DOM SiO2. The 0.93Au/11.2MnOx/3DOM SiO2 sample performed the best (the temperature required for achieving a 90% toluene conversion was 255 °C at space velocity = 20,000 mL/(g h)) for toluene oxidation. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between Au and MnOx NPs as well as the unique bimodal porous structure were responsible for the good catalytic performance of 0.93Au/11.2MnOx/3DOM SiO2.

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