Photocatalytic formation of a gas permeable layer selectively deposited on supported metal nanoparticles for sintering-resistant thermal catalysis

Nanoparticle aggregation of supported metal catalysts at high temperatures is a serious problem that causes a drop in catalytic performance. This study investigates the protection of metal nanoparticles from sintering by selectively forming nanoscale SiO2 shells on Pd supported on TiO2 by ultraviolet (UV) light irradiation. The proton-coupled reduction reaction increases the local pH around Pd nanoparticles, resulting in hydrolysis of tetraethoxyorthosilicate (TEOS) in only the vicinity of the metal. An apparent quantum efficiency of only 0.6% is obtained for the Pd/TiO2 catalyst in H-2 evolution from ethanol-containing water under 370 nm excitation light. Therefore, the pH of raw slurry solution should be precisely controlled to that slightly below the threshold value for the TEOS hydrolysis reaction before the photodeposition. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) clearly show that the particle size of the Pd nanoparticles (similar to 40 nm) with the SiO2 shell (similar to 20 nm) was almost unchanged by the high-temperature treatment at 900 degrees C in air, suggesting that the SiO2 shell prevented thermal aggregation of Pd nanoparticles. The Pd/TiO2 without SiO2 shell decoration exhibited a drop in the number of active sites, which was likely due to aggregation of the Pd catalysts. However, the number of active sites on the Pd@SiO2/TiO2 catalyst was maintained even after the catalyst was calcined at 900 degrees C. Consequently, the Pd@SiO2/TiO2 catalyst maintained its catalytic performance for simulated exhaust gas purification even after treatment at 900 degrees C. This study presents a methodology to produce sintering-tolerant supported metal nanoparticles using the photocatalytic gas permeable layer fabrication method.

Automated summary

This study investigates the protection of metal nanoparticles from sintering by selectively forming nanoscale SiO2 shells on Pd supported on TiO2 by ultraviolet (UV) light irradiation. The SiO2 shell prevents thermal aggregation of Pd nanoparticles, maintaining the catalyst's activity even at high temperatures.