Catalysis Enhancement of Ceria Nanoparticles Embedded in Silica-Nanoparticle Assemblies for Organophosphate Hydrolysis

Cerium dioxide nanoparticles (CeO₂NPs) have been reported to act as active species for various catalytic reactions including organophosphate hydrolysis. The catalytic activity of CeO₂NPs embedded in silica nanoparticles assemblies (SiO₂NPAs) for p-nitrophenylphosphate (p-NPP) hydrolysis was enhanced to maintain high dispersity. CeO₂NPs capped with oleylamine with a size of 15–40 nm showed the low initial rate (<30 min) of 0.71 mM h⁻¹ in a HEPES buffer containing p-NPP (8.0 mM) at 60 °C. CeO₂NPs calcined at 800 °C showed the increased initial rate of 1.1 mM ⁻¹ by removal of oleylamine, although CeO₂NPs partially sintered. Conventional SiO₂ support was used for suppression of the sintering, however, the initial rate decreased to 0.75 mM h⁻¹ by high contact between CeO₂ and SiO₂. SiO₂NPAs were used to minimize contact between CeO₂ and SiO₂. The initial rate with CeO₂/SiO₂NPAs prepared by the impregnation method was as high as 1.8 mM h⁻¹. Furthermore, the initial rate with CeO₂/SiO₂NPAs prepared by a premixed method increased to 2.6 mM h⁻¹ by effective suppression of both CeO₂NPs aggregation and electronic interaction with SiO₂. Although the sintering of CeO₂NPs was effectively suppressed even at 1000 °C, the initial rate decreased because of the adsorption of p-NPP on SiO₂NPAs.