Active site design in a core - shell nanostructured catalyst for one - pot oxidation reaction Photon Factory Activity

Introduction One-pot oxidation reaction consisted of direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 gases and oxidation reaction using in situ generated H2O2 is promising synthetic method, because it is possible to use the unstable H2O2 immediately without isolation/purification steps, which would contribute to energy and time saving as well as avoid the risk of transportation of the concentrated H2O2. The one-pot oxidation reaction requires the catalysts for product H2O2 (e.g. Pd nanoparticle) and for oxidation reaction (e.g. TiO2), respectively. Until now, the conventional catalyst for one-pot oxidation reaction was physical mixture of both components or Pd supported TiO2 zeolite. However using such catalyst, the synthesized H2O2 on the Pd catalyst will diffuse to the solvent before contact to Ti site and most of them will be decomposed to water in the solvent. To improve the efficiency of H2O2, we present a new type of core-shell structured catalyst to enable the one-pot oxidation of sulfide to sulfoxide with high efficiency and selectivity, in which a uniform SiO2 core supporting Pd nanoparticles was covered with a Ticontaining mesoporous silica shell (Pd/SiO2@TiMSS). Meanwhile, it is well accepted that the formation of tetrahedral Ti species is crucial to achieve selective oxidation using H2O2, while octahedral Ti species and bulk TiO2 promote the decomposition of H2O2. Thus, local structure of Titanium species within the mesoporous silica shell was investigated by X-ray absorption fine structure (XAFS).