Enhanced Activity and Selectivity in the One-Pot Hydroxylation of Phenol by Pd/SiO2@Fe-Containing Mesoporous Silica Core–Shell Catalyst

A novel approach to enhance the catalytic performances in one-pot hydroxylation of phenol into catechol and hydroquinone was examined using core–shell type catalysts which consist of Pd nanoparticles (NPs) for direct synthesis of H 2 O 2 from H 2 and O 2 and Fe-containing mesoporous silica (Fe-MS) for hydroxylation of phenol using in situ produced H 2 O 2 . We have newly prepared three types of core–shell catalysts: (i) Pd/SiO 2 core covered with Fe-MS (Pd/SiO 2 @Fe-MS), (ii) SiO 2 core covered by Fe-MS with randomly distributed Pd NPs within the mesoporous silica structure (SiO 2 @Pd(R)/Fe-MS), where (R) indicates random, and (iii) SiO 2 core covered by Fe-MS with Pd NPs deposited on the outer surface of the mesopores SiO 2 @Pd(S)/Fe-MS, where (S) indicates the surface. The effects of the relative position between the Pd NPs and Fe-MS on the catalytic activity and the selectivity were investigated. As a result, it was clearly demonstrated that the relative position significantly affects not only the reaction rate but also the product selectivity, and the Pd/SiO 2 @Fe-MS showed the best performance among them. The applicability of the Pd/SiO 2 @Fe-MS is also demonstrated in the one-pot oxidation of adamantine. The present design strategy offers a very simple and efficient methodology to realize a one-pot reaction.