Hydrophobic Modification of Pd/SiO2@Single-Site Mesoporous Silicas by Triethoxyfluorosilane: Enhanced Catalytic Activity and Selectivity for One-Pot Oxidation

To enhance the catalytic activity in a selective one‐pot oxidation using in‐situ generated H2O2, a hydrophobically modified core–shell catalyst was synthesized by means of a simple silylation reaction using the fluorine‐containing silylation agent triethoxyfluorosilane (TEFS, SiF(OEt)3). The catalyst consisted of a Pd‐supported silica nanosphere and a mesoporous silica shell containing isolated TiIV and F ions bonded with silicon (SiF bond). Structural analyses using XRD and N2 adsorption–desorption suggested that the mesoporous structure and large surface area of the mesoporous shells were retained even after the modification. During the one‐pot oxidation of sulfide, catalytic activity was enhanced significantly by increasing the amount of fluorine in the shell. A hydrophobic surface enhanced adsorption of the hydrophobic reactant into the mesopore, while the less hydrophobic oxygenated products efficiently diffused into the outside of the shell, which improved the catalytic activity and selectivity. In addition, the present methodology can be used to enhance the catalytic activity and selectivity in the one‐pot oxidation of cyclohexane by using an Fe‐based core–shell catalytic system. Simplicity is the key: A new core–shell type catalyst with a hydrophobic surface was designed based on a simple method using triethoxyfluorosilane as a silylation reagent (see scheme). The hydrophobic surface improved catalytic performance significantly in the one‐pot oxidation of sulfides. Catalytic activity was approximately three times greater than that of previously reported unmodified catalysts, and selectivity toward sulfoxide was better due to the hydrophobic surface of the shell.