Improved catalytic performance by changing surface and textural properties of Ru supported bifunctional periodic mesoporous organosilicas in aerobic oxidation of alcohols

Abstract

The catalytic activity of several supported catalysts composed of perruthenate anions incorporated into mesochannels of a series of plugged and unplugged bifunctional periodic mesoporous organosilicas (Ru@BFPMOs) in the aerobic oxidation of alcohols were investigated. These nanostructures with bridged ionic liquid building blocks were successfully synthesized by the co-condensation of 1,3-bis(trimethoxysilylpropyl)imidazolium chloride (BTMSPCl) along with 1,4-bis(triethoxysilyl)benzene (BTEB) or 1,2-bis(trimethoxysilyl)ethane (BTME) as organosilica precursors and tetramethyl orthosilicate (TMOS) as a silica source in the presence of pluronic P123 as a structure-directing agent (SDA) under acidic conditions. The presence or absence of silica plugs inside the mesochannels of the final nanostructures could be controlled by the sequence of addition of the silica and organosilica precursors. The morphology and structure of all materials were characterized by various analyses such as N₂ adsorption desorption, high resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), elemental analysis (CHN), ¹³C and ²⁹Si cross-polarization magic angle spinning (CP-MAS) NMR spectroscopy, and Fourier transform infrared spectroscopy (FTIR). It was found that all of the prepared materials have a 2D-hexagonal symmetry structure with regular and narrow pore size distribution. Furthermore, perruthenate anions were introduced inside the nanopores of these plugged and unplugged BFPMOs and the efficiency of the resulting catalyst was evaluated and compared in the aerobic oxidation of a wide variety of primary, secondary and sterically hindered benzylic and aliphatic alcohols, affording corresponding carbonyl compounds in high yield and selectivity.