Pd-KIT-6: synthesis of a novel three-dimensional mesoporous catalyst and studies on its enhanced catalytic applications

Abstract

Synthesis of a novel three-dimensional mesoporous Pd-KIT-6 is carried out by a room temperature sol–gel method. The synthesised material is well crystalline observed from the Small angle powder X-ray diffraction. Calcination at 550 °C for 8 h retains the structure. The particle sizes are in the micron range. Si/Pd ratio of the as-synthesized material is found to be 45 against the input ratio 100. Transmission electron micrograph reveals the presence of the porous hexagonal structure. Thermogravimetric studies reveal that the KIT-6 (Korea Advanced Institute of Science and Technology number 6) undergo less weight-loss compared to Pd-KIT-6, which indicates the material is more crystalline than its metal-free counterpart due to the enhanced crystallisation rate. These results also supported by BET-surface area and Transmission electron microscopic picture. The 960 cm−1 band at Fourier transform Infrared spectroscopic analysis shows that the incorporation of Pd in the framework. These FT-IR results also supported by Raman Spectroscopic analysis. Electron spin resonance spectroscopic analysis shows that the Palladium is present in the +2 oxidation state in as-synthesized samples. Diffused reflectance Ultraviolet–Visible spectroscopic results show that Palladium is in tetrahedral coordination. Microwave irradiated Suzuki–Miyaura (SM) cross-coupling reactions studied by using the Pd-KIT-6 catalyst in detail without any organic solvent at 100 °C for 10 min. The reaction carried out in the presence of phenyl iodide, phenylboronic (PhB(OH)2), and K2CO3 produce biphenyl, with 98% yield. Change of halide to Phenyl bromide gave similar results, but Phenyl chloride gave lesser conversion (20%). It is due to the electronegativity difference between the halides. A plausible reaction mechanism is also proposed.