Hydrophobicity enhancement of Ti-MWW catalyst and its improvement in oxidation activity

Abstract

The effect of the preparation conditions of the Ti-MWW catalyst on the hydrophobicity of the catalyst and its catalytic activity was investigated. Our findings demonstrated that the condensation of interlayer hydroxyl groups was greatly affected by the preparation conditions, in particular washing conditions of the as-synthesized lamellar precursor of Ti-MWW, then further controlling the final hydrophobicity and oxidation properties. Using organic solvents, especially EAOH, instead of water to wash the wet lamellar precursor would synchronize the interlayer hydroxyl condensation with the decrease of interlayer distance mainly caused by the leaching of piperidine, which was used as structure-directing agent (SDA). After acid-treatment, less SDA was kept in the EAOH washed sample and 3D-MWW with less defects was formed by calcination. Both drying temperature and acid-treatment would also affect the amount of SDA occluded in the interlayer void space of the acid-treated samples and then further affect the final interlayer hydroxyl condensation upon the following calcination. The lower both drying temperature and acid-treatment temperature were favorite to unequal interlayer dehydroxylation to form MCM-56, while higher drying temperature such as 150°C not only caused the anatase phase in the calcined samples but also occluded more SDA molecules in the acid-treated samples which greatly affect the further interlayer hydroxyl condensation upon the calcination. Ti-MWW-OH-100 containing smallest amount of silanols and less defect sites showed the best hydrophobicity and the highest catalytic activity in 1-hexene oxidation.