Characterization of MCM-41 mesoporous molecular sieves containing copper and zinc and their catalytic performance in the selective oxidation of alcohols to aldehydes

Abstract

MCM-41 mesoporous molecular sieves containing copper and zinc with different metal contents were synthesized at room temperature (RT) by the method of direct insertion of metal ions as precursors in the initial stage of synthesis. The physicochemical properties of the materials were thoroughly investigated employing X-ray powder diffraction, high-resolution transmission electron microscopy, UV–Visible diffuse reflectance spectroscopy, electron paramagnetic resonance spectroscopy, temperature programmed reduction and N 2 adsorption–desorption methods. The results indicated that MCM-41 materials with long range hexagonal ordering could be successfully synthesized at RT in the presence of copper and zinc salts with the (Cu+Zn) contents of around 2–3 wt.%. A further increase in the metal content deteriorated the ordering of the materials. Removal of the template upon calcination resulted in the formation of CuO-like species with a distorted octahedral coordination. The Cu 2+ ions in the MCM-41 materials were reduced completely to metallic copper in the temperature range 230–260 °C. On the other hand, the presence of zinc together with copper impeded the Cu 2+ reducibility. The catalytic partial oxidation of methanol and ethanol over CuMCM-41 and CuZnMCM-41 materials yielded corresponding aldehydes as predominant products. The activity for alcohol conversion increased with increasing copper content, and this indicated that the Cu 2+ ions in the CuMCM-41 and CuZnMCM-41 materials were located on the readily accessible interior surfaces of the mesopores.