Silver catalyst for olefin epoxidation

Abstract

Ag/SBA-15 catalysts with different Ag contents were prepared by an impregnation method and were used for the gas-phase selective oxidation of benzyl alcohol to benzaldehyde with O2 as the oxidant. These catalysts were characterized using N2 adsorption-desorption, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. The effects of Ag loading, reaction temperature, and weight hourly space velocity of benzyl alcohol on the catalytic performance were investigated. The results showed that Ag was successfully incorporated into the mesoporous channels of SBA-15 and well dispersed on the surface as a result of the nano-confinement effect of SBA-15, which increased the specific surface area of the active components. Moreover, Ag/SBA-15 had a uniform pore size, a wall of thickness of 3–5 nm, and a high specific surface area of 411–541 m2/g. The catalytic activity of Ag/SBA-15 for the gas-phase selective oxidation of benzyl alcohol to benzaldehyde was enhanced by oxygen spillover of nucleophilic oxygen species from the Ag nanoparticles to the SBA-15 surface. The 5.3%Ag/SBA-15 exhibited excellent low-temperature catalytic properties; when the reaction temperature was 220 °C, the conversion of benzyl alcohol and the selectivity for benzaldehyde reached 87% and 95%, respectively. At 240 °C, the catalyst displayed the best catalytic properties, achieving a benzyl alcohol conversion of 94% and benzaldehyde selectivity of 97%, which remained almost constant at 240–300 °C. This showed that Ag/SBA-15 had excellent thermal gradient stability. The catalyst could be used for 40 h and retained high catalytic activity for oxidation after treatment at 500 °C.