Biosynthesized Ag/α-Al2O3 catalyst for ethylene epoxidation: the influence of silver precursors

Abstract

Biosynthesized Ag/α-Al₂O₃ catalysts toward ethylene epoxidation were prepared with Cinnamomum camphoratrees (CC) extract using AgNO₃, silver–ammonia complex ([Ag (NH₃)₂]⁺) and silver–ethylenediamine complex ([Ag(en)₂]⁺) as the silver precursors. The catalyst from [Ag(en)₂]⁺ demonstrated better activity compared to the catalysts from the other two precursors, 1.41% EO concentration with EO selectivity of 79.1% and 12.0% ethylene conversion were achieved at 250 °C. To investigate the influence of silver precursors on the catalytic performance, three catalysts were characterized by XRD, UV-Vis, XPS, SEM and O₂-TPD techniques. The results indicated that [Ag(en)₂]⁺ precursors could be reduced more effectively by CC extract, and Ag particles were successfully immobilized onto the α-Al₂O₃ support under mild conditions. Moreover, a silver defects surface on the Ag/α-Al₂O₃ catalyst from [Ag(en)₂]⁺ precursors had the best oxygen activation ability, playing an important role in the generation of electrophilic oxygen species which were responsible for the epoxidation reaction of CC to EO.