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

摘要

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 O 2-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-Al 2O3 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. ? 2014 the Partner Organisations.