Stability enhancement for silver catalyst in ethylene epoxidation by support treatment

Abstract

The high cost of the silver catalyst for ethylene epoxidation to ethylene oxide (EO) requires the development of the catalyst with a lower silver loading and a longer catalyst life span. Preventing silver particles from clustering could help maintain the activity for EO. In this work, we applied NH4F solution for an etching-treatment of the α-Al2O3 to improve the roughness of its internal surface before loading silver. The catalyst with etching-treated support showed close activity and EO selectivity initially when compared to the one that was prepared with untreated support while in the meantime its stability was greatly enhanced. The silver catalyst with untreated support lost its activity for EO to nearly zero after 22 days of test at 260 °C and 2 MPa(g), while the one with etching-treated support maintained stable activity from day 10 to 22. The detailed morphology study for the catalysts suggests that the loss of EO activity is mainly attributed to the migration of silver particles from the plane of the support flakes to the gaps that formed by the flakes and deep oxidation of ethylene was largely enhanced by the active sites crowded in the flake gaps. The support treatment effectively slowed down the formation of larger silver clusters and helped maintain a better dispersion of the silver particles on the support.

Keywords

• Ethylene epoxidation
• Ethylene oxide
• Silver catalyst
• Stability in activity