Dynamics of silver particles during ethylene epoxidation
Arno J. F. van Hoof, R. Poll, Heiner Friedrich, Emiel J. M. Hensen
Abstract
Structural changes in α-Al2O3 supported silver particles during ethylene oxidation under industrially relevant conditions (20 bar and 225 °C, with and without chlorine) were investigated by quantitative TEM. Identical locations of two powder samples with average silver particle sizes of 41 nm and 127 nm were investigated in the fresh state and after 60 h of ethylene oxidation with and without chlorine. Without chlorine, silver particles were only slightly affected with a tendency for smaller (< 30 nm) particles to shrink. These silver particles even rapidly disappeared in the presence of chlorine. Particles larger than 100 nm tended to break up into smaller ones, indicative of a chlorine-induced re-dispersion process. These results confirm the dynamic nature of silver particles during the EO reaction and emphasize the role of chlorine on the observed substantial morphological changes of the active silver phase.