Processes for the epoxidation of ethylene are provided in which, following start-up, an epoxidation catalyst is contacted with a feed comprising ethylene, oxygen, carbon dioxide in an amount below 2.0 vol. %, and a chloride moderator to achieve a desired work rate at a first operating temperature T1. The composition of the feed is subsequently adjusted (e.g., by decreasing the ethylene concentration, decreasing the oxygen concentration, increasing the carbon dioxide concentration and/or adjusting the concentration of the chloride moderator) so as to increase the first operating temperature T1 to a second operating temperature T2 while maintaining the desired work rate. As the catalyst activity declines, the composition of the feed is further adjusted so as to maintain the desired work rate at the second operating temperature T2.