Process for improving the activity of used supported silver catalysts

Claim 1

In a process for improving the selectivity of a supported silver catalyst for the direct oxidation of ethylene to ethylene oxide with molecular oxygen or air, of the type wherein on the used catalyst is applied caesuim, rubidium or mixture thereof by impregnating the used catalyst with an impregnating solution containing a compound of caesium, rubidium or mixture thereof, the improvement which comprises making said application at two different times interrupted by a period of using the catalyst, as follows: (a) making a first application on the catalyst of 10 to 300 ppm caesium, rubidium or mixture thereof; (b) thereafter using the catalyst for the production of ethylene oxide by direct oxidation of ethylene with molecular oxygen or air; (c) then interrupting said production after about 2 to 60 weeks, at the end of which time the selectivity of the catalyst is still at about the level which was achieved by said first application; (d) and next making a second application on the catalyst of 5 to 100 ppm caesium, rubidium or mixture thereof followed by using the resulting catalyst again for said production.