Catalyst composition for oxidation of ethylene to ethylene oxide

A catalyst for the epoxidation of ethylene to the ethylene oxide comprising a catalytically effective amount of silver impregnated on an inert, refractory solid support which support has an essential absence of fluoride anion, said catalyst further containing an efficiency enhancing amount, relative to the amount of silver metal, of promoter comprising cation selected from at least one member of the group of lithium, sodium, potassium, rubidium, cesium, and barium and anion comprising (i) sulfate, (ii) fluoride and (iii) at least one member of the group of oxyanions of elements having atomic numbers of 21 to 74, inclusive, selected from Groups 3b to 6b, inclusive, of the Periodic Table of Elements, wherein the sulfate and fluoride anions may be in the form of fluorosulfate and the fluoride anion is also in an amount sufficient to reduce ethylene oxide burning as compared to an otherwise identical catalyst but not containing the fluoride anion and its associated cation.