Catalyst with bimodal pore size distribution and the use thereof

1. A catalyst for the epoxidation of an olefin to an olefin oxide comprising a support having a bimodal pore size distribution, each pore size distribution possessing a different mean pore size and a different peak pore volume, the catalyst further comprising a catalytically effective amount of silver, a promoting amount of rhenium, and a promoting amount of one or more alkali metals, wherein the bimodal pore size distribution is within a pore size range of about 0.01 μm to about 5 μm.

2. The catalyst of claim 1 , wherein a first mode of pores of the bimodal pore size distribution comprises at most 50% of a total pore volume and a second mode of pores of the bimodal pore size distribution comprises at least 50% of the total pore volume.

3. The catalyst of claim 1 , wherein a first mode of pores of the bimodal pore size distribution comprises at most 40% of a total pore volume and a second mode of pores of the bimodal pore size distribution comprises at least 60% of the total pore volume.

4. The catalyst of claim 1 , wherein the support comprises alumina, charcoal, pumice, magnesia, zirconia, titania, kieselguhr, fuller's earth, silicon carbide, silica, silicon dioxide, magnesia, clays, artificial zeolites, natural zeolites, ceramics or combinations thereof.

5. The catalyst of claim 1 , wherein the support comprises alumina.

6. The catalyst of claim 1 , wherein the support comprises alumina with a surface area of less than about 1 m 2 /g.

7. The catalyst of claim 1 , further comprising a promoting amount of one or more promoters selected from the group consisting of one or more Group IIA metals, one or more transition metals, sulfur, fluoride, phosphorus, boron, and combinations thereof.

8. The catalyst of claim 7 , wherein the Group IIA metal is selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, and combinations thereof.

9. The catalyst of claim 7 , wherein the transition metal is selected from the group consisting of elements of Groups IVA, VA, VIA, VITA and VIIIA of the Periodic Table of the Elements, and combinations thereof.

10. The catalyst of claim 7 , wherein the transition metal is selected from the group consisting of molybdenum, tungsten, chromium, titanium, hafnium, zirconium, vanadium, thorium, tantalum, niobium, and combinations thereof.

11. The catalyst of claim 7 , wherein the transition metal is molybdenum, tungsten, or a combination thereof.

12. A process for the oxidation of an olefin to an olefin oxide which comprises the vapor phase oxidation of an olefin with molecular oxygen in a fixed bed, tubular reactor, in the presence of the catalyst of claim 7 .

13. A process for the oxidation of ethylene to ethylene oxide which comprises the vapor phase oxidation of ethylene with molecular oxygen in a fixed bed, tubular reactor, in the presence of the catalyst of claim 7 .

14. The catalyst of claim 1 wherein the catalyst further comprises a promoting amount of gallium, germanium, sulfur, phosphorus, boron, halogen, or a combination thereof, on the surface of the support.

15. The catalyst of claim 1 wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and combinations thereof.

16. The catalyst of claim 1 wherein the alkali metal is cesium.

17. A process for the oxidation of an olefin to an olefin oxide, the process comprising vapor phase oxidation of an olefin with molecular oxygen in a fixed bed, tubular reactor, in the presence of the catalyst of claim 1 .

18. A process for the oxidation of ethylene to ethylene oxide which comprises the vapor phase oxidation of ethylene with molecular oxygen in a fixed bed, tubular reactor, in the presence of the catalyst of claim 1 .