Hydrogenation catalyst, its preparation and use

1. A hydrogenation catalyst comprising metallic palladium supported on activated carbon support, wherein the penetration depth of metallic palladium in the support is at least 10 μm and up to 100 μm, the crystallite size of palladium is between 40 Å and 120 Å, and the palladium is present in a surface layer from the surface of the support to a depth of 1 μm in an atom number that is from 5% to 40% of a total atom number of palladium and other elements in the surface layer.

2. A catalyst according to claim 1 , wherein the activated carbon support is a granular or shaped activated carbon having a surface area of greater than 600 m 2 /g and a porosity of from 0.3 to 0.9 ml/g.

3. A catalyst according to claim 2 , wherein the activated carbon support is coconut carbon.

4. A catalyst according to claim 1 , wherein the penetration depth of metallic palladium in the support is at least 15 μm and up to 100 μm.

5. A catalyst according to claim 1 , wherein the crystallite size of palladium is between 40 Å and 80 Å.

6. A catalyst according to claim 1 , wherein the atom number of palladium in the surface layer from the surface of support to a depth of 1 μm is from 10% to 30% of the total atom number of palladium and other elements in the surface layer.

7. A catalyst according to claim 1 , wherein the amount of metallic palladium supported on the activated carbon support is from 0.1 to 5 wt % based on the total weight of catalyst.

8. A catalyst according to claim 7 , wherein the amount of metallic palladium supported on the activated carbon support is from 0.2 to 0.6 wt % based on the total weight of catalyst.

9. A catalyst according to claim 1 , further comprising a Group VIII metal selected from a group consisting of ruthenium, platinum, rhodium and iridium.

10. A process for preparing the catalyst according to claim 1 , wherein said process comprises placing the activated carbon support between two sieve plates in a fluidized bed, circularly passing upward an aqueous solution through the fluidized bed by using a pump under conditions of effectively fluidizing the activated carbon support, then adding a palladium salt solution under fluidizing state for impregnating the activated carbon support.

11. A process according to claim 10 , wherein the palladium salt solution is adsorbed by the activated carbon support at a temperature of 15 to 60° C.

12. A process according to claim 10 , wherein the palladium salt solution is treated by pre-adding an oxidant to form a palladium salt oxidation solution.

13. A process according to claim 12 , wherein the oxidant is hydrogen peroxide, sodium hypochlorite, or a mixture thereof.

14. A process according to claim 13 , wherein the oxidant is a mixture of hydrogen peroxide and sodium hypochlorite, wherein the concentration thereof is 0.01% to 10%, and the mass ratio of hydrogen peroxide to sodium hypochlorite is 1-30:1.

15. A process according to claim 10 , wherein the sieve plates in the fluidized bed have an orifice diameter of 1 to 3 mm and an orifice pitch of 2-6 mm.

16. A process according to claim 10 , wherein the motion of activated carbon support in solution is controlled by regulating the flow rate of aqueous solution.

17. A process according to claim 16 , wherein the flow rate of aqueous solution is from 3.0 to 35.0 L/min.

18. A process for purifying crude terephthalic acid, comprising purifying the crude terephthalic acid by hydrogenation in the presence of the hydrogenation catalyst according to claim 1 .

19. The hydrogenation catalyst according to claim 1 prepared by a process comprising placing the activated carbon support between a plurality of sieve plates in a fluidized bed, circularly passing upward an aqueous solution through the fluidized bed under conditions of effectively fluidizing the activated carbon support, then adding a palladium salt solution under fluidizing state for impregnating the activated carbon support.