Hydrogen separation membrane on a porous substrate

1. A hydrogen permeable membrane on a porous support prepared by:

(a) forming a mixture of metal oxide powder and ceramic oxide powder and optionally a pore former;

(b) pressing the mixture to form an article;

(c) pre-sintering the article at an elevated temperature in air to remove at least some of the pore former if present and to impart mechanical integrity and porosity to the article; and

(d) thereafter sintering the article in a reducing atmosphere to reduce metal oxide near the surface of the article to a metal and leave metal oxide in the core of the article, and thereby provide a dense hydrogen permeable portion near the surface of the sintered mixture and a porous core having a lower density relative to the dense surface layer;

wherein the dense hydrogen permeable portion has a higher initial concentration of metal than the remainder of the sintered mixture, the metal oxide is selected from the group consisting of oxides of Ni, Pd, Pd alloys, and mixtures thereof, the ceramic oxide is selected from the group consisting of yttria stabilized zirconia, shrinkable alumina, Y doped cerates, Gd doped cerates, titanates, barium zirconates strontium zirconates, and mixtures thereof, and the dense hydrogen permeable portion has a metal concentration in the range of from about 20 to about 80 percent by volume.

2. The membrane of claim 1 , wherein the pore former is selected from the group consisting of graphite, corn starch, organic grains, glass beads and mixtures thereof.

3. The membrane of claim 1 , wherein the reducing atmosphere includes hydrogen.

4. The membrane of claim 3 , wherein the reducing atmosphere includes nitrogen.

5. The membrane of claim 1 , wherein the average diameters of the powders are in the range of from about 0.1 to about 5 microns.

6. The membrane of claim 5 , wherein the average diameters of the powders are in the range of from about 0.1 to about 1 micron.

7. The membrane of claim 1 , wherein the dense hydrogen permeable portion of the composition is at least about 96% of theoretical density.

8. The membrane of claim 1 , wherein the ceramic oxide powder is selected from the group consisting of yttria stabilized zirconia, Y doped barium cerates, Gd doped barium cerates, Y doped strontium cerates, Gd doped strontium cerates, and mixtures thereof.

9. The membrane of claim 1 , wherein the coefficients of thermal expansion of the dense hydrogen permeable portion and the remainder of the composition are within about 10% of each other.

10. The membrane of claim 1 , wherein the metal oxide is an oxide of Ni or Pd and the ceramic oxide is a barium-cerium-yttrium oxide (BCY) or yttria stabilized zirconia (YSZ).

11. The membrane of claim 1 wherein the article is pre-sintered at a temperature of about 700° C.

12. A hydrogen permeable membrane on a porous support prepared by:

(a) forming a mixture of metal oxide powder and ceramic oxide powder and a pore former;

(b) pressing the mixture to form an article,

(c) pre-sintering the article at about 700° C. in air to remove at least some of the pore former and to impart mechanical integrity and porosity to the article; and

(d) thereafter sintering the article in a reducing atmosphere comprising about 200 ppm to about 4% hydrogen to reduce metal oxide near the surface of the article to a metal and leave metal oxide in the core of the article, and thereby provide a dense hydrogen permeable portion not greater than about 50 microns in thickness and at least about 96% of theoretical density near the surface of the sintered mixture and a porous core having a lower density relative to the dense surface layer;

wherein the dense hydrogen permeable portion has a higher initial concentration of metal than the remainder of the sintered mixture, the metal oxide is selected from the group consisting of oxides of Ni, Pd, Pd alloys, and mixtures thereof, the ceramic oxide is selected from the group consisting of yttria stabilized zirconia, shrinkable alumina, Y doped cerates, Gd doped cerates, titanates, barium zirconates, strontium zirconates, and mixtures thereof, and the dense hydrogen permeable portion has a metal concentration in the range of from about 20 to about 80 percent by volume.

13. The membrane of claim 12 , wherein the sintering is performed at a temperature greater than about 1000° C.

14. The membrane of claim 13 , wherein at least some of the sintering is performed at a temperature greater than about 1400° C.

15. The membrane of claim 12 , wherein the pore former is vaporizable at a temperature of less than about 1000° C.

16. The membrane of claim 12 , wherein the metal oxide is an oxide of Ni or Pd and the ceramic oxide is barium-cerium-yttrium oxide (BCY) or yttria stabilized zirconia (YSZ).

17. The membrane of claim 16 , wherein the dense hydrogen permeable portion is at least 96% of theoretical density.

18. A hydrogen permeable membrane comprising a reduced sintered mixture of a metal oxide and a ceramic oxide, disposed on a porous substrate, the membrane comprising a dense hydrogen permeable metal-containing surface layer not greater than about 50 microns in thickness and at least about 96% of theoretical density and a porous metal-containing core having a lower density relative to the dense surface layer;

wherein the dense hydrogen permeable metal-containing surface layer has a higher initial concentration of metal than the porous metal-containing core, the metal oxide is selected from the group consisting of oxides of Ni, Pd, Pd alloys, and mixtures thereof, the ceramic oxide is selected from the group consisting of yttria stabilized zirconia, shrinkable alumina, Y doped cerates, Gd doped cerates, titanates, barium zirconates, strontium zirconates, and mixtures thereof, and the dense hydrogen permeable metal-containing surface layer has a metal concentration in the range of from about 20 to about 80 percent by volume.