Pd menbrane having improved H

1. An H 2 -permeable membrane system ( 117 ), comprising:

an electroless-deposited plating ( 115 ) of Pd or Pd alloy on a porous support ( 110 , 110 ′), the electroless deposited plating of Pd or Pd alloy comprising face-centered cubic crystals cumulatively having a surface morphology of hexagonal platelets.

2. The H 2 -permeable membrane system ( 117 ) of claim 1 wherein the permeability to H 2 of the Pd or Pd alloy plating ( 115 ) on the porous support ( 110 , 110 ′) at an operating temperature of about 350° C. is greater than about 1.3×10 −8 mol·m −1 ·s −1 ·Pa −0.5 , which is equivalent to a H 2 permeance greater than about 15 m 3 /(m 2 ·hr·atm 0.5 ) for a 22-μm thick membrane.

3. The H 2 -permeable membrane system ( 117 ) of claim 2 wherein the permeability to H 2 of the Pd or Pd alloy plating ( 115 ) on the porous support ( 110 , 110 ′) after about 60 hours at said operating temperature is greater than about 1.7×10 −8 mol·m −1 ·s −1 ·Pa −0.5 , which is equivalent to a H 2 permeance greater than about 20 m 3 /(m 2 ·hr·atm 0.5 ) for a 22-μm thick membrane.

4. The H 2 -permeable membrane system ( 117 ) of claim 3 wherein the permeability to H 2 of the Pd or Pd alloy plating ( 115 ) on the porous support ( 110 , 110 ′) after about 200 hours at said operating temperature is greater than about 3.4×10 −8 mol·m −1 ·s −1 ·Pa −0.5 , which is equivalent to a H 2 permeance greater than about 40 m 3 /(m 2 ·hr·atm 0.5 ) for a 22-μm thick membrane.

5. The H 2 -permeable membrane system ( 117 ) of claim 2 wherein the porous support ( 110 , 110 ′) is a tubular structure ( 110 ) having an internal surface, a thin ceramic interlayer ( 110 ′) is formed on the internal surface of the porous support, and the Pd or Pd alloy plating ( 115 ) is formed on the ceramic interlayer.

6. The H 2 -permeable membrane system ( 117 ) of claim 5 wherein the porous support ( 110 ) is stainless steel.

7. The H 2 -permeable membrane system ( 110 ) of claim 1 wherein the porous support ( 114 ) is a tubular structure having an internal surface, a thin ceramic interlayer is formed on the internal surface of the porous support, and the Pd or Pd alloy plating is formed on the ceramic interlayer.

8. The method of forming an H 2 -permeable membrane ( 115 ) on a support surface of a porous metal substrate ( 110 , 110 ′) comprising the steps of:

a. preparing and preheating a Pd electroless plating solution to near a plating temperature substantially greater than a room temperature;

b. contacting the supporting surface of the porous metal substrate with the preheated Pd electroless plating solution for an interval at a plating temperature substantially greater than room temperature to provide an incremental electroless plated deposition of Pd;

c. following the interval, rinsing the porous metal substrate having the incremental electroless plated deposition,

d. repeating plating and rinsing steps b and c two or more times to complete the plating;

e. following completion of said plating, washing the plated porous metal substrate several times; and

f. drying the plated porous metal substrate;

wherein the Pd electroless plating solution comprises at least Pd and H 2 NNH 2 in solution, the H 2 NNH 2 being a relatively small portion of the total plating solution, and the step of preparing and preheating a Pd electroless plating solution to near a plating temperature substantially greater than a room temperature comprises the steps of preparing the Pd electroless plating solution without the H 2 NNH 2 , preheating said Pd electroless plating solution without the H 2 NNH 2 to near a plating temperature substantially greater than room temperature, and then adding the relatively small portion of H 2 NNH 2 nominally at room temperature, whereby the resulting Pd electroless plating solution remains heated substantially to near the plating temperature substantially greater than room temperature.

9. The method of forming an H 2 -permeable membrane ( 115 ) on a support surface of a porous metal substrate ( 110 , 110 ′) comprising the steps of:

a. preparing and preheating a Pd electroless plating solution to near a plating temperature substantially greater than a room temperature, the Pd electroless plating solution comprising at least Pd and H 2 NNH 2 in solution, the H 2 NNH 2 being a relatively small portion of the total plating solution, and comprising the included steps of preparing the Pd electroless plating solution without the H 2 NNH 2 , preheating said Pd electroless plating solution without the H 2 NNH 2 to near a plating temperature substantially greater than room temperature, and then adding the relatively small portion of H 2 NNH 2 nominally at room temperature, whereby the resulting Pd electroless plating solution remains heated substantially to near the plating temperature substantially greater than room temperature;

b. contacting the supporting surface of the porous metal substrate with the preheated Pd electroless plating solution for an interval at a plating temperature substantially greater than room temperature to provide an incremental electroless plated deposition of Pd;

c. following the interval, cleaning the porous metal substrate having the incremental electroless plated deposition;

d. repeating plating and cleaning steps b and c as, and if, needed to complete the plating to a desired thickness; and

e. drying the plated porous metal substrate.