A New Preparation Technique for Pd/Alumina Membranes with Enhanced High-Temperature Stability

Abstract

Pd/alumina composite membranes were fabricated using the generally practiced electroless plating process involving two-step activation of a symmetric 0.2 µm R-alumina microfilter with tin (Sn) chloride sensitizer (containing SnCl 2 and SnCl 4 ) and palladium(II) chloride (PdCl 2 ). Pd films were deposited on these activated supports with a hydrazine-(N 2 H 4 -) and PdCl 2 -containing electroless plating bath. When these membranes were tested at 823 K for several days, the ideal H 2 /N 2 separation factor (pure gas permeability ratio) declined substantially, depending on the membrane thickness. Modifications to the activation procedure minimized the amount of Sn chloride used in the sensitizing step. This reduced the selectivity decline, although the problem was not eliminated. The amount of Sn present at the Pd/ceramic interface was qualitatively related to the high-temperature performance. Possible routes for pore formation and selectivity decline are suggested. Sn chloride was removed from the process entirely with a new activation technique utilizing palladium(II) acetate (Pd(O 2 CCH 3 ) 2 ). Prior to electroless plating, substrates were dip-coated in a chloroform solution of Pd acetate, dried, calcined, and then reduced in flowing H 2 . At 973 K, nitrogen flux through these membranes remained constant for a period of at least a week. However, hydrogen permeability decreased at 873 K and above because of annealing.

Palladium/Copper Alloy Composite Membranes for High Temperature Hydrogen Separation From Coal-Derived Gas Streams

“…A seeding procedure has to be used prior to the palladium plating in order to insure adhesion between the metallic film and the ceramic surface [1]. That step involves impregnation of the ceramic support using an organic Pd salt solution, followed by calcination and reduction in flowing hydrogen.…”

Palladium/Copper Alloy Composite Membranes for High Temperature Hydrogen Separation

“…The ideal H 2/ N 2 selectivity for the membrane ranged from 1020 at 100 psi to 1320 at 10 psi. The data discussed above demonstrate that by reducing the membrane thickness and reducing carbon contamination in the Pd film, we've improved the H 2 flux by about a factor of five compared to similar membranes made using the same symmetric, ceramic support from GTC (CoorsTek) [5]. Using the same improvements developed for the ceramic support tubes, we have begun fabricating Pd and Pd-Cu alloy plated stainless steel tubes.…”

Process intensification aspects for steam methane reforming: An overview

“…Porous glass, alumina, and other metals are often employed as substrates and are proved to be good. [46][47][48] However, there are concerns like mechanical strength and different thermal expansion coefficients that create obstacles. Recently, Tong et al 49 used Pd/CeO 2 /MPSS membrane that overcomes these drawbacks and achieves 97% methane conversion at 5008C.…”