Abstract
Abstract The permeation characteristics of palladium pore filled (PF) membranes have been investigated with gas permeation and structural characterization of the membranes. PF membranes have been prepared by filling with Pd the nanoporous γ-Al2O3/YSZ (or pure YSZ) layer supported onto porous α-Al2O3 and ZrO2. The number of nanoporous layers and the applied vacuum level during the electroless plating process have been studied. Gas permeation properties of the PF membranes have been determined in a temperature range of 300–550 °C. The measured hydrogen permeances have been found to be lower than previously reported for similar membranes. It has been found that the hydrogen fluxes do not depend on the thickness of the nanoporous layers (γ-Al2O3/YSZ or pure YSZ) or on the vacuum pump employed for filling with Pd. The physicochemical characterization performed showed that the palladium deposited does not form a percolated network across the mesoporous layer(s), leading to low hydrogen permeances and thus low H2/N2 perm-selectivities.
Highlights
Several reports on the use of Pd-based membranes for hydrogen separation in fluidized bed membrane reactors have been published in the last few years [1,2,3,4,5]
It has been reported that, when Pd is filled in the nanopores composed of only γ-Al2O3 the membranes are not stable at temperatures above 400 °C due to the large difference in the thermal expansion coefficient of Pd and alumina; in addition, the hydrogen permeance of conventional Pd alloy membranes supported on alumina showed a decay when they were exposed to hydrogen at high temperature (650 °C) [9]
It was calculated that the crystal size of YSZ increases from 1.7 nm to 3.5 nm as the calcination temperature increased from 550 °C to 650 °C
Summary
Several reports on the use of Pd-based membranes for hydrogen separation in fluidized bed membrane reactors have been published in the last few years [1,2,3,4,5]. The pore-filled (PF) type membranes avoid direct contact of fluidized particles with the hydrogen selective material, since the Pd is located inside the nano-pores of the substrate [6,7], protected by a mesoporous layer composed of γ-Al2O3/YSZ or pure YSZ. Another advantage of this membrane configuration is that the embrittlement due to α-β phase transition is prevented due to the nanometric size of the palladium clusters, where the hydrogen loading preferentially occurs on the surface rather than on the interior of the particles [8]. The aim of the present work is to extend the study on PF membranes and understand the reason for the very low permeation rates observed in the previous work
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