Influence of Si and Fe/Cr oxides as intermediate layers in the fabrication of supported Pd membranes

Abstract

This paper presents for the first time relevant insights on the influence of tuning porous stainless steel (PSS) supports for the preparation of metallic membranes by the Electroless Pore-Plated (ELP-PP) method. Two types of oxides, used as intermediate layer between the support and the Pd layer, were deposited on raw PSS supports for reducing porosity and surface roughness. Both independent and combined routes were considered: (i) Fe2O3-Cr2O3 oxides obtained by direct calcination of the metallic support and (ii) dense and porous SiO2 deposited by dip-coating (DC) technique. Membranes morphology (porosity and surface homogeneity) was characterized by SEM and EDX analysis and gravimetric analysis was used to calculate the total amount of Pd deposited on the external selective layer. Preliminary screening tests suggested that the combined route (calcination followed by DC of SiO2) did not show evident beneficial effects for the preparation of Pd films by ELPPP. Based on those results, four tubular membranes were fabricated using independent routes: one by calcination and other three by DC, including 1, 2 and 3 layers of SiO2. The first one, including a Fe2O3-Cr2O3 oxides intermediate layer, maintained its mechanical integrity when tested up to ΔP = 4 bar. On the other hand, it was observed that the use of SiO2 intermediate layers noticeably affects the ELP-PP method. Extensive characterization of fresh and used samples has been performed in order to understand the influence of the oxides in the final preparation of a continuous and thin layer of Pd. Results obtained evidenced that the most adequate sample was the support prepared with 2 layers of SiO2 and studies continue to improve membrane stability and to reduce thickness.