Synthesis and characterization of TiO2 membrane with palladium impregnation for hydrogen separation

This paper reports the synthesis and characterization of TiO2 membranes impregnated with elemental palladium (Pd–TiO2) for hydrogen separation at elevated temperatures and pressures. The membranes were prepared by sol–gel method where the elemental Pd was introduced through sol-mixing of titania sol and Pd precursor solution. The Pd–TiO2 membranes were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric analysis (TG/DTA), N2 adsorb/desorption analysis, and single permeation test of H2 and N2. The XRD analysis revealed that the presence of Pd nanoparticles has retarded the crystallization and anatase-rutile phase transition. The TEM images indicated that the Pd–TiO2 membranes are composed of non-uniform particle size as compared to that of TiO2 membranes alone. For four times dip-coating, the membrane thickness was measured to be approximately 634 nm. By impregnating small concentration of Pd, it significantly enlarged the pore size of the original TiO2 membrane structure besides increasing its surface area and pore volume. However, a reverse trend was observed when the Pd concentration was increased further. Single permeance of H2 and N2 for both TiO2 and Pd–TiO2 membranes showed that the transport mechanism to be dominated by Knudsen diffusion and Poiseuille flow. The ideal selectivity of H2/N2 crossing through the Pd–TiO2 membrane was calculated and found to be less than the theoretical value of Knudsen diffusion based separation. The selectivity of Pd–TiO2 membrane increased with the temperature increment, whereas the same trend was not observed for TiO2 membrane. These results show that, there were other transport mechanisms involved apart from Knudsen diffusion and Poiseuille flow.

Research highlights▶ XRD analysis revealed that the presence of elemental Pd in the TiO2 matrix suppressed TiO2 crystal phase transformation. ▶ The introduction of Pd increased the surface area, pore volume and size of the membrane structure. However, higher amounts of Pd led to a decrease in pore volume and surface area. ▶ The permeabilities of H2 and N2 indicate the dominance of Knudsen diffusion transport mechanism across the Pd–TiO2 membrane. ▶ The ideal selectivity of H2/N2 indicates the ideal selectivity of Pd–TiO2 membrane is dependent on temperature and pressure difference.