Fabrication and hydrothermal stability of microporous Nb₂O₅ membrane for pre-combustion capture of CO₂

Polymeric Nb₂O₅ sols were successfully synthesized via sol-gel process by using niobium penta (n) butoxide as a precursor. Effects of synthesis parameters, including pH of system, hydrolysis ratio, reaction temperature, reaction time and chelating agent, on the state and size of Nb₂O₅ sols were investigated in detail. Microporous Nb₂O₅ membranes were deposited on defect-free γ-alumina membranes with an average pore size of ca. 3 nm, by using polymeric Nb₂O₅ sol with an average size of 4.8 nm. The properties of Nb₂O₅ powder and the supported Nb₂O₅ membranes were characterized by TG, XRD, NH₃ adsorption-desorption, CO₂ adsorption, Fourier-transform infrared spectroscopy of pyridine adsorption (Py-IR) and single gas permeance test. Results showed that the single hydrogen permeance and H₂/CO₂ permselectivity of 350°C-calcined microporous Nb₂O₅ membrane were 3.1 × 10^-9 mol · m^-2 · s^-1 · Pa^-1 and 21, respectively, measured at 200°C and 0.3 MPa. The single gas permeance and H₂/CO₂ permselectivity of the membrane remained fairly stable after in-situ exposure to 150 kPa steam for 8 h.