A supported Pd-Cu/Al2O3 membrane from solvated metal atoms for hydrogen separation/purification

Abstract

H2 utilization as a green energy carrier involved a growing interest towards inorganic H2 permeable membranes, useful for its separation and purification. On this regard, Pd resulted to be the dominant membrane material due to its particular behavior to be fully H2 perm-selective with respect to all the other gases. In the last decade, composite Pd-based membranes demonstrated their superiority over the unsupported Pd-based membranes owing to their lower cost (related to a reduced Pd content), better mechanical resistance and higher H2 permeability. In this work, a Pd70-Cu30/γ-Al2O3 membrane was prepared by metal vapor synthesis, depositing the two metals (Pd and Cu) in their active form from solvent-stabilized bimetallic nanoparticles (solvated metal atoms). An experimental campaign in terms of single gas (H2, N2, CO2, CH4) permeation tests was carried out by varying the temperature between 300 °C and 470 °C and the feed pressure from 150 to 250 kPa. The H2 partial pressure exponential factor (n-value), described in the equation reporting the relationship between the H2 permeating flux and the H2 permeation driving force, was analyzed as a function of temperature and pressure variation. An apparent activation energy of 18.5 kJ/mol was obtained, resulting comparable to other literature data. At 400 °C and 50 kPa of transmembrane pressure, the reference H2/N2 perm-selectivity was around 1800, remaining stable for around 1000 h under operation. Meanwhile, an excellent H2/CO2 selectivity (6500) at the same operating conditions was reached, overcoming greatly the Robeson's upper-bound and constituting an interesting result for the application of this Pd-Cu/Al2O3 membrane in pre-combustion capture.Furthermore, the effect of the thermal cycles in long-term experimental tests was also investigated and discussed.