(728f) Binary and Ternary Metallic Membranes for Natural-Carbon Hydrogen Production Via Water Gas Shift Reaction

There is an urgent need to decarbonize the conventional industrial energy system to limit global warming. One potential solution is the use of hydrogen, which is considered the energy carrier of the future due to its high energy density compared to hydrocarbon fuels and zero-carbon emissions. However, hydrogen is not directly available in nature and must be produced from diverse resources. Currently, most hydrogen is produced from fossil fuels, specifically natural gas, which releases 9-12 Kg_CO2/Kg_H2-produced [1]. A promising technology for generating clean carbon neutral H₂ from thermochemical reforming (TCR) reactions is the metallic membrane reactor (MR). This innovative approach has the intrinsic advantage of using metallic membranes, which exhibit high separation selectivity and efficiency in separating hydrogen from the reforming process. Unlike conventional methods, where the separation of hydrogen from the reformate stream requires additional and energy-intensive steps, metallic MRs integrate the separation function directly into the reforming reactor itself. Despite their advantages, the major technical issues and current technological limitations are the membrane's stability at intermediate temperatures (300-500 °C) and their poor tolerance for chemical poisoning and thermal cycling.

In this work, binary and ternary Pd-alloys membranes were synthesized with the aim to improve their thermal and chemical stability, and their performance was tested under a reaction environment to produce a carbon-neutral hydrogen stream. In detail, the electroless plating (ELP) technique was used to synthesize dense binary and ternary metallic membranes in various compositions. Binary Pd_(100-x)-Au_x and ternary Pd_(100-x-y)-Au_x-Ag_y metallic layers were deposited on porous disc supports characterized by a superficial pore size of 0.2 mm and 0.5 mm. The support surface was modified by zirconia doped Pd via vacuum-assisted infiltration technique to create an intermetallic layer and–thus–inhibit the intermetallic diffusion between the support and the selective layers. The as-synthesized membranes were annealed at 500 ⁰C at 4 bar for 24 hours under H₂. Each membrane was characterized by permeation tests using pure H₂ and N₂ at different temperatures and pressures, as 350 – 450 °C and 1 – 4 bar, respectively. Most of the membranes were fully selective towards hydrogen, and only few of them showed an ideal selectivity > than 10³. Ternary membranes will be investigated under a water-gas shift reaction environment to analyze their performance in terms of CO conversion, H₂ recovery, and the ability to produce neutral-carbon hydrogen. Long-term stability will be analyzed as well. Finally, the pristine and used membranes will be characterized by scanning electron microscopy (SEM-EDX) and X-ray diffraction (XRD) techniques to determine change in morphology phase formation.

Keywords: Palladium-based membrane; Binary (Pd-Au) and ternary (Pd-Au-Ag) membrane; Porous metal support; Hydrogen fuel; Water-gas shift reaction; Membrane Reactor.

References:

[1] Sun P, Elgowainy A. Updates of Hydrogen Production from SMR Process in GREET ® 2019, 2019.