The emission of greenhouse gases (GHGs) has risen to unprecedented levels, primarily driven by rapid industrialization and population growth. To mitigate the associated impacts of climate change, a global transition from fossil fuels to clean and renewable energy sources is imperative. Hydrogen has emerged as a promising energy vector due to its high energy density and clean combustion, and it can be produced from both conventional (e.g., fossil fuels) and renewable sources (e.g., biofuels, water electrolysis). Currently, hydrogen is predominantly produced via methane steam reforming (SMR), a process that is both energy-intensive and carbon-emissive, releasing approximately 9–12 kg CO2 per kg H2 produced. This underscores the need to adopt renewable feedstocks for hydrogen production. Among bio-based alternatives, biogas and bioethanol are particularly attractive due to their availability in decentralized regions and potential for carbon neutrality.
Membrane reactors (MRs) offer a process-intensified system for reforming reactions by integrating reaction and selective separation in a single unit. The in-situ removal of hydrogen shifts the thermodynamic equilibrium, enhancing reactant conversion, suppressing side reactions, and enabling operation under milder conditions. Palladium-based membranes are widely employed in MRs due to their near-complete hydrogen selectivity. However, pure Pd membranes are prone to hydrogen embrittlement and suffer from limited thermal and chemical stability. Alloying Pd with elements such as Ag, Cu, Au, and Y has been shown to improve mechanical robustness, hydrogen permeability, and resistance to degradation. In particular, Pd-Ag-Y alloys exhibit enhanced performance and stability, making them suitable candidates for long-term hydrogen separation and catalytic processes.
The summary of the projects that I completed during my PhD includes: (1) studying hydrogen permeation and material characterization of a Pd-Ag-Y membrane. The membrane showed one of the highest hydrogen permeation flux compared to the literature, and it maintained good stability in the presence of different gas mixtures. (2) Investigating the effect of metallic support on hydrogen permeation through the Pd-based membrane. A mass transfer limitation was caused by the support, which correlated with pore size and thickness. Larger pore sizes and thinner supports resulted in less mass transfer limitation. (3) Synthesizing a Pd-YSZ membrane for biogas dry reforming to produce hydrogen, using Ni/Al2O3 and Ru/CeO2 catalysts. The results demonstrated that biogas could be directly used for hydrogen and synthesis gas production, reducing CO2 emissions associated with hydrogen production. Additionally, the Ni catalyst indicated higher hydrogen production while Ru showed less coke formation. (4) Performing bioethanol steam reforming in the Pd-Ag-Y membrane reactor with Co and Ru catalysts. The results indicated that hydrogen could be obtained in decentralized units where bioethanol is available. (5) Conducting water gas shift reactions using a Pd-Ag-Au membrane for hydrogen production. In this project, biomass gasification residues were sent to a Pd-Ag-Au MR with a Cu-based catalyst to produce hydrogen. All CO was converted, and the MR remained stable over 30 days. (6) In order to transfer hydrogen over long distances, it should be in a liquid form. Making ammonia is one way to store hydrogen in a liquid form. Then, it can be decomposed in the final destination. In this regard, I performed ammonia decomposition on the Pd-Ag-Y membrane to produce hydrogen. The results indicated conversion of 90% and separation of 99.99% hydrogen.
Moreover, I worked on cations separation from mine tailing water using negatively and positively charged PES membranes. In this work, membranes with negative and positive charges were fabricated to remove cations from the water, achieving almost complete removal. The separated cations can be used for mineral carbonation.
Furthermore, I worked on zeolite membrane synthesis for methanol/water separation. I performed material characterization of Na-rich zeolite membrane and tested the membrane for methanol/water separation.