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Biogas Reforming on supported Ruthinium Catalysts

Damiri Aikaterina-Paraskevi

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Summary

This thesis focuses on the development and testing of supported ruthenium (Ru) catalysts for Dry Reforming of Methane, DRM. The process converts biogas, which contains methane (CH₄) and carbon dioxide (CO₂), into synthesis gas, composed of hydrogen (H₂) and carbon monoxide (CO). DRM is a significant reaction because it valorizes two powerful greenhouse gases while also producing syngas, which is extremely important for a variety of uses. The syngas can be separated in order to utilize pure hydrogen or used as is in Fischer-Tropsch processes or fuel cells. The goal of this research is to investigate the activity and stability of three newly created catalyst compositions and determine their applicability for the DRM process. High operating temperatures lead to carbon deposition from CH₄ breakdown and thermal sintering of metal particles, which impact catalyst performance during DRM. Non-noble metals, such as nickel (Ni), have been widely investigated, but are highly sensitive, particularly to carbon buildup. In contrast, the noble metal ruthenium, which was chosen as the active phase, is more resistant to both carbon deposition and sintering.In all three catalysts examined, Ru was present at a concentration of 3 wt%. Three alternative supports were chosen: γ-alumina (γ-Al₂O₃), CeO₂-NR produced by hydrothermal treatment, and zero-strontium perovskites (LSM00). All catalysts were synthesized using the impregnation method, which involves immersing the support in a solution containing the metal precursor. The experimental procedure included catalytic activity tests (Light-Off) at various and stability tests at reaction temperature to assess performance in relation to time. The catalysts underwent three phases of oxidative aging. Between these aging phases, the Light-Off and Stability studies were performed following the reduction of the catalysts once again. All studies used an equimolar feed composition of CH₄/CO₂=50%/50%, an inlet flow rate of Fin = 50 cc/min, and mass of catalyst equal to 20 mg. In addition, catalysts were characterized both in their fresh condition and after a 10-hour oxidative aging cycle. The measurements included BET surface area, reducibility by temperature-programmed reduction (TPR), metal particle size and dispersion using selective hydrogen chemisorption (Titration), and crystallographic analysis via X-ray diffraction.In the conclusions of this study, the catalytic behavior of three ruthenium-based catalysts (3%Ru/γ-Al₂O₃, 3%Ru/CeO₂-NR, and 3%Ru/LSM00) in the DRM reaction was compared through Light-Off and Stability experiments. The first two catalysts exhibited similar initial activity, with high conversion rates of CH₄ and CO₂ and significant H₂ production at 750℃. In contrast, the 3%Ru/LSM00 catalyst demonstrated low activity even at elevated temperatures. Regarding the oxidative aging stages, the 3%Ru/γ Al₂O₃ catalyst suffered a substantial decline in performance, whereas the 3%Ru/CeO₂-NR catalyst largely maintained its stability, showing resistance to carbon deposition and thermal sintering.

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