Alexandros Katsaounis

The CO₂ hydrogenation reaction is a cornerstone reaction in catalytic conversion technologies, with Ru/TiO₂ catalysts being amongst the most active and selective for CH₄ formation. A key factor in the preparation of such catalysts is the choice of chemical precursor for Ru impregnation, as it can substantially influence the physicochemical properties and catalytic performance. In this study, we deliberately employ a simple incipient wetness impregnation method to isolate the effect of the Ru precursor itself, using two different Ru precursors for the synthesis of Ru/TiO₂ catalysts intended for CO₂ hydrogenation and evaluating their properties using analytical techniques such as XRF, XRD, TEM, XPS and H₂-TPR. Our results show that catalysts prepared from ruthenium nitrosyl nitrate solutions display enhanced reducibility and slightly stronger metal–support interactions compared to those prepared from ruthenium chloride solutions. These features enable higher CO₂ conversion and CH₄ selectivity. The results of this work provide grounds for the targeted chemical precursor selection, while clarifying the reason behind the observed effects on catalytic performance.

This study explores the electrochemical promotion of dry reforming of methane (DRM) and reverse water–gas shift (RWGS) reactions over a ruthenium (Ru) catalyst supported on yttria-stabilized zirconia (YSZ). Physicochemical properties were examined using a range of surface and structural characterization techniques. Ru remained metallic after reaction, with minor oxidation under high CO₂ concentrations. While carbon was detected under all conditions, only oxidizing environments led to the accumulation of oxidized species, indicating surface-bound intermediates. Catalytic behavior was investigated under reducing (P CH₄ = 4 kPa, P CO₂ = 1 kPa) and stoichiometric (P CH₄ = 1 kPa, P CO₂ = 1 kPa) conditions. DRM dominated under reducing conditions, while stoichiometric feeds led to competition between DRM and RWGS, showing inverted volcano behavior. Positive polarization (+1 V) enhanced CO production by improving CH₄ adsorption, while negative polarization (−1 V) suppressed DRM and favored RWGS. Electrochemical promotion of catalysis (EPOC) was quantified by measuring the rate enhancement ratios (ρ). Under reducing conditions, positive polarization increased DRM rates tenfold at low temperatures, with reduced effect at higher temperatures. In contrast, negative polarization suppressed DRM and promoted RWGS. Under stoichiometric conditions, both reactions were enhanced, with selectivity determined by the polarity of the applied potential. Transient experiments at 380 °C confirmed reversibility of EPOC and its ability to dynamically steer selectivity. Reactive oxygen uptake provided insight into electrochemically active surface area and promotion mechanisms. These findings demonstrate the potential of EPOC to modulate the H₂/CO ratio and tailor selectivity in reforming processes, with relevance to renewable energy and biogas utilization.

The CO₂ (Dry) Reforming of Methane (DRM) is a key process for reducing CO₂ and CH₄ emissions while producing syngas with an H₂/CO ratio of 1, ideal for Fischer–Tropsch synthesis. This study explores DRM and the Reverse Water Gas Shift (RWGS) reaction under mild conditions using Ru-based catalysts supported on CeO₂, YSZ, TiO₂, and SiO₂, with three reactant ratios: (i) stoichiometric, PCO₂ = 1 kPa, PCH₄ = 1 kPa, (ii) oxidizing, PCO₂ = 2 kPa, PCH₄ = 1 kPa, and (iii) reducing, PCO₂ = 1 kPa, PCH₄ = 4 kPa. The results highlight the importance of redox support for catalyst stability, with mobile lattice oxygen aiding carbon gasification. While Ru/CeO₂ is stable at high temperatures, it rapidly deactivates at low temperatures, emphasizing the need for precise metal particle size control. This work demonstrates the necessity of fine-tuning catalyst properties for more sustainable DRM, offering insights for next-generation CO₂ utilization catalysts.

BACKGROUND: Direct alcohol fuel cells (DAFCs) are promising energy conversion devices, but their broader application is limited by slow kinetics of alcohol oxidation, catalyst poisoning, and high cost of Pt‐based materials. In the present study we investigate the impact of different carbon supports, specifically graphene nanoplatelets (GNPs) and carbon black (Vulcan XC‐72), on the electrochemical performance of Pt‐based anodes. Additionally, we investigate ternary PtRuSn catalysts, where the incorporation of Sn is intended to enhance catalytic performance while potentially reducing costs through the partial substitution of Ru.RESULTS: Catalysts were synthesized using the wet impregnation method, and their structural and electronic properties were thoroughly characterized using a variety of analytical techniques. Catalysts supported on GNPs exhibited smaller metal particle sizes and enhanced catalytic activity compared to those supported on Vulcan XC‐72. Electrochemical analysis (CO stripping, cyclic voltammetry, and chronoamperometry) revealed that the GNP‐supported catalysts demonstrated lower onset potential, higher electrochemical active surface area, and higher current densities during alcohol oxidation. Notably, the PtRuSn(5:4:1)/GNPs catalyst exhibited the highest activity for ethanol and glycerol oxidation, highlighting the role of GNPs in enhancing both the stability and catalytic performance.CONCLUSION: Overall, the findings indicate that GNPs can function as a highly effective support for anode catalysts in DAFCs, enhancing dispersion and stability. The use of ternary PtRuSn catalysts appears promising for improving alcohol oxidation while offering a more balanced approach to performance and material cost. These insights could contribute to the development of more efficient and economically viable fuel cell technologies. © 2025 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).