Michalis Konsolakis

Iron-based catalysts are widely investigated for CO₂ hydrogenation to light olefins due to their low cost, abundance, and ability to form oxidic and carbidic phases involved in the RWGS-FTS pathway. However, supports and promoters can obscure the intrinsic role of iron phase evolution. Here, unsupported Fe nanoparticles with distinct morphological, compositional and structural characteristics were synthesized, CO-pretreated, and evaluated for CO₂ hydrogenation toward C₂-C₄⁼. Their textural, structural, redox, and surface properties were examined to relate synthesis-induced differences to phase evolution and catalytic performance. CO pretreatment formed iron carbide phases in all samples, yet marked differences in catalytic behavior showed that the active state cannot be described solely by bulk phase composition. Iron oxide nanopolyhedra (Fe-NP) achieved 41.6% CO₂ conversion, the highest C₂-C₄⁼ selectivity of 27.7%, and the highest light-olefin yield of 11.5%. Surface analysis revealed notable differences in the relative contributions of carbidic and oxidic Fe species, suggesting that performance depends on the surface phase distribution established during activation and reaction. The coexistence of Fe₃O₄ and Fe_xC_y species appears to facilitate RWGS and subsequent Fischer-Tropsch pathways, as proposed in the literature. CO₂-TPD further showed that maximum CO₂ uptake did not correspond to superior performance, highlighting the combined influence of synthesis-induced structure, surface composition, and reduction-carburization behavior.

Herein, CO ₂ hydrogenation to light olefins via the modified Fischer‐Tropsch synthesis (mFTS) route was thoroughly explored over Zn‐Fe‐Al mixed oxides, derived by calcination of layered double hydroxides (LDHs). Two LDH synthesis strategies were employed: progressive substitution of Zn by divalent iron (Zn+Fe/Al series) or Al by trivalent iron (Zn/Al+Fe series), keeping the total divalent to trivalent ions ratio constant. Complementary characterization revealed that the elemental composition of the parent LDH and derived mixed oxides profoundly affected their structural and textural properties, with notable implications for catalytic performance. CO‐pretreatment of the mixed oxides induced iron carbide phase formation, the extent of which strongly depended on the substitution route and iron content. Still, the predominant phases were spinel ZnFe ₂ O ₄ (Zn+Fe/Al) and ZnO (Zn/Al+Fe). Both series exhibited similar CO ₂ conversion (∼40%) at 340°C, 20 bar, with a small superiority of the Zn/Al+Fe catalysts at lower Fe contents. However, the Zn+Fe/Al series was substantially more selective towards light olefins. Among all catalysts, Zn+Fe(40)/Al exhibited the highest light olefins selectivity (26.7%) and yield (10.6%) and maintained stable performance over 72 h on stream due to a balanced contribution of iron carbide phase and ZnFe ₂ O ₄ phase, which exhibited low crystallite size, enhanced porosity, and basicity.

For efficient alkaline water-splitting, it is crucial to have bifunctional electrocatalysts that exhibit low overpotentials, durability, and the possibility of being produced through scalable methods. This study involved the use of screen printing to apply a porous nickel microparticle/polymer interlayer onto commercial nickel foam, which then acted as a base for the solvothermal growth of cobalt-based oxide/hydroxide nanostructures. The optimized electrode showed excellent bifunctional capabilities in 1 M KOH, requiring only 61 mV for the hydrogen evolution reaction and 241 mV for the oxygen evolution reaction at a current density of 10 mA cm⁻². In comparison, the control electrodes, such as those with cobalt directly deposited on unmodified nickel foam and screen-printed nickel foam substrates without cobalt, exhibited poorer overall performance. Although the cobalt-modified nickel foam exhibited a higher C_dl-derived apparent electrochemical surface area, the cobalt-modified screen-printed electrode achieved the best ECSA-normalized HER and OER responses, indicating that the enhancement in activity was not solely due to the capacitive surface area of the electrode. The increased integrated redox charge suggests a greater contribution from electrochemically accessible Co/Ni redox-active species, while impedance analysis supports a more favorable apparent interfacial response under the tested HER- and OER-relevant conditions. Long-term chronopotentiometry and post-stability SEM confirmed stable bifunctional operation.

Bifunctional electrocatalysts that offer low overpotentials, robustness, and potential compatibility with scalable fabrication routes are essential for effective alkaline water splitting. In this study, a porous nickel microparticle/polymer interlayer was applied to commercial nickel foam via screen printing, serving as a framework for the solvothermal growth of cobalt-based oxide/hydroxide nanostructures. The optimized electrode demonstrated strong bifunctional performance in 1 M KOH, requiring only 61 mV for the hydrogen evolution reaction and 241 mV for the oxygen evolution reaction at a current density of 10 mA cm^-2. In comparison, the control electrodes, such as those with cobalt directly deposited on unmodified nickel foam and altered nickel foam substrates without cobalt, exhibited poorer overall performance. Although the cobalt-modified unaltered nickel foam exhibited a higher C_dl-derived apparent electrochemical surface area, the cobalt-modified screen-printed electrode achieved the best ECSA-normalized HER and OER responses, indicating that the enhancement in activity was not solely due to the capacitive surface area. The increased integrated redox charge suggests a greater contribution from electrochemically accessible Co/Ni redox-active species, while impedance analysis supports a more favorable apparent interfacial response under the tested HER- and OER-relevant conditions. Long-term chronopotentiometry and post-stability SEM supported stable bifunctional operation.

The development of structured ceramic catalysts capable of operating under both oxidative and reductive environments is critical for advanced energy and environmental applications. In this work, macrostructured ceramic supports were designed and wash‐coated with rod‐like Cu/CeO ₂ nanoparticles to meet industrial requirements, including flexural strength above 15 MPa, open porosity exceeding 45%, and high thermal shock resistance. Porous substrates based on zircon‐mullite (ZM), sodium zirconium phosphates (NaZr ₂ P ₃ O ₁₂ ; NZP), and cordierite (Cor) compositions were fabricated through the controlled addition of yttria‐stabilized zirconia (YSZ) and a sacrificial wax pore former, enabling the simultaneous optimization of mechanical strength and porous architecture. Thermal expansion analysis, phase and crystallographic characterization, and three‐point bending tests demonstrated that optimized compositions achieved the targeted balance of properties, with Weibull analysis confirming their mechanical reliability. Wash‐coating resulted in a uniform distribution of rod‐like Cu/CeO ₂ nanoparticles throughout the porous networks, showing excellent adhesion and stability after exposure to CO oxidation and CO ₂ hydrogenation conditions. Catalytic tests revealed that structured catalysts containing 10 wt.% active phase exhibited higher intrinsic activity and more efficient catalyst utilization compared with the corresponding powder catalyst. Overall, the developed systems show strong potential as robust, cost‐effective, and high‐performance structured catalysts for industrial applications.

Ceria shape effects on the redox and catalytic properties of Co/CeO ₂ oxides.

The aim of this study is to provide a comprehensive analysis of the outcome of two separate techno-economic studies that were conducted for the scaled-up and industrially relevant processes of a) synthetic natural gas (SNG) production from captured (cement-based) CO₂ and green-H₂ (via renewable-assisted electrolysis) and b) combined electricity and crude biofuel production through the integration of biomass pyrolysis, gasification, and solid oxide fuel cells. As was found, the SNG production process seems more feasible from an economic perspective as it can be comparable to current market values.

Layered double hydroxide (LDH)-derived mixed oxides offer a promising approach for CO₂ hydrogenation to light hydrocarbons. Herein, we explore the impact of various transition metals (X = Mn, Co, Cu, and Zn) incorporated into the M-Al or M-(Al+Fe) LDH structures, with the aim of exploring possible synergistic effects. Structural and compositional analyses reveal that an abundance of Fe over Al (Fe/Al ratio ~4) leads to the formation of mixed oxide crystalline phases attributed to CoFe₂O₄, CuFe₂O₄, and ZnFe₂O₄. Catalytic evaluation results demonstrate that the X-Al LDH-derived oxides exhibit high CO₂ conversion yet are selective to CH₄ or CO. In contrast, Fe incorporation shifts selectivity toward higher hydrocarbons. Specifically, the yield to higher hydrocarbons (C₂⁺) follows the order Ζn-Al-Fe > Cu-Al-Fe > Mn-Al-Fe > Co-Al-Fe >> Mn-Al, Co-Al, Zn-Al, Cu-Al, highlighting the pivotal role of Fe. Moreover, Zn-Al-Fe and Mn-Al-Fe catalysts have been shown to be the most selective towards light olefins. Zn-based systems also exhibit high thermal and structural stability with minimal coke formation, whereas Co-, Cu-, and Mn-based catalysts, when modified with Fe, experience increased carbon deposition or structural changes that may impact long-term stability. This work provides insights into the combined role of Fe and a second transition metal in LDHs for modulating catalytic activity, phase transformations, and stability, underscoring the need for further optimization to balance selectivity and catalyst durability in CO₂ hydrogenation applications.