Guillaume Clet

Alteration of the support structure via milling is a feasible yet rarely applied strategy for boosting the performance of the catalyst in dry methane reforming for syngas production. In this study, we introduce stable oxygen vacancies in the zirconia structure, which enhance the activation of the feedstock, specifically CO₂, while preserving the specific surface area and porosity of the material under reaction conditions. The activity of the tested Ni/ZrO₂ assemblies shows a clear dependence on the milling intensity of ZrO₂, with mild milling at 400 rpm yielding the most active catalyst. At 600 °C, this material achieved the highest feedstock conversion among the tested samples, with 29% for CH₄ and 39% for CO₂. Spectroscopic characterization indicates that the activity of the tested catalysts is controlled by a partial change in the phase composition of the support from monoclinic to tetragonal under reaction conditions, as well as the nature and population of O₂ ^– species, oxygen vacancies, Zr³⁺ defects, and Ni–ZrO₂ interfacial interactions.

Metal-organic frameworks (MOFs) offer a powerful platform for the rational design of photocatalysts, where systematic structural tuning can be employed for efficient solar-to-chemical energy conversion. Here, we establish a direct structure-activity relationship in a series of copper-metalated mixed-linker UiO-66 derivatives, UiO-66(COOH)_x-Cu (0 ≤ x ≤ 2), incorporating increasing densities of free carboxylate groups in their MOF backbone. These functionalities determine both Cu coordination and in situ restructuring under the photocatalytic dehydrogenation of formic acid (FAc). Operando Fourier-transform infrared (FTIR) and X-ray absorption spectroscopy (XAS) reveal that the -COOH content dictates the evolution of the surface of the framework and Cu speciation during photocatalysis. FTIR demonstrates that intraframework anhydride formation correlates linearly with photocatalytic efficiency, while XAS evidences a light-induced restructuring of coordinated Cu(II)/Cu(I) species into a catalytically active Cu(I)/Cu(0) binary system in the presence of FAc. Time-resolved spectroscopy further indicates a photoinduced charge transfer from the Zr-oxo clusters to the Cu centers, enhancing the overall reactivity. Density functional theory (DFT) calculations corroborate these findings, showing that the number and spatial arrangement of carboxylates influence the Cu coordination stability and its restructuring dynamics. These insights reveal how linker functionalization governs metal speciation and dynamics in MOFs, offering design principles for next-generation light-driven catalytic systems.

Solar-assisted gaseous CO₂ hydrogenation to CH₄ is a potential strategy for favoring the transition to net zero emissions. Here, we report the development of a series of efficient metal-organic frameworks with MIL-101(Cr or Fe) topology decorated with RuO_x nanoparticles (ca. 0.2-2 wt %) as heterogeneous photocatalysts for the selective methanation of CO₂ by H₂ under simulated sunlight irradiation. The activity of RuO_x(1 wt %)@MIL-101(Cr) is between 3 and 50 times higher than related MOF-based photocatalysts under similar reaction conditions. Among the different photocatalysts, the optimized RuO_x(2 wt %)@MIL-101(Cr) photocatalyst showed 98.1% CO₂ conversion with 98.8% CH₄ selectivity reaching a production rate of 7.85 mmol g^-1 h^-1 with 720 mW cm^-2 at 200 °C. Further, this photocatalyst exhibited a record apparent quantum yield of 9.2% at 600 nm and 200 °C after subtracting thermal activity contribution compared to any previous MOF- or other heterogeneous-based photocatalyst reported so far. The photocatalyst retained its activity and integrity upon reuse for about 110 h. Transient photocurrent, electrochemical impedance, photoluminescence, and laser flash photolysis spectroscopies together with additional photocatalytic experiments suggest the occurrance of dual photochemical and photothermal reaction pathways. The photocatalytic CO₂ methanation reaction mechanism was further investigated using operando Fourier transform infrared spectroscopy.

Membrane technology plays a central role in advancing separation processes, particularly in water treatment. Covalent organic frameworks (COFs) have transformative potential in this field due to their adjustable structures and robustness. However, conventional COF membrane synthesis methods are often associated with challenges, such as time-consuming processes and limited control over surface properties. Our study demonstrates a rapid, microwave-assisted method to synthesize self-standing COF membranes within minutes. This approach allows control over the wettability of the surface and achieves superhydrophilic and near-hydrophobic properties. A thorough characterization of the membrane allows a detailed analysis of the membrane properties and the difference in wettability between its two faces. Microwave activation accelerates the self-assembly of the COF nanosheets, whereby the thickness of the membrane can be controlled by adjusting the time of the reaction. The superhydrophilic vapor side of the membrane results from -NH₂ reactions with acetic acid, while the nearly hydrophobic dioxane side has terminal aldehyde groups. Leveraging the superhydrophilic face, water filtration at high water flux, complete oil removal, increased rejection with anionic dye size, and resistance to organic fouling were achieved. The TTA-DFP-COF membrane opens new avenues for research to address the urgent need for water purification, distinguished by its synthesis speed, simplicity, and superior separation capabilities.

In order to establish layered materials as heterogeneous catalysts in the liquid phase, acidic layered materials are evaluated here through the conversion of hexane‐2,5‐diol used as a model reaction. Such polyoxygenate reactant is representative of some of the biomass components and the interactions of the reagent or furan product with the interlayers surface is a key to the understanding of these lamellar materials features. Layered HNbMoO₆ catalyst is particularly active and stable for the studied reaction compared to several zeolites and its high activity is obtained without any pre‐activation step prior to reaction. The influence of temperature and water content in the reaction mixture are also studied for this catalyst. The importance of intercalation in the reaction process is specifically evaluated using Raman spectroscopy and powder X‐ray diffraction. On this layered catalyst, the reaction proceeds after intercalation of diol within the interlayer space followed by subsequent cyclodehydration giving rise to 2,5‐dimethyltetrahydrofuran with high selectivity. Comparison with related layered materials such as HNbWO₆ or H₂W₂O₇ highlights a distinct behavior both in reactivity and intercalation and emphasizes the role of the accessibility to the active sites.

Raman and transmission FTIR spectroscopic techniques have been coupled in a new homemade reactor-cell designed in a joint CSIC-LCS collaboration. The set-up is easily adapted to any FTIR and fibre-coupled Raman spectrometers and gas analysis techniques. It allows simultaneous operando FTIR and Raman spectroscopic measurement, which provide complementary characterization of adsorbed species, reaction intermediates, and structural properties of the catalyst. This system was validated with the study of vanadium based catalysts during propane OxyDeHydrogenation (ODH). The combined use of both spectroscopies with gas analysis techniques to measure the activity contributes to the understanding of propane ODH and the identification of the role of different oxygen species bound to vanadium sites. For example, the simultaneous characterization of the catalyst under the same conditions by IR and Raman confirms that the V=O mode has the same frequency in both spectroscopies, and that bridging oxygen sites (V-O-V, V-O-Zr) present higher activity than terminal V=O bonds. These results demonstrate the high potential of the new simultaneous transmission IR-Raman operando rig to correlate the activity and the structure of catalysts, thus assisting the rational design of catalytic processes.