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Abstract: The transition to net-zero emissions hinges on circular economy strategies that valorize waste and enhance resource efficiency. Among X-to-liquid (XTL) technologies, the Fischer-Tropsch (FT) process stands out for converting biomass, waste, and CO2 into hydrocarbons and chemicals, especially when powered by renewable hydrogen. Cobalt-based catalysts are preferred in FT synthesis due to their efficiency and CO2 tolerance, yet their catalytic performance is closely tied to their polymorphic structures─face-centered cubic (FCC), hexagonal close-packed (HCP), and stacking-faulted intergrowths thereof. HCP cobalt has been shown to exhibit high activity and selectivity for higher hydrocarbons and oxygenates, particularly when transformed into cobalt carbide (Co2C), which forms more readily at low H2/CO ratios. This study presents a quantitative analysis of cobalt polymorphs and stacking faults in Mn-promoted Co/TiO2 FT catalysts from in situ powder X-ray diffraction (XRD) data and X-ray Diffraction Computed Tomography (XRD-CT) data from spent catalysts in order to obtain a more complete correlation of structural features with catalytic performance. By modeling stacking fault probabilities using supercell simulations, the proportion of faulted FCC and HCP domains was determined across varying Mn loadings (0–5%). Increased Mn loading was found to decrease stacking faults in the FCC phase while increasing them in HCP, promoting the formation of HCP domains and ultimately Co2C under reaction conditions. Notably, the 3% Mn-loaded sample showed a marked rise in HCP content and Co2C formation, correlating with the highest observed alcohol and olefin selectivity. These findings highlight a critical structure–function relationship: Mn facilitates a transformation from FCC to HCP and then to Co2C, this final transition driven by similar stacking sequences and metal–support interactions. The findings show that Mn promotion not only stabilizes smaller Co particles and enhances its dispersion, but also modulates the distribution of Co polymorphs and stacking faults, leading to altered catalytic behavior. This highlights the importance of stacking fault characterization for optimizing FT catalyst design and performance, and suggests pathways to more efficient and selective carbon-neutral fuel production through engineered polymorphic and interfacial structures.

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Abstract: Direct hydrogenation of carbon dioxide to methanol is a promising strategy for carbon capture and utilization (CCU). Copper–zinc–alumina (CZA) catalysts are widely used for this transformation, yet the nature of the active Cu and Zn species and the reaction intermediates remains debated due to their sensitivity to feed composition and temperature. This challenge is compounded by the high metal loading in conventional CZA catalysts, which obscures active species signals with background contributions from spectator species. To address this, we synthesized model CuZn/Al2O3 catalysts using bimetallic coordination complexes, achieving low metal loadings that yield small Cu clusters and Cu+ single atoms adjacent to isolated Zn2+ sites. In situ XANES and UV–vis data were analyzed using multivariate curve resolution–alternating least-squares (MCR–ALS), revealing that Cu dispersion and reagglomeration─phenomena suspected in industrial systems─also occur at low loadings. Operando and modulation excitation with phase sensitive detection DRIFTS (ME-PSD-DRIFTS) showed: (a) Cu clusters dissociate H2 and activate CO2 via monodentate formate; (b) Al2O3 stabilizes Cu+ under reducing conditions, with Cu content correlating with methanol productivity via CO hydrogenation; and (c) Zn in ZnAl2O4 promotes CO2 activation through reactive carbonate formation and enhances oxygenate conversion kinetics. ZnAl2O4 also acts as a structural promoter, facilitating CO2 conversion via reverse water gas shift (RWGS) and CO hydrogenation. These findings reveal new structure–activity relationships, highlighting the role of the mixed-metal interface in stabilizing transient intermediates and providing some guidance in the rational design of improved catalysts for CO2 valorization.

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Abstract: A novel methodology is presented for preparing non-noble metal-based heterogeneous catalysts doped with low amounts of noble metals, yielding highly active and reusable materials for sustainable organic transformations. A new Co–Ru@C catalyst was developed by incorporating small ruthenium nanoparticles (1 wt %) and cobalt nanoparticles (10 wt %) on Vulcan carbon via pyrolysis of a ruthenium-doped cobalt metal–organic framework supported on carbon (2D-Co(Ru)MOF/C). Advanced characterization (in situ PXRD and XAS, HAADF-STEM, HRTEM) confirmed strong Co–Ru interactions, enhancing catalytic activity. The catalyst was evaluated in the one-pot reductive amination of dinitrobenzenes to benzimidazoles using molecular hydrogen and water, which is in line with green chemistry. The synergistic effect between Co and Ru enabled quantitative product yields under significantly milder reaction conditions than the existing ones. In addition, ruthenium was found to facilitate hydrogen activation in the bimetallic material compared with its undoped Co@C counterpart. Regarding stability, the Co–Ru@C catalyst retained its activity over at least five consecutive cycles without metal leaching or structural degradation. This material demonstrated a broad substrate scope, affording over 20 functionalized benzimidazoles in high yields. Half-gram-scale syntheses of commercial Diabazole and Fuberidazole further validated the scalability of this approach.

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Abstract: Mitigating climate change is one of the biggest challenges of today's society. The most direct way to achieve this goal is to capture and use CO2 as a source of energy and chemicals. This work, inspired by previous publications focused on homogeneous catalysis, proposes the transformation of the easy-to-prepare CO2 derivatives dialkylureas into C1 chemicals using Ru-MOFs as heterogeneous catalysts. This choice is due to (i) the well-known ability of Ru to catalyze hydrogenation reactions and (ii) that Ru-complexes were the pioneer homogenous catalyst in converting CO2 into an added-value C1 chemical, methanol. Apart from the already reported MOF Ru-HKUST-1, we have prepared a new Ru-MOF material, denoted Ru-BTC, analogous to the semiamorphous Fe-BTC. It has been found by XAS that Ru-BTC and Ru-HKUST-1 have different metal environment and oxidation states: only 3+ in Ru-BTC, a 50:50 mixture of 2+ and 3+ in Ru-HKUST-1. Both Ru-MOFs catalyzed the hydrogenation of N,N’-dimethylurea under relatively mild conditions, giving methane as the main product. Ru-BTC was particularly efficient: 67 % conversion and 96 % selectivity to CH4 at 150 ºC and 30 bars of H2 using a Ru/dimethylurea weight ratio of 1 %. Ru-MOFs were also able to transform CO2 into CH4, again being Ru-BTC the most effective catalyst, but giving much poorer selectivity to CH4. Ru-MOFs, particularly Ru-BTC, were damaged under reaction conditions, but no significant Ru leaching was observed.

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Abstract: Reducing CO2 to CO via the reverse water–gas shift (RWGS) reaction is a promising strategy for carbon capture and utilization (CCU). In this study, tailored magnetic catalysts were designed through the pyrolysis of a Co-based MOF to form well-defined nanoparticles. As a result, carbon-encapsulated cobalt nanoparticles (Co@C) and palladium-doped cobalt nanoparticles (CoPd/Co@C) were synthesized and thoroughly characterized using a variety of techniques, including in situ X-ray absorption and diffraction experiments. These carbon-based catalysts were simultaneously used as heating agents and catalysts for the magnetically induced RWGS reaction, exhibiting remarkable activity and selectivity for syngas production. CO2 conversions of 61.1% and 71.1% were obtained for Co@C and CoPd/Co@C (63 mT, 2 kW, 320 kHz), respectively. Using magnetic induction heating (MIH), these catalysts operate at lower local temperatures and with greater energy efficiency than conventional thermal heating, while achieving superior CO production efficiency. Notably, CoPd/Co@C achieved highly satisfactory CO production efficiency (478.5 mLCO/kW·h), demonstrating a significant improvement compared to the analogous process utilizing magnetically induced heating. Furthermore, CoPd/Co@C exhibited unwavering stability, maintaining its performance for more than 200 h without significant degradation or need for reactivation. This study highlights the potential of MIH for industrial applications in CO2 reduction, offering a more renewable and economically viable alternative to traditional methods.