On the Capabilities of Transition Metal Carbides for Carbon Capture and Utilization Technologies

The search for cheap and active materials for the capture and activation of CO2 has led to many efforts aimed at developing new catalysts. In this context, earth-abundant transition metal carbides (TMCs) have emerged as promising candidates, garnering increased attention in recent decades due to their exceptional refractory properties and resistance to sintering, coking, and sulfur poisoning. In this work, we assess the use of Group 5 TMCs (VC, NbC, and TaC) as potential materials for carbon capture and sequestration/utilization technologies by combining experimental characterization techniques, first-principles-based multiscale modeling, vibrational analysis, and catalytic experiments. Our findings reveal that the stoichiometric phase of VC exhibits weak interactions with CO2, displaying an inability to adsorb or dissociate it. However, VC often exhibits the presence of surface carbon vacancies, leading to significant activation of CO2 at room temperature and facilitating its catalytic hydrogenation. In contrast, stoichiometric NbC and TaC phases exhibit stronger interactions with CO2, capable of adsorbing and even breaking of CO2 at low temperatures, particularly notable in the case of TaC. Nevertheless, NbC and TaC demonstrate poor catalytic performance for CO2 hydrogenation. This work suggests Group 5 TMCs as potential materials for CO2 abatement, emphasizes the importance of surface vacancies in enhancing catalytic activity and adsorption capability, and provides a reference for using the infrared spectra as a unique identifier to detect oxy-carbide phases or surface C vacancies within Group 5 TMCs

Effective and Highly Selective CO Generation from CO₂ Using a Polycrystalline α‑Mo₂C Catalyst

Present experiments show that synthesized polycrystalline hexagonal α-Mo₂C is a highly efficient and selective catalyst for CO₂ uptake and conversion to CO through the reverse water gas shift reaction. The CO₂ conversion is ∼16% at 673 K, with selectivity toward CO > 99%. CO₂ and CO adsorption is monitored by DRIFTS, TPD, and microcalorimetry, and a series of DFT based calculations including the contribution of dispersion terms. The DFT calculations on most stable model surfaces allow for identifying numerous binding sites present on the catalyst surface, leading to a high complexity in measured and interpreted IR- and TPD-spectra. The computational results also explain ambient temperature CO₂ dissociation toward CO as resulting from the presence of surface facets such as Mo₂C­(201)-Mo/Cdisplaying Mo and C surface atomsand Mo-terminated Mo₂C­(001)-Mo. An <i>ab initio</i> thermodynamics consideration of reaction conditions, however, demonstrates that these facets bind CO₂ and CO + O intermediates too strongly for a subsequent removal, whereas the Mo₂C­(101)-Mo/C exhibits balanced binding properties, serving as a possible explanation of the observed reactivity. In summary, results show that polycrystalline α-Mo₂C is an economically viable, highly efficient, and selective catalyst for CO generation using CO₂ as a feedstock

Umweltgerechtes Verkehrsverhalten beginnt in den Köpfen

The control of the phase distribution in multicomponent nanomaterials is critical to optimize their catalytic performance. In this direction, while impressive advances have been achieved in the past decade in the synthesis of multicomponent nanoparticles and nanocomposites, element rearrangement during catalyst activation has been frequently overseen. Here, we present a facile galvanic replacement-based procedure to synthesize Co@Cu nanoparticles with narrow size and composition distributions. We further characterize their phase arrangement before and after catalytic activation. When oxidized at 350 °C in air to remove organics, Co@Cu core–shell nanostructures oxidize to polycrystalline CuO-Co₃O₄ nanoparticles with randomly distributed CuO and Co₃O₄ crystallites. During a posterior reduction treatment in H₂ atmosphere, Cu precipitates in a metallic core and Co migrates to the nanoparticle surface to form Cu@Co core–shell nanostructures. The catalytic behavior of such Cu@Co nanoparticles supported on mesoporous silica was further analyzed toward CO₂ hydrogenation in real working conditions