Epitaxially Directed Iridium Nanostructures on Titanium Dioxide for the Selective Hydrodechlorination of Dichloromethane

Dichloromethane (CH₂Cl₂) hydrodechlorination to chloromethane (CH₃Cl) is a pivotal step toward the successful implementation of chlorine-mediated methane-to-liquid technologies. This study investigates the performance of various noble metals supported on different carriers to identify important parameters for the design of selective catalytic systems. Iridium emerges as the most active and selective metal, and the performance is shown to be strongly influenced by the choice of carrier. Specifically, when supported on TiO₂-rutile (TiO₂-r), a 2-fold increase in the reaction rate and unprecedented CH₃Cl selectivity (≤95%) are observed, outperforming carriers such as SiO₂, ZrO₂, Al₂O₃, CeO₂, and MgO, as well as TiO₂-anatase, which all exhibit comparable activity and selectivity patterns (≤38% CH₃Cl). Moreover, Ir/TiO₂-r displays a lower deactivation rate (≤2.5 times) with respect to other supported systems. Microscopy analysis reveals that the epitaxial growth of IrO₂ on TiO₂-r impacts the size and morphology of the metal nanostructures obtained upon reduction compared to those formed on other carriers. These epitaxially directed nanostructures suppress the undesired over-hydrogenation of CH₃Cl to methane. Kinetic analyses evidence a lower reaction order with respect to H₂ pointing toward mechanistic differences as the origin of the enhanced performance. Finally, the higher stability of the epitaxially directed nanostructures derived from the stronger metal–support interaction is shown to impede sintering, the main deactivation mechanism over standard nanoparticle-based systems; instead, activity losses are linked to increased chlorine uptakes.