Dataset Information

Carbon-Supported Bimetallic Ruthenium-Iridium Catalysts for Selective and Stable Hydrodebromination of Dibromomethane.

ABSTRACT: Catalysts based on individual precious metals on carbon- and oxide-based carriers have shown remarkably selective behavior in the hydrodebromination of CH₂Br₂ to CH₃Br, an important transformation within halogen-mediated methane upgrading processes. However, the high susceptibility of the active phase to coking and to sintering, which cannot be overcome by controlling the nuclearity of the metal species, hinders their practical implementation. Herein, a platform of carbon-supported Ir-Ru catalysts with distinct metal ratios at comparable metal nanoparticle size (ca. 1.0 nm) was adopted to systematically study the effects of a second metal on reactivity and stability. Catalytic tests reveal ruthenium-doped iridium nanoparticles as the first system that combines high CH₃Br selectivity (up to 93 %) with unprecedented stability, outperforming any of the previously reported catalysts. This superior performance was rationalized by the intimate interaction between the two metals, forming ruthenium-poor surface alloys, which enable suppressing deactivation mechanisms as well as over hydrogenation/coking pathways.

SUBMITTER: Saadun AJ

PROVIDER: S-EPMC9300165 | biostudies-literature | 2022 Jan

REPOSITORIES: biostudies-literature

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Carbon-Supported Bimetallic Ruthenium-Iridium Catalysts for Selective and Stable Hydrodebromination of Dibromomethane.

Saadun Ali J AJ Mitchell Sharon S Bonchev Hristo H Pérez-Ramírez Javier J

ChemCatChem 20211129 2

Catalysts based on individual precious metals on carbon- and oxide-based carriers have shown remarkably selective behavior in the hydrodebromination of CH2Br2 to CH3Br, an important transformation within halogen-mediated methane upgrading processes. However, the high susceptibility of the active phase to coking and to sintering, which cannot be overcome by controlling the nuclearity of the metal species, hinders their practical implementation. Herein, a platform ...[more]

PMID: 35874462

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Project description:Bimetallic heterogeneous catalysts combining group 9 metals (Rh, Ir) or group 10 metals (Ni, Pd, Pt) with Mo on a silica-based support have been synthesized via surface organometallic chemistry and assessed in their catalytic activity for the hydrodeoxygenation (HDO) of alcohols with particular emphasis on the structural evolution of the catalysts and the role of Mo. The investigation was conducted with an air-free approach to isolate any sample alterations exclusively to those caused by the reaction. Structural analysis was performed using a combination of (S)TEM, IR, and XAS. It was found that Ir-Mo/SiO2, Rh-Mo/SiO2, and Pt-Mo/SiO2 display high activity for primary, secondary, and tertiary alcohol deoxygenation, while Pd-Mo/SiO2 selectively catalyses tertiary alcohol deoxygenation. Other combinations as well as the corresponding monometallic materials do not display the same activity. X-ray absorption spectroscopy confirmed metallic states for M (M = Ni, Rh, Pd, Ir, or Pt), while Mo K-edge XANES showed varying amounts of Mo(0), Mo(iv) and Mo(vi) depending on the metal counterpart in fresh materials, and indicated complete conversion of Mo(vi) to lower oxidation states (IV and 0) during the reaction. For Rh, Pd, Ir, and Pt, alloy formation (M-Mo) was identified via M-Mo paths in EXAFS and supported by CO-IR spectroscopy. In contrast to Ir, Rh, and Pt, where some Mo(0) is present at the nanoparticle surface, Pd-Mo forms an alloy but likely retains Mo in the nanoparticle core, as suggested by CO-IR spectroscopy and CO-chemisorption. Reactivity studies suggest that tertiary alcohols primarily undergo dehydration-hydrogenation, evidenced by olefin formation with MoO x /SiO2, as well as Ir/SiO2 and Ir-Mo/SiO2 under inert conditions. In contrast, primary and secondary alcohols follow a different mechanism, correlated with the presence of metallic Mo species on the nanoparticle surface, highlighting their role in C-O bond activation. These findings provide new insights into the structure-activity relationships of Mo-based bimetallic catalysts, underscoring the influence of Mo in different oxidation states and strong substrate dependence on mechanistic pathways.

Dataset Information

Carbon-Supported Bimetallic Ruthenium-Iridium Catalysts for Selective and Stable Hydrodebromination of Dibromomethane.

Publications

Carbon-Supported Bimetallic Ruthenium-Iridium Catalysts for Selective and Stable Hydrodebromination of Dibromomethane.

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