Group 10 Metal Allyl Amidinates: A Family of Readily Accessible and Stable Molecular Precursors to Generate Supported Nanoparticles

Alloyed molybdenum enables efficient alcohol hydrodeoxygenation with supported bimetallic catalysts

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.

Decoding the Promotional Effect of Iron in Bimetallic Pt-Fe-nanoparticles on the Low Temperature Reverse Water-Gas Shift Reaction

The reverse water-gas shift (RWGS) reaction is a key technology of the chemical industry, central to the emerging circular carbon economy. Pt-based catalysts have previously been shown to effectively promote RWGS, especially when modified by promoter elements. However, their active states are still poorly understood. Here, we show that the intimate incorporation of an iron promoter into metal-oxide-supported Pt-based nanoparticles can increase their activity and selectivity for the low temperature reverse water-gas shift (LT-RWGS) substantially and drastically outperform unpromoted Pt-based materials. Specifically, the study explores the promotional effect of iron in Pt-Fe bimetallic systems supported on silica (PtxFey@SiO2) prepared by surface organometallic chemistry (SOMC). The most active catalyst (Pt1Fe1@SiO2) shows high selectivity (>99% CO) toward CO at a formation rate of 0.192 molCO h-1 gcat-1, which is significantly higher than that of monometallic Pt@SiO2 (96% sel. and 0.022 molCO h-1 gcat-1). In-situ diffuse reflectance FT-IR spectroscopy (DRIFTS) and X-ray absorption spectroscopy (XAS) indicate a dynamic process at the catalyst surface under the reaction conditions, revealing distinct reaction pathways for the monometallic Pt@SiO2 and bimetallic PtxFey@SiO2 systems.

Reactivity Switch of Platinum with Gallium: From Reverse Water Gas Shift to Methanol Synthesis

The development of efficient catalysts for the hydrogenation of CO2 to methanol using "green" H2 is foreseen to be a key step to close the carbon cycle. In this study, we show that small and narrowly distributed alloyed PtGa nanoparticles supported on silica, prepared via a surface organometallic chemistry (SOMC) approach, display notable activity for the hydrogenation of CO2 to methanol, reaching a 7.2 molCH3OH h-1 molPt-1 methanol formation rate with a 54% intrinsic CH3OH selectivity. This reactivity sharply contrasts with what is expected for Pt, which favors the reverse water gas shift reaction, albeit with poor activity (2.6 molCO2 h-1 molPt-1). In situ XAS studies indicate that ca. 50% of Ga is reduced to Ga0 yielding alloyed PtGa nanoparticles, while the remaining 50% persist as isolated GaIII sites. The PtGa catalyst slightly dealloys under CO2 hydrogenation conditions and displays redox dynamics with PtGa-GaOx interfaces responsible for promoting both the CO2 hydrogenation activity and methanol selectivity. Further tailoring the catalyst interface by using a carbon support in place of silica enables to improve the methanol formation rate by a factor of ∼5.

Implications of Ga promotion and metal-oxide interface from tailored PtGa propane dehydrogenation catalysts supported on carbon

Propane Dehydrogenation is a key technology, where Pt-based catalysts have widely been investigated in industry and academia, with development exploring the use of promoters (Sn, Zn, Ga, etc.) and additives (Na, K, Ca, Si, etc.) towards improved catalytic performances. Recent studies have focused on the role of Ga promotion: while computations suggest that Ga plays a key role in enhancing catalytic selectivity and stability of PtGa catalysts through Pt-site isolation as well as morphological changes, experimental evidence are lacking because of the use of oxide supports that prevent more detailed investigation. Here, we develop a methodology to generate Pt and PtGa nanoparticles with tailored interfaces on carbon supports by combining surface organometallic chemistry (SOMC) and specific thermolytic molecular precursors containing or not siloxide ligands. This approach enables the preparation of supported nanoparticles, exhibiting or not an oxide interface, suitable for state-of-the art electron microscopy and XANES characterization. We show that the introduction of Ga enables the formation of homogenously alloyed, amorphous PtGa nanoparticles, in sharp contrast to highly crystalline monometallic Pt nanoparticles. Furthermore, the presence of an oxide interface is shown to stabilize the formation of small particles, at the expense of propene selectivity loss (formation of cracking side-products, methane/ethene), explaining the use of additives such as Na, K and Ca in industrial catalysts.