Laboratoire de Physique et Chimie des Nano-Objets

Colloidal nanoparticles (NPs) exhibit unique and tunable physical properties, making them highly attractive for advanced applications in sensing, photonics, flexible electronics, and beyond. Harnessing these properties in functional devices often requires assembling NPs into three-dimensional (3D) microstructures that combine substantial thickness to enhance their functional response, micrometer-scale resolution for precise pattern definition, and high selectivity to minimize material loss. Directed assembly techniques aim to meet these stringent requirements but face significant challenges when NPs are dispersed in non-polar solvents, commonly used for their role in synthesis and colloidal stabilization. Indeed, such solvents hinder NP assembly because of their high wettability and volatility. These limitations are particularly pronounced in Convective Self-Assembly (CSA), which performs efficiently with aqueous dispersions but struggles with non-polar media. In this study, we investigate how the properties of non-polar solvents influence CSA on topographically patterned substrates. To overcome these issues, we propose an upgraded CSA method that combines solvent selection, surface functionalization, and controlled evaporation. This approach enables reproducible and precise assembly of NPs into micrometer-scale 3D structures. The method is versatile, compatible with various nanoparticle types and patterns, and allows sequential co-assembly on a single substrate, offering a scalable route for high-resolution nanomanufacturing of complex multifunctional architectures.

Equilibrium-limited endothermic reactions play a crucial role in the transition toward a more sustainable chemical industry, but are typically plagued by the need for high operation temperatures (>500°C). Here, we show that the temperature gradients generated by the selective and localized heating of catalyst materials in a colder reactor environment shift the equilibrium of thermodynamically-limited endothermic reactions and improve their performance. In particular, the reverse water gas shift reaction and magnetic induction are selected as the model reaction and selective catalyst heating method, respectively. Magnetically induced catalysis using standard Cu-Al spinel-derived catalyst functionalized with carbon-coated iron nanoparticles enables high CO yield (up to 62%) at mild catalyst and reactor temperatures (estimated at 300°C and determined as 25-123°C, respectively). We demonstrate that the catalyst temperature and not the reactor temperature governs the equilibrium product composition of the rWGS, and that the temperature gradient promotes the in situ removal of water to shift the gas phase thermodynamic equilibrium. These two points synergistically result in a CO yield that would require a reactor temperature of 650°C in a conventionally heated gas phase reaction.

The parent diphosphene (HPPH) molecule is of fundamental interest, but its reactive nature renders it challenging to isolate and study. Metal-stabilization is an attractive approach for studying HPPH, but molecular derivatives are limited to three complexes of p-/d-metals reflecting a scarcity of synthetic methods for rationally preparing HPPH complexes. Here, we introduce f-element HPPH complexes, adding to f-element diazenes (HNNH) that were first reported over thirty years ago. By utilizing 7λ3-phosphadibenzonorbornadiene and uranium(III) reagents we show how parent diphosphene, phosphinidiide, and diphosphorus motifs can all be constructed, developing synthetic approaches for this area. Computed reaction profiles reveal common, initial reaction steps that subsequently diverge depending on the ancillary ligands, radical nature of intermediates, and the 7λ3-phosphadibenzonorbornadiene P-substituent. Calculations demonstrate a surprising prevalence of open-shell radical intermediates, and that the redox chemistry is P-, not U-, centred. This work thus provides insights to inform future synthetic endeavours in this area.

Abstract Strong metal–support interactions can significantly influence catalytic performance. On titania supports, these interactions often involve the formation of a substoichiometric TiO X overlayer during high‐temperature reduction, which can be reversed by treatments under dioxygen. Under CO 2 hydrogenation conditions, where water is produced, complete removal of the TiO X overlayer has been reported, raising questions about its stability in the presence of a mild oxidant such as CO 2 . In this study, in situ and operando techniques were employed to examine the effect of varying conditions on both the titania overlayer and cobalt species in a Co/TiO 2 catalyst. After reduction at 350 °C, the overlayer consisted of stoichiometric anatase TiO 2 , while cobalt remained partially reduced. Exposure to CO 2 /H 2 at 220 °C enabled complete cobalt reduction without affecting the TiO 2 overlayer. In contrast, pure CO 2 at 220 °C caused overlayer removal and full cobalt oxidation. The impact of this CO 2 ‐mediated reversibility on CO 2 hydrogenation was also evaluated. Although steady‐state activity was largely unaffected, the transient regime showed substantial changes in selectivity and behavior. These results demonstrate that different treatments can strongly influence both the stability and reactivity of Co/TiO 2 catalysts, highlighting the importance of dynamic SMSI effects in CO 2 hydrogenation.

Kurzzusammenfassung Es wurden Reaktionen zwischen Rosenthal‐Titanocen‐ (Cp 2 Ti) und Decamethyltitanocen‐ (Cp* 2 Ti) Synthonen mit verschiedenen Bis(alkinyl)boranen untersucht. Durch die Reaktion des Cp* 2 Ti‐Synthons mit (Me 3 Si) 2 NB(CCR) 2 oder PhB(CCPh) 2 wurde eine Reihe von titananellierten Boracyclobutenen erhalten. Dies ist die erste Umsetzung dieses Strukturmotivs durch die Umlagerung von Bis(alkinyl)boranen innerhalb der Koordinationssphäre eines d ‐Block‐Metalls. Diese Ergebnisse überwinden die bisherige Bedingung, dass der Borsubstituent eine Aminogruppe sein muss. Darüber hinaus führte die Reaktion des Cp* 2 Ti‐Synthons mit (Me 3 Si)PhNB(CCPh) 2 oder (Mes 2 B)PhNB(CCPh) 2 (Mes = 2,4,6‐Trimethylphenyl) zur Bildung neuartiger verknüpfter Metallocenkomplexe, bei denen die Titanacyclopentadienstruktur über eine –CH 2 –BR‐Brücke mit einer der Cyclopentadienylgruppen verbunden ist. Sowohl experimentelle als auch theoretische Studien lieferten Einblicke in einen noch nie dagewesenen Reaktionsmechanismus. Der Prozess beinhaltet die anfängliche Bildung eines η 2 ‐koordinierten Bis(alkinyl)boran‐Zwischenprodukts, das durch NMR‐Spektroskopie und Röntgenbeugungsanalyse nachgewiesen und analysiert wurde. Dieses Zwischenprodukt wird anschließend entweder durch eine B–C alkinyl ‐Bindung oder durch eine C Me –H‐Aktivierung des Cp*‐Liganden aktiviert, was zur Bildung von zwei verschiedenen Produkttypen führte.

The size and structural control of ultrasmall metal nanoparticles (NPs) remain a key area of research, as their unique nanoscale properties can significantly impact their utility and applications in industry. Among the different synthesis strategies, the formation of large clusters of metal precursors in solution, which favors a confined nucleation, has been less explored. Here, we report a simple synthesis protocol of ultrasmall silver NPs with an icosahedral structure, a mean diameter of 3 nm, and low polydispersity (down to 6%), through the reduction of AgNO3 by trialkylsilanes in a solution of oleylamine (OY) and hexane. Small- and wide-angle X-ray scattering (SAXS, WAXS) and pair distribution function (PDF) analysis reveal that the Ag NP size and structure remain constant regardless of Ag and reducing agent concentrations or temperatures up to 120 °C. The lack of correlation between the final NP size and the initial Ag concentration, temperature, and reaction rate, despite variations spanning 2 orders of magnitude, does not align with a classical nucleation/growth mechanism of isolated monomers in solution. SAXS analysis of the precursor solutions revealed the presence of {OY–Ag(I)–NO3}n clusters, which interact repulsively in solution. The final Ag particle size is closely tied to the size of the Ag(I) clusters. This suggests that size control is governed by a nucleation process involving Ag atoms within the clusters. The separation of nucleation and growth appears to be achievable through nucleation confined within the repulsively interacting {OY–Ag(I)–NO3}n clusters. Only two factors have been found to decrease the mean NP size: increasing the OY concentration or substituting AgNO3 with silver trifluoro-sulfonate or trifluoro-acetate, which reduces the mean size, in agreement with smaller initial Ag(I) clusters. The advantage of this synthesis route is the very high concentration of metals that can be achieved without degrading the morphological and structural quality of the final particles.

ABSTRACTThe reduction of CO2 toward CO and CH4 over Ni‐loaded MoS2‐like layered nanomaterials is investigated. The mild hydrothermal synthesis induced the formation of a molybdenum oxysulfide (MoOxSy) phase, enriched with sulfur defects and multiple Mo oxidation states that favor the insertion of Ni2+ cations via photo‐assisted precipitation. The photocatalytic tests under LED irradiation at different wavelengths from 365 to 940 nm at 250°C rendered 1% CO2 conversion and continuous CO production up to 0.6 mmol/(gcat h). The incorporation of Ni into the MoOxSy structure boosted the continuous production of CO up to 5.1 mmol/(gcat h) with a CO2 conversion of 3.5%. In situ spectroscopic techniques and DFT simulations showed the O‐incorporated MoS2 structure, in addition to Ni clusters as a supported metal catalyst. The mechanistic study of the CO2 reduction reaction over the catalysts revealed that the reverse water–gas shift reaction is favored due to the preferential formation of carboxylic species.

Metal nitride species are recognized as key intermediates in the conversion of dinitrogen (N2) to ammonia (NH3). In this work, we report the isolation of a multimetallic nitride-bridged thorium complex (2) by completely cleaving the N≡N triple bond of N2. The complex was synthesized through the reduction of a thorium precursor, {N[CH2CH2N-PiPr2]3ThCl}2 (1) and chromium dichloride (CrCl2) using potassium graphite (KC8) under an N2 atmosphere. Isotopic labeling with 15N2 confirms that the nitride in complex 2 originates from N2. Under ambient conditions, complex 2 exhibits remarkable catalytic activity, converting N2 to silylamine with yields of up to 9.9 equiv per thorium molecular catalyst. This work not only represents the first isolation of a thorium nitride complex from N2 reduction but also provides a rare example of N2 functionalization promoted by an actinide catalyst.