Theory as a driving force to understand reactions on nanoparticles: general discussion

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Organometallic Synthesis of Magnetic Metal Nanoparticles

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CHAPTER 5. Gases

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Enhancement of Carbon Oxides Hydrogenation on Iron-Based Nanoparticles by In-Situ Water Removal

International audienceThe carbidization of Fe(0) nanoparticles (NPs) under syngas (CO/H2) produces crystalline Fe2.2C iron carbide NPs (ICNPs) displaying excellent hyperthermia properties, however, this transformation is significantly delayed by the concomitant water formation. Consequently, very long carbidization times (∼140 h) are needed to obtain ICNPs with high specific absorption rate. In this paper, we show that the rate of the carbidization process can be greatly enhanced by the in‐situ removal of water using activated molecular sieves. As a result, ICNPs displaying very high heating power were obtained after only 40 h. Using this strategy, CO was successfully replaced by CO2 as a carbon source in the carbidization process, resulting in the efficient conversion of Fe(0) NPs to ICNPs at relatively low temperature (230 °C). Without water removal, carbidization did not occur under these conditions, and the Fe(0) NPs were clearly oxidized. In addition, this approach was successfully applied to displace the equilibrium of CO2 hydrogenation and accelerate the rate of the magnetically induced hydrogenation of CO2 on ICNPs. Interestingly, the in‐situ water removal had also a strong influence on the product distribution and especially the chain growth process, leading to a higher selectivity towards the formation of C3H8 (∼11 %)

A New Approach to the Mechanism of Fischer-Tropsch Syntheses Arising from Gas Phase NMR and Mass Spectrometry

International audienceWe used 13CO labeling to show that gas‐phase NMR spectroscopy and mass spectrometry are simple tools for mechanistic investigations of the Fischer–Tropsch (FT) reaction. Thus, monodisperse Fe nanoparticles (NPs) react with syngas to form monodisperse iron carbide (FeCx) NPs. As expected, the heating of 13C‐labeled monodisperse FeCx NPs under H2 results in the desorption of the carbide carbons as 13CH4 and, interestingly, restores the initial Fe NPs in terms of size and dispersity. The Fe13Cx NPs catalyze the hydrogenation of 12CO at 210 °C to yield only 12C‐labeled FT products, which evidences the absence of the incorporation of FeCx carbon atoms in the products. In addition, this approach shows for the first time that the formation of 13CH4 at 250 °C does not result from direct carbide hydrogenation but from an intermediate step that involves a reaction between Fe13Cx and H2O to give 13CO2, which is subsequently hydrogenated. These results rule out the involvement of FeCx carbon atoms in the chain growth process under our conditions

CO2 methanation activated by magnetic heating: life cycle assessment and perspectives for successful renewable energy storage

International audiencePurpose: Technologies with low environmental impacts and promoting renewable energy sources are required to meet the energetic demand while facing the increase of gas emissions associated to the greenhouse effect and the depletion of fossil fuels. CO2 methanation activated by magnetic heating has recently been reported as a highly efficient and innovative power-to-gas technology in a perspective of successful renewable energy storage and carbon dioxide valorisation. In this work, the life cycle assessment (LCA) of this process is performed, in order to highlight the environmental potential of the technology, and its competitivity with in respect to conventional heating technologies.Methods: The IMPACT 2002+ was used for this LCA. The process studied integrates methanation, water electrolysis and CO2 capture and separation. This “cradle-to-gate” LCA study does not consider the use of methane, which is the reaction product. The functional unit used is the energy content of the produced CH4. The LCA was carried out using the energy mix data for the years 2020 and 2050 as given by the French Agency for Environment and Energy management (ADEME). Consumption data were either collected from literature or obtained from the LPCNO measurements as discussed by Marbaix (2019). The environmental impact of the CO2 methanation activated by magnetic heating was compared with the environmental impact of a power-to-gas plant using conventional heating (Helmeth) and considering the environmental impact of the natural gas extraction.Results: It is shown that the total flow rate of reactants, the source of CO2 and the energy mix play a major role on the environmental impact of sustainable CH4 production, whereas the lifetime of the considered catalyst has no significant influence. As a result of the possible improvements on the above-mentioned parameters, the whole process is expected to reduce by 75% in its environmental impact toward 2050. This illustrates the high environmental potential of the methanation activated by magnetic heating when coupled with industrial exhausts and renewable electricity production.Conclusions: The technology is expected to be environmentally competitive compared with existing similar processes using external heating sources with the additional interest of being extremely dynamic in response, in line with the intermittency of renewable energy production

Selective hydrogenation of cinnamaldehyde by unsupported and few layer graphene supported platinum concave nanocubes exposing {110} facets stabilized by a long-chain amine

International audienceFree and supported platinum concave nanocubes exposing {110} facets have been prepared by a wet-chemistry route and used as catalysts for the selective hydrogenation of cinnamaldehyde. The nanocubes were directly grown on few layer graphene support in the presence of octadecylamine as a stabilizing agent. Immobilization improves both activity and selectivity towards the desired unsaturated alcohol. The presence of the organic stabilizer guarantees the stability of the nanoparticle morphology and influences the catalyst performances. While the activity is favored by small nanoparticles and low ligand contents, the selectivity to the unsaturated alcohol is favored by high ligand contents, most likely due to steric effects that favor adsorption through the C=O moiety. Apart from stabilizing the nanocubes, the support interacts with the long chain amine ligand, behaving as a ligand reservoir. Thus, an equilibrium is established between the ligand interacting with the nanoparticles, the free ligand in solution, and the ligand interacting with the support. Ligand redistribution during the catalytic reaction assures a good compromise between activity and selectivity even after three recycling tests. While a direct comparison with other catalysts is not straightforward, the FLG-supported concave nanocubes presented outstanding activity, and selectivity to cinnamyl alcohol higher than 80%

In situ synthesis of gold nanoparticles in polymer films under concentrated sunlight: control of nanoparticle size and shape with solar flux

International audienceWe propose an original technique for synthesizing plasmonic nanocomposites under concentrated sunlight. Polymer films doped with gold salts are prepared by spin-coating; the nanoparticle growth is triggered within the polymer matrix by exposing the film to concentrated solar irradiation. For the first time, we demonstrate that the variation of solar flux alone allows for controlling the nanoparticle size distribution and shape and, thereby, the final plasmonic response of the composite. Interestingly, thanks to this optical approach, the in operando measurement of the spectroscopic response permits monitoring of the growth of the nanoparticles in real time. The experimental results give us details about the differences in the nanoparticle growth mechanisms at different solar fluxes. At high flux, small nanospheres with a diameter centered around 3 nm to 6 nm are formed. At lower flux, bigger nanoprisms of 12–18 nm are synthesized. The mechanisms are discussed and different pathways are envisaged. Finally, we demonstrate the possibility of performing a fully green synthesis by using our method to grow gold nanoparticles in a biopolymer

Hydrogen spillover in the Fischer‐Tropsch synthesis on carbon‐supported cobalt catalysts

International audienceThe Fischer‐Tropsch reaction transforms syngas into high added value products, among which liquid fuels. Numerous parameters determine catalytic activity and selectivity towards the most desired hydrocarbons. The performances of cobalt‐based catalysts used in the reaction are known to depend critically on Co particle size and crystallographic phase. Here, we present a comparative study of Co‐based catalysts supported on three carbon supports: multi‐wall carbon nanotubes, carbon nanofibers and a fibrous material. Our results show that, while the selectivity towards C5+ follows the expected tendency with respect to Co particle size, this is not the case for the TOF. These results can be rationalized considering that the amount of H 2 uptake on each catalyst increases with oxygen and defect concentration on the support. The catalyst, on the support presenting many edges and oxygen surface groups, necessary for H 2 spillover, presents the highest activity. Furthermore, the hydrogen spillover contributes to the enhancement of olefin hydrogenation and methane production

Magnetically Induced Continuous CO 2 Hydrogenation Using Composite Iron Carbide Nanoparticles of Exceptionally High Heating Power

International audienceThe use of magnetic nanoparticles to convert electromagnetic energy into heat is known to be a key strategy for numerous biomedical applications but is also an approach of growing interest in the field of catalysis. The heating efficiency of magnetic nanoparticles is limited by the poor magnetic properties of most of them. Here we show that the new generation of iron carbide nanoparticles of controlled size and with over 80 % crystalline Fe2.2C leads to exceptional heating properties, which are much better than the heating properties of currently available nanoparticles. Associated to catalytic metals (Ni, Ru), iron carbide nanoparticles submitted to magnetic excitation very efficiently catalyze CO2 hydrogenation in a dedicated continuous‐flow reactor. Hence, we demonstrate that the concept of magnetically induced heterogeneous catalysis can be successfully applied to methanation of CO2 and represents an approach of strategic interest in the context of intermittent energy storage and CO2 recovery