Magnetic heating by nanoparticles has recently been successfully employed in heterogeneous catalysis. In such processes, the maximum temperature that can be reached depends on the Curie temperature (T c) of the heating material. Here, in order to extend the range of accessible temperatures and consequently the range of possible reactions, to those requiring high temperatures, we developed and fully characterized a series of FeCo nanoparticles containing different concentrations of cobalt, in order to tune their magnetic properties and Tc. Their efficiency is compared to that of iron carbide nanoparticles, which display a lower Tc. Specific Absorption Rate (SAR) measurements as a function of temperature, performed using a homemade pyrometer-based setup, clearly show that, although the heating power of iron carbide nanoparticles is higher at room temperature, it decreases more rapidly with temperature than that of iron cobalt nanoparticles, in agreement with their lower Tc. In a showcase, Fe 0.5 Co 0.5 nanoparticles allow, in addition to CO 2 hydrogenation, dry reforming of propane and methane, and dehydrogenation of propane, these reactions requiring temperatures of 350°C, 600°C and 700°C respectively. Furthermore, the use of Fe 0.5 Co 0.5 nanoparticles is less energy demanding, as it allows carrying out CO 2 hydrogenation at lower magnetic fields and at frequencies as low as 100 kHz. Dry reforming of methane and propane were carried out in the presence of a Ni nanoparticle-based catalyst whereas dehydrogenation of propane required as a catalyst PtSn nanoparticles synthesized through an organometallic route. Fe 0.5 Co 0.5 nanoparticles can therefore be used as universal heating agents allowing performing reactions up to ca. 700°C upon association with the appropriate catalyst.

Heating magnetic nanoparticles with high frequency magnetic fields is a topic of interest for biological applications (magnetic hyperthermia) as well as for heterogeneous catalysis. This study shows why FeC NPs of similar structures and static magnetic properties display radically different heating power (SAR from 0 to 2 kW.g -1 ). By combining results from Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and static and time-dependent high-frequency magnetic measurements, we propose a model describing the heating mechanism in FeC nanoparticles. Using, for the first time, time-dependent highfrequency hysteresis loop measurements, it is shown that in the samples displaying the larger heating powers, the hysteresis is strongly time dependent. More precisely, the hysteresis area increases by a factor 10 on a timescale of a few tens of seconds. This effect is directly related to the ability of the nanoparticles to form chains under magnetic excitation, which depends on the presence or not of strong dipolar couplings. These differences are due to different ligand concentrations on the surface of the particles. As a result, this study allows the design of a scalable synthesis of nanomaterials displaying a controllable and reproducible SAR.

Magnetically induced catalysis using magnetic nanoparticles (MagNPs) as heating agents is a new efficient method to perform reactions at high temperatures. However, the main limitation is the lack of stability of the catalysts operating in such harsh conditions. Normally, above 500 ºC, significant sintering of MagNPs takes place. Here we present encapsulated magnetic FeCo and Co NPs in carbon (Co@C and FeCo@C) as an ultra-stable heating material suitable for high temperature magnetic catalysis. Indeed, FeCo@C or a mixture of FeCo@C:Co@C (2:1) decorated with Ni or Pt-Sn showed good stability in terms of temperature and catalytic performances. In addition, consistent conversions and selectivities regarding conventional heating were observed for CO2 methanation (Sabatier Reaction), propane dehydrogenation (PDH) and propane dry reforming (PDR). Thus, the encapsulation of MagNPs in carbon constitutes a major advance in the development of stable catalysts for high temperature magnetically induced catalysis.

Magnetic nanoparticles have been used as heating agents in CO2 methanation under continuous flow catalyzed by nickel nanoparticles (Ni/SiRAlOx).

There is a theoretical and experimental controversy on the possibility for magnetic nanoparticles (MNPs) heated by high-frequency magnetic fields to reach a temperature much larger than the one of their environments. Here the internal temperature of magnetically heated magnetite MNPs is measured using the temperature dependence of their lattice parameter, and compared to the one of their environments, measured from reference non-magnetic particles. Within the uncertainty of our experimental methods, which is estimated to be below 5°C, the MNP temperature is the same as the one of their environments.

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Purpose 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. CO 2 methanation activated by magnetic heating has recently been reported as a highly efficient and innovative power-togas technology in a perspective of successful renewable energy storage and carbon dioxide valorisation. ln 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 electrol ys is and CO 2 capture and separation. Thi s "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 CH.i. 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 (AD EME). Consumption data were either collected from Iiterature or obtained from the LPCNO measurements as discussed by Marbaix (2019). The environmental impact of the CO 2 methanation activated by magnetic heating was compared with the environmental impact ofa power-togas plant using conventional heating (Helmeth) and considering the environmental impact of the natural gas extraction. Results lt is shown that the total flow rate of reactants, the source of CO 2 and the energy mix play a major role on the environmental impact of sustainable CH 4 production, whereas the lifetime of the considered catalyst has no significant influence. As a result ofthe possible improvements on the above-mentioned parameters, the whole process is expected to reduce by 75% in its environmental impact toward 2050. This illustra tes 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 sirnilar processes using external heating sources with the additional interest of being extremely dynamic in response, in Iine with the intermittency of renewable energy production.

opened discussion of the introductory lecture by Bruce Gates: As you have shown, EXAFS plays a crucial role in determining the structure and the nuclearity of nanoparticles (NPs). For each shell, the accuracy of this deter-mination depends on the error bar associated to the coordination number, that strongly correlates with the corresponding Debye-Waller (DW) parameter. This becomes even more important when in situ operando experiments are performed at reaction temperature. Based on your experience, what suggestions can you give to reduce this correlation and increase the potentiality of the technique? Do you believe it is possible to x or to determine, in a reliable way, DW parameters from independent experimental or computational works? Do you believe that in temperature-dependent experiments it is reliable to adopt the Debye or the Ein-stein model 1,2 to parametrize the evolution of DW parameters? 1 G. Dalba, P. Fornasini, R. Grisenti and J.