# Icosahedra CoPd Bimetallic Nanoparticles for Magnetically Induced Aromatic Ketone Hydrodeoxygenation

Felipe Quiroga-Suavita, Victor Varela-Izquierdo, Teresa Hungria, Alloyeau D., Nicolas Ratel-Ramond, Simon Cayez, Richard Tilley, Edwin Baquero, Bruno Chaudret, Lise-Marie Lacroix

► To cite this version:

Felipe Quiroga-Suavita, Victor Varela-Izquierdo, Teresa Hungria, Alloyeau D., Nicolas Ratel-Ramond, et al.. Icosahedra CoPd Bimetallic Nanoparticles for Magnetically Induced Aromatic Ketone Hydrodeoxygenation. Chemistry of Materials, 2025, 10.1021/acs.chemmater.4c03359. [PDF] [ DOI ]

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Distributed under a Creative Commons Attribution 4.0 International License
Icosahedra CoPd bimetallic nanoparticles for
magnetically induced aromatic ketone
hydrodeoxygenation

Felipe Quiroga-Suavita,ᵃ,ᵇ,ᶜ Victor Varela-Izquierdo,ª Teresa Hungria,ᵈ Damien Alloyeau,ᵉ

Nicolas Ratel-Ramond,ª Simon Cayez,ª Richard D. Tilley,ᵇ,f Edwin A. Baquero,*,c Bruno

Chaudret*ª and Lise-Marie Lacroix*ª,g

a Université de Toulouse, Laboratoire de Physique et Chimie des Nano-Objets, UMR 5215 INSA, CNRS, UPS, 135 avenue de Rangueil 31077 Toulouse, France

ᵇ School of Chemistry, University of New South Wales, Dalton Building, F12 University Mall, Kensington NSW 2033, Australia

c Estado Sólido y Catálisis Ambiental (ESCA), Departamento de Química, Facultad de Ciencias, Universidad Nacional de Colombia, Carrera 30 No. 45-03, 111321 Bogotá, Colombia

d Centre de MicroCaractérisation Raimond Castaing, Université de Toulouse, 3 rue Caroline Aigle, 31400 Toulouse, France

e Université Paris Cité, CNRS, Laboratoire Matériaux et Phénomènes Quantiques, 10 Rue Alice Domon et Léonie Duquet, 75013 Paris, France
f Electron Microscope Unit, Mark Wainwright Analytical Centre, June Griffith Building
Kensington UNSW Sydney, NSW 2052, Australia

g Institut Universitaire de France (IUF), 103 boulevard Saint Michel, 75005 Paris, France

ABSTRACT

The development of bimetallic nanomaterials with precisely controlled size, shape and
composition has emerged as a cornerstone of sustainable catalysis, offering innovative solutions
for chemical valorization processes. In this work, CoPd bimetallic nanoparticles (NPs) were
prepared via an organometallic approach using Co[N(SiMe₃)₂]₂(thf) and Pd(acac)₂ (acac:
acetylacetonate) as metal sources. Advanced structural characterization techniques including
high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and wide-
angle X-ray scattering (WAXS) revealed an icosahedral Pd-rich core with a less crystalline Co
rich shell. Thanks to a large magnetic anisotropy, these 10 nm particles are ferromagnetic at room
temperature and thus can be used as efficient heating agents under alternative magnetic field
(AMF). This nanomaterial was successfully tested as a catalyst in hydrodeoxygenation (HDO)
reactions using induction heating (IH) for energy-efficient activation. The CoPd catalyst
demonstrates the synergistic potential of non-noble/noble metal combination, achieving
challenging chemical transformations at relatively low temperatures, while keeping an optimal
balance between their heating capability and surface-to-volume ratio. This study underscores the
potential of CoPd systems for advancing sustainable catalysis through magnetically induced
reactions.
INTRODUCTION

The application of bimetallic nanostructured materials in catalysis has attracted significant attention through the last decades.¹,² In general, this interest stems from the strategic combination of two metals with different properties regarding stability and catalytic activity. The correct selection and design of bimetallic systems has resulted in interesting materials which tend to present cooperative or synergetic effects advantageous for multiple catalytic processes.¹ For instance, bimetallic nanoparticles (NPs) have been successfully applied in hydrogenation and hydrogenolysis reactions, in the context of increasing use of sustainable resources.³⁻⁶ These systems typically include noble metals such as Pd, Pt or Ru; non-noble metals as Co, Mo, Ni, Fe, W, or both groups.⁴,⁷

However, some of hydrogenation and hydrogenolytic reactions require harsh conditions in terms of pressure and temperature to achieve significant conversions in a reasonable time.⁸ Specifically, hydrodeoxygenation (HDO) of aromatic ketones is a difficult reaction which has been proven to be catalyzed by bimetallic systems. This behavior is typically attributed to electronic and structural effects coming from the interaction between both metals.¹,⁹ When conventional heating methodologies are used, temperatures of 130 to 150 °C and H₂ pressures of 30 to 60 bar are commonly required, underscoring the need for innovative approaches to improve efficiency and reduce operational demands.

In this context, induction heating (IH) emerges as a valuable alternative, offering significant advantages over conventional heating methods such as rapid heating/cooling and highly localized heating. Heat transfer in IH is achieved through the dynamic switching of the magnetic moments of nanoparticles under an external alternating magnetic field (AMF). The heating capacity of NPs strongly depend on their size and their magnetic anisotropy, which is mostly governed by their
chemical composition and shape, as reported previously.¹⁰, ¹¹ Furthermore, IH has demonstrated
higher energy efficiency compared to conventional heating processes¹², ¹³ as supported by the
growing research efforts in the field.¹⁴⁻¹⁷ Our group recently reported the application of FeNi¹⁸ or
CoNi based NPs, ¹⁹, ²⁰ which act both as heating agents and catalysts, showing remarkable activity
and selectivity for HDO of hydroxyacetophenone and lignin derivatives under IH and mild
conditions (3 bar H₂, bulk temperature below 100 °C).

In addition to the magnetic requirement, controlling the size, shape, chemical distribution and
the surface state of the bimetallic NPs is critical for tailoring their catalytic properties. In particular,
icosahedral nanostructures have demonstrated in specific cases relevant catalytic improvements
compared to face-centered cubic (fcc) structured nanocrystals with cubic or octahedral shapes.²¹
These improvements are evidenced in a wide range of electrocatalytic processes such as formic
acid oxidation (FAO) and methanol oxidation reaction (MOR), where the enhanced efficiency is
often attributed to the presence of surface strain.²², ²³

The combination of noble and non-noble metals such as Pt-M or Pd-M alloys (M = Fe, Co),
provides synergistic benefits, enhancing both catalytic activity and magnetic properties. These
alloys exhibit indeed a large magnetic anisotropy for the equimolar composition,²⁴ which allow
decreasing the NP size while maintaining large heating efficiency in IH applications.

Smaller NPs with higher surface-to-volume ratios are expected to exhibit superior catalytic
activity compared to larger counterparts. Herein, we focus on the CoPd system while Pd is a well-
known HDO catalyst due to its ability to adsorb and dissociate hydrogen,²⁵, ²⁶ incorporating Co on
the surface would facilitate the C=O adsorption and subsequent C-O cleavage, ²⁷ while allowing
the resulting particle to be heated magnetically.
We extended the organometallic approach to synthesize bimetallic CoPd magnetic NPs starting from Co[N(SiMe₃)₂]₂(thf) and Pd(acac)₂ (acac: acetylacetonate), which display relatively similar decomposition rates. The morphology and composition of the obtained NPs were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), low and high-resolution electron microscopy (TEM and HR-TEM), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and STEM coupled to energy dispersive X-ray spectroscopy (STEM-EDX). Their magnetic properties were studied by vibrating sample magnetometry (VSM) and specific absorption rate (SAR) to gather information about their performance for induction heating (IH). The catalytic activity was tested in the HDO of acetophenone derivatives in order to study the tolerance of the process to electron-donating and electron withdrawing substituents.

# EXPERIMENTAL SECTION

**Materials.** All air-sensitive procedures were carried out under an Ar atmosphere inside a glovebox or using a Schlenk line. The precursor Co[N(SiMe₃)₂]₂(thf) was commercially available from NanoMePS, Pd(acac)₂ (99 %) was purchased from Sigma Aldrich. Palmitic acid (PA, >98%) was purchased from Sigma Aldrich and dried dissolving it in toluene, adding molecular sieves (3 Å) filtered and recovered under dynamic vacuum. All other reagents were purchased from commercial suppliers without further purification. Tetrahydrofuran (THF, 99%), dichloromethane (DCM, 99%), toluene (99%) and mesitylene (99%) were purchased from VWR Prolabo, dried over alumina and degassed with Ar before use.

## General methods
**Thermogravimetric analyses (TGA)** experiments were performed using a TGA/DSC 1 STAR System equipped with an ultra-microbalance UMX5, a gas switch GC200 and DTA and DSC sensors as well. The sample was first heated under air to 500 °C leading to the oxidation of CoPd and the removal of the organic matter. After cooling down to room temperature, the sample is heated under a reductive atmosphere (96% Ar, 4% H₂) to 700 °C, to fully reduce CoPd. The total weight loss allows determining the organic content (typically 16 wt. %) and thus retrieve the metallic content of the powder (84 wt. %, see Figure S2).

**X-ray diffraction (XRD)** experiments were conducted on a PANalytical Empyrean diffractometer using Co-Kα radiation (λ=0.1789 nm) at 45 kV and 35 mA. Inside an Ar filled glove box, a few milligrams of the powder were placed between two Kapton sheets and sealed with grease to prevent air exposure.

**Wide angle X-ray scattering (WAXS)** experiments were carried out on a Malvern PANalytical Empyrean III diffractometer in transmission geometry equipped with a Mo anode (λ Kα=0.071 nm) operating at 60 kV and 40 mA and equipped with an incident focusing mirror combined with a GaliPIX3D detector. Glass capillaries of 0.5 mm diameter were filled with the powder samples under an argon atmosphere and further sealed with a butane flame to prevent specimen oxidation. The pair distribution function (PDF) extraction was done with PDFgetX3 software,²⁸ The procedure for PDF extraction from scattering data include the following steps: i) subtraction of sample container contribution, ii) normalization by the square of the average X-ray atomic form factor, iii) Fourier transform of the corrected signal. PDF refinement was performed using the diffpy-cmi package.²⁹ Icosahedra models where generated using Atomic Simulation Environment (ASE) python library.³⁰ For each considered structural model, a set of 4 parameters was refined against experimental PDF:
- A scale factor, used to scale the amplitude of the theoretical PDF to that of the experimental one.

- A so-called zoomscale factor was used to refine the peak positions of the PDF, and thus the interatomic distances, by the homothetic transformation of the structure. After refinement, this parameter should be close to 1.

- The isotropic atomic displacement parameters allow reproducing the experimental PDF peak width.

- The δ₂ parameter accounts for the displacement correlations of neighboring atoms in the structure and results in the narrowing of the first PDF peaks.

These 4 parameters were adjusted through least squares refinement so that the theoretical PDF computed from a structural model matches the experimental one.

The fitting criteria selected was the weighted profile R-factor, referred to as R<sub>wp</sub> and calculated as follow :

$$R_{wp} = \sqrt{\frac{\sum_{i=1}^{N} w(r_i)[G_{obs}(r_i) - G_{calc}(r_i)]^2}{\sum_{i=1}^{N} w(r_i)G_{obs}^2(r_i)}} \quad (1)$$

Where rᵢ is the iᵗʰ position, G<sub>obs</sub>(rᵢ) and G<sub>calc</sub>(rᵢ) the experimental and calculated PDF at the rᵢ position respectively, and w(rᵢ) the weighted factor. As classically done in Rietveld refinement, a lower R<sub>wp</sub> value indicates a better fit.

The structural model leading to the best refinement results was used to simulate the XRD pattern shown in Figure 1c using the Debye equation.

**Electron microscopy.** Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) was carried out to determine the Co:Pd metal ratio, the experiments were performed in a JEOL JSM-7800F microscope. The EDS quantifications were carried out using a Bruker
XFlash EDS detector coupled to the SEM. The size and morphology of the nanoparticles (NPs) were analyzed by transmission electron microscopy (TEM) using a JEOL 1011 microscope working at 100 kV. Micrographs were analyzed using ImageJ to determine size and size distribution. Bright-field high resolution TEM (BF-HR-TEM) images were obtained using an aberration-corrected JEOL ARM 200F microscope operating at 200 kV. This microscope is equipped together with a CEOS aberration corrector and a cold field emission gun (cold-FEG). The study of very small metal nanoparticles by HRTEM requires minimizing the electron dose rate to avoid affecting their atomic structure. This was done by exploiting an electrostatic dose modulator commercialized by IDES that uses a pre-sample electrostatic deflector in order to switch the electron beam on and off at very high frequency. This ultra-fast blanking system allows attenuating the electron illumination without affecting imaging conditions.

Scanning transmission electron microscopy (STEM) and STEM-EDX measurements were carried out in a JEOL cold-FEG JEM-ARM200F operated at 200kV equipped with a probe $C_s$ corrector reaching a spatial resolution of 0.078 nm. BF HR-TEM micrographs were studied and analyzed using the Gatan Microscopy Suite. EDX spectra were recorded on a JEOL CENTURIO SDD detector.

**Magnetic Characterization.** Magnetic measurements were performed using a vibrating sample magnetometer (VSM) Quantum Device PPMS Evercool II by placing about $w = 10$ mg of dry powder sample in a polypropylene holder under inert atmosphere. The magnetization versus magnetic field measurements (hysteresis loop) were conducted at 300 and 5 K, with an external magnetic field of $\pm 3$ T. Zero-field cooling/Field cooling (ZFC/FC) measurements were performed keeping an external magnetic field of 10 mT and ranging the temperature between 5 and 300 K.
The absolute magnetization measured in emu (cgs unit) were normalized by the sample weight and the metallic content determined by TGA to retrieve the magnetization in the SI unit

$$A \cdot m^2 \cdot kg^{-1}CoPd \text{ following Equation 2: } M(A \cdot m^2 \cdot kg^{-1}CoPd) = \frac{M(emu)}{m(g) \times Metallic \ wt.\%} \quad (2)$$

**Specific absorption rate (SAR)** property was studied by calorimetry measurements following a previously described protocol using a 93 kHz coil (*Five Celes*, 14 cm height and 4 cm width) using Equation 3, where C<sub>pi</sub> and m<sub>i</sub> are the specific heat capacity and the mass for each component respectively (C<sub>p</sub> = 296 J·kg<sup>-1</sup>·K<sup>-1</sup> for a CoPd (45:55) mixture, C<sub>p</sub> = 1750 J·kg<sup>-1</sup>·K<sup>-1</sup> for mesitylene, C<sub>p</sub> = 4186 J·kg<sup>-1</sup>·K<sup>-1</sup> for water and C<sub>p</sub> = 720 J·kg<sup>-1</sup>·K<sup>-1</sup> for glass), and m<sub>Co+Pd</sub> is the mass of metal in the CoPd NPs.<sup>31, 32</sup> In a typical experiment, 10 mg of NPs powder and 0.5 mL of mesitylene were added to a glass sample tube and subsequently sealed with a Teflon-lined screw cap. Outside the glovebox, the NPs were sonicated for a few seconds to achieve a good dispersion. For the calorimetric experiments, the sample was put inside a hollow cylinder located at the center of the coil, the cylinder was filled with 1.8 mL of deionized water. Two optic fiber probes were submerged, one near the socket's bottom and the second one close to the center. Then, the temperature increase under various magnetic field (in the range of 0 to 47 mT) was measured for 50 s. A correction factor was applied in order to consider the heat losses of the surroundings obtaining a more accurate SAR value (expressed in W·g<sup>-1</sup>).

$$SAR (W \cdot g^{-1}) = \frac{\sum_i c_{pi} m_i \Delta T}{m_{Co+Pd} \Delta t} \quad (3)$$

**Catalyst preparation.** Inside an Ar glovebox, Pd(acac)<sub>2</sub> (0.20 mmol, 60.9 mg) was added to an 80 mL Fisher-Porter (FP) bottle before rinsing the vial two times with 2.5 mL of mesitylene. Under constant stirring, Co[N(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(thf) (0.20 mmol, 90.4 mg) was dissolved in 2.5 mL of mesitylene and added to the FP bottle, followed by rinsing the weighting vial with other 2.5 mL
of solvent. Equally, palmitic acid (PA) (0.4 eq. total metal basis, 0.16 mmol, 41.0 mg) and hexadecylamine (HDA) (0.5 eq. total metal basis, 0.20 mmol, 48.3 mg) were added by dissolving each of them in 2.5 mL of solvent and then rinsing with other 2.5 mL (adding first the PA followed by HDA). The mixture was left at room temperature under magnetic stirring at 600 rpm for 10 min. Using a Schlenk line, the Ar atmosphere was removed, and the FP bottle was charged with 3 bar of H₂. The reaction was put inside a pre-heated oil bath at 110 °C and stirred at 600 rpm for 24h (Scheme 1). Once the reaction time concluded, the reactor was cooled down to room temperature and inside the Ar glovebox the remanent H₂ pressure was released. The NPs were magnetically decanted for at least 10 min and washed two times with 5 mL of toluene and two times with 5 mL of THF in order to avoid ligand excess. The solid was dried in the Schlenk line for at least 2h and stored under inert atmosphere (ca. 21.0 mg, approx. 54 % yield). (84 % of metal content determined by TGA. Co, 45 at % and Pd, 55 at % determined by SEM-EDX).

<figure><img src="image_2.png" /><figcaption>**Scheme 1.** Overview of synthetic route used for catalyst preparation.</figcaption></figure>

**Catalytic HDO tests.** In a typical experiment inside an Ar glovebox, 1 mmol of substrate was dissolved in 4 mL of THF together with dodecane (0.50 mmol, 85.2 mg) as internal standard, and 5.0 mg of NPs (0.05 mmol Pd-Co, metal-substrate ratio was kept at 1:20). The catalytic tests were carried out in an 80 mL FP bottle under 3 bar of H₂ at the center of a 300 kHz-coil (ID Partner, 4 cm height and 6 cm width) working at 5 kW with an amplitude of 44 mT. After the reaction, the
FP bottle was let to cool down and the NPs were magnetically decanted. The remanent H₂ pressure was released, and the reaction mixture was filtered through Celite. Approximately 10 drops of the collected liquid were diluted in 1.6 mL of dichloromethane (DCM) for analytical purposes. The samples were always analyzed by gas chromatography (GC) PerkinElmer 580 equipped with A BP-5 column of 30 m with H₂ as carrier gas. The GC was coupled to a mass spectrometer (Clarus SQ8T) for product identification and a first ionization detector (FID) detector for the internal standard quantification method. Figure S10 (see Supporting Information (SI)) shows a typical chromatogram obtained after analysis. The substrate conversion (X), the product yield (Y), selectivity (S) and carbon balances (CB) were calculated by comparing areas of the present analytes using the following formulas:

$$X_{\text{subs}} (\text{mol}\%) = \frac{n_{\text{subs}}^{0} - n_{\text{subs}}^{f}}{n_{\text{subs}}^{0}} \times 100 \quad (4)$$

$$Y_{i} (\text{mol}\%) = \frac{n_{i}}{n_{\text{subs}}^{0}} \times 100 \quad (5)$$

$$S_{i} = \frac{n_{i}}{\sum n_{\text{products}}^{f}} \times 100 \quad (6)$$

$$CB (\text{mol}\%) = \frac{\sum n_{\text{products}}^{f} + n_{\text{subs}}^{f}}{n_{\text{subs}}^{0}} \times 100 \quad (7)$$

# RESULTS AND DISCUSSION

## Composition and morphology

CoPd bimetallic NPs were synthesized through decomposition of equimolar amounts of Co[N(SiMe₃)₂]₂(thf) and Pd(acac)₂, in order to obtain the highly magnetic Co₀.₅Pd₀.₅ phase. To stabilize the NP surface and prevent the aggregation, a mixture of palmitic acid (PA) and hexadecylamine (HDA) was used as ligands. SEM coupled with Energy-Dispersive X-Ray spectroscopy (SEM-EDX) analysis confirmed that the Co-to-Pd ratio in the resulting NPs closely
matched the targeted composition (Figure S1, SI). After purification, the NPs obtained exhibit a
metallic content of 84 wt.%, the ligands at the surface leading to the additional organic content of
16 wt.%, as determined by thermogravimetric analysis (TGA), (Figure S2, SI).

TEM studies revealed that the NPs typically exhibited an irregular shape and were highly
monodispersed, with a mean size of 10.4 ± 0.6 nm following a Gaussian distribution. They were
generally well dispersed throughout the grid, rarely giving rise to agglomeration (Figure 1a,b,
Figure S3, SI). The X-ray diffractogram exhibits very broad peaks, evidencing a fairly low
crystallinity of the sample. The peaks could not be directly assigned to the expected fcc structure,
neither using CoPd nor pure Pd references (COD 96-152-4901 and COD 96-900-7479
respectively, Figure S4, SI). The NP structure was therefore further studied using wide-angle X-
ray scattering (WAXS) and atomic pair-distribution function (PDF) (Figure 1d). The first peak in
the experimental PDF indicates an average interatomic distance of about 2.71 Å, while expected
interatomic distances in pure Co or Pd are 2.42 Å and 2.82 Å respectively. This qualitative result
indicates that the core of the particles consists of a CoPd alloy. Several NP size and shape models
were designed starting from known structures and the theoretical PDF calculated.

Among different models, a 9-shells Pd icosahedron of 4.5 nm (2057 atoms) was generated. The
fitting shows a fairly good agreement with the experimental atomic PDFs (Figure S5a, SI). In line
with the chemical analysis, multiple CoxPd1-x models (i.e Co0.5Pd0.5, Co0.4Pd0.6 and Co0.3Pd0.7) with
the same structural features were tested, leading to a better adjustment. The fitting criteria (Rwp)
was slightly improved when increasing the Pd content in the model (Figure S5b,c, SI). A Co0.5Pd0.5
sphere-like nanoparticle with a 4.5 nm diameter exhibiting a fcc structure was also simulated.
However, the theoretical PDF exhibited a second-neighbor distance of 3.80 Å characteristic of
octahedral sites, which is nearly absent in the experimental PDF (Figure S5d, SI). Therefore, one
can conclude that the CoPd NPs consist of a Co<sub>0.3</sub>Pd<sub>0.7</sub> icosahedral core surrounded by an
amorphous shell (Figure 1d). Using the Debye equation on this model, the simulated diffractogram
showed good agreement with the experimental diffraction pattern in the reciprocal space (Figure
1c), all the main peak position being well reproduced by the Co<sub>0.3</sub>Pd<sub>0.7</sub> icosahedral model.

<figure><img src="image_3.png" /><figcaption>**Figure 1.** (a) TEM image of CoPd NPs (scale bar = 100 nm) and (b) the corresponding size distribution. (c) X-ray diffractogram and (d) PDF compared to the generated Co<sub>0.3</sub>Pd<sub>0.7</sub> 9-shells icosahedral core model (view from its 5-fold symmetry axis) (Co: orange, Pd: blue).</figcaption></figure>

Figure 2 shows the HR-TEM analyses carried out on isolated NPs. The core of the NPs exhibited an icosahedral structure (Figure S6, SI), as evidenced by distinct contrasts and fast Fourier transform (FFT) patterns for two-, three- and five-fold symmetry axes, confirming the icosahedral geometry (Figure 2a-e). HR-TEM micrograph and FFT simulations based on the same Co<sub>0.3</sub>Pd<sub>0.7</sub> icosahedral core model evidenced strong agreement with the experimental observations (Figure S7-S9, SI).<sup>33, 34</sup> The size of this core typically did not exceed the 5 nm in size, in good agreement
with the PDF results and the 4.5 nm models used. While the outer 2.5–3.0 nm shell is predominantly amorphous, small grains originated by a crystal overgrowth can be observed in few cases. The corresponding FFT patterns can be indexed to a fcc structure oriented along the <110> zone axis (Figure 2d,f).

<figure><img src="image_4.png" /></figure>

**Figure 2.** HR-TEM analyses on CoPd NPs: (a,b,c) Characteristic two-, three and five-fold axes of icosahedron and FFT patterns (inset) (scale bar = 5 nm). (d) HR-TEM image of a single NP (scale bar = 5 nm), (e) FFT pattern of icosahedral inner region (1) and (f) FFT pattern of overgrowth ultra-small crystal (2).

Bright-field STEM imaging (Figure 3a, Figure S10a-c, SI), high-angle annular dark field-STEM (HAADF-STEM Figure 3b, Figure S10d-f, SI) and STEM-EDX analyses (Figure 3c-e, Figure S11, SI) allowed comprehensive understanding of the elemental distribution within the NPs. Indeed, the results revealed a Pd-rich core and a Co-rich shell. The elemental distribution was further confirmed by extracting a line profile for each metal from the STEM-EDX mapping and compare
it with simulations (Figure 3f, Figure S12, SI) The EDX quantification on a single nanoparticle described a core composition close to Co<sub>0.3</sub>Pd<sub>0.7</sub>, in good agreement with the PDF result, while the amorphous shell exhibit a composition close to Co<sub>0.7</sub>Pd<sub>0.3</sub> (Figure S13, SI). This metal distribution indicates that despite similar precursor decomposition rates, the Pd nucleation occurs faster, leading to Pd-rich CoPd core surrounded by a Co-rich shell.

<figure><img src="image_5.png" /><figcaption>**Figure 3.** STEM analyses on CoPd NPs: (a) BF-STEM, (b) HAADF-STEM images and STEM-EDX elemental mapping of the sample, (c) Co (orange), (d) Pd (blue), (e) overlap of Co and Pd maps (scale bar = 5 nm), (f) Co-K and Pd-L lines intensity profile along the white box in (e).</figcaption></figure>

## Magnetic and calorimetric characterization

The magnetic properties of the CoPd NPs were evaluated through magnetometry measurements (VSM). Both the Pd-rich icosahedral core and the Co-rich amorphous shell contribute to the total magnetization determined. At 300 K, the hysteresis loop exhibited the characteristic behavior of a ferromagnetic material. It displayed a saturation magnetization (M<sub>s</sub>) of 69 A·m<sup>2</sup>·kg<sup>-1</sup>, in good
agreement with previous reports for CoPd thin films (approx. 65 A·m²·kg⁻¹).³⁵ The remanent magnetization (M<sub>R</sub>) of 14 A·m²·kg⁻¹, and the coercive field (μ<sub>0</sub>H<sub>C</sub>) of 13 mT (Figure 4a, Figure S14, SI) evidence a fairly open hysteresis cycle despite the small size of the NPs. The ferromagnetic behavior was further confirmed by the zero-field cooling/field cooling (ZFC/FC) experiment which indicated a blocking temperature (T<sub>B</sub>) above 300 K (Figure S15, SI). The presence of an oxide shell was studied using a field cooling procedure. Once cooled down under an external magnetic field, an oxide shell may couple antiferromagnetically to the core, leading to an exchange bias observed as a shift towards negative values of the hysteresis loop.³⁶ After field cooling the powder under μ<sub>0</sub>H = 3T down to 5K, the hysteresis cycle was perfectly centered, evidencing the metallic nature of the NPs.

As previously reported theoretically, the heating efficiency of nanoparticles strongly depends on their magnetic behavior.¹⁰ While moderate heat dissipation can be induced by superparamagnetic NPs, ferromagnetic one exhibit a higher efficiency due to hysteresis losses. One could thus expect that these CoPd NPs would be suitable for induction heating.
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 4.** (a) Magnetic characterization of CoPd NPs by (a) ± 3 T hysteresis cycles at 300 K (black) and 5K (dark blue), (b) calorimetric (SAR) characterization against 93 kHz AMF.</figcaption></figure>

To further investigate the heating capabilities of the CoPd NPs under high-frequency alternating magnetic field, SAR measurements were performed. The results revealed that the NPs were activated at a modest field of 15 mT in agreement with the coercive field measured by VSM. At the highest AMF (47 mT, 93 kHz) the obtained SAR value was 157 ± 7 W·g⁻¹ (Figure 4b). While this SAR value appears low compared to other catalysts used for magnetically-induced HDO, such as 600 W·g⁻¹ for 17 nm Fe<sub>0.3</sub>Ni<sub>0.7</sub>,³² and 513 W·g⁻¹ for 13 nm Co<sub>0.5</sub>Ni<sub>0.5</sub>¹⁹, it is however one of the highest value reported for such small NPs, allowing for IH catalysis.
Catalytic HDO tests

The catalytic performance of the synthesized NPs in HDO using acetophenone as the model
substrate was assessed. This substrate was selected due to its well-studied reactivity and the
presence of two prototypical functional groups: an aromatic phenyl ring and a ketone. This choice
enables a direct comparison with previously reported catalysts.³⁷ Using similar conditions to
previous reports for magnetically induced HDO (3 bar H₂, 300 kHz, 45 mT), we monitored the
conversion and product yields over time by gas chromatography (GC), taking care that the carbon
balance remained acceptable (above 92 %, Figure 5a,b, Figure S16, SI).¹⁹, ³⁸ As expected, the
reaction mechanism started with the hydrogenation of the ketone group, followed by the C–O bond
cleavage, which is a temperature limited step, as previously reported.⁷ Interestingly, after only 6
h, acetophenone (1) was fully converted to 1-phenylethanol (1a) (6 %) and ethylbenzene (1b) (94
%). After 7 h, the reaction reached full conversion to **1b** (Figure 5b). The bulk reaction
temperature, monitored with an infrared camera, quickly stabilized at 65 °C and was maintained
throughout the test. This temperature is interestingly low for HDO reactions compared to the usual
conditions used. As a comparison, the catalytic activity of CoPd NPs was tested under a higher
temperature of 100°C with conventional heating (3 bar H₂, 6h). Remarkably, only 79 % of **1** was
converted with a noticeable decrease in **1b** yield (43 %), evidencing that the temperature was not
high enough to reach same yield for the last reaction step (Figure 5c).

As previously reported, the surface temperature of the NPs exposed to IH can be significantly
higher than the one observed in the bulk.³⁹ Though the quantitative measurement of the surface
temperature remains challenging despite intensive efforts using fluorescent probes, quantum dots
or even internal lattice parameter evolution,⁴⁰ these catalytic results allow to conclude that the
temperature at the surface of the CoPd NPs exceeded 100 °C during IH catalysis.
<figure><img src="image_8.png" /><figcaption>**Figure 5.** Catalytic performance of CoPd NPs in acetophenone HDO under AMF. (a) Acetophenone conversion over time, (b) Product distribution over time and (c) Comparison of conversion and products yields between magnetic induced and conventional heating HDO at 6 h of reaction. **Reaction conditions:** Batch type reactor, 1.0 mmol of acetophenone, 0.5 mmol of dodecane as internal standard and 4 mL of THF, 0.05 mmol CoPd (metal-substrate ratio of 1/20, 5.0 mg NPs), 3 bar H₂. AMF 300 kHz, 45 mT. Conversion and selectivity were determined by GC-FID using dodecane as the internal standard.</figcaption></figure>

Previous studies have evidenced that HDO reactions are typically favored by the presence of Lewis acidic sites.⁴¹ Bimetallic systems such as Pd-M or Pt-M (M = Co, Fe) have shown improved HDO activity compared to catalysts based solely on noble metals. This effect is likely due to the oxophilic nature of Co or Fe, which promotes C–O adsorption and cleavage.²⁷, ⁴² In our CoPd system the high catalytic activity and the full conversion towards the HDO product evidence the presence of both Co and Pd on the NP surface. While a Co-rich shell was determined by STEM-EDX, Pd is clearly also present at the surface since first reaction step requires H₂ activation and transfer to the substrate. The presence of Co at the proximity has been proven to facilitate the C-
O bond cleavage, thus favoring the HDO over simple ketone hydrogenation.²⁷, ⁴³, ⁴⁴ To date, there have been only a few examples of CoPd-based nanomaterials applied in HDO reactions,⁴⁴ making this work a valuable contribution to understand bimetallic combinations for magnetically induced HDO.

<table><caption>**Table 1.** Scope of magnetic induced HDO of acetophenone derivatives using CoPd NPs.ᵃ</caption><thead><tr><th>Entry</th><th>Substrate</th><th>Conv. (%)<sup>b</sup></th><th>a/b Ratio</th></tr></thead><tbody><tr><td>1</td><td><img src="image_0_0.png" alt="Chemical structure of 4-tert-butylphenol"></td><td>65</td><td>43/57</td></tr><tr><td>2</td><td><img src="image_0_1.png" alt="Chemical structure of 4-fluorophenol"></td><td>40</td><td>79/21</td></tr><tr><td>3<sup>c</sup></td><td><img src="image_0_2.png" alt="Chemical structure of 4-(trifluoromethyl)phenol"></td><td>15</td><td>100/0</td></tr><tr><td>4</td><td><img src="image_0_3.png" alt="Chemical structure of 4-methoxyphenol"></td><td>57</td><td>39/61</td></tr><tr><td>5</td><td><img src="image_0_4.png" alt="Chemical structure of 4-(tert-butylphenyl)phenol"></td><td>42</td><td>48/52</td></tr><tr><td>6</td><td><img src="image_0_5.png" alt="Chemical structure of 4-(tert-butylphenyl)phenol"></td><td>65</td><td>68<sup>d/32</sup></td></tr></tbody></table>

<footnote>ᵃ Reaction conditions: Batch type reactor, 1.0 mmol of acetophenone, 0.5 mmol of dodecane, 4 mL of THF, 0.05 mmol of CoPd (metal-substrate ratio of 1/20, 5.0 mg NPs), 3 bar H₂. AMF 300 kHz, 45 mT. ᵇ Determined by GC-FID using dodecane as IS. ᶜ Conversion and selectivity</footnote>
determined after 12 h of reaction. 6a compound corresponds to the internal alkene instead of the respective alcohol, since the latter was not detected.

Electron donating/withdrawing substituents in aromatic ketones or aldehydes usually affects the reactivity and selectivity of HDO catalysts. To further explore the versatility of these CoPd NPs, we studied the scope of this reaction by changing the *para*-substituent of the phenyl ring in respect to the ketone group. The *para*- substitution would only change the electronic effects, without influencing the steric interactions. In order to observe differences in the reactivity of the substrates, conversion and selectivity were determined after 3 h of reaction (Table 1). While conversion remained largely unchanged across most substrates (ranging from 40 to 65%, Table 1, entries 1-6), except *p*-trifluoromethylacetophenone where its conversion was 15% (Table 1, entry 3), selectivity displayed notable variation. When electron withdrawing substituents were present, the HDO activity was significantly reduced, while electron donating ones either maintained or slightly favored the HDO product. The same trend has been also observed in other typical HDO catalysts under conventional heating conditions. A particularly interesting result was obtained when testing 2-phenylacetophenone (Table 1, entry 6). In this case only the dehydration product (stilbene) and the expected HDO product (6b) were detected. This suggested that after ketone reduction, dehydration of the alcohol intermediate (6a) led to the internal alkene, stilbene, facilitated by extra conjugation with the second phenyl ring, which preceded the formation of the final product 6b.

Reusability of NPs was evaluated through 5 catalytic cycles on **1** HDO at 6 h of reaction. In spite of keeping the same **1** conversion, selectivity to **1b** significantly decreased at the fifth cycle (96 % vs 63 %, Figure S17, SI). XRD pattern depicted no relevant changes in peak positions or width. VSM measurements revealed no significant oxidation since the 5K hysteresis cycle is perfectly centered. A slight decrease in magnetization is observed but can be explained by the weight uncertainty. TEM clearly showed strong NPs agglomeration, directly affecting the coercive field
and as a consequence the catalyst heating power. Therefore, the CoPd NPs were no longer prone
to catalyze correspondingly the last HDO step and stopped at hydrogenation, increasing the **1b**
yield. In order to face this issue, supporting magnetic NPs in carbonaceous materials has been
proven to be effective in improving recyclability in magnetically induced catalysis,²⁰ which will
be also tested in further studies with our CoPd system.

CONCLUSIONS

To conclude, CoPd magnetic NPs were synthesized using organometallic precursors, and their
structural, magnetic, and catalytic properties were thoroughly characterized. Advanced
characterization techniques, including SEM, XRD, WAXS, PDF, (S)TEM and EDX, revealed a
unique bimetallic structure with a Pd-rich CoPd icosahedral (Co<sub>0.3</sub>Pd<sub>0.7</sub>) core surrounded by a
highly disordered Co-rich shell (Co<sub>0.7</sub>Pd<sub>0.3</sub>), occasionally featuring small crystalline overgrowths.
The magnetization profiles displayed a remanence ratio of 0.2, a coercive field of 13 mT at 300 K,
and a SAR value of 157 ± 7 W·g<sup>-1</sup> (47 mT, 93 kHz), indicating remarkable heating efficiency
despite the small size of the NPs. This underscores the critical role of magnetic anisotropy in
enhancing heating capabilities in nano-objects.

The catalytic performance of these CoPd NPs was demonstrated in magnetic induced HDO of
acetophenone derivatives. The presence of Pd on the NPs surface was validated, with induction
heating significantly enhancing both activity and selectivity toward the hydrodeoxygenated
product compared to conventional heating. Furthermore, the NPs showed remarkable tolerance to
aromatic ring substitutions, favoring electron-donating groups. These results highlight the
successful design of a noble/non-noble bimetallic CoPd-based NPs with a desirable balance
between magnetic hyperthermia properties and catalytic activity. This work not only showcases
the potential of CoPd NPs for an energy-efficient magnetically induced catalytic process but also provides valuable insights into the synthesis of NPs optimized for combined magnetic and catalytic applications. This approach opens avenues for the development of multifunctional nanosystems for sustainable and selective chemical transformations.

## ASSOCIATED CONTENT

### Supporting Information

The Supporting Information is available free of charge at:

SEM-EDS spectra and mapping, TGA curve, extra XRD and WAXS/PDF characterization, further TEM, HR-TEM, simulated HR-TEM and STEM-EDX observations, coercive field measurement, ZFC/FC curves, GC-FID example, recycling tests and post-catalysis NPs characterization are included (PDF).

## AUTHOR INFORMATION

### Corresponding Authors

**Edwin A. Baquero** – Estado Sólido y Catálisis Ambiental (ESCA), Departamento de Química, Facultad de Ciencias, Universidad Nacional de Colombia, 111321 Bogotá, Colombia; orcid.org/0000-0002-9621-8914; Email: eabaquerov@unal.edu.co

**Bruno Chaudret** – Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, F-31077 Toulouse Cedex 4, France; orcid.org/0000-0001-9290-6421; Email: chaudret@insa-toulouse.fr
**Lise-Marie Lacroix** – Laboratoire de Physique et Chimie des Nano-Objets, INSA Toulouse, CNRS, UMR 5215, Université Toulouse 3, F-31077 Toulouse Cedex 4, France; Institut Universitaire de France (IUF), 75005 Paris, France; orcid.org/0000-0003-3351-7949; Email: lmlacroi@insa-toulouse.fr

## Authors

**Felipe Quiroga-Suavita** – Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, F-31077 Toulouse Cedex 4, France; School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia; orcid.org/0000-0001-8040-6446

**Víctor Varela-Izquierdo** – Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, F-31077 Toulouse Cedex 4, France; orcid.org/0000-0002-7806-8959

**Teresa Hungría** – Centre de MicroCaractérisation Raimond Castaing, Université de Toulouse, 3 rue Caroline Aigle, F-31400 Toulouse, France

**Damien Alloyeau** – Université Paris Cité, CNRS, Laboratoire Matériaux et Phénomènes Quantiques, 75013 Paris, France; orcid.org/0000-0002-6528-5698

**Nicolas Ratel-Ramond** – Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, F-31077 Toulouse Cedex 4, France; orcid.org/0000-0003-4979-211X

**Simon Cayez** – Université de Toulouse, UMR 5215 INSA, CNRS, UPS, Laboratoire de Physique et Chimie des Nano-Objets, F-31077 Toulouse Cedex 4, France
**AUTHOR CONTRIBUTIONS**

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

**ACKNOWLEDGEMENTS**

The authors want to acknowledge Bénédicte Warot from CEMES for fruitful discussion; Francis Chouzenoux from LPCNO for TGA measurements and general collaboration; Sourav Ghosh for SEM-EDX measurements; Myrtil Kahn and Alexis Aussonne from LCC for FT-IR measurements. The authors gratefully acknowledge the co-funding from the European Union's Horizon Europe research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 101081465 (AUFRANDE), the ERC Advance Grant (MONACAT 2015-694159) and the French National Research Agency (ANR) under the France 2030 framework (BiMAN, ANR-23-PEXD-0005). The authors also acknowledge financial support from the CNRS-CEA "METSA" French network (FR CNRS 3507) on the TEM platform of the MPQ Lab. F. Q.-S. is grateful to the NanoX Graduate School of Research program for his internship at LPCNO in Toulouse EUR (grant NanoX n° ANR-17-EURE-0009 in the framework of the « Programme des Investissements d'Avenir"). V. V.-I. would like to acknowledge the funding from POWERCO2PEPR-Spleen project. E. A. B. is grateful to Universidad Nacional de Colombia for their financial support through projects with HERMES codes 59659 and 56495.
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ABSTRACT GRAPHIC

<figure><img src="image_9.png" /></figure>