# Monolith Catalyst Design by Combining 3D Printing and Atomic Layer Deposition: Toward Green Palladium-Catalyzed Cross-Coupling Reactions

Hippolyte Dory, Eddy Petit, Syreina El-Sayegh, Lucie Badouric, Victoria

Castro, Mikhael Bechelany, Damien Voiry, P. Miele, Luc Lajaunie, Chrystelle

Salameh

► To cite this version:

Hippolyte Dory, Eddy Petit, Syreina El-Sayegh, Lucie Badouric, Victoria Castro, et al. Monolith Catalyst Design by Combining 3D Printing and Atomic Layer Deposition: Toward Green Palladium-Catalyzed Cross-Coupling Reactions. Advanced Engineering Materials, 2024, 27 (2), pp.2401546. 10.1002/adem.202401546. hal-05086499

HAL Id: hal-05086499

https://hal.science/hal-05086499v1

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# Monolith Catalyst Design by Combining 3D Printing and Atomic Layer Deposition: Toward Green Palladium-Catalyzed Cross-Coupling Reactions

Hippolyte Dory, Eddy Petit, Syreina El-Sayegh, Lucie Badouric, Victoria Castro, Mikhael Bechelany, Damien Voiry, Philippe Miele, Luc Lajaunie, and Chrystelle Salameh*

Catalysis plays a major role in various chemical processes including petroleum, pharmaceutical, fine chemistry, and energy. The development of highly functional catalysts is therefore essential. To meet the growing demand for advanced materials, we have developed ceramic catalyst supports known for their chemical inertness and thermal resistance. Using light-assisted 3D printing, we designed complex architectures for ceramic substrates tailored to specific technical requirements. We developed ordered porous silicon oxycarbide (SiOC) ceramic monoliths with an architecture suitable for use as catalyst supports. The active sites are introduced by functionalizing the ceramic surface with palladium (Pd) nanoparticles using Atomic Layer Deposition (ALD). This technique is advantageous for achieving highly dispersed nanoparticles with uniform size distribution and minimal aggregation. We evaluated the catalytic performance by studying the effect of Pd loading on a Suzuki–Miyaura coupling reaction in water, as well as the reusability of the 3D-printed catalytic monolith. The system demonstrates up to 82% yield and exhibits excellent stability, with no leaching of the active phase observed during the reaction cycles. These results underline the potential of 3D-printed SiOC monoliths to create highly efficient and reusable catalytic systems, paving the way for advanced applications in a variety of industrial sectors.

## 1. Introduction

Heterogeneous catalysis plays an essential role in various industrial sectors, such as petroleum, petrochemicals, fine chemicals, and energy conversion. In these processes, catalysts are typically used in fixed-bed reactors, often in the form of powders or small pellets compacted together to form the catalytically

active zone. Although powdered or pelleted catalysts offer a high specific surface area (SSA), they have disadvantages, including high-pressure drop, limited recyclability, and handling difficulties. Additionally, replacing these catalysts can entail significant maintenance costs and effort.[1] An alternative to traditional powders or granules is the use of monolithic catalysts, which offer several advantages due to their highly hierarchical pore structure (micro-, meso-, and macropores) providing abundant active sites. Homogeneous mass, flow, and heat transfer will significantly enhance their efficiency.[1–3] Monolithic catalysts can be fabricated from either inorganic, organic, or hybrid materials.[4–13] Organic materials offer limited thermal and chemical stability and are therefore primarily used in soft chemistry processes. The substrates are typically fabricated using various techniques such as molding, firing, electrospinning, foaming, hydrothermal synthesis, and sol-gel chemistry. Ceramic supports are used to withstand harsh conditions and are commonly found in highly reactive powdered catalysts (nanoparticles and pellets). However, their handling and removal from the reaction medium are not suitable for industrial applications. Although highly porous monolithic materials exist, their 3D structures are typically limited to the molding or postprocessing of the ceramic. Additive manufacturing (AM) offers a straightforward method for shaping ceramic

H. Dory, E. Petit, S. El-Sayegh, L. Badouric, M. Bechelany, D. Voiry, P. Miele, C. Salameh
Institut Européen des Membranes, IEM, UMR 5635
Univ Montpellier, ENSCM, CNRS
34095 Montpellier, France
E-mail: chrystelle.salameh@enscm.fr

<figure><img src="image_3.png" /></figure>

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adem.202401546.

© 2024 The Author(s). Advanced Engineering Materials published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

DOI: 10.1002/adem.202401546

V. Castro, M. Bechelany
Functional Materials Group
Gulf University for Science and Technology (GUST)
Mubarak Al-Abdullah 32093, Kuwait

L. Lajaunie
Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias Universidad de Cádiz 11510 Cádiz, Spain
catalytic supports, enabling the creation of complex, on-demand
shapes that are unattainable through conventional
methods.[14–16] These advanced structures are crucial for efficient
processes and high-yield chemical reactions.[17–19] Additive
manufacturing, commonly known as 3D printing, of ceramics
enables the fabrication of highly complex and intricate 3D struc-
tures with hierarchical porosities (macro-, meso-, micro-, and
nanoporosity). This process is based on computer-aided design
(CAD), which involves designing 3D complex structures on a
computer and then printing them with a dedicated printer.
Ceramic additive manufacturing typically relies on the layer-
by-layer deposition of ceramic powder dispersions (e.g., Al₂O₃,
SiO₂) in organic polymers. However, a significant drawback is
the low stability of the suspension, which can lead to sedimenta-
tion and inhomogeneity during the photopolymerization-based
3D printing process.[20] This will have a negative effect on the
physical integrity of the fabricated object. In addition, it hinders
the reproducibility of 3D objects. This is why the use of other
ceramic routes has been widely studied to obtain reproducible,
robust, and defect-free objects. The polymer-derived-ceramic
(PDC) route is a viable alternative for the manufacture of func-
tional ceramic shapes. In this method, ceramics are obtained
through high-temperature pyrolysis of silicon-based polymer
precursors containing heteroatoms such as carbon, oxygen,
nitrogen, boron, or aluminum. The chemical composition of
the final ceramic depends on the initial atomic chemistry of
the precursors. PDCs cover a large scope of ceramics, from
binary[21,22] to quaternary systems[23–25] through ternary
systems.[26,27] For example, SiBCN and SiAlCN ceramics were
successfully fabricated by the simple chemical modification of
a vinyl-polysilazane backbone with borane dimethylsulfide
(BDMS) and alane N,N-dimethylethylamine respectively.[23,28,29]
The facile chemical modification of PDCs makes their process-
ing easier compared to ceramic powders. As a result, the PDC
route is often used to synthesize suitable precursors for AM.
These precursors can be tailored to be either photoactive or ther-
moplastic, depending on the desired AM process.[30–36] Indeed,
AM of polymer precursors is mainly divided between fused depo-
sition modeling (FDM—fusion of thermoplastic polymers), and
stereolithography (UV polymerization of photoactive polymers).
The higher resolution of UV-based AM techniques compared to
FDM makes it a preferable choice for fabricating complex 3D
shapes for various applications, including catalysis. Finally,
owing to the surface state of most oxide ceramics featuring
hydroxyl groups, it is easy to functionalize 3D-printed ceramic
parts to impart catalytic activity to the monolith.[37–39] Loading
catalytically active components can be achieved through various
techniques. Typically, catalyst immobilization relies on intramo-
lecular interactions between the support and the catalyst. Three
types of interaction have been identified: covalent, noncovalent,
and encapsulation.[40] Covalent bonding involves attaching the
catalyst to the surface (sol-gel processes, wet impregnation,
coprecipitation, organometallic surface chemistry, or self-
assembly). This is facilitated by the presence of surface function-
alities such as silanols, amino groups, and carboxylic acids.
Noncovalent interactions, on the other hand, rely mainly on
the physisorption of the catalyst, where it adheres to the surface
of the support through van der Waals forces or hydrogen bond-
ing. Encapsulation differs from both covalent and noncovalent

interactions, involving the physical entrapment of the catalyst
within the cavities and pores of the support material. Under
harsh conditions, leaching of metal complexes can occur, espe-
cially when the active component is weakly bound to the surface,
which can significantly reduce catalyst performance. To address
this issue, alternative techniques have been developed to enhance
catalyst stability. These vapor-based methods typically involve two
key steps: the deposition of metallic precursors onto the support,
followed by a reduction step to form stable metallic particles.
These techniques are known as chemical vapor deposition,
which include atomic layer deposition (ALD), metalorganic
chemical vapor deposition (MOCVD), and plasma-enhanced
vapor deposition (PECVD). ALD is a process that involves
sequential pulses of gaseous precursors, each reacting one at
a time on the substrate surface in a self-limited manner. Each
ALD cycle follows a multistep procedure. First, a pulse of the
metal precursor reacts with the active sites on the substrate dur-
ing the exposure time. The self-limiting nature of this reaction is
crucial for achieving atomically precise films. Following this, a
purge step evacuates any unreacted precursors. Then, the coreac-
tant is introduced to reduce the metal, and a final purge removes
any excess precursors and reaction byproducts from the reactor.
These cycles are repeated until the desired particle distribution
and thickness are achieved. ALD has enabled the synthesis of a
wide range of materials, including oxides,[41] nitrides,[42–45]
sulfides,[46,47] fluorides,[48] metals,[49–51] and carbides.[52–56] The
versatility is largely due to the wide range of precursors that
can be used during the ALD process. The precursors must meet
three main criteria: high reactivity, volatility within the deposi-
tion temperature range, and thermal stability. Additionally, the
precursors should react rapidly with the substrate and with each
other without emitting reactive by-products. Beyond continuous
thin films, ALD also enables the preparation of highly dispersed
nanoparticles. This capability is attracting considerable attention
in the field of catalysis, as it allows for the design of nanosized
catalysts with precise control over their dimensions, distribution,
and composition. For example, the synthesis of highly dispersed
Pd nanoparticles by ALD on TiO₂-BN composites was
reported.[57] In addition, non-noble metals can be deposited as
nanoparticles. Ni can be deposited from bis(cyclopentadienyl)
nickel (Ni Cp₂) precursors under an H₂ atmosphere.[58] Cu nano-
particles and thin films can be synthesized from amidinate cop-
per complexes on silicon surfaces using ALD and CVD.[59] To
obtain highly reactive catalysts from ALD, noble metals are inter-
esting as being highly resistant to oxidation and corrosion, even
at high temperatures. Moreover, known for their catalytic prop-
erties, noble metals readily accelerate or control the rate of many
chemical reactions. However, the scarcity of noble metals must
be considered when designing new catalysts. ALD offers a solu-
tion in terms of atom economy, enabling the efficient deposition
of noble metals. Palladium, in particular, exhibits outstanding
performance in fields such as catalysis, hydrogen storage, and
photonics. Through ALD, palladium can be deposited either
as a continuous thin film or as dispersed nanoparticles, optimiz-
ing its use and enhancing its effectiveness in various technologi-
cal applications.[47,60,61] The production of many chemicals relies
on the C–C cross coupling of two organic moieties with the aid of
palladium. These reactions are primarily conducted with homo-
geneous catalysts to maximize the number of active sites.
However, the use of palladium in the pharmaceutical industry can be problematic due to residual metal contamination from coupling reactions.[62] To address this, heterogeneous catalysts based on supported palladium are essential. They not only minimize residual metal contamination but also enhance atom economy, making the process more efficient and cost-effective. The simplest heterogeneous Pd-based catalyst is Pd/C, which can be easily filtered at the end of the reaction.[63] Other studies have explored the use of various substrates to immobilize Pd(II) complexes or Pd(0) nanoparticles, enhancing their stability and reusability in catalytic applications.[64,65]

In this study, we designed highly stable 3D-printed SiOC monoliths and subsequently modified their surfaces through successive ALD cycles of Pd nanoparticles. The resulting catalysts were tested using a model Suzuki–Miyaura C–C cross-coupling reaction to evaluate their catalytic performance and recyclability.

## 2. Experimental Section

Methyl-silsesquioxane resin powder (SILRES MK, Wacker-Chemie GmbH) was used as a precursor of silicon oxycarbide ceramics (SiOC). 1,6-Hexanediolacrylate (HDDA, CAS: 13048-33-4, Sigma–Aldrich) was used as a photoactive monomer for photopolymerization-based 3D printing. Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO, CAS: 75980-60-8, Sigma–Aldrich) acted as the polymerization photoinitiator under UV light at 365–405 nm. To ensure controlled photopolymerization, Genorad 16 (Rahn AG) was used as a radical polymerization inhibitor. Dowanol tripropylene glycol monomethyl ether (TPM, CAS: 25498-49-1, Sigma–Aldrich) served as the solvent. For the ALD process, palladium hexafluoroacetylctonate (Pd(hfac)₂, CAS: 64916-48-9, Strem Chemicals) and formalin solution (HCHO, CAS: 50-00-0, Thermo Fischer) were employed. All chemicals were used as received without further purification. The pyrolysis was conducted in a tubular furnace under a flow of argon (Ar (5.0) 99.999%, Linde).

### 2.1. 3D Printing of the Ceramic Support

First, a resin was prepared by blending the preceramic polymer SILRES MK with the photocurable monomer HDDA in a 1:1 weight ratio, here 1 g of SILRES MK and 1 g of HDDA. Dowanol TPM was used as the solvent (1 g). To facilitate photopolymerization, 3 wt% of TPO powder was added. Additionally, a drop of Genorad 16 was included to prevent edge effects during 3D printing.

3D printing of the preceramic polymers was performed using a Phrozen Sonic 4 K printer (Phrozen, Taiwan) according to UV liquid crystal device (LCD) technology. The UV light source was provided by a 405 nm 4 K UV-LCD screen with a light intensity of 2.5 mW cm⁻². The printer offers a *xy*-axis resolution of 35 µm. The layer thickness (*z*-axis resolution) was set to 0.05 mm using a 3D computer-assisted design (CAD) system. Grid-shaped objects were printed in 45 min. Post-treatment of all printed objects involved a 120 min session in a UV curing chamber to ensure complete photopolymer conversion (Table 1).

<table><caption>Table 1. UV-LCD printing parameters.</caption><thead><tr><td>Parameter</td><td>Value</td><td>Unit</td></tr></thead><tbody><tr><td>Layer thickness</td><td>0.05</td><td>mm</td></tr><tr><td>Number of base layers</td><td>4</td><td>–</td></tr><tr><td>Illumination time of base layers</td><td>60</td><td>s</td></tr><tr><td>Illumination time of regular layers</td><td>10</td><td>s</td></tr></tbody></table>

### 2.2. Polymer-to-Ceramic Transformation

The polymer-to-ceramic transformation was carried out through high-temperature treatment of the hybrid 3D-printed green body in a tubular furnace (type ROS20/250/12 with a quartz tube, Thermconcept, Germany) under an argon flow of 150 mL min⁻¹. The pyrolysis profile, created on the basis of thermogravimetric analysis (TGA) of the green body, comprised three stages: first, initial heating, where the samples were heated to 200 °C at a rate of 1 °C min⁻¹ (hold time 2 h). Then, there was an intermediate heating stage where the temperature was raised to 400 °C at a rate of 1 °C min⁻¹ (hold time: 2 h). Lastly, there was final heating, where the samples were heated to 1000 °C at a rate of 1 °C min⁻¹ (hold time: 2 h). This controlled heating rate of 1 °C min⁻¹ was chosen to minimize crack formation and ensure the complete conversion of precursors to ceramics.

### 2.3. Atomic Layer Deposition

ALD of Pd nanoparticles (NPs) was carried out in a low-pressure hot-wall reactor (homemade), as described in previous work,[57] using Pd(hfac)₂ and formalin solution. Highly dispersed Pd NPs were synthesized by applying 50, 100, and 300 ALD cycles. The bubbler containing the Pd(hfac)₂ precursor was heated to 70 °C, while the formalin container was kept at room temperature. The deposition chamber was maintained at 220 °C, and the lines in the ALD system were heated to 80 °C to prevent condensation. A typical ALD cycle involves the sequential pulse, exposure, and purge of the Pd precursor and formalin, alternately. The pulse, exposure, and purge durations were 5:15:10 s and 1:15:60 s for Pd(hfac)₂ and formalin, respectively.

### 2.4. Characterizations

TGA of all polymers was performed using a TGA-SDT Q600 thermal analysis device (TA Instruments, USA) at atmospheric pressure. The heating rate was set to 5 °C min⁻¹, reaching up to 1000 °C under an inert atmosphere (N₂). The chemical structure of the preceramic polymers was determined by Fourier-transform infrared (FTIR) spectroscopy with a Nexus spectrometer (ThermoFisher Scientific, USA) using attenuated total reflection (ATR) mode in the range of 500–4000 cm⁻¹. The morphology of pyrolyzed 3D structures was observed using a super depth field 3D optical microscope (VHX-7000, KEYENCE, Japan) and scanning electron microscopy (SEM) (Hitachi S4800, Hitachi High-Tech Corporation, Japan) operating at an acceleration voltage of 2 kV. The chemical composition of SiOC 3D ceramics was analyzed with energy-dispersive X-Ray
spectroscopy (EDX) using an Oxford Instruments X-Max AZTEC
detector (UK) and a Zeiss EVO HD15 Microscope (Germany).
X-Ray photoelectron spectroscopy (XPS) was used to determine
the oxidation state of the elements and bond formation during
ALD and the polymer-to-ceramic transformation (ESCALAB
250 Thermo Electron, excitation source Al Kα (1486.6 eV)).
Scanning transmission electron microscopy (STEM) was used
to observe and characterize the dispersion and morphology of
the Pd nanoparticles. Lamellas for transmission electron micros-
copy (TEM) were obtained by means of the focused ion beam
(FIB) technique inside an SEM Double Beam Scios 2 from
Thermo Fisher Scientific, equipped with two Ga⁺ ion beams.
To extract the lamellas from the bulk material, the device was
operated at an acceleration voltage of 30 kV and a current of
5 nA. Later on, a more refined step-by-step thinning procedure
has been carried out, starting at 30 kV and 1 nA and decreasing
both parameters (acceleration voltage and current) in each sub-
sequent step till reaching 8 kV and 12 pA. A final cleaning of the
surface was performed at low current (≈50 pA) and high angles.
It is worth pointing out that before first extracting the lamella, the
surface is masked with a Pt layer. As it was observed in the 50 and
300 ALD-cycled specimens, some Pt nanoparticles are redepos-
ited later over the lamella, and they might be confused with the
Pd nanoparticles inside the specimen. For this reason, the
remaining sample (100 cycles) was prepared using C instead
of Pt. The FIB Scios2 microscope is also equipped with a
high-angle annular dark-field detector (HAADF) that can be oper-
ated in STEM mode. In addition, high-resolution STEM analyses
(HR-STEM) were carried out by using an FEI Talos F200X TEM
(Thermo Fisher Scientific) operated at 200 kV. It is equipped with
a high-brightness field emission gun (X-FEG) and a high-
sensitivity dispersive X-Ray spectroscopy detection system
(EDX) integrating four silicon drift detectors around the sample,
which have a symmetric design and are windowless and shutter-
protected. The samples were analyzed in scanning mode (STEM)
and with a HAADF for imaging. EDX quantification was per-
formed using the Velox software. The ¹H-NMR spectra were
recorded at 298 K on a Bruker AVANCE III 500 NMR spectrome-
ter equipped with a 5 mm ¹H/X BBO cryoprobe Helium. All
the data were processed with Bruker Topspin 3.6.2 software.
The structure and purity of the synthesized compounds were con-
firmed by gas chromatography (Trace 1300, Thermo Scientific)
hyphenated to a mass spectrometer (ISQ 7000, Thermo
Scientific). The electronic impact source was operated at 70 eV.
Analyses required a DB-5MS Plot capillary column (30 m ×
0.25 mm ID Agilent) and helium at 1.2 mL min⁻¹ as the carrier
gas. One µL with a split of 50 was injected for each sample. The
quantification method consisted of a prior 90 °C heating step
followed by two successive temperature gradients: 10 °C min⁻¹
up to 150 °C (hold time 3 min) and 20 °C min⁻¹ up to 200 °C
(hold time 10 min). A mass spectrometry scan was recorded in
a range of m/z = 50 to 350 with a dwell time of 100 ms.

**2.5. Catalytic Test: 4-Phenylphenol Synthesis by**
**Suzuki–Miyaura Coupling**

In a 20 mL flask, phenylboronic acid (122 mg, 1 mmol), 4-iodophenol (220 mg, 1 mmol) and K₂CO₃ (415 mg, 3 mmol) were dissolved

in deionized water (10 mL). A lab-made system was used to
immerse the 3D catalyst in the reaction medium (Figure S1,
Supporting Information). Teflon tape was used as a thread to
secure the 3D catalyst, which was then fixed at the end of the
thread. The thread was attached to the top of the condenser,
and the reaction was carried out under reflux for 1, 3, and
24 h, respectively. After the designated reaction time, the oil bath
was removed, and the reaction mixture was allowed to cool to
room temperature. Upon cooling, a white precipitate formed.
The product was recovered by vacuum filtration and drying
the precipitate at 80 °C for 12 h to remove residual water.
According to GC-MS analysis, the obtained compound was pure.
After the reaction, the catalyst was washed with acetone and
deionized water to remove any residual product and unreacted
reagents. The synthesized product was characterized using
¹H NMR and GC-MS. The ¹H NMR spectra (400 MHz CDCl₃
δ 7.26 ppm) are as follows: SiOC-Pd50: 7.55–7.53 (d, 2 H),
7.49–7.47 (d, 2 H), 7.43–7.39 (t, 2 H), 7.32–7.28 (t, 2 H),
6.91–6.89 (d, 2 H), 4.77 (s, 1 H); SiOC-Pd100: 7.55–7.53
(d, 2 H), 7.49–7.47 (d, 2 H), 7.43–7.39 (t, 2 H), 7.32–7.28
(t, 2 H), 6.91–6.89 (d, 2 H), 4.8 (s, 1 H); 7.55–7.53 (d, 2 H),
7.49–7.47 (d, 2 H), 7.43–7.39 (t, 2 H), 7.32–7.28 (t, 2 H),
6.91–6.89 (d, 2 H), 4.77 (s, 1 H).

**3. Results and Discussions**

**3.1. 3D Printing of Light Curable Preceramic Polymer**

First, a support structure was printed following the procedure
described in[32] to fabricate a 3D-printed support with high
roughness and macroporosity. Silres MK, a polysilsesquioxane
preceramic polymer, was blended with a light-curable monomer,
HDDA, and a photoinitiator TPO. FTIR, as shown in Figure S2,
Supporting Information, was used to assess the printability of the
preceramic resin by following the evolution of the vinyl C=C
bond intensity. Upon UV irradiation, the photoinitiator under-
goes radical cleavage, generating radicals that react with the vinyl
(C=C) groups of the light-curable monomer, thereby promoting
radical photopolymerization. The decrease in the intensity of the
C=C stretching band at 1636 cm⁻¹, ultimately disappearing,
confirms that our preceramic blend is photocurable and suitable
for use in 3D printing (UV-LCD) processes. Consequently, the
preceramic polymer Silres MK becomes homogeneously encap-
sulated in the cured HDDA network, forming an inorganic/
organic hybrid green body. After 3D printing, the composite
was post-treated under UV light for 2 h to achieve a fully
cross-linked structure.

**3.2. Polymer-to-Ceramic Transformation**

The transformation of the 3D-printed support from polymer to
ceramic was carried out by placing the objects into an alumina
crucible for pyrolysis under an Ar flow in a tubular furnace. The
thermal treatment program was defined using TGA to predict the
system's behavior at high temperatures, as shown in Figure S2,
Supporting Information. Three main weight loss stages were
observed: from 25 to 200 °C, 200 to 400 °C, and 400 to
1000 °C. Each stage corresponds to the release of gaseous or
volatile compounds from the organic components of the hybrid
system. The initial weight loss between 25 and 200 °C is associ-
ated with the evaporation of surface-adsorbed water and the sol-
vent. The second weight loss, occurring between 200 and 400 °C,
is due to the degradation of the organic moieties in the system
(Silres MK, HDDA, TPO). Finally, the third weight loss, occur-
ring between 400 and 1000 °C, is linked to the release of hydro-
gen and methane gases during the ceramization process,
resulting in silicon oxycarbide (SiOC). This process yields a black
object that retains the preceramized green body. The resulting
material is a silicon oxycarbide ceramic, referred to as SiOC.

**3.3. Characterization of 3D-Printed SiOC Ceramics**

In the first step, the ceramic support was fabricated using
UV-LCD 3D printing of a photocurable inorganic-organic
mixture composed of Silres MK and HDDA. This process
produced a macroporous monolith with pores ranging from
300 to 400 µm, consistent with the 3D CAD model. Figure S3,
Supporting Information shows the SEM image of the 3D-printed
object after pyrolysis. The image reveals a rough, porous surface
with random size pores. Those pores are formed throughout the
pyrolysis process and emanate from the thermal decomposition
of the organic moieties.

3.4. Characterization of Surface Functionalized 3D-Printed SiOC
Ceramics by Atomic Layer Deposition of Palladium
Nanoparticles

ALD was used to functionalize the surface of the 3D-printed
SiOC monoliths with Pd nanoparticles to create catalytically
active sites. The ALD process was carried out as described in
the Experimental Section. The samples were designated as
SiOC-Pd50, SiOC-Pd100, and SiOC-Pd300, corresponding to
50, 100, and 300 ALD cycles, respectively. Each sample was char-
acterized using multiple techniques, including SEM, EDX, XPS,
X-Ray diffraction (XRD), STEM, and HAADF imaging.

3.4.1. Low-Magnification Energy-Dispersive X-Ray and Scanning Electron Microscopy

To confirm the presence of Pd nanoparticles on the surface and the success of ALD deposition, EDX analysis was conducted. As shown in **Figure 1**, Pd is homogeneously dispersed on the surface of SiOC-Pd300. A similar homogeneous distribution is observed on SiOC-Pd50 and SiOC-Pd100, as shown in Figure S4 and S5, Supporting Information, respectively. The increasing distribution of Pd corresponds to the increase in the number of ALD cycles. However, using EDX and SEM, we could not determine precisely the particle size and their distribution.

**3.4.2. Scanning-Transmission Electron Microscopy Analyses**

To observe the microstructure and the distributions of the Pd
nanoparticles, the samples were prepared by FIB and studied
in STEM-HAADF mode, which provides high contrast between
the ceramic support and the Pd nanoparticles. The latter are, in
this case, highlighted due to their higher density compared to the
substrate (Z contrast). This type of image can clearly display how
particles distribute around the pores of the fabricated ceramic. As
shown in **Figure 2a**, Pd nanoparticles are homogeneously distrib-
uted inside the pores of the ceramic. The elemental EDX-STEM
mapping also validates the composition of the ceramic, showing
the presence of Si, O, and C. Additionally, the dense ceramic
walls are free of metallic nanoparticles, indicating a clear distri-
bution of Pd particles throughout the entire ceramic body, as
seen in the HAADF-STEM images (Figure 2a). The nanoparticles
exhibit a hexagonal shape, as observed in the HR-(S)TEM images
(Figure 2c and Figure S7c and S8c, Supporting Information),
and belong to the crystalline Pd cubic phase (Fm-3 m,
*a* = 0.3891 nm). For the SiOC-Pd300 system, the peak of the
distribution is located between 7.5 and 10.5 nm. In contrast,
the SiOC-Pd50 system shows a bimodal distribution, displaying
its first peak between 7.5 and 14.7 nm and the second one
between 29.1 and 36.3 nm (Figure S6, Supporting Information).
Using an intermediate number of ALD cycles results in a

<figure><img src="image_4.png" /><figcaption>**Figure 1.** (1st on the left) Macroscopic image of SiOC-Pd300; low-magnification SEM/EDX images of SiOC-Pd300 with elemental mapping.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Figure 2.** SiOC-Pd300: a) HAADF-STEM images showing the Pd nanoparticle distribution onto the ceramic, b) EDX-STEM elemental mapping, and c) HR-STEM detail of a Pd nanoparticle.</figcaption></figure>

monomodal distribution of Pd NPs, although these particles are larger (19.8–25 nm) than those obtained after 300 cycles of ALD. Moreover, FIB-SEM images reveal that the ALD precursors penetrate deeper within the SiOC-Pd300 than in the SiOC-Pd50, indicating a higher loading of palladium in the ceramic. The bimodal distribution observed in SiOC-Pd50 suggests that the ceramic support's surface state differentiates into two different nucleation sites, leading to the growth of nanoparticles of different sizes. In Figure S7, Supporting Information, we observe a higher number of 30–50 nm particles in SiOC-Pd50 compared to SiOC-Pd300. In SiOC-Pd300, there are fewer large nanoparticles (over 30 nm) and a greater number of smaller NPs (around 10–15 nm), indicating the presence of multiple nucleation sites on the SiOC surface. In Figure S8, Supporting Information, the SiOC-Pd100 sample shows similar trends, with few Pd particles exceeding 30 nm and smaller NPs than those observed after 50 cycles. However, the particles are larger than those formed after 300 cycles. This suggests that increasing the number of ALD cycles limits the growth of larger nanoparticles and promotes the formation of smaller ones, leading to a higher density of Pd particles. This higher density is evidenced in Figure S9, Supporting Information, and the penetration depth of ALD precursors is higher in SiOC-Pd300 compared to SiOC-Pd50. In SiOC-Pd50, Pd nanoparticles are localized within 700 to 2000 nm from the surface, whereas in SiOC-Pd300, Pd nanoparticles are distributed throughout the entire width of the material. This confirms that 50 ALD cycles promote the growth of particles near the surface, while 300 cycles enable deeper deposition.

### 3.4.3. X-Ray Diffraction

XRD analysis was conducted to detect palladium nanoparticles immobilized on the surface of the SiOC ceramic.

The results first confirmed the amorphous nature of the ceramic support. Additionally, the presence of palladium NPs on the surface was clearly detected.

The diffraction patterns, shown in **Figure 3**, can serve as a basis for estimating the particle size of Pd, allowing for a comparison with the size observed through STEM analysis. The particle size extracted from the diffraction was calculated using the Scherrer equation.

Scherrer equation for the crystallite size estimation is shown in Equation (1).

$$D = K\lambda/(\beta_{\text{obs}} - \beta_{\text{instr}}) \cos(\theta) \quad (1)$$

With:

$D$ = crystallite size (nm)

$\lambda$ = wavelength of the radiation (nm)

$K$ = Scherrer constant: fixed at 0.94

$\beta_{\text{obs}}$ = observed full width at half maximum (FWHM) (radian)

$\beta_{\text{instrm}}$ = instrumental broadening (radian)

$\theta$ = diffraction peak position/2 (radian)

The calculated diameters of palladium nanoparticles for each system are summarized in **Table 2**. By comparing these results with the size measured in STEM images, it becomes evident that only for the system with 300 cycles of ALD does the estimation prove itself accurate. In contrast, for the other two samples, the calculated particle sizes are considerably smaller than those measured using TEM images. This highlights the limitations of the Scherrer equation, which is subject to various approximations that can lead to errors. Thus, STEM emerges as the most accurate method for determining particle sizes.
<figure><img src="image_6.png" /><figcaption>**Figure 3.** XRD patterns of a) SiOC-Pd50, b) SiOC-Pd100, and c) SiOC-Pd300.</figcaption></figure>

<table><caption>**Table 2.** Supported particle size is calculated by the Scherrer equation.</caption><thead><tr><td>Sample</td><td>D [nm]</td></tr></thead><tbody><tr><td>SiOC-Pd50</td><td>11</td></tr><tr><td>SiOC-Pd100</td><td>9</td></tr><tr><td>SiOC-Pd300</td><td>11</td></tr></tbody></table>

### 3.5. Fourier-Transform Infrared Spectroscopy, ALD Mechanism, X-Ray Photoelectron Spectroscopy, and N₂ Absorption (Calculation of the Specific Surface Area with Brunauer-Emmett-Teller (BET) Method)

FTIR was used to identify the presence of silanol groups on the surface of the silicon oxycarbide. Indeed, silicon oxycarbide when pyrolyzed at 1000 °C is not chemically homogeneous, it comprises regions rich in SiO₂, graphitic carbon, or silicon oxycarbide.[66]

To gain insights into the chemical bonds between atoms in both the unmodified and modified ceramics, XPS analysis was carried out. Figure S11–S13, Supporting Information provide evidence of Si–O bonds, as indicated by peaks observed in the XPS analysis of Si 2p. Oxygen XPS analysis confirms the presence of Si–O bonds in the ceramic. This aligns with the

FTIR analysis of the ceramic, where the strong absorption band around 1000 cm⁻¹ corresponds to Si–O–Si bonds in SiOC. Furthermore, C 1s XPS spectra reveal the presence of graphitic carbon regions and oxycarbide carbon, affirming the multicomponent nature of SiOC.[67] As observed in **Figure 4**, the silicon oxycarbide support exhibits a characteristic band between 3000 and 3800 cm⁻¹, which can be attributed to Si-OH groups. These key groups are pivotal for the surface functionalization of the ceramic through ALD. The proposed mechanism of ALD, as illustrated in Figure 4, involves several steps. First, the Pd(hfac)₂ precursor is adsorbed onto the ceramic surface. In the second step, it reacts with surface silanol groups, forming Si–O–Pd(hfac) on the surface and releasing H-hfac gas. Subsequently, the surface is exposed to formaldehyde, which acts as a reducing agent, leading to the reduction of Si–O–Pd(hfac). This results in the formation of a Pd-Hx termination at the active site, with the release of H-hfac, CO, and H₂ during the final step. In each cycle, Pd(hfac)₂ reacts with the H-terminated Pd surface, releasing H-hfac. In the following pulse, formalin reacts with the hfac-terminated Pd surface, decomposing into H₂ and CO. The resulting atomic H then reacts with the Pd–hfac species, removing the remaining hfac ligands from the surface and regenerating the H-terminated surface for the next Pd(hfac)₂ pulse.[68]

XPS analysis of Pd 3 d, in **Figure 5**, was carried out to validate the reaction between surface hydroxyl and the precursor involved

<figure><img src="image_7.png" /><figcaption>**Figure 4.** a) FTIR analysis of the 3D-printed SiOC monolith and b) Proposed ALD mechanism on the surface of a SiOC ceramic.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Figure 5.** Pd 3d XPS spectra of a) SiOC-Pd50, b) SiOC-Pd100, and c) SiOC-Pd300 before Suzuki–Miyaura coupling.</figcaption></figure>

in the ALD process of Pd, as described in Figure 4. SiOC-Pd50 analysis provides evidence of Pd nanoparticles covalently bound to surface silanol groups, with peaks observed at 336 and 342 eV corresponding to Pd–O bonds. Similarly, the Pd 3d spectrum of SiOC-Pd100 exhibits Pd–O bonds at 340.50 and 334.56 eV. In addition, in the SiOC-Pd300 sample, binding energies of 335.48 and 340.22 eV were measured, corresponding to the Pd–O bond.[57]

Finally, to evaluate the SSA and porosity, each sample underwent nitrogen absorption analysis. Subsequently, the BET method was used to calculate the SSA of the catalysts. As illustrated in Figure S14, Supporting Information, each sample exhibits a type IV isotherm. BET calculations yielded SSA values of 21, 19, and 17 m² g⁻¹ for SiOC-Pd50, SiOC-Pd100, and SiOC-Pd300, respectively. While these SSA values are considered low, they could be improved by tuning the experimental parameters.

**3.6. Catalytic Testing: The Model Synthesis of**
**4-Hydroxybiphenyl Through Suzuki–Miyaura Carbon-Carbon**
**Cross Coupling**

The catalytic activity of the fabricated supported Pd on SiOC was tested using a simple Suzuki–Miyaura carbon–carbon cross coupling. According to the catalytic cycle theorized by Suzuki, we use an aryl halide, 4-iodophenol, phenylboronic acid, and a base, K₂CO₃. To emphasize the role of Pd as the active site, a control experiment was conducted using the unmodified SiOC support. As expected, the 3D SiOC support showed no catalytic activity for the C–C coupling reaction. This observation aligns with the Suzuki–Miyaura catalytic cycle, which requires Pd for catalytic activity. First, we know that, based on the XPS analysis, the palladium immobilized on the support is metallic (Pd(0)) and is not oxidized. Consequently, in the catalytic cycle, unlike homogeneous catalysts, there will be no need for a reduction step from Pd(II) to Pd(0) to obtain the active phase. The first step will be the oxidative addition of the 4-iodophenol onto the Pd nanoparticles, forming I-Pd(II)-phenol at the surface of the palladium nanoparticles. Then, a transmetallation with phenylboronic acid takes place to form I-B(OH)₂ as the byproduct and phenyl-Pd(II)-phenol. Finally, a reductive elimination of both the phenol

and phenyl moieties takes place to form the final product, 4-phenylphenol.[69] Palladium will then be reduced to Pd(0) during this final step, as evidenced by the XPS analysis of the catalyst after coupling.

The postreaction product was recovered by vacuum filtration to remove solvents and dissolved impurities. The product was washed multiple times with DI water and obtained as a crystal-line, flaky cream-white powder. The product was then analyzed by FTIR, proton nuclear magnetic resonance (¹H-NMR), and gas chromatography coupled with mass spectrometry (GC-MS). FTIR spectra show that the product obtained is similar to the commercial 4-phenylphenol. The intense, broadband between 3200 and 3500 cm⁻¹ can be associated with the hydroxyl group of 4-phenylphenol. The sharp band around 3000 cm⁻¹ can be associated with the compound’s aromatic C–H stretching band. In addition to infrared analysis, ¹H-NMR was conducted. As the spectra show (Figure 7), we conducted the analysis on each product related to each catalytic system (SiOC-Pd50, SiOC-Pd100, and SiOC-Pd300) and on pure commercial 4-phenylphenol. It is clear that the synthesized compounds correspond to the ¹H-NMR spectrum of the commercial product. Finally, for full characterization, we performed GC-MS. In Figure 6, the mass spectrum shows that, when comparing the commercially available compound with our products, each SiOC-Pd catalyst produces pure 4-phenylphenol. The m/z peak of the compound is at m/z = 171.

**Figure 7** shows the comparison of reaction yields across different catalytic systems. In graph (a), the evolution of reaction yield is shown as a function of the number of 1 h reaction cycles, while graph (b) depicts the yield of 3 h reaction cycles. Both graphs compare the yields of Suzuki–Miyaura reactions catalyzed by SiOC-Pd50, SiOC-Pd100, and SiOC-Pd300. For the 1 h reaction cycles, the SiOC-Pd300 catalyst demonstrated the highest efficiency with a yield of 83%, followed by SiOC-Pd100 at 73% and SiOC-Pd50 at 67%. In the 3 h reaction cycles, each catalyst was similarly tested for its performance. The catalyst performance for SiOC-Pd300 in 1 h reactions remains high, with a yield of 73%. In contrast, SiOC-Pd100 and SiOC-Pd50 exhibit even greater activity, achieving yields of 77% and 72%, respectively. Figure 7a also indicates a rapid decline in yield as the number of 1 h reaction cycles increases for each catalyst. Conversely, as shown in Figure 7b, the yield for 3 h reaction cycles decreases less significantly over 8 reaction cycles. Therefore, the catalysts
<figure><img src="image_9.png" /><figcaption>**Figure 6.** a) Infrared spectrum, b) ¹H-NMR spectrum, and c) Mass spectrum of products obtained with SiOC-Pd50, SiOC-Pd100, and SiOC-Pd300 and commercially available 4-phenylphenol.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Figure 7.** Yield evolution for a) 1 h reaction cycles and b) 3 h reaction cycles.</figcaption></figure>

exhibit greater stability during 3 h reactions compared to 1 h reactions.

Additionally, the number of ALD cycles was increased to evaluate how the catalyst's activity evolved with higher Pd loading. As noted in the supporting information, the yield was measured at 63%, which is lower than that of SiOC-Pd300. This decline in activity can be attributed to the increased palladium loading. As the number of ALD cycles increases, the nanoparticles tend to coalesce and form a thin layer, which is the typical outcome of ALD. The formation of this palladium thin film reduces the number of active sites, leading to lower catalytic activity.

To further demonstrate the effectiveness of the 3D grid-shaped catalyst, three additional samples were prepared, as described in the supporting information. First, a dense 3D-printed SiOC support was fabricated and coated with 300 ALD cycles of Pd. When tested under the same conditions as the 3D grid catalyst, this sample showed minimal activity,

yielding only 3%. Powdered catalysts were also tested. Two sets of samples were prepared: one by crushing a 3D-printed SiOC-Pd300 grid catalyst and the other by crushing a ceramic support and functionalizing it with 300 ALD cycles. Both samples achieved relatively high yields (67% and 61%), but these were still lower than those observed with the grid-shaped catalyst. Additionally, the use of powdered catalysts introduced extra processing steps, making the catalytic process less efficient. These results clearly demonstrate that the 3D grid structure is crucial for maximizing catalytic activity in the Suzuki–Miyaura coupling reaction. The grid design not only enhances yield but also simplifies the overall process, highlighting its practical advantage over other forms.

The presence of 4-iodophenol in the reaction system could lead to catalyst poisoning. Iodide ions can easily adsorb onto the palladium surface during oxidative addition, thereby reducing the accessibility of active sites for catalysis. This decline in active sites likely explains the decrease in yield over successive
<figure><img src="image_11.png" /><figcaption>**Figure 8.** a) Yield evolution for reactions over 1 h, 3 h, and 24 h and b) Iodine XPS spectra of SiOC-Pd100 (left) and SiOC-Pd300 (right).</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Figure 9.** ICP-MS analysis of Pd leaching in a) coupling solvent and b) coupling product.</figcaption></figure>

cycles. XPS analysis of each system after catalysis confirms this,
as adsorbed iodine is detected on the catalyst surface. **Figure 8**
shows the peaks associated with metallic iodide, appearing at
619.6 and 619.3 eV for SiOC-Pd100 and SiOC-Pd300, respec-
tively.[70,71] We can then conclude that iodine is likely bound
to palladium, affecting the catalytic properties by blocking the
oxidative addition of 4-iodophenol during catalysis. However,
no peaks related to iodide appear in the XPS for SiOC-Pd50 after
catalysis. Therefore, we cannot conclude if the adsorbed iodine
onto the palladium nanoparticles is responsible for the rapid
decrease in yield for this system. Moreover, we observe a shift
in the Pd(0) peaks of the Pd XPS for SiOC-Pd50 before and after
catalysis. This shift to higher binding energy indicates a higher
oxidation state of palladium. We hypothesize that, despite iodine
not being detected by XPS, the palladium is slightly oxidized,
leading to a decrease in the catalytic activity of the system.[72]
To assess the resistance and durability of each catalyst, 24 h reac-
tions were conducted under the same conditions as the 1 and 3 h
reactions. As shown in Figure 8a, the reaction yield remains over
50%, though it is slightly lower than the yields observed at
1 and 3 h reactions. This reduced yield in the 24 h reactions
can be attributed to the poisoning of Pd nanoparticles with
iodine. Additionally, we can confirm the possible formation of
PdI₂ on the surface of the Pd NPs using XRD. As shown in
Figure S10, Supporting Information, the diffraction patterns
for each system show the appearance of a peak at 28°, which

corresponds to PdI₂, with the main palladium iodide peak
occurring at 29°.

Finally, to fully characterize the durability of the catalyst, the
leaching of active palladium nanoparticles was measured.
Leaching was assessed using ICP-MS on both the obtained prod-
uct and the recovered reaction solvent after product isolation. As
shown in **Figure 9a**, the concentration of palladium in the recov-
ered solvent for each catalyst is below 0.6 ppb, which is consid-
ered trace amounts and indicates negligible leaching. Figure 9b
shows that the palladium concentration in the product is below
25 ppb, which can also be considered trace amounts. These
results suggest that no significant palladium leaching from
the support occurs, confirming that ALD is a suitable approach
for depositing palladium on SiOC-based catalysts.

4. Conclusion

In summary, we have developed a new class of SiOC-based cata-
lysts using innovative methods for fabricating the catalyst sup-
port and functionalizing the surface with Pd nanoparticles.
The 3D printing of SiOC-based resin was enabled by the acrylate
functionalities in the preceramic photocurable polymer, which
undergo photopolymerization under UV light during additive
manufacturing. Ceramic surface hydroxyls are essential for func-
tionalizing the catalyst support by ALD. This technique was
selected for depositing Pd nanoparticles due to its ability to achieve homogeneous surface coverage and a narrow size distribution. The successful deposition of Pd nanoparticles was confirmed through SEM, STEM imaging, EDX, XRD, and XPS analyses. Homogeneous surface coverage was verified using SEM, and the narrow size distribution was confirmed by STEM. The size of the nanoparticles ranged from 7.5 to 15 nm for 300 cycles and 20 to 25 nm for 100 cycles, with larger particles observed for 50 cycles. Varying the number of deposition cycles successfully produced catalysts with different Pd loadings and different catalytic activities. The catalytic performance was evaluated using a simple Suzuki–Miyaura C–C coupling reaction, characterized by FTIR, ¹H NMR, and GC-MS. The catalysts demonstrated activity for this type of reaction, but potential poisoning of the nanoparticle surface and the formation of PdI₂ contributed to a decrease in yield over successive reaction cycles. Additionally, the monolithic catalysts showed good reusability. The palladium nanoparticles remained well-bound to the ceramic surface, as evidenced by Pd–O bond peaks in XPS analysis. No significant palladium leaching was observed during the reaction. The use of 3D printing to fabricate complex catalyst systems is key to developing new catalysts with high activity, potentially leading to intensified processes due to their inherent 3D structure.

**Supporting Information**

Supporting Information is available from the Wiley Online Library or from
the author.

**Acknowledgements**

CS acknowledges funding from the French National Agency (ANR), grant no. ANR-20-CE08-0009 "MONOME project"; ANR Tremplin ERC, grant no. ANR-23-TERC-0009 "DESTINY project"; CAMPUS FRANCE PHC Projet Cèdre, grant no. 50512PC; the University of Montpellier "3D-FABSAC project"; and IEM Axe Energie "Solid-CeraLique project". LL acknowledges funding from the Spanish Ministerio de Economía y Competitividad, the Ministerio de Ciencia e Innovación MCIN/AEI/ 10.13039/501100011033/FEDER UE, and the European Union "NextGenerationEU"/PRTR (PID2022-140370NB-I00, RYC2021-033764-I, CPP2021-008986). The (S)TEM measurements were performed at the National Facility ELECMI ICTS ("Division de Microscopia Electronica", Universidad de Cadiz, DME-UCA).

**Conflict of Interest**

The authors declare no conflict of interest.

**Author Contributions**

**Hippolyte Dory:** Data curation (equal); Formal analysis (equal); Validation (supporting); Writing—original draft (equal); Writing—review and editing (supporting). **Eddy Petit:** Data curation (supporting); Formal analysis (supporting); Validation (supporting); Writing—review and editing (supporting). **Syreina El-Sayegh:** Data curation (supporting); Investigation (supporting); Writing—review and editing (supporting). **Lucie Badouric:** Methodology (supporting). **Victoria Castro:** Data curation (supporting); Formal analysis (supporting); Validation (supporting); Writing—review and editing (supporting). **Mikhael Bechelany:** Resources (supporting);

Writing—review and editing (supporting). **Damien Voiry:** Resources (supporting); Writing—review and editing (supporting). **Philippe Miele:** Writing—review and editing (supporting). **Luc Lajaunie:** Data curation (supporting); Investigation (supporting); Resources (supporting); Validation (supporting); Writing—review and editing (supporting). **Chrystelle Salameh:** Conceptualization (lead); Data curation (lead); Funding acquisition (lead); Investigation (lead); Methodology (lead); Project administration (lead); Resources (lead); Supervision (lead); Validation (lead); Visualization (lead); Writing—original draft (lead); Writing—review and editing (lead).

**Data Availability Statement**

The data that support the findings of this study are available in the supplementary material of this article.

**Keywords**

3D printing, atomic layer deposition, heterogeneous catalysis, monoliths, SiOC

Received: June 29, 2024

Revised: October 18, 2024

Published online: November 21, 2024

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