# Exploring chromium oxynitrides as efficient catalysts for the water-gas shift reaction

Sébastien Mathivet, Guillaume Dubois, Fabien Grasset, Stéphane Cordier, Franck Tessier

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Sébastien Mathivet, Guillaume Dubois, Fabien Grasset, Stéphane Cordier, Franck Tessier. Exploring chromium oxynitrides as efficient catalysts for the water-gas shift reaction. Solid State Sciences, 2026, 172, pp.108154. 10.1016/j.solidstatesciences.2025.108154. hal-05444228

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# Exploring chromium oxynitrides as efficient catalysts for the water-gas shift reaction

Sébastien Mathivet<sup>a, *</sup>, Guillaume Dubois<sup>a</sup>, Fabien Grasset<sup>b</sup>, Stéphane Cordier<sup>a</sup>, Franck Tessier<sup>a, **</sup> ∗

ARTICLE INFO

Keywords:

Powder

Mixed anion materials

Chromium oxynitride

Heterogeneous catalysis

Water-gas shift reaction

A B S T R A C T

Transition metal nitrides and oxynitrides exhibit catalytic properties that make them promising candidates as alternatives to noble metals. A series of high-surface-area chromium oxynitrides, CrOₓN₁₋ₓ (0.10 < x < 0.25), was synthesized from a cheap hydroxide precursor and investigated as unconventional heterogeneous catalysts for the Water-Gas Shift (WGS) reaction. Currently, this reaction is predominantly catalyzed by platinum. Replacing platinum with chromium oxynitrides could provide a more cost-effective and environmentally friendly solution.

1. Introduction

The aim of this work is to evaluate chromium (oxy)nitrides as potential alternatives to noble metal-based catalysts - particularly those using scarce and expensive elements like platinum - for the Water Gas Shift (WGS) reaction: CO + H₂O → CO₂ + H₂.

At the industrial level, noble metal catalysts such as Pt, Pd, or Rh are commonly supported on oxide substrates like ceria (CeO₂) or alumina (Al₂O₃). For example, Pt/CeO₂ catalysts exhibit high CO conversion rates at relatively low temperatures during the WGS reaction [1]. This reaction is a key step in several industrial processes, including ammonia synthesis, methanol production, and the Fischer–Tropsch process. In proton exchange membrane (PEM) fuel cell systems, RhPt/Al₂O₃–CeO₂ catalysts are often used to eliminate CO, which is toxic to the membrane, while simultaneously enriching the hydrogen feed through the WGS reaction [2].

Numerous parameters - such as feed composition, pressure, surface area, and catalyst composition - significantly affect WGS performance [3,4], making direct comparisons across studies challenging. In general, noble metals enable a reduction in activation temperature, particularly when finely dispersed on suitable supports like carbon, ceria, or alumina.

1.1. *Rationale for using chromium (oxy)nitrides*

Transition metal nitrides and oxynitrides are increasingly explored as viable alternatives to noble metals in catalysis. This interest stems not only from their greater natural abundance but also from their electronic properties, which often resemble those of noble metals [5]. Chromium nitrides, in particular, offer attractive properties such as high thermal stability, electronic conductivity, and chemical resistance - making them strong candidates for catalytic applications.

These materials have already been investigated in various contexts, such as ammonia synthesis [6], and in electrocatalysis for the oxygen reduction reaction (ORR) [7] and hydrogen evolution reaction (HER) [8]. For instance, N-coated carbon@CrN/Ni catalysts exhibit excellent HER performance across a range of current densities [8]. Furthermore, mesoporous chromium nitride has demonstrated high efficiency in ORR and methanol electrooxidation, owing to its corrosion resistance and good conductivity [9,10]. Chromium oxynitrides have also drawn attention for their tunable thermoelectric properties, which depend on their phase composition and stoichiometry [11].

1.2. *Scope of the present work*

This study focuses on the application of chromium oxynitrides in the

<footnote><sup>a</sup> Univ. Rennes, CNRS, Institut des Sciences Chimiques de Rennes – UMR 6226, F-35000, Rennes, France</footnote>

<footnote><sup>b</sup> CNRS - Saint-Gobain - NIMS, Laboratory for Innovative Key Materials and Structures - IRL CNRS 3629, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, 305-0044, Japan</footnote>

<footnote>This article is part of a special issue entitled: Mixed-Anion Materials published in Solid State Sciences.</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>** Corresponding author.</footnote>

<footnote>E-mail addresses: sebastien.mathivet@univ-rennes.fr (S. Mathivet), franck.tessier@univ-rennes.fr (F. Tessier).</footnote>
WGS reaction. These materials can be synthesized via nitridation of Cr₂O₃ or by calcining a mixture of chromium(III) chloride and urea at 800 °C under an argon atmosphere [12]. However, these methods often yield final products contaminated with Cr₂O₃ impurities. In this work, high-specific-surface-area chromium oxynitrides with the general formula CrOₓN₁-x (0.10 < x < 0.25) were successfully synthesized as single-phase powders from a reactive Cr(OH)₃ precursor. The ratio (x) was precisely controlled by adjusting the reaction temperature and dwell time. The catalytic performance of selected CrOₓN₁-x compositions is evaluated as a function of x, crystallite size, and specific surface area.

## 2. Experimental section

A series of high specific surface area chromium oxynitrides were synthesized following the protocol previously developed in our laboratory [13]. A chromium precursor solution (1.25 × 10⁻² mol L⁻¹) was prepared by dissolving chromium(III) nitrate nonhydrate (Acros Organics, 99 %) in distilled water at 70 °C. In parallel, an aqueous ammonia solution (0.8 mol L⁻¹) was preheated to 60 °C and then slowly added to the chromium solution under continuous stirring to promote homogeneous precipitation.

The resulting green precipitate, identified as Cr(OH)₃·9H₂O, was thoroughly washed with distilled water and ethanol to remove any residual ions or impurities. The washed solid was recovered by centrifugation (1000 rpm, 10 min) and subsequently dried under vacuum at 90 °C for several hours.

The dried Cr(OH)₃·9H₂O precursor was then placed in an alumina crucible and subjected to a two-step thermal treatment. First, the powder was preheated under a pure nitrogen atmosphere to 200 °C at a low heating rate. In the second step, nitridation was carried out by switching the gas flow to ammonia (Air Liquide, Ammoniac N36) at a flow rate of 30 L h⁻¹. The sample was heated from 200 to 700 °C at a rate of 5 °C·min⁻¹ and held at the target temperature for 24 h.

After the dwell time, the furnace was turned off, and the sample was allowed to cool to room temperature under continuous ammonia flow to avoid reoxidation. The resulting chromium oxynitride powders were collected for further characterization.

## 3. Characterizations

### 3.1. X-ray diffraction (XRD)

X-ray diffraction (XRD) patterns were recorded over the 2θ range of 10–90° using a PANalytical X'PERT powder diffractometer equipped with a Cu Kα radiation source (λ = 1.5406 Å, 40 kV, 40 mA) and a pIXcel 1D detector. Phase identification and qualitative analysis were carried out using HighScore Plus software. For structural analysis, Le Bail refinements were performed using the FullProf suite [14].

### 3.2. Elemental analyses

Nitrogen and oxygen contents were determined using a LECO TC-600 analyzer by the inert gas fusion method. Nitrogen was quantified as N₂ via thermal conductivity detection, while oxygen was measured as CO₂ using infrared detection. The instrument was calibrated with certified LECO reference standards.

It is important to note that factors such as water contamination, surface-adsorbed oxygen species, and the high specific surface area of the powders can significantly influence the measured oxygen content. Despite these challenges, hot gas extraction remains one of the most rapid and reliable techniques for accurately determining both nitrogen and oxygen concentrations in such materials [15].

### 3.3. Specific surface area and porosimetry

The Brunauer–Emmett–Teller (BET) specific surface areas and pore

<figure><img src="image_3.png" /><figcaption>Fig. 1. Scheme of the catalyst tests performed at the RealCat platform (Lille, France).</figcaption></figure>

size distributions were determined by nitrogen physisorption using a Micromeritics 3Flex surface characterization analyzer. Measurements were conducted with a N₂/He gas mixture (30 %/70 %). Prior to analysis, all samples were degassed under vacuum at 100 °C to eliminate surface-adsorbed moisture and prevent hydration-related artifacts.

### 3.4. Thermogravimetric analyses (TGA-DTA)

Thermogravimetric analysis (TGA) was performed in the temperature range of 30–600 °C under a nitrogen atmosphere using a TGA-DTA 2960 instrument (TA Instruments). The heating rate was set to 5 °C·min⁻¹.

### 3.5. Water-gas shift (WGS) reaction

The catalytic performances of the chromium oxynitride samples were evaluated at the RealCat Platform (Centrale Lille, France) using a Flowrence® T1219 high-throughput reactor system (Avantiq) (Fig. 1) [16]. The unit is equipped with 16 stainless steel reactor tubes (diameter = 2 mm), allowing for the simultaneous testing of 15 catalyst samples alongside one inert standard (SiC). Catalytic tests were conducted at atmospheric pressure over a temperature range of 200–500 °C (see Fig. SI-1). A second series of experiments was performed at higher temperatures, up to 750 °C, using a similar Flowrence® T1220 unit under identical operating conditions. For thermal stability considerations at elevated temperatures, quartz reactor tubes were used instead of stainless steel (see Fig. SI-2).

The feed gas consisted of a mixture of nitrogen (93 %, carrier gas), carbon monoxide (2 %, reactive gas), and helium (5 %) as an internal standard for monitoring CO conversion (see Table SI-1). Water vapor was introduced into the system at 130 °C with a controlled flow rate of 16 µL min⁻¹.

The catalytic bed was prepared by layering silicon carbide (SiC) particles of 100 µm and 200 µm grain sizes, with approximately 50 mg of catalysts placed between the layers, as illustrated in Fig. 1.

## 4. Results and discussion

### 4.1. Oxynitride catalysts characterization

The aim of this work was to synthesize a high specific surface area precursor via a controlled precipitation route, enabling the optimization of surface properties in the resulting nitride catalysts [13]. The nucleation and growth processes were carefully governed by three key parameters: temperature, stirring rate, and pH. The detailed synthetic
<table><caption>**Table 1**

Impact of the reaction temperature in the chromium oxynitrides characterizations. Compositional uncertainties are ± 0.01.</caption><thead><tr><th>Parameter (Å)</th><th>Reaction Temp. (°C)</th><th>Dwell time (h)</th><th>Product</th><th>N (wt %)</th><th>O (wt %)</th><th>S<sub>BET</sub> (m<sup>2</sup>/g)</th></tr></thead><tbody><tr><td>–</td><td></td><td></td><td>Cr(OH)<sub>3</sub></td><td>&lt;1.0</td><td>41.0</td><td>211 ± 1</td></tr><tr><td>4.137(3)</td><td>650</td><td>24</td><td>CrO<sub>0.25</sub>N<sub>0.75</sub></td><td>17.0</td><td>9.0</td><td>97 ± 1</td></tr><tr><td>4.144(2)</td><td>700</td><td>24</td><td>CrO<sub>0.21</sub>N<sub>0.79</sub></td><td>17.6</td><td>6.9</td><td>63 ± 1</td></tr><tr><td>4.145(3)</td><td>750</td><td>12</td><td>CrO<sub>0.14</sub>N<sub>0.86</sub></td><td>18.9</td><td>5.8</td><td>49 ± 1</td></tr><tr><td>4.147(1)</td><td>750</td><td>18</td><td>CrO<sub>0.12</sub>N<sub>0.88</sub></td><td>19.2</td><td>5.2</td><td>36 ± 1</td></tr><tr><td>4.151(1)</td><td>750</td><td>24</td><td>CrO<sub>0.10</sub>N<sub>0.90</sub></td><td>19.6</td><td>3.9</td><td>33 ± 1</td></tr><tr><td>4.153(4)</td><td>900</td><td>24</td><td>CrO<sub>0.02</sub>N<sub>0.98</sub></td><td>20.8</td><td>1.5</td><td>5 ± 1</td></tr></tbody></table>

procedure is provided in the Experimental section.

By optimizing these parameters, a highly reactive precursor suitable for nitridation was obtained, exhibiting an enhanced specific surface area of $211 \pm 1 \text{ m}^2 \text{ g}^{-1}$ (see Table 1).

The thermal analysis diagram shown in Fig. 2a reveals three distinct decomposition stages.

* Area 1: $Cr(OH)_3 \cdot 9H_2O \rightarrow Cr(OH)_3 + 9H_2O$

* Area 2: $Cr(OH)_3 \rightarrow CrO(OH) + H_2O$

* Area 3: $2CrO(OH) \rightarrow Cr_2O_3 + H_2O$

Chromium hydroxide decomposes gradually into a reactive intermediate, chromium oxyhydroxide (CrO(OH)), at around 200 °C [13]. Therefore, during nitridation, it is critical to promote the formation of this intermediate by incorporating a dwell step at 200 °C. This step helps prevent the premature formation of chromium oxide ($Cr_2O_3$). The formation of CrO(OH) as an intermediate facilitates the synthesis of chromium oxynitrides at lower temperatures while maintaining a high specific surface area and minimizing the formation of undesired secondary phases typically observed during direct nitridation of $Cr_2O_3$ [13].

Oxynitrides with controlled compositions, $CrO_xN_{1-x}$ (0.10 < x < 0.25), were synthesized by carefully adjusting reaction temperatures and dwell times (Table 1). The values of x in the $CrO_xN_{1-x}$ formulas were

calculated based on electroneutrality considerations and experimentally determined nitrogen contents.

Analysis of the data presented in Table 1 shows that higher nitrogen content - and consequently lower oxygen content - are favored by elevated temperatures and prolonged dwell times. However, this increase in nitridation temperature and duration leads to a decrease in specific surface area, consistent with the expected sintering effects in such conditions. Porosimetry results summarized in Table 2 reveal a mesoporous structure characterized by similar pore size distributions across samples, while the total pore volume decreases with increasing temperature.

The X-ray diffraction patterns (Fig. 2b) exhibit features consistent with the formation of a cubic CrN-type phase (NaCl-type), characterized by a lattice parameter within the range 4.137(3) - 4.153(4) Å. Detailed Le Bail refinements of the XRD data, performed on samples prepared at 700, 750, and 900 °C with a dwell time of 24 h, are presented in Table 2 and Fig. SI-3 to SI-5. The refinements reveal a clear increase in crystallite size from 12 to 77 nm as the synthesis temperature rises. The R² coefficient (around 0.90) of the linear trend between the unit cell parameter and nitrogen contents reflects the not very well crystallized state of the samples. This trend correlates with an expansion of the unit cell parameter, which reflects both the progressive substitution of oxygen by nitrogen and the presence of defects, as confirmed by the measured compositions: $CrO_{0.21}N_{0.79}$, $CrO_{0.10}N_{0.90}$, and $CrO_{0.02}N_{0.98}$.

Differential thermal analysis (DTA) identifies two exothermic events (Fig. 2c): the first corresponds to the dehydration of the precursor, while the second marks the complete oxidation of the oxynitride. Notably, nitrogen incorporation enhances the thermal stability of the oxynitrides, as evidenced by the increase in $Cr_2O_3$ crystallization temperature.

## 4.2. Evaluation of the catalytic performances

### 4.2.1. 1st evaluation in the temperature range 200–500 °C

The $CrO_{0.21}N_{0.79}$ and $CrO_{0.10}N_{0.90}$ samples were evaluated for the Water-Gas Shift (WGS) reaction over three consecutive runs between 200 and 500 °C. As shown in Fig. 3a, both materials exhibit measurable catalytic activity across this temperature range. The thermal equilibrium curve depicted is adapted from the work of Chein et al. [17].

<figure><img src="image_4.png" /><figcaption>**Fig. 2.** a. TGA analysis performed on the chromium hydroxide precursor, Fig. 2b. Evolution of the XRD profile of chromium oxynitrides phases by increasing reaction temperatures (700 °C, 750 °C and 900 °C) for a fixed 24 h dwell time, Fig. 2c. DTA analyses of the samples prepared at 650, 700 and 750 °C.</figcaption></figure>
<table><caption>**Table 2**
Le Bail refinements and porosimetry characteristics of the chromium oxynitrides prepared at 700, 750 and 900 °C (24h).</caption><thead><tr><th>Name</th><th>CrN(700)</th><th>CrN(750)</th><th>CrN(900)</th></tr></thead><tbody><tr><td>Product</td><td>CrO<sub>0.21</sub>N<sub>0.79</sub></td><td>CrO<sub>0.10</sub>N<sub>0.90</sub></td><td>CrO<sub>0.02</sub>N<sub>0.98</sub></td></tr><tr><td>Figures</td><td>Fig. SI-3</td><td>Fig. SI-4</td><td>Fig. SI-5</td></tr><tr><td>Unit cell</td><td></td><td></td><td></td></tr><tr><td>a (Å)</td><td>4.1403(4)</td><td>4.1430(2)</td><td>4.1496(1)</td></tr><tr><td>V (Å<sup>3</sup>)</td><td>70.97(1)</td><td>71.115(5)</td><td>71.5(1)</td></tr><tr><td>Space group</td><td colspan="3">Fm ¯3 m</td></tr><tr><td>Refinement</td><td></td><td></td><td></td></tr><tr><td>Nb. diffracted peaks</td><td>6</td><td>6</td><td>6</td></tr><tr><td>Nb. points (background)</td><td>28</td><td>27</td><td>43</td></tr><tr><td>Nb. refined parameters</td><td>35</td><td>34</td><td>50</td></tr><tr><td>Nb. atoms</td><td>0</td><td>0</td><td>0</td></tr><tr><td>Rp (%)</td><td>39.1</td><td>12.2</td><td>9.12</td></tr><tr><td>Rwp (%)</td><td>26.6</td><td>11.9</td><td>8.80</td></tr><tr><td>Rexp (%)</td><td>20.5</td><td>8.79</td><td>7.58</td></tr><tr><td>X<sup>2</sup></td><td>1.68</td><td>1.84</td><td>1.35</td></tr><tr><td>Berar and Lelann factors</td><td>1.9706</td><td>1.8750</td><td>1.2468</td></tr><tr><td>Microstructure</td><td></td><td></td><td></td></tr><tr><td>Apparent sizes (nm)</td><td>11.1(1)</td><td>19.0(1)</td><td>77.4(1)</td></tr><tr><td>Apparent strains (%)</td><td>0.56(1)</td><td>0.20(1)</td><td>0.08(3)</td></tr><tr><td>Porosimetry</td><td></td><td></td><td></td></tr><tr><td>BJH desorption average pore width (4V/Å) (nm)</td><td>23.7</td><td>33.2</td><td>27.4</td></tr><tr><td>BJH desorption cumulative volume of pores (cm<sup>3</sup>/g)</td><td>0.43</td><td>0.28</td><td>0.04</td></tr></tbody></table>

The CrO<sub>0.21</sub>N<sub>0.79</sub> catalyst demonstrates higher efficiency compared to CrO<sub>0.10</sub>N<sub>0.90</sub>. Although the maximum CO conversion was not reached at 500 °C, a notable 10 % difference in conversion between the two catalysts was observed. The synthesis temperature of the chromium oxynitrides affects both their chemical composition and specific surface area, which in turn significantly influences their catalytic performance. XRD analyses conducted after the initial evaluation (200–500 °C) confirm the structural stability of the catalysts under the applied reaction conditions. It is also worth noting that chromium oxynitrides exhibit a higher activation temperature than platinum-based catalysts [1].

In our previous work, Mo<sub>5</sub>N<sub>6</sub> molybdenum nitrides synthesized via

the cluster route from ((C<sub>4</sub>H<sub>9</sub>)<sub>4</sub>N)<sub>2</sub>Mo<sub>6</sub>Br<sub>14</sub> - a well-known cluster-based precursor - were tested as catalysts for the WGS reaction and exhibited promising CO conversion rates [18].

For comparison, Mo<sub>5</sub>N<sub>6</sub> was evaluated under identical conditions on the RealCat platform alongside the CrO<sub>0.21</sub>N<sub>0.79</sub> chromium oxynitride (Fig. 3b). While the catalytic activation temperature of Mo<sub>5</sub>N<sub>6</sub> is lower than that of CrO<sub>0.21</sub>N<sub>0.79</sub>, both catalysts achieve comparable CO conversion at 500 °C. Unlike the chromium-based catalyst, Mo<sub>5</sub>N<sub>6</sub> reaches its maximum conversion at 500 °C.

Additionally, at this temperature, molybdenum nitride begins to slowly decompose into MoO<sub>2</sub> without adversely affecting the catalytic performance [18], whereas the chromium oxynitride remains structurally stable. Therefore, both nitrided materials hold potential as WGS catalysts, with their suitability depending on the specific temperature range required for the intended application.

### 4.2.2. 2nd evaluation in the temperature range 200–750 °C

A second series of measurements was conducted using an Avantium unit capable of operating at temperatures up to 750 °C (Fig. 3c). For both CrO<sub>0.21</sub>N<sub>0.79</sub> and CrO<sub>0.10</sub>N<sub>0.90</sub> compositions, the maximum CO conversion was observed below 600 °C. Notably, the chromium oxynitrides maintained significant and reproducible catalytic activity across the entire temperature range, up to 750 °C.

Both materials displayed a CO conversion approaching thermal equilibrium, with a peak conversion of approximately 84 % achieved after the first run at 565 °C.

However, XRD analysis following high-temperature exposure revealed partial degradation of the catalysts into their corresponding oxide phase (Cr<sub>2</sub>O<sub>3</sub>) (Fig. 4). This degradation was not observed during the initial evaluation runs (200–500 °C). Among the two, CrO<sub>0.21</sub>N<sub>0.79</sub> - having a higher oxygen content - proved more prone to oxidation than CrO<sub>0.10</sub>N<sub>0.90</sub> after three consecutive runs from 200 to 750 °C. These results suggest that a higher nitrogen content enhances thermal stability and resistance to oxidation at elevated temperatures. This trend is confirmed by measuring the unit cell parameters (non-refined values) after the WGS test at 750 °C, a = 4.151(2) Å and a = 4.150(2) Å for CrN (700) and CrN (750) respectively.

After three successive runs at 750 °C, the formation of Cr<sub>2</sub>O<sub>3</sub> appears

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** a. WGS reaction results for the chromium oxynitride samples heated until 500 °C, Fig. 3b. WGS results comparison between CrO<sub>0.21</sub>N<sub>0.79</sub> and Mo<sub>5</sub>N<sub>6</sub>, Fig. 3c. WGS results of chromium oxynitrides until 750 °C, Fig. 3d. WGS results at 750 °C of alumina-supported chromium oxynitride.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 4. XRD analyses of CrN(700) and CrN(750) after WGS tests at 750 °C.</figcaption></figure>

to have a stabilizing effect on the oxynitride phase, without negatively impacting CO conversion during the WGS reaction. No significant differences were observed between the second and third runs, indicating stable and reproducible catalytic activity. The high intrinsic activity of chromium oxynitrides effectively compensates for their partial degradation, which does not represent a major drawback. Moreover, it is worth noting that chromium oxide is commonly used in industry as a promoter or support to activate catalytic phases such as platinum [3].

An initial evaluation using Al₂O₃ as a support was also performed under identical conditions, with a 10 wt% impregnation of CrO₀.₂₁N₀.₇₉ (Fig. 3d). Although the three consecutive runs at high temperature (750 °C) were reproducible, the supported catalyst exhibited lower CO conversion compared to the unsupported oxynitride. This result suggests that using alumina as a support in this context is less effective and may not be an advantageous strategy.

## 5. Conclusion

A synthetic route was developed to prepare a series of chromium oxynitride powders CrOₓN₁-x (0.10 < x < 0.25), featuring high specific surface areas. The values of x within the CrOₓN₁-x oxynitride were controlled by adjusting the reaction temperatures and dwell times. The higher the temperature, the lower the oxygen content; the higher the nitrogen content, the smaller the resulting specific surface area. A selection of corresponding materials was evaluated for the water gas-shift reactions. Chromium oxynitrides represent a promising class of heterogeneous catalysts for this process, exhibiting notable activity from 400 °C and maintaining thermal stability up to 700 °C.

### CRediT authorship contribution statement

**Sébastien Mathivet:** Writing – original draft. **Guillaume Dubois:** Writing – review & editing. **Fabien Grasset:** Writing – review & editing. **Stéphane Cordier:** Writing – review & editing. **Franck Tessier:** Writing – review & editing, Writing – original draft.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgements

The authors thank Svetlana HEYTE and Sébastien PAUL for their support for performing the catalytic tests at the RealCat platform (Centrale Lille, France). This work was financially supported by the

French ANR (Agence Nationale pour la Recherche) MENIHR program (ANR-21-CE08-0028).

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.solidstatesciences.2025.108154.

### Data availability

Data will be made available on request.

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