# Effect of Oxidized Tin Interfacial Atoms on Methylcyclohexane Dehydrogenation Catalyzed by γ-Alumina Supported Platinum Clusters

Masoud Shahrokhi, Céline Chizallet, David Loffreda, Pascal Raybaud

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Masoud Shahrokhi, Céline Chizallet, David Loffreda, Pascal Raybaud. Effect of Oxidized Tin Interfacial Atoms on Methylcyclohexane Dehydrogenation Catalyzed by γ-Alumina Supported Platinum Clusters. ChemCatChem, 2025, 17 (1), pp.e202401300. 10.1002/cctc.202401300. hal-04747228

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Distributed under a Creative Commons Attribution 4.0 International License
Effect of Oxidized Tin Interfacial Atoms on
Methylcyclohexane Dehydrogenation Catalyzed
by γ-Alumina Supported Platinum Clusters

Masoud Shahrokhi,[a] Céline Chizallet,[*a] David Loffreda,[*b] Pascal Raybaud*[a,b]

Tin (Sn) doped platinum (Pt) nanoparticles supported on γ-alumina are important materials catalyzing various reactions, such as the dehydrogenation of methylcyclohexane (MCH) into toluene, involved in liquid organic hydrogen carriers process, and naphtha catalytic reforming. The role of oxidized forms of Sn, remains misunderstood. Focusing on catalysts models of a Pt₁₃ cluster on the (100) surface of γ-alumina, the location and effects of Sn⁴⁺ and Sn²⁺ interfacial atoms are investigated by density functional theory (DFT) calculations. A simulated annealing approach based on *ab initio* molecular dynamics enables to explore the configurations of the catalytic systems. The Pt clusters' stabilities and of the adsorbed molecular intermediates are linked to the electronic properties of the cluster and to its ductility modulated by the adsorbed species, the alumina support and the Sn atoms. The Gibbs free energy profiles related to the reaction mechanism of the MCH dehydrogenation into toluene are quantified on the basis of transition state search. The energy span concept reveals that the dual (either detrimental or beneficial) impact of Sn oxidized forms on the intrinsic reactivity of the Pt₁₃ cluster depends on temperature. Based on this DFT analysis, we attempt to clarify the debated role of Sn oxidized species.

**Introduction**

Within the context of the decarbonization of the world econ-
omy, hydrogen appears as an appealing energy carrier which
may also be key as an alternative fuel in various areas such
as heavy transport, aviation, and maritime transport. Hy-
drogen can be considered as green if produced through wa-
ter electrolysis, when electricity itself is generated through
renewable sources. At the current stage of deployment,
numerous challenges remain from the production to the end
use. In particular, hydrogen needs to be transiently stored.
Numerous technologies may be envisaged such as compressed
tanks, solid metal hydrides[1,2] or liquid organic hydrogen
carriers (LOHC).[3-5]

In the case of LOHC, numerous potential molecules may

be considered in order to reach high hydrogen storage capacity (above 6 wt%) and other properties such as dehydrogenation enthalpy, stability, liquid temperature range, cost, toxicity inter alia. [4,5] Kinetic limitations are also an important factor inherent to the organic molecule involved in the formation/breaking of chemical bonds (such as C-H) during hydrogen storage/release. Hence, catalysis is expected to play a key role to overcome these limitations. Depending on the LOHC, several kinds of homogeneous or heterogeneous catalysts exist to accelerate the (de)hydrogenation steps. [6–10] The present study focuses on the prototypical methylcyclohexane (MCH) molecule exhibiting attractive storage capacities and cost. Its good cycling property reduces the environmental impact knowing that the molecule is easily accessible from oil or biomass resources. The dehydrogenation of MCH yielding dihydrogen and toluene is endothermic, with a reaction enthalpy of 68.3 kJ mol⁻¹ H₂ (in standard conditions), which is slightly higher than the targeted upper threshold of about 50 kJ mol⁻¹ H₂ usually accepted in the context of dihydrogen release from carriers. [5] Alumina (Al₂O₃) supported platinum (Pt)-based catalysts were identified to be active for this reaction for more than 6 decades. [11] This knowledge is historically inherited from a famous catalytic process of the refining industry, naphtha reforming, where the dehydrocyclization reaction of light linear alkanes (such as normal heptane) into aromatics (such as toluene) is at the core of the process. [12–16] MCH dehydrogenation into toluene plus dihydrogen is a milestone of the whole dehydrocyclization reaction. Thus, platinum (Pt)-based catalysts supported on various materials are considered as relevant catalysts in many experimental studies devoted to LOHC applications based on the MCH/toluene molecules. [17–22] It is worth mentioning that this family of catalysts is also used for light alkane (such as propane) dehydrogenation. [23] Within the context of naphtha reforming, gamma-alumina (γ-Al₂O₃) supported Pt-based catalysts have been the subject of numerous characterization studies featuring that platinum is present in the form of highly dispersed nano-clusters only containing a few Pt atoms and with sizes equal or smaller than 1 nm,[13] as highlighted by high resolution transmission electronic microscopy. [24]

The deactivation of pure platinum catalysts during MCH
dehydrogenation, is a well-known process.[25,26] Hence, to
counter-balance this trend and to simultaneously improve
the catalytic selectivity of naphtha reforming, the addition
of a second metallic element to the Pt active phase was
widely investigated.[27-34] The available experimental stud-
ies showed that Sn reduces significantly the deactivation
of the catalyst either in reforming or in MCH dehydro-
genation conditions. This allows a decrease of the partial
pressure of H₂ by comparison with operating conditions

[a] Dr. M. Shahrokhi, Dr. HDR C. Chizallet,* Dr. HDR P. Raybaud*
IFP Energies nouvelles, Rond-point de l'échangeur de Solaize,
BP3, Solaize, 69360, France
E-mail: celine.chizallet@ifpen.fr, pascal.raybaud@ifpen.fr

[b] Dr. HDR D. Loffreda,* Dr. HDR P. Raybaud
CNRS, ENS de Lyon, Université Claude Bernard Lyon 1, LCH,
UMR 5182, 69342, Lyon cedex 07, France
E-mail: david.loffreda@ens-lyon.fr
with the pure platinum catalyst. The impact of Sn on the dehydrogenation of MCH and cyclohexane (CH) was also investigated experimentally, both molecules being considered as model molecules for the reforming reaction[33,34] or as LOHC molecules.[18,19,35] However, the precise effect of Sn on the intrinsic activity of MCH or CH dehydrogenation is more debated. In some works, no significant improvement was observed experimentally, estimated activation energies being more or less nonsensitive to the presence of Sn.[17,33,34] However, other experimental studies on CH and MCH dehydrogenation suggested that an optimal Sn/Pt ratio is mandatory to maximize activity and stability which may result on direct or indirect effects of Sn on Pt particles.[19,35] One of the main reason for this difficult interpretation of the role of Sn species, originates from their numerous oxidation states and from their various locations: segregated on the support, alloyed with Pt and/or at the support-Pt interface. All these Sn species may be involved in the MCH dehydrogenation at different levels. Mössbauer spectroscopy revealed that after reduction, Sn speciation is very complex since Sn may coexist in three distinct oxidation states: 0, 2+ and 4+, depending on the preparation methods.[36–39] However, the experimental interpretation of the various oxidation states of Sn in these materials is by far not a trivial task. According to some of these studies, PtSnₓ alloyed nanoparticles are composed of Sn⁰ species. Sn²⁺ would correspond to Sn species in interaction with alumina exhibiting loose contact with Pt (Al-O-Sn···Pt). Finally, Sn⁴⁺ would be present either in segregated SnO₂ species or in interaction with alumina or at the alumina-platinum interface (Al-O-Sn-Pt). As a consequence, in the light of the experimental state of the art, it remains difficult to disentangle the catalytic role of each Sn species.

Theoretical modeling through density functional theory (DFT) is a relevant approach to scrutinize the catalytic properties of supported metallic clusters.[40,41] Indeed, several theoretical works reported on the (de)hydrogenation elementary mechanisms involving aromatics/cyclic alkanes catalyzed by metallic sites located on either terraces or steps of large Pt particles.[42–48] However, there are significantly fewer DFT studies focusing on the reactivity of alumina supported Pt based nanoparticles[49] and even less on the addition of Sn as a promoter.[30,50] Previous DFT works showed the impact of Sn⁰ on the γ-Al₂O₃ supported Pt₁₃-xSnₓ nanosStructures, for instance by altering the affinity of Pt₁₀Sn₃ for hydrogen atoms.[50] This effect of Sn (when alloyed with Pt) on the hydrogen stability, may more generally impact the catalytic reactivity in MCH dehydrogenation. Moreover, the mechanism of MCH dehydrogenation catalyzed by alumina supported Pt₁₃ was thoroughly analyzed by DFT calculations.[49] All these studies (with or without Sn) also highlighted the ductility of the metallic cluster whose structure is very sensitive to operating conditions. A recent study combining experimental and DFT approaches revealed that an optimal number of Pt atoms (such as 4 or 13) is required to maximize the CH dehydrogenation on carbon supported Pt, whereas Pt single atoms or Pt extended surfaces are less efficient.[20] This underlines the high interest of further studying the support effects on such few atoms Pt clusters.

Since the role of Sn⁴⁺ and Sn²⁺ species observed experimentally at the interface of alumina and Pt, remains misunderstood and unexplored from theoretical modeling, there is a strong need for developing *ab initio* models to address this question. In this work, we report on a periodic DFT study

performed at the PBE-dDsC level to investigate the location and the role of oxidized forms of tin (Sn⁴⁺ and Sn²⁺) interfacial atoms on the model (100) surface of γ-alumina. We analyze the structure, electronic properties and stability of Pt₁₃ clusters on the Sn doped γ-alumina surface. Biplanar Pt₁₃ clusters are chosen as representative models as they exhibit a diameter close to 0.9 nm and a two-layer structure, in line with experimental results.[24,51] Finally, the Gibbs free energy profiles of MCH dehydrogenation into toluene and dihydrogen, catalyzed by pure Pt versus Sn-doped Pt subnanometric clusters supported on γ-alumina, are compared to unravel the role of tin on the barriers of each elementary step. For that purpose, we apply a systematic simulated annealing approach (*ab initio* molecular dynamics (AIMD) followed by a quench process) to explore the various catalyst structures in presence of the various intermediates. The nature and impact of oxidized forms of interfacial tin atoms on the reactivity of the γ-alumina supported Pt₁₃ clusters is thus identified, as a function of the temperature, and linked to the electronic properties of the clusters and to their ductility.

# Results and Discussion

## Catalysts models and nature of interfacial oxidized Sn atoms

The Pt₁₃H₆/γ-Al₂O₃ model shown in Figure 1(a),(b) was described previously[49,52,53] and reoptimized in this work after AIMD at the PBE-dDsC level. It was indeed shown that in relevant catalysis conditions, such a hydrogen coverage is thermodynamically relevant and opens the possibility for the methylcyclohexane molecule to adsorb and react.[49] The cluster adopts a (distorted) bi-planar structure, where 7 atoms are close to the support (see the dark blue atoms in Figure 1(a),(b)), the 6 remaining ones forming a second layer (as depicted by the light blue atoms). The Sn-doped catalyst model was initially constructed by substituting two Al atoms from the surface of the support by two Sn atoms (see Figure 1(c),(d) for the most stable optimized structure). From the formal point of view of oxidation states, this substitution should lead to one Sn²⁺ and one Sn⁴⁺ instead of two Al³⁺ cations, knowing that Sn²⁺ and Sn⁴⁺ species have been previously observed by several techniques (X-Ray photoelectron, X-Ray absorption and Mössbauer spectroscopies) on platinum-tin catalysts supported on alumina.[30,54–59] To select relevant Sn atoms positions on the complete catalyst model, we performed a preliminary analysis of the preferred relative positions for two Sn atoms in the alumina slab model (see Table 1 for energetics and Bader charge analysis, Figure 1(e),(f) for the definitions and Figures S1-S3 of the Supporting Information for the optimized structures). This preliminary study was performed at the standard GGA PBE level, with the exception of the “for cluster” configuration (where the Sn atoms are located at the same position as in the presence of the cluster) for which the PBE-dDsC level was also computed. Among the various simulated structures, the “for cluster” configuration, exhibiting two Sn that substitute Al atoms that would have been in octahedral geometry in the bulk structure, is the most stable one (see Figure 1(e),(f)). Being exposed at the surface, they initially harbor five oxygen neighbors. After geometry optimization, one of the two Sn (Sn2) relaxes upward, so that one of the Sn-O bonds is strongly elongated
(2.79 Å instead of 2.25-2.47 Å for the four other bonds, at the GGA PBE level). The situation where the two Sn atoms are fourfold coordinated corresponds to a tetrahedral environment (see Figure S2 (b),(d)), slightly below the topmost surface. This is the least stable configuration of the series, which shows that longer Sn-O distances than those of Al-O bonds are better accommodated at the topmost surface.

This preliminary study led us to select the "for cluster" configuration where two surface pentahedral sites are substituted by Sn, in order to build a starting structure of the catalyst in the presence of the cluster. The latter was refined by AIMD simulations and the most stable model, which was optimized from the lowest potential energy structure of the AIMD trajectory, is shown in Figure 1(c), (d). Various catalyst structures extracted from the AIMD trajectories and completely optimized were described in Figures S4-S6. They exhibit metal thickness differences (two versus three platinum layers in the supported cluster, the latter structure resembling a pyramid) and tin-atom extraction from the support. The most stable system is bi-layered and noted Pt<sub>13</sub>H<sub>6</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub>. One of the two Sn atoms (Sn1 in Figure 1(c)) was extracted from the surface layer, and connects to two surface oxygen atoms and two platinum atoms from the cluster. The second tin atom (Sn2) lies in the surface plane, close to 3 oxygen atoms and one platinum atom.

The Bader charge analysis shows that in all cases, the two Sn atoms are strongly positively charged, one being close to that of Sn atoms in SnO, the other close to that of Sn atoms in SnO<sub>2</sub>, in line with the formal description of respective oxidation degrees 2+ and 4+, intuitively expected after the substitution of two Al<sup>3+</sup> sites. The level of theory (PBE versus PBE-dDsC) does not substantially affect these results. The tetrahedral coordination state is more prone to favor high oxidation levels. In the presence of the Pt<sub>13</sub> cluster (Table 2), the Bader charges of Sn1 atom (the one that is extracted during AIMD) is significantly reduced by its interaction with Pt. The charge of Sn2, on the other hand, slightly increases. Regarding the Pt<sub>13</sub> cluster, while its mean Bader charge is strongly negative in the Pt<sub>13</sub>/γ-Al<sub>2</sub>O<sub>3</sub> system, due to charge transfer from the support,<sup>[60,61]</sup> Pt<sub>13</sub> becomes almost neutral in the presence of the two Sn atoms, suggesting that the major part of the Sn1 reduction is due to charge transfer occurring from the Pt<sub>13</sub> cluster to the Sn-doped alumina support. This result seems counter-intuitive if one considers the respective electronegativities of Pt and Sn, that should induce oxidation of Sn and reduction of Pt. This suggests non-alloyed Pt-Sn bonds between Pt<sub>13</sub> cluster and the Sn-doped alumina support. The trend expected from electronegativity difference was indeed observed in previous DFT models showing the co-existence of Pt and Sn(0) in the alloyed Pt<sub>13-x</sub>Sn<sub>x</sub> cluster supported on γ-Al<sub>2</sub>O<sub>3</sub>,<sup>[50]</sup> where the charge of Sn atoms appeared to be lower than 1, and that of the Pt<sub>13-x</sub> entity being significantly more negative than in the present case (-0.99 to +0.17 e). The opposite trend observed in the present work comes from the fact that we start by oxidized forms of tin, included in the support. Hydrogen atoms (on average) exhibit a similar hydride nature, in the presence or absence<sup>[52]</sup> of Sn, by electron transfer from Pt<sub>13</sub>. Combining the effects of Sn and H, the Pt<sub>13</sub> cluster is thus slightly positively charged in the Pt<sub>13</sub>H<sub>6</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub> system.

This analysis allows us to revisit the former assignment based on Mössbauer experiments (as presented in introduc-

tion).<sup>[37–39]</sup> In the presence of the Pt<sub>13</sub> cluster, both Sn atoms (Sn1 and Sn2) which are interacting with the Pt<sub>13</sub> cluster exhibit Bader charges (1.19-1.24 and 1.71-1.81 e) which are smaller than the ones expected for Sn species in the formal oxidation state 4+ (2.52 e in SnO<sub>2</sub>) and are closer to Sn<sup>2+</sup> (1.25 e in SnO). Hence, the former assignment based on Mössbauer experiments that proposed that Sn<sup>4+</sup> would be located at the interface between alumina and platinum is not confirmed.<sup>[37–39]</sup> Our interpretation would be more in line with the one earlier proposed by Burch who assigned Sn oxidized species to Sn<sup>2+</sup> potentially in close vicinity of Pt.<sup>[36]</sup> By contrast, Sn<sup>4+</sup> species (with Bader charges above 2.20 e) should correspond to either SnO<sub>2</sub> or octahedral Sn<sub>VI</sub> (so called Sn1 above). The latter is strongly interacting with the alumina surface thus restricting its outward surface relaxation and interaction with Pt atoms. In all cases, tetrahedral Sn<sub>IV</sub> species seem to be ruled out in our DFT models for energetic reason, although their Bader charges could correspond to Sn<sup>4+</sup> species.

Regarding the impact of Sn on the stability, tin strongly enhances the interaction with the Pt<sub>13</sub>H<sub>6</sub> cluster, as illustrated by interaction energies reported in Table S1. The extraction of Sn1 plays a very significant role in this stabilization. The charge density difference analysis reported in Figure S7 illustrates the electron accumulation in Pt-Sn bonds, illustrating the strong contribution of the latter in the platinum-support interaction.

## Reaction sequence

The reaction sequence and the name of the most relevant intermediates for the dehydrogenation of methylcyclohexane are depicted in Figure 2. We follow a step-by-step CH bond breaking sequence, elucidating at each step the preferred adsorption mode on the Pt<sub>13</sub>H<sub>6</sub> cluster. From MCH, the six successive C-H cleavage steps produce the following surface intermediates:

* methylcyclohexyl (C<sub>7</sub>H<sub>13</sub>)

* methylcyclohexene (C<sub>7</sub>H<sub>12</sub>)

* methylcyclohexenyl (C<sub>7</sub>H<sub>11</sub>)

* methylcyclohexadiene (C<sub>7</sub>H<sub>10</sub>)

* methylcyclohexadienyl (C<sub>7</sub>H<sub>9</sub>)

* adsorbed toluene (C<sub>7</sub>H<sub>8</sub>)

The reconstruction of the cluster was shown to occur between some of these elementary steps,<sup>[49]</sup> including H migration as well as H<sub>2</sub> desorption steps, so as to maintain the hydrogen coverage enclosed between 6 and 8 coadsorbed atoms on the platinum cluster. Indeed, each time a C-H bond is broken, an extra-H atom is harbored by the cluster. Each time two steps of this kind occur, we consider that a H<sub>2</sub> molecule will desorb in the gas phase in the next step. To determine the best adsorption structures of each reaction intermediate all along the elementary steps, we performed systematically AIMD simulations to take into account the ductility effect of the Pt<sub>13</sub> clusters. Table 3 summarizes all the intermediates and transition states for the most relevant steps under investigation for the Pt<sub>13</sub>H<sub>6</sub>/γ-Al<sub>2</sub>O<sub>3</sub> (see the optimized structures in Figures S8-S25) and Pt<sub>13</sub>H<sub>6</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub> systems (see the optimal geometries in Figures 3 and 4, as well as detailed structures in Figures S26-S43).

Notably, the terminology of the states follows the one previously published for Pt<sub>13</sub>H<sub>6</sub>/γ-Al<sub>2</sub>O<sub>3</sub>,<sup>[49]</sup> but with some
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Lateral and top views of the most stable optimized structures of the Pt<sub>13</sub> bi-planar cluster supported on (a) and (b) γ-Al<sub>2</sub>O<sub>3</sub>(100) surface, on (c) and (d) Sn-doped γ-Al<sub>2</sub>O<sub>3</sub>(100) surface, and of the Sn-doped γ-Al<sub>2</sub>O<sub>3</sub> surface (named "for cluster" configuration) on (e) and (f) (at the PBE-dDsC level). The color labels of the atoms are defined on the lateral views. Note in passing the light and dark blue colors used to represent the bi-layer Pt<sub>13</sub> cluster: the dark bl atoms are interfacial atoms. The metallic cluster and the surface layer of the support are represented with balls and sticks, whereas the subsurface support layers only with sticks. The notations Sn1 and Sn2 refer to the ones used in Tables 1 and 2.</figcaption></figure>

<table><caption>**Table 1.** Relative energy (with respect to the most stable configuration) and Bader charges of Sn atoms for Sn-doped alumina models. For the "for cluster" configuration, figures in parenthesis correspond to the Bader charge analysis performed at the PBE-dDsC level on the PBE-dDsC optimized system. The average Bader charges of Sn atoms in bulk SnO and SnO<sub>2</sub> are also reported.</caption><thead><tr><th>Coordination of Sn</th><th>System</th><th>Relative energy (eV)</th><th>Bader charge Sn1 (e)</th><th>Bader charge Sn2 (e)</th></tr></thead><tbody><tr><td rowspan="3">2Sn<sub>VI</sub></td><td>Far</td><td>1.96</td><td>2.23</td><td>1.26</td></tr><tr><td>Near</td><td>0.78</td><td>2.20</td><td>1.36</td></tr><tr><td>For cluster</td><td>0.00</td><td>2.27 (2.27)</td><td>1.38 (1.39)</td></tr><tr><td rowspan="2">Sn<sub>IV</sub>-Sn<sub>VI</sub></td><td>Far</td><td>1.05</td><td>2.29 (Sn<sub>IV</sub>)</td><td>1.36 (Sn<sub>VI</sub>)</td></tr><tr><td>Near</td><td>0.54</td><td>2.31 (Sn<sub>IV</sub>)</td><td>1.37 (Sn<sub>VI</sub>)</td></tr><tr><td>2Sn<sub>IV</sub></td><td></td><td>3.11</td><td>2.24</td><td>1.51</td></tr><tr><td rowspan="2">Bulk</td><td>SnO</td><td>-</td><td>-</td><td>1.25 (av.)</td></tr><tr><td>SnO<sub>2</sub></td><td>-</td><td>2.52 (av.)</td><td>-</td></tr></tbody></table>

<table><caption>**Table 2.** Bader charges (e) of Sn atoms, Pt<sub>13</sub> and H<sub>6</sub> entities of supported clusters, with or without adsorbed hydrogen, with or without Sn doping on the support. Note that in the case of Pt<sub>13</sub> and H<sub>6</sub> entities, the Bader charge is averaged over all atoms.</caption><thead><tr><th>System</th><th>Sn1 (e)</th><th>Sn2 (e)</th><th>Pt<sub>13</sub> (e)</th><th>H<sub>6</sub> (e)</th></tr></thead><tbody><tr><td>Pt<sub>13</sub>/γ-Al<sub>2</sub>O<sub>3</sub></td><td>-</td><td>-</td><td>-0.99</td><td>-</td></tr><tr><td>Pt<sub>13</sub>H<sub>6</sub>/γ-Al<sub>2</sub>O<sub>3</sub></td><td>-</td><td>-</td><td>-0.61</td><td>-0.40</td></tr><tr><td>Pt<sub>13</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub></td><td>1.19</td><td>1.71</td><td>-0.07</td><td>-</td></tr><tr><td>Pt<sub>13</sub>H<sub>6</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub></td><td>1.24</td><td>1.81</td><td>0.17</td><td>-0.38</td></tr></tbody></table>

<figure><img src="image_3.png" /><figcaption>**Figure 2.** Formal reaction sequence followed for the dehydrogenation of methylcyclohexane into toluene. In practice, radicals and double carbon-carbon bonds are stabilized by metal atoms of the clusters.</figcaption></figure>
<table><caption>**Table 3.** Various intermediates and nature of elementary steps along the dehydrogenation of methylcyclohexane on Pt<sub>13</sub>H<sub>6</sub>/2Sn@Al<sub>2</sub>O<sub>3</sub> and Pt<sub>13</sub>H<sub>6</sub>/Al<sub>2</sub>O<sub>3</sub>.</caption><thead><tr><th>Surface intermediates</th><th>Elementary formation step</th><th>TS</th><th>Reaction type</th></tr></thead><tbody><tr><td>(ref) - Catalyst + MCH<sub>(g)</sub></td><td>-</td><td>-</td><td></td></tr><tr><td>(A) Methylcyclohexane</td><td>MCH<sub>(g)</sub> → A</td><td>-</td><td>MCH adsorption</td></tr><tr><td>(B) Methylcyclohexyl + H</td><td>A → B</td><td>TS<sub>A-B</sub></td><td>C-H bond cleavage</td></tr><tr><td>(C) Methylcyclohexene + 2H</td><td>B → C</td><td>TS<sub>B-C</sub></td><td>C-H bond cleavage</td></tr><tr><td>(D) Methylcyclohexene</td><td>C → D + H<sub>2</sub>(g)</td><td>-</td><td>H<sub>2</sub> desorption</td></tr><tr><td>(E) Methylcyclohexenyl + H</td><td>D → E</td><td>TS<sub>D-E</sub></td><td>C-H bond cleavage</td></tr><tr><td>(H') Methylcyclohexadiene + 2H</td><td>E → H'</td><td>TS<sub>E-H'</sub></td><td>C-H bond cleavage</td></tr><tr><td>(H) Methylcyclohexadiene + 2H</td><td>H' → H</td><td>TS<sub>H'-H</sub></td><td>H atom migration</td></tr><tr><td>(I) Methylcyclohexadiene</td><td>H → I + H<sub>2</sub>(g)</td><td>-</td><td>H<sub>2</sub> desorption</td></tr><tr><td>(K) Methylcyclohexadienyl + H</td><td>I → K</td><td>TS<sub>I-K</sub></td><td>C-H bond cleavage</td></tr><tr><td>(M) Toluene + 2H</td><td>K → M</td><td>TS<sub>K-M</sub></td><td>C-H bond cleavage</td></tr><tr><td>(N) Toluene</td><td>M → N + H<sub>2</sub>(g)</td><td>-</td><td>H<sub>2</sub> desorption</td></tr><tr><td>Catalyst + Toluene<sub>(g)</sub></td><td>N → Toluene<sub>(g)</sub></td><td>-</td><td>Toluene desorption</td></tr></tbody></table>

missing states (F, G, J, L). Conversely, a new H' state appears. Indeed, in our previous work,[49] the various possible morphologies of the Pt<sub>13</sub>H<sub>6</sub>/γ-Al<sub>2</sub>O<sub>3</sub> clusters were sampled by AIMD at the PBE level, while the energetics and the geometries of the final structures were refined at the PBE-dDsC level. In the present work, we revisit these results by sampling at the PBE-dDsC level, which leads to some differences in intermediate structures and Gibbs free energies (see Figures S49 and S50 for a detailed comparison of the optimal structures of A and B surface intermediates, at the beginning of the reaction mechanism). The major difference lies in the position of the molecules with respect to the cluster. For the first elementary step (first C-H dissociation of MCH), we previously found that a Pt atom on the topmost layer of the cluster was the preferred adsorption site for the methylcyclohexyl group, we now find that an atom at the interface between the cluster and the alumina surface is a better stabilization site for the methylcyclohexyl group. This may be induced by the consideration of dispersion interactions during AIMD simulations in the present work. As a consequence, in the next steps of the reaction, we consider the situation where the various intermediates stabilize themselves at the border of the cluster, involving both topmost and interfacial sites, whereas only topmost sites were involved previously.[49] In the present work, we thus consider this new location for intermediates throughout all the pathway.

The total electronic energy, enthalpy, entropy and Gibbs free energy of all species discussed in the present work, computed at 0 (see Figure 5), 500, 550, (see Figure 6), 625 (see Figure S45) and 800 K (see Figure S44), and at pressure of 1 bar, are reported in Supporting Information SI4 (see for instance Figures S46 and S47 for a comparative analysis of the five different temperatures). Indeed, the temperature range 500-700 K is typical of MCH dehydrogenation tests,[17–19,34,35] whereas 800 K is close to the conditions of naphtha reforming catalysis.[62–66] Similar to our previous work,[49] the Gibbs free energy profiles were represented in terms of dehydrogenation Gibbs free energy, using gas phase MCH and supported cluster (pure or Sn-doped) as references:

$$ \Delta_r G(i) = G_i + nG_{H_2(g)} - G_{MCH(g)} - G_{Pt_{13}}/\gamma - Al_2O_3 \quad (1) $$

with n = 1, 2, 3, and where i = C<sub>7</sub>H<sub>14-2n</sub>. Electronic energy (E), enthalpy (H) and entropy (S) variations of the same dehydrogenation reaction were defined similarly.

For each elementary step of the reaction mechanism, the dehydrogenation energies (Δ<sub>r</sub>E), corresponding Gibbs free energies (Δ<sub>r</sub>G) and activation energies, either expressed by total electronic energies (E<sub>a</sub>) or by Gibbs free energies (G<sub>a</sub>), are reported in Table 4 for the Sn-doped catalyst, and in Table S7 for the non-doped system.

Whatever the catalyst, the Gibbs free energy of the MCH dehydrogenation yielding toluene plus three dihydrogen molecules is favored from an entropic point of view. Its Gibbs free energy is slightly positive at 500 K (13.6 kJ/mol) and becomes negative above 550 K. Note also that the reaction enthalpy is endothermic at any temperature considered here (for instance +71.8 kJ/mol at 500 K, see Table S6), in agreement with experimental data.

## Energy profiles at 0 K, key-intermediates and transition states

On the Pt<sub>13</sub>H<sub>6</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub> catalyst model, the associative adsorption of the MCH molecule (intermediate A, in Figure 3) is stronger than the one on the non-doped catalyst model (at 0 K, ΔE<sub>ads</sub>=-85.1 kJ/mol for the Sn-doped system versus -67.3 kJ/mol for the undoped system). The Bader charge analysis reported in Table S2 shows that a negligible charge transfer occurs, from the surface to the MCH molecule (net value of 0.04 e), which is of similar extent with or without Sn. The dDsC dispersion component of the energies is the main contribution of those adsorption energies (-83.8 versus -70.5 kJ/mol) which also explains the largest part of the difference between the two catalysts. Thus, due to dispersion interactions, Sn-doping enhances the interaction of the MCH molecule with the catalyst. Moreover, we quantified the deformation energy of the supported cluster before and after adsorption of MCH. It appears that it is rather modest with respect to the adsorption energy: 16.4
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Lateral views of the optimized structures of the reaction intermediates considered for the MCH dehydrogenation on the Pt<sub>13</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub>(100) catalyst model (at the PBE-dDsC level). The color labels of the atoms are defined on A and TS<sub>A-B</sub> structures. At the transition states, the C and H atoms concerned by the C-H bond cleavages or by the H migration are depicted in black and yellow, respectively. Detailed views are displayed when necessary to better identify the transition state structures.</figcaption></figure>
<table><caption>**Table 4.** Reaction energy (Δ<sub>r</sub>E), reaction Gibbs free energy (Δ<sub>r</sub>G) and corresponding activation barrier (E<sub>a</sub>, G<sub>a</sub>) for the elementary steps involved in the methylcyclohexane dehydrogenation over Pt<sub>13</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub> at 0 K, 500 K, 550 K, 625 K and 800 K.</caption><thead><tr><th rowspan="2">kJ/mol</th><th colspan="2">0 K</th><th colspan="2">500 K</th><th colspan="2">550 K</th><th colspan="2">625 K</th><th colspan="2">800 K</th></tr><tr><th>Δ<sub>r</sub>E</th><th>E<sub>a</sub></th><th>Δ<sub>r</sub>G</th><th>G<sub>a</sub></th><th>Δ<sub>r</sub>G</th><th>G<sub>a</sub></th><th>Δ<sub>r</sub>G</th><th>G<sub>a</sub></th><th>Δ<sub>r</sub>G</th><th>G<sub>a</sub></th></tr></thead><tbody><tr><td>MCH<sub>(g)</sub> → A</td><td>-85.1</td><td>—</td><td>-0.9</td><td>—</td><td>6.9</td><td>—</td><td>18.5</td><td>—</td><td>45.0</td><td>—</td></tr><tr><td>A → B</td><td>-3.4</td><td>56.7</td><td>-9.1</td><td>40.8</td><td>-8.7</td><td>40.5</td><td>-8.1</td><td>39.9</td><td>-7</td><td>38.9</td></tr><tr><td>B → C</td><td>-22.5</td><td>95.4</td><td>-31.1</td><td>77.6</td><td>-32.2</td><td>77.3</td><td>-31.4</td><td>76.8</td><td>-31.9</td><td>76</td></tr><tr><td>C → D</td><td>96.4</td><td>—</td><td>36.7</td><td>—</td><td>31.4</td><td>—</td><td>23.4</td><td>—</td><td>4.9</td><td>—</td></tr><tr><td>D → E</td><td>-10.1</td><td>110.3</td><td>-21.3</td><td>90.1</td><td>-21.1</td><td>89.7</td><td>-20.9</td><td>89</td><td>-20.6</td><td>87.5</td></tr><tr><td>E → H'</td><td>21.4</td><td>73.4</td><td>0.7</td><td>44.1</td><td>-1.0</td><td>42.0</td><td>-3.5</td><td>39</td><td>-9.5</td><td>31.8</td></tr><tr><td>H' → H</td><td>-35.2</td><td>17.8</td><td>-39.3</td><td>2.3</td><td>-35.2</td><td>6.0</td><td>-40.8</td><td>spontaneous</td><td>-43.1</td><td>spontaneous</td></tr><tr><td>H → I</td><td>133.1</td><td>—</td><td>73.6</td><td>—</td><td>68.5</td><td>—</td><td>60.8</td><td>—</td><td>43.1</td><td>—</td></tr><tr><td>I → K</td><td>-67.5</td><td>36.8</td><td>-81.1</td><td>20.2</td><td>-81.7</td><td>19.8</td><td>-82.6</td><td>19</td><td>-84.9</td><td>17.4</td></tr><tr><td>K → M</td><td>-30.2</td><td>108.0</td><td>-37.1</td><td>91.6</td><td>-37.0</td><td>91.6</td><td>-37.1</td><td>91.5</td><td>-37.4</td><td>91.3</td></tr><tr><td>M → N</td><td>118.9</td><td>—</td><td>53.7</td><td>—</td><td>47.5</td><td>—</td><td>38.3</td><td>—</td><td>16.9</td><td>—</td></tr><tr><td>N → Toluene<sub>(g)</sub></td><td>168.4</td><td>—</td><td>68.8</td><td>—</td><td>59.6</td><td>—</td><td>46.0</td><td>—</td><td>14.9</td><td>—</td></tr></tbody></table>

<figure><img src="image_5.png" /><figcaption>**Figure 4.** Lateral views of the optimized structures of the transition states TS<sub>B-C</sub> and TS<sub>D-E</sub> involved in the MCH dehydrogenation on the Pt<sub>13</sub>/γ-Al<sub>2</sub>O<sub>3</sub>(100) and Pt<sub>13</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub>(100) catalyst models (at the PBE-dDsC level). The color labels of the atoms are defined. At the transition states, the C and H atoms concerned by the C-H bond cleavages or by the H migration are depicted in black and yellow, respectively. The C-H distances (red dotted lines) and related imaginary frequencies of C-H bond breaking are reported in each case.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Figure 5.** Total electronic energy profiles for the MCH dehydrogenation compared on $Pt_{13}H_6/\gamma$-Al$_2$O$_3$(100) and $Pt_{13}H_6/2Sn/\gamma$-Al$_2$O$_3$(100) catalyst models (at the PBE-dDsC level). Energies are given in kJ.mol$^{-1}$.</figcaption></figure>

kJ/mol for the non-doped cluster and 24.5 kJ/mol for the doped cluster. As expected, this contribution is slightly destabilizing, but as it will be illustrated in the following, it is far less than the one obtained once the molecule dehydrogenates on the cluster.

After adsorption of the MCH molecule, the first two steps correspond to C-H bond breaking reactions, producing methylcyclohexene plus 2H atoms co-adsorbed (species C). The corresponding electronic energy profiles for both types of catalysts at 0 K are illustrated in Figure 5. When comparing the two catalysts, these two steps exhibit similar barriers and reaction energies. The saddle point of these transformations corresponds to a three-center transition state, involving one platinum atom, the hydrogen and the carbon atoms from the breaking C-H bond (see Figures 4(a), (c) illustrating $TS_{B-C}$ on pure $Pt_{13}$ and Sn-doped-$Pt_{13}$ catalysts, respectively). On both catalysts, the second step requires higher activation energies than the first one (95.4 versus 56.7 kJ/mol for the doped catalyst). In line with observations made for the respective stabilities of A species on the doped and non-doped catalysts (see above), the profile remains shifted to lower energies for the $Pt_{13}/2Sn/\gamma$-Al$_2$O$_3$ system, although the difference tends to decrease as the reaction goes on. This cannot be assigned to the dispersion term of the dehydrogenation energy (being -72.0 and -58.2 kJ/mol for the C species on the doped and non-doped catalyst, respectively), of which the difference (between the two catalysts) remains about the same from A to C (-13.2 and -13.8 kJ/mol respectively, in favour of the doped catalyst).

The next step ($C \rightarrow D$) corresponds to $H_2$ desorption, which is slightly less endothermic on the doped catalyst (96.4 kJ/mol) than on the Pt catalyst (101.5 kJ/mol). $D \rightarrow E$ is the third C-H bond breaking step leading to methylcyclohexenyl,

which exhibits a significantly higher activation barrier in the case of the Sn-doped catalyst (110.3 kJ/mol versus 75.5 kJ/mol for the non-doped catalyst). The origin of the ranking in energy of $TS_{D-E}$ from one catalyst to the other cannot be found in the dispersion energy terms (still in the favor of the Sn-doped catalyst). To demonstrate this, the energy of the supported cluster hosting the transition structure was computed at the fixed geometry of $TS_{D-E}$. It reveals that the cluster is less deformed in the presence of Sn than in its absence (deformation energy with respect to the reference cluster: 31.9 versus 53.8 kJ/mol, respectively). This shows that interfacial oxidized tin makes the cluster less ductile, contrary to what was observed for tin(0) in the supported $Pt_{13-x}Sn_x$ cluster.[50] A compared analysis of the optimized structures of $TS_{D-E}$ with or without tin is provided in Figures 4 (b) and (d). The length of the breaking C-H bond is larger in the case of the Sn-doped catalyst, hence the transition state is a later one with respect to the non-doped catalyst. This suggests that although oxidized interfacial tin leads to a stabilization of the hydrocarbon moieties by dispersion interaction, the strong polarisation of the platinum cluster induced by oxidized tin decreases its ability to change its shape for some transition structures, and leads to less covalent interactions.

The two steps that come afterwards (one C-H bond breaking, yielding methylcyclohexadiene, and one H migration) exhibit similar features for both catalysts, whereas the profile for the Sn-doped catalysts systematically lies at lower energy than the one of the non-doped, as it was the case from A to D.

Once methylcyclohexadiene is formed, a second $H_2$ desorption takes place ($H \rightarrow I + H_2$). For the pure-platinum cluster, the electronic energy cost of this second $H_2$ des-
orption (104 kJ/mol) is about the same as that of the first
desorption (101.5 kJ/mol). The situation is more contrasted
for the Sn-doped catalyst (133.1 versus 96.4 kJ/mol for the
second and first desorption, respectively). A Bader charge
analysis (Table S2) performed on the I species (adsorbed
methylcyclohexadiene on both catalysts shows that the Pt<sub>13</sub>
cluster adapts its charge much more strongly to the adsorp-
tion of molecules in the absence of tin than in its presence
. In the presence of methylcyclohexadiene and 6 H atoms
 cor respond ing to species I), the charge of Pt<sub>13</sub> becomes sig-
nificantly negative (-0.73 e) on Pt<sub>13</sub>H<sub>6</sub>/γ-Al<sub>2</sub>O<sub>3</sub>, whereas it
is slightly positive (0.15 e) on Pt<sub>13</sub>H<sub>6</sub>/2Sn@γ-Al<sub>2</sub>O<sub>3</sub>. As
the molecule itself is positively charged (0.15 and 0.08 e re-
spectively), a small electrostatic repulsion is expected in the
case of the doped catalyst, whereas an attractive one may
take place on the non-doped catalyst.

Finally, the last part of the profile corresponds to the for-
mation of toluene from adsorbed methylcyclohexadiene (I)
through two successive C-H bond breaking (the fifth and
the sixth ones among the whole sequence), followed by H₂
and toluene desorption. On both catalysts, the activation
energy of the fifth C-H bond breaking (producing toluene)
is much lower than the sixth one: for example, on the Sn-
doped catalyst, Eₐ=36.8 and 108.0 kJ/mol for the fifth and
the sixth C-H bond breaking, respectively. Moreover, the
fifth C-H bond breaking exhibits the lowest activation en-
ergy among the six C-H bond cleavages. The specificity of
this step is the assistance of a slight rotation of the molecule
to bring the C atom of the breaking C-H bond closer to the
binding surface Pt atom. The corresponding C-Pt bond of
the three-center C-H-Pt structure is indeed the shortest one
in TSᵢₖ in comparison with any other TS (2.24 and 2.23 Å
for the doped and non-doped catalysts, respectively). In
this TS, the molecule accesses a much stable η₅μ₃ adsorp-
tion configuration formally corresponding to two π and one
σ bonds between the intermediate and the cluster. Species
M corresponds to adsorbed toluene (still in the presence of
the two extra H atoms transferred to the cluster by the fifth
and the sixth C-H bond scissions). The energy difference
between the two catalysts for M (-51.5 and -37.1 kJ/mol
for the doped and non-doped catalysts, respectively) again
reflects the stabilizing effect of dispersion energy on the Sn-
doped system. Adsorbed toluene in presence of the 6 initial
H atoms (species N) is formed from M after the third H₂
desorption. It is remarkable that the energy level of N is sig-
nificantly higher on Sn-doped catalyst (115.8 kJ/mol) than
on the pure platinum catalyst (80.0 kJ/mol). In this case,
the dispersion component to the dehydrogenation energy
is about the same for the doped and non-doped catalysts.
However, a decomposition of the energy of N shows that
the deformation of toluene (103.8 versus 80.1 kJ/mol on
the non-doped and doped catalysts respectively) and of the
supported cluster (227.5 versus 109.2 kJ/mol on the non-
doped and doped catalysts, respectively) is stronger on the
non-doped catalyst, the interaction energy between toluene
and the cluster being much more negative on the non-doped
system (-535.5 versus -357.8 kJ/mol on the non-doped and
doped catalysts, respectively). Thus, when toluene is ad-
sorbed on Pt₁₃H₆/2Sn@γ-Al₂O₃, the cluster is less prone to
be deformed than in the absence of tin, making the interac-
tion with the molecule weaker. The phenomenon is stronger
than the one reported on TS₉ₐ above. This is likely a con-
sequence of the increased metal/support interaction in the
presence of oxidized tin, that would make the cluster less

ductile under the influence of the toluene molecule.

Gibbs free energy profiles and application
of the energy span concept

According to the data reported in the section SI4 of the Supporting Information and due to entropy/enthalpy compensations, the adsorption Gibbs free energy of MCH on the Sn-doped catalyst is nearly zero (-0.9 kJ/mol) at 500 K, whereas it is slightly positive for the non-doped catalyst (12.1 kJ/mol). Nevertheless, the (free) adsorption energy difference between the two catalysts is similar with or without entropic effects.

Increasing the temperature makes the intermediates of
the first part of the profile (until B or C, depending on
the catalyst and the temperature) appear at a positive de-
hydrogenation reaction Gibbs free energy, while the next
intermediates all exhibit a negative dehydrogenation reac-
tion Gibbs free energy. This is an expected consequence of
entropy contribution, as the first steps pay the penalty for
MCH adsorption, while starting from C, gradual H₂ desorp-
tion compensates this loss, until the final toluene desorption
(from species N).

The profiles at 550 K for both catalysts, as illustrated by
Figure 6, show that most intermediates are most stable on
the Sn-doped catalyst, although TS<sub>D-E</sub> is higher in Gibbs
free energy. From a kinetic perspective, the intermediate
C, which is much lower in Gibbs free energy than D, will
be kinetically relevant, thus the effective activation barrier
has to be computed between C and TS<sub>D-E</sub> instead of the
direct activation barrier between D and TS<sub>D-E</sub>. The same
holds true for H versus I. Regarding the last two steps of
the reaction, M is the kinetically relevant intermediate to
be considered for the Sn-doped catalysts, whereas N has to
be invoked for the pure platinum one.

We applied the energy span concept[67,68] to compare the
turn over frequency (TOF) determining transition states
(TDTS) and intermediates (TDI), depending on the cat-
alyst, and analyse the kinetically relevant Gibbs free energy
barriers. The Gibbs free energy span (ΔG<sub>ES</sub>) results from
the difference between the energies of the highest TS found
throughout the Gibbs free energy profile and of the low-
est surface intermediate. When the TDTS appears after
the TDI, ΔG<sub>ES</sub> = G<sub>TDTS</sub> - G<sub>TDI</sub>. Alternatively ΔG<sub>ES</sub> =
G<sub>TDTS</sub> - G<sub>TDI</sub> + Δ<sub>r</sub>G, if the TDTS appears before the TDI.
Δ<sub>r</sub>G is the reaction Gibbs free energy for the global reac-
tion (production of gas phase toluene and hydrogen from gas
phase methylcyclohexane). In the present case, the Gibbs
free energy of the overall reaction (from methylcyclohexane
to toluene and three molecules of dihydrogen) is positive
at 550 K, whereas it is negative at 550 K and higher tem-
peratures, so that the energy span concept can be applied
for temperatures higher than 550 K, where the reaction be-
comes catalytically favorable. The results of this analysis
are reported in Table 5. For the non-doped catalyst, irre-
spective of the temperature, we find that the TDI is species
N (toluene co-adsorbed with 6 H atoms) and the TDTS
is TS<sub>A-B</sub> (first C-H bond cleavage). The Gibbs free energy
span gradually decreases as the temperature decreases, from
164.0 (550 K) to 155.6 kJ/mol (800 K). Figure S46 which
displays the profiles for the non-doped catalyst computed
at all temperatures, indicates that this decrease is mainly
due to the fact that the Gibbs free energy of reaction (Δ<sub>r</sub>G)
intervenes in the calculation of the Gibbs free energy span
<figure><img src="image_7.png" /><figcaption>**Figure 6.** Gibbs free energy profiles at 550 K for the MCH dehydrogenation compared on $Pt_{13}H_6/\gamma$-Al$_2$O$_3$(100) and $Pt_{13}H_6/2Sn@\gamma$-Al$_2$O$_3$(100) catalyst models (at the PBE-dDsC level). Energies are given in kJ.mol$^{-1}$.</figcaption></figure>

(as aforementioned, the TDI appearing after the TDTS in the reaction sequence) and decreases more abruptly with temperature than the Gibbs free energies of the TDI and of the TDTS. For the Sn-doped catalyst, at 550 and 625 K, the TDI is species M (toluene co-adsorbed with 8H atoms) and the TDTS is $TS_{D-E}$ (third C-H bond cleavage). However, at 800 K, the nature of the TDTS changes and becomes $TS_{B-C}$. The Gibbs free energy increases with temperature is indeed much pronounced for $TS_{B-C}$ than for $TS_{D-E}$, of which the Gibbs free energy is weakly dependent on temperature (see Figure S47). Despite this change, the increase in Gibbs free energy of the TDTS with temperature remains modest with respect to the decrease of the Gibbs free energy of reaction, making the Gibbs free energy span drop significantly when temperature increases.

Thus, comparing the Gibbs free energy spans from one catalyst to the other shows that oxide forms of tin induce a loss of reactivity of the platinum clusters at 550 and 625 K: the Gibbs free energy span differences are 31.3 and 14.4 kJ/mol at 550 and 625 K, respectively, in favor of undoped catalyst. However, the Gibbs free energy span becomes lower by about 9.8 kJ/mol for the Sn doped system at 800 K which may reveal a beneficial role of Sn. As a consequence of this analysis, the role of Sn on the catalytic reactivity is dual. Indeed, the catalytic enhancement should be observable at higher temperatures only, whereas for the lower ones, interfacial Sn oxide species would inhibit the dehydrogenation activity.

## Comparison with experimental data

It remains rather challenging to compare in a consistent way our calculated data with experimental ones. Among

the numerous previous kinetic experiments reported on Pt and Sn-doped Pt catalysts, the conclusions disagree on the nature of the apparent limiting step and activation energies.[11,26,62,63] Starting from the earlier study by Sinfelt *et al.* proposing that the toluene desorption step would be the limiting one,[11] the subsequent ones have proposed alternative steps based on different kinetic models, catalytic properties and experimental conditions. Alternatively, we have previously proposed an analysis based on the energetic span concept which allows to identify TDI and TDTS and the corresponding Gibbs free energy of activations for the two model catalysts. Interestingly, in both catalysts the TDI corresponds to the late species (N for the non-doped and M for the doped system), which could be qualitatively in line with the earlier finding by Sinfelt *et al.* and more recent proposals[19,69] stating that adsorbed toluene is key for the catalysts' reactivity or its inhibition. However, the energetic span analysis also shows that TDTS would be driven by the energy levels of a TS located in the first part of the reaction ($TS_{A-B}$ for Pt and $TS_{B-C}$ or $TS_{D-E}$) corresponding to one of the first three C-H bond cleavages. This aspect would be in line with other studies[62] showing that the limiting step involves the first dehydrogenation step. The first interpretation is that experimental kinetic analysis cannot be achieved by considering one single rate limiting step controlled by two subsequent energy levels. By contrast, the MCH dehydrogenation reactivity is controlled by TDTS and TDI which are far away from each other. Such a property cannot be captured by simple kinetic modeling assuming one given rate limiting step and may explain the large discrepancies observed between the various kinetic data reported in the literature. A more systematic comparison with previous experimental data could be achieved by building a complete
microkinetic modeling of the reaction based on the current DFT data, which remains beyond the scope of the present work.

Considering the comparison of the two different catalytic systems and the role of Sn oxidized species, our DFT analysis is also in qualitative agreement with the experimental knowledge. Indeed, no positive effect of the Sn dopant on the intrinsic activity has been experimentally highlighted so far. For instance, kinetic studies on cyclohexane (CH) dehydrogenation by Passos *et al.* revealed that the presence of Sn slightly decreases the dehydrogenation activity with respect to pure Pt supported on alumina for temperatures between 520 and 570 K, while the apparent activation energy were poorly affected.[34] A similar result was found by Gonzalez-Marcos *et al.* who showed that TOF in CH dehydrogenation decreases upon Sn addition.[33] More recently, Murata *et al.* shows that the TOF of MCH dehydrogenation is weakly sensitive to Sn/Pt ratio.[19] This is compatible with the higher activation Gibbs free energy estimated with energetic span for the Sn-doped catalyst at 550 and 625 K.

Tin is often invoked to improve the stability of Pt based catalysts, particularly in model reactions relevant for naphtha reforming.[27–34] This trend is also illustrated by Murata’s work highlighting the decrease of MCH conversion as a function of time on stream in the case of Pt catalyst, while this decrease is prevented in the case of Sn-doped Pt catalyst.[19] The interpretation of this deactivation process is still open and its origins may be rather diverse. On the one hand, the structure and size of the metallic particles may evolve and in particular, the sintering of Pt particles may occur. On the other hand, the over-stabilization of MCH dehydrogenated intermediates, such as methylcyclohexadiene or toluene on the catalyst, could inhibit the reaction or even favor the formation of diphenylmethane or dicyclopentadiene compounds, invoked as coke precursors.[70,71] The role of Sn species located either on the support (as oxidized species) or in Pt particles could thus influence both aspects. Considering the effects of Sn oxidized interfacial atoms as simulated in the present work, we showed that the interaction of the Pt cluster with the alumina support is significantly enhanced by oxidized Sn interfacial atoms located on the alumina surface. This stronger interaction is induced by the formation of Pt-Sn-O bridges (with covalent Pt-Sn bonds) at the interface of the alumina surface and the cluster (see Table S1 and Figure S7). This effect may explain the beneficial impact of oxidized Sn on the stronger anchoring of small Pt particles which prevents them from their surface diffusion and their possible sintering.

Moreover, this stronger Pt/Sn-doped alumina interaction induces a second effect on the structural behavior (ductility) of the Pt cluster in presence of the dehydrogenated intermediates/products of MCH. We found that the stabilities of methylcyclohexadiene and toluene adsorbed on the pure Pt cluster (species I and N in Figure 6) are decreased because of a weaker ductility of the Pt cluster in presence of oxidized Sn atoms. Considering the Gibbs free energy profile (Figure 6), we thus observe that it is easier for species I and N to be transformed into K or for toluene to desorb when Sn oxidized atoms are present. Indeed, the corresponding energy barriers are decreased by about 16.4 and 27.7 kJ/mol for I → K and N → Toluene(g), respectively, for Sn-doped alumina vs non-doped alumina. Hence, Sn atoms seem to reduce the probability of these intermediates to act as coke precursors through diphenylmethane or dicyclopentadiene

compounds. This interpretation seems to corroborates an interpretation made by Nagatake *et al.* who revealed that Pt/TiO₂ catalyst is less deactivated than Pt/Al₂O₃ due to a stronger metal-support interaction (SMSI) effect which reduces the inhibiting effect of toluene.[69] However, this analysis may strongly depend on the H-coverage chosen for our DFT approach. If we consider species H and M (containing two additional coadsorbed hydrogen atoms), the order of stability is now reversed between the two catalysts. So, to refine this result, one may propose for future works to analyse more closely the intermediates stability as a function of H-coverage and reaction conditions. Similar approaches have been undertaken for analyzing the stability of C₂Hₓ and C₁Hₓ species on Pt clusters supported on alumina in experimental conditions.[72]

## Conclusion

Thanks to DFT calculations performed at the PBE-dDsC level, we identified the nature and role of oxidized forms of tin on the reactivity of Pt₁₃ cluster supported on Sn-doped γ-Al₂O₃(100) surface for the dehydrogenation of methylcyclohexane into toluene, a relevant reaction in the context of LOHC and catalytic naphtha reforming.

We first proposed models for the γ-Al₂O₃(100) doped with Sn⁴⁺ and Sn²⁺ interfacial atoms, by substitution of two surface Al³⁺ species. The most stable configuration found exhibits two Sn atoms substituting two pentahedral surface Al atoms (that would have been octahedral in the bulk). In presence of the Pt₁₃ cluster, the oxidation state of Sn atoms becomes closer to 2+. At the same time, the Pt₁₃ cluster experiences stronger metal-support interaction when the alumina surface is doped by Sn. Moreover, from Bader charge analysis, the Pt₁₃ cluster shows a strongly negative charge on the non-doped surface due to charge transfer from the support, whereas it is almost neutral on the Sn-doped support, a trend that does not follow the respective electronegativities of Sn and Pt. This is likely due to the fact that we consider here already oxidized forms of tin. The stronger Pt/Sn-doped alumina interaction is proposed to prevent the sintering of Pt particle and thus to be beneficial for the stabilization of the Pt cluster as invoked experimentally.

The identification of reaction intermediates in methylcyclohexane dehydrogenation into toluene was performed by starting from Pt₁₃H₆ clusters, and by making use of a simulated annealing approach for exploring configurations. Transition states were identified for each C-H bond breaking and for H migration elementary steps. The Gibbs free energy profiles were quantified and the energy span concept was used to compare the reactivity of both doped and non-doped catalysts. The impact of oxidized forms of tin on the reactivity of the supported Pt₁₃ clusters is shown to vary with temperature, being slightly detrimental at 550 and 625 K (typical of LOHC), but beneficial at 800 K (typical of catalytic reforming). This result is not in contradiction with the experimental literature where the impact of tin on the intrinsic dehydrogenation of LOHC is either slightly negative or negligible.

Moreover, the energetic span analysis showed that TDI and TDTS are well separated species along the energy profile, which may explain why numerous published experimental kinetic models based on the hypothesis of one rate limiting step provided diverging results on activation energies
<table><caption>**Table 5.** Nature of TOF-determining intermediate (TDI) and transition state (TDTS), Gibbs free energy span $\Delta G_{ES}$ and global reaction Gibbs free energy $\Delta_r G$ (kJ/mol) for the given temperature, for Sn-undoped and doped catalysts.</caption><thead><tr><th rowspan="2">Catalyst</th><th rowspan="2">TDI</th><th colspan="3">550 K</th><th colspan="3">625 K</th><th colspan="3">800 K</th></tr><tr><th>TDTS</th><th>ΔG<sub>ES</sub></th><th>Δ<sub>r</sub>G</th><th>TDTS</th><th>ΔG<sub>ES</sub></th><th>Δ<sub>r</sub>G</th><th>TDTS</th><th>ΔG<sub>ES</sub></th><th>Δ<sub>r</sub>G</th></tr></thead><tbody><tr><td>Pt<sub>13</sub>/γ-Al<sub>2</sub>O</td><td>N</td><td>TS<sub>A-B</sub></td><td>164.0</td><td>-6.6</td><td>TS<sub>A-B</sub></td><td>161.4</td><td>-37.3</td><td>TS<sub>A-B</sub></td><td>155.6</td><td>-109.6</td></tr><tr><td>Pt<sub>13</sub>/2Sn@γ-Al<sub>2</sub>O</td><td>M</td><td>TS<sub>D-E</sub></td><td>195.3</td><td>-6.6</td><td>TS<sub>D-E</sub></td><td>175.8</td><td>-37.3</td><td>TS<sub>B-C</sub></td><td>145.8</td><td>-109.6</td></tr></tbody></table>

and mechanisms. In the future, a complete microkinetic model based on our DFT data should be built to revisit these earlier experimental data.

For most species, Sn-doping induces an increase of the stabilisation of adsorbed molecules and radicals thanks to an excess of dispersion interactions with respect to the non-doped system. On some specific cases however, electrostatic effects play a destabilizing role (positively charged substrate and slightly positively charged cluster due to electronic transfer to Sn), and/or tin reduces the ductility of the platinum cluster due to enhanced metal-support interactions. This leads to less stable methylcylohexadiene and toluene in the presence of tin. Since these intermediates are experimentally regarded as potential coke precursors, this effect was proposed to be beneficial for preventing from the destabilization of Sn-doped catalyst as observed experimentally. To further confirm this interpretation, we suggest to investigate more thoroughly the effect of hydrogen coverage on the stability of these intermediates for both catalysts in the future.

## Methodology

The catalyst models are built based on the dehydrated (100) γ-Al₂O₃ surface model by Digne *et al.*, [73,74] constructed on the basis of the γ-Al₂O₃ bulk model by Krokidis *et al.* [75] The validity of this surface model was recently confirmed by simulating the topotactic transformation of boehmite slabs into γ-Al₂O₃ slabs. [76] In the present work, we consider a 4-layer thickness (without numbering the tetrahedral aluminum atoms) (2×3) slab (plus 15 Å vacuum, leading to a supercell of dimensions 16.71×16.79×25.80 Å³), on which a biplanar Pt₁₃ cluster is supported, [52,60] holding 6 coadsorbed hydrogen atoms.

Periodic DFT calculations were performed with the VASP code [77,78] using the PBE (Perdew, Burke, and Ernzerhof) exchange-correlation functional [79], with the dDsC [80] dispersion correction. The choice of the dispersion correction scheme was made on the basis of the computation of the lattice parameters, cohesion energy and bulk modulus of Sn, SnO and SnO₂ (see supporting information SI5). The projected-augmented-wave (PAW) method [81] was used to describe the core-electrons interactions. For Sn, the pseudopotential chosen is the one with the most extended valence available (14 valence electrons). The plane wave basis set was limited to a kinetic cut-off energy of 400 eV. A Gaussian smearing with $\sigma$ equal to 0.02 eV was applied. The convergence criterion for the electronic self-consistent field relaxation was fixed to $10^{-6}$ eV, and all calculations were performed at the Γ-point of the Brillouin zone. Spin-polarized calculations performed on the supported Pt and PtSn clusters with and without hydrogen revealed that they are non-magnetic, consistently with previous reports. [50,60]

Thus, the next parts of the investigation were performed by non-spin polarized calculations. Due to the non-symmetric nature of the slabs, a dipolar correction was applied perpendicular to these. Charges were estimated thanks to the approach of Bader, [82,83] with an increased energy cutoff of 500 eV.

Geometry optimizations were made with a convergence criterion on forces of 0.02 eV.Å⁻¹. In relaxation processes, the degrees of freedom of two alumina layers, the cluster and its adsorbates were completely relaxed. The sampling of local energy minima was performed thanks to velocity-scaled *ab initio* molecular dynamics (AIMD) at 500 K, with a time-step of 5 fs over 2000 steps. The hydrogen mass was fixed at 10 g/mol instead of 1 g/mol to accelerate the exploration of the potential energy surface. The same set of atoms as during geometry optimization was kept fixed during AIMD simulations. Selected low energy configurations identified during AIMD were then quenched by geometry optimization. This protocol is the same as the one previously used in ref. [49], but with the difference that herein, this exploration has been done at the PBE-dDsC level, instead of PBE in the previous work. Thus, we completely re-explored the potential energy surface for the Pt₁₃ supported on the non-doped alumina surface with this new intermediate location hypothesis.

Transition state search was performed by using the nudged elastic band (NEB) method [84,85] as implemented in the VASP Transition State Theory (VTST) module, [86] with 10 images including reactant and product, then picked up the points near the higher energy point among the results and performed a climbing-image NEB (CI-NEB) calculation. [87] When necessary, a quasi-Newton algorithm [88] relaxation was performed to reach the saddle point, with a convergence criterion on forces of 0.01 eV.Å⁻¹. The species are concluded to be transition states when only one imaginary frequency is found.

The atomic structures of all intermediates and transition states for the two catalysts are provided in [89,90].

Harmonic vibration frequencies were computed by the finite difference method, with a displacement of $\pm 0.01$ Å in each direction for all relaxed atoms (the same as for optimization steps). They are performed both to identify saddle points and to compute reaction Gibbs free energies, assuming that condensed phase (including adsorbed molecules) only exhibit vibrational degrees of freedom, and that the partial pressure of gases is 1 bar.
Acknowledgements

This work is part of the “RatiOnAl Design for CATalysis”
(ROAD4CAT) industrial chair, project IDEXLYON funded
by the French National Research Agency (ANR-16-IDEX-
0005) and the Commissariat General for Investment (CGI)
within the framework of Investissements d’Avenir program
(“Investment for the future”). Calculations were performed
using HPC resources from IFP Energies nouvelles (ENER440).

Conflict of Interest

No conflict of interest to declare.

Keywords: dehydrogenation • platinum • tin • alumina •
density functional theory

References

[1] L. Schlapbach, A. Züttel, *Nature* **2001**, *414*, 353.

[2] J.-N. Chotard, W. S. Tang, P. Raybaud, R. Janot, *Chem. Eur. J.* **2011**, *17*, 12302.

[3] D. Teichmann, W. Arlt, P. Wasserscheid, R. Freymann, *Energy Environ. Sci.* **2011**, *4*, 2767.

[4] P. Preuster, C. Papp, P. Wasserscheid, *Acc. Chem. Res.* **2017**, *50*, 74.

[5] D'Ambra, Florian, Gébel, Gérard, *Sci. Tech. Energ. Transition* **2023**, *78*, 32.

[6] E. Gianotti, M. Taillades-Jacquin, J. Roziere, D. J. Jones, ACS Catal. **2018**, *8*, 4660.

[7] C. Wang, D. Astruc, *Chem. Soc. Rev.* **2021**, *50*, 3437.

[8] Y. Sekine, T. Higo, *Top. Catal.* **2021**, *64*, 470.

[9] Z. Dong, A. Mukhtar, H. Lin, *Top. Catal.* **2021**, *64*, 481.

[10] J. Meng, F. Zhou, H. Ma, X. Yuan, Y. Wang, J. Zhang, *Top. Catal.* **2021**, *64*, 509.

[11] J. H. Sinfelt, H. Hurwitz, R. A. Shulman, *J. Phys. Chem.* **1960**, *64*, 1559.

[12] P. Leprince, *Le raffinage du pétrole. Tome 3. Procédés de transformation, Chapitre 4: Reformage catalytique, Editions Technip, Weinheim* **1998**.

[13] J. Sinfelt, *Catalytic Reforming, in Handbook of Heterogeneous Catalysis*, Wiley-VCH, Weinheim **1997**.

[14] P.-Y. L. Goff, W. Kostka, J. Ross, *Catalytic Reforming, in Springer Handbook of Petroleum Technology*, Springer **2017**.

[15] P. Avenier, D. Bazer-Bachi, F. Bazer-Bachi, C. Chizallet, F. Deleau, F. Diehl, J. Gornay, E. Lemaire, V. Moizan-Basle, C. Plais, P. Raybaud, F. Richard, S. Lacombe, *Oil Gas Sci. Technol.- Rev. IFPEN* **2016**, *71*, 41.

[16] O. Said-Aizpuru, F. Allain, F. Diehl, D. Farrusseng, J.-F. Joly, A. Dandeu, *New J. Chem.* **2020**, *44*, 7243.

[17] J. Chaouki, A. Touzani, D. Klvana, J. Bournonville, G. Belanger, *Rev. Inst. Fr. Pét.* **1988**, *43*, 873.

[18] S. Tschudin, T. Shido, R. Prins, A. Wokaun, *J. Catal.* **1999**, *181*, 113.

[19] K. Murata, N. Kurimoto, Y. Yamamoto, A. Oda, J. Ohyama, A. Satsuma, *ACS Appl. Nano Mater.* **2021**, *4*, 4532.

[20] Y. Deng, Y. Guo, Z. Jia, J.-C. Liu, J. Guo, X. Cai, C. Dong, M. Wang, C. Li, J. Diao, Z. Jiang, J. Xie, N. Wang, H. Xiao, B. Xu, H. Zhang, H. Liu, J. Li, D. Ma, J. Am. Chem. Soc. **2022**, *144*, 3535.

[21] F. Auer, D. Blaumeiser, T. Bauer, A. Bösmann, N. Szesni, J. Libuda, P. Wasserscheid, *Catal. Sci. Technol.* **2019**, *9*, 3537.

[22] C.-I. Ahn, Y. Kwak, A.-R. Kim, M. Jang, A. Badakhsh, J. Cha, Y. Kim, Y. S. Jo, H. Jeong, S. H. Choi, S. W. Nam, C. W. Yoon, H. Sohn, *Appl. Catal. B* **2022**, *307*, 121169.

[23] J. J. H. B. Sattler, J. Ruiz-Martinez, E. Santillan-Jimenez, B. M. Weckhuysen, *Chem. Rev.* **2014**, *114*, 10613.

[24] A. T. F. Batista, C. Chizallet, F. Diehl, A.-L. Taleb, A.-S. Gay, O. Ersen, P. Raybaud, *Nanoscale* **2022**, *14*, 8753.

[25] E. E. Wolf, E. E. Petersen, *J. Catal.* **1977**, *46*, 190.

[26] G. Maria, A. Marin, C. Wyss, S. Muller, E. Newson, *Chem. Eng. Sci.* **1996**, *51*, 2891.

[27] A. Muller, P. Engelhard, J. Weisang, *J. Catal.* **1979**, *56*, 65.

[28] R. Burch, L. Garla, J. Catal. **1981**, *71*, 360.

[29] R. Burch, A. J. Mitchell, *Applied Catalysis* **1983**, *6*, 121.

[30] A. N. Jahel, V. Moizan-Baslé, C. Chizallet, P. Raybaud, J. Olivier-Fourcade, J.-C. Jumas, P. Avenier, S. Lacombe, J. Phys. Chem. C **2012**, *116*, 10073.

[31] N. Macleod, J. Fryer, D. Stirling, G. Webb, *Catal. Today* **1998**, *46*, 37.

[32] B. H. Davis, *Catal. Today* **1999**, *53*, 443.

[33] M. González-Marcos, B. Íñarra, J. Guil, M. Gutiérrez-Ortiz, *Appl. Catal. A* **2004**, *273*, 259.

[34] F. B. Passos, D. A. Aranda, M. Schmal, *J. Catal.* **1998**, *178*, 478.

[35] J. Yan, W. Wang, L. Miao, K. Wu, G. Chen, Y. Huang, Y. Yang, *Int. J. Hydrog. Energy* **2018**, *43*, 9343.

[36] R. Burch, *Journal of Catalysis* **1981**, *71*, 348.

[37] J. Olivier-Fourcade, M. Womes, J.-C. Jumas, F. Le Peltier, S. Morin, B. Didillon, *ChemPhysChem* **2004**, *5*, 1734.

[38] M. Womes, F. Le Peltier, S. Morin, B. Didillon, J. Olivier-Fourcade, J. Jumas, *J. Mol. Catal. A* **2007**, *266*, 55.

[39] A. Jahel, P. Avenier, S. Lacombe, J. Olivier-Fourcade, J.-C. Jumas, *J. Catal.* **2010**, *272*, 275.

[40] C. Chizallet, P. Raybaud, *Catal. Sci. Technol.* **2014**, *4*, 2797.

[41] E. Fernández, M. Boronat, *Journal of Physics: Condensed Matter* **2018**, *31*, 013002.

[42] D. N. Gemechu, A. M. Mohammed, M. Redi, D. Bessarabov, Y. S. Mekonnen, K. O. Obodo, *Int. J. Hydrog. Energy* **2023**, *48*, 33186.

[43] M. Saeys, M.-F. Reyniers, J. W. Thybaut, M. Neurock, G. B. Marin, *J. Catal.* **2005**, *236*, 129.

[44] H.-Y. Ma, G.-C. Wang, *J. Catal.* **2011**, *281*, 63.

[45] M. K. Sabbe, G. Canduela-Rodríguez, M.-F. Reyniers, G. B. Marin, *J. Catal.* **2015**, *330*, 406.

[46] F. Chen, Y. Huang, C. Mi, K. Wu, W. Wang, W. Li, Y. Yang, *Int. J. Hydrog. Energy* **2020**, *45*, 6727.

[47] C. Mi, Y. Huang, F. Chen, K. Wu, W. Wang, Y. Yang, *Int. J. Hydrog. Energy* **2021**, *46*, 875.

[48] K. Onyebuchi, *Appl. Surf. Sci.* **2022**, *584*, 152590.
[49] W. Zhao, C. Chizallet, P. Sautet, P. Raybaud, J. Catal. **2019**, *370*, 118.

[50] A. Gorczyca, P. Raybaud, V. Moizan, Y. Joly, C. Chizallet, *ChemCatChem* **2019**, *11*, 3941.

[51] A. T. F. Batista, W. Baaziz, A.-L. Taleb, J. Chaniot, M. Moreaud, C. Legens, A. Aguilar-Tapia, O. Proux, J.-L. Hazemann, F. Diehl, C. Chizallet, A.-S. Gay, O. Ersen, P. Raybaud, *ACS Catalysis* **2020**, *10*, 4193.

[52] C. Mager-Maury, G. Bonnard, C. Chizallet, P. Sautet, P. Raybaud, *ChemCatChem* **2011**, *3*, 200.

[53] A. Gorczyca, V. Moizan, C. Chizallet, O. Proux, W. DelNet, E. Lahera, J.-L. Hazemann, P. Raybaud, Y. Joly, *Ang. Chem., Int. Ed.* **2014**, *53*, 12426.

[54] G. Meitzner, G. H. Via, F. W. Lytle, S. C. Fung, J. H. Sinfelt, J. Phys. Chem. **1988**, *92*, 2925.

[55] A. Caballero, H. Dexpert, B. Didillon, F. LePeltier, O. Clause, J. Lynch, J. Phys. Chem. **1993**, *97*, 11283.

[56] J. Olivier-Fourcade, M. Womes, J.-C. Jumas, F. Le Peltier, S. Morin, B. Didillon, *ChemPhysChem* **2004**, *5*, 1734.

[57] G. J. Siri, J. M. Ramallo-López, M. L. Casella, J. L. Fierro, F. G. Requejo, O. A. Ferretti, *Appl. Catal. A* **2005**, *278*, 239.

[58] L. Shi, G.-M. Deng, W.-C. Li, S. Miao, Q.-N. Wang, W.-P. Zhang, A.-H. Lu, *Ang. Chem., Int. Ed.* **2015**, *54*, 13994.

[59] N. Kaylor, R. J. Davis, J. Catal. **2018**, *367*, 181.

[60] C. H. Hu, C. Chizallet, C. Mager-Maury, M. Corral-Valero, P. Sautet, H. Toulhoat, P. Raybaud, J. Catal. **2010**, *274*, 99.

[61] C. Mager-Maury, C. Chizallet, P. Sautet, P. Raybaud, *ACS Catal.* **2012**, *2*, 1346.

[62] M. Usman, D. Cresswell, A. Garforth, *Ind. Eng. Chem. Res.* **2012**, *51*, 158.

[63] F. Alhumaidan, D. Cresswell, A. Garforth, *Ind. Eng. Chem. Res.* **2011**, *50*, 2509.

[64] J. H. Sinfelt, J. Mol. Catal. A **2000**, *163*, 123.

[65] A. Rochefort, F. Lepeltier, J. Boitiaux, J. Catal. **1994**, *145*, 409.

[66] P. A. Van Trimpont, G. B. Marin, G. F. Froment, *Ind. Eng. Chem. Fund.* **1986**, *25*, 544.

[67] S. Kozuch, S. Shaik, *Acc. Chem. Res.* **2011**, *44*, 101, https://doi.org/10.1021/ar1000956.

[68] C. Amatore, A. Jutand, J. Organomet. Chem. **1999**, *576*, 254, https://doi.org/10.1016/S0022-328X(98)01063-8.

[69] S. Nagatake, T. Higo, S. Ogo, Y. Sugiura, R. Watanabe, C. Fukuhara, Y. Sekine, *Catal. Lett.* **2016**, *146*, 54.

[70] J. Barbier, *Appl. Catal.* **1986**, *23*, 225.

[71] M. Guisnet, P. Magnoux, *Appl. Catal. A* **2001**, *212*, 83.

[72] P. Raybaud, C. Chizallet, C. Mager-Maury, M. Digne, H. Toulhoat, P. Sautet, J. Catal. **2013**, *308*, 328.

[73] M. Digne, P. Sautet, P. Raybaud, P. Euzen, H. Toulhoat, J. Catal. **2002**, *211*, 1.

[74] M. Digne, P. Sautet, P. Raybaud, P. Euzen, H. Toulhoat, J. Catal. **2004**, *226*, 54.

[75] X. Krokidis, P. Raybaud, A.-E. Gobichon, B. Rebours, P. Euzen, H. Toulhoat, J. Phys. Chem. B **2001**, *105*, 5121.

[76] T. Pigeon, C. Chizallet, P. Raybaud, J. Catal. **2022**, *405*, 140.

[77] G. Kresse, J. Hafner, *Phys. Rev. B* **1994**, *49*, 14251.

[78] G. Kresse, J. Furthmüller, *Comput. Mater. Sci.* **1996**, *6*, 15.

[79] J. P. Perdew, K. Burke, M. Ernzerhof, *Phys. Rev. Lett.* **1996**, *77*, 3865.

[80] S. N. Steinmann, C. Corminboeuf, *J. Chem. Theo. Comput.* **2011**, *7*, 3567.

[81] G. Kresse, D. Joubert, *Phys. Rev. B* **1999**, *59*, 1758.

[82] G. Henkelman, A. Arnaldsson, H. Jónsson, *Comput. Mater. Sci.* **2006**, *36*, 354.

[83] E. Sanville, S. D. Kenny, R. Smith, G. Henkelman, *J. Comput. Chem.* **2007**, *28*, 899.

[84] G. Henkelman, H. Jónsson, *J. Chem. Phys.* **2000**, *113*, 9978.

[85] D. Sheppard, R. Terrell, G. Henkelman, *J. Chem. Phys.* **2008**, *128*, 134106.

[86] VTST Tools, http://theory.cm.utexas.edu/vtsttools/.

[87] G. Henkelman, B. P. Uberuaga, H. Jónsson, *J. Chem. Phys.* **2000**, *113*, 9901.

[88] P. Pulay, *Chem. Phys. Lett.* **1980**, *73*, 393.

[89] M. Shahrokhi, C. Chizallet, L. D., P. Raybaud, Atomic structures of the Methyl-cyclohexane dehydrogenation on Pt$_{13}$/Al$_{2}$O$_{3}$, NOMAD Repository Archive, https://doi.org/10.17172/NOMAD/2024.09.19-2 2024.

[90] M. Shahrokhi, C. Chizallet, L. D., P. Raybaud, Atomic structures of the Methyl-cyclohexane dehydrogenation on Pt$_{13}$/Sn-doped-Al$_{2}$O$_{3}$, NOMAD Repository Archive, https://doi.org/10.17172/NOMAD/2024.09.19-3 2024.
## Entry for the Table of Contents

<figure><img src="image_8.png" /></figure>

**Tin on-tune with Platinum:** density functional theory calculations reveal the impact of oxidized interfacial tin on methylcyclohexane dehydrogenation into toluene catalyzed by Pt/alumina catalysts. It is assigned to the strengthening of metal/support interactions, and of dispersion interactions with hydrocarbons, counterbalanced by repulsive electrostatic effects and decrease of the platinum ductility.