# Hydrodesulfurization of Thiophene over Ni doped MoS₂-supported mesoporous silica

Joël Aguesse¹, Abdallah Amedlous¹,* Chunzheng Wang¹, Xavier Portier², Francesco Dalena¹, Mathias Barreau¹, Davide Salusso³, Spyridon Zafeiratos⁴, Valérie Ruaux¹, Nicolas Barrier⁵, Svetlana Mintova¹,*

¹ Normandie Université, ENSICAEN, CNRS, Laboratoire Catalyse et Spectrochimie (LCS), 14050 Caen, France.

² CIMAP-CEA-CNRS-ENSICAEN-Université de Caen, 6 Boulevard Maréchal Juin, 14050 CAEN Cedex 4, France

³ European Synchrotron Radiation Facility, CS 40220, Grenoble, Cedex 9 38043, France

⁴ Institut de Chimie et Procédés pour l’Energie, l’Environnement et la Santé (ICPEES), ECPM, UMR 7515 CNRS – Université de Strasbourg, 25 rue Becquerel, 67087 Strasbourg Cedex 02, France

⁵ Normandie Université, ENSICAEN, UNICAEN, CNRS, Laboratoire de Cristallographie et Science des Matériaux (CRISMAT), 14050 Caen, France.

*Corresponding author: svetlana.mintova@ensicaen.fr; abdallah.amedlous@ensicaen.fr

## ABSTRACT

The growing demand for ultra-low sulfur fuels requires the development of advanced hydrodesulfurization catalysts with improved activity and selectivity. In this work, we present a one-pot synthesis of mesoporous SBA-15-supported MoS₂ (SBA-15@MoS₂) and Ni-doped MoS₂ (SBA-15@Ni-MoS₂) catalysts for the hydrodesulfurization (HDS) of thiophene. Structural and spectroscopic characterizations confirmed the formation of few-layered MoS₂ nanosheets and the successful incorporation of Ni, which modifies the electronic environment and surface acidity of active sites. CO-IR spectroscopy revealed a higher density and diversity of catalytically relevant edge sites, particularly S-edge sites, upon Ni doping. Catalytic performance results demonstrated that Ni-doped catalyst (SBA-15@Ni-MoS₂) significantly outperforms the non-doped catalyst (SBA-15@MoS₂), doubling the reaction rate and exhibiting higher selectivity toward paraffinic products via the hydrogenation pathway. These findings highlight the synergistic effect of Ni in enhancing hydrogen activation and promoting the formation of Ni–Mo–S phases, offering rational design of HDS catalysts.
# 1. Introduction

The increasing global demand for cleaner fuels, combined with the declining oil quality, resulted in increased concentrations of sulfur-containing compounds in petroleum-derived fuels. Among these, heterocyclic molecules such as thiophene (TP), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and alkylated derivatives like 4-MDBT and 4,6-DMDBT are particularly problematic due to their chemical stability and steric hindrance, which render them resistant to conventional refining[1,2]. These compounds not only deactivate catalysts and corrode processing equipment, but also generate sulfur oxides ($SO_x$) during combustion, contributing to air pollution and health risks[3-5].

To mitigate these environmental impacts and comply with increasingly stringent emission standards, refineries are shifting toward the production of environmentally friendly fuels, both fossil-based and bio-based, with ultra-low or zero sulfur content[6]. Achieving these goals requires highly efficient desulfurization technologies capable of removing even the most refractory sulfur species. Hydrodesulfurization (HDS) is the most widely used catalytic process in refineries for removing sulfur-containing compounds from petroleum feedstocks. It plays a key role in producing ultra-low sulfur fuels (<10 ppm), as mandated by environmental regulations in European Union[7]. However, the chemical inertness and steric hindrance of certain sulfur species significantly reduce the effectiveness of conventional HDS catalysts[1,8]. This has stimulated research into the development of next-generation catalytic systems that offer improved activity, selectivity, and stability under practical operating conditions.

Commercial hydrodesulfurization (HDS) catalysts are predominantly composed of molybdenum disulfide ($MoS_2$) supported on γ-alumina, with nickel or cobalt promoters enhancing catalytic activity[6,9-12]. In recent years, unsupported bulk sulfide catalysts, such as NiMoS or CoMoS, have attracted attention and have been introduced as an alternative to conventional supported systems[13-15]. These materials are designed to improve metal utilization and avoid the detrimental effects of strong metal-support interactions observed with γ-alumina which result on the formation of inactive compounds such as $NiAl_2O_4$. However, unsupported catalysts often face critical challenges, including phase segregation into catalytically inactive metal sulfides (e.g., $NiS_x$), which not only contribute little to hydrogenation or hydrodesulfurization activity but can also block the active sites at the $MoS_2$ slab edges[16]. This lowers the number of available Ni-Mo-
S active sites, complicates structure–activity correlations, and ultimately diminishes catalytic efficiency. To mitigate these limitations, post-synthetic treatments such as selective acid leaching have been proposed to remove inert phases, however, such steps add complexity and may compromise catalyst stability[16]. Consequently, the development of supported catalyst systems that offer precise control over metal dispersion and interaction remains a compelling strategy.

Building on the limitations of unsupported bulk sulfide catalysts, it is worth noting that while HDS is predominantly carried out with heterogeneous catalysts in industry, some studies have explored homogeneous transition-metal complexes (e.g., Mo, W, Ru, Ni) for C–S bond cleavage under hydrogen[17]. Despite their well-defined active sites, these systems face major drawbacks, including low stability under HDS conditions, difficult separation from products, and poor recyclability.

Mesoporous silica has emerged as a promising alternative support, offering high surface area, high specific pore volume and weaker metal-support interactions[18]. These characteristics enable improved distribution of active components and facilitate the formation of well-dispersed, catalytically efficient metal sites[19]. Furthermore, the mesopores enhance molecular transport, making it particularly suitable for the conversion of sulfur compounds under practical HDS conditions.

In the present study, we report a one-pot synthesis of Ni-doped MoS₂ supported on mesoporous SBA-15 as an effective strategy to enhance hydrogenative desulfurization performance. This approach enables the direct formation of well-dispersed active phases with high site-specific activity, while minimizing undesirable interactions with the support. The resulting catalysts provide a platform to explore the correlation between structural features, electronic modifications induced by Ni, and catalytic behavior, contributing to a deeper understanding of the active sites governing HDS activity.

# 2. Experimental section

## Synthesis of SBA-15 Supported MoS₂ and Ni-MoS₂ Catalysts

### Materials.

Tetraethyl orthosilicate (TEOS, reagent grade, 98%), Pluronic® P-123 (PEO₁₀–PPO₇₀–PEO₁₀,
M☐ ~ 5800 g·mol⁻¹), and ammonium molybdate ((NH₄)₂MoO₄, 99.98%) were purchased from Sigma-Aldrich. Hydrochloric acid (HCl, 37%) was obtained from J.T. Baker. All chemicals were used as received without further purification.

## Synthesis of Mesoporous SBA-15.

The SBA-15 support was synthesized using TEOS as the silica source and Pluronic P123 as the structure-directing agent under acidic conditions. In a typical procedure, 2.8 g of P123 was dissolved in 30 mL of 1.4 M of HCl under stirring at room temperature (25 °C). Once the surfactant was fully dissolved, 4.6 mL of TEOS was added dropwise to the solution. The mixture was stirred for 4 h at 25 °C to allow for hydrolysis and condensation reactions. Subsequently, the mixture was transferred to a Teflon-lined stainless-steel autoclave and subjected to hydrothermal treatment at 100 °C for 40 h. The solid product was recovered by filtration, thoroughly washed with distilled water, and dried overnight at 60 °C. Finally, the organic template was removed by calcination in air at 550 °C for 6 h, yielding highly ordered mesoporous SBA-15.

## Synthesis of Mesoporous SBA-15@MoS₂ and SBA-15@Ni-MoS₂ catalysts

SBA-15@MoS₂ and SBA-15@Ni-MoS₂ composites were synthesized via a one-pot synthesis method. Following the initial 4 h stirring step during SBA-15 formation, metal precursors were introduced directly into the reaction mixture. For SBA-15@MoS₂, 0.17 g of ammonium molybdate was added, while a combination of 0.17 g of ammonium molybdate and 0.12 g of nickel nitrate hexahydrate was used for SBA-15@Ni-MoS₂. The resulting mixtures were stirred for an additional hour at room temperature, yielding a homogeneous solution. The mixtures were then transferred into Teflon-lined autoclaves and subjected to hydrothermal treatment at 100 °C for 40 h. The resulting solids were filtered, thoroughly washed with hot distilled water, and dried overnight at 60 °C. Finally, the samples were calcined at 550 °C for 6 h in air to remove the organic template and obtain the mesoporous composite materials.

The oxidized SBA-15@MoOₓ and SBA-15@Ni-MoOₓ samples were subjected to post-sulfidation under a flow of 10% H₂S/H₂ (30 mL/min) at atmospheric pressure. The temperature was ramped at 5 °C/min to 350 °C and maintained for 2 hours to ensure complete sulfidation. After the treatment, the system was cooled to room temperature (25 °C) under nitrogen flow (30 mL/min), and the resulting catalysts were transferred into an argon-filled glove box to prevent
exposure to air. The resulting sulfided samples were labeled as SBA-15@MoS₂ and SBA-
15@Ni-MoS₂, respectively.

Characterization

XRD patterns at both low and high angles were recorded using a Dynamic 500 diffractometer (Anton Paar) equipped with Cu Kα radiation (λ = 0.15418 nm, 45 kV, 40 mA), with a step size of 0.00012°.

Raman spectra were collected using a Jobin Yvon LabRAM 300 confocal Raman spectrometer coupled with a microscope (100× objective) and a CCD detector. A 532 nm wavelength laser with a 10% power filter was employed, and spectra were accumulated three times with 60-second acquisitions.

The spatial distribution of the active phases were examined by High-Resolution Transmission Electron Microscopy (HR-TEM) and Scanning Transmission Electron Microscopy (STEM-HAADF). All TEM observations were performed using a double-corrected cold FEG ARM 200 JEOL microscope operated at 200 kV (with a spatial resolution in STEM mode of 0.8 Å). The samples were stirred in ethanol, and a few drops of the resulting suspension were put on a 300-mesh copper grid with a holey carbon film. All the images were processed using Gatan DigitalMicrograph (GMS 3) software.

The elemental composition of the samples was determined using a 7900 ICP-MS system (Agilent Technologies). For sample preparation, 50 mg of each solid sample was dissolved in a mixture of 0.5 mL of aqua regia (HNO₃ :HCl = 1:3, v/v) and 3 mL of hydrofluoric acid. The mixture was heated at 110 °C for 1 h to ensure complete digestion, followed by the addition of 2 g of boric acid to complex the excess fluoride. The solution volume was then adjusted to 100 mL with deionized water. The resulting mixture was stirred overnight using a shaker to ensure homogeneity. Prior to analysis, an aliquot of the solution was filtered and diluted 10 times.

Textural properties were evaluated by nitrogen physisorption at -196 °C using a Micromeritics ASAP 2020 volumetric adsorption analyzer. Prior to measurement, samples were degassed under vacuum at 300 °C for 12 h. Adsorption/desorption isotherms were recorded over a relative pressure (P/P₀) range of 0.05-1.0. Specific surface areas were calculated using the BET method, while pore size distributions were derived from the NLDFT method.

*In situ* CO adsorption FTIR experiments were performed using a Nicolet iZ10 spectrometer
equipped with an MCT detector (spectral range: 1100–4000 cm⁻¹, resolution: 4 cm⁻¹, 128 scans). A self-supported sample pellet (~7.5 mg, ~2 cm²) was subject to post-sulfidation at 350 °C for 2 h under 10% H₂S/H₂ flow at atmospheric pressure. After sulfidation, the system was purged with argon for 15 minutes and cooled to room temperature under vacuum. CO was gradually introduced until saturation at 1 Torr. The FTIR measurements were conducted in a cryogenic cell equipped for in-situ gas handling, allowing CO adsorption experiments to be performed at a controlled temperature of -173.15 °C. The areas of the v(CO) bands associated with CO adsorption on M- and S-edges were obtained by first using OMNIC (Series 9.9.473) to subtract the spectrum recorded before CO contact (i.e. after sample activation) from the spectrum after CO adsorption. The resulting spectra were then processed using the Savitzky–Golay second derivative method to identify the characteristic v(CO) bands of the M- and S-edges. Based on this information, Gaussian peak fitting of the v(CO) bands was performed using Fityk v1.3.1 on the equilibrium dose spectrum at 1 Torr and also at a dose of 1 Torr.

Pyridine adsorption followed by FTIR spectroscopy was applied to assess the surface acidity of the materials. Pyridine was introduced into the cell and allowed to adsorb at 1.035 mbar. Physisorbed pyridine was removed by evacuation, and spectra were recorded at various desorption temperatures ranging from 150 to 400 °C to distinguish between Lewis and Brønsted acid sites.

Ex situ X-ray Photoelectron Spectroscopy (XPS) analyses were conducted on an ultrahigh vacuum system equipped with a Thermo-VG Scientific spectrometer, a CLAM4 (MCD) hemispherical electron analyzer and a dual-anode X-ray source employing Al Kα line at 1486.6 eV) as the excitation radiation. The samples were first mounted on carbon tape, then degassed overnight at a 10⁻⁶ mbar vacuum pressure, before being transferred into the analysis chamber. Survey and high-resolution spectra (Si 2p, Mo 3d – S 2s, Ni 2p₃/₂, O 1s, and C 1s) were recorded in constant pass energy modes of 100 eV and 20 eV. To correct for electrostatic charging, energy calibration was performed by centering the Si 2p peak at 103.7 eV. The accuracy of the energy calibration was further verified by examining the peak of adventitious carbon in the C 1s region. Peak areas were determined following Shirley background subtraction using CasaXPS software, and spectra were deconvoluted with a 70/30 Gaussian–Lorentzian line shape. Surface atomic compositions were quantified after correcting elemental peak intensities using Scofield sensitivity
factors. The deconvolution of the Mo 3d – S 2s region was performed following previous works reported in the literature[20,21]. More precisely, seven peaks were used to deconvolute the region with 0.5–1 eV position constraints, corresponding to sulfur and three Mo oxidation states (IV, V and VI). Owing to spin-orbit splitting, a 2:3 area ratio was imposed between the 3d<sub>3/2</sub> and 3d<sub>5/2</sub> components for each Mo species during the fitting procedure.

Mo K- and Ni K-edges X-ray Absorption Spectra (XAS) were collected at the BM23 beamline[22] of the European Synchrotron Radiation Facility during beamtime IH-CH-1935[23]. Mo K-edge XAS spectra were collected in transmission mode with mass optimized pellets with Ø ≈ 13 mm. A Si(111) Double Crystal Monochromator (DCM) was employed for energy selection while a Rh-coated double reflection mirror was set at 2.6 mrad for harmonic rejection. Incoming beam (I₀), beam transmitted by the sample (I₁) and beam transmitted by reference metal foil (I₂) were measured with three ionization chambers (IC) set at 1 kV. I₀ was filled with 0.6 mbar of Ar (topped up to 2.2 bar in He) while I₁ and I₂ were filled with 2.2 bar of Ar. Mo metal foil was placed between I₁ and I₂ and its spectrum was measured together with each XAS scan for further energy calibration and alignment. Mo spectra were collected in continuous mode in the 19.6-21.6 keV energy range with 0.3 eV/point energy resolution and 40 ms/point integration time. Every reported spectrum resulted from the average of 5 consecutive scans. Ni K-edge XAS spectra were instead measured in fluorescence mode using a multi-element Si drift detector. Spectra were collected on 5 mm pellets while Ni metal foil was placed between I₁ and I₂ for energy calibration and alignment. For Ni K-edge IC were set at 2kV and filled with 1.248 bar of N₂ (I₀, topped up to 2 bar in He) and 0.16 bar Ar + 1.84 bar of N₂ (I₁ and I₂). The mirrors were set on the Si stripe at 2.8 mrad. Spectra were collected in continuous mode in the 8.2-9 keV energy range with 0.25 eV/point energy resolution and 0.1 s/point integration time. Every reported spectrum resulted from the average of 22 consecutive scans. All the spectra were energy aligned, background subtracted and edge jump normalized with the Athena software from the Demeter Package[24]. FT-EXAFS was extracted with the Hanning window in the 3.3-12.4 Å⁻¹ k-range for Ni K-edge and 3–14 Å⁻¹ k-range for Mo K-edge.

## Catalytic Test

The HDS of thiophene was carried out in a continuous-flow fixed-bed reactor at 350 °C and 1 bar using 100 mg of sulfided catalyst. Thiophene (10,000 ppm per injection; injection volume =
100 µL) was introduced into the reactor via a hydrogen stream (70 mL/min) passed through a saturator containing thiophene at 25 °C. This stream was subsequently mixed with 20 mL/min of 10 vol.% H₂S in H₂. The resulting gas mixture had partial pressures of 0.08 bar for thiophene, 0.912 bar for H₂, and 0.021 bar for H₂S.

After a 2 h reaction time, the effluent gases were analyzed using a Varian 3900 gas chromatograph equipped with a flame ionization detector (FID). The concentrations of thiophene, butane, 1-butene, and 2-butene were monitored. The overall HDS reaction rate was calculated according to:

$$r_{\text{HDS}} = (F/m) \times \tau$$

where F/m is the molar flow rate of thiophene per gram of catalyst, and τ is the thiophene conversion.

The apparent pseudo-first-order rate constants were determined from the following equation:

$$k_{\text{HDS}} = (F/m) \ln[1 / (1 - \tau)]$$

where kHDS is the rate constant of thiophene HDS in mol g⁻¹ s⁻¹, F is the feeding rate of the reactant in mol s⁻¹, m is the catalyst mass in grams, and τ is the total HDS conversion of thiophene.

The selectivity between the hydrogenation (HYD) and direct desulfurization (DDS) pathways was estimated using a two-lump product scheme:

* HYD products: butane

* DDS products: all butenes (1-butene, cis-2-butene, trans-2-butene)

The selectivities were calculated as follows:

$$S_{\text{HYD}} = \frac{n_{\text{Butane}}}{n_{\text{Butane}} + \sum n_{\text{Butenes}}}$$

$$S_{\text{HYD}} = 1 - S_{\text{HYD}}$$

The partial rate constants are calculated as[25].
$$k_{\text{HYDS}} = k_{\text{HDS}} \times S_{\text{HYDS}}$$

$$k_{\text{DDS}} = k_{\text{HDS}} \times S_{\text{DDS}}$$

The turnover frequency (TOF) was calculated by the equation[11]:

$$TOF = \frac{F \tau}{n_{Mo} f_{Mo}}$$

where n<sub>Mo</sub> indicates the number of Mo atoms on the catalyst surface, and the dispersion of Mo species (f<sub>Mo</sub>) was determined using the following equation:

$$f_{Mo} = (n_{Mo-M-edge} + n_{Mo-S-edge})/n_{Mo-total}$$

where n<sub>Mo-total</sub> was obtained from ICP-MS analysis, and the edge-site contributions (n<sub>Mo-M-edge</sub> and n<sub>Mo-S-edge</sub>) were estimated from CO-FTIR measurements.

# 3. Results and discussion

## Synthesis and structural characterization

To investigate the structural integrity and ordering of the mesoporous framework of the samples, small-angle X-ray diffraction (SAXRD) measurements were carried out for pure SBA-15, MoS<sub>2</sub>-modified SBA-15 (SBA-15@MoS<sub>2</sub>), and Ni-doped MoS<sub>2</sub>-modified SBA-15 (SBA-15@Ni-MoS<sub>2</sub>), as shown in **Figure 1**.

The unmodified SBA-15 sample exhibits three distinct diffraction peaks centered at approximately 0.9°, 1.6°, and 1.8° 2θ, which can be indexed to the (100), (110), and (200) reflections of a well-ordered two-dimensional hexagonal mesostructure (space group p6mm)[26,27]. This confirms the successful synthesis of a highly ordered mesoporous silica. Upon the incorporation of MoS<sub>2</sub> or Ni-MoS<sub>2</sub>, the (100), (110), and (200) reflections in the small-angle XRD patterns exhibit noticeable attenuation and slight shifts to lower 2θ angles. This behavior is attributed to partial pore blockage by MoS<sub>2</sub>, which disrupt the long-range meso-structural order of SBA-15, as well as strong X-ray absorption by Mo species[28,29]. Simultaneously, the shift in diffraction peaks suggests an expansion of the d-spacing, likely due to the incorporation of MoS<sub>2</sub> species within or onto the mesoporous framework.
The wide-angle XRD patterns (Figure S1) of the samples exhibit a broad diffraction peak in the 15°–30° 2Theta region, which is characteristic of the amorphous silica. Upon loading with MoS₂ or Ni-MoS₂, no distinct diffraction peaks corresponding to crystalline MoS₂ are observed in the patterns of samples SBA-15@MoS₂ and SBA-15@Ni-MoS₂. This suggests that the MoS₂ phase is either poorly crystalline or highly dispersed within the mesoporous matrix.

<figure><img src="image_1.png" /><figcaption>**Figure 1.** Small-angle XRD patterns of samples SBA-15, SBA-15@MoS₂ and SBA-15@Ni-MoS₂</figcaption></figure>

Raman spectroscopy was employed to further confirm the successful formation of MoS₂ and Ni-MoS₂ onto the SBA-15 support (Figure 2). The spectrum of pristine SBA-15 sample exhibits broad features attributed to the vibrational modes of the amorphous silica, with characteristic bands at 494 cm⁻¹ and 609 cm⁻¹, corresponding to the O–Si–O bending and Si–O–Si stretching vibrations, respectively[³⁰]. In contrast, both SBA-15@MoS₂ and SBA-15@Ni-MoS₂ samples display distinct peaks characteristic of MoS₂. The prominent peaks at 378 cm⁻¹ (E¹₂g mode) and 404 cm⁻¹ (A₁g mode) correspond to the in-plane and out-of-plane vibrations of MoS₂, respectively, confirming the formation of the 2H-MoS₂ phase[³¹,³²]. Additionally, the presence of Raman peaks located at 222 cm⁻¹ (J₂) and 286 cm⁻¹ (E₁g) corresponds to the characteristic phonon vibration patterns of 1T MoS₂. The new peak appearing at 300 cm⁻¹ originates from the modes of the Ni-S[³¹,³³⁻³⁵]. Moreover, the appearance of small and broad bands centered around
350 cm⁻¹ and 445 cm⁻¹ suggests the existence of amorphous MoS₂ as a minor residual phase[³⁶].

<figure><img src="image_2.png" /><figcaption>**Figure 2.** Raman spectra of samples SBA-15, SBA-15@MoS₂, and SBA-15@Ni-MoS₂</figcaption></figure>

Ex situ XPS analysis provided detailed insights into the surface chemical states and distribution of molybdenum and sulfur in both amorphous oxide forms formed before sulfidation (SBA-15@MoOₓ and SBA-15@Ni-MoOₓ) and the sulfide catalysts (SBA-15@MoS₂ and SBA-15@Ni-MoS₂). Regarding the oxide forms (**Figure S2**), SBA-15@MoOₓ shows the presence of Mo⁶⁺ (0.57 at%) with minor Mo⁵⁺ species (0.48 at%), while SBA-15@Ni-MoO₃ showed a significant decrease in Mo⁶⁺ (0.21 at%) and an increase in Mo⁵⁺ (0.35 at%), suggesting the impact of nickel on molybdenum electronic configuration.

Following sulfidation (**Figure 3**), both samples SBA-15@MoS₂ and SBA-15@Ni-MoS₂ showed predominant Mo⁴⁺ (0.47 and 0.33 at. %, respectively), confirming the formation of MoS₂ phases. However, residual Mo⁵⁺ and Mo⁶⁺ species were still detected, most likely due to partial surface oxidation to MoOₓS₂-x upon air exposure, with slightly greater oxidation observed in the Ni-containing sample (SBA-15@Ni-MoS₂). The Mo/S atomic ratios of 0.98 for SBA-15@MoS₂ and 1.07 for SBA-15@Ni-MoS₂ indicate near-stoichiometric sulfidation, consistent with effective sulfur incorporation. Interestingly, Mo⁴⁺/S ratios of 0.46 were found for both samples, suggesting that sulfur is primarily coordinated with Mo⁴⁺ to form MoS₂, while Mo⁵⁺ and Mo⁶⁺ are predominantly present as oxides. The average molybdenum oxidation states decreased
significantly from the oxide precursors (5.38 for SBA-15@MoOₓ and 5.24 for SBA-15@Ni-MoOₓ) to the sulfide catalysts (4.77 and 4.82, respectively), verifying effective reduction during the sulfidation.

Complementary ICP-OES results show overall Si/Mo ratios of 10.0 for SBA-15@MoS₂ and 14.3 for SBA-15@Ni-MoS₂, while surface-sensitive XPS measurements yield significantly higher Si/Mo values of 34.2 and 41.9, respectively (**Table S1**). This discrepancy indicates that Mo species are predominantly confined within the SBA-15 mesopores rather than distributed on the outer surface. The absence of detectable surface Ni by XPS, despite its identification by ICP (0.6 wt%), further supports the Ni incorporation within the mesoporous framework.

<figure><img src="image_3.png" /><figcaption>**Figure 3.** Deconvoluted Mo 3d – S 2s XPS spectra of samples SBA-15@MoS₂ and SBA-15@Ni-MoS₂</figcaption></figure>
To further explore the Mo and Ni local coordination environment and oxidation states, ex-situ X-ray absorption spectroscopy (XAS) measurements were carried out at the Mo and Ni K-edges. MoS₂ can be distinguished from MoO₂ by the absence of the oxide-characteristic 1s → 4d transition (A in **Figure 4a**) and the presence of a clear feature in the rising-edge (B). The Mo K-edge spectrum of SBA-15@Ni-MoS₂ does not exhibit the 1s → 4d transition, while it displays a less intense feature B compared to commercial MoS₂ and a broader whiteline. These are characteristic of MoS₃ [³⁷⁻⁴¹], whose presence is further confirmed by the (phase uncorrected) |FT-EXAFS| spectra. Indeed, SBA-15@Ni-MoS₂ presents two clear coordination shells (**Figure 4b**) with position comparable to MoS₂, which can be ascribed to Mo-S and Mo-Mo single scattering paths. However, these two shells exhibit lower amplitude and broader width, again suggesting the presence of amorphous MoS₃, which has a different local coordination environment [⁴²].

The Ni K-edge XANES spectrum of SBA-15@Ni-MoS₂ exhibits a clear 1s → 3d pre-edge transition attributable to Ni²⁺ in octahedral coordination[⁴³⁻⁴⁵]. This transition is absent in NiSₓ materials, thus indicating their absence or minor presence[⁴⁶]. The XANES spectrum differs from that of bulk NiO (**Figure 4c**), displaying a significant broadening of the main spectral features indicative of a loss in local coordination around Ni. This suggests a likely nanostructured or disordered NiO local environment[⁴⁷], as confirmed by the EXAFS spectrum showing weak oscillations. The |FT-EXAFS| spectrum (**Figure 4d**) contains only a broad Ni-O first coordination shell.
<figure><img src="image_4.png" /><figcaption>**Figure 4.** (a,b) Mo K-edge and (c,d) Ni K-edge ex-situ (a,c) XANES and (b,d) the corresponding (phase uncorrected) k²-weighted |FT-EXAFS| spectra (k²-weighted EXAFS spectra are reported in **Figure S5**)</figcaption></figure>

Nitrogen adsorption–desorption measurements were conducted to evaluate the textural properties of samples, including the BET surface area, total pore volume, and pore size distribution (Figure 5 and Table S2). As shown in Figure 5a, the nitrogen adsorption–desorption isotherms of SBA-15, SBA-15@MoS₂, and SBA-15@Ni-MoS₂ exhibit typical type IV curves with H1 hysteresis
loops, confirming their mesoporous structure. Pristine SBA-15 exhibits the highest nitrogen uptake, corresponding to a high specific surface area of 646 cm³/g and total pore volume of 1.1 cm³/g. Upon formation of MoS₂ and Ni-MoS₂, a slight decrease in nitrogen uptake is observed, suggesting that the MoS₂ particles are primarily formed along the pore walls rather than completely filling or blocking the mesopores. The pore size distribution curves (Figure 5b) determined via the non-local density functional theory (NLDFT), display narrow peaks centered at 8.6 nm for SBA-15, 9.5 nm for SBA-15@MoS₂ and 9.3 for SBA-15@Ni-MoS₂. These results confirm that the mesoporous structure of SBA-15 is largely retained after the growth of MoS₂ and Ni-MoS₂.

<figure><img src="image_5.png" /><figcaption>**Figure 5.** (a) N₂ physisorption isotherms and (b) the corresponding NLDFT pore size distribution</figcaption></figure>
of samples SBA-15, SBA-15@MoS₂, and SBA-15@Ni-MoS₂

High-resolution transmission electron microscopy (HRTEM) was employed to investigate the mesoporous structure and to further verify the formation of MoS₂. **Figure 6a,b** corresponds to pristine SBA-15 observed along two orthogonal directions. In **Figure 6a**, the linear arrangement of mesoporous channels shows a view along the cylindrical pore axis, while **Figure 6b** shows a hexagonally ordered array perpendicular to the channel direction, characteristic of the 2D hexagonal (p6mm) symmetry. Additionally, the intensity profile extracted from the HR-TEM image (**Figure S3**) of the pristine SBA-15 reveals sharp, periodic peaks corresponding to the regular mesoporous channel arrangement. These observations collectively confirm the long-range periodicity and high structural order of the SBA-15 sample.

The SBA-15@MoS₂ sample displays the mesoporous channels with the presence of MoS₂ nanosheets grown on the pore walls (**Figure 6c**). These nanosheets consist of fewer stacked layers with an interlayer spacing approximately 0.66 nm for the (002) plane, slightly larger than that of bulk MoS₂ (0.66 nm)[⁴⁸]. Furthermore, the TEM images of SBA-15@Ni-MoS₂ (**Figure 6d**) reveal that the Ni-MoS₂ exhibits also a lamellar structure, resembling MoS₂. One can notice the presence of layered fringes with interplanar spacings of approximately 0.67 nm and 0.27 nm, corresponding to the (002) and (100) planes of hexagonal MoS₂, respectively[⁴⁹].
<figure><img src="image_6.png" /><figcaption>**Figure 6.** TEM images of (a, b) SBA-15, (c) SBA-15@MoS₂, and (d) SBA-15@Ni-MoS₂ samples</figcaption></figure>

**Identification of MoS₂ active sites by CO adsorption followed by FTIR spectroscopy**

To investigate the nature and distribution of MoS₂ active sites, CO adsorption at low temperatures (-173.15 °C) was followed by FTIR spectroscopy. The analysis revealed two primary edge terminations in SBA-15-supported MoS₂: the Mo-terminated edge (M-edge), with characteristic IR bands in the range of 2130–2106 cm⁻¹, and the S-terminated edge (S-edge), observed
between 2100 and 2080 cm⁻¹ [⁵⁰]. In the case of sample SBA-15@MoS₂, two distinct bands were detected at 2121 cm⁻¹ and 2091 cm⁻¹, corresponding to the M-edge and S-edge, respectively (Figure 7a). The importance of distinguishing between these sites lies in their distinct roles in the HDS process: the M-edge plays a critical role in thiophene adsorption and activation (a key step in desulfurization) while the S-edge, particularly in the form of terminal –SH groups, facilitates proton donation, thereby promoting H₂ activation through protonation, oligomerization, and C–S bond cleavage.

Upon incorporation of nickel into the MoS₂ structure, the SBA-15@Ni-MoS₂ material exhibits a greater diversity of active sites, as evidenced by five distinct CO adsorption bands. The M-edge now consists of two types of sites: a Ni-promoted M-edge, identified by a band at 2124 cm⁻¹, and a non-promoted M-edge at 2109 cm⁻¹. Similarly, the S-edge presents three distinct environments: a non-promoted S-edge at 2091 cm⁻¹, along with two Ni-promoted S-edge sites characterized by bands at 2078 cm⁻¹ and 2056 cm⁻¹ (Figure 7b). Additionally, the IR bands observed at 2157 cm⁻¹ and 2138 cm⁻¹ are attributed to CO interactions with surface silanol groups and to CO condensation (physisorption) within the mesoporous channels of the SBA-15 support, respectively.

Pyridine adsorption provides direct evidence of changes in the acidity of the catalyst surface, indicating that the SBA-15@MoS₂ exhibits stronger acidity compared to the Ni-promoted SBA-15@Ni-MoS₂, as shown in Figure S4 and Table S3. This is further supported by CO adsorption results, which show a shift of 9 cm⁻¹ for the M-edge and 4 cm⁻¹ for the S-edge in the CO stretching frequencies at the non-promoted sites, indicating a slight weakening of acidity in the Ni-modified sample (Figure 7a and 7b). The introduction of Ni, while enhancing hydrogenation activity, may also lead to a reduction in acid strength, which can affect the catalytic performance in hydrodesulfurization reactions.

The deconvolution of the CO adsorption spectrum at equilibrium pressure for SBA-15@MoS₂ (Figure S6a) reveals a higher concentration of non-promoted M-edge sites (12.60 µmol/g) and a comparatively lower concentration of S-edge sites (2.12 µmol/g), resulting in an S-edge/M-edge ratio of 0.17. This low ratio suggests limited redox-active metal presence on the S-edge, which may restrict its contribution to hydrogen activation. In contrast, the SBA-15@Ni-MoS₂ (Figure S6b) exhibits a markedly higher S-edge/M-edge ratio of 0.28, attributed to a significant increase
in S-edge site concentration (7.27 µmol/g) following Ni incorporation, along with a notably
higher M-edge site concentration (25.87 µmol/g). This shift in edge site distribution reflects
enhanced catalytic functionality, as Ni doping facilitates the formation of the Ni-Mo-S phase,
which is known to increase the number of accessible active sites on both the M-edge and S-edge,
thereby improving hydrodesulfurization performance.

<figure><img src="image_7.png" /><figcaption>**Figure 7.** FTIR spectra of CO adsorbed on (a) SBA-15@MoS₂ and (b) SBA-15@Ni-MoS₂ samples</figcaption></figure>

Hydrodesulfurization Catalytic Test

The HDS of thiophene is a crucial catalytic process for removing sulfur impurities from fuels, yielding various hydrocarbon products depending on the reaction pathway. The main products of thiophene HDS include butane, 1-butene, cis-2-butene, and trans-2-butene, with hydrogen sulfide
(H₂S) as a byproduct. Some of the butenes may undergo further hydrogenation to form butane, or isomerization to different butene isomers[51]. The formation of these products follows two distinct mechanistic routes: (1) the hydrogenation (HYD) pathway and (2) the direct desulfurization (DDS) pathway. While both pathways ultimately produce butane and butenes, they proceed through different reaction mechanisms, which significantly influence the product distribution and catalytic selectivity[52,53]. These mechanistic routes and their associated products are schematically illustrated in **Figure 8**.

<figure><img src="image_8.png" /><figcaption>**Figure 8.** Hydrodesulfurization of thiophene proceeds via two distinct mechanistic pathways: the HYD pathway and the direct DDS pathway.</figcaption></figure>

The HYD pathway involves an initial hydrogenation of the thiophene ring prior to sulfur removal. In this process, thiophene is first converted into tetrahydrothiophene, a fully saturated intermediate. This intermediate then undergoes C–S bond cleavage, resulting in the formation of butane and H₂S as the primary products. The presence of multiple hydrogenation steps favors higher selectivity toward paraffins (alkanes), making butane the dominant product in this pathway. The HYD mechanism is commonly associated with S-edge sites in MoS₂[54].

In contrast, the DDS pathway proceeds via direct cleavage of the C–S bond without prior hydrogenation of the thiophene ring, leading to the formation of 1-butene and H₂S as the primary products. The resulting 1-butene can subsequently undergo isomerization to yield cis-2-butene and trans-2-butene. Because the thiophene ring remains unsaturated before desulfurization, this
pathway typically exhibits higher selectivity toward olefins (alkenes), making butenes the dominant products compared to butane. The DDS mechanism is generally associated with M-edge sites in MoS₂, which facilitate sulfur removal *via* a Lewis acid mechanism[55-57].

Brønsted and Lewis acid sites play complementary roles in these pathways. Lewis acid sites, such as coordinatively unsaturated Mo or Ni centers, serve as electron pair acceptors and facilitate thiophene adsorption via π-complexation. This interaction is particularly relevant for activating the DDS route[57]. On the other hand, Brønsted acid sites, typically associated with SH or OH groups, function as proton donors and contribute to hydrogen activation and transfer. This protonation capability enhances the HYD pathway by stabilizing intermediates and enabling C–S bond cleavage[58].

To gain deeper insight into how metal promotion affects these pathways, the catalytic performance of SBA-15@MoS₂ and SBA-15@Ni-MoS₂ was evaluated in the HDS of thiophene. The conversion profiles (Figure 9a) reveal that both catalysts exhibit a gradual decay in activity with time-on-stream, likely due to coke deposition or sulfur poisoning. However, the SBA-15@Ni-MoS₂ consistently achieves higher thiophene conversion compared to SBA-15@MoS₂, clearly demonstrating the promotional effect of Ni incorporation. This enhancement is attributed to the increased hydrogenation capacity of the Ni-MoS₂ system, as Ni promotes H₂ dissociation and facilitates hydrogen spillover onto the MoS₂ surface, thereby favoring the HYD pathway. This interpretation is consistent with CO adsorption analyses, which indicated a higher proportion of S-edge sites in MoS₂, known to favor the hydrogenation reactions. The calculated initial reaction rates further support these observations. The mass-based apparent rate constants (kHDS, kHYDS, kDDS) and the TOF values normalized to edge Mo sites are summarized in Table 1. ICP analysis shows that SBA-15@MoS₂ contains 3.9 wt% Mo, while SBA-15@Ni-MoS₂ contains 3.0 wt% Mo and 0.6 wt% Ni. SBA-15@MoS₂ displays an apparent rate constant of 0.2666 × 10⁻⁸ mol·s⁻¹·g⁻¹, while SBA-15@Ni-MoS₂ reaches 0.2985 × 10⁻⁸ mol·s⁻¹·g⁻¹, reflecting a 12% enhancement in overall catalytic activity. However, when normalized to edge Mo sites (TOF, using ICP-Mo to determine nMo and CO-FTIR to estimate the edge fraction fMo), the intrinsic turnover frequency decreases from 0.181 s⁻¹ for SBA-15@MoS₂ to 0.090 s⁻¹ for SBA-15@Ni-MoS₂. This suggests that Ni primarily increases the number and accessibility of active edge sites, rather than accelerating the intrinsic per-site C–S bond cleavage rate.
The product selectivity (Figure 9b) further confirms the distinct mechanistic behavior of the two catalysts. SBA-15@Ni-MoS₂ exhibits significantly higher selectivity toward butane (30.43%), characteristic of the hydrogenation pathway, whereas SBA-15@MoS₂ favors the formation of 2-butene (70.19%), indicating a preference for the DDS route. The negligible amounts of 1-butene detected in both cases suggest rapid isomerization into cis- and trans-2-butene isomers. These differences in product distribution clearly demonstrate that Ni incorporation shifts the reaction toward paraffin formation, while unpromoted MoS₂ predominantly yields olefins.

The paraffin-to-olefin ratio over time (Figure 9c) corroborates these findings. A gradual increase in this ratio is observed for both catalysts, with SBA-15@Ni-MoS₂ maintaining a slightly higher value throughout the reaction. This trend confirms the enhanced hydrogenation ability of the synergistic effect of Ni, which promotes the formation of Ni–Mo–S phases, and thus facilitates initial ring saturation and favors subsequent hydrogenation of intermediate olefins into paraffinic products.

<figure><img src="image_9.png" /></figure>
<figure><img src="image_10.png" /><figcaption>**Figure 9:** Catalytic performance of SBA-15@MoS₂ and SBA-15@Ni-MoS₂ samples as a function of time in the thiophene hydrodesulfurization: (a) Thiophene conversion (%), (b) Product selectivity, and (c) paraffin/olefin ratio.</figcaption></figure>

<table><caption>**Table 1.** Dynamic parameters of the catalysts in thiophene hydrodesulfurization</caption><thead><tr><th rowspan="2">Catalyst</th><th>k<sub>HDS</sub></th><th>S<sub>HYD</sub></th><th>S<sub>DDS</sub></th><th>k<sub>HYD</sub></th><th>k<sub>DDS</sub></th><th rowspan="2">TOF (s<sup>-1</sup>)</th></tr><tr><th>(10<sup>-8</sup> mol.g. s<sup>-1</sup>)</th><th></th><th></th><th>(10<sup>-8</sup> mol.g. s<sup>-1</sup>)</th><th>(10<sup>-8</sup> mol.g. s<sup>-1</sup>)</th></tr></thead><tbody><tr><td>SBA-15@MoS<sub>2</sub></td><td>0.2666</td><td>0.3031</td><td>0.6969</td><td>0.0806</td><td>0.1859</td><td>0.1811</td></tr></tbody></table>
<table><thead><tr><th rowspan="2">Catalyst</th><th rowspan="2">k<sub>HDS</sub><br>(10<sup>-8</sup> mol.g. s<sup>-1</sup>)</th><th colspan="2">k<sub>HYD</sub></th><th rowspan="2">k<sub>DDS</sub><br>(10<sup>-8</sup> mol.g. s<sup>-1</sup>)</th><th rowspan="2">TOF (s<sup>-1</sup>)</th></tr><tr><th>S<sub>HYD</sub></th><th>S<sub>DDS</sub></th></tr></thead><tbody><tr><td>SBA-15@ Ni-MoS<sub>2</sub></td><td>0.2985</td><td>0.3048</td><td>0.6952</td><td>0.0908</td><td>0.2077</td><td>0.0901</td></tr></tbody></table>

The comparison of thiophene and 4,6-DMDBT HDS activity over SBA-15@MoS₂ and SBA-15@Ni-MoS₂ with the results reported in literature is presented in **Table 2**. The SBA-15@Ni-MoS₂ shows a TOF of 0.0901 s⁻¹, indicating enhanced accessibility of active edge sites due to Ni incorporation, while the unpromoted SBA-15@MoS₂ exhibits a TOF of 0.1897 s⁻¹, reflecting the intrinsic activity of MoS₂ edges. Overall, SBA-15@Ni-MoS₂ demonstrates superior mass-specific HDS performance relative to other Mo- or Ni- promoted SBA-15 and Ni₂ P-based catalysts, achieving a favorable balance between HYD and DDS pathways. These results highlight the beneficial role of Ni in increasing site density and optimizing HDS activity for thiophene desulfurization.

<table><caption>**Table 2.** Comparison of thiophene and 4,6-DMDBT HDS activity over SBA-15@Ni-MoS₂ with the results reported in literature.</caption><thead><tr><th>Catalyst</th><th>Temp (°C)</th><th>Pressure (kPa)</th><th>LHSV/WHSV or space-time</th><th>TOF (s<sup>-1</sup>)</th><th>Reference</th></tr></thead><tbody><tr><td>SBA-15@MoS<sub>2</sub></td><td></td><td></td><td>m/F<sub>0</sub> ≈ 5.7</td><td>0.1897<sup>b</sup></td><td></td></tr><tr><td>Ni-MoS<sub>2</sub> -SBA-15</td><td>350</td><td>100</td><td>h·g·mol<sup>-1</sup> (gas; H<sub>2</sub> /H<sub>2</sub> S/Th)</td><td>0.0901<sup>b</sup></td><td>This work</td></tr><tr><td>8%Mo / SBA-15</td><td></td><td></td><td></td><td>0.075<sup>a</sup></td><td></td></tr><tr><td>3%Co-8%Mo / SBA-15</td><td></td><td></td><td></td><td>0.154<sup>a</sup></td><td></td></tr><tr><td>3%Ni-8%Mo / SBA-15</td><td></td><td></td><td>Atmospheric microreactor; gas-phase Th (no H<sub>2</sub> S)</td><td>0.124<sup>a</sup></td><td>[59]</td></tr><tr><td>3%Co-8%Mo / 25%Zr-SBA-15 (post-syn.)</td><td>400</td><td>100</td><td></td><td>0.227<sup>a</sup></td><td></td></tr><tr><td>3%Ni-8%Mo / 25%Zr-SBA-15 (post-syn.)</td><td></td><td></td><td></td><td>0.212<sup>a</sup></td><td></td></tr><tr><td>NiMo/Al(20)-SBA-15</td><td></td><td></td><td>Fixed-bed; H<sub>2</sub> 100</td><td>0.0315<sup>a</sup></td><td></td></tr><tr><td>NiMo/Ti(20)-SBA-15</td><td></td><td></td><td>mL min<sup>-1</sup>; 4.7</td><td>0.0126<sup>a</sup></td><td>[60]</td></tr><tr><td>NiMo/Zr(20)-SBA-15</td><td></td><td></td><td>mol% Th; CS<sub>2</sub> /H<sub>2</sub> presulfidation</td><td>0.0120<sup>a</sup></td><td></td></tr><tr><td>ZrSBA-15 (Mo = 2wt%)</td><td></td><td></td><td>m/F<sub>0</sub> = 18.9</td><td>0.0161<sup>a</sup></td><td></td></tr><tr><td>ZrSBA-15 (Mo = 6wt%)</td><td>400</td><td>1bar</td><td>h·g·mol<sup>-1</sup> (gas; H<sub>2</sub> /Th)</td><td>0.0170<sup>a</sup></td><td>[61]</td></tr><tr><td>ZrSBA-15 (Mo = 12wt%)</td><td></td><td></td><td></td><td>0.00886<sup>a</sup></td><td></td></tr></tbody></table>
<table><thead><tr><th>Catalyst</th><th>Temp (°C)</th><th>Pressure (kPa)</th><th>LHSV/WHSV or space-time</th><th>TOF (s<sup>-1</sup>)</th><th>Reference</th></tr></thead><tbody><tr><td>Ni<sub>2</sub> P/Al<sub>2</sub> O<sub>3</sub></td><td>330</td><td>3.0</td><td>LHSV = 3.0</td><td>0.000444<sup>a</sup></td><td></td></tr><tr><td>Ni<sub>2</sub> P/MCM-41</td><td>310</td><td>3.0</td><td>WHSV = 6.0</td><td>0.00114<sup>a</sup></td><td>[11]</td></tr><tr><td>Ni<sub>2</sub> P/GaAlO<sub>x</sub>-0.5</td><td>340</td><td>3.4</td><td>LHSV = 4.8</td><td>0.000644<sup>a</sup></td><td></td></tr><tr><td>NiS<sub>2</sub> -MoS<sub>2</sub> -0</td><td></td><td></td><td></td><td>0.003<sup>b</sup></td><td></td></tr><tr><td>NiS<sub>2</sub> -MoS<sub>2</sub> -0.1</td><td>290-350</td><td>4000</td><td>LHSV = 14; H<sub>2</sub> /oil</td><td>0.034<sup>b</sup></td><td>[62]</td></tr><tr><td>NiS<sub>2</sub> -MoS<sub>2</sub> -0.2</td><td></td><td></td><td>= 500</td><td>0.064<sup>b</sup></td><td></td></tr><tr><td>NiS<sub>2</sub> -MoS<sub>2</sub> -0.5</td><td></td><td></td><td></td><td>0.055<sup>b</sup></td><td></td></tr></tbody></table>

$^{a}$ICP-TOF<sub>total-Mo</sub> = (k<sub>HDS</sub>/n<sub>Mo</sub>)

$^{b}$CO-FT-IR-TOF-edge = (k<sub>HDS</sub>/n<sub>Mo</sub>*f<sub>Mo</sub>)

## Conclusions

This study demonstrates the successful synthesis of SBA-15-supported Ni-doped MoS<sub>2</sub> catalysts that ensures uniform dispersion of active phases within the mesoporous silica framework. The incorporation of Ni not only modifies the distribution and nature of active sites particularly by enriching S-edge terminations, but also enhances hydrogenation capacity by promoting H<sub>2</sub> dissociation. Compared to non-doped MoS<sub>2</sub>, the Ni-doped MoS<sub>2</sub> catalysts exhibits superior thiophene conversion, higher selectivity toward paraffins, and a two-fold increase in initial HDS reaction rate. These improvements are attributed to the formation of an active Ni–Mo–S phase and a favorable S-edge/M-edge site ratio. This work highlights the critical role of metal promotion and support engineering in optimizing HDS catalyst performance and offers a promising pathway toward more efficient desulfurization strategies for cleaner fuel production.

## Acknowledgments

The authors gratefully acknowledge financial support from the French Agence Nationale de la Recherche (ANR) and LabEx EMC³ through the HOSMoS project (Grant No. ANR-10-LABX-0009 and the Centre for Zeolites and Nanoporous Materials, Label of Excellence, Normandy Region (CLEAR, 239216). The authors also acknowledge the BM23 beamline from the European Synchrotron Radiation Facility for provision of beamtime.
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