Governing the Efficiency of Ni/SiO₂-Al₂O₃ Catalyst for Methane Dry Reforming via Strategic Calcination Conditions

Abstract

This study investigates the improvement of Ni/SiO₂-Al₂O₃ catalysts in the dry reforming of methane (DRM) process by detailed adjustments of calcination temperature (600–900 °C) and duration (1–9 h). N₂ physisorption, H₂-TPR, XRD, TGA, and TEM show that elevated calcination temperatures result in increased surface roughness and reduced specific surface areas. The present investigation indicates that the ideal calcination parameters are 900 °C and 3 h. This helps the catalyst work better. This condition gave the best initial activity (54% CH₄ conversion and 61% CO₂ conversion) and the best long-term stability and resistance to carbon deposition. Using MATLAB R2025b (ODE45) for kinetic analysis, it was found that these factors have a big effect on activation energy. Shorter calcination of 1 h gave high initial activity, but it quickly lost its effectiveness. On the other hand, a longer calcination time of 9 h made the material more stable but less able to condition convert because it sintered too much. These results show that it is very important to carefully control the conditions of calcination in order to make long-lasting, high-performance catalysts for making syngas. Moreover, a 20-h DRM stability run of the optimum catalyst exhibited nearly constant activity, highlighting its strong structural integrity and superior ability to alleviate rapid coke formation.

1. Introduction

The increasing global warming issue caused by the buildup of CO₂, CH₄, and other greenhouse gases is one of the most pressing issues we are currently confronting [1,2]. From a chemical point of view, CH₄ and CO₂ absorb a huge amount of infrared radiation [3]. Currently, CO₂ conversion can be achieved using photocatalysis [4], electrocatalysis [5], and other chemical processes, but dry reforming of methane (DRM) reactions have unique efficiency benefits [6]. DRM reactions cannot only convert CH₄ and CO₂ at the same time but also produce syngas (H₂ + CO) with an H₂/CO ratio close to one during the reforming process. The syngas provides critical industrial raw materials for the synthesis of long-chain hydrocarbons, light olefins [7], methanol [2], and other valuable industrial products [8]. However, DRM reactions still face various challenges in practical applications, such as catalyst sintering and coke deposition [9]. Over the last few decades, significant effort has been put into studying active centers suited for DRM reactions. Undoubtedly, precious metal catalysts such as Ru, Pt, and Pd offer superior catalytic characteristics and resistance to carbon deposition in DRM processes, but their scarcity and high cost limit their use on a broad scale [10,11]. Compared to noble metals, Ni metal in Group VIII has high catalytic activity in practical applications, although it is prone to sintering and carbon deposition during the reaction process, as well as deactivation [12,13,14]. Several studies have emphasized the critical importance of the catalyst’s structural and chemical characteristics in clarifying the deactivation mechanisms of Ni-based catalysts in DRM procedures. The choice of support material has a considerable impact on Ni’s catalytic performance [15]. Pizzolitto et al. [16] reported that a variety of outcomes were obtained depending on the characteristics of the various supports used for the Ni catalyst in the DRM process, including ceria, alumina, silica, zirconia, and titania. The low dispersion of Ni over silica limits its catalytic application for reforming reactions [17], whereas alumina support attains good dispersion of Ni. Using a small amount of alumina along with silica may offer good dispersion of Ni. The silica-alumina dual support was also reported to increase the reducibility of NiO [18]. A mixture of 10% Ni/SiO₂-Al₂O₃ (75:25) was chosen to achieve the best structural benefits from both supports. Al₂O₃’s acid-base properties make it more thermally stable and help activate CO₂, while SiO₂ provides a framework with a large surface area for better Ni dispersion. The 10 wt.% Ni loading is an industry standard for achieving the right balance between cost and performance. It establishes an optimal threshold that guarantees enough active sites for high conversion while avoiding excessive metal agglomeration related to bigger loadings. This combination makes the metal and the support stick together really well, which stops Ni particles from sintering and making carbon filaments. These are the two main things that cause catalysts to halt working when the hard dry reforming process is going on. As critical controls in governing the efficiency of Ni/SiO₂-Al₂O₃ catalysts for DRM, the present work explores how calcination temperature and duration affect the efficiency. The study’s novelty lies in detecting a precise ideal calcination at 900 °C for 3 h, which produces an optimal balance between high initial activity and long-term structural stability. Unlike typical investigations that focus mainly on temperature, this work delivers a comprehensive dual-parameter analysis, depicting that extended calcination time (up to 9 h) can actually improve stability by creating deactivation-resistant Ni crystallites, in spite of a reduction in total surface area. Furthermore, the paper integrates a strong kinetic dimension using MATLAB (ODE45) to solve ordinary differential equations based on the Arrhenius equation, which permits the exact determination of activation energies, linking physical catalyst properties directly to chemical performance metrics. A delicate framework for designing industrial catalysts that resist carbon deposition and sintering, ultimately providing a clearer roadmap for efficient syngas production, was specified via the transition from unstable, high-surface-area states at low calcination times to stable, coarsened states at higher durations.

In this study, a 10 wt.% Ni catalyst supported on a mixed silica–alumina support (75% SiO₂ and 25% Al₂O₃) was investigated, with the catalyst prepared using the impregnation method. The catalyst will be subjected to different calcination temperatures (600, 700, 800, and 900 °C) for a fixed duration of 3 h. Following the determination of the optimal calcination temperature, the effect of calcination time (1, 6, and 9 h) at this selected temperature will be further investigated. Characterization of the produced catalysts, their calcined forms, and the spent catalysts will be performed using N₂ adsorption, H₂-TPR, XRD, TGA, and TEM. A vertical fixed-bed reactor operating at 700 °C will be used to assess the materials’ catalytic performance in terms of activity and stability for the DRM process.

2. Results and Discussion

2.1. Catalyst Activity Evaluation

Figure 1A shows that a higher calcination temperature generally leads to better initial CH₄ conversion over Ni/SiO₂-Al₂O₃ catalysts. The catalyst calcined at 900 °C exhibits the highest initial CH₄ conversion (55%) and the best stability over 360 min Time on Stream (TOS), with only a minor decline. In contrast, catalysts calcined at 600 °C and 700 °C exhibited lower initial CH₄ conversions of approximately 42% and 41%, respectively, and experienced more pronounced deactivation during TOS. The catalyst calcined at 800 °C shows intermediate initial activity (52%) and a moderate deactivation trend. Figure 1B, which focuses on the effect of calcination duration on CH₄ conversion for catalysts calcined at a fixed temperature of 900 °C, reveals a non-linear relationship between calcination time (1–9 h) and catalytic performance. The 1 h calcination yields the highest initial CH₄ conversion (58%) but the least stability, dropping to 46% after 360 min. A 3 h calcination provides a good balance of initial activity (55%) and the best stability (54%). Longer calcination durations (6 and 9 h) lead to lower initial methane conversions of 42% and 44%, respectively. The catalyst calcined for 6 h exhibits noticeable deactivation during TOS, whereas the 9 h-calcined catalyst demonstrates markedly improved stability. Although methane conversion initially decreases with increasing calcination time, a relative improvement in performance is observed upon further prolongation of calcination beyond 6 h. This behavior is attributed to structural equilibration of Ni species and enhanced resistance to carbon deposition, which together improve the effective catalytic activity. Previous studies have demonstrated that methane conversion does not vary linearly with calcination time; instead, intermediate calcination durations can reduce activity, whereas prolonged calcination enhances structural stability and partially restores catalytic performance [19].

As shown in Figure 2A, the catalyst calcined at 900 °C exhibited the highest initial CO₂ conversion (61%) and the best stability over time. The catalyst treated at 800 °C showed slightly lower initial activity (58%) and more pronounced deactivation. In contrast, the catalysts calcined at 700 °C (44%) and 600 °C (49%) demonstrated the lowest initial conversions and suffered from steady deactivation. Although conversion generally decreases with decreasing calcination temperature, the trend is not linear between 700 and 600 °C. The difference in conversion level can therefore be attributed to variations in the stability and effectiveness of the active Ni sites rather than to differences in deactivation kinetics. Similar non-linear trends in the DRM process with calcination temperature have been reported in the literature due to competing effects of Ni stabilization and metal–support interaction [20].

Figure 2B shows how the CO₂ conversion is affected by calcination times of 1, 3, 6, and 9 h at 900 °C. The highest initial conversion (about 65%) and mild deactivation are displayed by the 1 h catalyst. High initial activity (61%) and good stability are well-balanced by the 3 h catalyst. The catalyst with the lowest initial activity (around 47%) and least stable performance is the 6 h catalyst. The 9 h catalyst shows good stability but a reduced first conversion (50%). At 900 °C, the effect of calcination time on CO₂ conversion is non-linear. The catalyst calcined for 6 h exhibits a lower conversion profile compared to the catalyst calcined for 9 h, because the 6 h sample has inadequate stabilization of Ni species and increased carbon deposition that lowers the effective availability of active Ni0 sites, resulting in lower methane conversion. The longer 9 h calcination makes stronger active sites that are less likely to become inactive and can better handle carbon production than the 6 h treatment [19]. A period of 3 h seems to be ideal for striking a balance between initial activity and stability.

The 900 °C catalyst’s greater stability for both processes suggests that the higher temperature encourages the development of stronger, more deactivation-resistant active sites. Higher CO₂ conversion than CH₄ conversion suggests the reverse water-gas shift (RWGS) reaction (CO₂ + H₂ ⇌ CO + H₂O) is active. In the presence of H₂ (likely from methane reforming), RWGS consumes CO₂, increasing its apparent conversion beyond that of CH₄ in the primary reaction over the Ni catalyst [21]. Overall, increasing the calcination temperature notably enhances both the initial CO₂ conversion and the long-term stability of the catalyst, with 900 °C yielding the most favorable results. Figure 3A illustrates how far the ratio of H₂/CO reached in the product stream over the Ni/SiO₂-Al₂O₃ catalyst. The outcomes are displayed for catalysts calcined at 600, 700, 800, and 900 °C. The catalyst with the highest initial H₂/CO ratio (0.92) and the best stability is the one that is calcined at 700 °C. The catalyst at 800 °C begins at about 0.915 and gradually drops. With oscillations and a downward trend, the 600 °C catalyst exhibits the least stable ratio, starting at about 0.89. Despite having the lowest initial H₂/CO ratio (0.84), the catalyst at 900 °C exhibits good stability. In short, the relative positions of the H₂/CO ratio profiles in Figure 3A reflect the competing contributions of dry reforming of methane and the reverse water–gas shift (RWGS) reaction. Calcination at 700 °C provides an optimal balance between methane reforming activity and suppression of RWGS, resulting in the highest and most stable H₂/CO ratio. At higher calcination temperatures, particularly 900 °C, enhanced RWGS activity consumes H₂ and increases CO formation, thereby lowering the H₂/CO ratio despite high CH₄ conversion. In contrast, the catalyst calcined at 600 °C exhibits an unstable H₂/CO ratio due to weaker resistance to carbon deposition, leading to fluctuating syngas composition.

Figure 3B shows the H₂/CO ratio in the product stream over TOS for a Ni/SiO₂-Al₂O₃ catalyst that was calcined for 1, 3, 6, and 9 h at 900 °C. The catalyst that has been calcined for 1 h has the highest initial H₂/CO ratio (0.885), but it rapidly decreases and stabilizes at 0.84. The 3 h calcined-catalyst displays a relatively high starting ratio (0.838) and the highest stability, varying minimally around 0.835–0.84. After a brief decline, the 9 h calcined-catalyst retains good stability between 0.78 and 0.79. It begins at about 0.805. With H₂/CO varying between 0.77 and 0.84, the 6 h calcined-catalyst exhibits the least steady performance and the lower H₂/CO ratio (0.785). Generally, the gradual decrease in the H₂/CO ratio with increasing TOS is mainly attributed to the progressive contribution of the reverse water gas shift reaction, which consumes H₂ while producing additional CO. Furthermore, surface carbon accumulation during prolonged operation can alter the availability of active Ni sites, resulting in a relative reduction of H₂ formation compared to CO. Consequently, catalysts with insufficient structural stabilization exhibit a more pronounced decline in the H₂/CO ratio over time. Also, before the system stabilizes, the amount of H₂ made compared to CO can be lowered by quickly turning off the system and letting carbon build up on the catalyst surface. A divergent trend was reported by Nouf A. Bamatraf et al., where enhanced catalytic performance of the NiO-based catalyst for syngas production was achieved when the catalyst was calcined at lower temperatures [22].

2.2. Characterization of the Catalyst

2.2.1. N₂ Physisorption

To investigate the influence of calcination conditions (temperature and duration) on the porosity and surface properties of the Ni/SiO₂-Al₂O₃ catalyst, the N₂ adsorption–desorption isotherms of catalysts calcined at different temperatures (Figure 4) and different durations (Figure 5) were presented. All samples of the Ni/SiO₂-Al₂O₃ catalyst exhibited Type IV isotherms with H1 hysteresis loops, indicating mesoporous structures with cylindrical pores. The pore size distribution over the catalyst remains monomodal in the size range 8.4 nm to 9 nm upon different calcination temperatures. As the calcination temperature and duration increased, a consistent decrease in the volume of N₂ adsorbed was observed. This decline in N₂ uptake suggests a reduction in specific surface area (SA) and specific pore volume (PV). Interestingly, SA and PV are decreased, but the pore diameter is increased upon increasing the calcination temperature. It indicates the structural degradation or collapse of smaller pores into larger pores upon increasing calcination temperature/time [22].

Table 1. Textural properties of fresh catalysts of Ni/SiO₂-Al₂O₃ during 3 h calcination time.

Calcination Temperature (°C)	SA (m2/g)	PV (cm3/g)	PS (nm)
600	374	0.51	5.9
700	343	0.50	6.1
800	308	0.47	6.3
900	238	0.41	6.9

and

Table 2. Textural properties for fresh catalysts of Ni/SiO₂-Al₂O₃ calcined at 900 °C.

Calcination Time (h)	SA (m2/g)	PV (cm3/g)	PS (nm)
1	261	0.43	6.6
3	238	0.41	6.9
6	220	0.39	7.1
9	213	0.39	7.2

show that increasing either calcination temperature or duration has a similar impact on the porosity of the Ni/SiO₂-Al₂O₃ catalyst, with pore diameter increases, while specific surface area and pore volume decrease. This suggests that prolonged thermal treatment, whether by higher temperature or extended time, leads to structural coarsening and reduced accessible surface area. The catalyst calcined at 900 °C for 3 h facilitates gas diffusion and improves access to active sites through pores of average size 6.85 nm. These pore features will help attain high catalytic activity over the 900 °C calcined catalyst.

Achieved optimum catalytic activity towards the DRM reaction by facilitating. However, further pore enlargement to 72.1 Å after 9 h of calcination at the same temperature affects diminished activity, likely due to fewer accessible active sites at a lower specific surface area [23]. The pore size distribution does not change upon increasing the calcination time. It remains monomodal in the size range of 8.4 nm. The adsorbed quantity profiles in Figure 5A are in order from 9 h to 1 h because the amount of N₂ adsorbed always goes down as the calcination time goes up. This trend shows a steady decrease in specific surface area and pore volume because the structure becomes coarser, and smaller pores collapse into bigger ones when they are heated for a long time. The 9 h sample has the least pore volume and surface area (213 m²/g) compared to the 1 h sample (261 m²/g). This means that its adsorption profile is near the bottom of the graph.

2.2.2. Temperature-Programmed Reduction TPR

The TPR profile for a Ni/SiO₂-Al₂O₃ catalyst that has been calcined at 600 °C, 700 °C, 800 °C, and 900 °C is shown in Figure 6A. The presence of many Ni oxide species with differing reducibility is indicated by the multiple peaks in the TPR profiles for all calcination temperatures. These species are ascribed to variations in levels of interaction between the support material (SiO₂-Al₂O₃) and the NiO phase. The 600 °C calcined sample has a notable three reduction peaks that begin at about 450 °C, peak at about 600 °C, and peak at 800 °C. This implies that the reduction in dispersed Ni²⁺ interacts with the support under weak to strong interaction, respectively [24]. NiO under strong interaction generates stable active sites upon reduction. Upon increasing the calcination temperature, the intensity of the low temperature reduction peak decreases, the intermediate temperature reduction peak is shifted towards relatively higher temperatures, and the reduction peak’s intensity at high temperature is increased. Clearly, upon increasing the calcination temperature, the interaction of NiO with the support is translating from weak to a stronger level, and the concentration of stable active sites is also growing [25]. Figure 6B shows that the TPR profiles of Ni/SiO₂-Al₂O₃ calcined at 900 °C for different durations (1, 3, 6, and 9 h) show minimal variation in the position and intensity of the reduction peaks, which consistently appear around 700 °C and 850 °C. This suggests that the calcination time has little effect on the nature of the reducible species. At a 900 °C calcination temperature, thermally stable phases are already formed during the early stages of calcination. As a result, the metal-support interactions and reducibility remain largely unchanged with increasing time, leading to nearly identical TPR profiles.

2.2.3. XRD Analysis

The structural evolution of Ni/SiO₂-Al₂O₃ catalysts was investigated using X-ray diffraction (XRD), as presented in Figure 7A,B. The identified crystalline phases include cubic NiO, with prominent reflections at 2θ = 43.3°, 62.9°, and 75.4°, corresponding to the (200), (220), and (311) planes, respectively, as indexed to (Code 01-071-1179). While reflections at 2θ = 45° and 67° may be assigned to a poorly crystalline solid solution of SiO₂·Al₂O₃ (Code 00-048-0276). At 2θ = 37°, diffraction peaks for SiO₂·Al₂O₃ solid solution and cubic NiO overlap with each other. Catalyst calcined at 600 °C showed a broad hump around 2θ = 22°, which is attributed to amorphous SiO₂ (Code 01-083-2465) [22].

Increasing the calcination temperature from 600 °C to 900 °C induced only minor changes in the XRD profiles, suggesting that significant crystallization and NiO phase formation occurred predominantly at lower temperatures, with higher temperatures contributing little further structural change. As shown in Figure 7B, extending the calcination time from 1 to 6 h led to organization of a more crystalline NiO. The peaks corresponding to SiO₂ and SiO₂·Al₂O₃ are present across all catalysts calcined at different times, indicating that these phases are relatively stable under the applied calcination conditions. The increase in peak intensity and sharpness at higher calcination time (up to 6 h) indicates enhanced crystallinity and better-defined NiO domains. However, a slight reduction in intensity was observed at 9 h, which may be attributed to particle agglomeration or surface sintering effects that reduce the effective crystallite dispersion. Overall, the changes in diffraction peak positions and intensities across the different treatments were not substantial, indicating that the NiO phase was relatively stable and well-formed under all conditions. The catalyst calcined for 3 h showed the best performance in methane dry reforming, likely due to a balanced combination of crystallinity, dispersion, and phase purity.

2.2.4. TGA

Figure 8A presents a thermogravimetric analysis (TGA) plot illustrating the impact of different calcination temperatures (600 °C, 700 °C, 800 °C, and 900 °C), each maintained for a 3 h duration, on the thermal stability of the catalyst. The Ni/SiO₂-Al₂O₃ catalysts show a mass loss profile as they are heated up to 1000 °C. There is a minor mass loss initially, due to volatile impurities, followed by a significant mass loss region at 600 °C, attributed to the oxidation of the carbon formed on the surface of the catalyst. Higher calcination temperatures generally result in lower overall mass loss and a slight shift in the major decomposition towards higher temperatures, suggesting that increased calcination promotes the oxidation of coke deposited on its surface. Figure 8B presents the thermogravimetric analysis (TGA) of Ni/SiO₂-Al₂O₃ catalysts calcined at 900 °C for varying durations (1, 3, 6, and 9 h). The results indicate a general decrease in total weight loss with increasing calcination time, reflecting improved thermal stability. The catalyst calcined for only 1 h exhibits the highest total mass loss (55%), suggesting huge mass deposition over the improperly calcined catalyst sample. Increasing the calcination duration to 3 h reduces the weight loss to approximately 10%, indicating more effective removal of coke. This improvement is attributed to the enhanced crystallinity of NiO and stronger interactions between NiO particles and the SiO₂·Al₂O₃ support, which improve structural integrity and thermal resistance. However, further extending the calcination time to 6 and 9 h results in increased mass retention (80%) but reduced catalytic performance. Overall, catalyzed at 900 °C for 3 h, it is found to attain an impressive coke resistance property [26].

2.2.5. TEM Analysis

To study the effect of both dry reforming and calcination temperature on catalyst morphology, TEM characterizations were carried out for Ni/SiO₂-Al₂O₃ catalysts calcined at 600 °C and 900 °C for 3 h before and after reaction (Figure 9A,B and Figure 10A,B). In the fresh state, in both catalysts, the particles are agglomerated on a porous support; the catalyst calcined at 600 °C shows a little better dispersion than the catalyst calcined at 900 °C. Images after reaction depict the presence of filamentous carbon (CNFs/CNTs), a common product of methane decomposition on Ni surfaces [27].

Figure 11 explores how temperature affects the conversion of CH₄ and CO₂ for the optimal catalyst (Ni/SiO₂-Al₂O₃ calcined at 900 °C for 3 h). As the reaction temperature rises from 700 to 825 °C, conversion rates for both CH₄ and CO₂ rise. This improvement is attributed to the endothermic nature of the DRM process. Raised temperatures provide reactant molecules with greater kinetic energy, facilitating collisions and aiding in the breaking of bonds, thereby increasing product formation. The Arrhenius equation (Equation (1)) permits us to calculate the activation energy (E_a) for the system using reaction temperature data and matching conversion rates. This equation relates the (r) rate constant (mol.g⁻¹.s⁻¹), (A) pre-exponential factor (mol.g⁻¹.s⁻¹.bar^−(a+b)), (P_CH4 and P_CO2) partial pressures of CH₄ and CO₂ (bar), and $b$ are the apparent reaction orders (dimensionless), (E_a) activation energy (KJ.mol ⁻¹), (R) universal gas constant (8.314 J.mol⁻¹.K⁻¹), and (T) temperature (K) [28].

$$\mathrm{r}=\mathrm{A}{\mathrm{P}}_{{\mathrm{C}\mathrm{H}}_4}^{\mathrm{a}}{{\mathrm{P}}_{{\mathrm{C}\mathrm{O}}_2}^{\mathrm{b}}\mathrm{e}}^{-{\mathrm{E}}_a/\mathrm{R}\mathrm{T}}$$

(1)

The Arrhenius equation is solved using ordinary differential equations via MATLAB (ODE45) to obtain the activation energy of the system based on Equation (1). Experimental data are used to solve the numerical ordinary differential equations that show how fast methane and carbon dioxide change into other substances. A linear regression analysis is adopted on the Arrhenius plot (ln k versus 1/T) by changing the temperatures (600–900 °C) and measuring the reaction rates (k) that happen at those temperatures. The rate law is probably shown by Equation (1), with the unknown parameter being the pre-exponential factor A and activation energy E_a. The ODE45 algorithm changes the kinetic parameters over and over again to make the differences between the predicted and experimental concentration profiles as small as possible over time. The slope of the resulting linear fit (−E_a/R) gives the exact activation energy needed for the dry reforming process. This lets the researchers measure the catalytic efficiency and the energetic barrier for each calcination condition.

The rates are derived from the given conversions at different temperatures. These values can be used in the method above to determine the activation energy for the system. Activation energy was estimated from the Arrhenius equation [1]. The approximate value of 99.1138 kJ/mol was determined based on the data presented in Figure 11. Figure 12 illustrates the Arrhenius plot of the temperature dependence of CH₄ reaction rates. The experimental data align closely with the predicted model line.

Figure 13 graph illustrates what happened after a 20-h stability test of the DRM. It shows how the conversion of reactants and the quality of syngas change over time on stream (TOS). The performance profile has gotten worse because the reverse water-gas shift reaction happened at the same time. The catalyst’s catalytic activity stays the same throughout the experiment because it works well and can handle quick coking.

3. Experimental

3.1. Catalyst Preparation

A catalyst containing 10 wt.% NiO supported on commercial SiO₂-Al₂O₃ (75 wt.% SiO₂ + 25 wt.% Al₂O₃) was prepared by gradually adding 30 mL of a 0.1 M aqueous solution of nickel (II) nitrate hexahydrate (Ni (NO₃)₂·6H₂O, 98%, Alfa Aesar) to 2.441 g of SiO₂-Al₂O₃. The mixture is subjected to heating and stirring until it turns into a paste, and the fluid evaporates. It went through two calcination processes. A portion was calcined at 600 °C, 700 °C, 800 °C, and 900 °C for 3 h. While the other part was calcined at 900 °C for periods ranging from 1 to 9 h. Catalyst is abbreviated in the article as Ni/SiO₂-Al₂O₃.

3.2. Catalyst Activity Test

0.1 g of catalyst was utilized in a tubular stainless-steel fixed-bed reactor (D = 9.1 mm and H = 300 mm). The catalyst bed’s center has a K-type thermocouple. The catalyst was reduced with hydrogen at a flow rate of 30 mL/min for an hour at 700 °C. N₂ was also used to remove the hydrogen gas from the reactor’s catalyst bed. The temperature of the reactor is 700 °C. The total flow rate of the feed was 70 mL/min. A gas chromatograph fitted with a PropakQ column, molecular sieve columns, and a thermal conductivity detector was used to examine the products. The conversions of CH₄, CO₂, and H₂/CO were all calculated using Equations (2)–(4) [29].

$${CH}_4 (conversion \%)={\displaystyle \frac{{CH}_{4,in}-{CH}_{4,out}}{{CH}_{4,in}}}$$

(2)

$${CO}_2 \left(\%\right)={\displaystyle \frac{{CO}_{2,in}-{CO}_{2,out} }{{CO}_{2,in}}}\times 100$$

(3)

$${\displaystyle \frac{H_2}{CO}}={\displaystyle \frac{mole of H_2 produced}{mole of CO produced}}$$

(4)

3.3. Catalyst Characterization

The Micromeritics Tristar II 3020 instrument (Micromeritics, GA, USA) was used to determine the catalyst sample’s N₂ adsorption–desorption profile versus relative pressure (P/Po), specific surface area, specific pore volume, and pore diameter. The Brunauer–Emmet–Teller equation estimates the specific surface area, while the nonlocal density function model estimates the pore size distribution. On a Micromeritics AutoChem II 2920 system (Malvern Panalytical, Westborough, MA, USA) with a thermal conductivity detector (TCD), the reducibility, basicity, and acidity of the catalysts were investigated using H₂-temperature-programmed reduction (H₂-TPR). Hydrogen temperature-programmed reduction (H₂-TPR) was performed using 70 mg of catalyst under a 10% H₂/Ar gas mixture (40 mL/min). The sample was heated from room temperature to 900 °C at a linear ramp rate of 10 °C/min. Water produced during the process was eliminated using a cold trap. Changes in conductivity corresponding to gas desorption or H₂ consumption were measured by the TCD. X-ray diffraction (XRD) analysis of the fresh catalyst was conducted using a Rigaku MiniFlex diffractometer (MiniFlex, Rigaku, Akishima City, Japan), equipped with Cu Kα₁ radiation (λ = 0.15406 nm), operated at 40 kV and 40 mA. Thermogravimetric analysis (TGA) was performed in air using a Shimadzu TGA-51 thermobalance (Shimadzu, Kyoto, Japan) to evaluate the thermal stability and compositional characteristics of the spent catalysts based on their mass change as a function of temperature. Inside the apparatus, a platinum pan containing 10–15 mg of the utilized catalysts is carefully placed. In an air environment, it is heated from room temperature to 1000 °C at a rate of 20 °C/min. As the heating process advanced, the mass change was continuously recorded. TEM analysis was performed to investigate the morphological and structural features of the Ni/SiO₂-Al₂O₃ catalysts. Samples calcined at 600 °C and 900 °C were examined both before and after the methane dry reforming reaction. The measurements were carried out using a JEOL JEM-100CX transmission electron microscope (Akishima, Japan) operated at an accelerating voltage of 80 kV.

4. Conclusions

This study investigated the impact of calcination temperature (600–900 °C) and duration (1–9 h) on the performance of a Ni/SiO₂-Al₂O₃ catalyst in methane dry reforming (DRM). The results highlighted the critical role of these pre-treatment conditions in shaping the catalyst’s structural and chemical properties, thereby influencing its catalytic behavior. Higher calcination temperatures generally enhanced both initial activity and long-term stability. Calcination conditions significantly influenced the H₂/CO product ratio. The optimal temperature for achieving a high and stable output was determined to be 700 °C. Among all samples, the catalyst calcined at 900 °C demonstrated the highest initial methane conversion (54%) and exhibited remarkable resistance to deactivation. This enhanced behavior correlated with increased NiO crystallite size (XRD), stronger metal-support interactions (TPR, indicating less reducible NiO), and improved resistance to carbon deposition, as shown by the TGA. However, calcination also induced NiO sintering, resulting in a reduction in specific surface area and pore volume (N₂ physisorption). While both the 1 h and 3 h calcined samples exhibited high initial catalytic activity, the 3 h calcined catalyst proved more effective at maintaining long-term performance. Extended calcination times (6 and 9 h) resulted in lower initial activity but enhanced stability, likely due to further evolution of NiO crystallites and increased resistance to carbon formation. The TEM study of used catalysts gave direct evidence of carbon deposition, a major cause of catalyst deactivation. Interestingly, a lower calcination temperature of 600 °C appeared to increase carbon production compared to the higher 900 °C treatment. The higher rate of CO₂ conversion compared to CH₄ indicates that the reverse water–gas shift reaction is occurring concurrently. Additionally, calcination conditions affected the product’s H₂/CO ratio; at 700 °C, the calcination temperature was identified as optimal for achieving a high, stable yield. The study established [30] the activation energies (E_a) for the best catalyst (Ni/SiO₂-Al₂O₃ calcined at 900 °C for 3 h), predicting around 99.1138 kJ/mol using the Arrhenius equation (Equation (1)). The activation energy aligns with the endothermic nature of the DRM process, in which the conversion rates of both CH₄ and CO₂ increase at higher reaction temperatures (500 to 825 °C).