Strontium-Promoted Ni-Catalyst Supported over MgO for Partial Oxidation of Methane: Unveiling a Cost-Effective Catalyst System for Fast Mitigation of Methane

Abstract

CH₄ is a powerful greenhouse gas that is thought to be one of the main causes of global warming. The catalytic conversion of methane in the presence of oxygen into hydrogen-rich syngas, known as the partial oxidation of methane (POM), is highly appealing for environmental and synthetic concerns. In search of a cheap catalytic system, the Ni-supported MgO-based (5Ni/MgO) catalyst and the promotional supplement of 1–3 wt.% Sr over 5Ni/MgO are investigated for the POM reaction. Catalysts are characterized by N₂ sorption isotherm analysis, X-ray diffraction spectroscopy, Raman spectroscopy, temperature-programmed desorption techniques, and thermogravimetry. Increasing the loading of strontium over Ni/MgO induced a strong interaction of NiO with the support, pronouncedly. In the presence of oxygen during the POM, the moderate-level interaction of NiO with the support grows markedly. Overall, at a 600 °C reaction temperature, the 5Ni2Sr/MgO catalyst shows 72% CH₄ conversion (~67% H₂ yield) at 14,400 mL/h/g_cat GHSV and ~86% CH₄ conversion (84% H₂ yield) at 3600 mL/h/g_cat GHSV. Achieving a higher activity towards the POM over cheap Ni, Sr, and MgO-based catalysts might draw the attention of environmentalists and industrialists as a low-cost and high-yield system.

1. Introduction

An increase in the concentration of greenhouse gases leads to global warming, which in turn disrupts seasonal cycles and frequently triggers extreme weather events. Methane and carbon dioxide are major contributors of greenhouse gases, where the global warming potential of methane is 3.7 times that of carbon dioxide on a molar basis [1]. Natural and anthropogenic methane emission sources trigger methane concentration in the atmosphere. Anthropogenic sources like livestock farming, waste decomposition, incomplete burning of biomass-biofuel, fossil fuel transportation, and agriculture emissions contribute 64% of total methane emissions [2,3,4]. Wetlands are natural emission sources of methane along with carbon dioxide, which cannot be stopped. To achieve the goal of synthetic/clean energy, it is preferable to oxidize methane using molecular oxygen (by partial oxidation of methane; POM) or CO₂ (by dry reforming of methane; DRM) over a suitable catalyst [5]. Among DRM and POM, POM operates at a lower reaction temperature, and it produces hydrogen-rich syngas, as the H₂/CO ratio in POM is double that of DRM [6]. By using molecular oxygen in the POM, the cokes are also oxidized regularly, which results in less coke deposition. Noble metals (Rh, Ru, Pd, Pt) and transition metals like Ni catalyze the POM reaction [7,8]. The low cost of Ni over noble metals bears interest to the catalytic community, but the major drawback with Ni-based catalysts is their agglomeration at high temperatures. The catalyst eventually deactivates due to the coke deposition (from CH₄) caused by the increasing size of Ni. Therefore, the development of a support capable of holding Ni against high temperatures and maintaining the catalytic continuum is necessary for Ni-based reactions. Silica, alumina, titania, ceria, magnesia, etc., as supports are investigated for this purpose [9,10,11,12,13,14]. Ni exhibits poor dispersion over a silica support, diffuses into the crystalline lattice of alumina (leading to the loss of active sites), and undergoes frequent oxidation by titania (leading to deactivation of the active sites). However, Ni/Al₂O₃ promoted with MgO achieved a 76% H₂ yield through the POM reaction [15]. It is well known that MgO interacts with NiO in the form of a solid solution, making it a cheap support [12,16,17]. However, solid solution is hard to reduce, and it produces a lower amount of metallic Ni (or active sites) upon reduction, and “Ni supported over MgO” was found to deactivate fast [12]. Recently, the promotional role of Sr over Ni-catalyst dispersed over silica-alumino-phosphate (SAPO) was found to increase the metal-support interaction and H₂ yield of up to 42% at 600 °C during the POM reaction [18]. The addition of Sr over the Ni-catalyst dispersed over titania-zirconia was found to increase the reducibility, basicity, and concentration of active sites. This catalyst achieved a 47% H₂ yield at 600 °C through the POM. Among different alkaline promoters (Mg, Ca, Sr, Ba), the Sr-promoted catalyst was found to optimize the size of Ni to a minimum as well as induce the highest dispersion of Ni over the Al₂O₃–ZrO₂ support [19]. Over alumina support, Sr addition was found to increase the metal support interaction in Ni-based catalysts [20].

Ni-supported MgO catalysts suffer from lower reducibility, and the addition of Sr as a promoter has been found to enhance the reducibility significantly, optimize the size of Ni particles, and induce the formation of a higher concentration of active sites over different supports [16,17]. To develop a more cost-effective and efficient catalytic system based on Ni-supported MgO for the POM reaction, the use of Sr as a promoter is a promising approach that warrants further investigation. Herein, the “Ni-dispersed MgO catalyst system” and the advantages of Sr over the catalyst are investigated for the POM reaction. These catalysts are characterized by N₂ sorption isotherms analysis, X-ray diffraction study, Raman spectroscopy, temperature-programmed desorption/reduction/oxidation, and thermogravimetric analysis. The precise relationship between catalytic activity and characterization outcomes marks the potential futuristic application of a cost-effective catalytic system for the POM reaction.

2. Results and Discussion

2.1. Characterization Results

The 5Ni/MgO and 5NixSr/MgO (x = 1, 2, 3 wt.%) catalysts are reduced at 700 °C under H₂ for 1 h before the POM process. The X-ray diffraction study of reduced catalysts is shown in Figure 1 and Figure S1. The diffraction pattern for the cubic MgO phase is observed in all reduced catalysts at Bragg’s angles of 36.8°, 42.8°, 62.2°, 74.6°, and 78.6° (JCPDS Card# 01-075-0447), whereas the diffraction pattern of the cubic MgNiO₂ phase is merged with the diffraction pattern of MgO at 42.8°, 62.2°, 74.6°, and 78.6° Bragg’s angles (JCPDS Card 00-003-0999). In strontium-promoted catalysts, the phases for cubic SrO are also evident at Bragg’s angle 25.2° [21,22,23]. The absence of the metallic Ni phase in the reduced catalyst samples indicates the fine distribution of small metallic Ni crystallites over the support. Notably, the same phases also appear over fresh catalysts, but the intensity of these phases is less than that of reduced catalysts (Figure S1B). It indicates that upon reduction, the crystallinity of the catalyst increases. Upon increasing the Sr loading over 5Ni/MgO, the diffraction peak intensity for orthorhombic SrO is increased substantially, which indicates the rise of highly ordered crystals of strontium oxide. XRD of spent catalysts is also carried out (Figure 1C–F). It is observed that the crystalline peak intensity is decreased in the spent catalyst. It indicates that during the POM reaction, sintering is halted and dispersion of active sites is induced.

Furthermore, Figure 2 and

Table 1. Textural characteristics of reduced 5Ni/MgO, reduced 5Ni xSr/MgO and (x = 1, 2, 3 wt.%), spent 5Ni/MgO, and spent 5NixSr/MgO and (x = 2, 3 wt.%) catalysts.

Catalyst	Surface Area (m2/g)	Pore Volume (cm3/g)	Average Pore Diameter (nm)
Reduced 5Ni/MgO	68	0.48	34
Reduced 5Ni1Sr/MgO	72	0.50	33
Reduced 5Ni2Sr/MgO	61	0.45	35
Reduced 5Ni3Sr/MgO	55	0.42	38
Spent 5Ni/MgO	48	0.41	41
Spent 5Ni2Sr/MgO	40	0.36	44
Spent 5Ni3Sr/MgO	39	0.33	42

display the surface area and porosity of reduced 5Ni/MgO and 5NixSr/MgO (x = 1, 2, 3 wt.%) catalysts. The adsorption–desorption isotherm study shows type IV and H3 hysteresis loops, which means that slit-type mesopores are present. MgO support has the least surface area, pore volume, and pore diameter (Table S1). Interestingly, upon the addition of Ni, the surface area and pore volume are increased by more than double, whereas pore diameter grows by 70%. The 5Ni/MgO catalyst attains a 68.3 m²/g surface area, a 0.48 cm³/g pore volume, and a 33.8 nm pore diameter. The massive rise in surface area, pore volume, and pore diameter upon the addition of 5 wt.% Ni can be explained by the expansion of the MgO framework due to the insertion of Ni. The expansion of surface area and pore volume is continued up to a loading of 1 wt.% Sr too. Each framework has its capacity to accommodate foreign metal oxide up to a certain extent. Upon further loading of Sr (>1 wt.%), surface area and pore volume were decreased. It indicates that beyond 1 wt.% Sr loading, SrO crystallite is deposited into the pores of the catalyst [24]. The reduced 5Ni3Sr/MgO catalyst displays a surface area of 55.2 m²/g, a pore volume of 0.42 cm³/g, and a pore diameter of 37.7 nm. The average pore diameter of the current catalyst system remains in the ~32–38 nm range. The dV/log(w) vs. w plot (where ‘V’ is volume and ‘w’ is pore width) illustrates the pore size distribution pattern over the catalyst. The resulting pore size distribution is found to be multimodal, with a higher frequency of pores in the range of 100–150 nm, as shown in the inset figures. The average pore size across the catalysts is calculated using the BJH method, yielding values in the range of 33 nm to 44 nm, as summarized in Table 1. It is interesting to note that after the POM reaction, the surface area and pore volume of spent catalysts were found to decrease due to the deposition of coke inside the pore during the POM reaction (Table 1).

The reduction profile of catalysts is a matter of immense discussion. Before the POM, the catalyst is reduced by hydrogen, and active sites are created. Then, the reaction feed (CH₄ and O₂) is blown over the catalyst surface, where, upon the POM reaction, the hydrogen-rich syngas is evolved. Molecular oxygen and hydrogen also oxidize and reduces gases. Now, molecular oxygen can oxidize the active sites Ni (into NiO), and hydrogen (from syngas) reduces the NiO (into Ni). Overall, the presence of oxygen and hydrogen during the POM modifies the distribution of active sites.

To understand the distribution of active sites, the H₂-TPR-O₂-TPO-H₂-TPR cyclic experiment was carried out (Figure 3). In this cycle experiment, the first H₂-TPR is intended to reduce the NiO (into Ni). The sequential O₂-TPO oxidizes the metallic Ni (into NiO). The last H₂-TPR reduces the NiO again into Ni. On comparing the first and last H₂-TPR, the change in reduction pattern in the sequential exposure of oxidizing gas (O₂) and reducing gas (H₂) can be understood. The reduction profile of 5Ni/MgO and 1–3 wt.% Sr promoted 5Ni/MgO catalysts is composed of a deep negative peak, broad peaks with a peak maximum at 400 °C, and a peak maximum at 800 °C. The negative peak in H₂-TPR may be due to four causes: (1) decarbonization (removal of CO₂ [25]), (2) dihydroxylation (removal of interlayer water), (3) decomposition of metal hydride (it is generally shown with noble metal hydrides) [26], and (4) hydrogen spillover into mesopores [27,28]. The presence of carbonate crystals is omitted by XRD. The current catalysts are mesoporous. In many mesoporous catalyst systems, a negative peak was mentioned due to the spill of hydrogen into the mesopores. So, here the negative peak can be claimed to be hydrogen spillover into the mesopores [27,28]. Ni²⁺ can interact with MgO in two ways. (1) Ni²⁺ ions in the outermost layer and subsurface layers of the MgO (2) Ni²⁺ ions in the MgO matrix. The previous one constitutes a relatively weaker interaction of Ni⁺² than the latter. The migration of Ni²⁺ in the MgO matrix is reported at about 800 °C [29]. Overall, the peaks at about 400 °C and 800 °C are attributed to “NiO under weak interaction with support” and “NiO under strong interaction with support”, respectively [30]. Upon sequential exposure of O₂ and H₂, the negative peak has vanished, and the low-temperature reduction peak is pronounced as well as shifted towards a relatively higher temperature. Again, a broad reduction peak in the intermediate temperature region is also observed. During the first H₂-TPR, hydrogen is spilled over into mesopores. After the first H₂-TPR (in the cyclic experiment), such hydrogen is not evacuated from the mesopores, and thus the spillover phenomenon is halted during the second H₂-TPR. Overall, the distribution of active sites appears to be modified, as indicated by the changes in the reduction profile and metal-support interactions, which grow (as shown by the peak shift in the reduction profile) during exposure to oxygen and hydrogen. Upon addition of 1–3 wt.% Sr over 5Ni/MgO, the first H₂-TPR shows a more intense peak at high temperature (about 775 °C) than a lower temperature reduction peak (about 400 °C). It indicates that Sr addition induces a strong interaction with NiO [31]. Upon exposure to oxygen and then hydrogen, the reduction pattern of 5Ni1Sr/MgO is similar to that of 5Ni/MgO except for the shifting of the high-temperature reduction peak towards a relatively lower temperature (600 °C). It can be concluded that the sequential exposure of oxygen and hydrogen over 5Ni1Sr/MgO [5] makes the reduction of NiO easier than the 5Ni/MgO catalyst, and the reduction peak at about 600 °C can be attributed to the reduction of NiO, which is under moderate interaction. In the sequential exposure of oxygen and hydrogen, 2 wt.% Sr incorporated 5Ni/MgO catalyst attains a comparable low-temperature reduction peak (at about 425 °C) and the most intense high-temperature reduction peak (at about 600 °C). It is noticeable that under O₂ and H₂ sequential exposure over the catalyst, the reduction peak is shifted from high temperature (>700 °C) to 600 °C. That means catalyst active sites are created by NiO to Ni at relatively lower temperatures (600 °C) in the sequential exposure of O₂ and H₂. In the current reaction, the reaction/reduction temperature of the POM is also at 600 °C and so the reduction peaks up to 600 °C are more informative in the context of estimating the population of active sites vis-à-vis the concerned catalytic activity. In the last H₂-TPR, it is observed that the amount of H₂-consumption over the 5Ni2Sr/MgO catalyst becomes the highest (Table S2), which indicates the presence of the highest concentration of active sites in the sequential exposure of O₂ and H₂ over the 5Ni2Sr/MgO catalyst.

Figure 4 displays the Raman spectra and thermogravimetric analysis of the employed 5Ni/MgO and 5Ni + xSr/MgO (x = 1, 2, and 3 wt.%) catalysts. Used 5Ni/MgO used shows a sharp weight loss of 14% up to 400 °C. The weight loss at 250 °C over the spent catalyst is due to evaporation of water [32], whereas after 250 °C, it may be attributed to the dehydration of Mg (OH)₂ as well as oxidation of easily oxidizable carbon deposits [32,33]. Upon the addition of 1 wt.% Sr, the weight loss drops to minimal. The stabilization of SrO-based material by MgO was reported in the literature [34,35]. The mutual interaction between SrO and MgO enhances both the material stability and the weight loss profile. It is noticeable that a weight loss was also observed at about 87 °C over the spent 5Ni1Sr/MgO catalyst. From the literature, decomposition of SrCO₃ was reported at about 900 °C. In the presence of MgO, the carbonation of Sr was also reported by André et al. [35]. So, the significant weight loss near 875 °C can be claimed to be due to the decomposition of SrCO₃. Overall, there is a minimum weight loss of 5.8% for the spent 5Ni1Sr/MgO catalyst. At roughly 500 °C, an additional weight loss is seen by adding 2 wt.% Sr over 5Ni/MgO, and the weight loss resulting from the decomposition of SrCO₃ becomes more noticeable. The decomposition of MgCO₃ was reported to initiate after 400 [36]. Overall, MgO, SrO, and CO₂ have enriched interactions with each other, and an intermediate amorphous species among these can be expected at particular Sr loading [37]. So, the weight loss at about 500 °C over spent 5Ni2Sr/MgO may be claimed to be due to the decomposition of this species. The weight loss (%) over 5Ni2Sr/MgO is slightly increased to 7.5% (than 5.8% over spent 5Ni1Sr/MgO). The weight loss at about 500 °C is not evident at the highest Sr loading (spent 5Ni3Sr/MgO). That means the particular species (formed by Sr, Mg, and CO₂) exists at specific compositions [37]. In spent 5Ni3Sr/MgO, the weight loss due to the decomposition of SrCO₃ (at 875 °C) is most prominent. Overall, 5Ni3Sr/MgO shows 6.52% weight loss. Defect carbon peaks (D), ordered carbon peaks (G), and 2D peaks at 1347 cm⁻¹, 1585 cm⁻¹, and 2658 cm⁻¹, respectively, are characteristics of the Raman spectra of spent 5Ni/MgO and 5NixSr/MgO (x = 1, 2, and 3 wt.%) catalyst systems. Carbon deposit over the spent 5Ni2Sr/MgO catalyst has a maximum I_D/I_G ratio or a minimum degree of graphitization.

2.2. Results of Catalytic Activity and Discussion

During the POM reaction, the catalyst surface is exposed to O₂ (as one of the components of the reactant’s gas feed) and H₂ (as one of the components of syngas). The cyclic H₂TPR-O₂-TPO-H₂TPR experiment over current catalysts shows that the sequential exposure of O₂ and H₂ over the catalyst during the POM reaction induces the creation of an active site at a lower temperature, near 600 °C. The reducibility profile gives us an idea to keep the reduction pretreatment temperature and reaction temperature at 600 °C over the current catalyst system for the POM reaction. The lower temperature operation is economically feasible, as it requires low energy demand. Figure 5 and Figure S2 display the catalytic activity findings of 5Ni/MgO and 5NixSr/MgO (x = 1, 2, 3 wt.%) catalysts in terms of CH₄ conversion, H₂ yield, CO₂ yield, CO yield, and the final H₂/CO ratio. While the CO₂ yield varies between 17% and 22% during the 240 min on stream, the CH₄ conversion and H₂ yield are consistently above 60% for the full catalyst systems. It denotes that the POM is the major reaction and the total oxidation of methane (TOM) is a minor reaction over 5Ni/MgO and 5NixSr/MgO (x = 1, 2, 3 wt.%) catalysts. Again, it is noticeable that the H₂/CO ratio over each catalyst remains about 2.5. The TOM possesses no contribution to the H₂/CO ratio, as its products are CO₂ and H₂O, whereas the POM reaction is solely responsible for the contribution to the H₂/CO ratio. However, according to the stoichiometry of the POM, the H₂/CO ratio should be equal to 2, but here it is above 2. It appears that some components of TOM products, specifically CO₂ and H₂O, may further participate in the oxidation of CH₄ over current catalysts through Dry Reforming of Methane (DRM) and Steam Reforming of Methane (SRM). This process results in an increased H₂/CO ratio. This method of syngas production, whether by TOM followed by DRM or TOM followed by SRM, is referred to as the indirect pathway of the POM. The water gas shift reaction (WGS) is an exothermic reaction, and it is thermodynamically feasible at low temperatures, as is the POM [38]. The co-presence of the water gas shift reaction ($\mathrm{C}\mathrm{O}+{\mathrm{H}}_2\mathrm{O}\leftrightarrows {\mathrm{C}\mathrm{O}}_2+{\mathrm{H}}_2;{∆\mathrm{H}}_{298\mathrm{k}}^{\mathrm{o}}=-41\mathrm{k}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}$) along with the POM may also contribute to exceeding the H₂/CO ratio above 2.

The framework of MgO is expanded upon, incorporating 5 wt.% Ni. The surface area of 5Ni/MgO is double that of the MgO support. It has an average mesopore size of 34 nm and a surface area of 68 m²/g. It contains a cubic MgNiO₂ phase as well. NiO, which interacts with the support with varying degrees of strength, forms the active Ni sites during reductive pretreatment. The POM reaction is initiated, and with exposure to O₂, the weak to moderate interaction between NiO and the support grows further. As a result, more active Ni sites are generated from the interacted NiO species, allowing the 5Ni/MgO catalyst to convert 67–68% of CH₄ into syngas while achieving an H₂ yield of 64–65%. However, this catalyst also accumulates a significant amount of carbon deposits, which further limits its activity.

The MgO framework is further expanded by incorporating 5 wt.% Ni and 1 wt.% Sr. The surface area and pore volume of the 5Ni1Sr/MgO catalyst are the highest among all catalysts. Upon increasing Sr loading (from 1 to 3 wt.%) to the 5Ni/MgO catalyst, it leads to a decrease in surface area and pore volume. Strontium addition induces the formation of a greater amount of NiO, which is under strong interactions with the support. Upon exposure to O₂, the POM reactions start, leading to an alteration in the distribution of active sites. Upon sequential treatment of the catalyst by H₂ (during reductive treatment before the POM reaction) and O₂ (during the POM reaction), a moderate interaction of NiO with the support is formed. The active sites are formed from NiO species that have experienced moderate interactions at the reaction temperature of 600 °C. It is observed that the highest number of active sites is generated over the 5Ni2Sr/MgO catalyst. Additionally, the carbon deposit on 5Ni2Sr/MgO is half that of 5Ni/MgO, and it also exhibits the lowest degree of graphitization among the tested catalysts. Among the strontium-promoted catalysts, 5Ni2Sr/MgO performs the best, achieving a CH₄ conversion rate of 72–74% and an H₂ yield of 66–70%. In contrast, the 5Ni3Sr/MgO catalyst has a minimal surface area and a lower amount of “NiO species under moderate interaction” compared to 5Ni2Sr/MgO. The carbon deposits on the 5Ni3Sr/MgO catalyst are also more graphitic carbon than those on 5Ni2Sr/MgO. Overall, the catalytic activity of 5Ni3Sr/MgO for the POM is found to be inferior. The effect of the gas hour speed velocity (GHSV) of feed gas on CH₄ conversion and H₂ yield over the best catalyst (5Ni2Sr/MgO) is determined (Figure S3). It is observed that as GHSV increases from 3600 mL/h/g_cat to 14,400 mL/h/g_cat, CH₄ conversion decreases monotonously from 86.3% to 71.8%, and in the same line, H₂ yield also decreases monotonously from 84% to 67%. At a lower GHSV, the contact time between reactants and the active sites (over catalysts) increases, which further results in higher catalytic activity [39]. Overall, at a 600 °C reaction temperature and 3600 mL/h/g_cat GHSV; the CH₄ conversion and H₂ yield reach as high as ~86% and 84%, respectively, over the 5Ni2Sr/MgO catalyst.

A comparison between the experimental methane conversions and the thermodynamic equilibrium conversion (denoted as “Thermo with C”) is presented in Figure S4, which shows that all catalytic samples exhibited CH₄ conversions significantly below the equilibrium line, indicating that the reactions proceeded under non-equilibrium conditions, governed primarily by the catalytic surface activity and kinetics rather than thermodynamics alone. While the observed differences in catalytic performance between the samples (e.g., higher conversion over 5Ni2Sr/MgO) are attributed to intrinsic catalytic properties, we recognize that thermodynamic factors also play a significant role in shaping the product distribution, particularly when the overall conversion does not reach the thermodynamic equilibrium limit under the given conditions. The product distribution can therefore be influenced by both kinetic and thermodynamic factors, with the relative contributions of each depending on the specific reaction conditions.

3. Experimental Section

3.1. Resources

Hexahydrate of nickel nitrate (Ni(NO₃)₂·6H₂O, 98%, Alfa Aesar, Heysham, UK), hexahydrate of strontium nitrate (Sr(NO₃)₃·6H₂O, Fisher, Wiesbaden, Germany), magnesium oxide (MgO, 99.5%, BDH Chemicals, Dubai, United Arab Emirates), and distilled water are used to prepare catalysts.

3.2. Catalyst Preparation

Nickel (Ni) as the active metal, along with the Sr promoter (x = 0, 1, 2, 3 wt.%), is incorporated into an MgO support. The MgO-based catalyst was prepared with a nickel loading of 5 wt.% using nickel nitrate hexahydrate (Ni(NO₃)₃·6H₂O, sourced from Alfa Aesar) through an incipient wetness impregnation (WI) technique. The Ni and Sr metal precursors were made as an aqueous solution, which was gradually added to the samples at 80 °C while being constantly stirred until a slurry formed. This slurry was then dried at 120 °C overnight and subsequently calcined at 600 °C for 3 h. The catalyst was finely ground into a fine powder before catalytic application. The resulting catalysts were labeled as 5Ni + x/MgO (where x = 0, 1, 2, 3 wt.%). The detailed description of catalyst characterization techniques (S1) and the catalyst activity evaluation (S2) are mentioned in the Supplementary Information [40].

4. Conclusions

To find a cheaper way to convert methane into hydrogen-rich syngas, we looked at a Ni-supported MgO catalyst that has strontium (Sr) added to it. The framework of MgO is expandable, and the surface is grown upon incorporation of 5 wt.% Ni and 1 wt.% Sr. The catalyst’s active sites originate from NiO interacting with the support in varying strengths, namely, “NiO under weak interaction” and “NiO under strong interaction.” During the POM reaction, oxygen (O₂) acts as an oxidant, and its presence modifies the distribution of active sites throughout the reaction. Further, the generation of hydrogen (as one of the compositions of products) during the POM may help to stabilize the metallic state of Ni. The cyclic H₂TPR-O₂-TPO-H₂TPR experiment showed the shift in the reduction profile to a relatively lower temperature (near 600 °C) in the sequential exposure of O₂ and H₂. It indicates the shift in interaction of NiO from a strong level to a moderate level in the sequential exposure of O₂ and H₂. Overall, the sequential exposure of O₂ and H₂ during the POM helps to establish a higher edge of reducibility. By obtaining an idea of the reduction profile, the reduction temperature and reaction temperature for the POM over the current catalyst system are kept at 600 °C. Up to the addition of 2 wt.% Sr over 5Ni/MgO, the maximum concentration of active sites is built up during the POM reaction. Furthermore, carbon deposition during the POM using the 5Ni2Sr/MgO catalyst is reduced by half compared to the unpromoted catalyst, and the deposited carbon has the lowest degree of graphitization too. Ultimately, the 5Ni2Sr/MgO catalyst demonstrates superior performance, achieving a 72% CH₄ conversion, a 70% H₂ yield, and a 2.5 H₂/CO ratio at 600 °C at 14,400 mL/h/g_cat GHSV after 240 min. Upon decreasing GHSV to 3600 mL/h/g_cat, the contact time between reactants and active sites is increased, which results in ~86% CH₄ conversion and an 84% H₂ yield over 5Ni2Sr/MgO. Over the entire catalyst system, the H₂/CO ratio is found to be above the stoichiometric value of H₂/CO ratio (that is, 2). It is due to the parallel presence of indirect pathways of the POM and the water gas shift reaction, along with direct pathways of the POM. However, a detailed kinetic study including various elementary steps is needed to understand the reaction mechanism quantitatively. The current research work highlights the potential of the cost-effective 5Ni2Sr/MgO catalyst for industrial production of hydrogen-rich syngas at lower reaction temperatures.