Highly efficient Ni/Ac–Al₂O₃ catalysts in the dry reforming of methane: influence of acetic acid treatment and Ni loading

Abstract

The presence of abundant hydroxyl groups on the surface of Al₂O₃ can promote the dispersion of Ni species but produce an inactive NiAl₂O₄ phase at high temperatures. Moreover, the catalysts prepared by the conventional incipient wetness impregnation method lack the sites for the activation of CO₂, which leads to coke deposition and thus affects the catalyst activity. The above restricts the utilization of Ni in conventional Ni/Al₂O₃ catalysts. In this paper, Al₂O₃ support was pre-treated by acetic acid to selectively remove hydroxyl groups without affecting the coordination environment of Al. Results revealed that the Al₂O₃ support after hydroxyl removal not only showed moderate metal–support interaction but also produced more sites for the adsorption and activation of the reactant, which significantly improves the utilization of nickel species and the stability of the catalyst. The conversion of CH₄ and CO₂ at 700 °C was as high as 88% and 90%, respectively, and has an excellent stability of 50 h. This study provides a feasible strategy for the design of highly active methane dry-reforming catalysts.

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Introduction

Syngas plays a significant role in the production of varied chemicals.^1–3 Producing syngas by the dry reforming of methane (DRM) with carbon dioxide is a kind of reaction process of natural gas reforming to syngas.⁴ The basic principle is that methane (CH₄) reacts with carbon dioxide (CO₂) to produce syngas at high temperatures with the catalyst.^5,6 Syngas generation is a highly thermally absorbent reaction, which usually requires temperatures above 700 °C. The H₂ : CO ratio of syngas produced by the DRM process is approximately 1,^7,8 which is favourable for the synthesis of chemicals.^9–11 Compared to the conventional methane steam reforming process to syngas, the DRM method has remarkable advantages, as follows. (1) The process consumes no water but a large amount of carbon dioxide, reducing energy consumption as well as alleviating greenhouse gas emissions;¹² (2) the feedstock can be attained by a wide range of sources, such as biogas, coke oven gas, coalbed methane, and natural gas;^13,14 (3) two kinds of greenhouse gases are involved in the reaction, which is favourable to the environment; (4) compared to wet reforming and partial oxidation, it reduces methane consumption by 50%.^15–17 However, during the DRM reaction process (eqn (1)), the high-temperature environment in the reactor inevitably leads to the occurrence of several parallel reactions such as methane decomposition (eqn (2)), inverse Boudouard reaction (eqn (3)), and reverse water-gas shift (RWGS) (eqn (4)).^18–21 These adverse reactions can seriously affect the process efficiency. Coke deposition causes catalyst deactivation and reactor clogging, especially at 550–700 °C, which is a crucial challenge for industrialization. Additionally, the RWGS reaction reduces the H₂/CO molar ratio in syngas,^22,23 affecting the downstream processing of syngas. Therefore, there is an urgent demand to develop a catalyst with superior catalytic activity, resistance to coke deposition and high temperature for DRM.

CH₄ + CO₂ → 2CO + 2H₂ ΔH^θ, 298 K = 247.3 kJ mol⁻¹ (1)

CH₄ → C + 2H₂ ΔH^θ, 298 K = 75.0 kJ mol⁻¹ (2)

2CO → C + CO₂ ΔH^θ, 298 K = −171.0 kJ mol⁻¹ (3)

CO₂ + H₂ → CO + H₂O ΔH^θ, 298 K = 41.0 kJ mol⁻¹ (4)

Currently, the focus of increased research into the dry reforming of methane catalysts has been mostly on transition metals (e.g., Ni, Fe, and Co)^24,25 and noble metals (e.g., Pd,²⁶ Pt,^27,28 Rh,^29,30 and Ru^31,32) catalysts. Among these, noble metals are widely used in DRM based on the high reactivity, stability and excellent resistance to the deposition of coke. With the same metal size and active component dispersion, the noble metals Ru and Rh exhibited higher activity compared to active components such as Ni, Pd and Pt.³³ Zhang et al. modified nickel-based catalysts by introducing a second metal and using a unique support. This provides new ideas for the widespread use of nickel-based catalysts.^34–37 However, noble metal-based catalysts are not widely industrialized due to the high cost.

Therefore, attention was gradually focused on transition metals with similar catalytic activities as alternative components. Nickel metal (Ni), usually in the form of nanoparticles, has been widely investigated for the catalysis of DRM because of its high hydrocarbon activation capacity and low cost. For example, Tokunaga et al. investigated the catalytic activity of Ni, Co, and Fe loaded on Al₂O₃ and found that the catalytic activity of Ni was comparable to that of the noble metal Ru.^38,39 However, Ni-based catalysts are vulnerable to catalyst deactivation owing to the deposition of coke and aggregation of Ni particles at high reaction temperature. Currently, two strategies are proposed to solve this problem. On the one hand, the capacity of CO₂ adsorption and activation is enhanced by adding alkali metals and defect induction.^40,41 On the other hand, the aggregation of Ni particles is inhibited by dispersing Ni on the support with a high specific surface area or tuning the strong interaction between Ni and the support.^42,43 It is reported that Al₂O₃ is widely used as a support for the dry reforming of methane due to its excellent mechanical strength, high thermal stability, tunable surface acidity and alkalinity, and abundant hydroxyl species.^44,45 The abundant hydroxyl groups on the Al₂O₃ surface are favourable for the dispersion of Ni species, but the inactive nickel aluminate phase (NiAl₂O₄) is readily generated due to high temperature during the preparation of Ni/Al₂O₃ catalysts and methane dry reforming reaction, which restricts the effective utilization of Ni species and reduces the catalytic activity of methane dry reforming.^46,47 Commercial alumina support without any special treatment lacked vacancy defects for the adsorption and activation of CO₂.⁴⁸ Promoting the adsorption and activation of CO₂ molecules in the Ni/Al₂O₃ catalyst for the dry reforming of methane without reducing the utilisation of nickel species is a major challenge in the catalyst design.

Herein, a series of nickel-based alumina catalysts with different Ni loadings and Al₂O₃ support treated with different concentrations of acetic acid were synthesized. The treatment concentration of acetic acid was modulated to remove some of the hydroxyl groups on the Al₂O₃ surface, which can improve the utilization of Ni species and the adsorption and activation of CO₂ molecules. In this paper, the effect of acetic acid treatment on Ni/Al₂O₃ catalysts during the DRM reaction is systematically explored by various characterization results. Meanwhile, insights into the acetic acid treatment strategy might be helpful for the design of new catalysts for the DRM reaction.

Experimental

Catalyst preparation

Ni(NO₃)₂·6H₂O (99.0%), commercial γ-Al₂O₃, and acetic acid (CH₃COOH, 99.5%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

Synthesis of acid-treated Al₂O₃

2 g of γ-Al₂O₃ was dispersed in a pre-prepared 0.5/1/2 mol L⁻¹ solution of 80 mL of CH₃COOH solution, respectively, and stirred continuously for 2 h at 500 rpm. Then, the mixture was centrifuged and washed at pH 7 several times. All of the obtained catalysts were dried in an oven at 100 °C for 4 h and named as xAc–Al₂O₃ (x = 0.5, 1 and 2).

Synthesis of 1Ni/xAc–Al₂O₃ and yNi/Al₂O₃

1Ni/xAc–Al₂O₃ and yNi/Al₂O₃ catalysts were prepared by conventional incipient wetness impregnation method. In a typical procedure, a certain amount of Ni(NO₃)₂·6H₂O was dissolved in deionized water under stirring for 2 h. Then, 2 g Al₂O₃ or Ac–Al₂O₃ support was added into the above Ni(NO₃)₂·6H₂O solution. The precipitate was dried at 100 °C for 12 h and then calcined in air from room temperature to 700 °C at a ramp rate of 10 °C per minute for 5 h. The obtained samples were denoted as 1Ni/xAc–Al₂O₃ and yNi/Al₂O₃ (x = 0.5, 1, and 2; y = 1, 2, and 5) catalysts, respectively.

Characterization

The detailed methods for X-ray diffraction (XRD), temperature-programmed reduction (H₂-TPR), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), pyridine-dosing FTIR (Py-FTIR), in situ Fourier transform infrared (in situ FTIR), in situ diffuse reflectance Fourier transform infrared spectroscopy (in situ DRIFT), and temperature-programmed desorption of CO₂ (CO₂-TPD) are given in the ESI.†

Catalytic evaluation

The catalytic activity and stability of the xNi/Ac–Al₂O₃ and xNi/Al₂O₃ catalysts in the dry reforming of methane were tested in a fixed-bed flow reactor. 100 mg catalyst (40–60 mesh) was loaded into a quartz reactor and reduced in situ at 750 °C by flowing 10 vol% H₂/Ar (30 mL min⁻¹) for 1 h. The reaction gas consisting of CH₄, CO₂ and N₂ (CH₄ : CO₂ : N₂ = 1 : 1 : 1) was fed at a GHSV of 36 000 mL h⁻¹ g_cat⁻¹. The gas products were analysed by an on-line gas chromatograph (GC).

The CH₄/CO₂ conversion and H₂/CO ratio were calculated as follows.

Results and discussion

Catalytic activity measurements

To optimize the concentration for acetic acid treatment and Ni loading, a series of Ni-loaded Al₂O₃ catalysts was prepared by the impregnation method. Among other things, we carried out warming operations during the continuous feeding process. The resultant activity performance of 1Ni/xAc–Al₂O₃ (A–C) and yNi/1Ac–Al₂O₃ (D–F) is shown in Fig. 1. As displayed in Fig. 1A–C, for the 1Ni/xAc–Al₂O₃ catalysts, three catalysts showed significant differences under treatment with different concentrations of acetic acid. Among them, the 1Ni/1Ac–Al₂O₃ catalyst exhibited the highest conversion of CH₄/CO₂, while the 1Ni/0.5Ac–Al₂O₃ catalyst showed the lowest level of conversion. The H₂/CO ratio varies between 0.4 and 0.9 throughout the temperature range and increases with increasing temperature. The trend lines of the 1Ni/1Ac–Al₂O₃ catalyst and 1Ni/2Ac–Al₂O₃ catalyst largely overlap, and that of the 1Ni/0.5Ac–Al₂O₃ catalyst remains lower than that of the other two catalysts. This result identified the optimal acetic acid treatment concentration of 1 mol L⁻¹. Moreover, the catalytic performance of yNi/1Ac–Al₂O₃ catalysts with different Ni loadings in methane dry reforming reaction was also tested, as shown in Fig. 1D–F. From Fig. 1D–F, it is found that the CH₄/CO₂ conversion and H₂/CO ratios of the three catalysts prepared with different Ni loadings are 5Ni/1Ac–Al₂O₃ > 2Ni/1Ac–Al₂O₃ > 1Ni/1Ac–Al₂O₃ in a descending order. Higher CO₂ and CH₄ conversions were observed over the 5Ni/1Ac–Al₂O₃ samples in comparison with those of the xNi/1Ac–Al₂O₃ samples, indicating that the optimal Ni loading for xNi/1Ac–Al₂O₃ catalyst is 5 wt%.

Fig. 1 CH₄ and CO₂ conversions and H₂/CO₂ for the dry reforming of methane with 1Ni/xAc–Al₂O₃ (A–C) and yNi/1Ac–Al₂O₃ (D–F) (x = 0.5, 1, and 2; y = 1, 2, and 5).

The conversions of the yNi/Al₂O₃ (y = 1, 2, and 5) catalyst and the long-term DRM reaction results of the 5Ni/1Ac–Al₂O₃ catalyst are shown in Fig. 2 and S1.† It can be seen that the reaction conversions of the 5Ni/Al₂O₃ catalyst without acetic acid treatment is lower than that of the 5Ni/1Ac–Al₂O₃ catalyst. However, the catalysts for acetic acid treatment showed obvious advantages in terms of stability, CH₄/CO₂ conversion rate and H₂/CO ratios (Fig. 2B and S1†). In particular, the 5Ni/1Ac–Al₂O₃ catalyst showed the best performance among all the catalysts. During the 3000 min stability test, it maintained a high conversion rate of 90% and a high H₂/CO ratio of 0.97. This indicates that the 5Ni/1Ac–Al₂O₃ catalyst is extremely stable for the methane dry reforming reaction. It may be a very desirable and reliable choice in production. A comparison of the catalytic performance results revealed that the catalyst treated with acetic acid treatment could maintain the catalytic activity better than the untreated catalyst in the dry reforming of methane. By analysing these data results, it can be concluded that the acetic acid treatment played a positive role in enhancing the catalyst stability and conversion. Further study and exploration of how acetic acid treatment can improve the catalytic performance of the catalyst in the DRM reaction will be very important to further improve the catalyst effect.

Fig. 2 CH₄ and CO₂ conversions of 5Ni/Al₂O₃ (A) and stability test of 5Ni/1Ac–Al₂O₃ (B). Stability test reaction conditions: T_reaction = 700 °C, GHSV = 36 000 mL h⁻¹ g_cat⁻¹, CH₄/CO₂/N₂ = 1/1/1.

We then compared the reaction rate at 700 °C, and the results are shown in Fig. 3. The rates of conversion of CH₄ and CO₂ in 1Ni/Al₂O₃ catalyst are almost zero, which can be attributed to the formation on the catalyst surface of the much inactive NiAl₂O₄ phase (Fig. S2†). However, the acetic acid-treated catalyst of 1Ni/1Ac–Al₂O₃ shows high CH₄ and CO₂ conversion rates and increases from 0 to 444 L_CH4 per h per g per Ni and 504 L_CO2 per h per g per Ni, respectively. A similar trend is observed in 2Ni/Al₂O₃, 2Ni/1Ac–Al₂O₃ and 5Ni/Al₂O₃, 5Ni/1Ac–Al₂O₃ catalysts.

Fig. 3 The CH₄ and CO₂ reaction rate during dry reforming of methane over yNi/1Ac–Al₂O₃ and yNi/Al₂O₃ (y = 1, 2, and 5) at 700 °C.

Apparent activation energy (E_a) experiments were carried out under the conditions of less than 20% conversion. From Fig. 4, the E_a of CH₄ (A) and CO₂ (B) on 5Ni/1Ac–Al₂O₃ and 5Ni/Al₂O₃ catalysts before and after acetic acid treatment was calculated. It can be seen that the E_a of CH₄ and CO₂ on the 5Ni/Al₂O₃ catalyst are 57.39 kJ mol⁻¹ and 44.24 kJ mol⁻¹, respectively. However, the E_a values of CH₄ and CO₂ on the acetic acid-treated catalyst of the 5Ni/1Ac–Al₂O₃ catalyst are 44.5 kJ mol⁻¹ and 39.6 kJ mol⁻¹, respectively, which are lower than those of the acid-treated 5Ni/Al₂O₃ catalyst. According to the above results, it can be concluded that the acetic acid-treated catalyst is more effective for both CH₄ and CO₂ activation, and the specific reasons for promoting the activation are discussed in a later section.

Fig. 4 CH₄ (A) and CO₂ (B) apparent activation energies over 5Ni/Al₂O₃ and 5Ni/1Ac–Al₂O₃ catalysts.

Effect of acetic acid treatment on the structure of the catalysts

The structure of the unreduced Ac–Al₂O₃ Ac–Al₂O₃, Al₂O₃, yNi/1Ac–Al₂O₃ and yNi/Al₂O₃ (y = 1, 2, and 5) samples was determined by XRD and ²⁷Al-NMR characterization. The XRD patterns are displayed in Fig. 5A. As seen, three distinct reflections at 2θ = 38°, 46°, and 66° were detected, which corresponds to the standard for γ-Al₂O₃ (PDF#10-0425). There were no additional peaks in Fig. 5A after acetic acid treatment, indicating that the structure of these catalysts did not change significantly. Moreover, the diffraction peaks of Ni species were not observed in the XRD results of the yNi/1Ac–Al₂O₃ and yNi/Al₂O₃ (y = 1, 2, and 5) catalysts, suggesting that Ni species were well dispersed on the Al₂O₃ support or formed amorphous phase Ni species.^49,50 Additionally, it can be seen from the TEM images in Fig. S3† that the acetic acid treatment has no significant effect on the morphology of Al₂O₃, which also corresponds to the XRD results before and after the acetic acid treatment in Fig. 5A.

Fig. 5 (A) XRD patterns of the yNi/1Ac–Al₂O₃ and yNi/Al₂O₃ (y = 1, 2, and 5), (B) ²⁷Al NMR spectra over 1Ac–Al₂O₃ and Al₂O₃ samples.

The ²⁷Al NMR data are presented in Fig. 5B; it can be observed that there is no significant change in the peak intensity of ²⁷Al NMR before and after acid treatment. This is because ²⁷Al NMR is a holistic detection technique, and changes in the coordination environment of a few aluminum species cannot be detected. Similar ²⁷Al NMR data can only indicate that acid treatment did not damage the overall structure and morphology of the alumina support, which corresponds to the TEM data.

At the same time, the acidic and functional group changes on the catalyst surface after acetic acid treatment were also investigated. As shown in Fig. 6A, the pyridine adsorption peak at 1450 cm⁻¹ is attributed to the Lewis acid sites of xAc–Al₂O₃ (x = 0.5, 1 and 2) and Al₂O₃ samples.⁴⁷ With the increase in the acetic acid concentration, the peak gradually decreased, indicating that the Lewis acid sites of the catalyst are reduced. According to reports, Lewis acid sites can be attributed to hydroxyl species or unsaturated coordination metal species, and nitric acid treatment can remove the hydroxyl group from the surface of Al₂O₃.^47,51

Fig. 6 (A) Py-IR spectra and (B) IR of Al₂O₃, xAc–Al₂O₃ and Al₂O₃ (x = 0.5, 1, and 2).

The process of hydroxyl removal was further confirmed by IR. The IR spectra of hydroxyl groups before and after acetic acid treatment are compared in Fig. 6B. Three peaks at 3723 cm⁻¹, 3683 cm⁻¹ and 3561 cm⁻¹ were observed, corresponding to the surface terminal hydroxyl, bridged hydroxyl, and tri-bridged hydroxyl groups, respectively.^47,52,53 The increase in the acetic acid concentration decreased the intensity of the hydroxyl peaks on the surface of Al₂O₃, indicating that the surface hydroxyl groups were removed by acetic acid treatment. Additionally, a weak bridged hydroxyl peak was observed on the 2Ac/Al₂O₃ catalyst surface. This may be attributed to the high concentration of acetic acid treatment, resulting in the exposure of the hydroxyl group of the Al₂O₃ bulk phase. Therefore, the hydroxyl group on 2Ac/Al₂O₃ may interact with Ni to form the nickel aluminate phase, which can justify the weaker activity of 1Ni/2Ac–Al₂O₃ than that of 1Ni/1Ac–Al₂O₃. According to the results obtained from pyridine-IR and IR analyses, it has been observed that the reduction of Lewis acid sites after acid treatment can be attributed to the elimination of hydroxyl groups. Dehydroxylation can reduce the production of nickel aluminate phases, which helps to form more active sites.

Inhibition of NiAl₂O₄ phase formation by acetic acid treatment

Fig. 7A compares the H₂-TPR profiles of the 5Ni/1Ac–Al₂O₃ and 5Ni/Al₂O₃ catalysts. It can be seen that a significantly reduced peak at 600–800 °C is present, which can be attributed to the reduction of nickel species, and the peak appears at 400–500 °C for 5Ni/1Ac–Al₂O₃ due to the reduction of NiO with intermediate size.⁵⁴ The reduction peak shifted to lower temperature after acetic acid treatment, indicating that the interaction between metal Ni and the Al₂O₃ support was weakened, and the Ni species were more easily reduced. Therefore, the 5Ni/1Ac–Al₂O₃ catalyst has more active phases, resulting in higher catalytic activity, which is consistent with the activity data.

Fig. 7 H₂-TPR profiles (A) and XPS spectra (B) over the 5Ni/1Ac–Al₂O₃ and 5Ni/Al₂O₃ catalysts.

Similar results were confirmed by the XPS characterization. The Ni 2p XPS spectra of 5Ni/1Ac–Al₂O₃ and 5Ni/Al₂O₃ are illustrated in Fig. 7B. According to literature, the peaks at 852.5 eV, 855.9 eV, and 857.5 eV are attributed to Ni⁰, Ni_oct²⁺ (Ni²⁺ in octahedral coordination sites), and Ni_tet²⁺ (Ni²⁺ in tetrahedral coordination sites), respectively.^55–58 Ni_oct²⁺ and Ni_tet²⁺ are Ni species with strong metal–support interaction and difficult to reduce. For the 5Ni/Al₂O₃ sample, the contents of Ni⁰, Ni_oct²⁺, and Ni_tet²⁺ are 2.04%, 43.09%, and 16.11%, respectively. For the Ni/1Ac–Al₂O₃ sample, the contents of Ni⁰, Ni_oct²⁺, and Ni_tet²⁺ are 4.11%, 42.59%, and 14.79%, respectively. Although small Ni⁰ species may be oxidized due to off-line reduction, it is still observed that after acetic acid treatment, the content of Ni species in the strong metal–support interaction decreases and the content of Ni⁰ increases. The possible reason is that acetic acid treatment decreases the number of hydroxyl groups on the Al₂O₃ support, which is conducive to the reduction of Ni species and improves the activity of the catalyst in DRM.

Acetic acid treatment promotes the adsorption and activation of CO₂

In situ DRIFTS experiments of reactants were carried out to further identify the intermediate species and compare with the activation abilities of CO₂ and CH₄ on the 5Ni/Ac–Al₂O₃ (Fig. 8A–C) and 5Ni/Al₂O₃ (Fig. 8D–F) catalysts. Both catalysts show peaks located at 3016 cm⁻¹ and 1305 cm⁻¹, which are attributed to the gas phase CH₄, as well as another broad one at ∼2360 cm⁻¹ corresponding to the deformation vibration of gas phase CO₂ is observed.^59–61 Notably, the signals attributed to CH₄ and CO₂ in the 5Ni/1Ac–Al₂O₃ catalyst weaken at lower temperatures compared to the 5Ni/Al₂O₃ catalyst, indicating that the activation capacity for the reactants of the 5Ni/1Ac–Al₂O₃ catalysts is greater. This is probably because the 5Ni/1Ac–Al₂O₃ samples have more active sites. The signals corresponding to the reaction intermediates appear from 1200 cm⁻¹ to 1800 cm⁻¹ (Fig. 8C and F). Two signals located at 1442 cm⁻¹ and 1342 cm⁻¹ can be attributed to the deformation vibrations of the species,^62,63 and two other bands at 1655 cm⁻¹ and 1227 cm⁻¹ appear, which are attributed to bicarbonate and carbonate, respectively.^64,65 The species are produced by the activation of methane, while the oxygen-containing species (bicarbonate) can be produced by the activation of CO₂.^59,66 Additionally, it can be observed that the intermediate signals on the 5Ni/1Ac–Al₂O₃ catalyst is stronger than that on the 5Ni/Al₂O₃ catalyst. This is because the 5Ni/1Ac–Al₂O₃ catalyst has more active sites after being treated with acetic acid; thus, its ability to activate the reactants is better than that of the 5Ni/Al₂O₃ catalyst.

Fig. 8 In situ DRIFTS spectra of 5Ni/1Ac–Al₂O₃ (A–C) and 5Ni/Al₂O₃ (D–F) catalysts.

To further prove the CO₂ activation capacity over the 5Ni/1Ac–Al₂O₃ catalyst, CO₂-TPD characterization was carried out, as shown in Fig. 9. It can be seen that all the samples show a low temperature adsorption peak at about 100 °C, which could be attributed to the adsorption of CO₂ by the supports,⁶⁷ and the CO₂ adsorption signal at 200–500 °C can be attributed to the impregnated Ni species.⁶⁸ The acetic acid-treated 1Ac/Al₂O₃, 5Ni/1Ac–Al₂O₃ exhibits strong CO₂ absorption peaks in the 200–500 °C range, whereas no obvious CO₂ absorption peaks are observed over the non-acid-treated Al₂O₃, 5Ni/Al₂O₃ in the same range. This confirms that the acetic acid-treated catalyst facilitates the adsorption and activation of CO₂, corresponding to the in situ DRIFTS results.

Fig. 9 CO₂-TPD patterns over Al₂O₃, 1Ac–Al₂O₃, 5Ni/Al₂O₃ and 5Ni/1Ac–Al₂O₃.

Conclusions

In summary, a strategy to directly remove hydroxyl groups from the surface of alumina support has been developed. The hydroxyl species can be removed by simple acetic acid treatment, inhibiting the formation of NiAl₂O₄ and significantly improving the utilization efficiency of the nickel species, thereby enhancing the catalytic activity. Additionally, the catalyst after acetic acid treatment promoted the activation of CO₂. This study provides a feasible approach for nickel-based alumina catalysts to undergo the methane dry-reforming methane reaction through simple acetic acid treatment.

Data availability

Data will be made available on request to the corresponding author.

Author contributions

Han Xiao: methodology, writing – original draft. Jiaming Dong: writing – original draft. Yimin Zhang: conceptualization. Xiaohua Cao: writing-review & editing. Yanhong Li: formal analysis. Dedong He: conceptualization, investigation. Yongming Luo: methodology, investigation. Pingyan Wang: supervision, investigation. Hao Wang: supervision, writing-review & editing.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

The authors acknowledge the financial support from the National Natural Science Foundation of China (42030712, 22306081), Excellent Youth Project of Natural Science Foundation of Yunnan Province (202201AW070007), Young Academic and Technical Leader Raising Foundation of Yunnan Province (202205AC160011). Thanks for the support by Key Laboratory of Yunnan Province for synthesizing sulfur. Containing Fine Chemicals/The Innovation Team for Volatile Organic Compounds Pollutants Control and Resource Utilization of Yunnan Province/The Higher Educational Key Laboratory for Odorous Volatile Organic Compounds Pollutants Control of Yunnan Province, Kunming 650500, P. R. China.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra06740a

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