DBD plasma-assisted dry reforming of methane over Ni/SiO₂

Dry reforming of methane reaction (DRM) can convert CH₄ and CO₂ into syngas, which can be further utilized to produce valuable chemicals, such as hydrocarbons and liquid oxygenates. Traditionally, nickel-based catalysts have been employed for thermal catalytic DRM, which requires relatively high temperatures (>700 ℃). However, the high temperatures lead to issues such as nickel sintering, carbon deposition, and low energy efficiency, limiting the practical applications. Dielectric barrier discharge plasma (DBD) can cooperate with Ni-based catalysts, allowing the reaction to work under lower temperatures. Developing catalysts with strong synergy and high resistance to carbon coking is crucial for this technique. In this work, nickel phyllosilicate was used as a precursor to prepare highly dispersed Ni-based catalysts using H₂ plasma reduction. The obtained catalysts were then used with DBD plasma to catalyze the DRM reaction. Nickel phyllosilicate was prepared using deposition-precipitation method, followed by calcination and reduction to obtain Ni/SiO₂-DP. As a comparison, Ni/SiO₂-IMP was prepared using the traditional impregnation method. All catalysts were characterized using XRD, XPS, N₂-adsorption-desorption, H₂-TPR, chemisorption, FT-IR, TEM, TG and Raman spectroscopy. The catalytic performance of DRM reaction was evaluated in a DBD reactor. Ni/SiO₂-DP exhibited higher activity and stability in DRM reaction compared to Ni/SiO₂-IMP. Combining with the characterization results, the better performance was attributed to the enhanced interaction between Ni and SiO₂ in Ni/SiO₂-DP, resulting from the NiPS precursor. Such interaction led to higher dispersion and smaller particle sizes, which effectively suppressed carbon coking and improved the stability. In contrast, the weaker interaction between Ni and SiO₂ in Ni/SiO₂-IMP, along with larger Ni particles, resulted in rapid carbon deposition and sintering, leading to a rapid decrease in catalytic activity. Additionally, according to the CO₂-TPD results, Ni/SiO₂-DP has stronger CO₂ adsorption capacity than Ni/SiO₂-IMP, which allows an enrichment of a large amount of CO₂^*, CO^*, and O^* active oxygen species on the catalyst surface. These species can further react with CH_x^* and C^*, slowing down the formation of carbon deposits and improve the stability of Ni/SiO₂-DP. The effects of the reduction method, plasma reduction time, and precursor deposition-precipitation time of Ni/SiO₂-DP were investigated. The results show that the catalytic activity of Ni/SiO₂-DP-PR prepared using H₂ plasma reduction (PR) is superior to that of Ni/SiO₂-DP-TPR prepared using temperature programmed reduction (TPR). This is because the DBD plasma reactor contains a large number of high-energy particles, including H atoms, excited H atoms, and ionic hydrogen (H⁺, H²⁺, H³⁺) under discharge conditions. H₂ plasma can fully reduce the catalyst precursor at low temperatures, avoiding the Ni particle aggregation during TPR. The reduction ability of H₂ plasma is much higher than that of temperature programmed reduction. H₂ plasma can fully reduce the precursor at low temperature, avoiding the aggregation during TPR. The optimal H₂ PR time is 30 min at an input power of 25 W. The optimal deposition-precipitation time is 10 h. As the deposition-precipitation time increases, the deposited components gradually block the pores, and the specific surface area of the catalyst gradually decreases, thereby reducing the catalytic activity. Under the optimal conditions, the CH₄ and CO₂ conversion in the DRM reaction over Ni/SiO₂-DP are 72.5% and 78.2%, respectively, with H₂ and CO selectivity of 86.7% and 94.2%, respectively, and H₂/CO is 0.89. The energy efficiency is 4.36 mmol/kJ.