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

Dry reforming of methane reaction(DRM) utilizes both CH₄ and CO₂ greenhouse gases to convert them into synthesis gas (H₂ and CO), which can be further synthesized into value-added chemicals such as hydrocarbons or liquid oxygen-containing compounds. The traditional thermal method for catalyzing DRM reaction often uses Ni-based catalysts. And it requires high reaction temperature (>700 ℃). The high temperature leads to sintering and carbon deposition of Ni-based catalysts, as well as low energy efficiency, which limits the application of this reaction. Dielectric barrier discharge plasma (DBD) can synergistically drive the reaction with Ni-based catalysts at low temperature, thereby addressing the drawbacks of thermal catalysis. The key of this technology is to develop catalysts that have synergistic effects with plasma and strong resistance to carbon deposition. Therefore, this paper uses nickel phyllosilicate as precursor and H₂ plasma reduction to prepare highly dispersed Ni-based catalyst, which synergistically catalyze the DRM reaction with DBD plasma. Nickel phyllosilicate was prepared by deposition-precipitation method, and Ni/SiO₂-DP was obtained after calcination and reduction. Ni/SiO₂-IMP was prepared by impregnation method. The prepared catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N₂-adsorption-desorption, chemisorption, Fourier transform infrared, transmission electron microscope, thermogravimetric analysis and Raman spectra. The catalytic performance for dry reforming of methane (DRM) to synthesis gas was investigated in the dielectric barrier discharge(DBD) reactor. The research results indicate that Ni/SiO₂ -DP has higher catalytic activity and stability, which benefits from its smaller Ni particles size, stronger interaction between Ni and support, and stronger adsorption ability for the reactants, compared with Ni/SiO₂ -IMP. The CH₄ and CO₂ conversions of Ni/SiO₂-DP are 61.7% and 70.0%. The selectivities of H₂ and CO are 86.9% and 94.3%, and H₂/CO is 0.92. The CH₄ and CO₂ conversions of Ni/SiO₂-IMP are 44.2% and 28.4%. The selectivities of H₂ and CO are 62.7% and 42.4%, and H₂/CO is 1.48. After stability testing, the catalysts were characterized by TG. The weight loss of Ni/SiO₂- IMP is 84.45%, while the weight loss of Ni/SiO₂-DP is only 34.06%. The preparation conditions of Ni/SiO₂ -DP were investigated. The results show that the Ni/SiO₂-DP-PR from H₂ plasma reduction(PR) exhibits higher catalytic activity than the Ni/SiO₂-DP-TPR from temperature programmed reduction(TPR). DBD plasma reactor contains a large number of high energy particles, including H atoms, excited state H atoms, and ionic hydrogen (H⁺, H²⁺, H³⁺). 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 of Ni particles caused by temperature programmed reduction, resulting in smaller Ni particles size in the obtained catalyst. When the deposition-precipitation time is 10 hours, the catalytic activity of the catalyst is optimal. When the deposition-precipitation time is less than 10 hours, the content of Ni in the catalyst is relatively low, resulting in low activity. When the deposition-precipitation time exceeds 10 hours, long deposition-precipitation time may lead to an increase in the crystallinity and nickel phyllosilicate particles size. As the deposition-precipitation time increases, the deposition components gradually block the pores and reduce the specific surface area of the catalyst, resulting in a decrease in the catalytic activity of the catalyst. Under optimal preparation conditions, the conversions of CH₄ and CO₂ are 72.5% and 78.2%. The selectivities of H₂ and CO are 86.7% and 94.2%, and H₂/CO is 0.89. The energy efficiency is 4.36 mmol/kJ.