Hidrogenação de dióxido de carbono para a produção de metano utilizando catalizadores de níguel-sílica

Abstract

The growing population and economic development have intensified the global demand for energy, traditionally met by the combustion of fossil fuels, which has led to significant environmental impacts in recent years. In this context, renewable energy sources have gained prominence. Methanation, a reaction that converts hydrogen (H₂) and carbon dioxide (CO₂) into methane (CH₄) and water (H₂O), emerges as a promising alternative for diversifying the energy matrix. However, due to unfavorable kinetics, the use of catalysts is fundamental to enable this reaction pathway. This work aimed to evaluate the influence of reaction temperature and nickel content in catalysts on methanation conversion and selectivity through a literature review and experimental data analysis. For this purpose, nickel-silica catalysts were prepared by the dry impregnation method and characterized by X-ray Fluorescence (XRF), Temperature-Programmed Reduction with H₂ (TPR), and Thermogravimetric Analysis (TGA). Catalytic tests were performed in a continuous system, evaluating CO₂ conversion, methane (CH₄) selectivity, and catalyst stability under different operating conditions. The light-off test results demonstrated that CO₂ conversion remained relatively low, and CH₄ selectivity remained reduced in both samples (10% and 20% Ni/SiO₂), indicating that increasing the metallic content did not lead to significant gains in selectivity. In stability tests at 350 °C, the 10% Ni/SiO₂ catalyst maintained CO₂ conversion at approximately 20% and CH₄ selectivity close to 60%, while the 20% Ni/SiO₂ catalyst showed about 30% conversion and 75% selectivity, evidencing stable behavior over 20 hours of testing. XRF analyses revealed discrepancies between theoretical and experimental nickel concentrations, with deviations of approximately 62% for the 10% Ni catalyst and about 18.8% for the 20% Ni catalyst, possibly due to synthesis process factors. Thermogravimetric analysis (TGA) of the used catalysts indicated a mass gain, attributed to the oxidation of carbonaceous deposits (coke), which was more pronounced in the catalyst with 20% nickel, suggesting that higher metallic content, while potentially enhancing activity, also contributes to deactivation by coking. Thus, the optimization of the metallic composition should seek a balance between catalytic performance and operational stability."