A new green synthesis approach using sodium palmitate in the synthesis of a Ni/Al2O3 catalyst for CO2 methanation

Abstract

CO₂ methanation with Ni/Al₂O₃ catalysts is a key technology for converting CO₂ emissions into sustainable methane. However, conventional impregnation synthesis often results in poor nickel dispersion and in the emission of gaseous NO_x species. Thus, for the first time, sodium palmitate flocculant properties were used to isolate nickel nanoparticles and disperse them over an Al₂O₃ support. Ni/Al₂O₃ catalysts were synthesized by mechanochemical and wet impregnation methods (MI and WI, respectively) to evaluate the impact of the synthesis route on the catalytic performance. Nickel nanoparticles with 9.7–12.6 nm were produced. Influences of temperature (300–500°C) and gas hourly space velocity (GHSV, 2490–14,920 h⁻¹) were evaluated, and a stability study was performed. Best performances were reached at 400°C and the lowest GHSV (2490 h⁻¹). Ni/Al₂O₃-WI catalyst showed a slightly better performance in terms of CO₂ and H₂ conversion ($X_{{\mathrm{CO}}_2}=79\%$, $X_{H_2}=77\%$), when compared to Ni/Al₂O₃-MI ($X_{{\mathrm{CO}}_2}=77\%$, $X_{H_2}=76\%$). In addition, CH₄ selectivity was kept stable at >99% for all studies. The stability test showed that Ni/Al₂O₃-WI had a stable performance during the 50 h. These results indicate that this synthesis approach is a viable method for producing catalysts with strong activity and reduced environmental impact. Furthermore, the incorporation of sodium palmitate in the synthesis opens the possibility for the direct application of residual bio-oils in the synthesis of Ni/Al₂O₃ catalysts for CO₂ methanation.