A new green synthesis approach using sodium palmitate in the synthesis of a Ni/ <scp> Al ₂ O ₃ </scp> catalyst for <scp> CO ₂ </scp> methanation

Abstract CO 2 methanation with Ni/Al 2 O 3 catalysts is a key technology for converting CO 2 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 Al 2 O 3 support. Ni/Al 2 O 3 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/Al 2 O 3 ‐WI catalyst showed a slightly better performance in terms of CO 2 and H 2 conversion (, ), when compared to Ni/Al 2 O 3 ‐MI (, ). In addition, CH 4 selectivity was kept stable at &gt;99% for all studies. The stability test showed that Ni/Al 2 O 3 ‐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/Al 2 O 3 catalysts for CO 2 methanation.