CO 2 Methanation Process over Highly Active and Nanostructured NiO-Al 2 O 3 Catalyst Synthesized by Various Methods

This study is centered on the synthesis of NiO-Al2O3 catalysts using multiple preparation methods, which encompass mechanochemical, impregnation, sol-gel, co-precipitation, and combustion techniques. These various methods were employed to create catalyst samples, subsequently utilized in the carbon dioxide methanation process. Comprehensive characterization of the prepared samples encompassed H2-TPR, XRD, BET, and FESEM analyses. The outcomes of the BET and XRD analyses unveiled that the 20wt.% NiO-Al2O3 catalyst, synthesized via the mechanochemical preparation approach, exhibited exceptional efficiency in relation to CO2 conversion and selectivity of methane. This was especially pronounced at lower temperatures. Notably, this catalyst showcased a specific surface area measuring 240.7 m2/g, coupled with a reduced crystal size of 29.4 nm. The 20wt. % NiO-Al2O3 catalyst demonstrated a carbon dioxide conversion of 68%, coupled with a methane selectivity of 96% under the operational condition of 400 ℃. Notably, this catalyst demonstrated the highest degree of stability when compared to the other catalysts studied. To comprehensively assess the impact of varying nickel loadings, spanning from 5 to 25 wt. %, on both textural attributes and the catalytic efficacy of mechanochemically synthesized NiO-Al2O3, an in-depth investigation was undertaken. The experimental findings from this investigation unveiled that the augmentation of nickel loading up to 20 wt% led to a discernible enhancement in CO2 conversion efficiency. However, beyond this threshold, a decline in CO2 conversion was detected. This can be linked to the phenomenon of particle sintering, which subsequently leads to a decrease in the dispersion of the active catalytic phase. Furthermore, the study delved into the exploration of processing conditions and the temperature of calcination, assessing their influence on the catalytic efficiency of the chosen catalyst.