Influence of Activation Method on Coconut-Shell-Derived Carbon Supports for Ni and Ni–Ce Catalysts in CO2 Methanation

Three activated carbons derived from coconut shell were investigated as catalyst supports, each prepared using a different activation method: physical activation with CO2 and chemical activation with H3PO4 and ZnCl2. Ni and Ni−Ce catalysts were synthesized via incipient wetness impregnation and co-impregnation, respectively, and characterized using ICP analysis, N2 adsorption, TGA, SEM-EDX, and TEM. Prior to catalytic evaluation, the materials were assessed in terms of hydrophobicity, textural properties (pore volumes, surface areas), and metal dispersion. Catalytic performance was tested under both conventional and aging conditions at atmospheric pressure over a temperature range of 240−450 °C (GHSV = 86100 mL h−1 gcat −1, H2:CO2 = 4:1). The activation method was found to strongly influence the structural properties of the supports. In particular, CO2 activation produced a predominantly microporous carbon, whereas chemically activated carbons exhibited different pore structures and contained residual species from the activating agents. Among the Ni-based catalysts, the one supported on CO2-activated carbon showed the best performance, attributed to its higher basicity, measured by the determination of the pHPZC. The incorporation of Ce further enhanced catalytic activity by improving Ni dispersion and promoting CO2 activation on CeO2 sites. Overall, the highest CH4 yield (∼80% at 370 °C) was achieved with catalysts containing 20 wt % Ni and 20 wt % Ce supported on H3PO4 and CO2-activated carbons. The CO2-activated support was identified as the most promising due to its greener preparation route and superior performance, maintaining stable activity under aging tests without significant deactivation.