Olive stone-derived biochar as a sustainable catalyst support for CO2 methanation

The hydrogenation of carbon dioxide (CO 2 ) into methane presents a promising strategy for CO 2 utilization. However, the large-scale implementation of this process remains limited by the lack of cost-effective and sustainable catalytic materials. This study explores the potential of biochar derived from agro-industrial waste, specifically olive stones, as an innovative and eco-friendly support for Ni-based catalysts in CO 2 methanation. Three different chemical activation methods (KOH, ZnCl 2 , and H 3 PO 4 ) were applied to enhance the textural and structural properties of the biochar, significantly influencing its catalytic performance. Among the tested materials, KOH-activated biochar (10Ni-KOH) exhibited superior Ni dispersion, enhanced surface area, and an increased number of moderately strong basic sites, which are crucial for CO 2 activation. This catalyst achieved a CO 2 conversion of 72 % and a CH₄ selectivity of 95.5 %, outperforming the other formulations. In contrast, biochar activated with H 3 PO 4 led to the encapsulation of Ni particles within a phosphorus matrix (as demonstrated by TEM images), while ZnCl₂ activation promoted the formation of Ni-Zn alloys (as indicated by XPS and XRD analysis), both of which hindered methanation efficiency. These findings highlight the transformative potential of biochar as a low-cost and sustainable catalyst support, offering a viable alternative to conventional materials for CO 2 methanation. By leveraging agricultural residues, this approach not only contributes to circular economy principles but also enhances the economic and environmental feasibility of Power-to-Methane (P2M) technologies. • Valorizing of agricultural waste into carbon-based catalyst supports. • KOH activation increased surface (1020 m²/g) and micropore area (1073 m²/g). • ZnCl₂ activation formed Ni-Zn alloys and larger Ni particles. • 10Ni-H₃PO₄ performed worse due to smaller surface area and larger Ni particles. • 10Ni-KOH catalyst achieved 72.5 % CO₂ conversion and 95.4 % CH₄ selectivity.