Role of the Oxide Support on the CO2 Hydrogenation over Supported Ni Catalysts

Abstract

In Brazil, CO₂ generated during sugarcane ethanol fermentation offers a biogenic CO₂ providing an excellent opportunity for carbon recycling and reduction of the overall ethanol carbon footprint. The hydrogenation of CO₂ into value added C₁ products, such as CH₄, remains challenging due to its thermodynamic stability of CO₂ and the difficulty in controlling product selectivity. The influence of support on the performance of Ni-based catalysts in CO₂ hydrogenation was investigated by comparing Ni/Al₂O₃ and Ni/HAP (hydroxyapatite). Commercial Al₂O₃ was used as a conventional acidic support, while HAP was synthesized by chemical precipitation as a bifunctional material exhibiting both acid and basic surface sites. The catalysts were characterized by XRD, BET, TPD–NH₃, and TPD–CO₂ to determine crystallinity, surface area, and the distribution of acidic and basic sites. Catalytic tests were carried out in a fixed-bed reactor at temperatures ranging from 250 to 550 °C and a WHSV of 6,000 mL h^-1 g^-1, using a H₂/CO₂ ratio of 7. The Ni/HAP showed higher CO₂ conversion than Ni/ Al₂O₃ due to higher density of weak and medium basic sites in the catalyst surface.