CO₂ hydrogenation over 5%Ni/CeO₂–Al₂O₃ catalysts: effect of supports composition

In current work, the investigation centered on assessing the impact of the CeO₂ to Al₂O₃ ratio in a 5%Ni/CeO₂–Al₂O₃ catalyst on the CO₂ hydrogenation reaction within the temperature range of 240–400 °C. The primary aim was to achieve enhanced conversion rates, while minimizing coke deposition on the catalyst surface. Nickel was incorporated into the CeO₂–Al₂O₃ supports via the deposition–precipitation method. The various physicochemical properties of fresh, reduced and spent catalysts were studied using techniques such as thermal gravimetric analysis (TGA), X-ray diffraction (XRD), N₂ adsorption/desorption, temperature programmed reduction (TPR), H₂-chemisorption, X-ray fluorescence (XRF), and CHNS analyzer. XRD results revealed that the addition of CeO₂ to the Ni/Al₂O₃ catalyst and the increase in ceria loading in the hybrid support had no obvious effect on the crystalline structure. However, several properties including reducibility, coke deposition, and coke formation quantity, coke structure on the catalyst surface, catalytic performance, and thermal stability were altered. The CO₂ conversion remained relatively stable (41.25%) up to 35 h initial on stream for Ni/Al₂O₃ catalyst, indicating no significant deactivation. Conversely, Ni/CeO₂–Al₂O₃ catalyst exhibited high stability up to 45 h initial. The highest CO₂ conversion (58%) was achieved with the Ni/CeO₂ (50%)–Al₂O₃ (50%) at 400 °C, primarily attributed to a lower interaction between nickel species and the support, along with a higher reduction degree. Ni/CeO₂–Al₂O₃ catalysts displayed higher methane selectivity and lower CO selectivity compared to both Ni/Al₂O₃ and Ni/CeO₂ catalysts across the entire temperature range of 240–400 °C.