Tuning the Ca content of Ni–Ca–Al layered-double hydroxide catalysts for low-temperature CO2 methanation

Abstract

CO₂ valorization as carbon feedstock is a good strategy to reduce its environmental effects and produce fuels and chemicals such as CH₄, which can be used as synthetic natural gas (SNG). Layered double hydroxide (LDH)-derived Ni–Ca–Al catalysts with variable Ca content (3–33% mol) were synthesized through co-precipitation, characterized by N₂ physisorption, X-ray diffractometry (XRD), temperature-programmed analyses (H₂-TPR, CO₂-TPD, H₂-TPD, and TPO), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) and evaluated in CO₂ methanation (200–400 °C, 1 atm, and a GHSV of 60 000 mL (g_cat h)⁻¹). Outstanding performance was observed at temperatures as low as 200 °C, where the catalyst containing 6% Ca achieved 79.4% CO₂ conversion and 100% CH₄ selectivity, attributed to the improved metal–support interaction that provided a high surface area, dispersion, and small-sized crystallites, thus presenting plenty of Ni active sites, and to the high basicity in the weak-medium range, which facilitated the adsorption and activation of H₂ and CO₂. A stability test (250 °C for 10 h) demonstrated high resistance to deactivation by sintering and carbon deposition. Therefore, the Ni–Ca–Al LDH-derived catalysts were proved as feasible catalysts for CO₂ methanation, where the proper adjustment of Ca content in the lattice improves their properties, allowing the process to be performed closer to thermodynamic equilibrium at low temperatures and preventing high energy spending.