CO₂ Methanation on Zeolite/Mesoporous Silica Composites Prepared from Fly Ash and Rice Husk

Composites consisting of NaX and Na-LTA zeolites and mesoporous silica in different ratios were successfully synthesized from coal fly ash and rice husk, and subsequently modified with Ni and Mn using the incipient wetness impregnation method. The initial composite and the modified materials were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), N₂ physisorption, temperature-programmed reduction (TPR-TGA) and X-ray photoelectron spectroscopy (XPS). The formation of finely dispersed Ni, Fe spinel nanoparticles was registered in the Ni- and NiMn-containing catalysts. The presence of Mn has a favorable effect on the Ni dispersion. The support composition, including zeolite phases and the content of mesoporous silica phase, effects the formation of catalytically active metallic species for CO₂ hydrogenation to methane. The formation of Fe⁰ and FeNi₃ crystalline phases was detected for the reduced catalysts. Additionally, 3D printing technology was applied for the macrostructuring of the catalyst prior to the modification of the powdered supports with metal precursors, aiming to enhance their catalytic performance. The stabilization of Fe⁰ and FeNi₃ phase dispersion in the 3D-printed samples is beneficial for long-term catalytic performance. The advantage of the 3D-printed catalyst was demonstrated, showing its higher CO₂ consumption rate relative to the external geometric surface area compared to its powder analogue.