Synthesis of Ni/Cerium-Zirconium Mixed Metal Oxides Via Combustion Method for CO2 Methanation

Abstract

Methanation presents a promising strategy for CO2 utilization. However, the stability of CO2 requires the presence of an effective catalyst to overcome the kinetic barrier. Cerium-zirconium mixed metal oxides, known for their high oxygen vacancy concentration, surface basicity and nickel dispersion, serve as efficient supports in methanation reactions. In this study, a series of 20Ni/CexZr1-xO2 catalysts was synthesized using the rapid and energy-efficient solution combustion method and tested for CO2 methanation. The most promising Ce-to-Zr ratio was selected for further optimization by varying Ni content. All catalysts were thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, and thermogravimetric analysis (TGA) to evaluate structure, morphology, textural properties, and thermal stability. Upon catalytic testing, the Ce-to-Zr ratio of 9:1 (20Ni/Ce0.9Zr0.1O2) resulted in the highest CO2 conversion of 90% with 100% methane selectivity at 325°C under GHSV=60,000 mL/g.h. Despite this, 20Ni/Ce0.75Zr0.25O2 showed low-temperature activity, attaining 74.3% conversion and 98.25% selectivity at 250 °C, while conversion in other catalysts, including 20Ni/Ce0.9Zr0.1O2, did not exceed 48% at the same temperature. Based on these findings, Ce0.75Zr0.25O2 support was selected for further optimization by varying Ni loading in xNi/Ce0.75Zr0.25O2 (x = 10, 20, 30, 40 wt%). The 40Ni/Ce0.75Zr0.25O2 catalyst exhibited the best performance, achieving 93% CO2 conversion at 300 °C. Upon reducing GHSV to 30,000 mL/g·h, conversion further improved to 95.22% at 275 °C. Additionally, the catalyst demonstrated good stability, maintaining activity over five days of continuous operation at 300 °C and a GHSV of 60,000 mL/g·h.