Methane Combustion Over Ni/Ce_xZr_1–xO₂ Catalysts: Impact of Ceria/Zirconia Ratio

A series of Ce_xZr_1–xO₂ (x=1, 0.83, 0.17, 0) supports and 2 wt.% Ni/Ce_xZr_1–xO₂ catalysts were synthesized and evaluated for CH₄ oxidation. The Ce_xZr_1–xO₂ supports showed moderate activity (T₅₀=519-638 °C) with CO by-product formation. Nickel incorporation onto Ce_xZr_1–xO₂ lowered the T₅₀ to 438–477 °C and eliminated the formation of CO. The results indicated that moderate Zr doping improved the support oxygen storage capacity (OSC) and reducibility of the catalyst at low temperatures (H₂-TPR) leading to an enhanced CH₄ combustion turnover frequency: Ni/ZrO₂<Ni/Ce_0.17Zr_0.83O₂<Ni/CeO₂<Ni/Ce_0.83Zr_0.17O₂. The apparent activation energies of Ni/Ce_xZr_1–xO₂ catalysts (87-92 kJ/mol) were much lower than the ones of Ce_xZr_1–xO₂ supports and Ni/quartz sand (111-120 kJ/mol) indicating that CH₄ oxidation is facilitated when Ni is deposited on Ce_xZr_1–xO₂. Moreover, stability tests with H₂O and CO₂ showed that Zr doping can improve the catalyst stability, while H₂O had a stronger reversible inhibition effect than CO₂ for CH₄ combustion.