Study of nitrous oxide utilization for syngas production via partial oxidation of methane using Ni-doped perovskite catalysts

Abstract

Four different materials—pure NiO, pure LSCF (La_0.3Sr_0.7Co_0.7Fe_0.3O_3−δ), 10% Ni/LSCF, and 20% Ni/LSCF—were studied. The Ni/LSCF catalysts demonstrated superior catalytic performance for both N₂O decomposition and the partial oxidation of methane (POM) compared to pure NiO and pure LSCF. This enhancement is attributed to an increase in oxygen vacancies and improved oxygen mobility within the catalyst, as evidenced by O₂-TPD analysis. During N₂O decomposition, both LSCF and 10% Ni/LSCF achieved complete N₂O conversion at 800 °C, whereas pure NiO provided 81.7% at the same temperature. However, 10% Ni/LSCF is more active at lower temperatures, as evidenced by its T₅₀ value of 536 °C, compared to 546 °C for the unmodified LSCF. For the POM reaction using N₂O as an oxidant, 10% Ni/LSCF achieved 70.9% CH₄ conversion, 96.6% CO selectivity, and 97.4% H₂ selectivity at 600 °C. In contrast, both pure LSCF and 20% Ni/LSCF catalysts exhibited significantly lower efficiency, with approximately 20% CH₄ conversion and less than 5% syngas selectivity. The enhanced performance of the 10% Ni/LSCF compared to the 20% Ni/LSCF is likely attributed to its smaller Ni crystallite size (23.7 nm vs. 32.3 nm) and the lower temperature required for reducing Ni²⁺ to the active Ni⁰ species (480 °C vs. 500 °C). Kinetic analysis of the POM reaction using N₂O over the 10% Ni/LSCF catalyst revealed a second-order reaction with respect to CH₄ and a zero-order reaction with respect to N₂O, with an apparent activation energy of 71.8 kJ mol⁻¹.