Enhanced low-temperature methane oxidation over Pd supported Mn-doped NiO catalyst

Abstract

This study introduces a novel catalyst system comprising Pd nanoparticles loaded onto Mn-doped NiO for the efficient oxidation of methane (CH₄) at low temperatures. The loading of Pd nanoparticles onto the Mn-doped support has yielded a catalyst with exceptional activity and stability, as evidenced by the lowest T₅₀ temperature of 276 °C and a CH₄ conversion reaching 97% at 325 °C. The catalyst demonstrates optimized reaction kinetics with the lowest activation energy of 69.2 kJ mol^–1. The catalyst's superior performance is attributed to the synergistic effects of the Pd/Mn-NiO composite, which include a higher Pd²⁺/Pd⁴⁺ ratio, increased adsorptive oxygen concentration (O_ads/O_total), and a reduced Ni³⁺/Ni²⁺ ratio. These characteristics collectively enhance the catalytic activity for CH₄ oxidation. The Mars-van Krevelen mechanism underpins the oxidation process, with Pd²⁺ identified as the principal active site for CH₄ adsorption and dissociation. Diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry elucidates the pathway of surface reactive oxygen species in the formation of key intermediates, such as formates, and underscores the accelerated decomposition of carbonate facilitated by the Pd modification on the Mn-NiO surface. The findings signify a significant advancement in the development of catalysts for environmental and energy-related applications, particularly in the mitigation of CH₄ emissions.