Ultrafine PdOx nanoparticles on spinel oxides by galvanic displacement for catalytic combustion of methane

Abstract

High light-off temperature and poor water-tolerance at low temperature are the main drawbacks of catalysts for catalytic methane combustion. Herein, the galvanic displacement method was adopted to obtain ultrafine PdO_x nanoparticles (∼1 nm) on NiCo₂O₄ and build a tight Pd–NiCo₂O₄ interface. As a comparison, additional reference samples were prepared by conventional synthetic methods. The synthesized catalysts were characterized by XRD, TEM, XPS, H₂-TPR, CH₄-TPR, CO₂-TPD and in situ DRIFT techniques. It is found that the catalyst obtained by galvanic displacement has more Pd⁴⁺ and oxygen vacancies. The high oxidation state of Pd is more conducive to the activation of methane, and a large number of oxygen vacancies can promote the catalytic reaction rate. Thus, this catalyst displays outstanding catalytic activity with T₉₀ = 260 °C and excellent water-tolerance below 300 °C. In addition, a simple model was built based on the obtained results to understand the catalytic mechanism and provide a universal strategy for rational design of catalysts for low temperature complete oxidation of methane.