Dispersing La₂O₃ crystallites in a 5 wt% La₂O₃–CaO mixed oxide system significantly enhances the intrinsic rate of NO reduction by CH₄ in the presence of 5% O₂ at 550°C compared to pure La₂O₃ and CaO phases. A synergistic effect between La₂O₃ and CaO crystallites due to doping of lanthana with Ca²⁺ ions at 800°C is largely responsible for the observed catalytic behavior. Support of this view was provided by photoluminescence studies and a large number of transient experiments for determining the surface reactivity of x wt% La₂O₃/CaO (x wt%=0, 5, 80, 100) solids toward NO, CH₄, O₂, and CO₂. The intrinsic site reactivity of the 5 wt% La₂O₃–CaO system at 550°C (TOF=6×10⁻³ s⁻¹) competes favorably with that of other similar oxides for the same reaction reported in the literature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques have been used for crystal phases and particle morphology characterization of the x wt% La₂O₃/CaO mixed oxide system. The information obtained from the XRD measurements was related to that obtained from the surface transient reactivity studies. By the addition of La₂O₃ crystallites to CaO crystallites in a wet mixing procedure followed by calcination in air at 800°C, results in dramatic changes in the chemisorptive properties (amount and bond strength) of NO, O₂, and CO₂ compared to the case of pure oxide phases. Pretreatment of the catalyst surface with H₂ or CH₄ was found to strongly affect the amount of NO chemisorption and the kinetics of its desorption. These alterations were found to strongly depend on catalyst composition.