NO decomposition over a Pd/MgO catalyst prepared from [Pd(acac) ₂]

A Pd/MgO catalyst was prepared by adsorption of palladium bis-acetylacetonate [Pd(acac)₂] onto highly dehydroxylated MgO from toluene solution and subsequent reduction in flowing H₂ at 300°C. The resultant catalyst was characterized by Pd K-edge X-ray absorption fine structure (XAFS) spectroscopy, temperature-programmed desorption (TPD), and Fourier transform infrared (FTIR) spectroscopy of adsorbed NO. The adsorbed [Pd(acac)₂] species decomposes on heating in H₂ to form 20-25 Å supported Pd particles; however, organic residues from the acetylacetonate ligands remain on the catalyst surface. The FTIR spectrum of NO adsorbed on the reduced Pd/MgO catalyst at 25°C contains one principal band at 1722 cm^-1 due to atop Pd nitrosyl species. In situ XAFS of the Pd/MgO catalyst indicates that neither Pd oxidation nor particle sintering occurs during heating in flowing 1% NO/He to 300°C. NO decomposition over the Pd/MgO catalyst was investigated using temperature-programmed reaction spectroscopy (TPRS) and steady-state activity measurements. During the initial TPRS cycle in flowing 1% NO/He, nearly complete NO consumption occurs at ∼270°C due to oxidation of organic residues. O₂ evolution commences at approximately 350°C, and steady-state catalytic decomposition of NO to N₂ and O₂ occurs at 600°C. Transient NO consumption during rapid cooling in 1% NO/He (after steady-state catalysis) is attributed to NO_x adsorption on the Pd/MgO catalyst.