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

Abstract

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 20–25Å 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 1722cm−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 NOx adsorption on the Pd/MgO catalyst.