In Situ Spectroscopic and Computational Studies on a MnO₂–CuO Catalyst for Use in Volatile Organic Compound Decomposition

Abstract

In situ near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory calculations were conducted to demonstrate the decomposition mechanism of propylene glycol methyl ether acetate (PGMEA) on a MnO₂-CuO catalyst. The catalytic activity of MnO₂-CuO was higher than that of MnO₂ at low temperatures, although the pore properties of MnO₂ were similar to those of MnO₂-CuO. In addition, whereas the chemical state of MnO₂ remained constant following PGMEA dosing at 150 °C, MnO₂-CuO was reduced under identical conditions, as confirmed by in situ NEXAFS spectroscopy. These results indicate that the presence of Cu in the MnO₂-CuO catalyst enables the release of oxygen at lower temperatures. More specifically, the released oxygen originated from the Mn-O-Cu moiety on the top layer of the MnO₂-CuO structure, as confirmed by calculation of the oxygen release energies in various oxygen positions of MnO₂-CuO. Furthermore, the spectral changes in the in situ NEXAFS spectrum of MnO₂-CuO following the catalytic reaction at 150 °C corresponded well with those of the simulated NEXAFS spectrum following oxygen release from Mn-O-Cu. Finally, after the completion of the catalytic reaction, the quantities of lactone and ether functionalities in PGMEA decreased, whereas the formation of C=C bonds was observed.