Structure of MnOx/Al2O3 catalyst: A study using EXAFS, in situ laser ramanspectroscopy and ab initio calculations

The structure of a MnOx/Al2O3 catalyst used for ozone decomposition was eva luated using extended X-ray absorption fine structure (EXAFS) and in situ R aman spectroscopy. EXAFS results suggest that the manganese center is surro unded by four or five oxygen atoms with a Mn-O distance of 0.21 nm. The Ram an frequency for the Mn-O band was found to be 660 cm(-1). The structural p ossibilities were explored with ab initio quantum calculations using the Ha rtree-Fock method. The structure that best agreed with experimental results and literature information was the four oxygen coordinated manganese cente r. During the ozone decomposition reaction, an adsorbed peroxide species wa s observed on the catalyst surface at 880 cm(-1). The predicted vibrational frequencies calculated for peroxide species on the manganese structure wer e within 3% of the experimental data.