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

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