Local environment of manganese incorporated in mesoporous MCM-41

Manganese containing MCM-41 was synthesised by the direct hydrothermal method (DHT) in the presence of cetyltrimethylammonium chloride (CTACl) as a template. The local environment of manganese incorporated in mesoporous silicate MCM-41 was investigated by XAS (X-ray Absorption Spectroscopy). XANES (X-ray Absorption Near Edge Structure) studies showed the coexistence of Mn2+ and Mn3+ cations in both, as-synthesised and template-free MnMCM-41 samples. The major part of manganese cations in the as-synthesised MnMCM-41 was Mn2+, while in the template-free MnMCM-41 the amount of Mn3+ was increased. EXAFS (X-ray Absorption Fine Structure) analyses revealed that major part of manganese cations in the as-synthesised MnMCM-41 were extra-framework with the Mn-O distance of 2.19 Å. Manganese cations in the template-free MnMCM-41 were incorporated into the framework and coordinated to three oxygens in the first coordination shell, with two of them at a shorter distance of 1.92 Å and one at a longer distance of 2.21 Å. Pulsed ESR (Electron Spin Resonance) and ESEEM (Electron Spin-Echo Envelope Modulation) investigations were in agreement with the XANES and EXAFS results.