EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE STUDY OF MANGANESE-ORE SPECIES AND RELATED-COMPOUNDS ON THE SURFACE OF MCM-41 CHANNELS

It has been previously shown that passing Mn-2(CO)(10) vapour over MCM -41 mesoporous silica at 50 degrees C followed by heat treatment in ai r resulted in a material with high catalytic activity for propene oxid ation. EXAFS studies of the Mn-2(CO)(10) precursor, MCM-41 treated wit h Mn-2(CO)(10) before and after the calcination in air have therefore been carried out and the results are presented in this paper. Upon imm obilisation of the Mn-2(CO)(10), the EXAFS data indicate four Mn-(CO) groups with a Mn-Mn interaction at 3.112 Angstrom; new interactions su ch as Mn-O (at the much shorter distance of 1.705 Angstrom) and Mn-Si( via Mn-O-Si) at a distance of 3.529 Angstrom are evident. This clearly suggests that the Mn species anchor onto the surface of MCM-41 formin g Mn-O-Si bonds, presumably through the reaction of surface silanol an d Mn carbonyl species. After heat treatment in air, the EXAFS data ind icate further loss of carbonyl groups with the formation of more Mn-O interactions(three Mn-O at 1.900 Angstrom and one Mn-O at 1.747 Angstr om). The best fitted model for the surface Mn-oxo species has a struct ure resembling Mn2O7. With reference to this structure, an active site in the Mn-modified MCM-41 for propene oxidation is therefore proposed .