A study about the possible species of copper present in Cu-MCM-41 type mesoporous molecular sieves

CORINA M. CHANQUIA, KARIM SAPAG, SANDRA G. CASUSCELLI, MÓNICA E. CRIVELLO, EDUARDO R. HERRERO, GRISELDA A. EIMER

Bélgica

Congreso; International Mesostructureed Materials Symposium; 2008

Since MCM-41 type mesoporous materials exhibits very high surface areas of about 1000 m2g-1 and ordered mesopores in the range of 2-13 nm, the introduction of a transition metal in this mesoporous network open new possibilities for oxidation catalysts of interest in fine chemistry where large molecules can freely diffuse through their pores. In this work, the synthesis of copper containing mesoporous materials has been studied. Copper species can occupy extra-framework sites or can be incorporated into the skeleton of the material. Depending on that, various active centers can be formed [1]. There are a few reports on Cu containing mesoporous materials synthesized by direct insertion of metal ions as precursors in the initial stage of the synthesis [2]. Because it is generally difficult to introduce a divalent cation in a tetravalent silicon framework [3] most of the works focused on the methods of ion exchange, grafting or impregnation [4,5]. Although some authors have suggested the presence of Cu2+ in exchange positions, weakly coordinated to four oxygen atoms in the silicate structure, in materials Si-MCM-41 [6,7], so far the location and condition of the metal species has not been clarified. In this work, we varied the conditions of synthesis - temperature, time, metal source and metal- in order to obtain materials with high structural quality and to identify possible copper species. Several techniques such as XRD, DRUV-vis, H2-TPR, FTIR-pyr, ICP, XAS, XPS, EPR, NMR and physisorption of N2 were used for the characterization of these MCM-41 type mesoporous molecular sieves. All the materials displayed a good structural order and specific surface area. Three possible copper species could be identified in these materials: isolated Cu2+ species possibly incorporated into the framework, (Cu-O-Cu)2+ species probably as nano-clusters weakly interacting with the framework and extra-framework nanomeric copper oxides, which could not be detected by XRD.