Nature and location of copper nano-species in mesoporous molecular sieves

CORINA M. CHANQUIA; KARIM SAPAG; ENRIQUE RODRÍGUEZ-CASTELLÓN; EDUARDO R. HERRERO; GRISELDA A. EIMER

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2010 vol. 114 p. 1481 - 1490

1932-7447

Copper-mesoporous molecular sieves type MCM-41 have been successfully prepared by different direct incorporation methods of the metal in the initial synthesis gel. Various techniques including XRD, AAS, adsorption/desorption of N2, UV-vis-DR, TPR, and XPS were employed for the materials characterization. All of the materials exhibited a good structural regularity, even for loadings of copper of 10 wt %, besides high specific surface areas and pore volumes. An extended and detailed study about the nature of copper oxidation state as well as of the copper species distribution on the siliceous nanostructure has been made. It was found that copper is present on the mesoporous silica in the form of various species: isolated mononuclear Cud+ cations possibly in coordination with the lattice oxygen; linear oligonuclear [Cud+...Od-...Cud+]n clusters probably inserted into mesoporous channels; and bulky CuO oxide segregated of the structure. The distribution of copper species in the final solid depends on the preparation method used as well as of the copper content in the initial gel. Moreover, we infer the coexistence of the both copper oxidation states +1 and +2 (+d) in the major species of these materials: isolated and oligonuclear copper species.