Synthesis and characterization of Cu(I)-salen complex immobilized aluminosilicate MCM-41

Copper(I)-salen: N,N--ethylenebis(salicylidene-iminato)copper(I), immobilized into the structure of Al-MCM-41 has been synthesized by a liquid-phase adsorption of salen through Cu(I)-exchanged Al-MCM-41 (Cu(I)-salen/M-imp) and by a flexible ligand method (Cu(I)-salen/M-ss). The ligand and complex were characterized by various physico-chemical measurements such as elemental analysis, powder XRD, mid-spectral FT-IR, thermal analysis (TGA, DTGA), surface texture and scanning electron microscopy (SEM). A comparative in situ FT-IR study of CO adsorption onto simple Cu(I)-exchanged Al-MCM-41 and the complex-immobilized Al-MCM-41 has been carried out. The structure of Al-MCM-41 after modification remains intact, which was evident from XRD and FT-IR studies. The surface characteristics and thermal analysis have provided evidence for successful immobilization of the copper complex inside Al-MCM-41. The structure of Cu(I)-salen complex in Al-MCM-41 prepared by the liquid-phase adsorption of salen was more thermally stable than the analogous prepared by the flexible ligand method. The in situ FT-IR investigation of CO adsorption showed a band at 2124 cm(-1) due to Cu(I)-CO in the spectrum of Cu(I)-exchanged Al-MCM-41. This band was shifted to 2146 cm(-1) in the spectra of Al-MCM-41-containing complex due to a stronger mode of CO interaction. The Cu(I)-salen/M-imp sample was more active than the Cu(I)-salen/M-ss one in the generation of CO2 (2336 cm(-1)), which was produced from CO and H2O by the water-gas shift reaction. Surface bound adsorbed species like carbonate (1636, 1590, 1488 and 1434 cm(-1)) and formate (1727 cm(-1)) were also detected. The spectrum of the Cu(I)-salen/M-ss sample was characterized by a band at 2278 cm-1 assigned to isocyanate ion, NCO-, coordinated to a Cu(I) ion which was absent in the spectra of other samples. The extent of this band depends on the interaction of the immobilized complex with the Al-MCM-41 lattice. (C) 2007 Elsevier Inc. All rights reserved.