Design, synthesis and characterization of Cobalt-zeolites: Microstructured magnetic and acid materials

L.B.PIERELLA; H.R.BERTORELLO; C.SAUX; P.G.BERCOFF

Buenos Aires

Workshop; Recent developments in complex materials: production and characterization; 2005

Abstract The effect of incorporation of cobalt cations into ZSM-5 zeolites was investigated by different characterization techniques (AA, XRD, Raman Spectroscopy, TPR, FTIR and BET). Co cations were incorporated by different methods: (a) Ion-exchange or (b) Wet Impregnation. The built-in technique effect was evaluated as well as Co percentage or thermal treatments applied. The incorporation of cobalt ions into ZSM-5 does not affect the high degree of purity, cristallinity and orthorhombic symmetry of the samples, verified at long range by XRD and at short range by FTIR. The Raman spectra and TPR profiles showed presence of Co3O4 for impregnated samples but not for the exchanged ones. According to FTIR experimental data of pyridine adsorbed all the samples present both Brönsted (~1550 cm-1) and Lewis (~1450 cm-1) acidic sites. The magnetic properties were studied, analyzing the effect of the built-in cation type and the amount of it. Hysteresis loops were measured at room temperature, and the results were correlated with the nature of the present ions in the zeolite. Magnetization as a function of temperature was measured for Co-ZSM-5 3.5 wt%, obtained by ion-exchanged at constant magnetic field. Good results were obtained adjusting M (T) curves with Langevin and Brillouin functions. According to the results, the number and shape of Co clusters depend on Co concentration over the sample. Blocking Temperature was not found, so clusters present spontaneous order below 2.5 K.  In the future, the magnetic properties of the Co-ZSM-5 materials will be correlated with the catalytic properties.