Effect of the pretreatment conditions on the physico-chemical and catalytic properties of cobalt- and iron-containing Ti-MCM-41 materials

Abstract

Cobalt and/оr iron modified Ti-MCM-41 materials, prepared by an incipient wetness impregnation technique, were investigated using X-ray diffraction (XRD), N 2 physisorption, temperature-programmed reduction (TPR-TGA), FT-IR spectroscopy, EPR and Mössbauer spectroscopy. Formation of finely dispersed metal oxide species could be observed for the cobalt and/or iron modified Ti-MCM-41 samples. The surface properties of the mesoporous support and the pretreatment procedure (media and temperature) predetermine the types of the formed metal oxides, their dispersion, reducibility and the catalytic activity in total oxidation of toluene. It was also found that incorporation of lower amount of titanium into the mesoporous support favors the formation of finely dispersed iron or/and cobalt ions on Fe/Ti-MCM-41 and CoFe/Ti-MCM-41 samples. The high and stable catalytic activity of Co/Ti-MCM-41 samples was due to the formation of finely dispersed Co 3O 4 nanoparticles. Cobalt oxide with optimal dispersion could be obtained by pretreatment in air and subsequently in hydrogen at 773 K. This effect was more pronounced for Co/Ti-MCM-41 catalyst with higher titanium content (Si/Ti = 10). Formation of finely dispersed cobalt ferrite particles in CoFe/Ti-MCM-41 samples following pretreatment in air and subsequently in hydrogen at 773 K had an additional positive effect on the catalytic performance.