Mesoporous TiO2 powders as host matrices for iron nanoparticles. Effect of the preparation procedure and doping with Hf

Abstract

The aim of the current investigation is to follow the formation of iron phase in mesoporous nanocrystalline titania and Hf-doped titania powders and its influence on the physicochemical and catalytic properties of the obtained materials. The parent host matrices were synthesized by using either template-assisted hydrothermal approach or homogeneous precipitation with urea. The iron modifications were prepared by incipient wetness impregnation with Fe(NO3)3.9H2O. Nitrogen physisorption, X-ray diffraction, TEM analysis, Moessbauer spectroscopy, UV–Vis spectroscopy and TPR with hydrogen were the techniques used for samples characterization and their catalytic behaviour was studied in methanol decomposition and ethyl acetate oxidation as catalytic tests. The hydrothermal treatment, the iron modification and the doping with Hf lead to the appearance of a significant absorption in the visible region for the studied samples, which together with the red shift of the absorption edge could be advantageous because of increased yield of photogenerated electron–hole pairs. The presence of very highly dispersed and uniform iron oxide particles with sizes below 4 nm and superparamagnetic behaviour are most beneficial for the catalytic activity in ethyl acetate total oxidation. On the other hand, the iron introduction retards the methanol conversion by blocking some of the supports active sites and alone or together with Hf changes the selectivity to predominant methane formation.