Cordierite as catalyst support for nanocrystalline CuO/Fe2O3 system

CuO, Fe2O3 and CuO–Fe2O3 samples supported on cordierite (commercial grade) were prepared by wet impregnation method using finely powdered support material, copper and/or iron nitrates. The extent of loading was varied between 5 and 20 wt.% CuO, Fe2O3 or CuO–Fe2O3. The physicochemical, surface and catalytic properties of the various solids calcined at 350–700 °C were investigated using XRD, EDX, nitrogen adsorption at 77 K and CO-oxidation by O2 at 220–280 °C.The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg2Al4Si5O18). Loading of 20 wt.% CuO or Fe2O3 on the cordierite surface calcined at 350 °C led to a partial dissolution of the added oxides in the support lattice forming solid solutions. The other portions remained as separate nanocrystalline CuO or Fe2O3 phases. The dissolved portions of the transition metal oxide increased upon increasing the calcination temperature from 350 to 500 °C. Loading of 20 wt.% CuO–Fe2O3 on the cordierite surface followed by calcination at 350 °C resulted in a solid–solid interaction between some of CuO and Fe2O3 yielding iron cuprate Fe2CuO4, which decomposed at ≥500 °C yielding copper and iron oxides. The portion of Fe2O3 dissolved in the cordierite lattice at 500 °C is twice that of CuO.The SBET of cordierite increased several times by treating with small amounts of Fe2O3 or CuO. The increase was more pronounced by treating with Fe2O3. The catalytic activity of the cordierite increased progressively by increasing the amount of oxide(s) added. The mixed oxides system supported on cordierite and calcined at 350–700 °C showed catalytic activities much bigger than those measured for the individual supported systems. The synergistic effect manifested in case of solids calcined at 350 °C was attributed to the formation of surface iron cuprate. The significant increase in surface concentration of copper species on top surface layers of the solids treated with mixtures of copper and ferric oxides could be responsible for the synergistic effect for the mixed oxide catalysts calcined at 500 or 700 °C.