Cordierite as catalyst support for nanocrystalline CuO/Fe 2O 3 system

Abstract

CuO, Fe 2O 3 and CuO–Fe 2O 3 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, Fe 2O 3 or CuO–Fe 2O 3. 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 O 2 at 220–280 °C. The results obtained revealed that the employed cordierite preheated at 350–700 °C was well-crystallized magnesium aluminum silicate (Mg 2Al 4Si 5O 18). Loading of 20 wt.% CuO or Fe 2O 3 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 Fe 2O 3 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–Fe 2O 3 on the cordierite surface followed by calcination at 350 °C resulted in a solid–solid interaction between some of CuO and Fe 2O 3 yielding iron cuprate Fe 2CuO 4, which decomposed at ≥500 °C yielding copper and iron oxides. The portion of Fe 2O 3 dissolved in the cordierite lattice at 500 °C is twice that of CuO. The S BET of cordierite increased several times by treating with small amounts of Fe 2O 3 or CuO. The increase was more pronounced by treating with Fe 2O 3. 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.