Surface and catalytic properties of CuO/MgO system doped with K2O and Cr2O3

The effects of doping of CuO/MgO system with K2O or Cr2O3 (1-6 wt.\%) on its surface and catalytic properties were investigated. The analytical techniques employed were XRD, nitrogen adsorption at - 196 degreesC and decomposition of H2O2 at 30-50 degreesC. The results revealed that K2O-treatment of the system investigated, followed by calcinations at 400 degreesC resulted in the conversion of some of the surface copper oxide into potassium coprate K3Cu5O4 phase whose diffraction lines disappeared upon heating at 500 degreesC. Chromium oxide-doping did not lead to the formation of any copper oxide-Cr2O3 compound(s) in the treated sarples calcined at 400 and 500 degreesC. Also, K2O-doping conducted at 400 degreesC increased the degree of crystallinity and particle size of MgO phase and exerted opposite effects in the crystallinity and particle size of CuO phase. The doping process either with K2O. or Cr2O3 effected a measurable progressive decrease (42-53\%) in the specific surface area of the investigated system, subjected to heat treatment. at 400 and 500 degreesC. However, the opposite effect was observed upon doping with 1 and 2 wt.\% Cr2O3 followed by heating at 500 degreesC. The catalytic activity of the investigated system decreased by doping with K2O. The addition of 6 wt.\% effected a decrease of 78\% and 68\% in the value of the reaction rate constant per unit surface area for the catalytic reaction carried out at 30 degreesC (k((30) over bar degreesC)) over the doped catalysts calcined at 400 and 500 degreesC, respectively. Cr2O3-doping on the other hand, much increased the catalytic activity of the treated samples and an increase of 106\% and 80\% in the value of k(30degreesC) was observed upon doping with 6 wt.\% Cr2O3 for the solids calcined at 400 and 500 degreesC, respectively. The results were discussed in terms of creation of new in pairs and conversion of some active sites (surface CuO) into less active site (K3Cu5O4). (C) 2002 Elsevier Science B.V All rights reserved.