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 °C and decomposition of H₂O₂ at 30–50 °C. The results revealed that K₂O-treatment of the system investigated, followed by calcinations at 400 °C resulted in the conversion of some of the surface copper oxide into potassium coprate K₃Cu₅O₄ phase whose diffraction lines disappeared upon heating at 500 °C. 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 °C. Also, K₂O-doping conducted at 400 °C 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 °C. However, the opposite effect was observed upon doping with 1 and 2 wt.% Cr₂O₃ followed by heating at 500 °C. 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 °C (k_{30 °C}⁻) over the doped catalysts calcined at 400 and 500 °C, 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_{30 °C} was observed upon doping with 6 wt.% Cr₂O₃ for the solids calcined at 400 and 500 °C, 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).