Synthesis and characterization of pure and ZrO 2 -doped nanocrystalline CuO–NiO system G.A. El-Shobaky a, * , Nagi R.E. Radwan b , M. Samy El-Shall c , A.M. Turky d , Hassan M.A. Hassan b a National Research Center, Dokki, Cairo, Egypt b Chemistry Department, Faculty of Education,Suez Canal University, Suez, Egypt c Chemistry Department, Virginia Commonwealth University, Richmond, Virginia, United States d Chemistry Department, Faculty of Science, Suez Canal University, Ismailia, Egypt Received 14 June 2007; received in revised form 10 July 2007; accepted 11 July 2007 Available online 20 July 2007 Abstract The physicochemical, surface and catalytic properties of pure and doped 0.25CuO–NiO solids prepared by sol–gel method were investigated. The dopant concentration was 2, 4 and 6 mol% ZrO 2 . The solids investigated were calcined at 400 and 600 8C. The techniques employed were XRD, EDX, TEM, surface excess oxygen, nitrogen adsorption at 196 8C and catalytic oxidation of CO by O 2 using both static and flow methods. The results revealed that the investigated system dissolved 4 mol% ZrO 2 by heating at 400 8C. This process was accompanied by a significant increase in the S BET and V p with subsequent decrease in the (r) values of the doped adsorbent. ZrO 2 -doping of the system investigated followed by calcination at 400 and 600 8C led to a considerable increase in its catalytic activity in CO oxidation by O 2 using static and flow methods. The doping process was not accompanied by any change in the activation energy of the catalyzed reaction. # 2007 Elsevier B.V. All rights reserved. Keywords: CuO–NiO system; Nanocrystalline solids; CO oxidation by O 2 1. Introduction CO oxidation is a serious environmental concern, since small exposure (ppm) to this odorless invisible gas can be lethal. Therefore, there is a need to develop highly active CO oxidation catalysts to remove even a small amount of CO from the local environment [1,2]. Catalytic oxidation is the process thought by many research studies to curb CO emissions of combustion engines into the atmosphere [3]. The results obtained communicate enough evidence for the importance of metal oxides in the chemical composition of active catalysts [3–6]. The appropriateness of a metal oxide for the catalytic CO oxidation function is gauged [4–8] by its (i) tolerance to perfectly reversible redox cycles, (ii) stability for extended defective bulk and surface structures, and (iii) high capacity towards adsorption and activation of CO and O 2 molecules. During CO oxidation, copper oxide can exhibit activities per unit surface area similar to those of platinum [9]. In addition, zirconia has shown a good catalytic activity towards oxidation reactions [10–13]. Therefore, association of copper and zirconia in the same matrix should be an interesting catalyst for oxidation reactions, since zirconia is able to interact strongly with the supported metal [14], particularly copper [15] which is determinant for good catalytic activities [16,17]. Mixed oxides homogeneously dispersed and having nanocrys- talline particles have been the subject of a big number of published studies [18–20]. These types of materials are commonly prepared through a chemical process starting from a homogeneous suspension of the respective alkoxides to reach the gel state. Subsequently, through thermal treatments it is possible to stabilize the solid obtained [21–25]. The synthesis of sol–gel materials includes several key steps: hydrolysis of the precursors to form a homogeneous sol, condensation of the sol to form a nanocrystalline gel network, several stages of washing to remove excess solvent and un-reacted precursors, and drying followed by calcination treatments (aging) to form www.elsevier.com/locate/apsusc Applied Surface Science 254 (2008) 1651–1660 * Corresponding author. Fax: +2023700931. E-mail address: elshobaky@yahoo.com (G.A. El-Shobaky). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.07.132