ORIGINAL PAPER Copper-modified sulfated stannia: surface properties and catalytic activity towards phenol hydroxylation Hussein A.Khalaf • Saber E.Mansour • Enas A.El-Madani Received: 17 September 2009 / Accepted: 2 May 2010 / Published online: 3 June 2010 Ó Springer-Verlag 2010 Abstract Stannia,sulfatedstannia,and Cu-modified sulfated stannia samples were prepared by an impregnation method using different loading levels of Cu (5, 10, and 20% by weight). These samples were characterized by means ofthermal gravimetric analysis (TGA and DTA), X-ray powder diffraction (XRD), and nitrogen sorption at 77 K. Potentiometric titration was used to characterize the surface acidity of these samples and their catalytic activity was investigated by phenol hydroxylation in the presence of hydrogen peroxide at 333 K. The obtained data revealed sulfated species with differenthermal stabilities in the samples containing Cu, and the rutile structure of stannia remained unchanged by the addition of sulfate and Cu. A surface texture study showed that Cu modification and the addition ofsulfate resulted in modified surface area and porosity.The additionof copperto sulfatedstannia increases the acid strength. Thus,Cu-modified sulfated stanniasampleshavehighercatalyticactivity towards phenol hydroxylation and selectivity towards hydroquinone production. Keywords Stannia Sulfation Texture Acidity Phenol hydroxylation Introduction Porous solids with uniform pore size in the micropore and mesopore range are extensively used in industrial catalytic processes. Thesematerialspossesshighsurfacearea, thermal stability, uniform pore structure, and tunable acid base and redox properties. Chemical and physical proper- ties of solid materials strongly depend on both the size an the shape of the microscopic particles they are made up from [ 1–3].Modification of metal oxides with the sulfate anion can generate a strong acidity, even stronger than 100% sulfuric acid, and hencethey become superacid catalysts useful in reactions like isomerizations, low tem- perature esterification, alkylation, and cracking [4, 5].For sulfated metal oxides, the textural properties and catalytic activity can be improved by the addition of another metal component. Metal-promoted sulfated oxides are receiving increasing interestowing to their enhancedcatalytic activity. The promoting effect of different metals like Mn, Fe, Ni, and Alon some metal oxides such as Fe 2 O 3 and ZrO 2 has been reported [6, 7].Since metal oxide systems containing tin oxide are widely used in oxidation reactions it is expected that their sulfated analogues can show enhanced activity. Matsuhashi et al. [8] reported that the addition of sulfate anion to SnO 2 improves its oxidation activity in the dehydrogenation of cyclohexanol. Stannia- based catalysts exhibit good activity towards CO/O 2 and CO/NO reactions [9]. The activity and selectivity of stannia catalysts can be substantially improved by incorporation o heteroelements [10]. The copper ion and complexes con- taining copper ions have long been found to be effective catalysts and are used in a wide range of organic synthese [11, 12].Hydroxylation of phenols gives three different compounds, namely catechol, hydroquinone, and resorcin These phenolic derivatives are widely used as photograph chemicals, antioxidants, polymerization inhibitors, and als in medicine [13]. Copper-containing porous materials appear to be prom- ising catalysts for phenol hydroxylation with hydrogen H. A. Khalaf (&) S. E. Mansour E.A. El-Madani Chemistry Department, Faculty of Science, Omer El-Mukhtar University, P.O. Box 919, El-Beida,Libya e-mail: hkhalaf70@yahoo.com 123 Monatsh Chem (2010) 141:729–735 DOI 10.1007/s00706-010-0321-5