ORIGINAL PAPER Textural properties of sulfated iron hydroxide promoted with aluminum Hussein A. Khalaf Received: 24 July 2008 / Accepted: 9 January 2009 Ó Springer-Verlag 2009 Abstract Aluminum-promoted sulfated iron hydroxide samples were prepared by a coprecipitation method with different loading levels of Al III followed by sulfation and calcination at 870 K. These samples were characterized by means of thermal gravimetric analysis, X-ray powder dif- fraction, nitrogen adsorption at 77 K, diffuse reflectance spectroscopy, and FT-IR spectroscopy using KBr pellets. TGA profiles showed sulfated species with different ther- mal stabilities in the samples, and incorporation of Al III causes an increase in the thermal stability of the surface sulfate species. The presence of sulfate ions and Al III promotion did not modify the crystal phase of a-Fe 2 O 3 , but it did increase the crystallite size. A textural study showed that the incorporation of Al III into the sulfated samples led to diminished surface area and pore volume. The pore size distribution exhibited a wide spectrum of mesoporosity in all samples. Keywords Iron hydroxide  Sulfation  Promotion  Texture Introduction Solid acid catalysts have found widespread application in many catalytic reactions relating to hydrocarbons, such as isomerization, alkylation, oligomerization, and cracking. These acid-catalyzed reactions are large-scale industrial processes that play a most important role in the petroleum and petrochemical industries [1]. Solid acids of sulfated metal oxides have been investigated for their use as envi- ronmentally friendly catalysts in many organic reactions [2–4]. Sulfated zirconium, titanium, and iron oxides dis- playing high thermostability, very strong acidity, and high catalytic activity have aroused increasing interest [5, 6]. The addition of some metals to these sulfated oxides can lead to catalysts that are more active and more resistant to deactivation [7]. Therefore, several metals such as plati- num, palladium, aluminum, nickel, cobalt, and manganese have been added to sulfated metal oxides, producing active and selective catalysts [8]. At the beginning of the last decade, Hsu et al. [9] reported that sulfated zirconium oxide promoted with iron and manganese increases the rate of n-butane isomerization by two or three orders of magnitude compared to unpro- moted sulfated zirconium oxide. Recently, Gao et al. [10, 11] found that the addition of aluminum to sulfated zirconium oxide significantly enhances the activity and stability of the catalysts for n-butane isomerization. They also found that the addition of Al 2 O 3 to pure oxides (zirconium, titanium, and iron oxides) before sulfation increases the acidity, activity, and stability of the catalyst for n-butane isomerization. The promoting effect of tran- sition metals is generally recognized to be related to a bifunctional mechanism associated with the isomerization reaction, where the presence of transition metals acceler- ates the dehydrogenation of the reactants [10, 12]. Sulfated iron oxide has many catalytic applications, and hence it would be worth trying to improve its surface texture. Therefore, in this work, iron hydroxides promoted with different loading levels of Al III were prepared by coprecipitation followed by sulfation and calcination at 870 K for 3 h. The surface and bulk characteristics of these catalysts were then studied in order to monitor the H. A. Khalaf (&) Chemistry Department, Faculty of Science, Omer–Elmoukhtar University, B.O. 919, El-Beida, Libya e-mail: hkhalaf70@yahoo.com 123 Monatsh Chem DOI 10.1007/s00706-009-0118-6