Chemical Engineering Journal 158 (2010) 325–332 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Deposition of SBA-15 layers on Fecralloy monoliths by washcoating Hermicenda Pérez a,∗ , Paloma Navarro b , Mario Montes b a División Académica de Ciencias Básicas, Universidad Juárez Autónoma de Tabasco, Km 1 Carretera Cunduacán-Jalpa de Méndez, A.P. 24, C.P., 86690 Cunduacán, Tabasco, Mexico b Department of Applied Chemistry, University of the Basque Country (UPV-EHU), Apdo. 1072, 20080 San Sebastián, Spain article info Article history: Received 22 September 2009 Received in revised form 15 January 2010 Accepted 18 January 2010 Keywords: SBA-15 Slurry Viscosity SBA-15 Washcoating Metallic monoliths abstract Stable slurries or suspensions were prepared in order to carry out deposition of SBA-15 layers onto Fecralloy monoliths by washcoating. The suspensions presented an important evolution with ageing time under magnetic stirring, that consisted of a change in viscosity. This change was directly related to the abrasive effect of the magnetic stirring, and caused the breakdown of the big aggregates of the par- ent SBA-15 into rod-shaped units that became more and more irregular, and the slurries to become less viscous compared with the established usual trend. The viscosity was suitable for washcoating after 120 h of magnetic stirring. Although a clear macroscopic effect was observed, the mesoporous nature of the solid was preserved. The amount loaded and the adherence of the coatings depended on the formulation of the slurry. The best results were obtained when colloidal silica was used as a binder. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Monolithic catalysts are widely used in processes such as purification of car exhaust gases, abatement of NO x and catalytic combustion of VOCs [1]. The use of monolithic structures is a very good option due to the low-pressure drop associated with the high flow rates of these mentioned processes. The materi- als most used to construct the monolithic structure are ceramics and metals. In the case of metallic monoliths, these are usually manufactured by rolling or piling up alternate corrugated and flat thin sheets [2]. The malleability and easy to perforate and to cut properties of the metallic substrates make it possible to prepare many different and complicated forms adapted to the needs of each process. Many different metals and alloys have been proposed to manufacture these metallic monoliths, but a good mechanical, chemical and thermal stability, as well as a good surface adherence of the catalytic coating, is always desirable. Two different strate- gies can be followed to deposit a catalyst coating on a metallic substrate: - direct in situ growth of the catalytic phase on the metallic sub- strate, or - washcoating (or dip-coating) of the synthesised catalyst from a slurry. ∗ Corresponding author. Tel./fax: +52 914 33 60928. E-mail address: hermicenda.perez@dacb.ujat.mx (H. Pérez). Washcoating is widely used to deposit catalytic materials as it provides a uniform coating on complex-structured substrates. In washcoating, the support is immersed in a suspension with the appropriate rheology, and is then withdrawn at a constant rate [3]. The deposited wet film, after drying and calcination, transforms into a solid coating adhered to the support. The properties of the final coating films are determined mainly by the composition parameters of the suspension, such as the pH, solid content and particle size distribution. The homogeneity and adherence of the coating are dependent on the physico-chemical properties of the metallic alloy and on the interaction between the alloy and the coating. Although monolithic and structured catalysts are commonly used, little information is available in the open and scientific liter- ature on the preparation methods for coating metallic monoliths with catalytic supports or catalytic active phases. More exten- sive studies on ceramic monoliths exist due to their wide use in three-way automobile catalysts. For this purpose, alumina is the most common catalytic support used to coat cordierite [4–12] but parameters in the slurry such as particle size [13], pH and isoelectric point [14] have to be precisely adjusted to get the main objective: loading the honeycomb with a predetermined amount of washcoat in the form of a uniform and homogeneous layer with a minimum number of impregnation [5]. Agrafiotis et al. have also studied other oxides to coat ceramic monoliths, such as CeO 2 [15–17], TiO 2 [18], ZrO 2 [19] and YSZ [20]. For any catalytic process, the catalysts usually require high surface area, appropriate pore structure, and thermal stability. Since the first reports of the ordered mesoporous material, named 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.01.032