Support effects on Ru–HPA bifunctional catalysts: Surface characterization and catalytic performance B. Bachiller-Baeza a,c, * , J. Alvarez-Rodrı ´guez b,c , A. Guerrero-Ruiz b,c , I. Rodrı ´guez-Ramos a,c a Instituto de Cata ´lisis y Petroleoquı ´mica, CSIC, c/ Marie Curie No. 2, Cantoblanco, 28049 Madrid, Spain b Dpto. Quı ´mica Inorga ´nica y Te ´cnica, Fac. de Ciencias, UNED, c/ Senda del Rey No. 9, 28040 Madrid, Spain c Grupo de Disen ˜o y Aplicacio ´n de Catalizadores Heteroge ´neos, Unidad Asociada UNED-CSIC (ICP), Spain Received 25 July 2007; received in revised form 10 September 2007; accepted 20 September 2007 Available online 25 September 2007 Abstract The behaviour of three metal–acid bifunctional catalysts, where the metal was Ru and the acid function was a heteropolyacid (HPA), was compared in the hydroconversion of n-hexane. Both the activity and the selectivity pattern depended on the used support: silica, high surface area graphite (HSAG) or zeolite KL. While Ru–HPA–SiO 2 gave selectivity to isomerization products of 97%, the Ru–HPA–KL sample gave a selectivity of 96% to hydrogenolysis products. And, the performance of Ru–HPA–HSAG lied between that for Ru–HPA–SiO 2 and Ru–HPA–KL, giving both isomerization and hydrogenolysis products, with selectivities of 45 and 54%, respectively. The series of techniques applied to characterize the catalysts have assisted in understanding the catalytic performance. The HPA phase has been detected over all the HPA-modified supports, but different acid sites strength distributions have been determined by calorimetry of NH 3 adsorption, following the order HPA– SiO 2 > HPA–HSAG > HPA–KL. Also, different Ru species have been observed on the catalysts surface due to the interaction between the Ru precursor and the HPA support. Finally, the analysis of the results has suggested that the support determines the role played by both metal and acid functions, which separately would lead to hydrogenolysis and isomerization reactions, respectively. # 2007 Elsevier B.V. All rights reserved. Keywords: Heteropolyacid; Bifunctional catalysts; n-Hexane hydroconversion 1. Introduction Bifunctional heterogeneous catalysts consisting in a noble metal supported on a solid metal oxide with acidic properties have been widely studied due to its application on the hydroisomerization of paraffins, an important process in petroleum refinery for the production of high octane number gasoline, and on other catalytic industrial processes [1,2]. Many bifunctional catalysts commercially used to isomerise alkanes contain a zeolitic component in combination with a noble metal, usually Pt, which provides the hydrogenating–dehy- drogenating function. Furthermore, modified metal oxides, like sulphated zirconia, have also received a lot of attention in the last years due to its excellence catalytic performance [3,4]. In general, most of the investigations carried out on this topic try to evaluate the most suitable combination of acidic and metallic components since the improvement of the catalyst properties (catalytic activity, selectivity and stability of the catalyst) is reached by getting a balance between the two catalytic functions. As for the acidity is concerned, the concentration and the strength of acid sites seem to be the crucial aspect and may be tuned in different ways. Heteropoly acids (HPAs) are compounds with very strong Brønsted acid characteristics. Taking advantage of these properties, the HPA have been applied as catalysts for isomerization, Friedel-Crafts acylation or alkylation reactions in the synthesis of fine chemicals [5,6]. They also appear as potential candidates for hydroisomerization of alkanes, and in fact they have been investigated for light alkane isomerization, n-C4 and n-C6 [7–9]. The cesium salts of 12-tungstophosphoric acid promoted with Pd or Pt have resulted very efficient in reducing the hydrogenolysis processes that take place on the metal [8]. The loading of HPA on a support is a straightforward method to increase the number of acid sites. But, the acidity strength can be affected, since it is known to depend on the www.elsevier.com/locate/apcata Available online at www.sciencedirect.com Applied Catalysis A: General 333 (2007) 281–289 * Corresponding author at: Instituto de Cata ´lisis y Petroleoquı ´mica, CSIC, Marie Curie 2, Cantoblanco, 28049 Madrid, Spain. Fax: +34 915854760. E-mail address: b.bachiller@icp.csic.es (B. Bachiller-Baeza). 0926-860X/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2007.09.027