Applied Catalysis A: General 264 (2004) 43–51 Hydrogenation of aromatics over Au-Pd/SiO 2 -Al 2 O 3 catalysts; support acidity effect  A.M. Venezia a,∗ , V. La Parola b , B. Pawelec b , J.L.G. Fierro b a Istituto per lo Studio dei Materiali Nanostrutturati, ISMN-CNR Sezione di Palermo, via Ugo La Malfa 153, 90146 Palermo, Italy b Istituto de Catalysis y Petroleoquimica, CSIC, Campus UAM, Cantoblanco, 28049 Madrid, Spain Received in revised form 16 December 2003; accepted 16 December 2003 Abstract Bimetallic Au-Pd catalysts supported on amorphous silica-alumina (ASA) with vary amount of alumina (0, 8, 14, 28 and 100%) were prepared by the simultaneous reduction of palladium and gold precursors by ethanol in the presence of the polyvinylpyrrolidone (PVP). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses indicated formation of alloyed Au–Pd particles. Measurements of temperature-programmed desorption (TPD) of ammonia were performed to monitor the acid strength and the amount of acid sites on the catalysts after their reduction with 10% H 2 /Ar at 573 K for 1 h. The effect of the support acidity on the catalytic activity was investigated in the simultaneous hydrogenation (HYD) of toluene (T) and naphthalene (NP) in the presence of dibenzothiophene (DBT). The amount of coke formed during the catalytic tests was also determined. Under the selected conditions (P = 5.0 MPa, T = 523 K, WHSV = 41.2h -1 ), all the catalysts were resistant to poisoning with 113 ppm of S (as DBT). The hydrogenation activity of toluene and the HDS activity of DBT correlate with the concentration of the medium strength acid sites. The enhancement of the HYD activity and the S-tolerance were related to modifications of the electronic properties of the metal atom upon interaction with the acid sites and upon intermetallic interaction. © 2003 Elsevier B.V. All rights reserved. Keywords: Aromatics hydrogenation; Silica; Alumina; Au-Pd catalysts 1. Introduction More stringent requirements for reducing the content of aromatics and sulfur in fuels have brought increasing attention to new catalysts involved in hydrotreating pro- cess. For deep hydrogenation (HYD) of aromatics and deep hydrodesulfurization (HDS) in diesel fuel, the single- and two-stage approaches have been proposed. The single stage method combines severe hydrodesulfurization with aro- matics hydrogenation (HDA) by the use of a conventional CoMo, NiMo, or NiW catalyst at high temperature and H 2 pressures substantially higher than the H 2 pressure at which current HDS units operate [1,2]. In the two-stages method, the conventional hydrotreating catalyst is used in  Part of the content of this paper appeared in the Proceedings of the Gold 2003: New Industrial Applications for Gold; Conference held in Vancouver, Canada. ∗ Corresponding author. Tel.: +39-09-16809372; fax: +39-09-16809399. E-mail address: anna@pa.ismn.cnr.it (A.M. Venezia). the first reactor and a noble-metal catalyst in the second re- actor [3]. This method yields a low aromatic diesel stream at moderate hydrogen pressure. However, noble metals are very susceptible to sulfur poisoning [4]. Since the use of noble metal catalysts is limited by the severe pretreatment conditions in the first reactor, the commercial experience with sulfur tolerant noble metal catalysts is limited [1,5]. The high intrinsic hydrogenation activity and their sulfur tolerance may be enhanced, modifying the physicochemi- cal characteristics of the metal atoms by: (i) changing the acid–base properties of the carrier [6]; (ii) changing the metal particle size or (iii) alloying [7]. Concerning the for- mer, it was reported that the sulfur tolerance of Pt or Pd catalysts can be greatly enhanced by using acidic supports such as zeolites [1,5–11] whereas less acidic supports, such as SiO 2 –Al 2 O 3, can generate moderate [5,12–14] or large sulfur resistance [7]. The high S-tolerance of zeolite-based Pt or Pd catalysts is commonly attributed to the formation of electron-deficient metal particles, Pt + or Pd + , upon in- teraction of the reduced metal with the Brønsted acid sites of the zeolite, which in turn lowers the strength of the S–Me 0926-860X/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2003.12.025