Journal of Catalysis 230 (2005) 406–419 www.elsevier.com/locate/jcat Promoted Ru–hydroxyapatite: designed structure for the fast and highly selective oxidation of alcohols with oxygen Z. Opre, J.-D. Grunwaldt, M. Maciejewski, D. Ferri, T. Mallat, A. Baiker ∗ Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Hönggerberg, CH-8093 Zürich, Switzerland Received 1 November 2004; revised 6 December 2004; accepted 8 December 2004 Available online 25 January 2005 Abstract Ru-containing hydroxyapatite (HAp) catalysts have been developed for the oxidation of alcohols with molecular oxygen in an organic solvent. The working hypothesis has been that fine-tuning of the location and surroundings of the active Ru species would provide outstanding performance. The highest oxidation activity was achieved when (i) the contact time between the metal salt solution and HAp was limited to a few minutes to minimize restructuring via dissolution–redeposition, (ii) low Ru content was applied, (iii) Co 2+ and Pb 2+ promoters were incorporated to occupy the poorly accessible “hidden” sites in HAp before the introduction of Ru 3+ , thus facilitating egg-shell-type Ru distribution in the particles, and (iv) after Ru incorporation the catalysts were dried at moderate temperature to avoid restructuring induced by dehydration of the active sites and their neighborhood. It is assumed that the active sites are Ru(OH) 2+ species stabilized by the phosphate O atoms and adsorbed (H-bonded) water. Various methods have been used for characterization of these catalysts, including XPS, DRIFT spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), XRD, thermogravimetry combined with mass spectroscopy (pulse thermal analysis), and nitrogen adsorption. One of the two best catalysts (RuCoHAp-10min) was used in the partial oxidation of benzylic, allylic, aliphatic and cycloaliphatic alcohols. Most carbonyl compounds were produced in excellent yields without the formation of any detectable by-product. The catalytic activity seems to be higher than that of other Ru-based solid catalysts developed for the aerobic oxidation of alcohols.  2004 Elsevier Inc. All rights reserved. Keywords: Promoted Ru–hydroxyapatite; Aerobic oxidation; Alcohols; Ru–Co–hydroxyapatite; Ru–Pb–hydroxyapatite 1. Introduction The transformation of alcohols into carbonyl compounds is an important reaction in organic synthesis. From envi- ronmental and technical points of view, an attractive so- lution is the application of a heterogeneous catalyst and molecular oxygen as the sole oxidant (Scheme 1) [1–6]. There has been a growing interest in recent years in the application of ruthenium-based solid catalysts [7], includ- ing RuO 2 · x H 2 O [8], RuO 2 /FAU zeolite [9], Ru/Al 2 O 3 [10], Ru–Al–Mg–hydrotalcite [11], Ru–silicotungstate [12], and Ru–hydroxyapatite (RuHAp) [13]. Their activity is mod- * Corresponding author. Fax: +41 1 6321163. E-mail address: baiker@chem.ethz.ch (A. Baiker). + 1 2 O 2 catalyst → + H 2 O R,R ′ : H, alkyl, cycloalkyl, allyl, aryl Scheme 1. Oxidation of alcohols to aldehydes and ketones. erate compared with some platinum- and palladium-based catalysts, but the selectivity for the aldehyde intermediate is usually high in the oxidation of a wide range of activated and nonactivated alcohols. Stoichiometric calcium hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 (CaHAp), has a hexagonal structure constructed from columns of calcium ions and oxygen atoms that are located parallel to the hexagonal axis [14–16]. Three oxygen atoms 0021-9517/$ – see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2004.12.012