Journal of Molecular Catalysis A: Chemical 251 (2006) 185–193 Inorganic compounds and materials as catalysts for oxidations with aqueous hydrogen peroxide V´ eronique Nardello a , Jean-Marie Aubry a , Dirk E. De Vos b , Ronny Neumann c , Waldemar Adam d , Rui Zhang e , Johan E. ten Elshof f , Peter T. Witte g , Paul L. Alsters h,∗ a LCOM, Equipe de Recherches “Oxydation et Formulation”, UMR CNRS 8009, ENSCL BP 90108, F-59652 Villeneuve d’Ascq Cedex, France b Centre for Surface Chemistry and Catalysis, K.U. Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium c Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel d Department of Chemistry, Facundo Bueso 110, University of Puerto Rico, Rio Piedras 00931, Puerto Rico e Institute of Organic Chemistry, University of W¨ urzburg, Am Hubland, 97074 W¨ urzburg, Germany f University of Twente, Inorganic Materials Science, MESA + Institute of Nanotechnology and Faculty of Science and Technology, P.O. Box 217, 7500 AE Enschede, The Netherlands g Engelhard De Meern B.V., Strijkviertel 67, P.O. Box 19, 3454 ZG De Meern, The Netherlands h DSM Pharma Chemicals, Advanced Synthesis, Catalysis, and Development, P.O. Box 18, NL-6160 MD Geleen, The Netherlands Available online 3 April 2006 Abstract This paper reviews our work on oxidations with aqueous hydrogen peroxide catalyzed by inorganic catalysts devoid of organic ligands. In the first part of the review, the use of the [WZn 3 (ZnW 9 O 34 ) 2 ] 12- “sandwich” polyoxometalate as a multi-purpose oxidation catalyst is described. Attention is paid to practical aspects that are of relevance for large-scale, industrial use of this catalyst, such as catalyst preparation, handling, and recycling. Its activity in cyclooctene epoxidation compared to other W-based catalyst systems has been determined under ceteris paribus conditions. The second part of the review deals with homogeneous and heterogeneous inorganic catalysts for “dark” singlet oxygenation, i.e., singlet oxygenation by catalytic disproportionation of hydrogen peroxide into singlet oxygen and water. The industrial advantages of “dark” singlet oxygenation compared to conventional photo-oxidation are described. It is pointed out that the reaction medium and nature of the catalyst strongly influence the selectivity and scope of the method. © 2006 Elsevier B.V. All rights reserved. Keywords: Hydrogen peroxide; Epoxidation; Singlet oxygen 1. Introduction The industrial, large-scale application of catalysts makes high demands upon these catalysts in order to meet technical, eco- nomical, and environmental requirements. Thus, the catalyst should be cost-efficient in term of catalyst costs per kilogram product. Catalyst separation from the product should be facile in order to avoid contamination of the latter with catalyst residues. In the down-stream processing, the catalyst should not interfere negatively with the waste-water treatment or affect the waste- water quality in a negative way that conflicts with environmental legislation. ∗ Corresponding author. Tel.: +31 46 476 13 48; fax: +31 46 476 76 04. E-mail address: paul.alsters@dsm.com (P.L. Alsters). In the area of liquid-phase oxidation catalysis, it is often par- ticularly hard to meet industrial demands. One of the underlying reasons for this is that liquid-phase oxidation catalysts often dis- play a relatively low catalyst activity when compared to, for example, typical reduction catalysts used for hydrogenations. Accordingly, typical catalyst loadings used in oxidative trans- formations are relatively high in order to compensate for the lack of catalyst activity. In contrast to catalytic reductions, cat- alytic oxidations usually suffer from an intrinsic instability of the catalyst under the reaction conditions, since most catalysts contain organic ligands that are inherently susceptible to oxida- tive degradation [1]. This catalyst instability is another cause for the high catalyst loadings commonly employed in oxidation catalysis. In addition, it negatively affects the overall process robustness. In this article, we will review our work on inorganic oxi- dation catalysts devoid of any organic ligands for affecting 1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2006.02.052