DOI: 10.1002/cctc.201000049 Characterization of Synthetic Iron Oxides and their Performance as Support for Au Catalysts. Paolo Centomo,* [a] Marco Zecca,* [a] Vito Di Noto, [a] Sandra Lavina, [a] G. Giorgio Bombi, [a] Luca Nodari, [a] Gabriella Salviulo, [b] Roberta Ingoglia, [c] Candida Milone,* [c] Signorino Galvagno, [c] and Benedetto Corain [a] Introduction Nanostructured gold exhibits remarkable catalytic activity, in particular for the low temperature oxidation of CO. [1, 2] How- ever, for several reactions, the catalytic performance not only depends on the metal nanostructure, but also on the effects of the support. [3] Galvagno and associates showed that Fe 2 O 3 is best suited for the preparation of gold catalysts for the selective hydroge- nation of a,b-unsaturated aldehydes and ketones [4] to the cor- responding a,b-unsaturated alcohols under (mild) gas–liquid– solid conditions. The selective hydrogenation of a,b-unsaturat- ed ketones is of particular interest, because no heterogeneous metal catalysts but Au/Fe 2 O 3 are known to promote the selec- tive transformation of these substrates into the corresponding a,b-unsaturated alcohols. The latter products can be easily achieved under hydrogen transfer conditions, [5, 6] but saturated ketones are invariably the main reaction products upon hydrogenation with classical metal catalysts (i.e., Pt, Ru). [7–9] In their previous investigation, Galvagno and associates dis- covered that the Au/Fe 2 O 3 combination was the key to high selectivity: neither gold over different supports nor different metals over ferric oxide possessed the desired selectivity. [4b] However, they did not find any correlation between the activity and the selectivity to unsaturated alcohol (UA) and the morphology and size of the gold nanoparticles, [4e] but the regioselectivity was very strongly affected by the nature of the support. To this respect, the best catalyst was gold dispersed on goethite (a-FeOOH), maghemite (g-Fe 2 O 3 ), and iron oxy- hydroxides prepared by precipitation from a solution of iron nitrate. [4c] Gold supported on hematite (a-Fe 2 O 3 ) showed the lowest selectivity. [4b, c, e] A recent report from our laboratories described the synthe- ses of iron(III) oxides and their characterization by means of Mçssbauer spectroscopy (MbS) and X-ray powder diffraction (XRPD). [10] Some of them turned out to be composed of sen- sible amounts of nanostructured matter. The relevance of the nanostructure of the supports in gold catalysts has already been highlighted in the oxidation of CO [11] and alcohols. [12] Therefore, we used our iron oxide samples for the preparation of new gold catalysts for the chemoselective hydrogenation of trans-4-phenyl-3-buten-2-one (BA) to 4-phenyl-3-buten-2-ol (BOL). [a] Dr. P. Centomo, Prof. M. Zecca, Prof. V. DiNoto, Dr. S. Lavina, Prof. G. G. Bombi, Dr. L. Nodari, Prof. B. Corain Department of Chemical Sciences Università degli Studi di Padova Via Marzolo 1, 35131 Padova (Italy) Fax: (+ 39) 0498275223 E-mail : marco.zecca@unipd.it paolo.centomo@unipd.it [b] Prof. G. Salviulo Department of Geosciences Università degli Studi di Padova Via Giotto 1, 35137 Padova (Italy) [c] Dr. R. Ingoglia, Prof. C. Milone, Prof. S. Galvagno Dipartimento di Chimica Industriale e Ingegneria dei Material Università degli Studi di Messina Contrada di Dio, 98166 Messina (Italy) Fax: (+ 39) 090391518 ; E-mail : cmilone@ingegneria.unime.it Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201000049. Gold(0) catalysts supported on ferric oxide are effective cata- lysts, and so far, the only heterogeneous ones known for the regioselective hydrogenation of a,b-unsaturated ketones to the corresponding a,b-unsaturated secondary alcohols. A set of ferric oxide samples, synthesized under strictly controlled conditions and thoroughly characterized (X-ray powder diffrac- tion, Mçssbauer spectroscopy, micro-Raman spectroscopy, transmission electron microscopy, temperature-programmed reduction), were employed as supports of gold(0) catalysts for this reaction. The activity and selectivity of the catalysts changed in the same direction from one catalyst to another; increasing fractions of nanostructured ferric oxide phases in the support (with nanoparticles size lower than 10 nm) in- creased both. With a 4 % gold catalyst supported on the ferric oxide sample containing the highest proportion of nano- structured matter, we achieved a selectivity of 66 % towards the unsaturated alcohol at more than 90 % conversion in the hydrogenation of benzalacetone (ethanol, 60 8C, 103 kPa), which is one of the best performances ever reported for this reaction. ChemCatChem 2010, 2, 1143 – 1149  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1143