Ultrasonic irradiation as activity and selectivity improving factor in the hydrogenation of cinnamaldehyde over Pt/SiO 2 catalysts Gyo Èrgy Szo Èllo Èsi a , Be Âla To Èro Èk b , Gerda Szakonyi c , Istva Ân Kun a , Miha Âly Barto Âk a,b,* a Department of Organic Chemistry, Jo Âzsef Attila University, Szeged, Hungary b Organic Catalysis Research Group of the Hungarian Academy of Sciences, Do Âm te Âr 8, H-6720 Szeged, Hungary c Department of Biochemistry, Albert Szent-Gyo Èrgyi University, Medical School, Szeged, Hungary Received 10 February 1998; received in revised form 10 February 1998; accepted 7 April 1998 Abstract The effect of ultrasounds on the platinum-catalyzed hydrogenation of cinnamaldehyde was studied in the liquid phase over Pt/SiO 2 , Pt/Al 2 O 3 , Pt/C and EuroPt-1 catalysts under mild experimental conditions (333 K, 1 atm H 2 ). The sonochemical pretreatment was found to be highly bene®cial for the selective formation of cinnamyl alcohol (up to 80%) over silica- supported catalysts, besides the signi®cant reaction rate increase (two-fold increase). The actual changes of the catalysts were studied by transmission electron microscopy, and the mechanistic interpretation of the sonochemical effect is also given. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Ultrasounds; Hydrogenation; Cinnamaldehyde; Transmission electron microscopy; Particle size morphology 1. Introduction The chemo- and regioselective catalytic hydroge- nation of a,b-unsaturated carbonyl compounds is one of the most active research areas in catalysis research to produce ®ne chemicals [1,2]. Cinnamaldehyde, one of these compounds, is of great practical importance: both the aldehyde and its semi-hydrogenated products (the unsaturated alcohol and the saturated aldehyde) are widely used in perfume industry. In addition, cinnamyl alcohol has an important role as a useful synthon in synthetic organic chemistry [2]. The selec- tive synthesis of unsaturated alcohols including cin- namyl alcohol, however, is dif®cult to achieve despite the extensive efforts to develop suitable catalysts [3± 11]. The most successful attempts were carried out in the presence of osmium [4], iridium [5] and bimetallic platinum catalysts [6]. Due to their importance and potential these hydrogenation reactions are still in the forefront of recent catalysis research [7] including the preparation of new catalysts [8±10] or their modi®ca- tion by adding metal salts [11]. Although, the best selectivity for the cinnamyl alcohol formation is as high as 94%, the catalyst preparation requires the addition of GeCl 4 and special conditions [3](a). Applied Catalysis A: General 172 (1998) 225±232 *Corresponding author. Address: Organic Catalysis Research Group of the Hungarian Academy of Sciences, Do Âm te Âr 8, H-6720 Szeged, Hungary. Fax: 0036 62 322 668; e-mail: bartok@chem.u-szeged.hu 0926-860X/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0926-860X(98)00132-X