Ethyl acetate production from water-containing ethanol catalyzed by supported Pd catalysts: Advantages and disadvantages of hydrophobic supports

Selective oxidation of water-containing ethanol in the presence of excess e thanol provides a onestep preparation of ethyl acetate. Acetic acid is form ed from the oxidation of ethanol catalyzed by a supported Pd catalyst and i s further catalytically esterified to ethyl acetate by the protons dissocia ted from acetic acid. The difference of the catalytic performance between h ydrophilic and hydrophobic Pd catalysts was investigated by a continuous fi xed-bed reactor run at 95 degrees C, 35.4 atm, and a air/ethanol molar rati o of 2.37. The experimental results indicated that, after the induction per iod, the conversion of ethanol catalyzed by a styrene-divinylbenzene copoly mer (SDB)-supported Pd catalyst is more than 20 times that catalyzed by a g amma-alumina-supported Pd catalyst at a weight hourly space velocity (WHSV) of 2.4 h(-1). However, it may be caused by weak metal-support interactions and the formation of palladium(II) acetate during the reaction. For the Pd /SDB catalysts, the Pd clusters were leached out concomitantly with the gro wth of Pd particles. Inductively coupled plasma (ICP) optical emission spec troscopy characterizing the fresh and used catalysts shows that about 10% o f Pd was leached after 60 h on stream. Extended X-ray absorption fine struc ture (EXAFS) spectroscopy results further indicate that the average particl e size of the Pd clusters on SDB support increases from 6 to 20 Angstrom.