A study on the synthesis of diethyl oxalate over Pd/alpha-Al2O3 catalysts

The synthesis of diethyl oxalate from ethyl nitrite and carbon monoxide was studied in a continuos flow micro fixed-bed reactor at atmospheric pressur e. Two palladium catalysts supported on alpha -Al2O3 of different pore stru ctures were studied under mild conditions. One catalyst (1 wt.% Pd/alpha -A l2O3-1) showed higher catalytic activity and selectivity than the other cat alyst (1 wt.% Pd/alpha -Al2O3-2). X-ray diffraction patterns have confirmed that both supports are well-defined alpha -Al2O3. Palladium dispersions we re greater on the 1 wt.% Pd/alpha -Al2O3-1 catalyst than that on the 1 wt.% Pd/alpha -Al2O3-2 catalyst as determined by hydrogen chemisorption. The FT IR spectroscopy study indicated that the 1 wt.% Pd/alpha -Al2O3-1 catalyst adsorbed CO easily in the Linear form (band at 2089 cm(-1)) and bridge form (bands at 1950 and 1880 cm(-1)), and as carbonate species (at 1628 cm(-1)) . There was little CO adsorption on 1 wt.% Pd/alpha -Al2O3-2. The average p ore size of the support alpha -Al2O3-1 was 41.6 Angstrom, and 14.0 Angstrom for alpha -Al2O3-2 This study reveals that the pore structure of the suppo rts remarkably affects the palladium dispersion of the catalysts and alters the CO adsorption behavior, therefore, dramatically affect the catalytic p erformance. In the case of CO + C2H5ONO reactions, diethyl oxalate was effi ciently formed over the 1 wt.% Pd/alpha -Al2O3-1 catalyst. (C) 2001 Elsevie r Science B.V. All rights reserved.