Oxygen adsorption on Au/Al2O3 catalysts and relation to the catalytic oxidation of ethylene glycol to glycolic acid

Static oxygen adsorption and hydrogen pulse titration of chemisorbed oxygen were checked and successfully used as tools for characterisation of the dispersity and surface area of Au/Al2O3 catalysts tested in the oxidation of ethylene glycol. Using a stoichiometry of Au-s:O = 2 a good agreement was obtained between the average gold particle size calculated from oxygen chemisorption results and the particle size preferentially observed by TEM. A correlation of the catalytic activity with the oxygen adsorption of Au/Al2O3 catalysts having different An dispersity and content showed a steady increase of the rate of the glycolic acid formation with increasing oxygen chemisorption and Au surface area, respectively. No differences in the selectivity of the reaction were observed with low- and high-disperse Au/Al2O3 catalysts, a selectivity to glycolic acid higher than 95% was obtained on all the samples. Therefore, we could clearly demonstrate that the selective oxidation of ethylene glycol to glycolic acid is not a structure-sensitive reaction, i.e. this reaction is not restricted to a defined gold particle size, as for example in the epoxidation of propylene over Au/TiO2. (C) 2002 Elsevier Science B.V. All rights reserved.