Thermal desorption study of the acetic acid decomposition on clean Ni/Cu(110) alloy surfaces

The decomposition of acetic acid was studied on a clean Ni/Cu(110) alloy single crystal by means of thermal desorption spectroscopy. The primary alloy surface composition employed in this work was 37% Ni and 63% Cu as measured by Auger electron spectroscopy. Acetate was the predominant surface intermediate observed, giving rise to the CO₂ and H₂ decomposition products observed, in analogous fashion to the decomposition of formic acid. Surface carbon residue was also detected and could be driven into the bulk by annealing the sample above 900 °K. The rate constant for the decomposition of the acetate intermediate on the alloy was found to be 10^13.5 exp(?33(kcal/mol)/RT)sec^?1. The autocatalytic decomposition of both carboxylic acids previously observed on a clean Ni(110) surface was totally suppressed. The product distribution from acetic acid observed on both the 37% Ni/65% Cu alloy and the carburized Ni(110) surfaces were very similar, indicating chemical similarities between these two surfaces. At high coverages of the acetate intermediate the activation energy for CO₂ formation increased by 14 kcal/gmol. This effect was attributed to strong attractive interactions in the adsorbate layer.