ADSORPTION AND AUTOCATALYTIC DECOMPOSITION OF ACETIC-ACID ON PD(110)

The adsorption and decomposition of acetic acid has been studied on Pd(110) using temperature-programmed desorption (TPD). On the clean surface, the acid dissociates to form a stable acetate, and hydrogen is desorbed at 300 K. Some of the acetate then decomposes at around 353 K to yield CO2 and H-2 into the gas phase and leaves adsorbed carbon. The latter stabilises some of the acetates and results in the desorption temperatures being increased by as much as 100 K. Oxygen pre-dosing leads to changed characteristics including stabilisation of the acetate in a manner which produces an autocatalytic acetate decomposition, a 'surface explosion'. In this way, mixed surface layers can be obtained showing characteristics of the clean surface acetate, the carbon-contaminated acetate and the oxygen-induced explosion. A model based on atomic adsorbate-induced ordering of the acetate layer is used to describe the autocatalytic decomposition.