Reactions and reaction intermediates on iron surfaces: II. Hydrocarbons and carboxylic acids

The reactions of hydrocarbons and carboxylic acids on Fe(100) were studied by temperatureprogrammed reaction spectroscopy (TPRS) and X-ray photoelectron spectroscopy (XPS). Adsorbed methyl groups were observed to be stable surface intermediates formed from CH₃Cl adsorption. The methyl groups reacted to form H₂ and surface carbide; the rate of this reaction was given by −dσ_CH3 /dt = (8 × 10¹² s⁻¹)σ_CH3 exp(− 110 kJ/mole/RT). TPRS results did show that oleflns formed stable surface intermediates, though no definitive identification was possible from the studies reported here. Carboxylic acids were found to form stable carboxylate intermediates, which decomposed by first-order kinetics to form H₂ and either CO₂ or CO and adsorbed oxygen. The rates for formate and acetate decomposition were −dσ_HCOO/dt = (7 × 10¹³s⁻¹)σ_HCOOexp (−130 kJ/mole/RT), −dσ_CH3COO/dt = (8 × 10¹³s⁻¹)σ_CH3COOexp(−140 kJ/mole/RT). The stability of surface formates on various metal surfaces were compared and shown to correlate with the oxygen metal bond strength.