Adsorption and Decomposition of Hydrazine on Carbon Monoxide-Modified Pt(111) Surfaces

The decomposition of hydrazine has been studied on a CO-modified Pt(111) surface. Hydrazine decomposition on the clean Pt(111) surface proceeds with a maximum rate at 310 K and an apparent first-order activation energy of approximately 18.7 kcal/mol. Decomposition results in the formation of nitrogen, hydrogen, and ammonia. Coadsorbed carbon monoxide inhibits hydrazine decomposition by increasing the decomposition temperature. No new reaction products are observed. At a carbon monoxide coverage of 0.43 ML, the maximum hydrazine decomposition rate occurs at 340 K with an apparent activation energy of 20.6 kcal/mol. The hydrazine decomposition product distribution on the CO-modified surface is shifted to favor ammonia production, relative to the 2:1 ammonia/nitrogen ratio observed for decomposition on the clean surface. The order of coadsorption does not affect the desorption spectra for partial CO coverages. The observed shift in product distribution and lack of dependence on order of exposure indicate that hydrazine decomposition is not mediated by a multihydrazine surface complex. A simple reaction mechanism consistent with the data and previous studies is proposed. Hydrazine dehydrogenation is postulated as the rate-limiting step common to nitrogen and ammonia formation. Since hydrazine decompostion products desorb below the CO desorption temperature, no perturbation in the CO desorption spectra is observed.