Abstract
The thermal decomposition of hydrazine, N 2H 4, adsorbed on a Pt(111) surface at 60 K has been investigated by temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and temperature programmed secondary ion mass spectroscopy (TPSIMS). Condensed multilayer and chemisorbed states of hydrazine can be distinguished. Submonolayer hydrazine coverages start to decompose between 150 and 200 K by dissociation of NH, not NN, bonds. In TPD, H 2, NH 3, and N 2 all peak near 310 K. N 2 and NH 2 desorb in processes limited by the rates of the reactions forming them. N 2 is formed by an intramolecular process. No nitrogen containing species are detected above 400 K in HREELS or XPS. Depending on the surface coverage and temperature, dihydrogen desorption is probably limited by both the recombination rate and the rate of NH cleavage. We propose that: (1) the low temperature NH bond cleavage and the retention of NN bonds are facilitated by the chemisorption of N 2H 4 through both nitrogen atoms, and (2) relative to the N-metal bond, the H-metal bond is stronger on Pt(111). As a result, the barrier to NH cleavage is lowered much more than the barrier to NN cleavage, and the former is preferred.
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