SURFACE-CHEMISTRY OF HYDRAZINE ON PT(111)

The thermal decomposition of hydrazine, N2H4, 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 N-H, not N-N, bonds. In TPD, H2, NH3, and N2 all peak near 310 K. N2 and NH3 desorb in processes limited by the rates of the reactions forming them. N2 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 N-H cleavage. We propose that: (1) the low temperature N-H bond cleavage and the retention of N-N bonds are facilitated by the chemisorption of N2H4 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 N-H cleavage is lowered much more than the barrier to N-N cleavage, and the former is preferred.