Mechanism of ammonia decomposition on (100) oriented polycrystalline tungsten and single-crystal W(100)

Journal Article · Thu May 10 04:00:00 EDT 1984 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j150654a008· OSTI ID:6721526

Reed, A P.C.; Lambert, R M

The interaction of NH/sub 3/ with single-crystal W(100) and (100) oriented polycrystalline W has been characterized by using electron diffraction, Auger spectroscopy, and temperature-programmed reaction measurements. At 300 K chemisorption occurs rapidly (sticking probability approx. = 0.4) with partial decomposition of the adsorbate; the overall decomposition which takes place upon subsequent heating exhibits two distinct stages. At 600 K decomposition (evolving only H/sub 2/) and desorption of NH/sub 3/ become competing processes. Preadsorbed N inhibits the decomposition very efficiently, but preadsorbed H has no such effect; D/sub 2/ and NH/sub 3/ do not appear to compete for a common adsorption site. Rapid equilibration between H (from NH/sub 3/) and coadsorbed D occurs in this regime, although exchange into the N-H bond itself is slow. The stoichiometry of this intermediate surface phase and the mechanism of its subsequent decomposition are investigated. Simultaneous evolution of N/sub 2/ and a small amount of H/sub 2/ occurs above 750 K. The principal pathway for this stage is shown to involve a small amount of NH/sub x/ species in the presence of an otherwise completely dehydrogenated layer. In contradistinction with earlier work, no evidence was found for the presence of stable uniform intermediate phases such as NH or NH/sub 2/; these apparent discrepancies are acounted for. Auger spectroscopy reveals the onset of W nitridation under reaction conditions, and experiments with N/sub 2/H/sub 4/ confirm certain aspects of the mechanism proposed here for NH/sub 3/ decomposition. 23 references, 8 figures.

• Research Organization: Univ. of Cambridge, England
• OSTI ID: 6721526
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 88:10; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

090310* -- Inorganic Hydrogen Compound Fuels-- Properties-- (1976-1989)
10 SYNTHETIC FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
AMMONIA
AUGER ELECTRON SPECTROSCOPY
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
COHERENT SCATTERING
CRYSTALS
DATA
DECOMPOSITION
DIFFRACTION
ELECTRON DIFFRACTION
ELECTRON SPECTROSCOPY
ELEMENTS
EXPERIMENTAL DATA
HIGH TEMPERATURE
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
KINETICS
MEDIUM TEMPERATURE
METALS
MONOCRYSTALS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUMERICAL DATA
POLYCRYSTALS
REACTION INTERMEDIATES
REACTION KINETICS
SCATTERING
SEPARATION PROCESSES
SORPTION
SORPTIVE PROPERTIES
SPECTROSCOPY
STOICHIOMETRY
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TEMPERATURE MEASUREMENT
TRANSITION ELEMENTS
TUNGSTEN
ULTRAHIGH VACUUM
VERY HIGH TEMPERATURE