Interactions of ammonia with platinum and ruthenium surfaces

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1987

OSTI ID:6365993

Tsai, W

Specific reaction rates (cm/sup /minus/2/-s/sup /minus/1/) of the catalytic decomposition of NH/sub 3/, the isotopic exchange between NH/sub 3/ and D/sub 2/, and the inhibition of the decomposition of NH/sub 3/ by H/sub 2/ on a polycrystalline platinum wire have been measured in a continuous stirred tank microreactor at pressures between 5 /times/ 10/sup /minus/7/ and 0.6 Torr and temperatures between 400 and 1200 K. The kinetics of decomposition of NH/sub 3/ as well as the results for the NH/sub 3/ /plus/ D/sub 2/ exchange reaction are described quantitatively by a mechanistic model employing independently measured adsorption-desorption parameters of NH/sub 3/ and H/sub 2/, and desorption parameters of N/sub 2/. The model was extended to incorporate the N/sub 2/ coverage-dependence of the rate coefficient of H/sub 2/ desorption to describe the inhibition of the decomposition by H/sub 2/. The hydrogenation of NH/sub 2/(a) to produce molecularly adsorbed NH/sub 2/ is predicted to be the dominant factor in the inhibition of the decomposition of NH/sub 3/. Steady-state specific reaction rates have also been measured for the catalytic decomposition of NH/sub 3/ on a Ru(001) surface at pressures of 10/sup /minus/6/ and 2 /times/ 10/sup /minus/6/ Torr and temperatures between approximately 500 and 1250 K. The isotopic exchange reaction between /sup 15/NH/sub 3/ and D/sub 2/ at steady-state has been studied on Ru(001) for a partial pressure ratio of NH/sub 3/ to D/sub 2/ of 4:1 with a total pressures of 2.5 /times/ 10/sup /minus/6/ Torr at temperatures between 380 and 720 K. Direct comparison between the estimated barrier for the dissociative adsorption of N/sub 2/ on polycrystalline Pt and Ru(001) surfaces indicates clearly that Ru is a superior catalyst to Pt for the synthesis of ammonia.

• Research Organization: California Inst. of Tech., Pasadena (USA)
• OSTI ID: 6365993
• Country of Publication: United States
• Language: English

Related Subjects

090320* -- Inorganic Hydrogen Compound Fuels-- Preparation-- (1976-1989)
10 SYNTHETIC FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
ADSORPTION
AMMONIA
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPARATIVE EVALUATIONS
CRYSTALS
DECOMPOSITION
DESORPTION
DEUTERIUM
ELEMENTS
HIGH TEMPERATURE
HIGH VACUUM
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROGENATION
ISOTOPES
ISOTOPIC EXCHANGE
KINETICS
LIGHT NUCLEI
MATHEMATICAL MODELS
METALS
NITROGEN
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
NUCLEI
ODD-ODD NUCLEI
PLATINUM
PLATINUM METALS
POLYCRYSTALS
REACTION KINETICS
RUTHENIUM
SORPTION
STABLE ISOTOPES
STEADY-STATE CONDITIONS
SYNTHESIS
TRANSITION ELEMENTS
VERY HIGH TEMPERATURE