Platinum catalyst deactivation in low-temperature ammonia oxidation reactions. I. Oxidation of ammonia by molecular oxygen. [368 to 473/sup 0/K]
Deactivation of 2.0 to 15 nm Pt crystallites supported on alumina and Pt black was studied in a fixed-bed differential reactor during NH/sub 3/ oxidation by molecular oxygen between 368 and 473/sup 0/K. Marked deactivation caused by surface oxidation took place during the first 12 hr on stream. Deactivation occurred only in the presence of both reactants, and was more severe with smaller crystallites and at lower temperatures. The rate decay was best described by a second-order deactivation process. At 433/sup 0/K oxygen present in the deactivated 2.7 nm crystallites was about 5 atoms per surface Pt atom, giving an estimated bulk composition of PtO/sub 1/./sub 7/. For the 15.5 nm crystallites the oxygen present in the deactivated crystallites was about 7 atoms per surface Pt atom but the resultant bulk composition was PtO/sub 0/./sub 5/. Deactivation was reversible and activity could be restored by raising the temperature above 473/sup 0/K or by reacting with H/sub 2/ or NH/sub 3/. Deactivated catalyst slowly released oxygen in reaction with NH/sub 3/ chemisorbed on the support after the feed O/sub 2/ and NH/sub 3/ were turned off. This is a form of reverse spillover. Platinum black studies confirmed the results with the supported catalysts.
- Research Organization:
- Univ. of Delaware, Newark
- OSTI ID:
- 7142542
- Journal Information:
- J. Catal.; (United States), Vol. 41:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AMMONIA
OXIDATION
PLATINUM
CATALYTIC EFFECTS
DEACTIVATION
ALUMINIUM OXIDES
CHEMICAL REACTION KINETICS
HIGH TEMPERATURE
MEDIUM TEMPERATURE
OXYGEN
QUANTITY RATIO
TEMPERATURE DEPENDENCE
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
CRYOGENIC FLUIDS
ELEMENTS
FLUIDS
HYDRIDES
HYDROGEN COMPOUNDS
KINETICS
METALS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
REACTION KINETICS
TRANSITION ELEMENTS
090310* - Inorganic Hydrogen Compound Fuels- Properties- (1976-1989)