Decomposition of formic acid on copper, nickel, and copper-nickel alloys. III. Catalytic decomposition on nickel and copper-nickel alloys
Turnover rates for the catalytic dehydrogenation and dehydration of formic acid (HCOOH) on nickel/silica (Ni/SiO/sub 2/) and Ni and copper-nickel (CuNi) powders between 390 and 490 K are reported. The decomposition rate constants calculated from these data are compared with values reported previously for the temperature-programmed decomposition (TPD) of HCOOH preadsorbed on Ni and CuNi. Catalytic dehydrogenation and dehydration seem to proceed through the same intermediate, believed to be a formate ion. The selectivity S, defined as the ratio of dehydrogenation to dehydration turnover rates, is independent of temperature, and between 4 and 6 on Ni and alloys with a surface Cu fraction less than 0.8. The observed selectivity is not affected by secondary reactions among the products. The intermediate appears to be bound to two adjacent Ni atoms. In contrast, TPD or HCOOH preadsorbed at low coverage on CuNi single crystals seems to involve a formic anhydride species that requires four adjacent Ni atoms, and decomposes with S equal to unity and a rate constant 5 x 10/sup 3/ times greater than that corresponding to the catalytic decomposition. This study demonstrated the differences in rate constant and S when reactive intermediates change with surface coverage because they require different ensembles for adsorption; in other words, they are structure sensitive.
- Research Organization:
- Stanford Univ., CA
- OSTI ID:
- 5960427
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 81:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201 -- Chemical & Physicochemical Properties
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACTIVATION ENERGY
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BINARY MIXTURES
CARBOXYLIC ACIDS
CATALYST SUPPORTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMATOGRAPHY
COMPARATIVE EVALUATIONS
COPPER
DATA
DECOMPOSITION
DEHYDROGENATION
DISPERSIONS
ELEMENTS
ENERGY
EXPERIMENTAL DATA
FORMIC ACID
GAS CHROMATOGRAPHY
HIGH TEMPERATURE
INFORMATION
KINETICS
LOW PRESSURE
MEDIUM TEMPERATURE
METALS
MINERALS
MIXTURES
MONOCARBOXYLIC ACIDS
NICKEL
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POWDERS
PRESSURE DEPENDENCE
REACTION INTERMEDIATES
REACTION KINETICS
SEPARATION PROCESSES
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SPECIFICITY
TEMPERATURE DEPENDENCE
THERMAL CONDUCTIVITY
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS