Electrocatalytic reduction of nitrite to ammonia based on a water-soluble iron porphyrin

Journal Article · Wed Sep 17 04:00:00 EDT 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00279a036· OSTI ID:5365477

Barley, M H; Takeuchi, K J; Meyer, T J

In aqueous solution at either pH 4.5 or 6.7, the water-soluble porphyrin (Fe/sup III/(H/sub 2/O)(TPPS))/sup 3 -/ (H/sub 2/TPPS/sup 4 -/ = tetraanonic form of meso-tetrakis(p-sulfonatophenyl)porphyrin) is an effective electrocatalyst for the reduction of nitrite ion to ammonia with hydroxylamine or N/sub 2/O also appearing as significant products, depending upon the reaction conditions. The reductions proceed via the nitrosyl complex (Fe/sup II/(NO/sup +/)(TPPS))/sup 3 -/ as an intermediate. The nitrosyl complex forms at pH < 3.0 by a reaction between the Fe(III) porphyrin and NO arising from disproportionation of HONO or, at 4.0 < pH > 7.0, following reduction of Fe(III) to Fe(II) (E/sub 1/2/ = -0.23 V vs. SSCE) via an acid-base reaction. Reduction of the nitrosyl complex occurs by sequential 1-electron steps at E/sub 1/2/ = +0.35 and -0.63 V vs. SSCE, the second of which is pH-dependent at pH < 2.6. Evidence for a third 1-electron step has been found by differential pulse polarography at pH 2.1. The first two reductions are followed by a multiple-electron wave which is greatly enhanced as the pH is decreased from 4 to 2.6. Although NH/sub 3/ is the ultimate reduction product at -0.9 V, NH/sub 2/OH appears to be an intermediate stage in the reduction and electrolysis to the 2-electron stage at -0.63 V gives increasing yields of N/sub 2/O. The redox properties of the nitrosyl complex and probable mechanism of reduction of NO/sub 2//sup -/ to NH/sub 3/ are discussed and compared with earlier results obtained on polypyridyl complexes of Os and Ru.

• Research Organization: Univ. of North Carolina, Chapel Hill
• OSTI ID: 5365477
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:19; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

090320* -- Inorganic Hydrogen Compound Fuels-- Preparation-- (1976-1989)
10 SYNTHETIC FUELS
AMMONIA
AQUEOUS SOLUTIONS
CARBOXYLIC ACIDS
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL PREPARATION
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
COMPLEXES
DATA
DISPERSIONS
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
IRON COMPLEXES
MIXTURES
NITRITES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PH VALUE
PORPHYRINS
REACTION INTERMEDIATES
REDUCTION
SOLUTIONS
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
YIELDS