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Photocatalytic generation of hydrogen by 1:12 heteropolytungstates with concomitant oxidation of organic compounds

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic00197a037· OSTI ID:5528634
;
1:12 heteropolytungstates with the Keggin structures PW/sub 12/O/sub 40//sup 3 -/, SiW/sub 12/O/sub 40//sup 4 -/, FeW/sub 12/O/sub 40//sup 5 -/ and H/sub 2/W/sub 12/O/sub 40//sup 6 -/ undergo multielectron photoreduction in the presence of a great variety of organic reagents in near-visible and UV light. Photoaddition of electrons drives the redox potential to more negative values sufficient to reduce, from a thermodynamic point of view, hydrogen ions in the presence of a Pt catalyst. It turns out that hydrogen is produced in the presence and absence of Pt. Photoreduction proceeds to the extent that the rate of photoreduction matches the back-reoxidation by H/sup +/. The reduction step at which this takes place depends on the tungstate used. Thus, for instance, with PW/sub 12//sup 3 -/ this happens at a higher reduction step than H/sub 2/W/sub 12//sup 6 -/, which is reduced at more negative reduction potentials. When Pt catalyst is present, the reduction potential at which the steady-state H/sub 2/ evolution is obtained is less negative. Average rate constants, from all four tungstates, of H/sub 2/ evolution at the steady state were (5.6 +/- 3.1) x 10/sup -4/ and (2.6 +/- 1.8) x 10/sup -4/ s/sup -1/ with and without Pt, respectively. The efficiency of H/sub 2/ production is of the order of one molecule of hydrogen per 100 photons absorbed. The low yield represents the low efficiency of photoproduction of higher reduction products. For PW/sub 12/O/sub 40//sup 3 -/ the quantum yields of photoaddition of the first and second electron are ca. 0.15 and 0.01, respectively. 13 references, 2 figures, 3 tables.
Research Organization:
N.R.C. Democritos, Athens, Greece
OSTI ID:
5528634
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 24:3; ISSN INOCA
Country of Publication:
United States
Language:
English

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Related Subjects

08 HYDROGEN
080106 -- Hydrogen-- Production-- Biosynthesis & Photochemical Processes
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
EFFICIENCY
ELEMENTS
EXPERIMENTAL DATA
HYDROGEN
HYDROGEN PRODUCTION
INFORMATION
KINETICS
METALS
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDATION
PHOTOCHEMICAL REACTIONS
PLATINUM
PLATINUM METALS
REACTION KINETICS
REDOX POTENTIAL
REDUCTION
REFRACTORY METAL COMPOUNDS
SPECTRA
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
TUNGSTATES
TUNGSTEN COMPOUNDS
ULTRAVIOLET SPECTRA
VISIBLE SPECTRA