Photocatalytic reduction of hydrazine to ammonia catalysed by [RuIII(edta)(H2O)]- complex in a Pt/TiO2 semiconductor particulate system

Article abstract of DOI:10.1016/S1381-1169(99)00291-5

The illumination of aqueous suspensions of Pt/TiO₂ semicondutor photocatalyst with [Ru^III(edta)(H₂O)]^- led to the reduction of hydrazine to ammonia. Coordination of hydrazine to [Ru^III(edta)(H₂O)]^- lowered the energy barrier significantly for the reduction of hydrazine. The rate controlling step of photocatalytic process was probably a surface chemical step (electron transfer) possibly coupled with adsorption of reactants and desorption of ammonia molecule. A working mechanism involving the formation of a [(Ru^III(edta)(N₂H₅)] species (adsorbed onto TiO₂ surface) that underwent two-electron transfer reduction followed by cleavage of the N-N bond of coordinated hydrazine was proposed.

Full text of DOI:10.1016/S1381-1169(99)00291-5

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Journal of Molecular Catalysis A: Chemical 154 2000 1–3
www.elsevier.comrlocatermolcata
Photocatalytic reduction of hydrazine to ammonia catalysed
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by Ru edta H2O complex in a PtrTiO2
semiconductor particulate system
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Debabrata Chatterjee
Chemistry Section, Central Mechanical Engineering Research Institute, Mahatma Gandhi AÕenue, Durgapur 713209, India
Received 29 March 1999; accepted 20 July 1999
Abstract
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Illumination of aqueous suspensions of PtrTiO2 semiconductor photocatalyst in the presence of Ru edta H2O
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resulted in the reduction of hydrazine to ammonia. A working mechanism involving the formation of a Ru edta N2H5
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species adsorbed onto TiO2 surface which undergoes two-electron transfer reduction followed by cleavage of the N–N
bond of coordinated hydrazine has been suggested. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Photocatalysis; Hydrazine reduction; Platinumrtitania; Ru–edta complex; Ammonia
III
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earlier 6,7 . The idea of introducing Ru -
1. Introduction
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edta H2O in TiO2 semiconductor particu-
late system was to examine that how the system
behaves in presence of the complex that can
Interest in ammonia photoproduction by a
TiO2 semiconductor particulate system was ini-
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essentially provide a coordination site through
rapid aquo-substitution for hydrazine to un-
tiated by Scrauzer and Guth 1 . The results
were followed by several reports on photo-
.
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reduction of N2 to NH3 2–5 . However, the
mechanism of the photoprocess, which involves
several intermediates, is not well documented.
Hydrazine is reported to be one of the interme-
diate which undergo two-electron reduction
followed by N–N bond cleavage to yield ammo-
nia in the dinitrogen reduction process. Cataly-
dergo reduction thus lowering the activation
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barrier and can form a surface complex with
TiO2 semiconductor particle through the pedant
carboxylate group. The present paper reports the
results of photocatalytic reduction of hydrazine
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to ammonia in presence of Ru edta H2O
complex.
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tic ability of Ru edta H2O in electro-
chemical reduction of hydrazines was reported
2. Experimental
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The complex K Ru HEDTA Cl was pre-
pared and characterized by following the proce-
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1381-1169r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
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PII: S1381-1169 99 00291-5

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D. ChatterjeerJournal of Molecular Catalysis A: Chemical 154 2000 1–3
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Fig. 1. Formation of NH3 with irradiation time see Section 2 for reaction conditions .
1
My sy1 at 258C, pHs3.1 6 . A series of
control experiments were performed in order to
examine the catalytic ability of complex 1 to-
wards reduction of hydrazine to ammonia. The
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x
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dure reported earlier 8 . K Ru HEDTA Cl
rapidly gets aquated when dissolved in water
and predominantly exists in its most labile form
.
complex 1 in the pH range
3–6 9 . Semiconductor grade TiO2 Degussa
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x
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Ru edta H2O
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y
5
yield of ammonia 1.98=10
mol hy1 is
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p25 was loaded with platinum 4% by follow-
shown in Fig. 1. No ammonia was detected in
the absence of any one of the following: UV-
light, hydrazine or PtrTiO2. Rate of formation
of ammonia was found to be low in absence of
complex 1. The decline in yield was observed
after 5 h. This may be due to deactivation of
TiO2 powder caused by the physico-chemical
change during the course of irradiation. A re-
covery of the activity was achieved by heating
the TiO2 photocatalyst obtained by filtration
at 5508C in presence of air. Based on the above
experimental results the following working
mechanism is developed reminiscent of the
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ing the procedure reported by Erbs et al. 10 .
All other chemicals used were of A.R. grade.
Double-distilled water used throughout the stud-
ies. In a typical photocatalytic experiment a
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reaction mixture 100 ml containing 300 mg of
PtrTiO2 photocatalyst, 25 mg of complex 1
q
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0.25 mmol and 1.0 mmol of hydrazine N2 H5
HSO4y was irradiated at 390 nm with a 250 W
Xe lamp. The pH of the reaction mixture was
kept at 3.1. Aliquots of the reaction mixture
were withdrawn at a chosen intervals of time
and subjected to spectrophotometric analysis
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indophenol blue method for NH3. Spectral
measurements were carried out with a GBC
complex 1 catalysed electrochemical reduction
of hydrazine for the photoreduction of hydra-
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Cintra 10 spectrophotometer.
zine to ammonia.
TiO2 360 nm TiO eyCB qhqVB
1
Ž .
2Ž
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3. Results and discussion
y
RuIII edta H O qN2 Hq5
The N2 Hq5 reacts with Ru edta H2O
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2
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complex 1 to produce Ru edta N2 H5
RuIII edta N H qH2O
2
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2
5
complex 2 in a stopped-flow scale ks0.48

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D. ChatterjeerJournal of Molecular Catalysis A: Chemical 154 2000 1–3
3
RuIII edta N H q2eyCB
sorption of reactants and desorption of ammonia
molecule.
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.
2
5
2
y
RuI edta N H
3
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Ž .
2
5
2
y
RuI edta N H
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5
4. Conclusion
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RuIII edta NH
yqNH3
4
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2
In conclusion, the salient indication of the
present study is that complex 1 acts as an
efficient catalyst to effect the photoreduction of
hydrazine to ammonia. Coordination of hydra-
zine to complex 1 lowers the energy barrier
substantially for the reduction of hydrazine. The
possible significance of the results of the pre-
sent work with respect to the use of a water-
soluble metal complex that can bind dinitrogen
2
RuIII edta NH
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.
2
Hq
RuIII edta H O yqNH3
5
Ž .
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.
2
H 2O
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.
Upon illumination at 390 nm the electrons
are generated in the conduction band of the
TiO2 semiconductor photocatalyst which are
channelled through the pre-deposited platinum
Ž .
or its reduced intermediate s in a kinetically
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to the surface adsorbed chemisorbed through
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preferred pathway is implied.
uncoordinated carboxylate group Ru edta -
III
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x
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N2 H5 formed in the reaction between Ru -
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complex and hydrazine to pro-
edta H2O
2
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Acknowledgements
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duce Ru edta N2 H5
intermediate which
subsequently undergoes N–N bond cleavage
The author is thankful to Sri Hardyal Singh,
Director of this institute for his encouragement
and kind permission to publish this work.
coupled with intramolecular electron transfer
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two-electron transfer process to produce
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one molecule of ammonia and Ru edta -
2
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2y
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x
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NH2
species. The Ru edta NH2
species further hydrolyses to give another
molecule of ammonia and complex 1 back in
the system. The basis of the proposed
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