This document summarizes research on the catalytic hydrogenation of aqueous nitrate over iron/carbon (Fe/C) catalysts. Key points: - Batch and continuous reactor experiments show that Fe/C catalysts can effectively reduce nitrate in water to nitrogen gas with high selectivity and activity. Up to 2.9 mmol/gmetal/min nitrate reduction rate was achieved in batch tests. - Column studies demonstrate the catalyst can reduce nitrate levels below 5 ppm from an initial 100 ppm concentration, with a breakthrough capacity of over 530 bed volumes to reach 45 mg/L. - Characterization with XRD, SEM-EDAX and XPS confirms the presence of iron dispersed on the

1. Catalytic Hydrogenation of Aqueous Phase Nitrate
Over Fe/C Catalysts
Anshu Shukla Æ Jayshri V. Pande Æ Amit Bansiwal Æ
Petre Osiceanu Æ Rajesh B. Biniwale
Received: 17 December 2008 / Accepted: 6 February 2009 / Published online: 26 February 2009
Ó Springer Science+Business Media, LLC 2009
Abstract Catalytic hydrogenation of nitrate in water has
been carried out over Fe/C catalysts at ambient temperature
using batch and continuous reactors. In batch reaction
nitrate reduction activity of 2.9 mmol gmetal
-1
min-1
with
nearly 100% selectivity towards nitrogen was obtained.
Column study shows nitrate reduction below 5 ppm for an
initial concentration of 100 ppm. Break through capacity, to
reach concentration of 45 mg L-1
, is more than 530 bed
volumes. The catalysts were characterized using XRD,
SEM–EDAX and XPS. With high selectivity and activity
the catalytic system in present study could be a potential
option for nitrate removal from water.
Keywords Catalytic hydrogenation Á Fe/C catalyst Á
Water treatment Á Nitrate
1 Introduction
High level of nitrate concentration in surface run-off water
has ecological impacts resulting into eutrophication of water
bodies. Nitrates are inorganic pollutants, whose mobility
and stability make them highly dangerous in aerobic sys-
tems such as ground water [1]. High nitrate concentration
causes severe methemoglobinemia (7–27% of Hb) in all age
groups, especially in the age group of less than 1 year and
above 18 years [2]. The conversion of nitrate to nitrite in
digestive system leads to the formation of nitroso com-
pounds, which are potential carcinogens [3]. Several
methods reported for nitrate removal including physico-
chemical processes such as ion exchange, electrodialysis,
reverse osmosis, and microbiological denitrification; have
associated economical and ecological disadvantages [4].
Catalytic hydrogenation of nitrate is ecologically acceptable
solution as aqueous nitrate converts to harmless N2, unlike
adsorption or membrane processes. Further, there is no
sludge formation during catalytic hydrogenation. The
reduction of aqueous nitrate by using hydrogen or formic
acid as reducing agents over a solid catalyst offers an eco-
nomically advantageous alternative process to biological
treatments as a means of purifying drinking water streams
and industrial effluents [5, 6]. In this process, nitrates are
converted via intermediates to nitrogen in a single reactor
system and at near ambient conditions. Palladium based
bimetallic catalysts are most reported catalysts for aqueous
phase hydrogenation of nitrate. Cu and Sn have been
reported as promoters for enhancing the catalytic activity of
Pd [5, 7]. The commonly used supports for these metal
catalysts are alumina, silica, zirconia, titania, activated
carbon and niobia. Similarly unsupported zero valent iron
under acidic condition is found to be effective for nitrate
reduction [8–10]. However, as reported the rate of nitrate
reduction rapidly decreases as the oxidation state of zero
valent iron changes into Fe2?
and Fe3?
retarding the rate of
reaction [11]. Recently, several monometallic and bimetal-
lic catalysts supported on activated carbon have been
compared for reduction of nitrate and nitrite. Based on the
screening of several monometallic catalysts namely Pt, Pd,
Cu, Sn, Ru, Rh, Ni, Ir, Fe and Zn it is reported that Ru/C
exhibits considerable activity and Fe/C shows relatively low
activity for nitrate reduction. Whereas all other
A. Shukla Á J. V. Pande Á A. Bansiwal Á R. B. Biniwale (&)
National Environmental Engineering Research Institute
(NEERI), CSIR, Nagpur 440020, India
e-mail: rb_biniwale@neeri.res.in; rajeshbiniwale@yahoo.com
P. Osiceanu
Institute of Physical Chemistry, Romanian Academy of Science,
Ile Murgulescu, Spl. Independentei 202, 060021 Bucharest,
Romania
123
Catal Lett (2009) 131:451–457
DOI 10.1007/s10562-009-9899-9

2. monometallic catalysts supported on carbon are inactive for
nitrate reduction. Most of the catalysts for selective reduc-
tion of nitrate are bimetallic catalysts [12]. The present study
deals with preparation, characterization and evaluation of
monometallic Fe catalyst supported on activated carbon
(Fe/C) for selective reduction of nitrate in water. Although
relatively low activity of conversion of 3% is reported in the
literature results obtained in our present study exhibits rel-
atively better activities for nitrate reduction particularly
under the reaction conditions in this work.
2 Materials and Methods
2.1 Catalyst Preparation
Fe/C catalysts were prepared by adsorption method. Acti-
vated carbon granules (E-Merck Germany, size ca.
1.0 mm) with BET surface area of ca. 800 m2
g-1
were
used as support. The activated carbon granules were stirred
with solution of FeCl3 in acetone for 24 h and subsequently
filtered and dried in oven at 100 °C. The catalysts were
heated at 450 °C in nitrogen flow for 6 h to achieve loading
of metal on activated carbon by decomposition of metal
salt.
2.2 Catalyst Characterization
Powder X-ray diffraction pattern obtained did not show any
peak this may be attributed to high surface area and
amorphous nature of support the metal presence was
unidentified. The scanning electron microscopy–energy
dispersive X-ray analysis (SEM–EDXA) analysis con-
firmed the presence of metal over activated carbon. The
oxidation states of the surface iron were identified by X-ray
photoelectron spectroscopy (XPS) technique. XPS mea-
surements were performed on a Vacuum Generators VG-
ESCALAB 250 photoelectron spectrometer by using
monochromatic AlKa radiation (hm = 1,486.6 eV). The
pressure of the XPS analysis chamber during the mea-
surement was 8 9 10-9
Pa and the energy resolution
measured as FWHM of the Ag 3d5/2 peak was 0.5 eV. All
the spectra were corrected by subtracting a Shirley—type
background and the binding energies (BEs) were practi-
cally uncorrected as the carbon 1 s photoelectron line was
very close to the internal reference value of 284.6 eV.
2.3 Catalytic Hydrogenation
Catalysts were tested using batch and continuous reactors.
Details of batch reactor are shown in Fig. 1a. Batch
experiments were performed using a glass reactor equipped
with a magnetic stirrer, inlet for introducing H2/N2 mixture,
thermocouple for monitoring temperature and arrangement
for withdrawing samples.
The known amount of catalyst was taken in the reactor
containing 250 mL de-ionized water. The content of the
reactor was flushed with nitrogen flow for 45 min to remove
excess oxygen. Hydrogen was used as a reducing agent. The
flow rates of hydrogen and nitrogen were maintained at 25
and 50 mL min-1
, respectively by mass flow controllers.
Nitrate solution (100 mL) with 350 ppm concentration has
been added to achieve the concentration in the reactor equal
to 100 ppm and total volume to 350 mL. The column tests
were performed using a glass column (10 mm diameter and,
50 mm length). The schematic diagram of column setup is
shown in Fig. 1b. The catalysts were packed upto 50 mm
height (catalyst weight of 1.68 g). The void volume in the
packed bed was estimated to be 0.125. A peristaltic pump
was used for feeding of nitrate solution in upflow mode. The
Peristaltic
pump
Nitrate
contaminated
water
Mass flow
controller
H2 + N2
Treated
water
Fe/AC Catalyst
Sampling
Port
H2 +N2
Thermocouple
Diffuser
Hot Plate and
Magnetic
Stirrer
Magnetic
Stirring Bar
Funnel for
feeding nitrate
solution
(b)
(a)
Fig. 1 Experimental setup for the reaction a batch mode b
continuous mode
452 A. Shukla et al.
123

3. co-current upward flow of hydrogen (diluted in N2) and
nitrate solution was provided to avoid flooding condition. In
a separate experiment, to detect the nitrogen in product gas,
feed of hydrogen diluted in helium was used. The product
gas analysis was carried out using TCD-GC (Shimadzu
2014, porapack Q column, 6 ft. length packed column).
Analysis of samples for concentration of nitrate was per-
formed using a Dionex model ICS-3000 ion chromatograph
equipped with Dionex Ionpac AG11-HC guard column and
AS11-HC separation columns, 25 lL sample loop and
conductivity detector. A 30 mM KOH was used as eluent at
flowrate of 1.0 mL min-1
. Nitrite was also determined
using the same configuration. For analysis of ammonium in
selective samples, same system was used in combination
with AG5 and AS5 cation exchange guard and separation
column, respectively. A 6 mM methanosulphonic acid was
used as eluent for cation analysis. Hydroxylamine was
detected using a reported spectrophotometer method [13].
Wherein, a 1000 lg mL-1
hydroxylamine stock solution
was prepared by dissolving 0.2106 g of hydroxylamine
hydrochloride (E-Merck) in distilled water. A 0.047 mol
L-1
iodate solution was prepared by dissolving KIO3 (E-
Merck) in distilled water. Similarly, a solution of
3.46 9 10-4
mol L-1
neutral red was also prepared by
diluting 0.1 g of neutral red in 100 ml distilled water.
Sulfuric acid solution of concentration of 3.0 M was pre-
pared by diluting 1.64 mL of H2SO4 (98%, sp. gravity 1.84)
distilled water. An aliquot of 1.0 mL of sample was taken to
which 1.0 ml of iodate solution was added followed by
1.0 mL sulfuric acid solution; the mixture was allowed to
stand for 5 min at room temperature. Then 2 mL of neutral
red solution was added as an indicator and the change in
absorbance was monitored on spectrophotometer at 525 nm
for 0.5–5 min after the addition of neutral red.
3 Result and Discussion
3.1 Catalyst Characterization
Due to the amorphous nature of activated carbon and very
high surface area, powder X-ray diffraction pattern of Fe/C
catalyst does not show any intense peak, which can be
assigned to Fe. The presence of Fe metal over the surface of
catalyst was therefore, confirmed by SEM–EDXA method.
SEM micrograph and EDXA pattern for fresh catalyst are
shown in Fig. 2a, b, respectively. The EDXA result reveals
the presence of chloride, oxide, iron and carbon. For the
given area in the SEM, the atomic % of C, O, Fe, and Cl
were 84.33, 8.87, 1.45 and 3.63, respectively. This indicates
that the metal is well dispersed over the support [6].
Impurities of about 1.72% were observed assigning peaks to
Al and Si which was not expected in the sample.
The survey analysis during XPS confirms the elements
present on the surface as C, O, Fe and Cl only. The surface
elemental composition and the relative concentrations on
fresh catalyst are presented in Table 1. The high resolution
XPS spectrum of iron is shown in Fig. 3. It is well known
that XPS spectra of iron oxides exhibit a characteristic
shake-up satellite structures by accompanying the Fe
(2p3/2, 2p1/2) main peaks on their high binding energies
side. XPS measurements on a standard Fe(III) oxide, grade
99.9995 ? %, (Alfa Aesar) show a quite similar spectrum
in shape and binding energies as that recorded for catalyst
sample. In case of fresh catalysts, the binding energy of
about 711.0 eV for the most intense Fe 2p3/2 peak is
consistent with typical values for the ferric oxides (Fe
3 ? oxidation state) reported in the literature [14]. This
(a)
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
001
0
80
160
240
320
400
480
560
640
720
800
Counts
CKa
OKaFKa
AlKa
SiKa
ClKa
ClKb
FeLlFeLa
FeKesc
FeKa
FeKb
(b)
Fig. 2 Characterization data for 5 wt% Fe/C catalyst a SEM b
EDXA
Table 1 XPS analysis peak identification and estimated elemental
contents on surface of fresh catalyst
Photoelectron line Peak binding
energy (eV)
Element
concentration (at. %)
Fe2p3/2 711 1.65
O1 s 530 6.67
C1 s 284 88.89
Cl2p3/2 198 2.79
Nitrate Reduction Over Fe/C Catalysts 453
123

4. confirms that the iron is present in its 3 ? oxidation state
without any contribution from 2 ? oxidation state or ele-
mental Fe for the fresh catalyst sample. In the case of used
catalysts Fe 2p3/2 peaks at the Binding Energy values of
711.0 and 709.4 eV were observed indicating presence of
3 ? and 2 ? oxidation states of Fe on the surface. The
ratio Fe2?
to Fe3?
species was 1:2.7.
The presence of Cl segregated from the bulk to the top
monolayer is the main reason for observed lower percent-
age of Fe under 2% in comparison with the intended bulk
value of 5%. The presence of chlorine is due to FeCl3 salt
used for synthesis of catalysts. The XPS spectrum of
oxygen exhibits a ‘‘band-like’’ profile instead of the well
known sharp peak at around 530.5 eV characteristic to its
bonding in the ferric oxide as a result of some traces of OH
groups adsorbed and C=O bonds on the surface. The
apparent disagreement between the quantitative element
concentrations (at. %) determined by XPS and EDXA
originates in their different detected volume as the XPS is a
very surface sensitive method.
3.2 Effect of Metal Loading
Effects of variation of metal loading on activated carbon for
catalytic activity towards hydrogenation of nitrate were
conducted in batch experiments. The percentage loading of
Fe was varied as 2, 5, 10, and 20 wt% on activated carbon.
The catalyst dose was kept at 5 g L-1
. The nitrate hydro-
genation batch reactions were conducted as described in
materials and methods section. In all these reactions pH was
observed in the range of 3.3–3.4. Flows of H2 and N2 were
maintained at 25 and 50 mL min-1
, respectively. A blank
experiment was carried out in similar conditions with bare
activated carbon which shows reduction in nitrate concen-
tration from 100 to 84 ppm (i.e., 0.33 mmol g-1
of
activated carbon), which can be attributed to adsorption on
activated carbon. The net catalytic activity in all subsequent
experiment was estimated as difference between total
activities minus nitrate adsorption on activated carbon.
Blank experiment in the presence of only hydrogen was
conducted and no nitrate reduction was observed. Figure 4
depicts variation in catalytic activity with respect to dif-
ferent metal loadings. In case of 2 wt% Fe/C catalyst the
nitrate concentration reduced from 100 to 65 ppm (net
catalytic activity of nitrate reduction 1.95 mmol gme-
tal
-1
min-1
). Whereas at Fe loading of 5, 10 and 20 wt% the
final concentrations of nitrate in treated water at 60 min
from start of reaction were observed to be 48, 55, 57 ppm,
respectively. As listed in Table 2 corresponding catalytic
activity (net activity after deducting contribution by
adsorption on activated carbon) were 2.9, 2.8, and
1.2 mmol gmetal
-1
min-1
, respectively. The catalytic activity
has increased when Fe loading increased from 2 to 5 wt%
due to increase in number of active sites. At higher Fe
loadings, 10 and 20 wt%, probably the dispersion of cata-
lyst was relatively low and therefore activity of catalysts
was low. The optimal loading of Fe is therefore about
Fe 2p
2200
2300
2400
2500
2600
2700
2800
700710720730740
Counts/s
Binding Energy (eV)
Fig. 3 The Fe 2p XPS spectrum for 5 wt % Fe/C fresh catalyst
0
0.5
1
1.5
2
2.5
3
3.5
0 10 20 30 40 50 60
Time (min)
Nitrateconverted(mmolg-1
metalmin-1
)
2 wt% Fe/AC
5 wt% Fe/AC
10 wt% Fe/AC
20 wt% Fe/AC
Fig. 4 Variation in catalytic activity of Fe/C at different metal
loading
Table 2 Catalytic activity of various Fe/AC catalysts
Catalyst Conversion of
nitrate (%)
Catalytic activity
(mmol gmetal
-1
min-1
)
2 wt% Fe/AC 35 1.95
5 wt% Fe/AC 52 2.9
10 wt% Fe/AC 45 2.8
20 wt% Fe/AC 43 1.2
454 A. Shukla et al.
123

5. 5 wt% and was used in further experiments. In a recent
study nitrate removal by zero valent iron [15] using CO2 as
a buffer (pressure of CO2 = 300 K Pa) at pH 5.7 with
catalyst dose of 33 g L-1
the nitrate removal of 85 wt% is
reported. Corresponding catalytic activity for nitrate
reduction in this report is 1.4 mmol gmetal
-1
min-1
. Whereas
in another study the catalytic conversion of 3% (in 5 h
period) of nitrate from initial concentration of 100 ppm in
volume of 800 mL with catalyst dose of 0.5 g L-1
over
1 wt% Fe/C has been reported [12]. This corresponds to
catalytic activity of 0.038 mmol gmetal
-1
min-1
at pH of 5.5.
When compared with reported catalytic activity the catalyst
in present study exhibits better nitrate removal activity of
1.5 mmol gmetal
-1
min-1
at pH of 5.0 and 2.95 mmol gme-
tal
-1
min-1
at pH 3.3 over Fe/C. This indicates that Fe/C
catalyst, prepared in the present study, exhibits excellent
catalytic activity. In the case of Fe, oxidation states Fe3?
and Fe2?
are easily interchangeable. A scheme of mecha-
nism of nitrate reduction is shown in Fig. 5. The Fe3?
on the
catalysts surface may be changed to Fe2?
by oxidation of H2
being bubbled into the reactor. Iron in Fe2?
oxidation state
is known to act as reducing agent. This reduces the nitrate to
nitrogen and converts back to Fe3?
. The XPS analysis
confirms the presence of only Fe3?
species on the surface of
the fresh catalysts. XPS analysis of used catalyst exhibits
the presence of both Fe3?
and Fe2?
species. Therefore the
reduction of nitrate can be explained by above mechanism
involving reduction of Fe3?
to Fe2?
within reactor.
3.3 Effect of pH Variation
After adding catalyst (5 wt% Fe/C) to D.I. water the initial
pH was 3.3. Since the hydrogenation reaction for nitrate is
effective at lower pH, all the reactions were performed
under acidic conditions. Figure 6 depicts that at pH of 2.1
and 5.0 the nitrate was reduced from initial concentration
of 100 ppm to final concentration of 77 and 74 ppm (with
corresponding net catalytic activity of 1.2 and
1.5 mmol gmetal
-1
min-1
). The nitrate conversion at pH 3.3
was found to be 3.0 mmol gmetal
-1
min-1
with concentration
reduction to 49 ppm. This indicates the optimal pH for
hydrogenation of nitrate in present system is 3.3.
3.4 Effect of Dose Variation
The dose of catalyst (5 wt% Fe/C) was varied as 1.0, 5.0
and 8.0 g L-1
. With the dose of 1.0 g L-1
the nitrate
reduction was relatively low with final concentration of
treated water reducing to 87 ppm from initial concentration
of 100 ppm (catalytic activity 0.6 mmol gmetal
-1
min-1
).
Similarly, with dose of 5 and 8 g L-1
the nitrate converted
was almost same with final concentration in treated water as
48 and 47 ppm (catalytic activity 2.9 and 2.8 mmol gme-
tal
-1
min-1
), respectively. Therefore, a dose of 5.0 g L-1
was preferred for further studies.
3.5 Effect of Initial Concentration
The effect of initial concentration on the reaction was
studied using initial nitrate concentrations of 25, 50, 100,
150 ppm. Without adjustment, pH was observed to be 3.3
for all the reactions. At high initial concentrations the
reaction is spontaneous as compared to at lower concen-
trations. The nitrate reduction is therefore a surface
saturation phenomenon wherein with higher initial con-
centration the nitrate removal increases.
3.6 Effect of Hydrogen Flow Rate
The flow rate of hydrogen was varied as 10, 20 and
25 mL min-1
to study the effect on nitrate reduction. From
results obtained with hydrogen flow rate of 10 and
20 mL min-1
, the nitrate conversion to final concentration
of 62.3 and 56.2 ppm (catalytic activity 2.0 and
2.5 mmol gmetal
-1
min-1
) was observed. With 25 mL min-1
the nitrate was effectively removed upto 48 ppm
(2.9 mmol gmetal
-1
min-1
).The results clearly show that there
is an effect of introducing hydrogen into the reaction media.
The nitrate reduction is directly proportional to hydrogen
flow rate. This can be attributed to efficient reduction of
ad3NO
2N
3
Fe
2H
aq3NO
2
Fe
Fig. 5 Mechanism of nitrate reduction
0
0.5
1
1.5
2
2.5
3
3.5
pH
Nitrateconverted(mmolg
-1
metal.min
-1
)
2.1 3.3 5.0
Fig. 6 Effect of pH on catalytic activity with 5 wt% Fe/C catalyst
Nitrate Reduction Over Fe/C Catalysts 455
123

6. Fe3?
to elemental state in presence of excess H2 and
therefore better catalytic reduction of nitrate.
3.7 Kinetics of the Reaction
In order to study long-term catalytic activity a batch study
for 5 h was performed. A 350 mL nitrate solution of
100 ppm concentration was used with catalyst dose of
1.75 g L-1
. From the observed phenomena, the catalytic
activity is relatively high in first 1 h and retards with
increase in time. The nitrate conversion after 1 h was
3.47 mmol gmetal
-1
min-1
. At the end of 5 h the same activity
of 3.47 mmol gmetal
-1
min-1
was maintained with final con-
centration of nitrate as 41 ppm. The graph of natural log of
rate of nitrate reduction, ln (-rA) verses natural log of
concentration, ln (con) was plotted. The observed results
reveal that the reaction follows pseudo first order with rate
constant as 1.38 9 10-3
min-1
for nitrate reduction over
5 wt% Fe/C.
3.8 Column Studies
Nitrate solution with 100 pmm concentration was passed
through a packed column containing the 5 wt% Fe/C cata-
lyst (1.68 g) in up flow mode at the rate of 10 mL min-1
.
The hydrogen and nitrogen flow rates were maintained as 3
and 6 mL min-1
. The reduction in nitrate concentration
with respect to time is shown in Fig. 6. With catalyst bed
volume of 3.85 cm3
, the breakthrough, reaching outlet
concentration to 45 mg L-1
, was observed at 110 min,
which is equivalent to 490 bed volumes. The nitrate con-
version rate was observed as 0.077 mmol gmetal
-1
min-1
at
107 min where concentration of nitrate was observed to be
35.8 ppm. The pH of outlet stream of water throughout the
reaction was constant around 3.0. The pH of treated water
was neutralized by addition of 0.1 N alkali solutions. The
bed was saturated after 220 min. The graph in Fig. 7 also
show the result for 7.7 cm3
of volume of packed column.
For which breakthrough was observed at 150 min, which is
equivalent to 530 bed volumes. The advantage of using
7.7 cm3
columns was that the nitrate concentration was
observed to be less than 5 ppm for first 100 min. The nitrate
conversion rate at 135 min was 0.037 mmol gmetal
-1
min-1
with nitrate concentration for treated water as 3 ppm. The
bed was saturated after 255 min. From the results of column
study, it is evident that the nitrate reduction is more effec-
tive when volume of the reactor is 7.7 cm3
. This is due to
increased contact time as compare to column of 3.85 cm3
bed volume.
As the system was assumed to be operated as plug flow
column and at steady state condition the following rate
equation has been used:
r ¼
Cin À C
h
ð1Þ
Where Cin, C is inlet and outlet concentration of nitrate
solution, and h is the hydraulic retention time (HRT). HRT
has been calculated taking into consideration the void vol-
ume of the catalyst bed. With column diameter 10-2
m and
length of 5 9 10-2
m, the rate was observed to be
3,462 mmol m-3
min-1
for HRT of 0.049 min (ca. 3 s).
Similarly, with column diameter of 10-2
m and length of
0.1 m the rate of nitrate removal was found to be
1,927 mmol m-3
min-1
for HRT of 0.083 min. The
observed trend is due to inverse relation between HRT and
rate of nitrate reduction. The empty bed contact time
(EBCT) for the column has been calculated as 0.33 min.
The concentration of nitrate in treated water is well below
WHO guidelines of 45 mg L-1
. The pH of outlet water is
relatively low at 3.3–3.5. This indicates the need of a neu-
tralization step downstream to column. With pH
adjustment, a potential catalytic system for nitrate removal
is demonstrated in continuous mode.
3.9 Selectivity of Catalysts
In order to establish the selectivity of the catalysts for
reduction of nitrate to nitrogen product gas was analyzed in
a separate experiment wherein H2 and He mixture was used
as feed to the reactor instead of H2 and N2. The outlet gases
were monitored using GC-TCD, which confirms the pres-
ence of N2 in the outlet stream. During the reaction there
was formation of nitrite (partially reduced product) as an
intermediate only upto first 5 min of reaction during batch
reaction. However, there was no nitrite formation observed
during continuous mode reaction. No ammonium was
detected in the samples. Similarly, no nitrite was observed
after 5 min of reaction in batch reaction. There was no
0
20
40
60
80
100
120
0 50 100 150 200 250 300 350
Time (min)
Nitrateconcentration(mgL
-1
)
Reactor with L = 4.9 cm
(5 wt%Fe/AC )
Reactor with L = 10 cm
(5 wt% Fe/AC)
Reactor with L = 4.9 cm
(bare activated carbon)
Fig. 7 Break through curves for nitrate removal in continuous mode
456 A. Shukla et al.
123

7. formation of hydroxylamine as determined by spectropho-
tometric method described in experimental section. The
overall selectivity towards the nitrogen was nearly 100%.
3.10 Effect of Other Ions on Catalytic Activity
The presence of hydroxides and carbonates (0.01 M)
increases the pH (10.6 and 8.8, respectively) and force to
precipitate out the iron from the support. Therefore, the
catalyst was not found to be effective in presence of
hydroxides and carbonates. Further modification of the
catalysts, such as designing new stable catalyst using
mixed metal oxide as support, is under progress to over-
come this limitation.
4 Conclusions
Monometallic Fe/C catalyst has been developed for effec-
tive hydrogenation of nitrate. The catalyst in this study
exhibits considerable activity of 1.5 and 2.95 mmol gme-
tal
-1
min-1
at pH of 5.0 and 3.3, respectively. The
selectivity towards the formation of nitrogen over Fe/C
catalysts is nearly 100%. There was no formation of nitrite,
ammonium or hydroxylamine. The main feature of this
work is selective reduction of nitrate on monometallic
catalysts.
Acknowledgments Authors would like to gratefully acknowledge
the financial support from Rajiv Gandhi National Drinking Water
Works Mission, Ministry of Rural Development, New Delhi. We also
acknowledge Dr. B. Sreedhar, scientist, Indian Institute of Chemical
Technology, Hyderabad for carrying out XPS analysis.
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Nitrate Reduction Over Fe/C Catalysts 457
123