8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 1/11
ELSEVIER
Applied Catalysis B: Environmental 7 ( 1996) 225-235
Catalytic oxidation of sulfide ions over nickel
hydroxides
A. Andreev a,*, P. Khristov a, A. Losev b
’ Institute of Catalysis, Bulgarian Academy of Sciences. 1 I13 Sojia, Bulgaria
’ Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, I1 I3 Sofia, Bulgaria
Received 17 February 1995; revised 10 August 1995; accepted 14 August 1995
Abstract
The catalytic sulfide ion oxidation by oxygen to elemental sulfur over P-Ni( OH) , and LiNiO Z has
been studied. As a result of experimental investigation performed, a reaction mechanism is suggested
which involves heterogeneous and homogeneous processes. Dioxygen activation in the heterogeneous
process proceeds via a redox Ni2+ @ Ni’+
transition and participation of OH- groups. Th e active
HO; species thus formed carries on the reaction in homogeneous phase. Nickel hydroxides are
promising catalysts for practical application.
Keywords:
Oxidation;
Nickel hydroxide; S’- oxidation
1 Introduction
The process of sulfide ion catalytic oxidation to elemental sulfur by oxygen from
air is important for environmental protection. Due to the high toxicity of sulfide
ions, water containing these ions is hardly purified throu gh biological treatment.
However, elemental sulfur is readily removed from waste and natural w ater by
biological treatment. Sulfide ion oxidation in aqueous medium can be successfully
used to manufacture colloidal sulfur on a large scale.
The oxidation process in alkali medium can be represented by the following
equations:
S*- + ;O,+H,O -+ S” +20H-
(1)
or
*
Corresponding author. Tel. ( + 35-92) 7249 01, fax. ( + 35-92) 756 116, e-mail [email protected].
0926 -3373 /96/ 15.0 0 0 199 6 Elsevier Science B.V. All rights reserved
.SSOIO926-3373(95)00045-3
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 2/11
226
A. Andrew et al. /Applied Catalysis B: Environmental 7 (1996) 225-235
HS- + 0, -+ S’+OH-
(2)
Transition metal complexes and some inorganic salts [ l] and transition metal
oxides
[
2,3] have been reported to manifest catalytic activity for that process. A
high catalytic activity for this reaction was found for NiP& and a reaction mecha-
nism has been proposed
[
41. Catalysts based on iron chelate compoun ds
[
5,6] and
cobalt phthalocyanines [ 7-101 have found practical application.
This work p resents results of a study of sulfide ion oxidation to elemental sulfur
in aqueous alkali solution by using a novel type of heterogeneous catalysts: nickel
hydroxides. By means of a set of experimental methods we aimed a t gaining
information about the catalytic reaction mechan ism and the possibilities for appli-
cation.
2. Experimental
2 I Sample preparation
A sample denoted as NH was prepared by precipitation of nickel from an aqueous
solution of Ni( N03)* *6H20 (p.a. grade, 450 g/l) and NaOH (250 g/l), aqueous
solution at 80°C an d pH = 9. After aging for 1 h the slurry was filtered and washed
until the NO , ions were absent and dried at 110°C . The dried sample contained
77.68 wt.-% nickel as NiO and had a BET area of ca. 110 m2/g. The X-ray
diffraction pattern of that sample indicated reflections at 0.46, 0.271, 0.233 and
0.156 nm, specific of /3-Ni( 0H)2, as well as the two most intense reflections at
0.175 and 0.148 nm for NiO
[
111. The NiO content in the sample could be evaluated
at no more than 20%.
Samp le NH/C was prepared by impregnation of activated charcoal (CEC A-
ACLH , BET area = 750 m2/g) with an aqueous solution of Ni( N03) 2. 6H2O , p.a.
grade. Further, NaO H (aqueous solution, 250 g/l) was added at 80°C to attain
pH = 9. After ag ing for 1 h at the same temperature the product was wash ed with
distilled water an d dried at 110°C . The dried sam ple co ntained 3 1.23 wt.-% n ickel
as NiO . We ak a nd very broad reflections for /3-Ni( OH), were observed in the
diffraction pattern which are consistent with a high dispersion of the deposited
phase.
Samp les NH and NH/C were calcined at 400°C for 2 h under inert atmosp here.
They are denoted as NH’ and NH/C ”, respectively. The BET surface area of NH’
was 87 m2/g.
A sample denoted as LN was LiNi02 prepared by calcination of a mixture of
Li20 and NiO and had a BET area of about 2 m2/g. The procedure is described in
detail elsewhere [ 121. The phase identity was verified by means of X-ray diffraction
(reflection at 0.467,0.245,0.235,0.203 and 0.144 nm) [ 131.
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 3/11
A. Andrew et al. /Applied Curalysis B: Environmental 7 (1996) 225-235 227
2.2. Catalytic activity measurements
The catalytic activity in S2- oxidation by oxygen was measured in a static system
under continuous stirring by monitoring the volume of oxygen consumed at 20°C.
Results were checked with a chemical method by determining the sulfide ion
concentration. For this purpose EDTA titration of excess C u2+ ions with respect
to the amount of S2- ions was carried out, the Cu2 + ions being a dded as Cu( Clod) 2
aqueous solution. A Na,S aqueo us solution of 19.47 g/l concentration, 10 ml for
each run, was used. The amoun t of catalyst (very fine powder) was 0.06 g for NH
and NH/C and 0.1 g for LN.
Catalyst activity was expressed as mol S*- converted per gram atom of nickel
(mol S2- /g,, Ni) on comparing supported with unsupported samples . Comparison
between unsupported samples was made by the productivity per 1 m*( mol S2- /
m2). On deducing the temperature dependence of the reaction rate, rate values were
determined as the first derivative of the time dependence of productivity in the
linear part of the curve.
2.3. X-ray diffraction
X-ray diffraction measurem ents were carried out by means of a conventional
powder diffractometer using Cu Ka radiation.
2.4. X-ray photoelectron spectroscopy XPS)
X-ray photoelectron spectra were recorded on an ESCA LAB MK II instrument
using Al Ka excitation source. Corrections related to a charge on the samples were
made with respect to the position of the C 1s peak at 284.6 eV.
2.5. Electrochemical measurements
A nickel hydroxide (NH) containing electrode was prepared by pressing the
powdered material in an insulated platinum holder. The potential difference
between the NH electrode and a calomel electrode was measured. A special glass
cell was used to conduct the measurem ents in which a 10% NaO H a queous solution
was introduced. The cell could be purged with both argon a nd air.
3. Results
3 I Catalytic activity
Fig. 1 shows data on the catalytic activity of the NH and LN samp les. Both
samples exhibit high catalytic activity in reaction ( 1) . The activity of sample LN
was one order of magnitude higher than that of sample NH.
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 4/11
228
A. Andreev et al. /Applied Catalysis B: Environmental 7 (1996) 225-235
1
“E
10
\
T
0
1
x
0.01 ~II:IlIl1’ ‘111,11,ij
0 10
20 30
time [min]
Fig. 1.Catalytic activity of samples NH and LN. (Final conversions: NH-38.5% and LN-16.6%).
These results were confirmed by studies of the temperature dependence of the
reaction rate. The following values were obtained: 8200, 107 00 and 3600 cal/mol
for NH, NH/C and LN, respectively.
Experimental results presented in Fig. 2 shows that calcination of the samples at
400°C caused a considerable decrease in catalytic activity.
A study of the effect of catalyst amoun t on the productivity demonstrated a
striking dependence. Samp les NH and NH /C manifested decreased amoun ts of
converted S2- ions as the amoun t of catalyst was increased (Fig. 3a and Fig. 3b).
3.2. X-ray photoelectron spectroscopy
XPS spectra of the investigated samples are described by stable charging which
allowed the acquisition of narrow and well resolved peaks. Three ranges w ere
scanned: 0 1 s (520-550 eV), Ni 2p (830-880 eV) and S 2p (140-190 eV).
Fig. 4 and Fig. 5 present the 0 1s peaks of fresh and used N H sam ple after
operation under the working conditions of reaction ( 1) . Substantial changes in the
spectrum of the fresh sample are observed after the treatment under the working
conditions, namely, considerable peak broadening and clearly resolved asymm etry.
These findings are good grounds to suggest the occurrence of several surface species
10.0
0.0
time [min]
Fig. 2. Effect of calcination on the catalytic activity of samples NH and NH/C. Catalyst productivity was measured
at 50°C. (Final conversions: NH 38.5%, NH’4.5%, NH/C 31.9% and NH/C’ 6.4%).
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 5/11
A. Andrew et al. /Applied Catalysis B: Environmental 7 (1996) 225-235
229
6.0
N 4.0
:
0
‘;; 2 0
“m
s
E 0 0
15.0
z
s 10.0
\”
A
2 5.0
z
0.0
0
10
20 30
time [min]
Fig. 3. Dependence of the catalytic activity on the catalyst amount with samples NH (a) and NH/C (b) at 50°C.
t
530.00 540.00 55i.00
binding energy [eV]
Fig. 4. 0 Is X-ray photoelectron spectra of fresh NH sample.
524.20
529.20
534.20
539.:
binding energy [eV]
Fig. 5.0 1s X-ray photoelectron spectra of the NH sample after the operation under reaction conditions
from oxygen. By means of computer simulation the experimental curve was pre-
sented as a sum of three comp onents. The first peak, hav ing 530.0 eV binding
energy, can be interpreted as due to nickel oxide ad mixtures
[
14,151 formed on
drying the sample. The second peak w ith 532.3 eV binding energy is determined
by the basic phase, P-Ni( OH), [ 14,161. This result is in agreement with X-ray
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 6/11
230 A. Andrew et al. /Applied Catalysis B: Environmental 7 (1996) 225-23.5
I,, 1/,,,/,,,,,,,,,,,
840.00 850.00 860.00 870.00 880.00
binding energy [eV]
Fig. 6. Ni 2p,,, X-ray photoelectron spectra of sample NH: (a) fresh; (b) after the operation under reaction
conditions.
diffraction data. The third peak, 535.0 eV binding energy, can be attributed to the
presence of oxygen-containing compound of trivalent nickel
[
171. M ost likely, this
is a surface species with NiOOH like structure. Similar b inding energies have been
found in the spectra of the active pha se in nickel batteries where redox transitions
are realized, con ditionally, between Ni( OH), and NiOO H [ 181. The quantitative
ratio between the three components can be evaluated as 30:60: 10.
Argum ents in favour of Ni”’ could be found on recording spectra in the 830-880
eV range. Fig. 6 shows spectra of sample NH in the region of Ni 2p. The relative
decrease in intensity of the satellite pea k and its broadening are consistent with the
presence of Ni”’
[
191.
The XPS spectra of the used LN sample are compatible with considerable
amou nts of Ni”‘.
Fig. 7 shows experimental data in the S 2p region ( 140-190 eV) on a NH sample
treated under working conditions and washe d w ith distilled w ater. The observed
peak at 163.5 eV is assigned to elemental sulfur, S8 [20], which is a reaction
product. Another peak at 168.9 eV is due to the surface SOi- groups [ 211. Small
amou nts of sulfates, b eing also the product of the oxidation, are strongly adsorbed
onto the catalyst surface. It is interesting to note that no emission of sulfide ion
from a surface metal sulfide w as observed at around 162.0 eV
[
191. Weak emission
in that region could not be registered because of the strong peak of elemental sulfur.
150.00 160.00 170.00
binding energy [ eV]
Fig. 7. S 2p,,, X-ray photoelectron spectra of the NH sample after operation under reaction conditions.
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 7/11
A. Andr eev et al. Appl ied Catal ysis B: Envi ronmental 7 1996) 225-235
231
3.3. Electrochemical measurements
The potential difference between a nickel hydroxide containing electrode and a
calomel electrode was measured under controlled atmosphere. Upon purging the
electrochemical cell with argon, a potential difference of about 63 mV was attained.
Adm ission of air caused a shift of the potential to more neg ative values. The air-
argon ‘cycles’ were reversible. They are related to interaction between oxygen and
the nickel hydroxide surface an d the occurrence of electron transition.
4. Discussion
Results of the catalytic activity measurem ents (Fig. 1 and Fig. 2) indicate that
the three samples studied (NH, NH/C and LN) exhibited high catalytic activity in
the oxidation of sulfide ions. The higher activity of sample NH/C , compared to
that of NH, is explained by the higher dispersion of the deposited active com ponent
which was verified by X-ray diffraction.
As was shown by X-ray diffraction phase analysis, P-Ni(O H), was the basic
component in the NH and NH/C samples. The presence of NiO admixtures did not
substantially affect the catalytic activity. Results in Fig. 2 show that thermal treat-
ment of samples NH and NH /C, causing the formation of nickel oxide phase, is
accompanied by a drastic fall in the catalytic activity. The low activity exhibited
by the nickel oxide samples can be interpreted in terms of a partial hydroxylation
of their surface at high alkalinity (pH = 14) of the working medium . This alkalinity
originates from a strong hydrolysis of the sodium sulfide and accumulation of OH-
ions, being the product of reaction ( 1) .
It
is worth noting that according to the XPS study under the reaction conditions
no significant amoun t of sulfide phase is formed on the catalyst surface. Mo st
probably, this is due to a shifted equilibrium to the hydroxide of the surface sulfide
hydrolysis in a strong alka li solution. In this connection an active nickel hydroxide
phase occurs on the surface under reaction conditions, despite the presence of sulfide
ions in the solution.
Based on the above mentioned, one can arrive at the conclusion that the nickel
hydroxide manifests high and stable catalytic activity in sulfide ion oxidation by
oxygen in aqueous solution.
Detailed notion about the active nickel hydroxide phase can be obtained from
XPS data. It is essential that, along with nickel hydroxide, NiOO H like structures
also occur in the working catalyst. This allows to model the catalytic redox process
with a reversible redox transfer between the active species, Ni” t) Ni”‘, like in the
anode phase of nickel batteries
[
221.
The higher catalytic activity of sample LN, compared to that of NH, can be
explained in the following way. Prior to any contact with the reaction medium ,
only trivalent nickel occurs on the surface of that sample. Under the influence of
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 8/11
232
A. Andrew et al. /Applied Catalysis B: Environmental 7 (1996) 225-235
Fig. 8. Absorption spectrum
catalyst bed at 25°C.
18
240
300 360 420
Wavelength [nm]
in the 200-400 nm range of Na,S solution after passing it with air through a NH
the reaction med ium, however, the surface undergoes reduction hydrolysis with the
formation of NiOO H and Ni( OH), like structures
[
231. An optimum ratio between
Ni” and Ni”’ creates favourable conditions for the participation of high amount of
surface nickel ions in the redox transition Ni” ti Ni”‘. A detailed study of LN
samples related to the promising prospect of practical application is now in progress.
The XPS study is consistent with the conclusion that redox Ni” ++ Ni”’ transitions
proceed on the catalyst surface w hich are associated with hydroxide, Ni*+ (OH)*,
and oxyhydroxide, Ni3+O OH, structures.
Electrochemical studies indicated that the catalyst electrode was sensitive to
oxygen from the air. Summ arizing these studies one can draw the conclusion that
a reversible interaction between oxygen and the surface of the nickel hydroxide
electrode in an alkali solution was found w hich is related to the electron transfer
between oxygen and the catalyst.
Special attention should be given to the observed experimental finding of the fall
of the reaction rate on increasing the catalyst amoun t. It is assum ed that sulfide ion
oxidation by oxygen from the air in aqueous solution
[
241 as well as in the presence
of homogeneous catalyst [ 251 proceeds via a chain-radical mechan ism. A similar
mechan ism can operate in the oxidation of sulfide ions in aqueous solution in the
presence of heterogeneous catalysts. If the oxidation reaction proceeds both over
the catalyst surface and with the participation of active species from the solution,
the decrease in the reaction rate upon increasing catalyst amount should be consis-
tent with the destruction of the active sites on the solid catalyst [ 261.
For that reason an attempt was made to determine the active species in the liquid
medium under the conditions of reaction ( 1) . A solution of sodium sulfide w as
circulated with air through a specially designed cell containing the NH sample.
Fig. 8 shows the absorbency in the range 200-400 nm. The observed maxim um
around 290 nm can be ascribed to the HO; ion radical. This species has been
identified upon H202 dissociation in alkali solution
[
271.
Thus the observed antibate dependence of the catalytic activity in reaction ( 1)
on the amount of heterogeneous catalyst is a good reason to propose that the reaction
proceeds both on the surface and with the participation of active species in the
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 9/11
A. Andr eev et al. Appl ied Catal ysis B: Envi ronmental 7 1996) 225-235
233
HETEROGENEOUS PROCESS
(HS- + 02 - s + IiO2_)
HOMOGENEOUS PROCESS
KS- + H02-
- S + 20H-
Scheme 1
solution. Mo st likely, the HO; ion radical is the active species for that reaction.
Based on the experimental results and the conclusions made, a reaction mecha-
nism of sulfide ion oxidation over nickel hydroxide catalysts can be proposed
( Scheme 1) .
According to the experimental data, a steady state of the Ni” hydroxide catalyst
is assum ed, containing certain am ount of Nirn ions bonded to NiOO H-like struc-
tures. The mechan ism involves two processes: heterogeneous and homogeneous.
Considering the heterogeneous process, along with elemental sulfur active HO,
species are formed which carries on the reaction in homogeneous phase. Interaction
between the acid HS and the base O*- of the catalyst leads to an initially reduced
state of the active site.
The heterogeneous mechan ism envisages dioxygen activation through electron
transfer onto the oxygen species via the Ni*+ ++ Ni3+ transition.
Of essential importance is the formation of intermediate species from oxygen, a
hydroxyl group a nd the metal ion (Scheme 2). Such a type of dioxygen activation
with the participation of hydroxyl group has been described for oxidation processes
in aqueous solution with transition metal complex catalysts [ 241.
The Ni( OH), catalyst considered has a layered structure and can be represented
as a package of lamellas
no.
HO\
-
Ni,-
OH
) n.
Trivalent nickel ions
( . . .Ni. . ) are
0
build in the plane of divalent nickel as defects. In this case Na+ ions and water
molecules can intercalate into the interlamellar space thus increasing the interla-
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 10/11
234
A. Andreev et al. /Applied Catalysis B: Environmental 7 (1996) 225-235
Scheme 2.
mellar distance and promoting a highly defective structure. The nickel ions which
participate in catalysis are probably located on ‘edge sites’ at the end of the lamellae
(Scheme 2). W ater intercalation increases the number of defects and ‘edge sites’.
The presence of intercalated Na + ions into the interlamellar space is substantial.
Its considerable potential facilitates the formation of HO; ions.
Recently, a high catalytic activity of the nickel hydroxide catalysts, discussed in
the present work, ha s been reported in the water-gas shift reaction
[
281. Due to
their specific structure, the nickel hydroxides are potential catalysts for a wide range
of oxidative and other processes.
Acknowledgements
The authors are grateful to the Bulgarian National Scientific Research Foundation
for financial support.
References
[ 11 T. Sakano and K. Miyata, Chinetsu Gijutsu, 3 (1978) 35.
[2] C.H. Knight, J.W. Smith and R.A. Barton, Can. Pat. 1 212 819 Al.
[31 A. Andreev, K. Kirilov, V. Ivanova, L. Prahov and E. Manova, in Y.E. Fisher (Editor), NATO AS1 Chemical
Physics of Intercalation II, Series B, Vol. 305, Plenum, New York, 1993, p. 375.
[4] A. Andreev, V. Ivanova, K. Kirilov and G. Passage, Appl. Catal. A, 107 (1994) 189.
[5] H.F. Fang, D.S. Kushner and R.T. Scott, Oil Gas J., 54 March (1982) 169.
[6] Y. Yamamoto, D. Terasaki, H. Uchiola, T. Kojima and W. Izutsu, Aromatikkusu, 34 ( 1982) 152.
[7] K. Chen and J. Morris, Environ. Sci. Technol., 6 (1972) 529.
[
81 M. Hoffman and B. Lim, Environ. Sci. Technol., 13 ( 1979) 1406.
[9] A. Simonov, N. Kundo, E. Mamaeva and L. Akimova, Zh. Prakt. Khim., 50 ( 1977) 307.
[lo] M. Vassileva, A. Andreev, G. Schulz-Ekloff and D. Woherle, React. Kinet. Catal. Lett., 50 ( 1993) 139.
[ 111 H. Bode, K. Dehmeelt and J. Witte, Electrochim. Acta, 11 ( 1966) 1079.
[ 121 A. Lecerf, M. Broussely and J.P. Gabano, EP 0 345 707, US 4 980 080.
[ 131 T. Ohzuku, A. Veda, M. Nogayama, Y. Iwakoshi and H. Komori, Electrochim. Acta, 38 ( 1993) 1159.
[
141 T.L. Barr, J. Phys. Chem., 82 (1978) 1801.
8/16/2019 Catalytic Oxidation of Sulfide Ions Over Nickel
http://slidepdf.com/reader/full/catalytic-oxidation-of-sulfide-ions-over-nickel 11/11
A. Andrew et al. /Applied Catalysis B: Environmental 7 (1996) 225-235 235
[ 151 G.
Tynliev, P. Stefanov and M. Atanasov, J. Electron Spectrosc. Relat. Phenom., 63 ( 1993) 267.
[ 161 KS. Kim and N. Winograd, Surf. Sci., 43 (1974) 625.
[ 171 J. Jindra, I. Kreici, J. Mrha, B. Foekesson, L.Y. Johansson and R. Larsson, J. Power Sources, 13 (1984)
123.
[ 181 H. Bode, K. Dehmelt and J. Witte, Electrochim. Acta, 11 (1966) 1079.
[ 191 B. Nefedov, XPS Spectroscopy of the Chemical Compounds, Chemistry, Moscow, 1984.
[20] H. Rapp and U. Weser, Bioinorg. Chem., 5 ( 1975) 21.
1211 B.J. Lindberg e.a., J. Phys. Scripta, 1 (1975) 286.
1221 P. Oliva, J. Leonard and J.F. Laurent, J. Power Sources, 8 ( 1982) 229.
[ 23 1 .J. Braconnier, C. Delmas, F. Fouassier, M. Figlarz, B. Beaudonin and P. Hagenmuller, Rev. Chim. Minerale,
21 (1984) 496.
[24] K.B. Yatsimirskii, Pure. Appl. Chem., 6 ( 1963) 117.
[25] N.N. Kundo and N.P. Keijer, Kinet. Katal., 9 (1970) 91.
[26] P.G. Ashmore, Catalysis and Inhibition of Chemical Reactions, Buttetworths, London, 1963.
[27] G. Bredig, H.L. Lehmann and W. Kuhn, Z. Anorg. Allgem. Chemie, 218 ( 1934) 16.
[28] A. Andreev, V. Idakiev, K. Kostov and M. Gabrovska, Catal. Lett., 31 ( 1995) 245.