Reaction of [Pd(NH3)4]Cl2 with NH 4ReO4 in alkaline water solution at 190°C (autoclave process)

Article abstract of DOI:10.1134/S1070363211080019

A reaction of tetraammine palladium(II) chloride with ammonium perrhenate in aqueous alkaline solution in the autoclave conditions was studied. The possible routes of the palladium and rhenium reduction with ammonia were suggested. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1070363211080019

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 8, pp. 1579–1582. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.I. Zarazhevskii, V.V. Grebnev, E.V. Fesik, G.D. Mal’chikov, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 8,
pp. 1233–1236.
Reaction of [Pd(NH3)4]Cl2 with NH4ReO4
in Alkaline Water Solution at 190°C (Autoclave Process)
V. I. Zarazhevskii, V. V. Grebnev, E. V. Fesik, and G. D. Mal’chikov
Korolev Samara State Aerospace University, Moskovskoe sh. 34, Samara, 443086 Russia
e-mail: malchikow.chem@mail.ru
Received July 8, 2010
Abstract—A reaction of tetraammine palladium(II) chloride with ammonium perrhenate in aqueous alkaline
solution in the autoclave conditions was studied. The possible routes of the palladium and rhenium reduction
with ammonia were suggested.
DOI: 10.1134/S1070363211080019
The results of studies of chemical reactions of
ammonia–chloride complexes of noble and nonferrous
metals in water and alkaline solutions at elevated
temperatures (above 100°C) gave rise to the
development of a method of the autoclave thermolysis
for the synthesis of metal systems (powders, sols, and
the coatings of different materials) [1–4].
with NH4ReO4 contains three phases: palladium metal,
rhenium metal, and rhenium dioxide.
Table 2 summarizes the experimental results of the
determination of free ammonia and shows that its
content in the system corresponds to 24–30% of the
total value.
Based on product composition of this process, the
following pathways of the oxidation–reduction
reactions are presumable:
The process of autoclave thermolysis is based on an
irreversible reduction of the complexing metal ion by
its inner-sphere ammonia to afford the metal [5].
Reduction of rhenium
[М(NH3)4–iCli]2–i + 2 OH–
ReO–4 + 4H+ + 3е⎯ → ReO2 + 2 H2O,
→ М0 + 1/3N2 + (10/3-i)NH3 + iCl– + 2 H2O,
М = Pd, Pt, Rh, Ir, Ru, Co, Ni, Cu, etc.
(1)
ReO–4 + 8H+ + 7е⎯ → Re0 + 4 H2O.
Oxidation of ammonia
The products of autoclave thermolysis of complex
mixtures of different metal ammoniates are the solid
polymetallic precipitates [6, 7]. Studies of solid-state
thermal transformations of the double salts containing
complex cations and anions of different metals
performed in [8–10] resulted in obtaining metallic
phases.
2 NH3 + 6е⎯ → N2 + 6H+,
NH3 + H2O + 5е⎯ → NO + 5H+,
NH3 + 2 H2O + 7е⎯ → NO2 + 7H+.
Oxidation of ammonium
2 NH4+ + 6е⎯ → N2 + 8H+,
NH+4 + H2O + 5е⎯ → NO + 6H+,
NH+4 + 2 H2O + 7е⎯ → NO2 + 8H+.
This paper presents the results of studying the
reaction of [Pd(NH3)4]Cl2 with NH4ReO4 in alkaline
medium in the autoclave conditions at 190°C. We
assumed that like the reaction (1), the ammonia in
statu nascendi, as well as Pd2+, may behave as reducing
agents for rhenium.
These combined half-reactions can provide various
modes of perrhenate ion reduction with ammonia,
which differ by the products formed:
NH4ReO4 → NO2 + Re + 2 H2O,
5 NH4ReO4 → 3 NO + 5 ReO2+ 7 H2O + 2 NH3,
2 ReO–4 + 6 NH3 → 2N2 + ReO2+ 6 H2O + Re.
The phase composition of the solid reaction product
was determined by X-ray phase analysis. The results
listed in Table 1 show that the solid product of the
autoclave thermolysis of the mixture of [Pd(NH3)4]Cl2
Reduction of palladium from its complex
compounds with ammonia proceeds in an alkaline
1579

1580
ZARAZHEVSKII et al.
Table 1. X-ray characteristics of the solid autoclave thermolysis product of the [Pd(NH3)4]Cl2–NH4ReO4 mixture
Pd phase
ReO2 phase
Re phase
d, Å (exp)
2.421
2θ, deg I, % d, Å (exp) d, Å (ASTM) 2θ, deg I, % d, Å (exp) d, Å (ASTM) 2θ, deg I, %
d, Å (ASTM)
2.388
40.25 100
2.238
1.943
1.37
2.23
1.94
1.371
1.17
1.12
26.3
31.4
46.7
53.0
76.4
81.4
40
80
50
30
20
30
3.386
2.846
1.943
1.726
1.245
1.181
3.401
2.865
1.946
1.701
1.262
1.203
37.1
40.25
42.7
68.4
76.4
82.3
30
30
46.7
68.4
82.3
86.8
50
30
30
10
2.238
2.226
100
20
2.116
2.105
1.17
1.37
1.38
1.121
20
1.245
1.262
20
1.17
1.173
Table 2. Experimental values of the initial amount of reactants (based on metal and ammonia) and free ammonia experi-
mentally measured
Free NH3
Pd:Re
Assumed equation in
Table 3
Run no.
Pd, g
Re, g
ΣNH3, g
(atomic)
g
0.0140
0.0113
0.0121
0.0121
0.0090
0.019
%
1
2
3
4
5
6
7
8
0.057
0.057
0.057
0.057
0.057
0.1
0.1
0.1
1:1
1:1
0.0459
0.0459
0.0459
0.0459
0.0425
0.0728
0.0728
0.0728
30.5
4, 6
24.6
26.4
26.4
21.2
26.1
30.8
27.5
The same
0.1
1:1
''
0.1
1:1
''
0.066
0.1
0.1
0.1
1.5:1 (3:2)
1.75:1
1.75:1
1.75:1 (7:4)
5
(4), (6)
The same
''
0.1
0.0224
0.020
0.1
medium in the autoclave conditions according to the
equation:
the most closely, as the amount of free ammonia (%)
agrees well with experimental data obtained after
titration of free ammonia (Table 2 ).
3[Pd(NH3)4] + 6KOH → 3Pd + N2 + 10NH3
+ 6H2O + 6KCl.
Comparing the data in Tables 1–3, we assume that
two probable reaction equation are the most ap-
propriate to describe the process of autoclave thermo-
lysis of the mixture of complex salts [Pd(NH3)4]Cl2–
NH4ReO4: (i) Autoclave reduction at the parallel
occurrence of reactions (4) and (5). (ii). Autoclave
reduction along Eq. (6).
The fact that the reaction products are palladium
and rhenium metals, and rhenium dioxide, suggest
many versions of equation for the processes of
reduction of the [Pd(NH3)4]Cl2–NH4ReO4 mixture in
alkaline medium in the autoclave conditions. The most
plausible, as we believe, are the equations listed in
Table 3. Table 3 shows also the atomic ratio of metals,
the total number of ammonia molecules before the
reaction, the number of molecules of free ammonia
and its percentage with respect to the total number of
molecules in the corresponding reaction.
Based on the above experimental data we give
preference to the reaction Eq. (6).
EXPERIMENTAL
We used tetraammine palladium(II) dichloride
synthesized as described in [11], ammonium per-
As seen from the data of Table 3 the hypotheses
described by Eqs. (4)–(6) match the experimental data
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 8 2011

REACTION OF [Pd(NH3)4]Cl2 WITH NH4ReO4
1581
Table 3. Presumed versions of the reduction process in [Pd(NH3)4]Cl2–NH4ReO4 mixture
Equations
Free NH3
10
Possible reactions
Pd:Re
1:3
ΣNH3
no.
(1)
NH4ReO4 + 3 [Pd(NH3)4]Cl2 + 6 KOH →
3Pd0 + Re0 + N2 + 10 NH3 + 8 H2O + NO2 + 6 KCl
13
73
(2)
(3)
(4)
(5)
(6)
6 NH4ReO4 + 3 [Pd(NH3)4]Cl2 + 6 KOH →
3:6 (1:2)
6:11
18
35
14
36
23
2
14
4
11
3Pd0 + 6Re0 + 8N2 + 2 NH3 + 30 H2O + 6 KCl
11 NH4ReO4 + 6 [Pd(NH3)4]Cl2 + 12 KOH →
6Pd0 + 5 ReO2 + 6Re0 + 9N2 + 14 NH3 + 43 H2O + 3 NO + 12 KCl
40
2 NH4ReO4 + 2 [Pd(NH3)4]Cl2 + 4 KOH →
2Pd0 + 2Re0 + 3N2 + 4 NH3 + 4 KCl + 12 H2O
2:2 (1:1)
28.6
22.2
26.1
12 NH4ReO4 + 6 [Pd(NH3)4]Cl2 + 12 KOH →
6Pd0 + 10Re0 +13N2 + 8 NH3+ 12 KCl + 2 ReO2 + 54 H2O + 2 NO
6:12
(1:2)
8
7 NH4ReO4 + 4 [Pd(NH3)4]Cl2 + 8 KOH →
4Pd0 + 6Re0 +8N2 + 6 NH3 + 8 KCl + ReO2 + 33 H2O + NO
4:7
6
rhenate and potassium hydroxide (reagent grade) were
commercial chemicals.
DRON-2.0 diffractometer (λCoKα = 1.79 Å, Ua = 20 kV,
Ia = 20 mA, υcount = 2°/min). The diffraction pattern
assignment was carried out using the ASTM database
[13].
Experiments were carried out in fluoroplastic
autoclaves according to the methods previously des-
cribed in [1–5]. Weighed samples of salt [Pd(NH3)4]Cl2
and NH4ReO4 were added to a solution of potassium
hydroxide of required concentration, which is then
saturated with nitrogen to prevent side reactions with
oxygen. The autoclave with the alkaline solution of a
mixture of salts [Pd(NH3)4]Cl2 and NH4ReO4 was
sealed and kept at a temperature of 190°C for 150 min
while stirring. After the specified time the autoclave
was quickly cooled to room temperature, and the
solution was frozen to reduce the loss of free ammonia
contained in the system. Content of ammonia after the
reaction was determined by acid-base titration. The
procedure is described in detail in [12]. The amount of
free ammonia in the system was calculated from the
results of titration and compared with the theoretical
amount of ammonia calculated according to the
assumed reaction equation. The close values of the
theoretical and experimental masses of free ammonia
indicate the validity of the suggested stoichiometry of
the reaction of palladium and rhenium salts.
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