Solid-Phase Reaction of Tetraammineplatinum(II) Chloride with Ammonium Heptamolybdate

Article abstract of DOI:10.1134/S1070363220060134

Abstract: The solid-phase reaction of [Pt(NH₃)₄]Cl₂ and (NH₄)₆Mo₇O₂₄ under argon in the temperature range from 50 to 500°C was studied by thermal analysis and mass spectrometry.

Full text of DOI:10.1134/S1070363220060134

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 6, pp. 1020–1024. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Obshchei Khimii, 2020, Vol. 90, No. 6, pp. 929–934.
Solid-Phase Reaction of Tetraammineplatinum(II) Chloride
with Ammonium Heptamolybdate
a,
a
b
c
E. V. Fesik *, T. M. Buslaeva , T. I. Melnikova , and L. S. Tarasova
a
MIREA—Russian Technological University (Lomonosov Institute of Fine Chemical Technologies), Moscow, 119571 Russia
b
Non-Profit Partnership “Promoting Chemical and Environmental Education,” Moscow, 101848 Russia
c
Krasnoyarsk Scientific Center Federal Research Center, Siberian Branch, Russian Academy of Sciences,
Krasnoyarsk, 660036 Russia
*
e-mail: 1707-fesik@mail.ru
Received February 15, 2020; revised February 15, 2020; accepted February 27, 2020
Abstract—The solid-phase reaction of [Pt(NH ) ]Cl and (NH ) Mo O under argon in the temperature range
3
4
2
4 6
7
24
from 50 to 500°C was studied by thermal analysis and mass spectrometry. According to the X-ray powder diffrac-
tion, X-ray photoelectron spectroscopy, and elemental analysis data, the product consists of ordered Pt Mo phase
3
with an insignificant amount of molybdenum(VI) oxide. The described reaction is accompanied by reduction of
2
+
the metals, which is promoted by Pt ions in the presence of ammonia.
Keywords: platinum, molybdenum, thermal analysis
DOI: 10.1134/S1070363220060134
Two- and multi-component solid-phase syntheses
and ordered Pt Cr phase, respectively [12]. In the reaction
x y
of materials possessing new physical, chemical, and
functional properties have attracted much attention
with ammonium perrhenate under similar conditions, no
reduction to rhenium metal is observed, and a mixture
[1–11], and chemical methods of synthesis of powders
of Pt and ReO is formed [13]. These results are very
2
with different compositions are mainly discussed.
Materials based on the platinum–molybdenum system
consistent with the data of [3] where CuPt, NiPt, CoPt,
and other bimetallic alloys were prepared by adding a
mixture of metal salts to a solution of octadecylamine
at 180°C.
[4–11] are used as supported catalysts in the oxidation
4] and hydrogenation of carbon monoxide [5],
[
dehydrogentation of hydrocarbons [6, 7], electrochemical
oxidation of methanol in an alkaline electrolyte [8, 9],
reforming [10], and cracking [11].
We have studied the solid-phase reaction of
tetraammineplatinum(II) chloride with ammonium
heptamolybdate under argon in the temperature
range from 50 to 500°C with the goal of obtaining
fine platinum–molybdenum bimetallic powders.
According to the thermogravimetric analysis data,
the reaction includes five steps with six endothermic
effects. The low-temperature endothermic effect
with its maximum at 95.5°C is accompanied
Platinum–molybdenum bimetallic powders are
commonly prepared by thermal decomposition of
platinum and molybdenum compounds and/or their
mixtures after joint or successive impregnation of an
appropriate porous support (carbon, oxide, ceramic,
etc.), followed by drying and calcination in a reducing
atmosphere [4–11]. Usually, H [PtCl ]·6H O, [Pt(NH ) ]
2
6
2
3 4
by an insignificant weight loss (1.3%, Δmtheor =
Cl ·H O, (NH ) Mo O ·4H O, Na MoO ·2H O, and
2
2
4 6
7
24
2
2
4
2
1.35%). It corresponds to elimination of two water and
two ammonia molecules, which were detected in the
gaseous phase by mass spectrometry. In the temperature
range 200–300°C, the DSC curve showed a broadened
double endothermic peak at 265.2/278.3°C, which is
likely to arise from decomposition of [Pt(NH ) ]Cl
MoO (C H O ) are used as precursors to platinum–
2
5
7
2 2
molybdenum systems
The solid-phase reactions of tetraammineplatinum(II)
chloride with ammonium chromate and dichromate in
an inert atmosphere in the temperature range from 50 to
3
4
2
5
00°C give Pt Cr metal solid solution [a = 3.9271(6) Å]
via removal of two ammonia molecules with the formation
1–x
x
1
020

SOLID-PHASE REACTION OF TETRAAMMINEPLATINUM(II) CHLORIDE
1021
Table 1. Combined thermal and mass spectrometric analysis of a mixture of [Pt(NH ) ]Cl and (NH ) Mo O and assumed
3
4
2
4 6
7
24
compositions of solid intermediate products
Temperature, °C
Weight loss Δm, %
Compound
Stage Temperature
m
no.
range, °C
(compound)
gas
phase
DTG
92.4
DSC
95.5
experimental calculated
solid phase
Pt Mo O Cl N H
22 24 52 158
1
50–200
1.3
1.35
17 (NH3)
2NH3
12
7
1
8 (H O)
2H O
2
2
2
200–300
229.2
228.8
265.2
278.3
11.2
11.20
17 (NH3)
32NH3 Pt Mo O Cl N H
12 7 20 24 20 58
2
2
62.5
77.3
18 (H O)
2H O
2
2
Σ Δm1–2
335.8
12.5
20.2
12.55
20.00
3
4
300–350
350–500
337.9
17 (NH3)
9NH3
Pt Mo O Cl N H
12 7 15 4 5 21
1
3
2
8 (H O)
5 (Cl)
8 (N2)
5H O
2
2
20Cl
3N2
Σ Δm2–3
32.7
6.6
32.55
6.36
364.3
356.2
17 (NH3)
3NH3
Pt Mo O
12 7 9
3
5
66.9
00.0
18 (H O)
35 (Cl)
6H O
4Cl
N2
2
2
2
8(N2)
Σ Δm3–4
m (solid residue)
39.3
60.7
38.9
61.10
of trans-[Pt(NH ) Cl ] [17]. The left branch of that peak is
a platinum-based cubic solid solution Pt Mo [space
1–x x
3
2
2
1
unsymmetrical, which suggests simultaneous dehydration
and decomposition of (NH ) Mo O according to
group Fm-3m, a = 3.935(7) Å]. As in the systems derived
from tetraammineplatinum(II) chloride and ammonium
chromate, dichromate, or ammonium perrhenate [12,
13], the Pt Mo solid solution is likely to be formed as
4
6
7
24
Eqs. (1) and (2) (DSC maximum at 228°C).
(
NH ) Mo O ·4H O → (NH ) H Mo O ·1.5H O
4 6 7 24 2 4 4 2 7 24 2
1–x
x
6
–
+
2.5H O↑ + 2NH ↑,
(1)
a result of reduction of Mo O to molybdenum metal
7 24
in the presence of Pt and ammonia.
2
3
2
+
(
NH ) H Mo O ·1.5H O → (NH ) H Mo O ·0.5H O
4
4
2
7
24
2
4 3
3
7
24
2
+
H O↑ + NH ↑.
(2)
2
3
The DSC curve showed a strong endothermic effect in
the temperature range 300–350°C with its maximum at
337.9°C. Intense decomposition of the components was
accompanied a weight loss of 20.2% (Δmteor = 20.0%),
which was twice as high as that in the preceding stages;
it corresponded to removal of 20Cl, 5H O, 9NH , and
The gas phase contained ammonia (m/z 17) and water
H O (m/z 18) with their maximum release at 265.6 and
76.9°C, as well as NO (m/z 30) with its maximum at
2
2
2
65°C. The latter is formed by oxidation of ammonia.
The TG curve showed a significant weight loss in the
temperature range 200–290°C (11.2%, Δmtheor = 11.2%)
due to elimination of 32NH and 2H O (Table 1). The
overall weight loss in the first and second stages was
2.5% (Δmtheor = 12.55%), and it was accompanied by
2
3
3
N (Table 1). According to the XPD analysis data,
2
3
2
the thermolysis products formed at 340 and 367°C are
Pt1–xMo cubic solid solutions [space group Fm-3m,
x
1
a = 3.930(5) and 3.930(2) Å] and a small amount of
molybdenum oxides.
absorption of heat (ΔH = 333.5±6 J/g).
The X-ray powder diffraction (XPD) analysis of
intermediate compound obtained at 278°C showed
the presence of two phases, trans-[Pt(NH ) Cl ] and
1
We failed to identify phase composition of the intermediate product
obtained at 265°С.
3
2
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 6 2020

1022
FESIK et al.
Table 2. Electronic states, fraction of substances on the sample
surface, and binding energies
was reported previously [18]. The XPD patterns showed
a peak at 2θ = 42°–43° indicates formation of various
intermetallic Pt Mo phases [19–21]. The elemental
Fraction on the
surface, mol %
x
y
State
Peak
Eb, eV
composition of the compound obtained at 500°C under
argon corresponds to the formula Pt0.72Mo0.21O0.07. An
insignificant amount of oxygen therein may be related
to the presence of traces of molybdenum oxide phases
which were not included in the solid solution.
Pt0
Pt(OH)
PtO/Pt
Pt4f7/2
Pt4f7/2
Pt4f7/2
Mo3d5/2
Mo3d5/2
Mo3d5/2
Mo3d5/2
Mo3d5/2
O1s
71.7
72.8
73.8
8.70
1.90
1.01
0.90
1.72
2.10
9.50
9.40
33.60
25.90
5.20
2
ads
2
+
MoO
Mo
MoO /Mo
229.5
230.9
232.1
232.9
234.0
530.6
531.9
533.3
2
5
+
The electronic states and elemental composition
5
+
2
(
Table 2) were determined by X-ray photoelectron
2
-
5+
[
MoO ] /Mo
4
spectroscopy (XPS). The Pt4f and Mo3d spectra are
represented by the spin–orbit doublets Pt4f –Pt4f and
6
+
MoO /Mo
3
7/2
5/2
Oxides
Mo3d –Mo3d , respectively. Each spectrum consisted
5/2
3/2
Oxides/OHads
H O
O1s
O1s
of several components corresponding to different
electronic states of the elements. According to the XPS
data, the ratio Pt/Mo/O is 11.6:23.6:64 mol %; this
suggests that a part of molybdenum not included in the
solid solution undergoes oxidation. Line shape analysis
revealed platinum metal on the surface (E (Pt4f ) =
2
ads
The final decomposition stage in the temperature range
50–500°C gave two weakly separated endothermic
3
peaks at 356 and 366.9°C on the DSC curve. The gas
phase contained atomic chlorine, ammonia, water, and
nitrogen, indicating that the reduction to form metallic
phases continued. It is important that the mass spectra of
the gas phase at 338 and 365°C showed a peak of atomic
chlorine (m/z 35) in addition to molecular nitrogen (m/z
b
7/2
71.7 eV) in an amount of 8.7%, as well as several oxidized
platinum states such as Pt(OH) and PtO (1.9 and 1%,
2
respectively).
Molybdenum is present in the surface layer in different
2
8). The presence of atomic chlorine is likely to indicate
forms, in particular MoO [9.4 mol %, E (Mo3d ) =
3
b
5/2
not only complete decomposition of trans-[Pt(NH ) Cl ]
5+
3
2
2
2
34 eV], Mo (13.3 mol %), and MoO (0.9 mol %).
2
but also a probable contribution of chloride ion as
reducing agent. The weight loss (6.6% of the initial
weight, Δmtheor = 6.36%) corresponds to removal of 4Cl,
Presumably, during the process molybdenum is partially
reduced to form a solid solution with platinum. That
part of molybdenum which was not included in the solid
solution, remains in the oxidized state, which is well
consistent with the XPD and TG data.
3
3
NH , 6H O, and N . The overall heat effect for T =
3 2 2 3
37.9, T = 356.2, and T = 366.9°C is ΔH =325±3 J/g.
4
5
The formation of the final solid product was complete
at 400°C, and the weight of the solid residue almost did
not change in the temperature range from 400 to 500°C.
The overall weight loss was 39.3% (Δmtheor = 38.9%), the
weight of the solid residue was 60.7% (Δmtheor =61.09%),
and the metal content of the mixture was 55.2%. The
The observed peak of oxygen O1s has a complex
structure and consists of several components: E (O1s) =
b
5
30.6, 531.9, and 533.3 eV. The first component arises
from oxide oxygen, and the second and third, to hydroxy
group and water, respectively; the latter could appear on
the sample surface as a result adsorption of water from
air during sample preparation for the analysis.
weight of the solid residue based on 12Pt and 7MoO was
3
6
4.7% or 61.1% based on 12Pt, 4Mo, and 3MoO . In our
3
Our results led us to presume that [Pt(NH ) ]Cl and
opinion, the latter seems more pertinent (Table 1). The
fact that the experimental weight loss is insignificantly
higher than the calculated value suggests the possibility
3 4
2
(
NH ) Mo O react under argon according to Eq. (3); the
4 6 7 24
fraction of molybdenum oxide phase in the thermolysis
product is much lower than the fraction of metal phase.
6
–
of more complete reduction of Mo O to the metal. It
7
24
should be emphasized that, according to the XPD data,
the product obtained at 500°C (which was already formed
in the final state at 400°C) contained platinum metal and
12[Pt(NH ) ]Cl + (NH ) Mo O → 12Pt + 4Mo + 3MoO3
3
4
2
4 6
7
24
+ 4N ↑ + 46NH ↑ + 15H O↑ + 12Cl ↑.
(3)
2
3
2
2
As found by XPD analysis, the product obtained
from the same salts under oxic conditions (air) at 500°C
consisted of two phases, platinum-based cubic solid
solution [Pt Mo , space group Fm-3m, a = 3.928(3) Å]
ordered Pt Mo intermetallics.
3
The presence of an ordered Pt Mo phase in the
3
platinum–molybdenum binary alloy (x >0.5) at 773 K
Pt
1–x
x
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 6 2020

SOLID-PHASE REACTION OF TETRAAMMINEPLATINUM(II) CHLORIDE
1023
and oxide MoO ; the composition of that product matches
furnace in a stream of argon (40 mL/min) at a temperature
of the corresponding endo- or exothermic peak on the
TG curve.
3
the formula Pt0.68Mo0.19O0.13
.
The reaction of [Pt(NH ) ]Cl with (NH ) Mo O in
3
4
2
4 6
7
24
aqueous alkali at 190°C (under pressure) gave a product
consisting of platinum metal phase and platinum-based
cubic solid solution Pt0.734Mo0.266, a = 3.935(4) Å [22].
This reaction is described by Eq. (4).
The X-ray powder diffraction patterns were recorded
on a Thermo Fisher Scientific ARL X’TRA instrument
(Switzerland) with monochromatized CuK radiation
α
(λ = 1.54056 Å); linear wavelength correction
0
0
(1.54433 Å), scanning with a step of 2°; pulse duration
6
[Pt(NH ) ]Cl + (NH ) Mo O + 12KOH → 6Pt + 7Mo
3 4 2 4 6 7 24
3
s; 2θ range 5°–80°. Phases were identified using
+
9N + 12NH + 36H O + 12KCl.
(4)
2
3
2
PCPDFWIN PDF2 automated database. The unit cell
parameters were refined by DICVOL04 program [15].
The X-ray photoelectron spectra of powder samples
were measured with an Omicron ESCA+ spectrometer;
monochromatized Al radiation with an energy of
1486.6 eV and a power of 252 W; analyzer chamber
Unlike compounds formed in the solid-phase reactions
argon, air) in the temperature range from 50 to 500°C,
no oxide phases were detected in the products obtained
under pressure.
(
Thus, the solid-phase reaction of [Pt(NH ) ]Cl and
3
4
2
(
NH ) Mo O at 500°C in an inert atmosphere (argon) or
–9
4
6
7
24
pressure ≤10 torr; analyzer energy 20 eV. The positions
on exposure to air gives molybdenum and platinum metal
of lines of elements in the surface layer were referenced
to the C1s peak of residual hydrocarbon impurities in
the preparation of powders and from atmosphere. The
elemental compositions of the thermolysis products were
determined by energy dispersive spectroscopy using a
Jeol JED-2300 Analysis Station (Japan); accelerating
voltage 20 kV.
2
+
phases, which confirms our assumption that Pt ions in
6
–
the presence of ammonia promote reduction of Mo O
7
24
to molybdenum metal. Our results indicate the possibility
of obtaining finely dispersed platinum–molybdenum
intermetallic powders.
EXPERIMENTAL
CONFLICT OF INTEREST
Analytical grade ammonium heptamolybdate
tetrahydrate (NH ) Mo O ·4H O (GOST 3765-78,
4
6
7
24
2
No conflict of interest was declared by the authors.
REAKhIM) was commercial product; tetraammine-
platinum(II) chloride monohydrate [Pt(NH ) ]Cl ·H O
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