Influence of a precursor solution on the characteristics of platinum on alumina catalysts

Article abstract of DOI:10.1016/j.mencom.2017.01.022

The precursor solution aging does not influence the characteristics of platinum on alumina catalysts prepared by the impregnation of a support with platinum nitrate solutions. The precursor solution interaction with an oxide support and the annealing treatment following the impregnation determine the size of active component particles in the final catalysts.

Full text of DOI:10.1016/j.mencom.2017.01.022

Mendeleev
Communications
Mendeleev Commun., 2017, 27, 70–71
Influence of a precursor solution on the characteristics
of platinum on alumina catalysts
Anna V. Nartova,*a,b Larisa M. Kovtunova,a,b Yurii V. Larichev,a Alexander K. Khudorozhkov,a
Alessia N. Bobrovskaya,a Genrikh V. Shterka,b and Valerii I. Bukhtiyarova,b
a G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences,
630090 Novosibirsk, Russian Federation. Fax: +7 383 330 8056; e-mail: nartova@catalysis.ru
b Novosibirsk State University, 630090 Novosibirsk, Russian Federation
DOI: 10.1016/j.mencom.2017.01.022
PtIV
10
8
10
8
nitrate
precursor
solutions
The precursor solution aging does not influence the charac-
teristics of platinum on alumina catalysts prepared by the
impregnation of a support with platinum nitrate solutions.
The precursor solution interaction with an oxide support and
the annealing treatment following the impregnation determine
the size of active component particles in the final catalysts.
6
6
4
4
Pt/alumina
catalysts
2
2
0
0
0
5
10
15
20
25
Time of precursor solution aging/h
The platinum-based catalysts and, particularly, platinum on
alumina catalysts are of great practical importance.1–3 A number
of studies have been devoted to the investigation of the influence
of catalyst preparation conditions and precursor solution com-
position on the characteristics of prepared catalysts.4–7 At the
same time, the mechanisms of the formation of supported active
component particles remain unclear. In the context of particle size
effects in catalysis,6,8–10 the controlled preparation of catalysts
with particular parameters is a problem of considerable current
interest. It is well known that platinum nitrate solutions, which
are widely used for catalyst preparation, are very complicated
compositions.4,5 Only the solutions in nitric acid are stable.
Platinum nitrate solution is prone to hydrolysis upon dilution.4
This leads to the formation of a hydrated platinum oxide pre-
cipitate with the lapse of time.4 This work considers the influence
of the composition of platinum(iv) nitrate solutions and the
solution aging on the characteristics of Pt on alumina catalysts.
The platinum nitrate solutions were studied by small angle X-ray
scattering (SAXS), and the catalyst samples were characterized
by high-resolution transmission electron microscopy (HRTEM).
The platinum on alumina catalysts were prepared using a
method described elsewhere.8,11 Commercial platinum(iv) nitrate
solution (Delphi; Pt content, 24.77 wt%) and g-Al2O3 alumina
(Sasol, SBET = 198 m2 g–1) were used. To investigate the influence
of solution aging on the characteristics of the final catalyst, a
1% aqueous solution of platinum nitrate (pH ~ 1) was prepared
and its aliquot portions were taken 0.5, 6, 12, 18 and 24 h after
the mixing of the commercial platinum nitrate solution with water.
Both SAXS measurement and catalyst sample preparation were
started simultaneously for each time of aging. g-Al2O3 was dried
at 120°C for 8 h before impregnation. The 1 wt% Pt/g-Al2O3
catalysts were prepared by the wet impregnation of alumina. The
samples were dried at 120°C for 4 h and then calcinated at
400°C for 4 h in air.
Table 1 SAXS and TEM data depending on the time of the solution aging.
Time of platinum
nitrate solution
aging/h
Pt particle size
(catalyst)/nm
(HRTEM)
Sample
no.
RG(solution)/nm
(SAXS)
1
2
3
4
5
0.5
6
3.2±0.2
5.4±0.2
7.9±0.2
9.4±0.2
10.3±0.3
1.3±0.3
1.2±0.3
1.4±0.3
1.4±0.3
1.5±0.4
12
18
24
0.5 h
0.1
6 h
12 h
18 h
24 h
fitting curves
0.01
0.001
0.00
0.05
q/A–1
0.10
Figure 1 Small angle X-ray scattering curves depending on solution aging
time.
The results of HRTEM indicate that the mean size of platinum
particles on the surface of alumina does not depend on the aging
of precursor solution. The mean particle size of platinum particles
is similar for all prepared samples (Table 1 and Figure 2). The set
of experiments on solution aging was repeated and the result was
reproduced. No dependence of the particle size of platinum on the
surface of alumina on the platinum nitrate solution aging was found
.
Catalyst samples were tested in the total oxidation of propane
in a flow-circulation reactor at 300°C. The turnover frequencies
(TOF) for samples nos. 1 and 5 are similar, namely, 0.36 and
0.39 s–1, respectively. In comparison, TOF is 2.72 s–1 for the
reference sample with a mean Pt particle size of 7.9 nm, which
was prepared as described elsewhere.11 The direct size effect is
Based on the SAXS data (Figure 1), the radius of gyration of
the polynuclear species existing in platinum nitrate solution was
determined for each time (Table 1).12 It is evident that the size
of the species is growing significantly with time upon solution
aging due to hydrolysis. After a while a precipitate forms.
© 2017 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
– 70 –

Mendeleev Commun., 2017, 27, 70–71
such a modification was shown previously.11,14 The formation of
final particles is a result of the sintering of the active component
on the support surface upon precursor decomposition treatments
(such as reduction/air annealing etc.). The interaction of nitric
acid or TMA with alumina can affect the destruction of the
polynuclear species and the stabilization of the supported active
component particles towards sintering. Note that the destruction
of the polynuclear species in precursor solution as a stage of
supported particle formation can promote a nonuniform distribu-
tion of the active component over the support grains (so-called
shell distribution) observed in the prepared catalysts.
Therefore, the precursor solution interaction with oxide
support in combination with annealing treatment following
the impregnation determines the size of the active component
particles of the final catalyst. The composition of the precursor
solution influences this process. At the same time, under the
experimental conditions, the size of the polynuclear species
formed in the precursor solution is not critical for the charac-
teristics of the catalysts. The modification of the chemical com-
position of the oxide support is a key to control catalyst properties
in the course of preparation.
20 nm
Figure 2 HRTEM image for Pt/g-Al2O3 sample no. 5 (24 h aging).
well described6,8 for the total propane oxidation over platinum
on alumina catalysts. This effect is much stronger than TOF dif-
ference found for samples nos. 1 and 5. Thus, the precursor solu-
tion aging does not influence the behavior of the final catalysts,
pointing that there is no marked difference between catalysts
prepared using fresh and aged precursor solutions.
To study the influence of the precursor solution on supported
platinum particle size, two catalyst samples were prepared using
a Ptiv nitrate solution (pH ~ 1) and a Ptiv nitrate solution with
tetramethylammonium hydroxide (TMA) (pH ~ 6.5).11 TMA
was used to change the pH of the precursor solution.5 After
impregnation and drying the samples of catalysts were divided
into portions, which were treated under conditions described in
Table 2. For reduced samples, CO-chemisorption experiments
were performed using a published method.13 Table 2 summarizes
platinum particle sizes calculated from the chemisorption and TEM
data. According to the SAXS data,11 the species in Ptiv nitrate
solution have a larger size as compared with the Ptiv nitrate + TMA
solution.After gentle reduction, very small Pt particles were found
on the surface of both catalysts. At the same time, the samples
behaved differently upon further annealing both in hydrogen
and in air (Table 2). For the sample prepared with the solutions
modified with TMA, the particle size increased more intensely
under annealing conditions regardless of the treatment medium.
According to published data, varying the H2[Pt(OH)6]/HNO3
ratio made it possible to control the colloidal platinum particle
size in the precursor solution in wide ranges and, finally, the
degree of dispersion of platinum in the resulting catalysts.8,10
Thus, the size of the colloidal particles is determinative for the
supported particle size.8,10 The above data indicate that the size
of the polynuclear species existing in platinum nitrate solution
and formed due to solution aging or solution modification by
TMA is not so principal for the control of platinum particle size.
The observations can be explained by the assumption11 that the
interaction of platinum nitrate solution with the oxide support
leads to the destruction of polynuclear species existing in pre-
cursor solution forming smaller particles of active component on
the support surface. Precursor solution composition influences
the interaction of an active component with the alumina support,
particularly, due to alumina surface modification. Possibility of
This work was supported by the Russian Science Foundation
(grant no. 14-23-00146).
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2017.01.022.
References
1 J. M. Thomas and W. J. Thomas, Principles and Practice of Hetero-
geneous Catalysis, 2nd edn., Wiley-VCH, Weinheim, 2014.
2 V. P. Ananikov, L. L. Khemchyan, Yu. V. Ivanova, V. I. Bukhtiyarov,
A. M. Sorokin, I. P. Prosvirin, S. Z. Vatsadze, A. V. Medved’ko,
V. N. Nuriev, A. D. Dilman, V. V. Levin, I. V. Koptyug, K. V. Kovtunov,
V. V. Zhivonitko, V. A. Likholobov, A. V. Romanenko, P. A. Simonov,
V. G. Nenajdenko, O. I. Shmatova, V. M. Muzalevskiy, M. S. Nechaev,
A. F. Asachenko, O. S. Morozov, P. B. Dzhevakov, S. N. Osipov, D. V.
Vorobyeva, M. A. Topchiy, M. A. Zotova, S. A. Ponomarenko, O. V.
Borshchev, Yu. N. Luponosov, A. A. Rempel, A. A. Valeeva,
A. Yu. Stakheev, O. V. Turova, I. S. Mashkovsky, S. V. Sysolyatin,
V. V. Malykhin, G. A. Bukhtiyarova, A. O. Terent’ev and I. B. Krylov,
Russ. Chem. Rev., 2014, 83, 885.
3 M. K. Carpenter, T. E. Moylan, P. S. Kukreja, M. H. Atwan and M. M.
Tessema, J. Chem. Soc., 2012, 134, 8535.
4 D. Dou, D.-J. Liu, W. B. Williamson, K. C. Kharas and H. J. Robota,
Appl. Catal., D, 2001, 30, 11.
5 I. E. Beck, V. V. Kriventsov, M. A. Fedotov and V. I. Bukhtiyarov, Nucl.
Instrum. Methods Phys. Res., Sect. A, 2009, 603, 182.
6 H. Matsuhashi, S. Nishiyama, H. Miura, K. Eguchi, K. Hasegawa,
Y. Iizuka, A. Igarashi, N. Katada, J. Kobayashi, T. Kubota, T. Mori,
K. Nakai, N. Okazaki, M. Sugioka, T. Umeki, Y. Yazawa and D. Lu,
Appl. Catal., A, 2004, 272, 329.
7 I. E. Beck, V. V. Kriventsov, D. P. Ivanov, V. I. Zaikovsky and V. I.
Bukhtiyarov, Nucl. Instrum. Methods Phys. Res., Sect. A, 2009, 603, 108.
8 A. M. Gololobov, I. E. Bekk, G. O. Bragina, V. I. Zaikovskii, A. B.
Ayupov, N. S. Telegina, V. I. Bukhtiyarov and A. Yu. Stakheev, Kinet.
Catal., 2009, 50, 830 (Kinet. Katal., 2009, 50, 864).
9 K. Arnby, J. Assiks, P.-A. Carlsson, A. Palmqvist and M. Skoglundh,
J. Catal., 2005, 233, 176.
10 I. E. Beck, V. I. Bukhtiyarov, I. Yu. Pakharukov, V. I. Zaikovsky, V. V.
Kriventsov and V. N. Parmon, J. Catal., 2009, 268, 60.
11 A. V. Nartova, Yu. V. Larichev, L. M. Kovtunova, A. K. Khudorozhkov
and V. I. Bukhtiyarov, Mendeleev Commun., 2015, 25, 463.
12 L. A. Feigin and D. I. Svergun, Structure Analysis by Small-Angle X-ray
and Neutron Scattering, Plenum Press, New York, 1987.
Table 2 Chemisorption and TEM data.
Pt particle size
(catalyst)/nm
Treatment
tempera- Medium
ture/°C
Sample Precursor
Treatment
duration/h
no.
solution
Chemi-
sorption
TEM
6
Ptiv
nitrate
100
150
200
400
H2
H2
H2
air
1.5
1
1.3
1.6
1.9
n/a
1.7±0.4
1.7±0.4
1.4±0.3
1.2±0.3
1
4
13 J. Sarkany and R. D. Gonzalez, J. Catal., 1982, 76, 75.
14 A. V. Nartova, A. V. Bukhtiyarov, R. I. Kvon and V. I. Bukhtiyarov,
Appl. Surf. Sci., 2015, 349, 310.
7
Ptiv
nitrate +
TMA
100
150
200
400
H2
H2
H2
air
1.5
1
1.2
2.4
n/a
n/a
1.4±0.4
1.6±0.5
2.0±1.2
1.7±0.6
1
4
Received: 30th August 2016; Com. 16/5034
– 71 –