Platinum and palladium nanoparticles in modified mesoporous phenol - Formaldehyde polymers as hydrogenation catalysts

Article abstract of DOI:10.1134/S0965544116020055

Mesoporous polymeric supports modified with sulfo groups and PPI dendrimers have been prepared. Catalysts containing palladium and platinum nanoparticles have been synthesized on their basis. The resulting catalysts have been studied by transmission electron microscopy and X-ray photoelectron spectroscopy. It has been shown that the metal deposition procedure has an effect on the morphology of the resulting catalyst. Catalytic activity has been studied using the example of the hydrogenation of phenylacetylene and naphthalene at temperatures of 80 and 400°C, and pressures of 1.0 and 5.0 MPa, respectively.

Full text of DOI:10.1134/S0965544116020055

ISSN 0965ꢀ5441, Petroleum Chemistry, 2016, Vol. 56, No. 2, pp. 109–120. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © M.P. Boronoev, E.S. Subbotina, A.A. Kurmaeva, Yu.S. Kardasheva, A.L. Maksimov, E.A. Karakhanov, 2016, published in Neftekhimiya, 2016, Vol. 56, No. 2,
pp. 128–139.
Platinum and Palladium Nanoparticles in Modified Mesoporous
Phenol–Formaldehyde Polymers as Hydrogenation Catalysts
a
a
a
a
M. P. Boronoev , E. S. Subbotina , A. A. Kurmaeva , Yu. S. Kardasheva ,
b
a
A. L. Maksimov , and E. A. Karakhanov
Faculty of Chemistry, Moscow State University, Moscow, Russia
a
eꢀmail: kar@petrol.chem.msu.ru; max@ips.ac.ru
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
b
Received August 27, 2015
Abstract—Mesoporous polymeric supports modified with sulfo groups and PPI dendrimers have been preꢀ
pared. Catalysts containing palladium and platinum nanoparticles have been synthesized on their basis. The
resulting catalysts have been studied by transmission electron microscopy and Xꢀray photoelectron spectrosꢀ
copy. It has been shown that the metal deposition procedure has an effect on the morphology of the resulting
catalyst. Catalytic activity has been studied using the example of the hydrogenation of phenylacetylene and
naphthalene at temperatures of 80 and 400°C, and pressures of 1.0 and 5.0 MPa, respectively.
Keywords: mesoporous polymers, nanoparticles, catalytic hydrogenation
DOI: 10.1134/S0965544116020055
The use of polymeric supports with a regular strucꢀ dium, and can have a significant effect on the activity
ture for preparing metalꢀcontaining catalysts for variꢀ and selectivity of the catalyst [13–17].
ous petrochemical processes is one of the most intenꢀ
Possible ligands for immobilization on the support
sively developing fields of catalysis [1–3]. The comꢀ
surface are dendrimers, which are spherically symꢀ
posites formed via supporting metals contain particles
metrical macromolecules with a regular branched
structure. The use of dendrimers makes it possible to
effectively retain metal nanoparticles within the pores
of an active component with a narrow pore size distriꢀ
bution and can be used for the preparation of slurry
catalyst systems, particularly as precursors of catalytiꢀ
cally active nanoparticles. These supports include of the support owing to a large number of functional
mesoporous phenol–formaldehyde polymers (with a groups; this feature prevents the elution of the metal
pore size of 2–50 nm), which combine the qualities of during reaction; therefore, the catalyst can be used
both inorganic mesoporous materials (MCMꢀ41 [4, repeatedly [18–27].
5
], SBAꢀ15 [6]) and hydrophobic organic supports
act
Another practicable method of immobilizing partiꢀ
cles on the support surface is the modification of the
original polymer matrix with negatively charged sulfo
–
(
C , polystyrene) [7, 8]. It has been previously shown
that Pd nanoparticles supported on mesoporous pheꢀ
nol–formaldehyde polymers exhibit activity in the
hydrogenation of alkynes and dienes [9]. However, the
size distribution of nanoparticles in the resulting cataꢀ
lysts is inhomogeneous and relatively broad; this feaꢀ
ture is attributed to the fact that the metal ions are not
immobilized within the pores of the support.
groups (–SO ). An interaction between the metal
3
cation and the sulfo group of the support is intended to
provide the immobilization of the metal ions and the
nanoparticles formed from these ions in the pores of
the support [28].
Immobilization of metal ions can be implemented
by the surface modification of the polymer matrix with
various functional groups (NH , SO H, PPh2) [10–
In this study, a set of mesoporous phenol–formalꢀ
dehyde polymers modified with thirdꢀgeneration
polypropylenimine (PPI) dendrimers and sulfo groups
was synthesized. The modified polymers were subseꢀ
quently used as supports for synthesizing palladium
2
3
1
2]. The presence of these groups provides a further
immobilization of the metal ions, stabilization of the
nanoparticles, and a regular incorporation thereof
into the pore space. In addition, the above groups act and platinum catalysts for the hydrogenation of pheꢀ
as modifying agents for the surface of nanoparticles of nylacetylene and as precursors of catalysts for naphꢀ
transition metals, in particular platinum and pallaꢀ thalene hydrogenation under severe conditions.
109

110
BORONOEV et al.
EXPERIMENTAL
operating frequency of 125 MHz in a pulsed mode at a
speed of 10 kHz.
Materials
Atomic emission spectroscopy. The quantitative
The reactants were phenylacetylene (98%, Aldꢀ determination of palladium and platinum in the samꢀ
rich); naphthalene (analytical grade, Reakhim); 1,4ꢀ ples was conducted by inductively coupled plasma
diaminobutane (Ferak); acrylonitrile (99+%, Acros atomic emission spectroscopy (ICPꢀAES) on an IRIS
Organics); triblock copolymer Pluronic F127 (Mn
=
Interpid II XPL instrument (Thermo Electron Corp.,
1
2600, EO ꢀPO ꢀEO106, Aldrich); phenol (highꢀ United States) in radial and axial viewing configuraꢀ
106
70
purity grade, Reakhim); formaldehyde (37% aqueous tions at wavelengths of 310 and 95.5 nm.
solution, SigmaꢀAldrich); sodium hydroxide (reagent
grade, Irea 2000); hydrochloric acid (reagent grade,
Irea 2000); chloromethyl methyl ether (technical
grade, SigmaꢀAldrich); aluminum chloride (99+%,
Gas–liquid chromatography. The substrates and
the reaction products were analyzed using a
ChromPack CP9001 gas chromatograph equipped
with a flame ionization detector and a 30 m 0.2 mm
capillary column with the SEꢀ30 grafted stationary
phase.
×
SigmaꢀAldrich); and chlorosulfonic acid ( 98%,
≥
Fluka). The solvents were methanol (99+%, Acros
Organics); ethanol (analytical grade, Irea 2000); chloꢀ
roform (Purum, Ecosꢀ1); and dimethylformamide
Synthesis of Supports Based on Mesoporous Phenol–
Formaldehyde Polymers
(
reagent grade, Khimmed). The solvents were purified
by distillation over Å molecular sieves. Dendrimer
4
DAB(NH2) was synthesized under laboratory condiꢀ
tions as described in [29].
16
Synthesis of mesoporous phenol–formaldehyde
polymer MPF. Mesoporous phenol–formaldehyde
The source of the metal for the synthesis of Pd and polymers were synthesized as described in [31]. PF
Pt catalysts was palladium(II) acetate (99.9%, Aldꢀ resole, which is a soluble lowꢀmolecularꢀweight pheꢀ
rich) and tetraammineplatinum(II) chloride, respecꢀ nolic resin, was produced during the polymerization of
tively; the latter was prepared from H [PtCl ]
as described in [30].
·
6H O phenol and formaldehyde in the presence of a base.
2
6
2
The phenol/formaldehyde/NaOH molar ratio was 1 :
2
: 0.1.
In a typical procedure, 6.0 g of phenol (0.064 mol)
was melted in a glass reactor equipped with a magnetic
stirrer and a reflux condenser at 40–42 . After that,
.28 g (0.0064 mol) of a 20% aqueous solution of
NaOH was added under stirring for 10 min. Next,
0.39 g (0.128 mol) of a 37% aqueous solution of
formaldehyde was added dropwise to the resulting
reaction mixture at 50 ; the reaction was run at 70–
under stirring for 60 min; after that, the reaction
Equipment and Experimental Procedures
°С
Lowꢀtemperature nitrogen adsorption. Nitrogen
adsorption/desorption isotherms were recorded at a
temperature of 77 K using a Gemini VII 2390 instruꢀ
ment. Prior to the measurements, the samples were
degassed at 130°C for 6 h. The surface area (SBET) was
calculated by the Brunauer–Emmett–Teller (BET)
method on the basis of adsorption data at relative presꢀ
1
1
°С
75°С
mixture was cooled to room temperature. The pH of
the reaction mixture was adjusted to a value of ~7.0
using a 0.6 M HCl solution. Water was removed using
sures ((Р/Р0) of 0.04–0.20. The pore volume and the
pore size distribution were determined from the
adsorption branch of the isotherms using the Barrett–
Joyner–Halenda (BJH) model. The total pore volume
) was determined according to the amount of
Р0 = 0.995.
Transmission electron microscopy (TEM). TEM
analysis was conducted employing a LEO912 AB
OMEGA microscope. The processing of the microꢀ
graphs and the calculation of the average particle size
were conducted using the ImageJ software.
a rotary vacuum evaporator at 50°С. The final product
was dissolved in ethanol (a grayish brown 20% ethanol
solution); after that, the precipitate of sodium chloride
was separated by filtration.
The MPFꢀ1 and MPFꢀ2 samples were synthesized
using the procedure of solvent evaporation induced
selfꢀassembly. The carbon precursor was PF resole;
block copolymer Pluronic F127 (Mw ~ 12600) was
used as a template. For all the samples, the pheꢀ
nol/formaldehyde molar ratio was 1 : 2; the pheꢀ
( t
V
adsorbed nitrogen at
Р/
Xꢀray photoelectron spectroscopy (XPS). XPS
studies were conducted on a Kratos Axis Ultra DLD
electronic device. Photoelectrons were excited using
nol/template (F127) ratio was 1 : 0.013. In a typical
–4
procedure, 10.0 g (7.94 10 mol) of F127 was placed
×
the Al
1486.6 eV). Photoelectron peaks were calibrated
against the carbon C line at a binding energy of
84.8 eV. The pass energy of the energy analyzer was
60 eV (survey scans) and 40 eV (individual lines).
K
α
Xꢀray emission of an aluminum anode
in a roundꢀbottom flask equipped with a magnetic stirꢀ
rer and dissolved in 130 mL of ethanol at room temꢀ
perature under stirring. After that, 46 g of the PF resole
precursor containing 5.7 g (0.061 mol) of phenol and
(
1s
2
1
3.7 g (0.122 mol) of formaldehyde was added. The
Solidꢀstate NMR spectroscopy. Analysis by solid mixture was stirred for 10 min to obtain a homogeꢀ
state (CPMAS) 1 C NMR spectroscopy was conꢀ neous solution, which was subsequently poured into a
3
ducted on a Varian NMR Systems instrument at an Petri dish. The ethanol contained in the reaction mixꢀ
PETROLEUM CHEMISTRY Vol. 56
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2016

PLATINUM AND PALLADIUM NANOPARTICLES
111
ture was evaporated at room temperature for 5–8 h; water and three times with methanol. The yield of the
after that, the Petri dish was placed in a desiccator and MPF–PPIꢀG3ꢀ(1) product, which was a black powꢀ
13
held at 100°С for 24 h. The product, which was a der, was 1.35 g. C (ppm): 35.2 (CH ), 132.3(CH ),
2 Ar
semitransparent grayish brown film, was ground to a 150.3 (CArOH
).
powder.
The template was removed via calcining the sample
Synthesis of Pd and Pt Catalysts Based on Phenol–
Formaldehyde Polymers
in a muffle furnace at a temperature of 350
inert atmosphere of argon for 150 min. The heating
rate was °C/min; the volumetric flow rate was
0 mL/min. The resulting product was a black powder.
The yield of the MPFꢀ1 and MPFꢀ2 samples was 6.5
°С in an
Synthesis of catalyst MPF–PPIꢀG3–Pd. Pallaꢀ
dium catalysts based on dendrimerꢀmodified mesopoꢀ
rous phenol–formaldehyde polymers were syntheꢀ
sized by the impregnation of the original supports with
Pd(OAc)2 solution and the subsequent reduction of
NaBH4. In a typical procedure, 1.0 g of mesoporous
1
9
13
and 6.1 g, respectively. C NMR (ppm): 29 (CH ),
2
a
1
1
32 (CH ), 153 (CArOH) for sample 1 and 27 (CH ),
A
r
2
28.5 (CH ), 154.5 (CArOH) for sample 2.
Ar
polymer MP–PPIꢀG3 was preliminarily dried in a
Synthesis of mesoporous chloromethylated phenol–
rotary vacuum evaporator at a temperature of 60
°С for
formaldehyde polymer MPF–CH Clꢀ(1). Modificaꢀ
2
6
0 min. The dried sample was placed in a roundꢀbotꢀ
tion with chloromethyl groups was conducted as
described in [11]. Two grams of mesoporous polymer
MPFꢀ1 and 20 mL (0.26 mmol) of chloromethyl
methyl ether were placed in a roundꢀbottom flask
equipped with a magnetic stirrer and a reflux conꢀ
denser. The resulting suspension was admixed with
tom flask equipped with a magnetic stirrer and a reflux
condenser; after that, 420 mg (1.87 mmol) of pallaꢀ
dium acetate and 20 mL of CHCl3 were added. The
reaction was run at room temperature under stirring
for 12 h. After this period, CHCl3 was separated by
centrifugation. The resulting catalyst precursor was
suspended in 30 mL of CHCl3 and 20 mL of methanol;
–3
8
.0 g (1.5 10 mol) of AlCl ; after that, the reaction
×
3
was run under stirring for 10 h. After reaction, the susꢀ
pension was filtered off; the remaining black residue
was washed three times with water and three times
7
20 mg (18.95 mmol) of sodium borohydride was
added portionwise. Reduction was conducted at 70
°
C
for 24 h. To remove the borax formed as a byproduct,
the resulting mixture was washed three times with
water and three times with methanol. The remaining
solid product was dried in air. The resulting sample was
a black powder with a weight of 1.16 g.
with acetone. The resulting modified MPF–CH Cl
2
polymer was a black powder. The product yield was
.2 g 1 C (ppm): 27 (CH ), 128.5 (CH ), 154.5
3
2
(
2 Ar
CArOH).
Synthesis of sulfonated mesoporous phenol–formꢀ
XPS, eV: 400.1 (N 1s, N–C, 3.9%); 335.6 (Pd
°
aldehyde polymer (MPF–SO H). In a typical proceꢀ
3
3
C
2
3
d , 6.3%), 338.4 (PdО 3d , 0.2%); 285.0 (C 1s,
dure, a mesoporous phenol–formaldehyde polymer
powder was placed in a threeꢀnecked flask equipped
with a magnetic stirrer and a reflux condenser and disꢀ
5/2
5/2
⎯
C, 41.9%), 286.4 (C 1
, C=O, 6.5 %), 289.1 (C 1
.6%); 532.5 (O 1 , 17.3%). ICPꢀAES: 10.0 wt %.
Synthesis of catalyst MPF–SO H–Pdꢀb. Syntheꢀ
s
, C–O, N–C, 20.2%),
87.7 (C 1
s
s, O–C=O,
s
persed in anhydrous CH Cl2; after that, chlorosulꢀ
2
fonic acid was added dropwise [32]. The reaction was
3
sis was conducted similar to the above procedure. The
precursors were 620 mg of the sulfonated mesoporous
run at
0°C in an argon atmosphere under stirring for
2
4 h. Three materials with different amounts of deposꢀ
ited sulfo groups were prepared. The ratio between the
weight of the polymer (g) and the amount of acid (mL)
MPF–SO Hꢀb polymer and 65 mg (0.29 mmol) of
3
palladium acetate in 6 mL of CHCl3. The reaction was
run at room temperature with stirring for 8 h. Chloroꢀ
form was removed in a rotary vacuum evaporator at
was 0.55, 2.3, and 3.3 for the MPF–SO Hꢀa, MPF–
3
SO Hꢀb, and MPF–SO Hꢀc materials, respectively.
3
3
30°С.
The yield of the MPF–SO Hꢀa, MPF–SO Hꢀb, and
3
3
MPF–SO Hꢀc samples was 1.80, 1.35, and 1.25 g,
respectively.
Reduction was conducted via suspending the
resulting catalyst precursor in 6 mL of CHCl and
mL of methanol; 100 mg (2.7 mmol) of sodium
borohydride was added portionwise to the suspension.
The resulting sample was a black powder with a weight
3
3
3
Synthesis of DAB(NH ) dendrimerꢀfunctionalized
2
16
mesoporous phenol–formaldehyde polymer MPF–
PPIꢀG3. One gram of chloromethylated polymer
of 550 mg.
MPF–CH Cl and 1.0 g (0.59 mmol) of DAB(NH2)16
,
2
о
which was predissolved in a mixture of 5 mL of water
and DMF in a ratio of 1 : 1, were placed in a roundꢀ 1.7%), 337.9 (Pd2 3d5/2, 0.3%); 284.8 (C 1
bottom flask equipped with a magnetic stirrer and a 52.6%), 286.3 (C 1 , C–O, 14.5%), 287.4 (C 1
reflux condenser. The reaction was run at a temperaꢀ 5.3%), 288.8 (C 1 , O–C=O, 14.5%); 532.5 (O 1
ture of 80
under stirring for 24 h. An effective 21.7%). ICPꢀAES: 2.24 wt %.
occurrence of the reaction was evidenced by a gradual Synthesis of catalyst MPF–SO H–Pdꢀc. Syntheꢀ
XPS, eV: 167.9 (S 2p3/2, 0.1%); 335.3 (Pd 3d5/2
,
+
s
, C–C,
s, C=O,
s
s
s,
°С
3
discoloration of the solution above the precipitate. sis was conducted similar to the above procedure, yet
After reaction, the resulting solid precipitate was sepꢀ with some differences. The precursors were 815 mg of
arated by centrifugation and washed three times with sulfonated mesoporous phenol–formaldehyde polyꢀ
PETROLEUM CHEMISTRY Vol. 56
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112
BORONOEV et al.
To reduce Pt(II) to Pt(0), the resulting catalyst preꢀ
cursor was suspended in 5 mL of water; 51 mg
1.37 mmol) of sodium borohydride was added porꢀ
(
tionwise to the suspension. The product was a black
powder with a weight of 380 mg.
2+
XPS, eV: 71.2 (Pt
°
4
f7/2, 0.082%), 73.5 (Pt 4f7/2
.096%), 75.6 (Pt 4f7/2, 0.022%); 168.1 (S 2p3/2, R–
SO H, 0.1%); 284.8 (C 1 , C–C, 56.2%), 286.5 (C 1
C–O, 15.2%), 288.4 (C 1 , O–C=O, 4.6%); 532.5
O 1 , 23.8%). ICPꢀAES: 1.5 wt %.
,
4+
0
s
s,
3
s
100 nm
100 nm
(а)
(b)
(
s
Fig. 1. Micrographs of polymers (a) MPFꢀ1 and (b)
MPFꢀ2.
Catalyst Testing Procedure
Calculated amounts of the catalyst and the subꢀ
mer MPF–SO Hꢀ(с)ꢀc predried in a rotary evaporator
at 50°C and 86 mg (0.38 mmol) of palladium acetate
in 6 mL of CHCl3. The reaction was run for 24 h; after
that, CHCl3 was separated by centrifugation. Pd(II)
was reduced to Pd(0) using 162 mg (4.38 mmol) of
3
NaBH4 in 5 mL of CHCl3 and 3 mL of CH OH. The
3
mass of the resulting product, which was a black powꢀ
der, was 770 mg.
XPS, eV: 167.9 (S
2p3/2, 0.65%), 169.7 (C 2p3/2, R–
0
2+
SO H, 0.35%); 335.6 (Pd 3d5/2, 1.2%), 337.9 (Pd
3
3
d5/2, 0.1%); 284.8 (C 1
C–O, 13.3%), 287.3 (C 1
C 1 , O–C=O, 3.7%); 533 (O 1
.2 wt %.
Synthesis of catalyst MPF–SO H–Ptꢀa. Platinum
s
, C–C, 53.2%), 286.3 (C 1
, C=O, 3.7%), 288.9
, 23.8%). ICPꢀAES:
s,
s
(
3
s
s
3
catalysts based on sulfonated mesoporous phenol–
formaldehyde polymers were synthesized by a similar
procedure by impregnating the polymers with a
[
3 4 2
rous polymer predried in a rotary vacuum evaporator ronic F127 template by selfꢀassembly. The resulting
at 60
°С for 60 min and 3 mL of an aqueous solution of intermediate product was subjected to thermal polyꢀ
[
Pt(NH ) ]Cl (85 mg, 0.25 mmol). After the reaction,
3
4
2
merization at 100
and then to calcination in an inert atmosphere at a
temperature of 350 for 3 h to remove the template.
°C for strengthening the structure
water was removed in a rotary vacuum evaporator at
55°C.
°C
To reduce Pt(II) to Pt(0), the resulting catalyst preꢀ
cursor was suspended in 2 mL of water; 48.5 mg
1.3 mmol) of NaBH4 was added portionwise to the
Characteristics of the resulting materials are shown
in Table 1 and Figs. 1 and 2.
(
According to lowꢀtemperature nitrogen adsorpꢀ
suspension. The reaction was run at room temperature
under stirring for 1 h. The resulting product was a
black powder with a weight of 900 mg.
tion, the samples exhibit a high specific surface area of
2
3
83 and 579 m /g, respectively, and are characterized
0
2+
by type IV curves with a hysteresis loop in a relative
pressure range of 0.4–0.6, which indicate the presence
of micropores in the structure of the material.
XPS, eV: 71.4 (Pt 4f7/2, 0.1%), 73.4 (Pt
.2%); 167.6 (S 2p3/2, R–SO , 0.5%), 168.4 (C 2p3/2
4
f7/2
,
–
0
,
3
3
R–SO H, 0.5%); 284.8 (C 1
s
, C–C, 53.7%), 286.4
, O–C=O, 4.82%);
32.5 (O 1s, 23.7%). ICPꢀAES: 2.6 wt %.
(
5
C 1
s
, C–O, 16.3%), 288.2 (C 1
s
The TEM micrographs (Fig. 1) show clearly eviꢀ
dent channels and hexagonal cells with a diameter of
Synthesis of catalyst MPF–SO H–Ptꢀb. Synthesis ~10 nm characteristic of SBAꢀ15 mesoporous materiꢀ
3
was conducted by a procedure similar to the previous als [34]. Thus, the lowꢀtemperature nitrogen adsorpꢀ
one. The precursors were 490 mg of the mesoporous tion/desorption and TEM data suggest that all the
polymer predried in a rotary vacuum evaporator at samples have an ordered porous structure.
6
0
°
С
for 60 min, 41 mg (0.123 mmol) of Pt(NH ) Cl
The 13C NMR spectra of the samples (Fig. 2)
3
4
2
in 8 mL of distilled water. The reaction was run at exhibit signals in a region of 110–150 ppm correꢀ
room temperature under stirring for 24 h; after that, sponding to the C atoms of aromatic moieties; the sigꢀ
the solvent was removed by centrifugation.
nals in a range of 150–170 ppm are attributed
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PLATINUM AND PALLADIUM NANOPARTICLES
113
Table 1. Physicochemical characteristics of the mesoporous polymers before and after modification
Polymer mass
Pore size, nm (g)/amount
of acid (mL)
S
,
sp.
2
Pore volume,
Sample
MPFꢀ1
S, %
Cl, %
N, %
3
cm /g
m /g
579
383
541
170
75
0.50
0.44
0.46
0.21
0.10
0.12
0.22
4.5
4.2
4.6
3.7
5.2
3.7
3.3
–
–
–
–
–
–
–
–
–
–
MPFꢀ2
MPFꢀCH Cl
–
1.9
–
–
2
MPFꢀPPIꢀG3
–
2.9
–
MPFꢀSO Hꢀa
0.55
2.3
3.3
2.1
1.38
<1
–
3
MPFꢀSO Hꢀb
149
275
–
–
3
MPFꢀSO Hꢀc
–
–
3
to the phenol atoms carbon (ArOH); the signals at tion of PPI dendrimers and sulfo groups on the supꢀ
1
0–50 ppm correspond to methylene bridges and
ports. The surface modification of the MPFꢀ1 mateꢀ
rial was conducted in two steps: (1) activation with
chloromethyl methyl ether in the presence of AlCl3
formaldehyde residues [31].
Support Modification with PPI Dendrimers
and the subsequent introduction of CH Cl groups and
2
(
2) reaction of the activated polymer with PPI denꢀ
The prepared mesoporous supports were subjected
to functionalization for the subsequent immobilizaꢀ drimer DAB(NH2)16 (see Scheme 1).
H N
2
NH2
NH2
NH2
H N
H N
2
N
N
2
N
N
N
N
N
NH2
NH2
H N
H N
2
N
N
2
N
N
N
H N
H N
NH
2
2
N
N
NH
OH
OH
OH
2
OH
OH
OH
OH
OH
2
NH2
CH2 NH
Cl
Cl
CH OCH Cl, AlCl
3
DAB(NH )
2 16
2
3
CH2
DMF, 80°C
OH
OH
OH
CH HN
NH2
NH2
NH2
2
OH
H N
2
N
N
H N
2
N
N
N
H N
N
NH2
NH2
2
N
N
H N
2
N
N
N
N
H N
NH2
2
N
N
NH2
H N
2
NH2
NH2
Scheme 1. Stages of the synthesis of the mesoporous MPFꢀPPIꢀG3 support.
The chloromethylation of the mesoporous carbon both the unoccupied and occupied positions (ipso
polymers occurred by the mechanism of electrophilic attack); the lastꢀmentioned process led to the partial
destruction of the surface layer of the support and a
decrease in the specific surface area thereof, as conꢀ
firmed by lowꢀtemperature nitrogen adsorption–desꢀ
orption (Table 2). The chlorine content in the MPF–
aromatic substitution in the ortho and para positions
relative to the hydroxyl groups of the aromatic moiꢀ
+
eties. The ClCH2 particles were capable of attacking
PETROLEUM CHEMISTRY Vol. 56
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114
BORONOEV et al.
13C CP MAS NMR
ples preserved a regular porous structure, as evidenced
by lowꢀtemperature nitrogen adsorption–desorption.
The NMR spectra of the MPF–PPIꢀG3 material
preserved signals at 150–170, 110–150, and 10–
MPFꢀSO Hꢀa
3
5
0 ppm, which are characteristic of the aryl and pheꢀ
nol moieties and methylene bridges (Fig. 2). The sigꢀ
nals of the ꢀmethylene groups at the nitrogen atoms
40–55 ppm) are weak because they overlap with the
MPFꢀPPIꢀG3
α
(
MPFꢀ2
MPFꢀ1
methylene groups of the initial support. However, it is
evident that the peak maximum is shifted to the region
of 50–60 ppm corresponding to the
groups at the tertiary amino groups of the dendrimers
50–54 ppm) and the –N–CH –N– moieties formed
α
ꢀmethylene
(
2
2
00 180 160 140 120 100 80 60 40 20 0 –20
Chemical shift, ppm
during the crosslinking of the dendrimers with each
other.
Fig. 2. CPMAS 13C NMR spectra of the MPFꢀ1, MPFꢀ2,
MPFꢀPPIꢀG3, and MPFꢀSO Hꢀa samples.
3
Sulfonation of the Mesoporous Support
Surface modification with sulfo groups was conꢀ
CH Cl sample was determined by mercurimetric titraꢀ ducted using chlorosulfonic acid (Scheme 2, reaction
2
(
a)). Three sulfonated mesoporous polymers with difꢀ
tion.
ferent amounts of chlorosulfonic acid added during
Functionalization with PPI dendrimers was conꢀ the synthesis and, as a consequence, with different sulꢀ
ducted in a methanol–DMF mixture. The choice of fur content on the surface of the material were syntheꢀ
sized.
this solvent was based on the low solubility of amineꢀ
terminated dendrimers in most organic solvents
The data in Table 1 show that an increase in the
amount of chlorosulfonic acid used to modify the
polymers leads to an increase in the sulfur content in
the final product and a simultaneous decrease in the
surface area of the material; the decrease can be attribꢀ
uted to the occurrence of ipso substitution in the aroꢀ
matic moieties (Scheme 2, reaction (b)). This process
partially destroys the polymer structure and thus
(
(
including DMF), except for water and lower alcohols
ethanol, methanol), whereas it was DMF that conꢀ
tributed to the occurrence of the reaction by the SN2
mechanism. The grafting of the dendrimers to the
inner walls of the pores of the mesoporous carbon
polymers contributed to a significant decrease in the
specific surface area owing to steric hindrances generꢀ causes a decrease in the specific surface area and an
ated by the dendrimers (Table 2). However, both samꢀ increase in the pore size.
Table 2. Relative contributions of components of the XPS spectra and the corresponding chemical states of the elements
XPS, %
Pd 3d5/2, % (eV)
Pt 4f , % (eV)
7/2
No.
Catalyst
O
C
S
N
Pd
Pt
0
0
+2
+4
Pd , % PdO,% Pt , % Pt , % Pt , %
(eV)
(eV)
(eV)
(eV)
(eV)
1
2
3
4
5
MPFꢀPPIꢀG3ꢀPd
17.3
21.7
23.8
23.7
23.8
72.3
76.2
73.9
74.9
75.9
–
3.9
–
6.5
2.0
1.3
–
–
–
97
3
–
–
–
(
(
(
335.6) (338.4)
MPFꢀSO HꢀPdꢀc
0.1
1.0
1.0
0.1
85 15
–
–
–
–
–
–
3
335.3) (337.9)
92
MPFꢀSO HꢀPdꢀb
–
–
8
3
335.6) (337.9)
MPFꢀSO HꢀPtꢀa
–
0.3
0.2
–
–
–
–
26
74
–
3
(
71.4) (73.4)
MPFꢀSO HꢀPtꢀc
–
–
41 48
71.2) (73.5) (75.6)
11
3
(
PETROLEUM CHEMISTRY Vol. 56
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2016

PLATINUM AND PALLADIUM NANOPARTICLES
OH OH
OH OH
115
ClSO H
3
0°C, Ar
HO3S
SO H
3
n
n
(a)
OH
OH
OH
HOH C
OH
2
1) ClSO H, 0°C, Ar
3
SO H
2
2) H O
2
HO
HO
(
b)
Scheme 2. Sulfonation of the mesoporous support:
(a) sulfonation of the mesoporous phenolꢀformaldehyde polymer;
(b) ipso attack of the aromatic ring during the sulfonation of the polymer.
An additional peak with a maximum at 168– G3, MPF–SO H–Pdꢀb, and MPF–SO H–Ptꢀc
3
3
1
70 ppm corresponding to the carbon atoms of the samples were synthesized by the second method, in
aromatic ring that are directly bound to the introduced which, after impregnation, the solvent was removed by
13
sulfo groups is observed in the C NMR spectrum of centrifugation. The resulting catalysts were characterꢀ
the sulfonated sample (Fig. 2). A shift to the region of ized by TEM and XPS.
weaker fields is also observed for the carbon atoms corꢀ
The highest metal content is observed in the MPF–
responding to the bridging CH2 groups; it can be
PPIꢀG3–Pd sample, which was synthesized using a
support modified with dendrimers which are polydenꢀ
tate ligands and therefore capable of retaining a signifꢀ
attributed to the appearance of CH Clꢀ or CH OHꢀ
2
2
groups, which result from the ipso attack of the aroꢀ
13
matic ring, in the polymer structure. The C NMR
spectrum of the sulfonated sample exhibits a peak in
icantly larger amount of the metal than SO Hꢀ and
3
the region of 168 ppm; it can be assigned to the carꢀ OH groups. It has been found that the method of supꢀ
boxyl groups bound to the benzene ring. The appearꢀ porting of palladium has a considerable effect on the
ance of these groups suggests that, during synthesis, morphology of particles in the resulting catalyst. In the
the surface of the mesoporous polymer undergoes parꢀ first approach, the metal particles are located both
tial oxidation.
within the pores and on the surface of the polymer and
The above data show that, despite the partial degraꢀ have a larger average size and a broader size distribuꢀ
dation of the structure of the material during sulfonaꢀ tion. The use of the second approach (centrifugation)
tion, all the samples preserve regular porosity and provides the formation of catalysts in which the partiꢀ
exhibit the adsorption isotherm characteristic of a cles are mostly located within the pores of the support.
mesoporous material.
During evaporation, the entire deposited metal,
including the unadsorbed metal, remains on the samꢀ
ple surface; as a consequence, large particles are
formed outside the pores of the support (Figs. 3a, 3b).
Synthesis of Catalysts
The resulting mesoporous materials modified with
sulfo groups or polymers were used as supports for catꢀ
alysts based on platinum and palladium. The metal
was supported by two different methods. In the first
According to XPS, in the palladium catalysts, the
metal is mostly zeroꢀvalent and the fraction of oxide
does not exceed 15% (Table 2). At the same time, the
case, after the impregnation of the material with a fraction of the zeroꢀvalent metal in the platinum cataꢀ
respective metal salt, the solvent was removed using a lysts is significantly lower; in the MPF–SO H
3
–Ptꢀa
rotary vacuum evaporator (the MPF–SO H–Ptꢀa and catalyst, platinum is mostly in a divalent state (74%);
3
MPF–SO H–Pdꢀc samples); after that, the metal was in the MPF–SO H–Ptꢀc catalyst, it is in the form of
3
3
2+
4+
reduced with sodium borohydride. The MPF–PPIꢀ both Pt (48%) and Pt (11%).
PETROLEUM CHEMISTRY Vol. 56
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116
BORONOEV et al.
20
18
16
14
12
10
8
6
4
2
3.7 ± 0.4 nm
w(Pd) = 10%
w(Pd) = 3.2%
w(Pd) = 2.2%
100 nm
0
2
4
6
d
8
, nm
10 12 14
(
а)
20
18
16
14
12
10
8
6
4
2
3.3 ± 0.8 nm
100 nm
(b)
0
2
4
6
d
8
, nm
10 12 14
.7 ± 1.1 nm
30
25
20
15
10
5
4
200 nm
(c)
0
2
4
6
8
10 12 14
d, nm
Fig. 3. Micrographs and particle size distribution of (a) MPFꢀPPIꢀG3ꢀPd, (b) MPFꢀSO HꢀPdꢀb, (c) MPFꢀSO HꢀPdꢀc,
3
3
(
d) MPFꢀSO HꢀPtꢀa, and (e) MPFꢀSO HꢀPtꢀc.
3 3
The assignment of signals of carbon in the XPS (287.1–289.4 eV), the fraction of which is ~10%, is
spectra was conducted in accordance with [35]. On the apparently attributed to the partial oxidation of the
support during the calcination of the template.
surface of the synthesized catalysts, the spectrum is
represented mostly by aromatic moieties (284.8 eV)
corresponding to the structure of the original mesopoꢀ
rous phenol–formaldehyde polymer and aliphatic
chains (285.1 eV) corresponding to the bridging CH2
groups within both the support and the grafted denꢀ
In should be noted that the platinumꢀcontaining
samples do not exhibit a peak corresponding to the
C=O group. Apparently, the reduction of Pt(II) in an
aqueous medium is accompanied by the simultaneous
reduction of the C=O group to the C–OH group. In
drimers (in the case of the MPF–PPIꢀG3–Pd samꢀ addition, the absence of a peak corresponding to the
ple). The presence of the C=O and O–C=O moieties C=O bonds in the XPS spectra of the Pt catalysts, in
PETROLEUM CHEMISTRY Vol. 56
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PLATINUM AND PALLADIUM NANOPARTICLES
117
30
25
20
15
10
5
4.8 ± 1.4 nm
w(Pd) = 2.6%
100 nm
(d)
0
2
4
6
8
10 12 14
d, nm
25
20
15
10
5
4.1 ± 0.9 nm
100 nm
(
e) w(Pd) = 1.5%
0
2
4
6
8
10 12 14
d, nm
Fig. 3. Contd.
conjunction with the partial reduction of the metal, alyst with the highest sulfur content, sulfur is present
can indicate that the C=O and COOH groups formed in the form of both sulfo groups and sulfones.
during the calcination of the template are mostly
reduced precisely at the expense of Pt(0) or Pt(II).
Catalytic Experiments
The N 1s spectrum (for the dendrimerꢀcontaining
MPF–PPIꢀG3–Pd sample) exhibits the most intense
signal which, according to [36], corresponds to the
tertiary amino groups of the dendrimer NR3
+
The resulting mesoporous hybrid catalysts were
tested in the hydrogenation of phenylacetylene and
naphthalene (Tables 3, 4). The phenylacetylene
(
399.9 eV) and the signal of NR4 (401 5 eV), which hydrogenation products were styrene and ethylbenꢀ
zene. The catalyst activity in the phenylacetylene
hydrogenation increased in the following order:
can indicate the electron density transfer from the
amino groups of the dendrimer to the palladium nanoꢀ
particles the surface of which has a partial positive
charge.
MPF–SO H–Ptꢀa < MPF–SO H–Ptꢀc < MPF–
3
3
PPIꢀG3–Pd < MPF–SO H–Pdꢀb < MPF–SO H
Pdꢀc; it was 102, 930, 1032, 2619, and 2809 min ,
respectively (Table 3).
–
3
3
–
1
The signals at 167.6 (sulfones [37]), 167.9–168.4
(
(
sulfo groups according to [32, 38, 39]), and 169.7 eV
unionized sulfo groups according to [40]) correspond
In the case of dendrimerꢀcontaining catalyst 1, the
to sulfur on the surface of the sulfonated catalysts. In styrene selectivity was 92%. In this case, this feature
the case of the MPF–SO H–Ptꢀc and MPF–SO H can be attributed to the donor effect of the polydentate
–
3
3
Pdꢀb samples, sulfur is present only in the form of a Nꢀcontaining ligand, which increases the electron
sulfo group. The MPF–SO H–Pdꢀc sample, along density on the palladium surface and thus hinders the
3
with ions of sulfo groups, contains unionized sulfo readsorption of the alkene [41–43]. An increase in the
groups; this feature can be attributed to the adsorption reaction time to 1 h had hardly any effect on the selecꢀ
of chlorosulfonic acid. In the MPF–SO H–Ptꢀa catꢀ tivity.
3
PETROLEUM CHEMISTRY Vol. 56
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118
BORONOEV et al.
Table 3. Phenylacetylene hydrogenation
Conditions: 80
°C, 15 min, 1.0 MPa H2
substrate/
catalyst
–1
No.
Catalyst
conversion, %
styrene, % ethylbenzene, %
TOF , min
S
1
1
MPFꢀPPIꢀG3ꢀPd
MPFꢀPPIꢀG3ꢀPd*
37
98
92
92
88
35
86
96
89
8
8
9300
9300
8000
8000
9900
8000
8000
1032
–
2
MPFꢀSO HꢀPd (b)
95
12
65
14
4
2619
–
3
2
MPFꢀSO HꢀPd (b)*
100
87
3
3
MPFꢀSO HꢀPd (c)
2809
102
930
3
4
MPFꢀSO HꢀPt (a)
4.3
43
3
5
MPFꢀSO HꢀPt (c)
11
3
*
2 h.
Table 4. Naphthalene hydrogenation
Conditions: 400°C, 5 h, 5.0 MPa H , 10 wt % naphthalene in hexane
2
hydrogenation products, %
substrate/
catalyst
–1
No.
catalyst
conversion, %
TOF , h
S
tetralin
decalin
1
2
3
MPFꢀPPIꢀG3ꢀPd
90
20
30
19
5
81
95
91
67
82
99
222
82
MPFꢀSO HꢀPd (b)
3
MPFꢀSO HꢀPt (c)
9
103
3
Pdꢀcontaining catalysts 2 and 3 modified with sulfo gen of the sulfo group undergo a Coulomb interaction,
groups exhibited higher activity than platinum cataꢀ which results in the electron transfer from the metal to
the oxygen (Fig. 4) [28]. As a consequence, the resultꢀ
ing styrene much more readily undergoes readsorption
and hydrogenation on the electronꢀdepleted Pd surꢀ
face. Thus, it was shown [44] that the hydrogenation of
lysts 4 and 5 did. Thus, in the 15ꢀmin reaction over the
Pdꢀcontaining catalysts, the styrene selectivity was
fairly high (86–88%) at a high conversion of phenyꢀ
lacetylene (87–95%). With an increase in the reaction
time to 1 h, the main product became ethylbenzene.
These data are consistent with the electronic effect of
sulfo groups, which contribute to the formation of a
positive charge on the surface of the metal nanopartiꢀ
cles. It is assumed that the metal and the hydroxyl oxyꢀ
1
,3ꢀbutadiene over a palladium catalyst supported on
sulfo groupꢀmodified carbon nanofibers gives excepꢀ
tionally ꢀbutane.
n
The platinum catalysts, conversely, exhibited an
anomalously high styrene selectivity; in the 1ꢀh reacꢀ
tion, the proportion of styrene was 75–90% at a conꢀ
version of 45–100%. At the same time, it is known that
Pt catalysts typically higher activity and lower selectivꢀ
ity compared with Pd catalysts [45].
OH
OH
Catalyst 4 exhibited a significantly lower activity
than that of catalyst 5 (conversion of 4.3 and 43%,
respectively). The low activity of catalyst 4 is apparꢀ
ently due to a considerably lower specific surface area
of this sample; as a consequence, the metal particles
are distributed nonuniformly and undergo agglomeraꢀ
tion, which leads to a decrease in the number of accesꢀ
sible adsorption sites and in the specific catalytic
activity. It should also be noted that the concentration
of sulfo groups on the surface of catalyst 4 is higher.
More active catalyst 5, conversely, is characterized by
a lower content of sulfo groups on the surface and, at
S
O
O
H
n
O
⊕
Me
Fig. 4. Assumed scheme of interaction between the metal
and the sulfo group.
PETROLEUM CHEMISTRY Vol. 56
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2016

PLATINUM AND PALLADIUM NANOPARTICLES
119
the same time, a lower Pt content; platinum occurs
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0
(
both in the form of Pt , the proportion of which is
2
+
1
.5 times that in catalyst 4, and in the forms of Pt
4+
and Pt . Apparently, in the case of sulfonated Pt catꢀ
0
alysts, a special synergetic effect occurs between Pt ,
4+
–
3
Pt , and SO groups; it is responsible for activity and
8. L. Nikoshvili, E. Shimanskaya, A. Bykov, I. Yuranov,
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Naphthalene hydrogenation. It was of interest to use
the prepared nanocomposites as precursors of cataꢀ
lysts for the hydrogenation and hydrocracking of aroꢀ
(Part B), 179 (2015).
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. E. A. Karakhanov, A. L. Maksimov, I. A. Aksenov, et al.,
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1
1
1
0. R. Xing, Y. M. Liu, H. H. Wu, et al., Chem. Commun.,
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6
(
matic hydrocarbons. Under severe conditions (400
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It is evident that the highest activity was exhibited
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leads to a considerable decrease in the degree of
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ditions; for this reason, the formation of nanoparticles
in the suspension is significantly slowed down.
Thus, mesoporous polymeric supports modified
with sulfo groups and PPI dendrimers have been synꢀ
thesized. The Pd and Pt catalysts prepared on the basis
of these supports have been tested in the hydrogenaꢀ
tion of phenylacetylene and naphthalene. It has been
shown that the sulfonated Pd catalysts are most active
in the phenylacetylene hydrogenation, whereas the Pt
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4. M. GarcíaꢀMota, J. GómezꢀDíaz, G. NovellꢀLeruth,
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2
9. Y. Niu and R. M. Crooks, Chimie
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7
2
2
A
8, 114
(
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21
2
7. E. A. Karakhanov, A. L. Maksimov, E. M. Zakharian,
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Translated by M. Timoshinina
PETROLEUM CHEMISTRY Vol. 56
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2016