1026
MAGDALINOVA, KLYUEV
crystalline diamond core of particles of about 4 nm, Thiele criterion turned out to be substantially smaller
–6
–5
and a total concentration of noncarbon impurities of than 1 (Φ = 1.9 × 10 –1.9 × 10 ), which is indeed
no more than 0.2 wt %) synthesized according to the the evidence for the fact that the reaction proceeds in
procedure described in the patent [11] and in [12, 13] the kinetic region.
and 1 wt % Pd/С prepared according to the procedure
described in [12, 13] on the basis of activated carbon of
the PHO M200 brand (prepared on the basis of the
coconut shell) (Eurocarb, the United Kingdom) were
used.
The products of the hydrogenation reaction were
analyzed on a Series 3700 commercial chromatograph
equipped with a flame ionization detector: a glass col-
umn of a 3 mm diameter and a 2000 mm length packed
with 5% LucoPrene G-1000-coated Chromaton N-
AW-DMCS, the carrier gas was nitrogen, the evapora-
tor temperature was 80–230°С, the column tempera-
ture was 50–180°С (depending on the analyte), the
carrier-gas flow rate was 1.6 ± 0.02 L/h, and the injec-
tion volume was 0.5–1 μL.
Hydrogenation Procedure
The hydrogenation reaction of aromatic nitro com-
pounds and unsaturated organic compounds (see
Scheme 1) was carried out as follows: 30 mg of a cata-
lyst and 10 mg of sodium tetrahydroborate NaBH
4
Investigation Methods
were placed under a solvent layer (10 mL of ethanol)
into a glass reactor equipped with a thermostatting
jacket and a magnetic stirrer, the activation was carried
out for 10 min, and then 1 mmol of a substrate (cyclo-
hexene (CH), hexene-1 (H-1), allyl alcohol (AAl),
acrylic acid (AA), methacrylic acid (MA), cinnamic
acid (CA), nitrobenzene (NB), p-nitrophenol (p-NP),
p-nitrobenzoic acid (p-NBA), о-nitroaniline (о-NA),
p-nitroaniline (p-NA), or 2,4-dinitroaniline (2,4-
DNA)) was introduced in a hydrogen flow. The
The structure and composition of synthesized
wt % Pd/С and 1 wt % Pd/ND were studied by a set
1
of instrumental techniques, namely, X-ray microanal-
ysis (a VEGA TS 5130MM fully PC-controlled scan-
ning electron microscope), X-ray photoelectron spec-
troscopy (Kratos Axis Ultra DLD), and scanning elec-
tron microscopy (Zeiss LEO SUPRA 25) [12, 13].
The 1 wt % Pd–PEG-4000/ZnO and 1 wt % Pd–
PEG-6000/ZnO catalysts were examined using trans-
mission electron microscopy (Jeol JSM-6610LV) [3].
hydrogenation was carried out at Т = 45°С and РH2
=
0
.1 MPa. The reaction mixture was stirred at a con-
stant rate of 1250 stir bar revolutions/min during all
the experiments, which is sufficient for the process to
occur in the kinetic region. This value was determined
experimentally.
RESULTS AND DISCUSSION
Characterization of the Catalysts
Based on the data of transmission electron micros-
copy, it was shown [3] that the systems applied onto
zinc oxide from an aqueous palladium chloride solu-
tion are metal particles with a rather broad size spread
In studying the effect of NaBH on the hydrogena-
4
tion rate, the amount of the reducing agent was varied
from 0 to 25 mg.
The apparent reaction rate was measured volumet-
rically by the absorption of hydrogen. Under the reac-
(
20–40 nm). The palladium catalyst prepared using
PEG is characterized by the formation of small metal
particles with sizes from 3 to 8 nm which quite uni-
formly cover the support surface.
–1
tion conditions, a turnover number (TON, min ),
which shows how many moles of the substrate is con-
verted per mole of Pd per minute, was used for the
comparison of the catalytic activity of the objects
under study.
Preliminary Activation of the Catalysts
Under the given experimental conditions, the reac-
tions of interest were zero-order with respect to the
substrate and first-order with respect to the catalyst
and hydrogen [14]. To confirm that the processes
occurred in the kinetic region, the Thiele criterion (Ф)
was used [15]:
The samples under study were subjected to prelim-
inary activation using sodium tetrahydroborate. The
essence of the activation process in the case of palla-
dium-containing catalysts consists in the transition of
2+
0
Pd to Pd ; it is over the latter species that the activa-
tion of an H molecule occurs. The effect of the
2
amount of NaBH on the catalytic properties of 1 wt %
4
W
CD
Φ = R
,
Pd–PEG-6000/ZnO and 1 wt % Pd/С (М 200) was
act
examined in a model hydrogenation reaction of nitro-
where R is the average particle size of the catalyst, cm;
W is the reaction rate, mol/(L s), during the period of
time corresponding to the linear portion of the kinetic
benzene (PH2 = 0.1 MPa, Т = 45°С, solvent: ethanol).
Figure 1 shows the diagram of the dependence of
curve until a 10% conversion of the theoretically value the average rate constant of the model nitrobenzene
calculated for each substrate; С is the concentration of hydrogenation reaction on the weight of NaBH
4
the substrate, mol/L; and D is the diffusion coeffi- (0, 0.05, 0.10, 0.15, 0.20, 5, 10, 15, 20, and 25 mg) for
cient, 10–5 cm /s. In the conducted experiments, the 1 wt % Pd–PEG-6000/ZnO. A similar dependence
2
PETROLEUM CHEMISTRY
Vol. 57
No. 12
2017