Coating the Internal Surface of a Capillary Microreactor for the Selective Hydrogenation of 2-Methyl-3-Butyn-2-ol by PdxZn1 – x/TiO2 Catalysts: A Kinetic Study

Article abstract of DOI:10.1134/S0023158418040092

The kinetics of the liquid-phase hydrogenation of 2-methyl-3-butyn-2-ol (MBI) on the thin films of Pd₅₀Zn₅₀/TiO₂, Pd₈₀Zn₂₀/TiO₂, and Pd/TiO₂ was studied in a temperature range of 308–333 K at MBI concentrations of 0.1–0.6 mol/L. The films were applied to the internal walls of silica capillaries with an inside diameter of 530 μm. The reaction of MBI hydrogenation at its initial stage was of first order with respect to hydrogen, and the orders of reaction with respect to MBI on Pd₅₀Zn₅₀/TiO₂, Pd₈₀Zn₂₀/TiO₂, and Pd/TiO₂ were 0.3, 0.4, and 0.5, respectively. The yield of the target product 2-methyl-3-buten-2-ol on the bimetallic films was higher than that on Pd/TiO₂. The highest yield (94%) was achieved on the film of Pd₅₀Zn₅₀/TiO₂ at a conversion of 99%, a temperature of 313 K, and a partial hydrogen pressure of 1 atm. The higher selectivity of the reaction, which occurred according to the Langmuir–Hinshelwood mechanism, on the bimetallic films was explained by a decrease in the alkene/alkyne and alkene/alkane ratios of adsorption constants and by a decrease in the rate constants of 2-methyl-3-buten-2-ol hydrogenation.

Full text of DOI:10.1134/S0023158418040092

ISSN 0023-1584, Kinetics and Catalysis, 2018, Vol. 59, No. 4, pp. 450–458. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © L.B. Okhlopkova, M.A. Kerzhentsev, Z.R. Ismagilov, 2018, published in Kinetika i Kataliz, 2018, Vol. 59, No. 4, pp. 441–449.
Coating the Internal Surface of a Capillary Microreactor
for the Selective Hydrogenation of 2-Methyl-3-Butyn-2-ol
by PdxZn1 – x/TiO2 Catalysts: A Kinetic Study
L. B. Okhlopkovaa, *, M. A. Kerzhentseva, and Z. R. Ismagilova, b
aBoreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
bInstitute of Coal Chemistry and Chemical Materials Science, Siberian Branch, Russian Academy of Sciences,
Kemerovo, 650065 Russia
*e-mail: mila65@catalysis.ru
Received October 24, 2017
Abstract—The kinetics of the liquid-phase hydrogenation of 2-methyl-3-butyn-2-ol (MBI) on the thin films
of Pd50Zn50/TiO2, Pd80Zn20/TiO2, and Pd/TiO2 was studied in a temperature range of 308–333 K at MBI
concentrations of 0.1–0.6 mol/L. The films were applied to the internal walls of silica capillaries with an
inside diameter of 530 μm. The reaction of MBI hydrogenation at its initial stage was of first order with
respect to hydrogen, and the orders of reaction with respect to MBI on Pd50Zn50/TiO2, Pd80Zn20/TiO2, and
Pd/TiO2 were 0.3, 0.4, and 0.5, respectively. The yield of the target product 2-methyl-3-buten-2-ol on the
bimetallic films was higher than that on Pd/TiO2. The highest yield (94%) was achieved on the film of
Pd50Zn50/TiO2 at a conversion of 99%, a temperature of 313 K, and a partial hydrogen pressure of 1 atm. The
higher selectivity of the reaction, which occurred according to the Langmuir–Hinshelwood mechanism, on
the bimetallic films was explained by a decrease in the alkene/alkyne and alkene/alkane ratios of adsorption
constants and by a decrease in the rate constants of 2-methyl-3-buten-2-ol hydrogenation.
Keywords: 2-methyl-3-butyn-2-ol hydrogenation, kinetic simulation, PdZn nanoparticles, thin films, meso-
porous titanium dioxide
DOI: 10.1134/S0023158418040092
INTRODUCTION
is responsible for their catalytic properties [6, 7].
Therefore, a study of the effect of the composition of
PdxZn1 – x nanoparticles on the properties of catalysts
for MBI hydrogenation and a systematic analysis of
the kinetics of selective hydrogenation of an alkyne
alcohol are of considerable current interest. The high
rate of mass transfer in the microcapillary reactors
makes it possible to perform reactions in the kinetic
regime and, therefore, to calculate the numerical val-
ues of kinetic and adsorption constants.
Industrial wastes, which are potentially hazardous
to human health and the natural environment, belong
to the main ecological problems of modern times. The
introduction of microcapillary reactors with catalytic
coatings into fine organic synthesis and pharmaceuti-
cal industry can decrease the amount of wastes and
abandon the use of reagents that pollute the environ-
ment [1]. Furthermore, the occurrence of side reac-
tions in these reactors can be controlled by correctly
choosing contact time, which makes it possible to
increase selectivity for the formation of the target
product in successive reactions.
The kinetics of the selective hydrogenation of 2-
methyl-3-butyn-2-ol can be described by the Lang-
muir–Hinshelwood (LH) mechanism. The overall
The capabilities of selective liquid-phase hydroge- reaction rate is determined by the stage of substrate
nation in microcapillary reactors were studied previ- hydrogenation on the catalyst surface, whereas the
ously [2–5]. The yield of unsaturated alcohol in the stages of adsorption and desorption occur rapidly. Two
selective hydrogenation of 2-methyl-3-butyn-2-ol models of this reaction were proposed. According to
(MBI) reached in a microcapillary reactor was higher one of them, there are two types of adsorption centers
than that in a conventional batch reactor. The precise on Pd; in this case, hydrogen is adsorbed more weakly
control of the size and composition of an active com- than MBI [3, 8, 9]. The other model is based on the
ponent is of primary importance in the processes of competitive adsorption of a hydrogen atom and an
selective hydrogenation. The introduction of a second organic substrate molecule at a center [10, 11], after
metal into the catalyst composition facilitates the reg- which a slow stage of the addition of the second hydro-
ulation of the electronic state of nanoparticles, which gen atom to the reagent occurred [12]. As follows from
450

COATING THE INTERNAL SURFACE
451
Table 1. Composition of the powdered catalysts according
of 200 kV. The chemical composition of the catalysts
was determined on an EDAX energy-dispersive spec-
trometer (EDAX Inc., the United States) supplied
with a Si(Li) detector with a resolution of 130 eV. The
porous structure of the powders was analyzed by the
low-temperature adsorption of nitrogen on an ASAP
2400 instrument (Micromeritics, the United States).
The specific surface area was determined by the BET
method; the mean diameter of mesopores was calcu-
lated based on the desorption branch of an isotherm by
the Barrett–Joyner–Halenda (BJH) method.
to the XFA data
Concentration, wt %
Catalyst
TiO2
Pd
Zn
C
Pd50Zn50/TiO2
Pd80Zn20/TiO2
Pd/TiO2
0.84
0.96
1.1
0.56
0.09
0
70.5
66.4
62.3
28.1
32.6
36.6
published data, the hydrogenation of acetylene alco-
hols on Pd catalysts is first-order reaction with respect
to hydrogen; this fact indicates the presence of weakly
bound hydrogen on the metal surface [3, 5].
Catalytic Experiments
The catalyst powder preliminarily ground in an
agate mortar was placed in a 130-mL autoclave and
reduced at 523 K and a hydrogen pressure of 10 atm for
2 h; then, it was cooled to room temperature. The
solution of MBI in methanol (50 mL) with a concen-
tration of 0.1 mol/L was blown with nitrogen, trans-
ferred into the reactor, and hydrogenated at 333 K and
a hydrogen pressure of 5 atm with intense stirring at a
rate of 2000 rpm. For the determination of the con-
centrations of reaction mixture components, 1-buta-
nol (0.1 mol/L) was used as an internal standard.
In this work, we studied the kinetics of hydrogena-
tion of 2-methyl-3-butyn-2-ol on the thin catalytic
films of PdxZnx – 1/TiO2 supported onto the internal
walls of a silica capillary. The reaction was carried out
under the conditions of an annular two-phase flow in
the absence of limitations on mass transfer. We studied
the effects of reaction temperature; hydrogen pres-
sure; the concentrations of MBI, 2-methyl-3-buten-
2-ol (MBE), and 2-methyl-2-butanol (MBA); and
the composition of PdxZnx – 1 nanoparticles and pro-
posed a kinetic model to adequately describe the
experimental data.
The catalyst in the microcapillary reactor was pre-
liminarily reduced in situ in a flow of hydrogen
(2 mL/min) at 573 K for 2 h; then, it was washed for
5 h in a flow of methanol (20 μL/min) and reduced in
a flow of hydrogen (2 mL/min) at a temperature of
573 K for 2 h. The hydrogenation of MBI and MBE in
a solution of methanol at concentrations of 0.1–0.6
and 0.05–0.61 mol/L was performed in order to esti-
mate the kinetic and adsorption constants. The exper-
imental procedure was described elsewhere [14]. The
liquid flow rate was varied from 15 to 340 μL/min, and
the gas flow rate was 6 mL/min. Products were ana-
lyzed on a Kristall 2000M gas chromatograph (Khro-
matek, Russia) with a flame-ionization detector and
an SKTFT-50X capillary column (diameter, 0.22 mm;
EXPERIMENTAL
Synthesis and Physicochemical
Characterization of Films
Colloidal Pd and PdZn nanoparticles stabilized
with polyvinylpyrollidone were prepared by the reduc-
tion of the salts Pd(CH3COO)2 (46.5% Pd, Aurat) and
ZnCl2 (98%) in a solution of ethylene glycol [13]. The
mesoporous films of titanium dioxide doped with the
nanoparticles were obtained via one-stage synthesis
with the use of a precursor solution according to a pro-
cedure described earlier [14]. The Pd50Zn50/TiO2,
Pd80Zn20/TiO2, and Pd/TiO2 were prepared both as
powders (Table 1) and as films applied to the internal
surface of a capillary. The weights of the films were
1.10, 1.08, and 1.15 mg, respectively. The Pd, Zn,
TiO2, and C contents of the powdered catalysts were
determined by X-ray fluorescence analysis (XRF) on a
VRA-30 analyzer (ThermoFisher Scientific, Switzer-
land) with a Cr anode of the X-ray tube. Inductively
coupled plasma atomic emission spectroscopy (ICP
AES) was used for determining the composition of
catalytic films in the microcapillary reactors with the
aid of an OPTIMA 4300 DV instrument (Perkin
Elmer, the United States). The sizes of nanoparticles
and their particle-size distributions in powdered sam-
ples were calculated based on the micrographs
obtained by transmission electron microscopy (TEM)
on a JEM-2010 electron microscope (JEOL, Japan)
with a resolution of 0.14 nm at an accelerating voltage
length, 30 m). Balance on carbon was 100
2%.
Therefore, MBI, MBE, and MBA were the main
components of the analyzed mixture. The conversion
(x), selectivity for the formation of MBE (SMBE), the
yield of product (Y), and the process productivity (A)
were calculated from the following equations:
СМBI,0 − С
х =
МBI ×100,
СМBI,0
СМBЕ
СМBI,0 − СМBI
SМBЕ
=
×100,
СМBЕ
СМBI,0
Y =
×100,
C
− CМBI VY
tmPd
(
)
МBI,0
A =
A =
×100,
×100,
C
− CМBI vY
(
)
МBI,0
l
mPd
KINETICS AND CATALYSIS Vol. 59 No. 4 2018

452
OKHLOPKOVA et al.
Table 2. Effect of the composition of a catalyst and the type of a reactor on the process productivity and selectivity of the
hydrogenation of 2-methyl-3-butyn-2-ol
−1
s–1
SMBE, %
Catalyst
Reactor
Y, %
A, mol
gPd
Pd50Zn50/TiO2
Pd50Zn50/TiO2
Pd80Zn20/TiO2
Pd80Zn20/TiO2
Pd/TiO2
Microreactor
Batch reactor
Microreactor
Batch reactor
Microreactor
Batch reactor
Batch reactor
269*
95.3
74.6
94.1
74.8
92.1
68.4
89.0
68.0
94.5
95**
361*
138**
575*
151**
9***
94.9
67.8
89.7
67.6
Pd/TiO2
Pd + Pd/CaCO3
−****
*С
= 0.2 mol/L, v = 6.00 mL/min,
= 1 atm, and T = 313 K. **MBI/Pd = 2100, 50 mL of methanol,
= 5 atm, and T = 333 K.
Р
Н2
Р
Н2
MBI
g
***MBI/Pd = 326, 15 mL of hexane,
= 1 atm, and T = 323 K [22]. **** N/A.
Р
Н2
where CMBI, 0 is the initial concentration of MBI, CMBI
and CMBE is the current concentrations of MBI and
MBE respectively, V is the volume of the reaction
solution, vl is the liquid flow rate, t is the current reac-
tion time in an autoclave, mPd is the mass of Pd.
RESULTS AND DISCUSSION
According to the TEM data, the film thickness of
Pd50Zn50/TiO2 was 250–500 nm (Fig. 1a). The parti-
cle sizes of Pd50Zn50 both in a film (Fig. 1b) and in the
powder (Fig. 1c) varied from 2 to 3 nm. The pore
diameter in the film catalyst was 4–5 nm (Fig. 1a),
which is consistent with data for the powder catalyst
calculated based on the isotherms of low-temperature
nitrogen adsorption (Fig. 2). The composition of pow-
dered samples established by XFS was somewhat dif-
ferent from the specified composition (Table 1). The
relative concentration of Pd was somewhat higher than
the expected value; this can be due to the oxidation of
bimetallic nanoparticles in air and the segregation of
Zn [19]. Carbon, which resulted from template
decomposition, was present in the samples [6].
Table 2 summarizes the results of a comparison of
the main process characteristics of MBI hydrogena-
tion on Pd50Zn50/TiO2, Pd80Zn20/TiO2, and Pd/TiO2
in the microcapillary and loaded reactors. As can be
seen, the yield of product and the productivity of the
catalyst decreased upon the addition of Zn. The rate of
MBA formation at the initial stages of reaction in the
microcapillary reactor was low; this allowed us to
reach an MBE yield of 89–94%. The yield of the prod-
uct increased with the Zn content.
Kinetic Model
Mass and heat transfer in the microreactors is more
intense by two orders of magnitude than that in usual
chemical reactors [15]. The absence of diffusion lim-
itations makes it possible to carry out reactions in the
kinetic regime and to reach their chemical potentials.
The hydrogenation of MBI occurs consecutively with
the intermediate formation of MBE, which is further
hydrogenated to MBA. The direct hydrogenation of
MBI to MBA also cannot be excluded:
'
'
k1
k2
H2
H2
OH
МBЕ
OH
МBА
OH
МBI
'
k3
2H2
We used the LH model [12, 16], which implies the
quasi-equilibrium competitive adsorption of organic
molecules and hydrogen on the catalyst surface; there-
after, a slow stage of hydrogenation occurs. This
model was applied previously to study the kinetics of
MBI hydrogenation on PdBi and Pd/polymer cata-
lysts [17, 18]. The kinetic model of MBI hydrogena-
tion on the films of PdZn/TiO2 was reported previ-
ously [14]. The kinetic parameters were calculated
using the Fminsearch function for the minimization of
a discrepancy between experimental and calculated
data on the concentrations of components at the reac-
tor outlet. The Matlab software was used for this pur-
pose. The concentrations were calculated by solving a
system of differential equations with the use of the
“ode45” function.
In order to determine the order of reaction with
respect to MBI, we studied the dependence of the ini-
tial rate of hydrogenation of MBI on its concentration
within the limits from 0.1 to 0.45 mol/L (Fig. 3a).
Note that the occurrence of an induction period pre-
vents the determination of the reaction rate constant
'
k1
and the adsorption constant KMBI. Nikoshvili et al.
[18] assumed that the occurrence of an induction
period is related to the formation of active centers. The
initial concentration of MBI only slightly influenced
the rate of hydrogenation; this fact is consistent with
published data [20, 21]. The orders of reaction with
respect to MBI on the films of Pd50Zn50/TiO2,
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COATING THE INTERNAL SURFACE
(b)
453
(а)
(c)
500 nm
10 nm
10 nm
(d)
(e)
(f)
130
117
104
91
CK
OK
TiK
Ni/N, %
40
30
20
10
78
65
52
39
CuK
SiK
KK
ClK
26
CuL
PdL
13
ZnK
50 nm
0
1 2 3 4 5 6 7 8 9 10
keV
0
1
2
3
Average size, nm
Fig. 1. TEM micrographs of the (a, b, d) film and (c) powder Pd Zn /TiO catalyst and (e) the results of the TEM EDAX anal-
50
50
2
ysis of the film sample and (f) the bar diagram of particle sizes in the powder sample.
(а)
Adsorption, сm3 g–1
(b)
dV/dD, сm3 g–1 nm–1
100
80
60
40
20
0.008
0.006
0.004
0.002
0
0.2 0.4 0.6 0.8 1.0
0
5
10 15 20 25 30
Size, nm
P/P0
Fig. 2. (a) Isotherms of nitrogen adsorption and (b) pore-size distribution in the powder Pd Zn /TiO catalyst.
50
50
2
Pd80Zn20/TiO2, and Pd/TiO2 were 0.3, 0.4, and 0.5, Pd/TiO2. Note that, in this case, the catalysts were
respectively.
rapidly deactivated, but the activity was completely
restored after conducting the hydrogenation of MBI
on them. The hydrogenation of a mixture of MBE
with MBA was performed on the film of
Pd50Zn50/TiO2 (Table 3). Upon the addition of an
equimolar amount of MBA to MBE, the catalyst
activity decreased by a factor of 3. The point is that
MBA, which resulted from the hydrogenation of
In order to calculate the rate constant of MBE
hydrogenation
we studied the effect of MBE concentrations in a
range from 0.05 to 0.61 mol/L on the initial rate of reac-
tion on the films of Pd50Zn50/TiO2, Pd80Zn20/TiO2, and
Pd/TiO2 (Fig. 3b). The rate of MBE hydrogenation
increased in the order Pd50Zn50/TiO2 < Pd80Zn20/TiO2 <
'
and the adsorption constant KMBE,
k2
KINETICS AND CATALYSIS Vol. 59 No. 4 2018

454
OKHLOPKOVA et al.
(а)
(b)
–1
Activity, mol L–1
g
s–1
–1
Activity, mol L–1
g
s–1
Pd
Pd
25
80
15
10
5
15
10
5
3
2
3
1
2
1
0
0.1
0.2
0.3
0.4
0.5
0
0.2
0.4
0.5
СМBI, mol/L
СМBI, mol/L
Fig. 3. Effect of the initial concentrations of (a) 2-methyl-3-butyn-2-ol and (b) 2-methyl-3-buten-2-ol on the activity of the film
catalysts (1) Pd Zn /TiO , (2) Pd Zn /TiO , and (3) Pd/TiO . Reaction conditions: C
= 0.1–0.45 mol/L; gas flow
50
50
2
80
20
2
2
MBI,0
rate, 6.0 mL/min;
= 1 atm; and T = 313 K.
Р
Н2
MBE, was adsorbed on the catalyst surface, which tion of hexyne on a Pd/C catalyst [22]. This ratio
decreased as the Zn content was increased.
leads to decrease the number of active centers [17].
The addition of zinc decreased the rate constants of
MBI and MBE hydrogenation; moreover, this is true
Figure 4 shows selectivity for the formation of
MBE depending on the conversion of MBI. The selec-
tivity decreased at the high degrees of MBI conver-
sion. This is consistent with the results of the hydroge-
nation of acetylene alcohols on Pd catalysts [5, 18].
The adsorption constants of alkynes are much higher
than the adsorption constants of alkenes; therefore,
the adsorbed alkyne amount considerably exceeds the
alkene amount on the surface. The addition of Zn to
Pd nanoparticles increased selectivity for the forma-
tion of MBE at high conversions of MBI.
'
for the constant to a greater extent (Table 4). Con-
k2
sequently, the observed change in the relative apparent
rates of MBI and MBE consumption on the bimetallic
catalysts (Figs. 5c, 5d and Fig. 3b in ref. [14]) can be
related to changes in the adsorption constants and the
rate constants of MBE hydrogenation. On the con-
trary, the KMBA/KMBI and KMBA/KMBE ratios increased
upon the addition of Zn (Table 4). On the film catalyst
Pd50Zn50/TiO2, the ratio KMBA/KMBE > 1 caused a
decrease in the rate of MBE hydrogenation in the
presence of MBA (Table 3). The rate constant of the
Table 4 summarizes the kinetic parameters of the
reaction that occurs by the LH mechanism on the
films of Pd50Zn50/TiO2, Pd80Zn20/TiO2, and Pd/TiO2.
'
direct hydrogenation of MBI to MBA ( ) on the
k3
bimetallic catalysts is considerably higher than that on
Note that the induction period was not considered in Pd/TiO2. An increase in the rate of the direct hydroge-
the calculations. From the kinetic curves of MBI
hydrogenation (Figs. 5a, 5b and Fig. 3a in ref. [14]), it
Table 3. Effect of a 2-methyl-2-butanol additive upon the
rate of MBI hydrogenation on the film of Pd50Zn50/TiO2
follows that the consumption of MBI and the forma-
tion of MBE and MBA on the films of Pd50Zn50/TiO2,
Pd/TiO2, and Pd80Zn20/TiO2 were described by the
LH model with accuracies of 28, 29, and 27%, respec-
tively. The adsorption constant of MBE was lower than
the adsorption constant of MBI by a factor of 50–130.
The catalyst surface remained covered with the
adsorbed alkyne up to a 99% conversion of MBI. In
the presence of the alkyne, the alkene was not hydro-
genated, and it began to be converted into MBA only
upon the complete conversion of MBI. The ratio
between alkene and alkyne adsorption constants
−1
A, mol
s–1
CMBA, mol/L
gPd
0
2.7
0.05
0.10
0.19
2.1
1.4
0.8
С
= 0.2 mol/L; gas flow rate, 6.0 mL/min; liquid flow rate,
MBI,0
KMBE/KMBI is close to that observed in the hydrogena- 0.9 mL/min; PH = 1 atm; and Т = 313 K.
2
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COATING THE INTERNAL SURFACE
455
explained by a decrease in the KMBE/KMBI and
KMBE/KMBA ratios (the ligand effect). The active sur-
face of the catalyst was occupied predominantly by the
adsorbed molecules of MBI and MBA; as a result of
this, the rate of MBE hydrogenation decreased.
SМBЕ, %
100
3
2
1
Figure 6 represents results of a kinetic study of MBI
hydrogenation on the films of Pd50Zn50/TiO2,
Pd80Zn20/TiO2, and Pd/TiO2 at different tempera-
tures. The activation energies of the reaction on these
catalysts calculated according to the Arrhenius equa-
tion were 48 6, 47 6, and 44 3 kJ/mol, respec-
tively. These values are somewhat lower than those
obtained earlier on the film of Pd/TiO2 (63 kJ/mol)
[5]. It is interesting that, after reaching a limiting
value, the degree of conversion began to decrease with
the reaction temperature (Fig. 6a). In particular, the con-
version of MBI was almost the same at 323 and 333 K.
This fact can be explained by a decrease in the partial
pressure of hydrogen because of solvent evaporation
and diffusion into a gas phase. The partial pressures of
methanol at 313 and 333 K were 0.34 and 0.81 atm,
respectively. Because hydrogenation is a first-order
reaction with respect to hydrogen, the reaction rate
decreased by a factor of 2.4 as a result of the dilution of
hydrogen with methanol. As a result, an increase in
the reaction rate with temperature was compensated
80
60
20
40
60
80
100
0
x, %
Fig. 4. Dependence of selectivity for the formation of MBE
upon the degree of MBI conversion on the films of
(1) Pd Zn /TiO , (2) Pd Zn /TiO , and (3) Pd/TiO .
Reaction conditions: C
flow rate, 6.0 mL/min;
50 50
2
80 20
2
2
= (2) 0.3 and (1, 3) 0.2 mol/L; gas
= 1 atm; and T = 313 K.
MBI,0
Р
Н2
nation of MBI facilitates a decrease in reaction selec-
tivity at a low conversion of MBI (Fig. 4). The high
selectivity of MBE formation on the bimetallic cata-
lysts at a high degree of MBI conversion can be by its decrease caused by a decrease in the pressure of
Table 4. Kinetic parameters of the reaction of MBI hydrogenation on the films of PdxZn1 – x/TiO2
Pd50Zn50/TiO2
339
111 29
Pd80Zn20/TiO2*
Pd/TiO2
Parameter
−1
'
, mol
s–1
k1
gPd
2
356 16
130 50
513 23
559 47
−1
'
, mol
s–1
k2
gPd
−1
k3, mol gPd s–1
KMBI, L/mol
KMBE**
'
18
74
1
1
17
73
3
3
8 × 10–6 2 × 10–6
61
5
0.8 0.1
2***
1.3 0.1
0.5***
0.017
1.7 0.1
0.001***
0.28
KMBA
KMBE/KMBI
KMBA/KMBE
KMBA/KMBI
Max. deviation, %
0.011
2.5
1.6 × 10–5
0.39
2.7 × 10–2
28
6.8 × 10–3
27
4.54 × 10–7
29
* According to published data [14]. ** Calculated from the dependence of activity on the concentration of MBE (Fig. 3b). *** Fixed
value.
KINETICS AND CATALYSIS Vol. 59 No. 4 2018

456
OKHLOPKOVA et al.
C, mol/L
(а)
C, mol/L
(b)
0.20
0.20
3
1
2
0.15
0.10
0.05
0.15
0.10
1
3
0.05
2
0
4
8
0
4
8
t × 103, s/gPd
t × 103, s/gPd
(c)
(d)
–1 –1
dC/dt, mol L
g
s–1
–1 –1
Pd
dC/dt, mol L
g
s–1
Pd
100
1
800
2
2
50
0
400
3
1
3
2
4
6
8
0
2
4
6
t × 103, s/gPd
t × 103, s/gPd
Fig. 5. Dependences of the concentrations of (1) MBI and the products (2) MBE and (3) MBA upon contact time on the films
of (a) Pd Zn /TiO and (b) Pd/TiO and the dependences of reaction rates upon contact time on the films of (c)
50
50
2
2
Pd Zn /TiO and (d) Pd/TiO . Points and lines refer to the experimental data and the results calculated according to the Lang-
50
50
2
2
muir–Hinshelwood model, respectively. Reaction conditions: gas flow rate, 6.0 mL/min;
= 1 atm; and T = 313 K.
Р
Н2
(а)
SМBЕ, %
(b)
x, %
100
ln(x)
100
6
5
3
4.4
3
4
80
60
40
20
80
2
4.0
3.6
3.2
2.8
2
1
60
40
20
1
3.1
3.2
310
315 320 325 330 335
3.0
305
T, К
1/T × 103, 1/K
Fig. 6. (a) The temperature dependences of (1–3) the conversion of MBI and (4–6) selectivity for the formation of MBE on the
(1, 4) Pd Zn /TiO , (2, 5) Pd Zn /TiO , and (3, 6) Pd/TiO catalysts. (b) Arrhenius plots for reactions on the
50
50
2
80
20
2
2
(1) Pd Zn /TiO , (2) Pd Zn /TiO2, and (3) catalysts. Reaction conditions: CMBI, 0 = (2) 0.3 and (1, 3) 0.2 mol/L; fluid flow
50
50
2
80
20
rates, (1, 2) 0.120 and (3) 0.11 mL/min; gas flow rate, 6.0 mL/min;
= 1 atm; and T = 313 K.
Р
Н2
KINETICS AND CATALYSIS
Vol. 59
No. 4
2018

COATING THE INTERNAL SURFACE
457
Table 5. Dependence of the conversion of MBI and selec-
tivity for the formation of MBE on the partial pressure of
hydrogen on the film of Pd50Zn50/TiO2
reaction manifested itself to a greater extent in the
region of the high degrees of MBI conversion (Fig. 7).
The selectivity decreased upon a decrease in the par-
tial pressure of hydrogen in a mixture with argon due
to the oxidation of nanoparticles by an oxygen impu-
rity in argon. As found earlier [14], selectivity for the
formation of MBE became lower after the oxidative
treatment of the film of Pd80Zn20/TiO2. The greatest
yield of MBE was achieved at a partial H2 pressure of
1 atm.
Partial pressure
of Н2, atm
SMBE, %
x, %
0.28
0.50
0.76
0.100
1.5
24.2
44.9
63.6
56.6
94.5
94.4
95.9
CONCLUSIONS
С
= 0.2 mol/L; gas flow rate, 6.0 mL/min; liquid flow rate,
MBI,0
Thus, we studied the kinetics of MBI hydrogena-
tion on the films of Pd50Zn50/TiO2, Pd80Zn20/TiO2,
and Pd/TiO2 supported onto the internal walls of a
microcapillary reactor: the effects of the temperature
of reaction, the residence time of liquid in the reactor,
the initial concentration of MBI, and the partial pres-
sure of hydrogen on the activity of the catalysts and
selectivity for the formation of MBE. The greatest
yield of MBE (94%), which was comparable with its
yield on a commercial Lindlar catalyst (94.5%), was
obtained on the film of Pd50Zn50/TiO2 at a tempera-
ture of 313 K, an MBI conversion of 99%, a partial
hydrogen pressure of 1 atm, and a liquid residence
time of 10 min. The reaction is of first order with
respect to hydrogen, and its orders with respect to 2-
methyl-3-butyn-2-ol on the films of Pd50Zn50/TiO2,
Pd80Zn20/TiO2, and Pd/TiO2 are 0.3, 0.4, and 0.5,
respectively. A kinetic model of reaction was proposed
to satisfactorily describe the observed regularities. The
introduction of Zn into the nanoparticles of Pd
changed the ratios between alkyne, alkene, and alkane
adsorption constants to indicate the manifestation of
0.12 mL/min;
= 1 atm; and Т = 313 K.
P
H2
hydrogen. As the temperature was increased from 323
to 333 K, selectivity for the formation of MBE insig-
nificantly decreased (Fig. 6a).
Table 5 shows the dependence of the conversion of
MBI and selectivity for the formation of MBE on the
film of Pd50Zn50/TiO2 upon the partial pressure of
hydrogen. At
from 0.4 to 1.0 atm, the selectivity of
PH
2
approximately 95% remained almost constant. At a
low conversion of MBI (2%), which was observed
upon high dilution with argon (a partial hydrogen
pressure of 0.3 atm), it decreases to 57%. This can be
explained by the high rate of the direct hydrogenation
of MBI to MBA. The conversion of MBI increased
with the partial pressure of hydrogen; this fact is con-
sistent with the first order of reaction with respect to
hydrogen and the weak adsorption of H2 on the surface
of nanoparticles. The effect of
on the selectivity of
PH
2
SМBE, %
(а)
SМBE, %
(b)
100
100
2
1
1
80
60
80
2
60
0
20
40
60
80
100
x, %
20
40
60
80
100
x, %
0
Fig. 7. Dependences of selectivity for the formation of MBE on the films of (a) Pd Zn /TiO and (b) Pd/TiO upon the con-
80
20
2
2
version of MBI at partial hydrogen pressures of (1) 1 and (2) 0.5 atm. Reaction conditions: C
= 0.3 mol/L; fluid flow rate,
MBI, 0
0.070–0.300 mL/min; gas flow rate, 6.0 mL/min;
= 1 atm; and T = 313 K.
Р
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KINETICS AND CATALYSIS Vol. 59 No. 4 2018

458
OKHLOPKOVA et al.
8. Protasova, L.N., Rebrov, E.V., Skelton, H.E., Wheat-
ley, A.E.H., and Schouten, J.C., Appl. Catal., 2011,
vol. 399, p. 12.
9. Vernuccio, S., Goy, R., Rudolf von Rohr, Ph., Med-
lock, J., and Bonrath, W., React. Chem. Eng., 2016,
vol. 1, p. 445.
10. Semagina, N., Grasemann, M., Xanthopoulos, N.,
Renken, A., and Kiwi-Minsker, L., J. Catal., 2007,
vol. 251, p. 213.
11. Semagina, N., Joannet, E., Parra, S., Sulman, E., Ren-
ken, A., and Kiwi-Minsker, L., Appl. Catal., A, 2005,
vol. 280, p. 141.
the ligand effect. The KMBE/KMBI and KMBE/KMBA
ratios decreased with the zinc content. The higher
selectivity of reaction on the bimetallic films can be
explained by a decrease in the rate constants of hydro-
genation of 2-methyl-3-buten-2-ol and the ratios
between alkene/alkyne and alkene/alkane adsorption
constants with the Zn content. It was demonstrated
that the application of capillary microreactors with the
bimetallic films of PdZn/TiO2 to the selective hydro-
genation of acetylene alcohols is promising.
12. Singh, U.K. and Vannice, M.A., J. Catal., 2000,
ACKNOWLEDGMENTS
vol. 191, p. 165.
We are grateful to A.V. Ishchenko, T.Ya. Efimenko,
and I.L. Kraevskaya for their assistance in the physi-
cochemical characterization of the samples.
This work was supported by the Federal Agency for
Scientific Organizations (FANO) of Russia (project
no. 0303-2016-0004).
13. Dominguez-Dominguez, S., Berenguer-Murcia, A.,
Cazorla-Amoros, D., and Linares-Solano, A., J.
Catal., 2006, vol. 243, p. 74.
14. Okhlopkova, L.B., Kerzhentsev, M.A., and Ismagilov, Z.R.,
Kinet. Katal., 2018, vol. 59, no. 3, p. 1.
15. Kashid, M., Renken, A., and Kiwi-Minsker, L., Micro-
structured Devices for Chemical Processing, Wein-
heim;Wiley-VCH Verlag GmbH & Co. KGaA, 2014,
p. 384.
REFERENCES
16. Duca, D., Liotta, L.F., and Deganello, G., J. Catal.,
1. Renken, A. and Kiwi-Minsker, L., Adv. Catal., 2010,
1995, vol. 154, p. 69.
vol. 53, p. 47. doi 10.1016/S0360-0564(10)53002-5
17. Cherkasov, N., Ibhadon, A.O., McCue, A.J., Ander-
son, J.A., and Johnston, S.K., Appl. Catal., A, 2015,
vol. 497, p. 22.
18. Nikoshvili, L.Z., Makarova, A.S., Lyubimova, N.A.,
Bykov, A., Sidorov, A.I., Tyamina, I.Y., Matveeva, V.G.,
and Sulman, E.M., Catal. Today, 2015, vol. 256, p. 231.
19. Okhlopkova, L.B., Kerzhentsev, M.A., Tuzikov, F.V.,
Larichev, Y.V., Prosvirin, I.P., and Ismagilov, Z.R., J.
Nanopart. Res., 2012, vol. 14, p. 1089. doi
10.1007/s11051-012-1089-9
2. Rebrov, E.V., Berenguer-Murcia, A., Skelton, H.E.,
Johnson, B.F.G., Wheatley, A.E.H., and Schouten, J.C.,
Lab Chip, 2009, vol. 9, p. 503.
3. Rebrov, E.V., Klinger, E.A., Berenguer-Murcia, A.,
Sulman, E.M., and Schouten, J.C., Org. Process Res.
Dev., 2009, vol. 13, p. 991.
4. Cherkasov, N., Ibhadon, A.O., and Rebrov, E.V., Lab
Chip, 2015, vol. 15, p. 1952.
5. Okhlopkova, L.B., Kerzhentsev, M.A., and Ismagilov, Z.R.,
20. Bond, G.C., Focus Catal., 2006, p. 8.
Kinet. Catal., 2016, vol. 57, no. 4, p. 501.
21. Tew, W., Janousch, M., Huthwelker, T., and van Bok-
6. Okhlopkova, L.B., Matus, E.V., Prosvirin, I.P., Ker-
zhentsev, M.A., and Ismagilov, Z.R., J. Nanopart. Res.,
2015, vol. 17, p. 1.
7. Okhlopkova, L.B. Cherepanova, S.V., Prosvirin, I.P.,
Kerzhentsev, M.A., and Ismagilov, Z.R., Appl. Catal.,
A, 2018, vol. 549, p. 245.
hoven, J.A., J. Catal., 2011, vol. 283, p. 45.
22. Dobrovolna, Z., Kacer, P., and Cerveny, L., J. Mol.
Catal. A: Chem., 1998, vol. 130, p. 279.
Translated by V. Makhlyarchuk
KINETICS AND CATALYSIS
Vol. 59
No. 4
2018