Formal Kinetic Description of Photocatalytic Hydrogen Evolution from Ethanol Aqueous Solutions in the Presence of Sodium Hydroxide

Article abstract of DOI:10.1134/S0023158418060101

Abstract: The dependences of the rate of the photocatalytic hydrogen production in ethanol aqueous solutions on the concentration of ethanol and sodium hydroxide on the 1% Pt/10% Ni(OH)₂/Cd_0.3Zn_0.7S photocatalyst under vis

Full text of DOI:10.1134/S0023158418060101

ISSN 0023-1584, Kinetics and Catalysis, 2018, Vol. 59, No. 6, pp. 727–734. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © D.V. Markovskaya, E.A. Kozlova, 2018, published in Kinetika i Kataliz, 2018, Vol. 59, No. 6, pp. 685–693.
Formal Kinetic Description of Photocatalytic Hydrogen Evolution
from Ethanol Aqueous Solutions in the Presence of Sodium Hydroxide
D. V. Markovskayaa, b, * and E. A. Kozlovaa, b
aBoreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia
bNovosibirsk State University, Novosibirsk, 630090 Russia
*e-mail: madiva@catalysis.ru
Received April 3, 2018
Abstract—The dependences of the rate of the photocatalytic hydrogen production in ethanol aqueous solu-
tions on the concentration of ethanol and sodium hydroxide on the 1% Pt/10% Ni(OH)2/Cd0.3Zn0.7S pho-
tocatalyst under visible light irradiation (λ = 450 nm) are studied. To describe kinetic data, the Langmuir–
Hinshelwood equation was modified. An equation was proposed that reflects the dependence of the reaction
rate on the concentration of NaOH, and an equation was derived for the first time that shows the dependence
of the rate of photocatalytic hydrogen production from the concentrations of both reactants, ethanol and
sodium hydroxide. The validity of the proposed equations was confirmed by their use for the description of
the experimental data obtained in this work and reported earlier.
Keywords: photocatalysis, hydrogen production, Cd1–xZnxS, simulations, Langmuir–Hinshelwood equation
DOI: 10.1134/S0023158418060101
INTRODUCTION
mentally under various initial conditions and their
approximation by the equations. In this way, the
mathematical description of the photocatalytic oxida-
tion processes of organic substances in the gas phase
was obtained [12]. In the case of photocatalytic reac-
tions in solutions, several attempts have been made to
obtain mathematical models that show the relation-
ship between the rate of the photocatalytic process and
the reactant concentrations, but all of them described
the kinetic features of the photocatalytic hydrogen
production in the aqueous solutions of sodium sul-
fides and sodium sulfites [13–15]. For the photocata-
lytic decomposition of organic substances in aqueous
solutions an equation based on Langmuir–Hinshel-
wood model that describes the dependence of the
reaction rate only on the concentration of organic sub-
strate was proposed in [16, 17]:
A rapid decrease in the stocks of readily accessible
hydrocarbons requires extensive development of alter-
native energy sources and raw materials for the chem-
ical industry. One such alternative energy source is
hydrogen, the heat of combustion of which is very
high, and the product of combustion is water [1]. The
photocatalytic water decomposition under sunlight
illumination is a very promising method for obtaining
hydrogen since in this case hydrogen is formed directly
from renewable resources such as water and air. How-
ever, as indicated it the first works on the photocata-
lytic water splitting, in the case of the formation of
hydrogen and oxygen in a single volume, the reaction
between them can substantially reduce the quantum
efficiency of the process. Therefore, considerable
attention is given to the photocatalytic production of
hydrogen by the decomposition of available organic
and inorganic electron donors in aqueous solutions
rather than by water splitting [2–9]. The tendency of
using organic substances is attractive from the practi-
cal standpoint due to possible use of mono- and poly-
atomic alcohols formed by biomass processing [1].
kKC
1 + KC
(1)
W =
,
where W is the rate of the photocatalytic hydrogen
production, k is the apparent rate constant, and K is
the adsorption constant of the reactant molecule. With
Eq. (1), the kinetics of photocatalytic hydrogen pro-
duction in the aqueous solutions of alcohols (metha-
nol [18], ethanol [19], glycerol [20]), glucose [21],
acetic acid [22], triethanolamine [23], and organo-
phosphorus compounds [24]) has been described.
The prediction of reaction rates obtained by vary-
ing different conditions (e.g., reactant concentrations)
is one of the main problems of modern photocatalysis.
For conventional industrial heterogeneous catalytic
processes (such as the synthesis of sulfuric acid [10] or
ammonia [11]), this problem has been solved by accu-
However, there has been no equation published
mulating sets of reaction rate values obtained experi- that describes the dependence of the reaction rate on
727

728
MARKOVSKAYA, KOZLOVA
32–38% H2O), H2PtCl6 (Reakhim, reagent grade),
1
5
NaBH4 (Pulver, 98%), С2Н5ОН (96%).
The Cd0.3Zn0.7S photocatalyst was synthesized by
the procedure described in [28]. The 10%
Ni(OH)2/Cd0.3Zn0.7S catalyst was prepared as follows:
a solution of NiCl2 (0.1 mol/L, 3.66 mL) was added
dropwise to the 10-mL suspension containing 300 mg
of Cd0.3Zn0.7S, stirred for 5 min, and then the stoichio-
metric amount of NaOH (0.1 mol/L) solution was
added dropwise. The resulting suspension was stirred
for 30 min, washed by distilled water ten times, centri-
fuged for 15 min and dried for 4 h at 80°С. The pre-
pared photocatalyst was the solid solution of cadmium
sulfide and zinc sulfide Cd0.3Zn0.7S modified with
10 wt % of nickel hydroxide on the surface. Before
measurements of the hydrogen photoproduction rate
1 wt % of platinum was supported on the obtained
photocatalyst (the method of platinization was
described earlier in [25]).
6
2
4
3
Fig. 1. Setup for photocatalytic hydrogen production:
(1) LED, (2) reaction mixture, (3) magnetic stirrer,
(4) anchor, (5) quartz window, (6) sampling tube.
Measurement of the Rate of Photocatalytic
Hydrogen Evolution
the concentration of protons or hydroxide ions. Lyu-
bina et al. [25] showed that the photocatalytic hydro-
gen production from aqueous solutions of organic
alcohols can be approximated not in the full range of
substrate concentrations: for example, Eq. (1)
describes the dependence of the reaction rate on the
glycerol concentrations in the range 0–0.3 mol/L. A
similar pattern was reported for ethanol [26]. To con-
struct kinetic models, it is necessary to analyze the
reasons for the observed deviations.
The process of photocatalytic hydrogen production
was carried out in a glass reactor with a volume of 320
mL (Fig. 1), inside which the reaction suspension (2)
was stirred using a magnetic stirrer (3), and the photo-
catalyst was illuminated with LED (1) through a
quartz window (5).
The reaction rate of the photocatalytic hydrogen
production from ethanol aqueous solutions was mea-
sured as follows: the calculated amount of NaOH and
50 mg of the photocatalyst were added to the mixture of
ethanol and water (100 mL). The volume concentration of
ethanol was varied in the range from 0 to 70%, while the
concentration of NaOH was changed from 0 to 1 mol/L (a
further increase in the NaOH concentration was limited
by its solubility in the ethanol aqueous solutions). In all
experiments the reactor was preliminarily purged with
argon for 30 min until the complete removal of oxygen.
Then the reactor was irradiated by visible light (λ =
450 nm) for 90 min; LED (240 mW/cm2) was a light
source. The concentration of evolved hydrogen was
determined using a gas chromatograph (Khromos,
Russia). The carrier gas was argon. Origin Pro 2016
software was used to calculate the dependence of the
amount of evolved hydrogen on time. The linear part
of this dependence was approximated by the linear
equation using the least-squares method. The rate of
hydrogen production was taken equal to the slope.
The goal of this work was to derive and theoretically
justify an equation that allows one to accurately
describe the experimental dependences of the photo-
catalytic hydrogen production rate from aqueous eth-
anol solutions on the concentrations of ethanol and
sodium hydroxide. Ethanol was chosen as an organic
substrate, since it is the most convenient model com-
pound for studying the kinetics of hydrogen produc-
tion using aqueous solutions of alcohols. It has been
shown earlier that the rate of hydrogen evolution nor-
malized to the stoichiometric coefficient is a constant
value for major organic alcohols [27]. The kinetics of
photocatalytic hydrogen production was studied using
the
composite
photocatalyst
1%
Pt/10%
Ni(OH)2/Cd0.3Zn0.7S, which showed high activity in
the target process.
EXPERIMENTAL
Photocatalyst Preparation
RESULTS AND DISCUSSION
The Dependence of the Rate of Photocatalytic Hydrogen
Evolution on the Ethanol Concentration
The rate of photocatalytic hydrogen production
was measured for different initial concentrations of
ethanol and sodium hydroxide. The resulting values
To prepare catalysts and carry out kinetic experi-
ments, the following reagents were used: CdCl2
(Reakhim, reagent grade), Zn(NO3)2 (Reakhim, high
purity), NiCl2 (Reakhim, reagent grade), NaOH
(Reakhim, purity for analysis), Na2S ⋅ xH2O (Fluka,
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FORMAL KINETIC DESCRIPTION OF PHOTOCATALYTIC HYDROGEN
729
Table 1. Rate of the hydrogen photoproduction at different
initial conditions of ethanol and sodium hydroxide on the
1% Pt/10% Ni(OH)2/Cd0.3Zn0.7S photocatalyst
are shown in Table 1. The reaction rate dependence on
the ethanol concentration was considered at a con-
stant initial concentration of NaOH (0.1 mol/L). In
the absence of ethanol, low activity is observed in the
photocatalytic hydrogen production directly from the
aqueous NaOH solution. It has been shown earlier
that aqueous solutions of NaOH may play a role of the
hydrogen source in the photocatalytic reactions [29].
When a small amount of ethanol (5 vol %) was added,
the reaction rate becomes almost five times higher and
grows reaching 8.1 μmol/min at a volume concentra-
tion of ethanol of 50%. Table 1 shows that further
increase in the ethanol concentration leads to the
decrease in the reaction rate. Similar dependence of
the reaction rate on the ethanol concentration has
been described in the literature [26].
CC0H CH OH
,
CN0 aOH
,
W0,
μmol/min
3
2
, %
ϕ
CH3CH2OH
mol/L
0
5
0
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0
0.62 0.06
3.03 0.01
4.3 0.2
5.4 0.3
6.8 0.6
7.9 0.5
8.1 0.5
7.4 0.3
6.9 0.2
2.6 0.3
7.1 0.7
0.86
1.72
3.43
5.15
6.86
8.58
10.29
12.01
8.58
8.58
8.58
8.58
8.58
10
20
30
40
50
60
70
50
50
50
50
50
The analysis of the reaction mixture after 9 h of the
photocatalytic reaction from ethanol aqueous solu-
tions showed the presence of ethanol and acetalde-
hyde in the liquid phase. Therefore, at this stage of the
process, hydrogen is evolved according to the follow-
ing overall reaction:
0.05
0.2
0.4
1.0
10
14
25
1
1
2
(I)
CH3CH2OH → CH3CHO + H2.
According to Eq. (I), the rate of hydrogen forma-
tion is equal to the rate of ethanol consumption in the
photocatalytic oxidation process, and the rate-limiting
step of the photocatalytic alcohol decomposition is the
cleavage of С–Н bond in the α position relative to the
hydroxyl group [27]. The resulting experimental
dependences of the rate of photocatalytic ethanol oxi-
dation in aqueous solutions on the substrate concen-
tration are approximated by the Langmuir–Hinshel-
wood equation for a monomolecular reaction (Eq. (1))
[16, 17]. This approximation means that monomolec-
ular chemical reaction occurs on the surface, the
adsorption of the reagent on the photocatalyst surface
is described by the Langmuir isotherm. A specific fea-
ture of Langmuir–Hinshelwood approximation for a
monomolecular reaction (Eq. (1)) is the tendency of
the reaction rate to the maximum value with increas-
ing substrate concentration. It should be noted that,
for experimental data, this behavior is observed only
for a certain concentration range, after which the rate
of hydrogen production begins to decrease with
increasing ethanol content. In the literature, the
decrease in the rate of the hydrogen production at high
ethanol concentrations is attributed to the saturation
of the photocatalyst surface with ethanol and a rela-
tively low surface concentration of water that is neces-
sary for the formation of hydroxyl radicals and effi-
cient ethanol oxidation [30]. Note that, when the alco-
hol concentration in the suspension grows, both the
fraction of surface sites on which water and NaOH are
adsorbed that are potential sources of hydroxyl radi-
cals, and the fraction of free surface sites decrease. The
free sites can also be used during the process, because
they will adsorb the product of ethanol decomposi-
tion. Then from the formal point of view, the reactions
The experimental conditions: weight of the photocatalyst was
50 mg; volume of suspension was 100 mL; temperature was 20°С;
the light source was LED (λ = 450 nm).
occurring on the surface are recorded as follows in the
case of ethanol oxidation by directly photogenerated
holes (reaction (II)) or hydroxyl radicals (reaction (III)):
Z-CH3CH2OH + Z + h+
→ Z-CH3CH2Oi + Z-H+,
(II)
Z-CH3CH2OH + Z-OHi
(III)
→ Z-CH3CH2Oi + Z-H2O,
where Z is the free surface site, Z-CH3CH2OH, Z-
CH3CH2O∙, Z-H+, Z-OH∙ are the following species
adsorbed on the photocatalyst surface CH3CH2OH,
CH3CH2O∙, H+, OH∙, respectively.
According to reactions (II) and (III), the oxidation
of ethanol is a bimolecular reaction, and its rate can be
written as Eqs. (2) and (3), respectively, and the final
expression is represented by Eq. (4):
kIIKEtOHCEtOH
(1 + KEtOHCEtOH + KOHCOH
(2)
(3)
W = kIIθEtOHθ0 =
,
2
)
kIIIKEtOHCEtOHKOHCOH
(1 + KEtOHCEtOH + KOHCOH
W = kIIIθEtOH
θ
=
,
2
.
OH
)
i
W = kIIθEtOHθ0 + kIIIθEtOHθOH
(4)
KEtOHCEtOH(kII + kIIIKOHCOH
)
=
,
2
(1 + KEtOHCEtOH + KOHCOH
)
KINETICS AND CATALYSIS Vol. 59 No. 6 2018

730
W0, µmol/min
MARKOVSKAYA, KOZLOVA
Eq. (5). Figure 2 shows the resulting data, where the
solid line denotes the curve approximations by Eq. (5).
It is seen from Fig. 2 that chosen approximation cor-
rectly reflects the characteristic feature of the depen-
dence of the hydrogen production rate on the volume
concentration of ethanol (its passage through a maxi-
mum) and describes well the kinetics of the studied
process.
8
6
4
2
2
1
The Langmuir–Hinshelwood equation for the
monomolecular reaction (Eq. (1)) and Eq. (5) were
used to approximate data previously described in the
literature for photocatalytic hydrogen evolution from
aqueous solutions of methanol [30–32], ethanol [30,
31, 33], and n-propanol [33]; the parameters of
approximation are shown in Table 2. It is seen from
Table 2 that parameters kapp and K obtained in differ-
ent approximations differ several times for the same
systems. This fact is associated with different formulas
for the calculating of approximation parameters from
Eqs. (1) and (5), and also by the experimental difficul-
ties in determining the adsorption constants under
irradiation of the photocatalyst whose experimental
values could verify the reliability of the K determination
on the basis of the proposed simulations. Note that
kinetic data can be described by both approximations
almost in all cases, but the highest values of the correla-
tion coefficient R2 are achieved in the case of Eq. (5).
Moreover, when Eq. (5) is used, reasonable values of
errors in the approximation parameters are achieved,
which is not always possible when Eq. (1) is used. These
facts confirm the validity of the use of Eq. (5) for describ-
ing the dependence of the rate of photocatalytic hydro-
gen production on the ethanol concentration.
1.0
0.5
0
0
20
40
60
80
100
Ethanol content, vol %
Fig. 2. Approximation of the experimental data (curve 1,
R = 0.955) and data described in the literature (curve 2 [31],
R = 0.861) by Eq. (5). Experimental conditions: (1) 0.1 M
NaOH, photocatalyst 1% Pt/10% Ni(OH) Cd Zn S,
the catalyst concentration was 0.5 g/L, the volume of suspen-
sion was 100 mL, the temperature was 20°С, LED was the
light source (λ = 450 nm); (2) 0.1 M NaOH, photocatalyst
2
2
2/
0.3
0.7
–4
CdS, the catalyst concentration was 5.0 × 10 mol/L, the
volume of suspension was 40 mL, the temperature was
20°С, xenon–mercury arc lamp with light filter (λ > 400 nm)
was used as the light source.
where kII and kIII are the apparent rate constants,
KEtOH and KOH are the adsorption constants of ethanol
and sodium hydroxide, CEtOH and COH are the initial
concentrations of ethanol and NaOH.
At a constant concentration of NaOH and in the
absence of additional data on the value of the sodium
hydroxide adsorption constant, it is advisable to use
the general expression (Eq. (5)) as initial approxima-
tion, in which all the constant values, except for the
ethanol adsorption constant, belongs to the effective
rate constant, and the denominator is limited by the
first two terms. This assumption is reasonable, since
the surface of the photocatalyst is negatively charged
in the alkaline medium in all the discussed experi-
ments. Therefore, the negatively charged hydroxide
ions will predominantly repulse from the sample sur-
face, so the surface coverage by ОН– will be low com-
pared to coverages by other substrates.
Dependence of the Rate of Photocatalytic Hydrogen
Evolution on the Sodium Hydroxide Concentration
According to the experiments on the determination
of the optimal composition of the ethanol–water mix-
ture, the highest rates of photocatalytic hydrogen pro-
duction is achieved at a volume concentration of eth-
anol of 50%. Different amounts of sodium hydroxide
were added to ethanol solutions of this composition so
that its concentration in the resulting solution was
between 0 and 1 mol/L. The values of the reaction
rates obtained in this set of experiments are shown in
Table 1. In the presence of NaOH, a nonzero rate of
the photocatalytic hydrogen production is observed.
The oxidation of ethanol is likely to occur due to its
interaction with the photoinduced holes or hydroxyl
radicals formed from water. When a small amount of
NaOH was added, the rate of hydrogen photoproduc-
tion drastically increases due to the formation of
hydroxyl radicals.
KEtOHCEtOH(kII + kIIIKOHCOH
)
W =
2
(1 + KEtOHCEtOH
)
(5)
kappKEtOHCEtOH
=
,
2
(1 + KEtOHCEtOH
)
where
kapp = kII + kIIIKOHCOH
.
Figure 3 demonstrates that a further increase in the
Experimental data obtained in this work and reaction rate is linear with an increase in the NaOH
described earlier [31] were approximated using concentration. Therefore, according to the experi-
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FORMAL KINETIC DESCRIPTION OF PHOTOCATALYTIC HYDROGEN
731
Table 2. Approximation of the experimental data by Langmuir–Hinshelwood equations based on the monomolecular and
bimolecular approximations
Approximation by Eq. (1)
Approximation by Eq. (5)
Photocatalyst
Reference
kapp
μmol/min
,
kapp
μmol/min
,
R2
R2
K, L/mol
K, L/mol
Methanol
0.70
0.6% Pt/TiO2
0.83
0.99
[23]
[30]
0.07 0.03
4.2 0.8
0.2 0.1
0.6 0.2
1.0 0.3
0.07 0.02
0.09 0.01
Pt/TiO2
0.94
15
3
Ethanol
CdS
Pt/TiO2
Not approximated
1.9 0.6
3.9 1.1
0.31 0.09
0.18 0.01
0.08 0.01
0.86
0.87
0.96
[32]
[30]
0.86
0.88
5
12
2
4
20
34
2
5
1% Pt/10% Ni(OH)2/
Cd0.3Zn0.7S
0.3 0.1
This work
9% C/TiO2
0.84
0.96
0.96
0.97
[33]
[30]
0.2 0.1
0.5 0.3
1.8 0.5
2.1 0.4
0.9 0.1
0.07 0.02
0.20 0.02
Pt/CdS/TiO2/FTO
0.21 0.05
Propanol
0.71
9% C/TiO2
0.98
[33]
0.2 0.1
0.7 0.6
0.9 0.1
0.09 0.01
mental data, the dependence of the reaction rate on
Let us compare Eqs. (6) and (7). Since the equilib-
the NaOH concentration is described by the equation: rium concentration of ethanol and the adsorption
constant do not depend on the concentration of
(6)
W = a + bCOH
,
NaOH, then
−
where the coefficient a is equal to the rate of hydrogen
production in the absence of sodium hydroxide and b
is the apparent constant of the reaction rate.
KEtOHCEtOHkII
(8)
a =
,
2
1 + KEtOHCEtOH
(
)
Data on the dependence of the photocatalytic
hydrogen production rate on the sodium hydroxide
concentration described earlier in the literature [34–
38] were approximated by Eq. (6), and the approxima-
tion parameters are listed in Table 3. One can see that
the proposed equation describes the experimental data
with a high accuracy. Note that, earlier in the litera-
ture, no equations that describe the dependence of the
rate of hydrogen photoproduction rate on the NaOH
concentration were proposed.
W0, µmol/min
30
25
20
15
10
5
Special attention should be given to the relation-
ships between Eqs. (4)–(6). As noted earlier, the pro-
cess of ethanol oxidation can occur both directly with
the participation of the photogenerated holes (reac-
tion (II)) and with hydroxyl radicals (reaction (III)),
and Eq. (4) for the reaction rate takes into account
both oxidation routes. If the term containing the
dependence of the hydrogen production rate on the
NaOH concentration is separated at the fixed ethanol
concentration, then, taking into account that in the
alkaline media the contribution of KOHCOH can be
neglected in the denominator, the expression for the
reaction rate takes the following form:
0
0
0.2
0.4
0.6
0.8
1.0
NaOH concentration, mol/L
Fig. 3. Dependence of the rate of photocatalytic hydrogen
production on the NaOH concentration. The experimen-
tal conditions: 50 vol % ethanol, 50 mg of the 1% Pt/10%
Ni(OH) Cd Zn S photocatalyst, the volume of sus-
2/
0.3
0.7
pension was 100 mL, the temperature was 20°С, the light
source was LED (λ = 450 nm). The dashed line shows the
approximation by Eq. (6).
KEtOHCEtOHkII
(1 + KEtOHCEtOH
kIIIKEtOHCEtOHKOH
(7)
COH.
W =
+
2
2
)
1 + KEtOHCEtOH
(
)
KINETICS AND CATALYSIS Vol. 59 No. 6 2018

732
MARKOVSKAYA, KOZLOVA
Table 3. Approximation of the dependences of the hydrogen production rate on the NaOH concentration by Eq. (6)
Approximation by Eq. (6)
Concentration
of NaOH, mol/L
Photocatalyst
Reference
R2
a, μmol/min
b, μL/min
Methanol
0.09 0.01
0.05 0.01
Ethanol
1.2% Au/TiO2
0.875
0.888
[34]
[35]
0.08 0.01
0.16 0.04
0.1–5
3–9
Bi0.5Na0.5TiO3
1% Pt/10% Ni(OH)2/Cd0.3Zn0.7S
Ni(OH)2/CdS
0.995
0.996
This work
[36]
3.3 0.7
25
4
0–1
0.06 0.01
0.112 0.007
Glucose
0.01–5
InVO4 : Ni*
0.961
0.989
[37]
[38]
0.024 0.003
0
0.44 0.09
1.8 0.1
0–0.1
0.5% Pt/17% ZnS/ZnIn2S4
*Indium vanadate doped with nickel.
0–0.125
with the experimental results. If the ethanol concen-
tration is fixed, the reaction rate linearly depends on
the NaOH concentration, which also coincides with
the experimental results. In addition, using Wolfram
Mathematica 11.3 software, a counter plot was drawn
from the surface plot defined by Eq. (12) (Fig. 5). This
plot reflected a change in the rate of hydrogen produc-
tion when the initial concentrations of both reactants
are varied. Figure 5 shows that the highest values of the
rate of the target process (>25 μmol/min) are reached
in the ranges of rather high initial concentrations of
the reactants: the ethanol concentration should be
kIIIKEtOHCEtOHKOH
(9)
b =
.
2
1 + KEtOHCEtOH
(
)
Let us introduce new notation:
α = kIIKEtOH
β = kIIIKEtOHKOH
(10)
(11)
,
.
Then the dependence of the rate of photocatalytic
hydrogen production on the initial concentrations of eth-
anol and sodium hydroxide is described by Eq. (12).
(α + βCOH)CEtOH
(12)
W =
.
2
(1 + KEtOHCEtOH
)
Equation (12) was used to approximate experimental
data presented in Table 1. The approximation parameters
were α = 2.1 0.2 μL/min, β = 6.9 0.7 μL mol–1 min–1,
KEtOH = 0.08 0.01 L/mol, and the correlation coef-
ficient was 0.986. Thus, the proposed equation makes
it possible to describe the experimental data with a
high accuracy. Unfortunately, in the literature the
dependences of hydrogen production rate on the con-
centrations of both reagents are rarely measured, and
the set of available data is insufficient for accurate
mathematical description. Therefore, it is impossible
to consider the applicability of this equation to the lit-
erature data.
15
10
5
0
20
10
0
A surface plot defined by Eq. (12) reflects the main
kinetic features of photocatalytic hydrogen production
depending on the concentrations of ethanol and
sodium hydroxide (Fig. 4). If one fixes the value of the
initial NaOH concentration in Fig. 4 (this is most
clearly seen for a NaOH concentration of 1 mol/L)
and considers how the reaction rate changes with
increasing ethanol concentration, it is seen that this
dependence passes through a maximum, that agrees
1.0
0.5
0
Fig. 4. Surface plot defined by Eq. (12) that shows the
dependence of the rate of the photocatalytic hydrogen evo-
lution on the concentration of ethanol (0–17 mol/L) and
sodium hydroxide (0–1 mol/L).
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FORMAL KINETIC DESCRIPTION OF PHOTOCATALYTIC HYDROGEN
733
ACKNOWLEDGMENTS
NaOH concentration, mol/L
1.0
This work was conducted in the framework of the
budget project АААА-А17-117041710087-3 for Bore-
skov Institute of Catalysis.
25
20
15
10
5
0.8
0.6
0.4
0.2
0
REFERENCES
1. Kozlova, E.A. and Parmon, V.N., Russ. Chem. Rev.,
2017, vol. 86, no. 9, p. 870.
2. Savinov, E.N., Cand. Sci. (Chem.) Dissertation, Novo-
sibirsk: IC SB RAS, 1982.
3. Savinov, E.N., Doct. Sci. (Chem.) Dissertation, Novosi-
birsk: IC SB RAS, 1993.
4. Gruzdkov, Yu.A., Savinov, E.N., and Parmon, V.N.,
Khim. Vys. Energ., 1986, vol. 20, no. 5, p. 445.
0
5. Makhmadmurodov, A., Gruzdkov, Yu.A., Savinov, E.N.,
and Parmon, V.N., Kinet. Katal., 1986, vol. 27, no. 1,
p. 133.
0
5
10
15
Ethanol concentration, mol/L
6. Gruzdkov, Yu.A., Savinov, E.N., and Parmon, V.N.,
Khim. Fiz., 1988, vol. 7, no. 1, p. 44.
Fig. 5. Counter plot defined by Eq. (12).
7. Li, Y.X., Lu, G.X., and Li, S.B., Appl. Catal., A, 2001,
vol. 214, p. 179.
8. Vorontsov, A.V., Kozlova, E.A., Besov, A.S., Kozlov, D.V.,
Kiselev, S.A., and Safatov, A.S., Kinet. Catal., 2010,
vol. 51, no. 6, p. 801.
higher than 6 mol/L, which corresponds to 35 vol %,
and the concentration of NaOH should be higher than
0.86 mol/L. Note that, during kinetic experiments, a
rate of hydrogen production of 25 μmol/min was
reached, and the initial concentrations of reactants
shown in Table 1 were corresponded to the concentra-
tions at which the highest values of the reaction rates
were achieved in Fig. 5. Thus, Eq. (12) makes it possi-
ble to predict the rate of the photocatalytic hydrogen
production for the range of ethanol concentrations
from 0 to 17 mol/L and for the range of sodium
hydroxide concentrations from 0 to 1 mol/L.
9. Chen, J., Lin, Sh., Yan, G., Yang, L., and Chen, X.,
Catal. Commun., 2008, vol. 9, p. 65.
10. Malin, K.M., Spravochnik sernokislotchika (Sulfuric
Acid Production Engineer Guide), Moscow: Khimiya,
1971.
11. Boreskov, G.K., Geterogennyi kataliz (Heterogeneous
Catalysis), Moscow: Nauka, 1988.
12. Kozlov, D.V., Doct. Sci. Dissertation, Novosibirsk: IC
SB RAS, 2015.
13. Sabate, J., Cervera-March, S., Simarro, R., and
Gimenez, J., Chem. Eng. Sci., 1990, vol. 45, p. 3089.
14. Markovskaya, D.V., Cherepanova, S.V., Saraev, A.A.,
Gerasimov, E.Yu., and Kozlova, E.A., Chem. Eng. J.,
2015, vol. 262, p. 146.
15. Sadovnikov, S.I., Kozlova, E.A., Gerasimov, E.Yu.,
Rempel, A.A., and Gusev, A.I., Int. J. Hydrogen
Energy, 2017, vol. 42, p. 25258.
CONCLUSIONS
The dependences of the rate of the photocatalytic
hydrogen production from ethanol aqueous solutions on
the concentrations of ethanol and sodium hydroxide are
studied on the 1% Pt/10% Ni(OH)2/Cd0.3Zn0.7S photo-
catalyst. The rate of the hydrogen production passed
through a maximum with increasing ethanol concen-
tration and grew linearly with an increase in the
NaOH concentration. The obtained dependences
were approximated by the equations based on Lang-
muir–Hinshelwood mechanism for the bimolecular
reaction. These equations made it possible to describe
the experimental data published earlier for the photo-
catalytic decomposition of aqueous solutions of pri-
mary alcohols with a high accuracy. The equation
allowing one to determine the relationships between
the rate of the photocatalytic hydrogen production
and the concentrations of both reagents, ethanol and
sodium hydroxide, was derived for the first time.
16. Turchi, G.S. and Ollis, D.F., J. Catal., 1990, vol. 122,
p. 178.
17. Santacesaria, E., Catal. Today, 1997, vol. 34, p. 393.
18. Lin, W.C., Yang, W.D., Huang, I.L., Wu, T.S., and
Chung, Z.J., Energy Fuels, 2009, vol. 23, p. 2192.
19. Patsoura, A., Kondarides, D.I., and Verykios, X.E.,
Catal. Today, 2007, vol. 124, p. 94.
20. Fujita, S.I., Kawamori, H., Honda, D., Youshida, H.,
and Arai, M., Appl. Catal., B, 2016, vol. 181, p. 818.
21. Fu, X., Long, J., Wang, X., Leung, D.Y.C., Ding, Z.,
Wu, L., Zhang, Z., Li, Z., and Fu, X., Int. J. Hydrogen
Energy, 2008, vol. 33, p. 6484.
22. Zheng, X.J., Wei, Y.J., Wei, L F., Xie, B., and Wei, M.B.,
Int. J. Hydrogen Energy, 2010, vol. 35, p. 117094.
23. Chowdhury, P., Gomaa, H., and Ray, A.K., Chemo-
sphere, 2015, vol. 121, p. 54.
KINETICS AND CATALYSIS Vol. 59 No. 6 2018

734
MARKOVSKAYA, KOZLOVA
24. Kozlova, E.A. and Vorontsov, A.V., Int. J. Hydrogen 32. Lin, W.-C., Yang, W.-D., Huang, I.-L., Wu, T.-S., and
Energy, 2010, vol. 35, p. 7337. Chung, Z.-J., Energy Fuels, 2009, vol. 23, p. 2192.
25. Lyubina, T.P., Markovskaya, D.V., Kozlova, E.A., and 33. Ahmmad, B., Kanomata, K., and Hiorse, F., Int. J.
Parmon, V.N., Int. J. Hydrogen Energy, 2013, vol. 38,
p. 14173.
Chem. Mol. Nucl. Mater. Metall. Eng., 2014, vol. 8,
p. 24.
34. Meng, X., Yu, Q., Wang, T., Liu, G., Chang, K., Li, P.,
26. Strataki, N., Antoniadou, M., Dracopolous, V., and
Liu, L., and Ye, J., APL Mater., 2015, vol. 3, p. 104401-1.
Kianos, P., Catal. Today, 2010, vol. 151, p. 53.
35. Wang, L. and Wang, W., Int. J. Hydrogen Energy, 2012,
27. Bahruji, H., Bowker, M., Davies, P.R., and Pedrono, F.,
vol. 37, p. 3041.
Appl. Catal., B, 2011, vol. 107, p. 205.
36. Simon, T., Bouchonville, N., Berr, M.J., Vaneski, A.,
Adrovic, A., Volbers, D., Wyrwich, R., Doblinger, M.,
Susha, A.S., Rogach, A.L., Jackel, F., Stolarczyk, J.K.,
and Feldmann, J., Nat. Mater., 2014, vol. 13, p. 1013.
28. Lyubina, T.P. and Kozlova, E.A., Kinet. Catal., 2012,
vol. 53, no. 2, p. 188.
29. Wagner, F.T., and Somorjai, G.A., J. Am. Chem. Soc.,
1980, vol. 102, p. 5494.
37. Zhang, H., Catal. Lett., 2014, vol. 144, p. 1253.
30. Strataki, N., Bekiari, V., Kondarides, D.I., and Lianos, P.,
38. Li, Y., Wang, J., Peng, S., Lu, G., and Li, S., Int. J.
Appl. Catal., B, 2007, vol. 77, p. 184.
Hydrogen Energy, 2010, vol. 35, p. 7116.
31. Ryu, S.Y., Choi, J., Balcerski, W., Lee, T.K., and Hoff-
mann, M.R., Ind. Eng. Chem. Res., 2007, vol. 46,
p. 7476.
Translated by Andrey Zeigarnik
KINETICS AND CATALYSIS
Vol. 59
No. 6
2018