T. Feduschak et al. / C. R. Chimie xxx (2016) 1e11
5
At the same time, samples 3 to 5 (Table 1; Fig. 3b) me-
chanically activated for the same time of 8 h as is and in the
presence of equivalent 100 L amounts of methanol and
water show the changes of a different character: on the one
hand, doping of small amounts of polar liquids only slightly
affects the inter-planar spacing D002 (Table 1), although the
3.3. TEM micrographics
m
The TEM images of the microstructures of the catalyst
samples under study are shown in Fig. 4aed. The samples
consisted of disordered mono- and multi-layered MoS2-
nano-crystallites with L ꢃ 20 nm and the stacking number
from 10 to 20. The samples shown in Fig. 4a and b after the
MA treatment were strongly disintegrated. The MoS2 nano-
crystallites contained multiple defects. The separation of
the layers was also observed for these samples.
Fig. 4d demonstrates that when the MA local exfoliation
occurs, it may be accompanied by the formation of signif-
icant volumes of the interlayer spaces. Besides, some part of
the nano-crystallites was agglomerated. After the DBT HDS
reaction, the dispersion of the *MoS2 þ 100 CH3OH(8)
sample increased, new defects were formed, and the dis-
placed layers were separated and disoriented towards.
Dd/d
values
decrease
in
the
row
*MoS2(8) > *MoS2 þ 100 CH3OH(8) > *MoS2 þ100 H2О(8).
This indicates the presence of polar additives in MA elim-
inating the internal elastic micro-stresses and de-
formations in the nano-crystallites.
It should also be noted that in literature sources the
level of imperfection of crystal samples is associated with
internal elastic micro-deformations in their unit cells [13].
In a number of papers the viewpoint prevails that the
higher is the sample imperfection the higher is its activity.
For example, the highest concentration of defects, which
the authors evaluated in accordance with the XRD-
characteristics of the samples, is the main reference point
for preparing catalysts with high activity in the DBT HDS
reaction [7].
Water positively affected the formation of layered
structures and the catalytic activity in the HDS reaction. In
contrast, the results of this research indicate that small
amounts of water are not favourable for the increase of
DBT HDS activity of the bulky MoS2 catalyst (Fig. 3b;
sample 4 in Table 1). With methanol-containing systems
the situation is different. Within the range of the catalysts
3.4. XPS measurements
The MoS2 catalyst samples, mechanically activated for
8
h
in the presence of 100
mL
of methanol
(*MoS2 þ 100 СН3ОН(8) in Table 1) and subsequently sub-
jected to Ar-ion beam etching, were studied using XPS
before and after DBT HDS, being denoted as:
1. Catalyst *MoS2 þ100 CH3OH(8), fresh.
2. Catalyst *MoS2 þ100 CH3OH(8), used in DBT HDS.
presented in Table 1, the sample 5 has the values of
Dd/d
and c/a close to the average among the samples under the
scope. Thus, the size of its nano-crystallites is twice as big
(25 nm, Fig. 3b) as that of the comparison samples. This
result suggests the manifestation of the “inhibitory” effect
from the methanol at MoS2 grinding. Table 1 contains
more results worth noticing: the activity of sample 5
The values of binding energies of the photoelectron
peaks of elements measured in XPS of the samples are
given in Table 2. They correspond to sulphur, molybdenum,
carbon, and oxygen and the binding energies of the ele-
ments did not shift after the Ar-ion beam etching.
*
М
oS2 þ 100CH3OH(8) is the highest in respect of its
Figs. 5 and 6 show S 2s þ Mo 3d and S 2p core-level XPS
spectra. In the Mo 3d spectra of the studied samples the
value of binding energy of Mo 3d5/2 was equal to 229.2 eV.
This value of binding energy is typical for molybdenum in
sulphide surroundings like in MoS2 [12, 14e15] and corre-
sponds to the formal Mo4þ state with a part of the surface
molybdenum in the Mo5þ state (BE ¼ 231.4 eV). In the
Mo 3d spectrum of the *MoS2 þ 100 CH3OH(8), fresh sam-
ple, a shoulder at about 236 eV was observed, meaning a
part of molybdenum was in the oxidized Mo6þ state. The
shoulder from smaller values of binding energy (226.4 eV)
belonged to sulphur (S2s level). Ratios between oxidized
and sulphidized states of Mo and S are given in Table 2.
It should be noted that Ar-ion interaction with the
catalyst surface before and after the reaction leads to the
appearance of an additional shoulder from lower values of
binding energies due to partial reduction of the catalyst
surface. Thus, in the course of Ar-ion beam etching of the
surface of the (*MoS2 þ 100 CH3OH(8), fresh) sample the
fraction of Mo6þ decreased from 0.61 to 0.16. For the
(*MoS2 þ 100 CH3OH(8), used) sample the fraction of the
Mo6þ was essentially lower, about 0.03, and after 5 min of
Ar-ion beam etching Mo6þ entirely disappeared.
hydrodesulphurization
ability
relative
to
DBT
(Sres ¼ 3 ppm; k ¼ 0.65 hꢂ1).
3.2. Sedimentation analysis of the catalyst samples
The integral and differential sedimentation curves of
the *
oS2 þ100 CH3OH(8) catalyst had typical shapes
М
observed for analogous suspensions. The shape of the
distribution curve of the particle sizes depicted in Fig. 1 is
asymmetric. This indicates a wide range of particle size
distribution in a solvent (in this case it is water; paragraph
2.2.2) even in spite of surfactants (synthanol). The differ-
ential curve has its maximum at 139 nm. At the integral
curve, the fraction of particles with a diameter of 139 nm
and below amounts to about 21%. The position of the peak
maximum among the catalysts presented in Table 1 varies
in the range of 120e145 nm. The size of the catalyst par-
ticles obtained in the sedimentation analysis significantly
exceeds the one of those reported in XRD data (Table 1),
which may be explained by the particle agglomeration in
aqueous suspensions also possibly observed in catalytic
reactions. The tendency in size variation, however, was
consistent for both XRD (Table 1) and sedimentation
analysis methods.
In the S 2p spectra of the samples, an intensive peak at a
binding energy of 162.3 eV was detected. This value is
typical for sulphides S2ꢂ
. Besides, for the *MoS2
Please cite this article in press as: T. Feduschak, et al., Synthesis and characterization of mechanically activated bulky molyb-
Feduschak, Taisia
