S.I. Serdyukov et al.
Molecular Catalysis 502 (2021) 111357
[20], for which nickel (II) 2-ethylhexanoate Ni(C7H15COO)2 was used as
a nickel source. The thiosalt cation nature can be substantially modified,
which inevitably implies changes in the catalyst properties. In this
paper, we have researched the triphenylsulfonium nickel-thiotungstate
precursor [Ph3S]2Ni(WS4)2 first synthesized by us [21,22]; we have
also studied its structure and the properties of the catalyst prepared on
its basis. Precursor [Ph3S]2Ni(WS4)2 contains no nitrogen atoms, while
carbon is only included in a sufficiently stable phenyl radical (unlike, for
example, precursor W(CO)6). As a result, a considerably lower content of
carbon can be expected on the surface of the respective catalyst. As
follows from the empirical formula, thiosalt [Ph3S]2Ni(WS4)2 contains
sulfur both in cation [Ph3S]+ and in anion [Ni(WS4)2]2ꢀ , which is an
important feature distinguishing it from other precursors. It is to be
expected that a high sulfur content will result in a greater degree of
catalyst sulfiding, which will positively affect its catalytic properties.
In this paper we used the X-ray diffraction and X-ray absorption
methods, XPS and TEM, and studied the properties of the catalyst pre-
pared by the decomposition of thiosalt [Ph3S]2Ni(WS4)2 in the reaction
media in the model hydrocarbon hydrodearomatization processes in
detail. Naphthalene and methylnaphthalenes were used as a feedstock.
The studied catalyst is a system of stable nanoparticles dispersed in the
reaction medium.
dedicated crystal growth stage. The dataset was collected at 100 K. In
total, 720 frames were collected with an oscillation range of 1.0◦ in the φ
scanning mode using two different orientations of a crystal. The data
were indexed and integrated using the utility iMOSFLM from the CCP4
software suite [25]. The semiempirical correction for absorption was
applied using the Scala program [26]. The structures were solved by
intrinsic phasing modification of direct methods [27] and refined by a
full-matrix least-squares technique on F2 with anisotropic displacement
parameters for all non-hydrogen atoms and hydrogen atoms involved in
H-bonding. Hydrogen atoms were placed in calculated positions and
refined within the riding model with fixed isotropic displacement pa-
rameters. All calculations were carried out using the SHELXTL program.
For details, see Table S1 in Supporting Information. X-ray powder
diffraction patterns for [Ph3S]2Ni(WS4)2 were measured at the same
beamline and wavelength in the transmission geometry at room
temperature.
Ni K-edge and W L3-edge XANES/EXAFS spectra for [Ph3S]2Ni(WS4)2
and its derived catalyst were measured at the Structural Materials Sci-
ence beamline of the Kurchatov Synchrotron Radiation Source [28]. The
spectra were measured in the transmission mode at room temperature
using ionization chambers filled with N2/Ar mixtures providing 20 %
and 80 % absorption for I0 and It, respectively. For the sake of com-
parison, X-ray absorption spectra of several relevant reference com-
pounds, including NiO, NiS, WO3, and WS2 (nanostructured powder
used as a support for catalysts), were measured under identical condi-
tions. Standard data processing was performed using Athena and
Artemis programs of the IFEFFIT suite [29] with FEFF [30] ab initio
photoelectron amplitude and phase functions.
2. Experimental
2.1. Precursor and catalyst synthesis procedures
The precursor triphenylsulfonium nickel-thiotungstate [Ph3S]2Ni
(WS4)2 was prepared by the following method. A solution of nickel
chloride hexahydrate containing 0.12 g of NiCl2⋅6H2O (Aldrich, ≥98 %)
and 7 mL of a H2O–CH3CN mixture (a volume ratio of H2O:CH3CN =
1:2.5) was added to a solution containing 0.35 g of ammonium thio-
tungstate (NH4)2WS4 (Aldrich, ≥99.9 %) and 13 mL of a H2O–CH3CN
mixture (a volume ratio of H2O:CH3CN = 1:1.4). A solution containing
2.0 g of [Ph3S]CF3SO3 (Aldrich) and 7.5 mL of CH3CN was added to the
resulting mixture through a drop funnel. The formed brown precipitate
was filtered off, washed with water and diethyl ether, and then dried in
the air.
Electron microscope images of the samples were obtained using a
Hitachi TM3030 desktop scanning electron microscope. Before imaging
by the vacuum deposition method, a gold layer was deposited on the
surface of the samples. The information on the local composition of el-
ements and the distribution of elements on the sample surface was ob-
tained using an add-on energy dispersive spectrometer with a Quantax
70 EDS system.
The structure and morphology of the catalyst samples were studied
using a JEOL JEM 2100 analytical electron microscope composed of a
base transmission electron microscope (TEM) for recording electron
microscopic images and electron diffraction patterns, a computer con-
trol system with an integrated scanning transmission electron micro-
scopy (STEM) image observation device, and an energy dispersive X ray
spectrometer (JED 2300). The distribution of the sulfide particles with
respect to particle length and the number of layers in multilayer ag-
glomerates was derived from the statistical estimation of sizing features
of more than 300 particles of the active component in different TEM
images for each catalyst. Based on the statistical analysis conducted after
the processing of micrographs, the average length of the sulfide particles
(L) and the average number of layers (N) were determined. Considering
that the formed particles have a hexagonal shape, the geometric char-
acteristics of the sulfide phase were calculated by the method proposed
in [31]: the number of W atoms along one side of the WS2 crystallite (ni),
the number of W atoms located at the WS2 crystallite edges (We ), the
number of W atoms located at the WS2 crystallite corners (Wc ), the total
number of W atoms in the average WS2 particle (WT ), dispersity of
particles (D).
Unsupported catalyst was prepared in situ by the decomposition of
precursor [Ph3S]2Ni(WS4)2 directly in an HC feedstock [21]. The for-
mation of the catalyst took place in the course of a catalytic reaction
under process conditions (T = 350 ◦C, PH2 = 5.0 MPa, 5 h).
The catalyst prepared on the basis of [Ph3S]2Ni(WS4)2 was desig-
nated as NiWS-tfs. The earlier studied catalysts were designated as
NiWS-bmp (on the basis of [BMPip]2Ni(WS4)2 [18]), NiWS-wsp (on the
basis of Ni(NO3)2/(NH4)2WS4 [19]) and NiWS-osp (on the basis of
tungsten hexacarbonyl and nickel (II) 2-ethylhexanoate [20]). Specific
surface areas for the in situ obtained catalysts are (m2/g) 33.6
(NiWS-bmp), 25.3 (NiWS-wsp), 41.2 (NiWS-osp) [23] and 26
(NiWS-tfs)|.
2.2. Catalyst characterization
X-ray powder diffraction patterns for catalysts were obtained using a
Rigaku Rotaflex RU-200 rotating-anode X-ray machine equipped with a
D/Max-B wide-angle horizontal goniometer. The anode material is
copper; the wavelength of copper Kα radiation is λ = 1.542 Å; Kβ radi-
ation was absorbed by a nickel filter. The X-ray pattern was recorded
using a scintillation detector. Patterns were taken according to the
Bragg-Brentano scheme in the θ-2θ geometry within the angular range of
5–115 degrees (by 2θ) by means of scanning in increments of 0.02 de-
gree and at a rate of 1 degree per minute.
∑
∑
li
L =
N =
(1)
(2)
n
Nini
n
L
10⋅ 3,2 + 1
ni =
(3)
(4)
Single-crystal X-ray diffraction data for [Ph3S]2Ni(WS4)2 were
collected at the ‘Belok’ beamline (λ = 0.96990 Å) of the Kurchatov
Synchrotron Radiation Source [24]. Single crystals suitable for analysis
were picked out from nominal polycrystalline powder without a
2
We = (6⋅ni ꢀ 12)⋅N
2