R. Palcheva et al. / Applied Catalysis A: General 520 (2016) 24–34
25
rations has been found to be very efficient in an increasing number
of Co (Ni)–Mo–S sites [28–40]. When a chelating agent, like citric
acid, EDTA, or nitrilotriacetic acid (NTA) is added to the impregna-
tion solution containing Co (or Ni) and Mo precursors, the formed
Co(Ni)-chelating agent complex retards the sulfidation of the Co
or Ni promoter until a more complete sulfidation of Mo, leading
to an increased number of Co(Ni)–Mo–S sites, simultaneously sup-
pressingthe formation of bulk Co or Ni sulfides [28,30,31,33–36,38].
Ohta et al. studied the role of NTA, EDTA and CyDTA on CoMo, NiMo
and NiW type catalysts [30]. They observed a positive effect of the
organic molecule on the CoMo and NiW catalysts, and slightly less
effect on the NiMo catalysts.
The use of thioglycolic acid (TGA) as a chelating agent in prepa-
ration of HDS catalysts has not been systematically studied up to
now. The treatment of the CoMo oxidic phase with aqueous solution
of thioglycolic acid was successfully applied to improve the per-
formance of thiophene hydrodesulfurization catalysts [39]. Raman
affected the sulfidation of the supported metals. A higher catalytic
performance was attributed to the optimization of the nature and
morphology of the active phase obtained by the use of this chelat-
ing agent which enabled to carry out a simultaneous sulfidation of
both Co and Mo atoms [39].
the molar ratio Ni/Mo = 0.3. The catalysts were labeled as NiMo/Nb-
SBA-15 and NiMo/Nb-HMS.
Parts of the NiMo/Nb-SBA-15 and NiMo/Nb-HMS catalysts
(dried at 120 ◦C and calcined at 400 ◦C) were treated with an aque-
ous solution of thioglycolic acid (TGA). The TGA:Mo molar ratio was
4.0. After 2 h of treatment, the so obtained solids were dried at 80 ◦C
under N2 for 15 h. These catalysts are labeled as TGA/NiMo/Nb-SBA-
15 and TGA/NiMo/Nb-HMS.
The third series of catalysts were prepared by simultaneous
impregnation of the supports with an aqueous solution of nickel
nitrate, ammonium heptamolybdate and TGA. The catalysts were
dried at 80 ◦C under N2. They contained the same amounts of Ni
and Mo as their calcined counterparts mentioned above. They were
labeled as NiMoTGA/Nb-SBA-15 and NiMoTGA/Nb-HMS.
2.2. Catalyst characterization
The supports and NiMo catalysts were characterized by N2
physisorption, small- and wide-angle XRD, acidity tests (TPD-NH3,
cumene cracking), SEM, UV–vis DRS, FTIR and XPS.
The textural properties of the supports and of the sulfided cata-
lysts were investigated with a Micromeritics ASAP 2010 apparatus.
Prior to the analysis, the oxide precursors were sulfided under the
same conditions as described in the section on catalytic activity
tests and evacuated at 105 ◦C for 12 h before the N2 adsorption. Spe-
cific surface area and pore size distributions were determined from
nitrogen adsorption–desorption isotherms at −195 ◦C, after drying
the samples at 105 ◦C for 12 h and evacuation until the pressure
10−5 Pa was achieved (usually 2–5 h). To calculate the specific sur-
face area (SBET), the data were treated by the standard BET method.
Total volume of mesopores V was determined from the amount of
N2 adsorbed at P/P0 = 0.98. Surface area of mesopores (Smeso) and
volume of micropores (Vmicro) were calculated from t-plot accord-
ing to Schneider [41].
The aim of the paper is to study the effect of both the mesoporous
supports doped with niobium (Nb-SBA-15 and Nb-HMS) and the
application of thioglycolic acid (TGA) as a chelating agent on cat-
alytic performance of NiMo catalysts in HDS of 1-benzothiophene
and thiophene at 350 ◦C.
2. Experimental
2.1. Synthesis of supports and catalysts
The X-ray patterns of the supports, oxide precursors and fresh
sulfided samples were recorded on a Bruker AXS 2D analyzer with
filtered CuK␣ radiation ( = 0.154056 nm) at 30 kV acceleration and
10 mA current of the X-ray tube, scan step 0.05◦ and 1 s accumula-
tion time.
The scanning electron microscopy (SEM) was performed on a
Philips SEM 515 apparatus, working at acceleration of 20 kV. The
samples were covered with gold before putting them into the SEM
chamber.
Nb-SBA-15 support was prepared as follows: Pluronic P123
(Aldrich, MW = 5800) (4.971 g) was dissolved on gentle heating in
145 mL of 1.6 M hydrochloric acid. After that, 11.2 mL of tetraethyl
orthosilicate was added to this solution while mixing. Afterwards,
the solution of 0.43 g of ammonium niobium oxalate (CBMM) in
8 mL of methyl alcohol was added. The mixture was put in a water
bath with the temperature 45 ◦C and stirred for one day. The white
suspension obtained was transferred to a Teflon lined autoclave and
kept at 100 ◦C for 30 h. Then the content of the autoclave was fil-
tered, washed extensively with water, dried and calcined at 600 ◦C
in air for 8 h to liberate the organic template.
The DR UV–vis spectra were taken with a Thermo Evolution 300
spectrometer equipped with a Praying Mantis diffuse reflectance
accessory.
To prepare Nb-HMS, three solutions were prepared. The first
contained 5.04 g of dodecylamine, 6.56 g of mesitylene, 2 mL of
1.6 M hydrochloric acid and 36.6 mL of ethanol. On slight heat-
ing and mixing, dodecylamine was dissolved and the true solution
was obtained. The second solution contained 23 mL of tetraethyl
orthosilicate and 20 mL of ethanol. The third solution was prepared
from 0.879 g of ammonium niobium oxalate, which was dissolved
in 23 mL of water. The second and third solutions were simul-
taneously added to the first solution under stirring. The stirring
continued at 40 ◦C for 2 h and then the mixture was let stand at
the laboratory temperature for 48 h. The precipitate was filtered,
washed with water once and then several times with small por-
tions of ethanol. The obtained cake was dried and calcined in air at
600 ◦C for 8 h. The Nb-SBA-15 and Nb-HMS materials showed Si/Nb
atomic ratio 40.
The IR spectra of the samples mixed with KBr at approx-
imately 1 wt% concentration were recorded on Nicolet 6700
FTIR spectrophotometer, Thermo Electron Corporation, USA, in
4000–400 cm−1 region at 0.4 cm−1 resolution accumulating 50
scans per spectrum. The XPS measurements of all samples were
carried out in the analysis chamber of the electron spectrometer
Escalab-MkII (VG Scientific) with a base pressure of ∼ 5 × 10−8 Pa.
The Nb2O5 and MoS2 standards along with Nb-SBA-15 and Nb-HMS
supports in powder form were pressed into sample holders, the pel-
lets thus obtained had diameter of 10 mm and thickness of ∼ 1 mm.
The energy calibration was made by using C1s photoelectron line
at 285.0 eV as a reference. The sulfided NiMo supported samples
(400 ◦C, ramp 10 ◦C/min, 2 h, H2S/H2 1/10) were carefully mounted
on scotch tape in order to avoid mechanical crushing of the par-
ticles. In this case, the energy reference was performed by taking
O1s peak at 533.5 eV as a reference in order to avoid possible inter-
ference of the weak C1s signal from the samples surface with the
stronger one arising from the scotch tape. The C1s, O1s, Si2p, Nb3d,
Mo3d, Ni2p and S2p photoelectron lines were recorded and the
surface compositions were evaluated by using the normalized pho-
The studied supports were impregnated with an aqueous
solution of nickel nitrate (Ni(NO3)2·6H2O) and ammonium hep-
tamolybdate. After the impregnation the obtained catalysts were
dried at 120 ◦C and calcined at 400 ◦C in air flow. The nominal com-
position of the catalysts was 2.2 wt% Ni and 12 wt% Mo, reaching