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promoting a wide range of different reactions such as sulfur and
nitrogen extrusions, as well as hydrogenation and acid catalyzed
tion through competitive adsorption, even when they are present at
considerably low concentrations. Basic nitrogen compounds, such
as quinoline (Q), are considered to be stronger inhibitors of the
HDS reaction than the corresponding non-basic moieties. Kwak
et al. [18] reported the occurrence of an obvious poisoning effect
caused by carbazole and Q in the HDS reactions of DBT, 4-MDBT
and 4,6-DMDBT over a sulfided NiMoP/Al2O3 catalyst. According
to this particular report, Q exhibited a stronger poisoning effect
than carbazole in the HDS reactions studied.
current study were purchased as the high purity grades from Wako
Chemical Company. All of the chemicals were used as received
without any further purification.
2.2. Synthesis of MoS2
The nanosized MoS2 catalyst was synthesized via a two-stage
process involving the heat treatment of the Mo-precursor (ammo-
nium heptamolybdate) under specific conditions. The precise
details of this procedure have been reported elsewhere [28]. Briefly,
a specific amount of the molybdenum precursor was charged to a
quartz microreactor tube, and the microreactor then was loaded
to a tube furnace equipped with electronically temperature con-
troller system. The inlet of the reactor was connected to a gas line
providing 10 wt% H2S balanced with hydrogen, whereas the outlet
gases together with the reaction products were scrubbed through
a saturated solution of NaOH. The temperature of the reaction was
increased at a rate of 3 ◦C min−1 to a maximum temperature of
400 ◦C. The system was then held at this temperature for 2 h, before
being further heated to 830 ◦C at a rate of 6 ◦C min−1. The annealing
treatment during the first stage was conducted under a stream of
argon, whereas the annealing treatment during the second stage
was accomplished under a continuous flow of a 10% v/v H2S/H2
gas mixture. The sulfiding gas mixture was set to flow with a fixed
applied flow rate of 60 SCCM (S percm3). Upon reaching the pre-
scribed annealing temperature, the sample was held under these
conditions for 3 h under a continuous flow of the sulfiding gas. Fol-
lowing this 3 h period, the sulfiding gas was switched off and the
Ar gas flow was turned on for 30 min with a flow rate of 100 SCCM.
ysis by X-ray diffraction (XRD) on a Rigaku Diffractometer using
For the hydrodenitrogenation (HDN) of aromatic nitrogen-
containing species, the reaction initially proceeds through the
saturation (hydrogenation) of the heteroring followed by the
cleavage of the C–N bond. The resulting aliphatic or aromatic
amine intermediates are ultimately converted to hydrocarbons and
ammonia. Thus, aromatic nitrogen-containing compounds (espe-
cially the basic species) exhibit a strong affinity for the active
sites associated with hydrogenation reactions. To achieve an ultra
sulfur-containing compounds, including inhibition by the feed-
stock matrices and the identity of the catalytic species. Nano-MoS2
catalysts have shown recently significant promise with superior
levels of activity toward HDS reactions [19–26]. In the HDS reac-
tion of DBT, for instance, over conventional catalysts, the reaction
proceeded to yield two primary hydrocarbon products, includ-
ing biphenyl (main product), which was produced via direct C–S
bond cleavage, and cyclohexylbenzene, which was produced as a
result of ring hydrogenation prior to C–S bond cleavage. More-
over, nanosized MoS2 catalysts are well-known to preferentially
pounds of this type through the hydrogenation pathways [19,20].
Refractory sulfur-containing compounds exhibit higher levels of
reactivity when the selectivity of the reaction toward hydrogena-
tion predominates over hydrogenolysis. In our previous studies
[21–24], it has been shown that distinct unsupported MoS2 exhib-
ited enhanced HDS performance under certain circumstances when
H2S was present in the reactor. To the best of our knowledge,
however, no studies have been reported in the literature con-
cerning the effects of nitrogen-containing compounds on the HDS
reactions over such catalysts. The majority of the studies pub-
lished in this area have reported the poisoning effects produced
by nitrogen-containing compounds on the performance of conven-
tional transition metal supported catalysts in HDS reactions [27]. It
was envisaged that nanosized MoS2, as a good hydrogenation cat-
alyst, would show distinct features in the HDN reactions. In this
study, we have investigated the HDN and HDS reactions of Q and
DBT, respectively, as well as the inhibiting effect of each of these
compounds on the reaction of the other over a synthetic nanosized
MoS2 catalyst. Q, which is an important species that is present in
significant concentrations in the middle distillates, was adopted as
a consistent representative model of the lesser reactive nitrogen-
containing compounds. It was also envisaged that this study would
provide some important insights into the impact of H2S and DBT
on the HDN of Q over this catalyst.
˚
Cu K␣ radiation (ꢀ = 1.54056 A) indicated that treatments of this
type allowed highly crystalline MoS2–2H phase structure with a
crystallite size of ca. 20 nm to be obtained (Fig. 1A).
The chemical compositions of the sulfided molybdenum sam-
ples were determined gravimetricallyusing an ex situ microbalance
from the weight differences of the sample before and after the sul-
fidation manipulation. The result indicated the occurrence of a fully
complete sulfidation process to give the highly crystalline MoS2–2H
structure. The sample was then subjected to a milling process using
zirconia beads under an Ar atmosphere to obtain small crystallite
sizes of MoS2. Before the catalytic investigation, the catalyst was
once more subjected to sulfidation at 400 ◦C under a flow of the
10 v/v % H2S/H2 gas mixture. The nanosized MoS2 obtained was
further characterized by XRD. The patterns illustrated scans that
were characteristic of the MoS2–2H structure, but with an obvious
reduction in the crystallinity relative to the original phase before
comminution. A particle size of ca. 5 nm was estimated from the
width of the line broadening at the Miller index peak of (0 0 2). Sur-
face measurements pointed to a mesoporous structure with a BET
surface area determined to be ca. 120 m2 g−1 [23].
2.3. Catalytic activity measurements
Two model compounds, DBT and Q, were selected to repre-
sent the refractory S-containing and N-containing compounds in
the HDS and HDN reactions, respectively. Three set of experiments
were conducted, including (1) the HDS reaction of DBT in a decane
solvent; (2) the HDN reaction of Q; and (3) the simultaneous HDS
and HDN reactions of a mixture of DBT and Q. A mixture composed
of DBT and Q of 667 and 67 ppmw, respectively, with an S/N ppm
weight ratio of 10 was used for the current investigation. The reac-
tion was conducted in a batch system using a 100 mL magnetically
stirred micro-autoclave reactor (1000 rpm). The nanosized MoS2
(ca. 0.5 to 1.5 g) was loaded in situ into the reactor together with
2. Experimental section
2.1. Materials
Ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24
4H2O) was purchased as the high purity grade (99.9%) from TCI
Company. Q, DBT, decane, and all of the other chemicals used in the
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