An ordinary nickel catalyst becomes completely selective for partial hydrogenation of 1,3-butadiene when coated with tributyl(methyl)phosphonium methyl sulfate

Article abstract of DOI:10.1016/j.apcata.2018.06.016

Performance of an ordinary supported nickel catalyst was tuned to reach an almost complete selectivity for partial hydrogenation of 1,3-butadiene by coating it with a phosphonium-type ionic liquid (IL), tributyl(methyl)phosphonium methyl sulfate, [P₄₄₄₁][MeSO₄]. Thanks to high chemical and thermal stability of [P₄₄₄₁][MeSO₄], the reaction conditions could be pre-optimized for high partial hydrogenation performance before the deposition of the IL coating. When the catalyst was coated with IL, it provided a total butene selectivity of 99.5 ± 0.2%, a record high partial hydrogenation selectivity ever reported for a nickel-based catalyst. X-ray photoelectron spectroscopy results illustrated that the IL donates electrons to nickel sites and makes them selective for partial hydrogenation. The conductor like screening model for realistic solvents (COSMO-RS) calculations indicated that the IL coating also exerts a filter effect, which helps to maintain this high partial hydrogenation selectivity at all conversion levels.

Full text of DOI:10.1016/j.apcata.2018.06.016

Applied Catalysis A, General 562 (2018) 321–326
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Applied Catalysis A, General
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An ordinary nickel catalyst becomes completely selective for partial
hydrogenation of 1,3-butadiene when coated with tributyl(methyl)
phosphonium methyl sulfate
Ahsan Jalala,b, Alper Uzuna,b,c,⁎
a
Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey
KÜTEM (Koç University TUPRAS Energy Center), Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey
Koç University, Surface Science and Technology Center (KUYTAM), Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
Supported nickel catalyst
Ionic liquid
Performance of an ordinary supported nickel catalyst was tuned to reach an almost complete selectivity for
partial hydrogenation of 1,3-butadiene by coating it with a phosphonium-type ionic liquid (IL), tributyl(methyl)
phosphonium methyl sulfate, [P4441][MeSO ]. Thanks to high chemical and thermal stability of [P4441][MeSO ],
4 4
the reaction conditions could be pre-optimized for high partial hydrogenation performance before the deposition
of the IL coating. When the catalyst was coated with IL, it provided a total butene selectivity of 99.5 ± 0.2%, a
record high partial hydrogenation selectivity ever reported for a nickel-based catalyst. X-ray photoelectron
spectroscopy results illustrated that the IL donates electrons to nickel sites and makes them selective for partial
hydrogenation. The conductor like screening model for realistic solvents (COSMO-RS) calculations indicated that
the IL coating also exerts a filter effect, which helps to maintain this high partial hydrogenation selectivity at all
conversion levels.
SCILL
1
,3-butadiene partial hydrogenation
Phosphonium ionic liquid
1. Introduction
enation of cyclooctadiene increased from 40 to 70%, when the catalyst
was coated with 1-n-butyl-3-methylimidazolium octylsulfate, [BMIM]
Partial hydrogenation of 1,3-butadiene is an important industrial
[OS]. Moreover, the same group extended this approach to a com-
mercial Pd catalyst and coated it with different imidazolium-type ILs.
Their results on partial hydrogenation of 1,3-butadiene showed im-
proved partial hydrogenation performance [6–8]. Motivated with these
reports, we worked on a commercial nickel catalyst and coated it with a
different IL (1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM]
process. It paves the way to the feedstocks for the units producing
polymers and/or high-octane number gasoline components. Moreover,
it also helps to clean up the feeds in which 1,3-butadiene is present
together with valuable C4 olefins. This way the corresponding feed
becomes ready for further processing on different catalysts, which,
otherwise, would be poisoned if 1,3-butadiene remains in the stream
4
[BF ]) and used this coated catalyst for the partial hydrogenation of
[
1,2]. Currently, palladium-based catalysts are considered as the best
1,3-butadiene at 40 °C and atmospheric pressure [9]. The performance
measurements illustrated a partial hydrogenation selectivity of 96%.
Even though these results illustrated the high potential of coating
nickel-based catalysts with ILs, the limited thermal stability of the IL
coatings poses a major limitation on the applicability of this novel
concept. In this respect, the imidazolium type ILs might not be a sui-
table family because of their limited thermal stabilities, which become
even more limited when the ILs are supported on metal oxides [10–12].
Moreover, the unsaturated C]C bonds present on the imidazolium ring
of the IL are susceptible to hydrogenation especially when the IL is
coated on a hydrogenation catalyst at high temperatures and under
high hydrogen partial pressures [9]. Moreover, the imidazolium ring
can also undergo different reactions with the reactants present under
catalysts for this reaction because of their high yields for partially hy-
drogenated products [3,4]. However, the cost of palladium is quite high
and it has stability problems. Because of these drawbacks, there is a
strong need for developing an efficient inexpensive catalyst for this
reaction. Nickel, one of the cheapest metals, can be a very good can-
didate for this reaction. However, it is too active for hydrogenation
reactions; hence, it is very challenging to control its performance for
partial hydrogenation.
A promising report by Kernchen et al. [5] illustrated that the partial
hydrogenation performance on a commercial nickel catalyst can be
improved when the surface of the catalyst was coated with an ionic
liquid (IL). Accordingly, the selectivity of cyclooctene in the hydrog-
⁎
Corresponding author at: Department of Chemical and Biological Engineering, Koç University, Rumelifeneri Yolu, Sariyer, 34450, Istanbul, Turkey.
E-mail address: auzun@ku.edu.tr (A. Uzun).
https://doi.org/10.1016/j.apcata.2018.06.016
Received 31 May 2018; Received in revised form 8 June 2018; Accepted 9 June 2018
Available online 15 June 2018
0926-860X/ © 2018 Elsevier B.V. All rights reserved.

A. Jalal, A. Uzun
Applied Catalysis A, General 562 (2018) 321–326
the reaction condition over the different components of supported
catalysts (support or metal). For instance, Bauer et al. illustrated this
2.2.2. Thermal stability
4 4
Thermal stabilities of the bulk [P4441][MeSO ] and [P4441][MeSO ]-
possibility during ethene hydrogenation on a Pd/Al
2
O
3
catalyst coated
coated catalysts were determined by thermogravimetric analysis (TGA)
using a TA Instruments TGA Q500 model instrument. Approximately
15 mg of each sample was subjected to a heat treatment at 100 °C for 4 h
in flowing nitrogen at a rate of 60 ml/min. Then, the temperature was
raised to 600 °C at a ramp rate of 2 °C/min (in high resolution mode of
with 1-ethyl-3-methlimidazolium ethylsulfate. Their results indicated
that ethene was incorporated into the imidazolium moiety in a reaction
catalyzed by palladium [13].
Besides, the imidazolium type ILs do not provide any significant cost
benefits. Hence, the potential of ILs from different families should be
investigated. Here, we aimed to explore the potential of phosphonium
type ILs, this family of ILs are thermally and chemically more stable
compared to their imidazolium-based counterparts [14]. Thus, they can
potentially offer opportunities to operate at higher temperatures than
imidazolium ILs do. Moreover, phosphonium-based ILs are manu-
factured on a multi-ton scale and are at least one-order of magnitude
cheaper than the imidazolium type ILs [15,16]. However, the utiliza-
tion of these ILs in catalysis [17–19] is limited with only a few reports,
most of which use them as solvents to dissolve metal complexes in
homogenous catalysis applications [18,19].
′
the equipment). Tonset values were considered as the short-term thermal
stability limits, as reported before [10,12,20]. After determining the
decomposition temperatures under inert atmospheres, the [P4441
[MeSO ]-coated catalyst was subjected to additional stability tests
under H environment as discussed in a previous work [9]. For this
purpose, the IL-coated sample was exposed to isothermal treatment at
150 °C for 30 min in flowing H (30 ml/min) in a ¼-in stainless steel
]
4
2
2
reactor heated in a Thermcraft three-zone resistively heated furnace
(model # XST-3-0-18-3 V) equipped with PC-controlled temperature
controllers. Then the resulting samples were analyzed spectroscopically
to identify any structural changes.
Here, to contribute filling this gap, we coated a commercial sup-
ported nickel catalyst with tributyl methyl phosphonium methyl sul-
2.2.3. Fourier transform infrared (FTIR) spectroscopy
fate, [P4441][MeSO
4
], and tested the performance for 1,3-butadiene
A Bruker Vertex 80v FTIR spectrometer was used for the FTIR
measurements. Approximately 30 mg of catalyst was pressed between
two KBr windows and loaded into a transmission cell. The resolution of
hydrogenation. Because this phosphonium IL offers a higher thermal
stability limit than the imidazolium ILs do, it offers a flexibility on
setting the reaction conditions. Thus, we first started with optimizing
the reaction conditions for high partial hydrogenation selectivity on the
uncoated catalyst focusing on relatively high temperatures, which
would not be possible with imidazolium-type IL coatings. Then, we
−1
each spectra was set to 2 cm
with an average of 256 background
scans and 512 sample scans under vacuum (employed by evacuating
the sample chamber of the spectrometer).
coated the catalyst with [P4441][MeSO
4
] and tested its performance
2.2.4. X-ray photoelectron spectroscopy (XPS)
under these optimized conditions. Results illustrated that the ordinary
commercial supported nickel catalyst becomes almost completely se-
lective for partial hydrogenation upon coating it with this phospho-
nium-type IL. To the best of our knowledge, this stable partial hydro-
genation selectivity presented here is the highest ever reported on a
supported nickel catalyst and presents the benefits of using phospho-
nium type ILs as coatings over supported metal catalysts.
A ThermoScientific K-Alpha spectrometer with an aluminum anode
(Al Kα = 1468.3 eV) at an electron take-off angle (between the sample
surface and the axis of the analyzer lens) of 90° was used for the XPS
measurement. Data was recorded using Avantage 5.9 software. The
binding energy calibration was performed based on the C1s signal at
284.3 eV.
2.2.5. Elemental analysis
2. Experimental and computational methods
For quantitative analysis of carbon, nitrogen, and sulfur contents in
samples, a Thermo Scientific Flash 2000 CHNS/O Analyzer was used.
Under continuous supply of oxygen, samples were placed in a reactor at
a temperature of approximately 1000 °C. Oxidation of the samples
produces elemental gas, which are separated by chromatography
equipped with thermal conductivity detector.
2
.1. Materials and synthesis
6
5 wt.% Ni on silica-alumina (commercial catalyst, Ni65), silica,
and [P4441][MeSO ] were purchased from Sigma-Aldrich. Ni65 was first
reduced at 650 °C for 2 h under pure hydrogen (Linde, 99.99 vol%)
flow. Reduced Ni65 was then passivated in 4 vol.% O (balance He, Air
4
2
2.2.6. Brunauer–Emmet–Teller (BET) surface Area
Liquide, 99.9 vol%) for 20 min. at room temperature. The IL-coated
sample was prepared by dipping 50 mg of activated and passivated
To determine the BET surface area, a Micromeritics ASAP 2020
physisorption analyzer was used. For each analysis, approximately
150 mg of sample was used. At first, the samples were degassed at
125 °C under vacuum for overnight. After degassing, free space mea-
surement of samples was performed using He gas at 77 K. Volumetric
Ni65 into 284 mg of [P4441][MeSO
mixture was mixed with 182 mg of calcined SiO
4
] and stirred for 1 h. Later, this
to dry the suspension
2
by absorbing the excess IL. The resulting solid sample prepared as a
physical mixture in powder form has an overall IL and Ni loadings of 55
and 6.2 wt.%, respectively. Table S1 in Supporting Information, SI,
compares the pore volume, average pore diameter, and surface area of
these physical mixtures with or without the IL. Based on the data pre-
sented in Table S1, the pore filling degree was calculated as approxi-
mately 96% (calculated by dividing the IL volume into the pore volume
of the physical mixture in the absence of IL) [7].
−
6
adsorption of N
2
gas was obtained between 10
and 1 bar, and the
pressure steps between 0.05 and 0.3 bar were fit to BET equation to
estimate the surface areas of samples. The pore volume of the samples
were derived using the t-plot method from N adsorption isotherm
2
measured at 77 K.
2.2.7. Catalytic activity testing
The as-received Ni65 catalyst was first reduced at 650 °C in a ¼-inch
stainless steel tubular reactor in H (Linde, 99.9 vol.%) flow (30 ml/
min) for 2 h. A Thermcraft three-zone resistively heated furnace was
used to maintain reactor temperature. Then, the reactor was cooled
down to the room temperature in He flow (Air liquid, 99.9 vol%) and
2
2
.2. Catalyst characterization
2
.2.1. Temperature programmed reduction (TPR)
A Micromeritics AutoChem II 2920 automated catalyst character-
ization system coupled with an MKS Cirrus II mass spectrometer was
employed for the TPR measurement. The samples were first dried in He
flow at 100 °C for 30 min. Then, the samples were heated up to 700 °C at
the catalyst was passivated in 4% O
passivated catalysts were then activated in H
Electronic mass flow controllers (Aalborg, model GFC17) were em-
ployed to control the flow rates. The uncoated sample was diluted with
2
(balance He) for 15 min. The
flow at 150 °C for 30 min.
2
a ramp rate of 5 °C/min in flowing H
2
, while the effluent gas stream was
monitored by a TCD detector and a mass spectrometer.
2
SiO , which was calcined in static air at 500 °C for 5 h, at a ratio of
322

A. Jalal, A. Uzun
Applied Catalysis A, General 562 (2018) 321–326
1
:300 g:g. The coated catalyst was used as-prepared without further
diluting with silica. The reaction was carried out at ambient pressure
and various temperature and partial pressures of H and 1,3-butadiene
1,3-butadiene, Linde, 99.6 vol.%). The concentration of reactants and
products at the exit stream were quantified by an online gas chroma-
tograph (Agilent GC 7890 A) with GS-Alumina column
2
(
a
(
50 m × 530 μm) and a flame ionization detector (FID) at a constant
3
column temperature of 130 °C and He flow at a rate of 6.5 cm /sec, and
having sample injections every six min. The conversion was controlled
−
1
−1
by varying the space velocity from 4.09 (1.13 × 10 ) to 3.75 × 10
(
(
-
3
−1
7.6 × 10 ) (mol of 1,3-butadiene) × (mol of Ni × s)
coated) Ni65 catalyst under constant temperature and partial pres-
for uncoated
sures.
2.3. COSMO-RS calculations
COSMOThermX (version 1601) software was employed for esti-
mating the relative solubilities of butenes and 1,3-butadiene in the IL
using the Ionic Liquid Screening Module and setting the temperature at
1
45 °C. The structures of 1,3-butadiene, 1-butene, cis/trans-2-butene
4 4
Fig. 1. TGA results for bulk [P4441][MeSO ] ( ) and [P4441][MeSO ]-coated
Ni65 ( ). Data were collected at a ramp rate of 2 °C/min under flowing ni-
trogen.
were first optimized by density functional theory (DFT) calculations
performed at a level of B3LYP with 3-21G + basis sets using Gaussian09
[
21] software and used as input files [22]. The input geometries for
butane and IL were obtained from the COSMO and COSMO-IL database,
respectively. Calculations were performed using TZVP parameterization
(
full geometry optimized with DFT and medium sized basis set for 1,3-
butadiene). The inverse of activity coefficients at infinite dilution [23]
in [P4441][MeSO ] for each gas was considered as the capacity. Math-
4
ematically, the capacity is defined as:
1
∞
Ci
=
∞
γ
i

where
C
i
is the solvent capacity at infinite dilution for component “i”

in [P4441][MeSO
4
], while
γ
i
is activity coefficient of component “i” at
].
infinite dilution in [P4441][MeSO
4
3. Results and discussions
As illustrated in Fig. S1 in Supporting Information (SI), the as-re-
ceived Ni/SiO -Al catalyst with a nickel loading of approximately
5 wt% (Ni65) catalyst requires an activation treatment in flowing H
at temperatures exceeding 500 °C. However, this activation tempera-
ture is quite high for the ILs, most of which decompose below 400 °C
under inert atmospheres [10–12]. Consistently, our thermogravimetric
2
2 3
O
6
2
Fig. 2. IR spectra of the activated-passivated IL-coated Ni65: (a) As prepared
activated-passivated IL-coated Ni65; (b) after a reactivation treatment at 150 °C
in flowing H for 30 min (c) after using the reactivated catalysts for partial
2
hydrogenation of 1,3-butadiene at 145 °C at a 1,3-butadiene:H
time-on-stream period of 48 h.
2
ratio of 1:2 for a
analysis (TGA) measurements indicate that the [P4441][MeSO
4
] starts to
decompose at 285 °C in N flow (Fig. 1). Moreover, this thermal stabi-
2
lity limit slightly decreases to 279 °C, when the IL was coated over the
Ni65 catalyst, which was activated at 650 °C and passivated at room
temperature prior to be coated with the IL (Fig. 1). Such small decrease
in thermal stability limit (slightly larger than the error range of our TGA
measurements) might be originated from the presence of interactions
between the IL and the supported metal catalysts, consistent with our
previous reports [10,11]. We also note that the amount of IL loading
was fairly high (approximately 55 wt%), and this might be the reason
for why the deviation from the bulk decomposition temperature was
not that significant.
−
1
Moreover, the band located at approximately 2900 cm represents the
stretching vibration of the OeCH on the anion, another group that can
3
readily react with hydrogen on a hydrogenation catalyst. Data indicated
that these bands (and any other features) do not show any detectable
changes upon reactivation; thus, we infered that the IL structure re-
mains intact during the reactivation of the passivated IL-coated Ni65.
After determining a suitable condition for the reactivation without
damaging the structure of the IL coating, we focused on investigating
the reaction conditions at which the reactivated Ni65 catalyst provides
the highest possible selectivity for partial hydrogenation of 1,3-buta-
diene before depositing the IL coating. The investigated conditions and
the consequent results obtained under these conditions are given in Fig.
S2 and S3, SI. Accordingly, the selectivity for total butenes (summation
of the individual selectivities for 1-butene, and cis- and trans-2-butenes)
on the uncoated catalyst can be increased to approximately 95%, when
Thus, the Ni65 was first activated in flowing hydrogen at 650 °C and
passivated at room temperature in very dilute O flow, before being
2
coated with the IL. Temperature programmed reduction (TPR) data
confirm that this passivated Ni65 can be reactivated at a temperature
lower than 150 °C, as shown in Fig. S1.
Results presented in Fig. 2 compare the IR spectra of IL-coated re-
duced and passivated catalyst before and after undergoing reactivation
the partial pressures of 1,3-butadiene and H
with balance He), respectively, at 145 °C (Fig. 3a). Data showed that
this selectivity remains at this level up to a 1,3-butadiene conversion of
7%. Results further indicated that 1-butene selectivity was
2
were 120 and 240 Torr
(
treatment for 30 min in flowing H
ν(S]O) bands of the anion located at 1161 and 940 cm
susceptible to hydrogenation over Ni in the presence of hydrogen.
2
at 150 °C. In [P4441][MeSO
4
], the
−1
[24] are
9
323

A. Jalal, A. Uzun
Applied Catalysis A, General 562 (2018) 321–326
Fig. 3. Change in selectivities of total butenes ( ), trans-2-butene ( ), 1-butene ( ), cis-2-butene ( ), and butane ( ) with conversion over (a) uncoated Ni65
catalyst and (b) [P4441][MeSO ]-coated Ni65. Reaction was carried out in a once-through flow reactor under a 1,3-butadiene and H partial pressure of 120 and
40 Torr (balance He), respectively, at 145 °C and atmospheric pressure in balance helium flow. The conversion was varied by changing the space velocity keeping
4
2
2
the other reaction conditions the same.
4
performance of [P4441][MeSO ]-coated Ni65 catalyst was measured
under the identical partial pressures and temperature. Results presented
in Fig. 3b illustrate that the IL-coated catalyst provides an almost
complete selectivity (> 99.5 ± 0.2%) towards partial hydrogenation
throughout the whole conversion range. To the best of our knowledge,
this is the highest partial hydrogenation selectivity ever reported on a
supported nickel catalyst. As it was reported previously [25], im-
provements in catalytic selectivity are often achieved at the expense of
a drop in activity. Consistently, rate of the coated catalyst was lower
−
3
−1
(
7.4 × 10
(mol of 1,3-butadiene converted) × (mol of Ni × s)
)
−2
compared to that of the uncoated sample (3.2 × 10
(mol of 1,3-bu-
−
1
tadiene converted) × (mol of Ni × s) ). However, we also note that
the presence of IL coating also induces a mass transfer barrier limiting
the reaction rate. Besides, this lower activity might also originate from a
change in the electron-density of the metal [26], and/or a simple re-
duction in the number of accessible active sites by the presence of IL
layer. Here, it’s also worth mentioning that the partial hydrogenation
performance was stable for 48 h (Fig. 4) and the IL structure remains
intact as illustrated by the comparison of IR (Fig. 2) and CHNS/O re-
sults (Table S2) of the catalysts before and after a time-on-stream period
of 48 h. The increase in catalytic stability might be because of the IL
layer, which controls the active concentrations of the intermediates/
products; and thus, helps their removal from the surface before getting
any chance for forming carbonaceous deposits.
Fig. 4. Change in conversion (left vertical axis, black) and selectivity (right
vertical axis, blue) on uncoated Ni65 (dotted lines) and [P4441][MeSO
Ni65 (solid lines) in time (hours). Reaction was carried under 1,3-butadiene and
partial pressures of 120 and 240 Torr (balance He), respectively, at 145 °C
4
]-coated
H
2
and atmospheric pressure. The space velocities were adjusted such that the
initial conversions are the same on both catalysts. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web
version of this article).
Data on the IL-coated catalyst further indicated that the selectivity
of 1-butene was approximately 42% with a corresponding trans- to cis-
2
-butene ratio of approximately 4.7. An almost complete partial hy-
approximately 60% throughout the whole conversion range. Similarly,
the ratio of trans- to cis-2-butene was constant at approximately 2.0.
Even though these results indicate a high performance for partial hy-
drogenation, extended time-on-stream runs indicated that the perfor-
mance was not stable on the uncoated catalyst. The catalyst deactivates
slightly within 48 h and this decrease in conversion was accompanied
by a decrease in partial hydrogenation selectivity (Fig. 4). Accordingly,
the 1,3-butadiene conversion and the selectivity for total butenes de-
creased from approximately 12 to 9% and 95 to 92%, respectively, at a
space velocity of approximately 1.19 (mol of 1,3-butadiene) × (mol of
drogenation selectivity and such a high ratio of trans/cis isomers of 2-
butene indicate the presence of a higher electron density on the active
sites in the presence of the IL coating compared to that on uncoated
catalyst [27]. Aiming at investigating the presence of possible electron
donation from IL to the metal sites, we employed XPS on uncoated and
coated catalysts (Fig. S4 presents the raw data). Fig. 5 shows high re-
solution Ni2p spectrum consisting of 2p3/2 and 2p1/2 multiplet-split
peaks of nickel. In Fig. 5a, the activated-passivated Ni65 catalyst has
four peaks in the 2p3/2 region located at binding energies of 852.6 (Ni
28]), 853.6 (Ni2+ [29]), 856.1 (Ni
31]). Upon coating the activated-passivated Ni65 catalyst with [P4441
MeSO ], Fig. 5 shows three peaks in the 2p3/2 region at binding en-
2+
[30]), and 860.8 eV (satellite
[
[
[
−
1
Ni × s)
(Fig. 4). Among different possible routes of deactivation,
]
carbonaceous deposit formation might be the dominant one, as sin-
tering might not be possible on a catalyst which was pre-reduced at
4
ergies of 852.1, 855.8, and 860.8 eV. The peak at 853.6 eV observed on
uncoated catalyst disappeared from the spectra with a simultaneous
decrease in the intensity of the Ni peak associated with an increase in
the intensity of the peak positioned at 856.1 eV, indicating the presence
650 °C and used at 145 °C.
Following the optimization of reaction conditions for the highest
partial hydrogenation selectivity on the uncoated catalyst (even though
the time-on-stream data show that this performance was not stable), the
324

A. Jalal, A. Uzun
Applied Catalysis A, General 562 (2018) 321–326
4
Fig. 5. XPS data of (a) activated passivated Ni65 and (b) [P4441][MeSO ] coated activated and passivated catalyst.
of nickel oxide species as expected for a passivated sample. We inferred
that because of the presence of IL coating, the surface concentration of
nickel-based species decreases resulting in a reduction of peak intensity
of Ni phase and subsequent disappearing or agglomeration of peak at
should be very limited, because the relative solubility of 1,3-butadiene
is not that significantly high. Thus, we infer that the ligand effect of the
IL is the major effect controlling the partial hydrogenation perfor-
mance. The filter effect, on the other hand, helps to maintain such high
partial hydrogenation selectivity at all conversion levels. Thanks to
both of these effects, the performance of a commercial supported nickel
catalyst could be improved to provide an almost complete partial hy-
drogenation selectivity. Here, we note that choosing the IL from a fa-
mily with high chemical and thermal stability offers a great degree of
flexibility in optimizing the reaction conditions even before introducing
the IL coating.
8
8
53.6 eV. Furthermore, a shift in the peak position of Ni from 852.6 to
52.1 eV indicating a possible electron donation from IL to the nickel
sites. These results are strongly consistent with our previous report on a
γ-Al -supported atomically dispersed single-site iridium catalyst
2 3
O
coated with 1,3-dialkylimidazolium ILs. High-energy resolution fluor-
escence detection X-ray absorption near edge structure (HERFD
XANES) measurements on these iridium catalyst presented direct evi-
dence on the presence of electron donation from IL coatings to the
active metal sites [25]. These HERFD XANES results indicated a strong
correlation between the edge energy of iridium adjusted by the choice
of imidazolium IL and the total butene selectivity for the same reaction
4. Conclusions
Here, we showed that an ordinary commercial nickel catalyst can be
taught to behave like palladium-based catalysts towards partial hy-
drogenation, when coated with an inexpensive, yet thermally and
[
25]. Thus, consistent with these previous observations on imidazolium
type ILs, we infered that the phosphonium type-IL that we used in this
study also works as a ligand to adjust the electronic environment over
the nickel sites.
One other possible effect of IL coating is that it can work as a filter
over the active sites to control the active concentrations of the reactants
and intermediates [32,33]. To investigate the consequences of this ef-
fect on the exceptional partial hydrogenation selectivity obtained on IL-
coated catalyst, we performed the COSMO-RS calculations. The esti-
mated solubilities of 1,3-butadiene, 1-butene, cis- and trans-2-butenes,
4
chemically stable IL. Data illustrate that [P4441][MeSO ]-coated Ni65
gives a record high selectivity of 99.5 ± 0.2% towards butenes at any
conversion level in 1,3-butadiene hydrogenation under optimized
conditions. This almost complete partial hydrogenation selectivity ir-
respective of conversion is associated with the ligand and filter effects
of the IL. XPS results indicated that the IL donates electrons to the
nickel sites. Moreover, COSMO-RS calculations showed that butenes are
approximately 1.5-times less soluble than 1,3-butadiene in [P4441
]
and butane in [P4441][MeSO
results indicate that the solubility of 1,3-butadiene in [P4441][MeSO
4
] at 145 °C are listed in Table 1. These
] is
[
MeSO ], and this difference in solubility helps to maintain the high
4
4
partial hydrogenation selectivity at all conversion levels. Results pre-
sented here provide opportunities towards controlling the catalytic
performance by coating the catalysts with chemically and thermally
stable ILs, which offer a flexibility in optimizing the reaction conditions
for high performance even before depositing the IL coatings.
approximately 1.5-times higher than those of butene intermediates/
products (Table 1). Such difference might provide an increase in se-
lectivity towards partial hydrogenation. However, even if it does, it
Table 1
Capacity of individual components in [P4441][MeSO
45 °C as determined by COSMO-RS calculations.
4
] at
Acknowledgements
1
This study is supported by TUBITAK National Young Researchers
Career Development Program (CAREER) (Project number: 113M552)
and by Koç University TÜPRAŞ Energy Center (KUTEM). A.J. ac-
knowledges HEC-Pakistan scholarship and A.U. acknowledges the
support from the Science Academy, Turkey under the BAGEP program
and the Young Scientists Award of the Turkish Academy of Sciences
Component
Capacity mol/mol
1
,3-butadiene
trans-2-butene
-butene
1.22
0.81
0.86
0.82
0.58
1
cis-2-butene
Butane
(
TUBA-GEBIP) . We thank Dr. Barış Yağcı and Amir Motallebzadeh of
325

A. Jalal, A. Uzun
Applied Catalysis A, General 562 (2018) 321–326
Koç University Surface Science and Technology Center (KUYTAM) for
providing help with XPS and BET measurements, respectively. Authors
would also like to thank TARLA for the collaborative research support.
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[
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Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.apcata.2018.06.016.
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