Nickel oxide-silica core-shell catalyst for acetylene hydroxycarbonylation

Article abstract of DOI:10.1016/j.catcom.2019.02.009

Acrylic acid and its ester derivatives are important chemicals utilized to synthesize numerous end products. Acrylic acid is industrially produced via propylene oxidation. We report in this study a nickel oxide-silica core-shell catalyst (NiO@SiO₂) for acetylene hydroxycarbonylation as an alternative way to synthesize acrylic acid. NiO@SiO₂ catalyst provided the higher turnover frequency and yield than commercial nickel oxide catalyst on acetylene hydroxycarbonylation. The carbon monoxide/acetylene ratio influenced more significantly to initial reaction rate than final acrylic acid yield. The silica shell protected the nickel oxide from sintering during reaction, however, the catalyst was deactivated by coke formation, attributed to acetylene decomposition.

Full text of DOI:10.1016/j.catcom.2019.02.009

Accepted Manuscript
Nickel oxide-silica core-shell catalyst for acetylene
hydroxycarbonylation
Hong Sub Choi, Ji Hoon Park, Jong Wook Bae, Jin Hee Lee, Tae
Sun Chang
PII:
S1566-7367(19)30044-5
DOI:
Reference:
https://doi.org/10.1016/j.catcom.2019.02.009
CATCOM 5620
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
9 November 2018
21 January 2019
10 February 2019
Please cite this article as: H.S. Choi, J.H. Park, J.W. Bae, et al., Nickel oxide-silica
core-shell catalyst for acetylene hydroxycarbonylation, Catalysis Communications,
https://doi.org/10.1016/j.catcom.2019.02.009
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ACCEPTED MANUSCRIPT
Nickel
Oxide-Silica
Core-Shell
Catalyst
for
Acetylene
Hydroxycarbonylation
Hong Sub Choi,a,b Ji Hoon Park,a Jong Wook Bae,b Jin Hee Lee,a,* Tae Sun
Changa,*
aCenter for Environment & Sustainable Resources, Korea Research Institute of
Chemical Technology, 141 Gajeong-ro, 34114 Daejeon, Republic of Korea.
bSchool of Chemical engineering, Sungkyunkwan University(SKKU), Suwon
16419, Republic of Korea
*Corresponding authors. Fax: (+82)-042-860-7593, e-mail: leejh@krict.re.kr
(J.H. Lee), tschang@krict.re.kr (T.S. Chang)
Abstract
Acrylic acid and its ester derivatives are important chemicals utilized to
synthesize numerous end products. Acrylic acid is industrially produced via
propylene oxidation. We report in this study a nickel oxide-silica core-shell
catalyst (NiO@SiO2) for acetylene hydroxycarbonylation as an alternative way
to synthesize acrylic acid. NiO@SiO2 catalyst provided the higher turnover
frequency and yield than commercial nickel oxide catalyst on acetylene

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hydroxycarbonylation. The carbon monoxide/acetylene ratio influenced more
significantly to initial reaction rate than final acrylic acid yield. The silica shell
protected the nickel oxide from sintering during reaction, however, the catalyst
was deactivated by coke formation, attributed to acetylene decomposition.
Keywords
Acetylene, Hydroxycarbonylation, Nickel oxide, Acrylic acid, Core-shell,
Sintering process.
1. Introduction
Acrylic acid (AA) is the simplest unsaturated carboxylic acid, which
vinyl group is directly connected to carboxylic acid functionality. AA and its
ester derivatives are transformed to numerous functional polymer materials via
self-polymerization and/or co-polymerization with acrylamide, acrylonitrile,
styrene, and butadiene etc [1-5]. The resulting materials are utilized to
manufacture a variety of products such as textile, plastic, adhesive, coating, and
elastomer [6].
AA is mainly produced by oxidation of propylene originated from
petroleum. Although the propylene oxidation is well established, new synthetic
routes that reduce the use of petroleum derived chemicals are required to
withstand an increasing oil-price. Acetylene hydroxycarbonylation is a plausible

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alternative to synthesize AA (acetylene + CO + H2O  acrylic acid)[7-10].
Reppe first reported the acetylene hydroxycarbonylation in 1939 using nickel
tetracarbonyl (Ni(CO)4) as a catalyst [11]. However, the high toxicity of nickel
tetracarbonyl limited the commercial application. Other nickel catalysts have,
thus, been developed to replace nickel tetracarbonyl. Tang et al. synthesized AA
with high yield and selectivity using nickel acetate [12]. Hao Xie and co-
workers reported the use of heterogeneous nickel oxide in acetylene
hydroxycarbonylation [13]. The nickel oxide supported on MCM-41 resulted
the highest yield and turnover frequency (TOF). Lin et al. studied the effects of
the nickel oxide preparation method in acetylene hydroxycarbonylation activity
[14].
In this study, we employed a nickel oxide coated with porous silica shell
(NiO@SiO2) as a catalyst for acetylene hydroxycarbonylation. The silica shell
inhibits the leaching and aggregation of active nickel oxide nanoparticles while
allowing diffusion of the reactants and the product. The effects of numerous
reaction parameters on the AA yield and reaction rates are examined.
2. Experimental
2.1 Materials
Carbon monoxide (99.95%) was purchased from Bingrae gases Co., Ltd

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and acetylene (97%) was purchased from Sinchun gas. Nickel nitrate
hexahydrate (Ni(NO3)2∙6H2O), polyethylene glycol (MW20000) were purchased
from Alfa aesar. Pluronic P123 (Poly(ethylene glycol)-block-poly(propylene
glycol)-block-Poly(ethylene glycol)-block), Polyvinylpyrrolidone (PVP,
MW40000), ammonium hydroxide solution (28%), tetraethyl orthosilicate
(TEOS, 98%), mesitylene (98%), ammonium fluoride (NH4F, 98%),
hydrochloric acid (HCl, 35-37%) were purchased from Sigma Aldrich. Sodium
hydroxide, ethanol (95%), acetone (95%) were purchased from Samchun
Chemical. All the chemicals were used without purification.
2.2 Catalystsynthesis
The NiO@SiO2 was synthesized by a slight modification of reported
procedure [15]. Nickel nitrate hexahydrate (2.9 g) was dissolved in distilled
water (40 mL, and the solution was stirred at room temperature for 30 min. The
solution was added dropwise to the mixture of distilled water (100 mL),
polyethylene glycol (330 mg), and sodium hydroxide (1.0 g). The resulting
mixture was stirred at room temperature for 1 h, then filtered and washed using
distilled water and ethanol. The mixture was dried at 50 °C for 24 h and
calcined at 350 °C for 2 h to give the nickel oxide nanoparticles. 100 ml of an
ethanolic solution containing PVP (0.10 g) and nickel oxide nanoparticles (0.20
g) was stirred for 12 h at room temperature. 25% aqueous ammonia solution (10

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ml) was added into the solution and sonicated for 30 min. The ethanol solution
(5.0 mL) containing TEOS (0.10 mL) was added and stirred for 1 h. The
resulting suspension was washed by centrifugation for three times using ethanol
and distilled water. The precipitate was collected and dried at 80 °C for 6 h to
give 0.21 g of NiO@SiO2.
For the synthesis of NiO/SiO2, the mesoporous silica was prepared by
reported procedure [16]. Pluronic P123 (16 g) was dissolved in 1.6 M aqueous
HCl solution (150 mL). Mesitylene (4.0 g) and NH4F (0.046 g) were added to
the solution and stirred at room temperature for 1 h. TEOS (8.8 g) was added,
o
and the mixture was stirred at 40 C for 24 h. The resulting suspension was
o
filtered with water and the obtained solid was dried for 24 h at 100 C.
o
Calcination for 8 h at 500 C gave the mesoporous silica. The nickel nitrate
hexahydrate (0.33 g dissolved in 2.0 mL distilled water) aqueous solution was
impregnated to the mesoporous silica (1.0 g) and dried at 80 °C. The resulting
solid was calcined at 400 °C for 3 h to give NiO/SiO2.
2.3 Catalystcharacterization
The crystal structure of catalysts was characterized by X-ray diffraction
(XRD, Bruker) using Cu Kα radiation (λ=1.5406 Å) at 40 kV and 100 mA. The
scan was performed in the 2 ºmin-1 range of 10 ° to 80 ° with 0.02 °step-1, and 1

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s•step-1. For transmission electron microscopy (TEM) measurement, the
material was dispersed in ethanol and a few drops were deposited onto a copper
grid. TEM was performed on a Talos F20S (FEI Talos) at an acceleration
potential of 200 kV. The thermogravimetric analysis (TGA) was implemented
on a TGA Q5000 (TA). The 2.3290 g of analyte was loaded on a platinum
microcrucible and heated up to 700 °C at a ramping rate of 10 °Cmin-1 under an
air flow of 25 mL•min-1. Chemisorption were performed with ASAP 2020
(Micromeritics) at 35 °C using 99.999% hydrogen. Before analysis, the samples
were reduced at 450 °C under 99.999% hydrogen for 4 h followed by
evacuation at 450 °C.
2.4 Catalytic reaction.
The catalytic acetylene hydroxycarbonylation was performed in a 100
mL autoclave made of stainless steel. In a typical experiment, 12.9 mg of
NiO@SiO2 (3.78 mMNi), 10 mg of copper (II) bromide (1.12 mMCu) were added
to the 40 mL mixture of distilled water and acetone (acetone/water = 1:9 volume
ratio) The reactor was purged with argon and charged to 3 bar with acetylene
followed by pressurizing with CO up to 30 bar at 28 °C. The amounts of
introduced gas were monitored by mass flow controller. The reaction mixture
was heated to 220 °C while stirring at 300 rpm. The reaction temperature and
pressure were recorded automatically. After the reaction, the reactor was quickly

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cooled under 50 °C and purged with Ar. The reaction mixture were collected
and evaporated to remove residual acetone. The AA yield was determined by 1H
nuclear magnetic resonance (NMR) spectroscopy using ethanol as an internal
standard. For the quantification of AA, 30 mmol of ethanol was added to the
1
reaction mixture before H NMR analysis. The amount of AA was calculated
based on the integration ratio of CH3 proton of ethanol and CH proton of AA.
The AA yield and initial TOF of the reaction was calculated by following
equations. Identical mole concentration of nickel and copper were used for other
catalysts.
ꢀ푛푡푒푔푟푎푡ꢀ표푛 푣푎푙푢푒 표푓 퐶퐻 푝푟표푡표푛 표푓 퐴퐴
(
)
amounts of AA mmol =
× 30 (푚푚표푙)
ꢀ푛푡푔푟푎푡ꢀ표푛 푣푎푙푢푒 표푓 퐶퐻3 푝푟표푡표푛 표푓 푒푡ℎ푎푛표푙
(1)
1
amounts of AA determined by 퐻 NMR
AA yield (%) = amounts of acetylene measured by MFC × 100
(2)
TOF (ℎ−1) = (푝푟푒푠푠푟푢푒 푑푟표푝 푎푡 ꢀ푛ꢀ푡푎푙 5 푚ꢀ푛) × produced AA (mmol) ×
푡표푡푎푙 푝푟푒푠푠푢푟푒 푑푟표푝
1
60
×
(3)
푠푢푟푓푎푐푒 푁ꢀ (푚푚표푙)
5
3. Results and Discussion
Nickel oxide nanoparticles were prepared by precipitation using
polyethylene glycol as a stabilizer. The formation of 8.8 ± 4.1 nm nickel oxide

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nanoparticles were confirmed by TEM analysis (Figure 1a). The silica shell was
introduced on the surface of nickel oxide to cover and isolate nickel oxide
nanoparticles by modified Stober’s method. PVP was employed to give porous
structure to the silica shell. The formation of 8.5 ± 4.1 nm nickel oxide
nanoparticles enclosed by 5.1 ± 2.2 nm silica shell were found in the TEM
images (Figure 1b). The nickel oxide nanoparticles maintained the original size
during the silica shell formation. The TEM image showed the most of the nickel
oxide nanoparticles were isolated from other particles by silica. The nitrogen
isotherm plot of NiO@SiO2 showed the type II isotherm which had a hysteresis
in the P/P0 range of 0.4-0.9. This result indicates the mesoporous nature of
NiO@SiO2 (Figure S1a). The XRD patterns of nickel oxide and NiO@SiO2
exhibited a typical nickel (II) oxide structure (Figure S1b). No peaks correspond
to silica were observed due to amorphous nature of the silica shell.
Acetylene hydroxycarbonylation was performed to test the catalytic
activity of nickel catalysts. Nickel bromide produced 22% of AA and the yield
was improved to 47% in presence of copper bromide (Table 1, entries 1, 2). The
copper has known to promote the AA production by enhancing carbon
monoxide solubility [12]. Commercial nickel oxide exhibited poor AA yield due
to low metallic surface area (Table 1, entry 3). Both NiO/SiO2 and NiO@SiO2
showed comparable AA yield to nickel bromide (Table 1, entries 5, 6). However,
specific activity of NiO@SiO2 was higher than NiO/SiO2 as confirmed by TOF.

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This result signifies that the surface active sites on NiO@SiO2 are more active
toward acetylene hydroxycarbonylation than NiO/SiO2. When the copper oxide
was employed instead of copper bromide, the reaction did not proceed with both
NiO and NiO@SiO2.
The effect of carbon monoxide/acetylene molar ratios on the AA yield
and formation rate was investigated (Figure 2). The carbon monoxide/acetylene
ratios were adjusted by varying initial acetylene pressure. AA yield increased as
carbon monoxide/acetylene ratio increased from 0.6 to 0.9, then kept similar
yields between carbon monoxide/ acetylene ratios of 0.9-1.5. The AA yield
decreased over carbon monoxide/acetylene ratio of 1.5. However, the TOFs
followed a volcano curve, which had a peak value at the carbon
monoxide/acetylene ratios of 1.3-1.1. Because the solubility of carbon
monoxide is low, high carbon monoxide concentration increases the initial
reaction rate. Whereas, too high carbon monoxide concentration might increase
the surface coverage of carbon monoxide on nickel oxide, and retards AA
formation by inhibition of the acetylene coordination onto catalyst surface. In
contrast to TOF, the highest AA yield was achieved in the broad range of carbon
monoxide/acetylene ratio (1.5-0.9) regardless of initial reaction rate. Figure S2
shows the time on stream pressure changes of three reactions, which were
carbon monoxide/acetylene ratio of 1.5, 1.1, 0.9. In all the cases, the pressure
rapidly drops initially then, the decrease rates were slow down. The initial

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reaction rates were affected by carbon monoxide/acetylene ratios and the order
was 1.1 > 0.9 > 1.5. Although initial AA formation rates were different, the
reactions further proceeded for 3 h and resulted in the identical AA yields on
three different reactions (Figures 2 and S2).
AA formation rates were influenced by reaction conditions, such as
ratios of reactant, and catalyst. However, final AA yields were not significantly
affected to the varying initial reaction rates. The results implicate that acetylene
hydroxycarbonylation stops at certain conversion level due to inhibition of high
AA concentration in the reaction mixture. Thus, controlled amounts of AA were
added to reactor to investigate possible effects of AA on the acetylene
hydroxycarbonylation. Figure 3 clearly shows the negative effects of additional
AA to acetylene hydroxycarbonylation. Both initial reaction rates and final AA
quantities were reduced when AA was added. Because acetylene
hydroxycarbonylation is irreversible in our reaction condition, the retardation of
AA formation is not due to the reaction equilibrium but attributes to inhibition
of the catalytic cycle. Based on the previous reports of nickel and palladium
catalyzed hydroxycarbonylation, nickel oxide catalyzed acetylene
hydroxycarbonylation mechanism is proposed (Figure 4) [12, 17]. Copper (II)
bromide initially oxidized to copper (I) bromide by acetylene and produce
hydrogen bromide [18]. The catalytic cycle starts from hydroxylation of nickel
oxide by hydrogen bromide. The copper (I) forms copper-acetylene pi

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complex[19] to facilitate the adsorption of acetylene onto the nickel oxide. The
proton is transferred to the acetylene to form nickel-vinyl complex with
simultaneous nickel oxidation [17]. Following carbon monoxide insertion and
bromide assisted hydroxylation produce AA. Because produced AA
competitively coordinates onto nickel surface against acetylene and carbon
monoxide, excess AA likely hinders the catalytic cycle and decrease the reaction
rate. In addition, increased acidity of reaction medium prevents the formation of
AA and results in the low yield.
The reusability of the NiO@SiO2 was tested. The catalyst was recovered
by centrifugation and reused without a specific treatment. As shown in Figure
S3, the catalyst was deactivated in the three times of reuse. TEM images of the
reused catalyst showed that the catalyst maintained the core-shell structure
without significant aggregation (Figure 5). The particle size of the used
NiO@SiO2 was 8.4 nm. While, the particle size of the non-protected nickel
oxide was grown from 7.1 nm to 12.4 nm (Figure S4). Although the nickel
oxide nanoparticles were stable, substantial amounts of fiber-like carbon which
had a thickness of 31 ± 10 nm was observed on used NiO@SiO2. TGA revealed
12 wt% of carbon was contained in the spent catalyst (Figure S5). In addition,
nickel oxide was not leached out during the reaction as determined by
inductively coupled plasma (ICP) analysis of reaction mixture. Although the
nickel oxide was stable, the coke formation by acetylene decomposition

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influenced the durability of the catalyst. As reported by other nickel oxide
catalyst system, carbon product can be removed by oxidation process and
possibly recover catalytic activity [6, 13, 14].
4. Conclusions
In conclusion, we synthesized a NiO@SiO2 core-shell catalyst for
acetylene hydroxycarbonylation. The core-shell catalyst provided higher acrylic
acid yield and TOF than commercial nickel (II) oxide and mesoporous silica
supported nickel oxide. The optimum CO/acetylene ratio was critical to achieve
high TOF while final AA yield was less sensitive to CO/acetylene ratio. The
core-shell structure successfully protected the nickel oxide from sintering but
coke formation by acetylene decomposition caused catalyst deactivation. The
AA itself hinders the acetylene hydroxycarbonylation by binding onto the active
catalyst surface, thus the reaction cannot proceed to completion in current
catalytic system. The reaction system that prevents the inhibiting roles of AA
and/or the catalyst that resists to AA coordination are needed to achieve higher
AA yield.
Acknowledgements

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This research was supported by KRICT Steppingstone Program for SMEs R&D,
Korea Research Institute of Chemical Technology (KRICT).
References
[1] I.-T. Trotuş, T. Zimmermann, F. Schüth, Catalytic Reactions of Acetylene: A
Feedstock for the Chemical Industry Revisited, Chem. Rev., 114 (2014) 1761-
1782. https://doi.org/10.1021/cr400357r
[2] H. Xie, D. Yi, L. Shi, X. Meng, High performance of CuY zeolite for
catalyzing acetylene carbonylation and the effect of copper valence states on
catalyst,
Chem.
Eng.
J.,
313
(2017)
663-670.
https://doi.org/10.1016/j.cej.2016.11.043
[3] J. Hou, M.-L. Yuan, J.-H. Xie, Q.-L. Zhou, Nickel-catalyzed
hydrocarboxylation of alkynes with formic acid, Green Chem., 18 (2016) 2981-
2984. https://doi.org/10.1039/C6GC00549G
[4] T.J. Lin, H. Xie, X. Meng, L. Shi, Characterization and catalytic application
of Bi2O3/NiO composite oxides in the Reppe carbonylation to acrylic acid,
Catal. Commun., 68 (2015) 88-92. https://doi.org/10.1016/j.catcom.2015.04.032
[5] T.-j. Lin, X. Meng, L. Shi, Activity and Sediments Study for the
Hydrocarboxylation of Acetylene with Carbon Monoxide to Acrylic Acid on

ACCEPTED MANUSCRIPT
Ni–Cu Homogeneous Catalyst, Ind. Eng. Chem. Res., 52 (2013) 14125-14132.
https://doi.org/10.1021/ie4021446
[6] T.J. Lin, X. Meng, L. Shi, Ni-exchanged Y-zeolite: An efficient
heterogeneous catalyst for acetylene hydrocarboxylation, Appl. Catal. A-Gen.,
485 (2014) 163-171. https://doi.org/10.1016/j.apcata.2014.07.036
[7] H. Schobert, Production of Acetylene and Acetylene-based Chemicals from
Coal, Chem. Rev., 114 (2014) 1743-1760. https://doi.org/10.1021/cr400276u
[8] S. Quintero-Duque, K.M. Dyballa, I. Fleischer, Metal-catalyzed
carbonylation of alkynes: key aspects and recent development, Tetrahedron Lett.,
56 (2015) 2634-2650. https://doi.org/10.1016/j.tetlet.2015.04.043
[9] F. De Angelis, A. Sgamellotti, N. Re, Density Functional Study of the Reppe
Carbonylation of Acetylene, Organometallics, 19 (2000) 4104-4116.
https://doi.org/10.1021/om0002428
[10] G. Kiss, Palladium-catalyzed Reppe carbonylation, Chem. Rev., 101 (2001)
3435-3456. https://doi.org/10.1021/cr010328q
[11] W. Reppe, H. Kröper, Carbonylierung II. Carbonsäuren und ihre Derivate
aus olefinischen Verbindungen und Kohlenoxyd, Liebigs. Ann. Chem., 582
(1953) 38-71. https://doi.org/10.1002/jlac.19535820103
[12] C. Tang, Y. Zeng, P. Cao, X. Yang, G. Wang, The Nickel and Copper-
Catalyzed Hydroformylation of Acetylene with Carbon Monoxide to Acrylic
Acid, Catalysis Lette., 129 (2009) 189-193. https://doi.org/10.1007/s10562-008-

ACCEPTED MANUSCRIPT
9789-6
[13] H. Xie, T. Lin, L. Shi, X. Meng, Acetylene carbonylation over Ni-
containing catalysts: role of surface structure and active site distribution, RSC
Adv., 6 (2016) 97285-97292. https://doi.org/10.1039/C6RA17567H
[14] T.J. Lin, X. Meng, L. Shi, Catalytic hydrocarboxylation of acetylene to
acrylic acid using Ni2O3 and cupric bromide as combined catalysts, J. Mol.
Catal.
A-Chem.,
396
(2015)
77-83.
https://doi.org/10.1016/j.molcata.2014.09.027
[15] L. Li, S. He, Y. Song, J. Zhao, W. Ji, C.-T. Au, Fine-tunable Ni@porous
silica core–shell nanocatalysts: Synthesis, characterization, and catalytic
properties in partial oxidation of methane to syngas, J. Catal., 288 (2012) 54-64.
https://doi.org/10.1016/j.jcat.2012.01.004
[16] L. Wolski, I. Sobczak, M. Ziolek, Development of multifunctional gold,
copper, zinc, niobium containing MCF catalysts – Surface properties and
activity in methanol oxidation, Micropor. Mesopor. Mat., 243 (2017) 339-350.
https://doi.org/10.1016/j.micromeso.2017.02.038
[17] L. Crawford, D.J. Cole-Hamilton, E. Drent, M. Buhl, Mechanism of alkyne
alkoxycarbonylation at a Pd catalyst with P,N hemilabile ligands: a density
functional
https://doi.org/10.1002/chem.201403983
[18] G. Zhang, H. Yi, G. Zhang, Y. Deng, R. Bai, H. Zhang, J.T. Miller, A.J.
study,
Chem.,
20
(2014)
13923-13926.

ACCEPTED MANUSCRIPT
Kropf, E.E. Bunel, A. Lei, Direct Observation of Reduction of Cu(II) to Cu(I)
by Terminal Alkynes, J. Am. Chem. Soc., 136 (2014) 924-926.
https://doi.org/10.1021/ja410756b
[19] B.T. Worrell, J.A. Malik, V.V. Fokin, Direct Evidence of a Dinuclear
Copper Intermediate in Cu(I)-Catalyzed Azide-Alkyne Cycloadditions, Science,
340 (2013) 457-460. https://doi.org/10.1126/science.1229506

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Table 1. Catalytic activity comparison of various nickel catalysta)
Figure 1. TEM images of (a) NiO and (b) NiO@SiO2. Scale bars are 10 nm.
Figure 2. Effects of carbon monoxide/acetylene ratios on NiO@SiO2 catalyzed
acetylene hydroxycarbonylation.
Figure 3. Effects of AA addition on NiO@SiO2 catalyzed acetylene
hydroxycarbonylation.
Figure 4. Proposedreaction mechanism and inhibition byAA.
Figure 5. TEM images of reused NiO@SiO2. Scale bars are 100 nm.
Table 1. Catalytic activity comparison of various nickel catalysta)
AA yield
TOFc)
(x106)
0.036
0.040
15
Entry
Ni
Cu
(%)b)
22
47
14
-
1
2
3
4
NiBr2
NiBr2
NiO
CuBr2
CuBr2
CuO
NiO
-

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5
6
7
NiO/SiO2
NiO@SiO2 CuBr2
NiO@SiO2 CuO
CuBr2
48
48
-
0.99
15
-
a) The 3.78 mM of nickel and 1.12 mM of copper were added to the 1:9 mixture
of water/acetone mixture. Then, 3 bar of acetylene and 30 bar of carbon
monoxide were charged. The temperature of the reactor was increased to 220 °C
1
and kept for 4 h. b) Determined by H NMR using ethanol as an internal
standard. c) Calculated based on the amounts of surface nickel oxide determined
by H2-chemisorption.
(a)
(b)
Figure 1. TEM images of (a) NiO and (b) NiO@SiO2. Scale bars are 10 nm.

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50
40
30
20
10
0
175
150
125
100
75
50
25
0
1.3 1.5 2.1 2.9
1.1
0.6 0.9 1.0
CO/Acetylene ratio
Figure 2. Effects of carbon monoxide/acetylene ratios on NiO@SiO2 catalyzed
acetylene hydroxycarbonylation.

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50
40
30
20
10
0
175
150
125
100
75
50
25
0
10
50
0
20
Additional AA (mmol)
Figure 3. Effects of AA addition on NiO@SiO2 catalyzed acetylene
hydroxycarbonylation.

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Figure 4. Proposedreaction mechanism and inhibition byAA.
Figure 5. TEM images of reused NiO@SiO2. Scale bar is 100 nm.
Highlights
 The NiO@SiO2 core-shell catalyst provided higher acrylic acid yield and
turnover frequency.
 The core-shell structure protected the nickel oxide from sintering.
 The acrylic acid itself inhibits the catalytic cycle by binding onto the
active sites.
 Formation of coke by acetylene decomposition leads to deactivation of
catalyst.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5