Improved performance of SiO2-supported Ni3Ga intermetallic compound for deoxygenation of phenolic compounds

Article abstract of DOI:10.1016/j.catcom.2020.106001

Ni/SiO₂ and SiO₂-supported Ni₃Ga and Ni₅Ga₃ intermetallic compounds were prepared by the sol-gel method and evaluated for the hydrodeoxygenation of various phenolic compounds at 0.1 MPa. In the hydrodeoxygenation of anisole, Ni₃Ga/SiO₂ was more active for direct deoxygenation to benzene than the corresponding catalyst prepared by the impregnation method as well as Ni/SiO₂. The anisole conversion and selectivity to benzene reached 95.1% and 92.5% on Ni₃Ga/SiO₂ at 300 °C and WHSV of 2 h^?1, respectively. In the HDOs of cresols and guaiacol, Ni₃Ga/SiO₂ still more dominatingly facilitated the direct deoxygenation, while Ni/SiO₂ significantly promoted the C-CH₃ bond cleavage.

Full text of DOI:10.1016/j.catcom.2020.106001

CatalysisCommunications140(2020)106001
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Catalysis Communications
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Short communication
Improved performance of SiO2-supported Ni3Ga intermetallic compound for
deoxygenation of phenolic compounds
Xiongxiong Niu, Liwen Wang, Jixiang Chen⁎
Tianjin Key Laboratory of Applied Catalysis Science and Technology, Department of Catalysis Science and Engineering, School of Chemical Engineering and Technology,
Tianjin University, Tianjin 300350, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
Ni3Ga intermetallic compound
Sol-gel method
Ni-phyllosilicate
Hydrodeoxygenation
Direct deoxygenation
Phenolics
Ni/SiO2 and SiO2-supported Ni3Ga and Ni5Ga3 intermetallic compounds were prepared by the sol-gel method
and evaluated for the hydrodeoxygenation of various phenolic compounds at 0.1 MPa. In the hydro-
deoxygenation of anisole, Ni3Ga/SiO2 was more active for direct deoxygenation to benzene than the corre-
sponding catalyst prepared by the impregnation method as well as Ni/SiO2. The anisole conversion and se-
lectivity to benzene reached 95.1% and 92.5% on Ni3Ga/SiO2 at 300 °C and WHSV of 2 h−1, respectively. In the
HDOs of cresols and guaiacol, Ni3Ga/SiO2 still more dominatingly facilitated the direct deoxygenation, while Ni/
SiO2 significantly promoted the C-CH3 bond cleavage.
1. Introduction
generally proposed. That is, the CAr-O bond is activated through the
adsorption of oxygen on the oxophilic metal, followed by the attack of
To alleviate environmental and energy issues, biomass has attracted
great attention for producing liquid fuels and chemicals. Therein, the
lignin-based bio-oils are ideal resources for producing aromatics (e.g.,
benzene, toluene and xylene (i.e., BTX)) [1]. To achieve this, hydro-
deoxygenation (HDO) is a feasible strategy. In the HDO of phenol,
several pathways may take place, i.e., direct deoxygenation (DDO),
hydrogenation-deoxygenation (HYD) and tautomerization [2–4].To
produce BTX, the DDO pathway is desired because the CAr-O bond (CAr
denotes carbon in benzene ring) is directly cleaved with low H2 con-
sumption. To facilitate DDO pathway, the catalyst function plays a
crucial role.
Although supported CoMo and NiMo sulfides are commercially
available, it is urgent to develop sulfur-free catalysts to avoid introdu-
cing sulfur-containing agent during HDO [5]. Noble metals [6] (e.g., Pd
and Pt) and base metals (e.g., Ni [7] and Fe [8]) appear promising.
Given the low cost and high activity, metallic Ni is more attractive.
Unfortunately, nickel is also very active for some undesirable reactions
such as benzene ring hydrogenation, CeC bond hydrogenolysis and
methanation [9]. This not only reduces the BTX yield but also enhances
the H2 consumption. To circumvent this shortage, it is effective to
modify the geometric and electronic properties of metallic Ni with other
metals (especially oxophilic ones) via forming an alloy and inter-
metallic compound (IMC) as catalysts, such as NieRe [10], NieGa [9],
Ni-Fe [11] and NieIn [12]. On these catalysts, a synergetic effect is
hydrogen species on metallic Ni leading to the DDO pathway. This ef-
fect has also been suggested for the HDO of phenolics on noble metal-
based bimetallic catalysts, e.g., Pt-Zn [13], Pd-Fe [14] and Pt-Re [15].
Our previous work [9] indicated that SiO2-supported Ni3Ga IMC
(Ni3Ga/SiO2) gave both higher activity and selectivity to benzene than
Ni/SiO2 in the HDO of anisole. This is attributed to the geometric and
electronic effects of Ga. To be more specific, the Ni atoms are isolated
by the Ga ones and the electron density of Ni increases due to a charge
transfer from Ga to Ni [9,16–18]. On one hand, the DDO pathway is
promoted due to the synergetic effect between Ni and Ga, and this sy-
nergism also accelerates the HDO [9]. On the other hand, the benzene
ring hydrogenation, CeC bond hydrogenolysis and methanation are
suppressed on Ni3Ga IMC. Although Ni3Ga/SiO2 is very favorable for
the DDO pathway in the HDO of anisole, we consider that its activity for
HDO is still required to be enhanced. Also, it is very worth investigating
the performance of Ni3Ga/SiO2 in the HDO of other phenolic com-
pounds.
Herein, we prepared Ni3Ga/SiO2 by the sol-gel method to improve
its performance via increasing the Ni3Ga dispersion. Indeed, the as-
prepared catalyst gave significantly higher activity than that prepared
by the impregnation method in the HDO of anisole. Also, Ni3Ga/SiO2
was more beneficial to facilitating the DDO pathway than Ni/SiO2 in
the HDO of cresols and guaiacol.
⁎ Corresponding author.
E-mail address: jxchen@tju.edu.cn (J. Chen).
https://doi.org/10.1016/j.catcom.2020.106001
Received 3 January 2020; Received in revised form 23 March 2020; Accepted 27 March 2020
Availableonline29March2020
1566-7367/©2020ElsevierB.V.Allrightsreserved.

X. Niu, et al.
CatalysisCommunications140(2020)106001
2. Experimental
generated during the impregnation process. FT-IR further verifies the
existence of Ni-PS in Ni/SiO2 and NiGa(x/y)/SiO2 (Fig.S1, ESI). The IR
bands recorded at 670 and 3627 cm−1 are assigned to the δOH vibra-
tional mode and vOH stretching vibrational mode of Ni-PS, respectively
[22,23]. For im-NiGa(3/1)/SiO2, no IR bands related to Ni-PS are
visible.
2.1. Catalysts preparation
Ni/SiO2 and SiO2-supported Ni-Ga catalysts with Ni/Ga atom ratios
of 3/1 and 5/3 (i.e., NiGa(3/1)/SiO2 and NiGa(5/3)/SiO2) were pre-
pared by the sol-gel method [19]. For comparison, SiO2-supported Ni-
Ga catalyst with Ni/Ga atom ratio of 3/1 (i.e., im-NiGa(3/1)/SiO2) was
prepared by the impregnation method. Details of catalysts preparation
are presented in the Electronic Supplementary Information (ESI).
H2-TPR was used to investigate catalyst reducibility (Fig. S2, ESI).
For Ga/SiO2, the reduction peaks at 290 and 780 °C are assigned to the
reduction of highly dispersed Ga2O3 and large Ga2O3 particles, re-
spectively [24]. The peak centered at 650 °C for Ni/SiO2 is attributed to
the reduction of Ni-PS. Compared with that of Ni/SiO2, the reduction
peak of NiGa(x/y)/SiO2 shifted to higher temperatures (ca. 670 °C for
NiGa(3/1)/SiO2 and 690 °C for NiGa(5/3)/SiO2), and its area (pro-
portional to concentration) also became larger. This is ascribed to the
simultaneous reduction of Ga3+ species. im-NiGa(3/1)/SiO2 shows
multi-peaks in the 320–700 °C range. The peak at low temperature is
assigned to the reduction of NiO, while that above 550 °C is mainly
attributed to the reduction of Ga species [9].NiGa(3/1)/SiO2 gave a
higher reduction temperature than im-NiGa(3/1)/SiO2 due to the for-
mation of Ni-PS, where there is stronger interaction between Ni and
SiO2 [19,25].
2.2. Catalysts characterization
The powder XRD patterns were obtained on a D8 Focus powder
diffractometer. TEM images were taken on a JEOL JEM-2100F instru-
ment. FT-IR spectra were recorded on a Thermo Nicolet Nexus FT-IR
spectrometer. H2-TPR was conducted on an apparatus equipped with a
thermal conductivity detector (TCD). N2 sorption isotherms at -196 °C
were measured on a Quantachrom QuadraSorb SI instrument. TG
analysis (TGA) was carried out on a Mettler Toledo TGA 1/SF instru-
ment.
3.1.2. Reduced catalysts
2.3. Catalytic performance
As to the reduced Ni/SiO2 and NiGa(x/y)/SiO2 catalysts, the specific
surface areas were similar (413–419 m2/g). NiGa(5/3)/SiO2 had
smaller pore size and lower pore volume than Ni/SiO2 andNiGa(3/1)/
SiO2 (Table S1, ESI).
The catalytic performance of the various solids investigated was
tested using a quartz tube fixed-bed reactor operated at 1 atm [9,12].
The liquid effluent from reactor was analyzed on a SP-3420 gas chro-
matograph (GC) (equipped with a FID and a DB-1 capillary column).
The gaseous C1 products were on-line analyzed on a 102 GC equipped
with a TCD and a TDX-101 packed column. Details of the catalytic
performance measurements are presented in ESI.
Powder XRD patterns of the catalysts reduced at 650 °C are shown in
Fig. 2. The peaks belonging to Ni-PS are not visible, i.e., Ni-PS was
completely reduced. For Ni/SiO2, two small diffraction peaks (44.5 and
51.8°) are ascribed to metallic Ni (PDF#65–2865). The Ni crystallite
size was estimated to be 3.6 nm (use of Scherrer formula). For NiGa(3/
1)/SiO2, the peaks at 43.7, 50.9 and 74.9o are attributed to Ni3Ga
IMC(PDF#65–3246) with an average crystallite size of 6.5 nm. As to
NiGa(5/3)/SiO2, the sharp diffraction peaks at 43.3, 48.3and 75.8o
indicate the formation of Ni5Ga3 IMC (PDF#43–1376). Ni3Ga IMC was
formed in im-NiGa(3/1)/SiO2, while its average crystallite size (8.9 nm)
was larger than that (ca. 6.5 nm) in NiGa(3/1)/SiO2. Thus, the sol-gel
method gave rise to smaller Ni3Ga IMC crystallites due to the formation
of Ni-PS. The high Ni dispersion in Ni/SiO2 and NiGa(3/1)/SiO2 is also
demonstrated by TEM images (Fig. S3, ESI).
3. Results and discussion
3.1. Catalysts characterizations
3.1.1. Unreduced catalysts
As shown in Fig. 1, in the powder XRD patterns of unreduced Ni/
SiO2 and NiGa(x/y)/SiO2 catalysts, the small peaks recorded at 35.1
and 60.6o are attributed to Ni phyllosilicate (Ni3Si2O5(OH)4, Ni-PS)
[20,21]. That is, Ni-PS was formed during the sol-gel process. As to Ga/
SiO2, the non-appearance of diffraction peaks related to Ga2O3 indicate
the high dispersion of Ga3+ species. im-NiGa(3/1)/SiO2 gave diffrac-
tion peaks at 37.3, 43.3, 62.9 and 75.4o due to NiO; no Ni-PS was
3.2. Catalytic reactivity in HDO of phenolic compounds
Here, the HDO of anisole was first tested on the as-synthesized
Fig. 1. XRD patterns of unreduced (a) Ni/SiO2; (b) NiGa(3/1)/SiO2; (c) NiGa
Fig. 2. XRD patterns of reduced (a) Ni/SiO2; (b) NiGa(3/1)/SiO2; (c) NiGa(5/
(5/3)/SiO2; (d) Ga/SiO2; and (e) im-NiGa(3/1)/SiO2.
3)/SiO2; and (d) im-NiGa(3/1)/SiO2.
2

X. Niu, et al.
CatalysisCommunications140(2020)106001
Scheme 1. Proposed reaction pathway in HDO of anisole (Red arrows denote the DDO pathway) [9].
catalysts. As shown in Scheme 1, two main reaction routes take place.
The first one is the direct deoxygenation (DDO) and the second one is
the hydrogenation-deoxygenation (HYD). In the DDO route, the CAr
-
OCH3 bond is directly cleaved to yield benzene and methanol, and then
methanol can decompose to CO and H2. In the HYD route, phenol,
produced via the cleavage of CArO-CH3 bond, is firstly hydrogenated to
cyclohexanone and cyclohexanol, and then cyclohexanol is converted
to cyclohexane via dehydration‑hydrogenation.
3.2.1. Performance comparison of im-NiGa(3/1)/SiO2 and NiGa(3/1)/
SiO2 in HDO of anisole
It was found that NiGa(3/1)/SiO2 gave significantly higher con-
version (95.1%) than im-NiGa(3/1)/SiO2 (47.7%) at 300 °C and WHSV
of 2 h−1 (Fig.S4, ESI), attributed to the smaller Ni3Ga IMC crystallites.
The main product was benzene on both catalysts, i.e., the DDO route
was dominant on Ni3Ga IMC. However, NiGa(3/1)/SiO2 had higher
selectivity to benzene (92.5%) than im-NiGa(3/1)/SiO2(85.7%).
A great deal of CO was detected in the gaseous effluent stream from
the reactor. The molar ratios between CO and the converted anisole
were 0.72 and 0.82 on im-NiGa(3/1)/SiO2 and NiGa(3/1)/SiO2 cata-
lysts (Fig. S4, ESI), respectively. Such high molar ratios further indicate
that the DDO route dominated because CO was only derived from the
decomposition of methanol. Trace amounts of methanol were detected
due to its easy decomposition. The cleavage of CArO-CH3 led to phenol
and CH4, and the molar ratio between CH4 and the converted anisole
was about 0.1. Thus, methanation activity was very low on Ni3Ga IMC
catalyst.
Fig. 3. Anisole conversion and product selectivity on Ni/SiO2, NiGa(x/y)/SiO2
and Ga/SiO2 in HDO of anisole Reaction condition: 300 °C, 0.1 MPa, H2/anisole
molar ratio of 25, anisole WHSV of 4 h−1
.
preferentially is adsorbed on Ga site in Ni3Ga IMC, and then the acti-
vated CAr-O bond is cleaved via the attack of adsorbed hydrogen on Ni
surface atoms. Similar synergetic effect has also been found on PdeFe
and NieFe catalysts [11,14], where Fe has higher affinity to oxygen
atom. Unexpectedly, NiGa(5/3)/SiO2 gave lower conversion (ca.
56.6%) than NiGa(3/1)/SiO2, while Ga/SiO2 gave the lowest conver-
sion (ca. 9.42%) due to the absence of Ni.
NiGa(3/1)/SiO2 gave higher selectivity to benzene (ca.91.2%) than
Ni/SiO2 (ca. 51.5%), i.e., DDO pathway is more dominating on Ni3Ga
IMC. This is also confirmed by that CO was dominating on NiGa(3/1)/
SiO2 (Fig.S5, ESI). In contrast, metallic Ni is more active for HYD than
Ni3Ga IMC, reflected by the higher selectivities to phenol (ca. 12.7%),
to cyclohexanone (ca. 8.9%) and to cyclohexanol (ca. 4.5%) (Table S2,
ESI). Unexpectedly, the main products were phenol and cresol on NiGa
(5/3)/SiO2, similar to the case on Ga/SiO2. The selectivities toward
phenol and cresol were 28.1 and 23.1% on NiGa(5/3)/SiO2, respec-
tively, and they were 24.4 and 7.1% on Ga/SiO2, respectively. The
selectivity to benzene was very low (ca. ~1.0%) on NiGa(5/3)/SiO2 and
Ga/SiO2. The similar product distribution indicates that there may be
similar surface catalytic properties for NiGa(5/3)/SiO2 and Ga/SiO2.
Although Ni5Ga3 IMC formed on NiGa(5/3)/SiO2, the Ga species may
be rich on their crystallite surface due to the lower surface tension of Ga
(711.03 dyne/cm) than that of Ni (1796 dyne/cm) [26]. This also ac-
counts for the lower activity of NiGa(5/3)/SiO2 than that of NiGa(3/1)/
In short, NiGa(3/1)/SiO2 prepared by the sol-gel method showed
better performance in HDO of anisole compared to the other catalytic
systems investigated.
3.2.2. Performance of Ni/SiO2, NiGa(x/y)/SiO2 and Ga/SiO2 in HDO of
anisole
As indicated in the previous work [9], Ni3Ga IMC gave higher ac-
tivity and was more favorable for the DDO pathway than metallic Ni in
the HDO of anisole. We also wonder about the reactivity of Ni5Ga3 IMC.
Here, the performance of Ni/SiO2, NiGa(x/y)/SiO2 and Ga/SiO2 in HDO
of anisole are compared.
As depicted in Fig. 3, NiGa(3/1)/SiO2 gave higher anisole conver-
sion (ca. 76.2%) than Ni/SiO2 (ca. 45.9%). The higher activity of Ni3Ga
IMC is mainly ascribed to the synergetic effect between Ni and Ga [9].
As indicated by the XPS results [9], there was a charge transfer from Ga
to Ni in the Ni3Ga IMC solid phase. Also, metal Ga has higher affinity to
oxygen atom in anisole than metal Ni. The oxygen of anisole
3

X. Niu, et al.
CatalysisCommunications140(2020)106001
SiO2. The formation of phenol and cresol may be related to the hy-
drogen species (e.g., GaeH and dihydrides) and acid sites (e.g., Ga-OH)
that could catalyze the O-CH3 bond hydrogenolysis and methyl transfer
[9], respectively. Additionally, in the gaseous effluent stream, CH4 and
CO were dominating on Ni/SiO2 and NiGa(3/1)/SiO2(Fig.S5, ESI), re-
spectively, indicating that methanation was suppressed on Ni3Ga IMC
catalyst.
35.6%). On Ni/SiO2, the main products were phenol and benzene with
selectivities of 34.9 and 27.1%, respectively, where selectivities to cy-
clohexanone and cyclohexanol were 20.5 and 10.4%, respectively.
However, the selectivity to toluene was only 4.37%. Besides, the nCH4
nΔcresol molar ratio was 1.12 (higher than 1.0). Thus, the cleavage of
Ar-CH3 bond in o-cresol is dominant on Ni/SiO2, leading to phenol that
/
C
was then converted to cyclohexanone and cyclohexanol via hydro-
genation [29,30]. In addition, the selectivity to methylcyclohexane was
only 0.36%. Compared with Ni/SiO2, NiGa(3/1)/SiO2 exhibited lower
conversion, while it gave higher selectivities to toluene (ca. 38.5%) and
to methylcyclohexane (ca. 14.3%). Toluene may be derived from the
DDO pathway of o-cresol, followed by its hydrogenation to methylcy-
clohexane. This is reasonable because no methylcyclohexanone and
methylcyclohexanol were detected. Additionally, NiGa(3/1)/SiO2 gave
lower selectivity to phenol (ca. 10.2%), to benzene (ca. 3.56%) and to
cyclohexanone (ca. only 0.38%) than Ni/SiO2.
In the HDO of m-cresol, Ni/SiO2 also had higher conversion (ca.
59.0%) than NiGa(3/1)/SiO2 (ca. 46.3%). The main product was to-
luene on both catalysts, while NiGa(3/1)/SiO2 gave higher selectivity to
toluene (ca. 51.1%) than Ni/SiO2 (ca. 43.3%). Especially, NiGa(3/1)/
SiO2 also gave higher selectivity to methylcyclohexane (ca. 24.9%) than
Ni/SiO2 (ca. 1.5%). Additionally, the selectivity to phenol and benzene,
14.1% and 6.98%, respectively, on Ni/SiO2 were significantly higher
than those (ca. 0.36 and 0.18%, respectively) on NiGa(3/1)/SiO2.
Moreover, Ni/SiO2 gave a selectivity to cyclohexanone of 2.82% and to
cyclohexanol of 1.38%, while no cyclohexanone and cyclohexanol were
detected on NiGa(3/1)/SiO2 catalyst.
In HDO of p-cresol on Ni/SiO2, the conversion was 43.4%, and the
selectivities to toluene, phenol and benzene were 67.9, 3.23 and 5.71%,
respectively. The selectivity to methylcyclohexane was only 1.28%. On
NiGa(3/1)/SiO2, the conversion was 21.9%, and the selectivities to-
ward toluene and methylcyclohexane were 60.1 and 20.6%, respec-
tively, while the selectivities to benzene and phenol were only 0.32 and
0.77%, respectively. Although NiGa(3/1)/SiO2had lower selectivity to
toluene than Ni/SiO2, it gave significantly higher selectivity to me-
thylcyclohexane. Given the lower selectivity to benzene and phenol,
NiGa(3/1)/SiO2 is also more favorable for the DDO of p-cresol.
Here, the deoxygenation degree is further used to indicate syner-
getic effect between Ni and Ga in the deoxygenation of cresols. As
shown in Table 1, NiGa(3/1)/SiO2 had lower cresol conversion than Ni/
SiO2, however, it gave higher deoxygenation degree. It can be
In summary, NiGa(3/1)/SiO2 exhibited the best performance in
HDO of anisole.
3.2.3. Stability of NiGa(3/1)/SiO2 in HDO of anisole
To investigate the stability of NiGa(3/1)/SiO2 in the HDO of anisole,
the catalyst was tested at 300 °C, 0.1 MPa and WHSV of 2 h−1. As
shown in Fig. S6 (ESI), the anisole conversion decreased from 93.3 to
60.7% during 24 h time-on-stream, that is, NiGa(3/1)/SiO2 was deac-
tivated. The selectivity to benzene still maintained at ~90%. The initial
selectivities to cyclohexane and phenol were 2.74 and 0.08%, respec-
tively. During the reaction, the selectivity to cyclohexane scarcely
changed, and the selectivity to phenol slightly increased to 0.92%.
To explore the reason for the catalyst deactivation, the fresh and
spent NiGa(3/1)/SiO2 catalysts were characterized. As indicated by the
XRD patterns (Fig. S7and Table S1, ESI), there was no sintering of the
Ni3Ga IMC crystallites during the reaction. The TGA result (Fig. S8, ESI)
shows that there was a small amount of carbonaceous deposits (~1.3 wt
%) on the spent catalyst. It is estimated that a carbon deposit average
rate of 1.6 mg/(g·h) was applicable. As listed in Table S1 (ESI), the pore
diameter and pore volume of NiGa(3/1)/SiO2 was reduced from 12.5 to
9.8 nm and from 1.46 to 1.35 m3/g after reaction, respectively. We
suggest that the deactivation of NiGa(3/1)/SiO2 may be partially
caused by coke formation.
3.2.4. HDO of cresols and guaiacol on Ni/SiO2 and NiGa(3/1)/SiO2
It is challenging to facilitate the direct cleavage of CAr-OH bond in
phenolic compounds because the dissociation energy of CAr-OH bond
(468 kJ/mol) is higher than that of CAr-OCH3 bond (422 kJ/mol)
[2,27,28]. As indicated above, NiGa(3/1)/SiO2 was more active and
gave higher selectivity to benzene than Ni/SiO2 in HDO of anisole.
Herein, the HDO of other phenolic compounds (cresols and guaiacol)
was also tested on Ni/SiO2 and NiGa(3/1)/SiO2 catalysts.
As shown in Table 1, in the HDO of o-cresol, Ni/SiO2 gave sig-
nificantly higher conversion (ca. 97.2%) than NiGa(3/1)/SiO2 (ca.
Table 1
HDO of phenolics on Ni/SiO2 and NiGa(3/1)/SiO2.
Reactant
Catalyst
o-cresol
m-cresol
p-cresol
Guaiacol
Ni/SiO2
Ni/SiO2
NiGa(3/1)/SiO2
Ni/SiO2
NiGa(3/1)/SiO2
Ni/SiO2
NiGa(3/1)/SiO2
NiGa(3/1)/SiO2
Conversion
97.2
1.12
0
43.1
94.5
35.6
0.11
0
89.4
91.1
59.0
0.75
0
77.1
90.0
46.3
0
0
99.3
90.6
43.4
0.60
0
91.9
95.8
21.9
0
0
98.3
96.9
54.1
0.35
0.23
53.0
93.4
98.4
0.15
0.52
49.8
99.6
a
n
n
CH4/nΔphenolics
CO/nΔphenolics
b
HDO %
Carbon balance/%
Selectivity(%)
SBenzene
SToluene
SPhenol
27.1
4.37
34.9
0
0.36
0.06
0
3.56
38.5
10.2
0
14.3
1.03
0
0
0.38
0
6.98
43.3
14.1
0
1.50
0.04
0.18
4.45
2.82
1.38
0.27
0
0.18
51.1
0.36
0
24.9
2.24
0.02
0.28
0
5.71
67.9
3.23
0
1.28
0.09
3.94
0
0.50
0
0.12
0
0.32
60.1
0.77
0
20.6
2.75
0.17
0.27
0
5.81
2.34
66.6
1.63
0
0
0
0
4.71
2.38
0.60
14.3
7.63
1.09
72.2
0.77
0
0
0
0
1.04
0.54
1.92
12.8
SAnisole
SMCHANE
SMCHENE
SMCHONE
SMCHOL
SCHONE
SCHOL
0
20.5
10.4
1.5
0
0
0.06
0
0
0.07
0
SCH
SMethanol
1.52
0
a
The molar ratio between methane and the converted phenolics.
The molar ratio between CO and the converted phenolics; MCHANE-Methylcyclohexane, MCHENE-Methylcyclohexene, MCHONE-Methylcyclohexanone,
b
MCHOL-Methylcyclohexanol, CHONE-Cyclohexanone, CHOL-Cyclohexanol, CH-Cyclohexane.
4

X. Niu, et al.
CatalysisCommunications140(2020)106001
abundant product on Ni/SiO2-ZrO2 and NiCu/Ti-MCM-41 was cyclo-
hexane. It is clear that the high pressure favors the hydrogenation of
benzene ring. In the gas-phase reaction under 0.1 MPa, however, ben-
zene was the main product on NiMo/SiO2.
Here, Ni3Ga IMC favored the removal of the methoxy group in
guaiacol and anisole as well as the cleavage of CAr-OH bond in cresols at
atmospheric pressure. The as-prepared Ni3Ga/SiO2 gave higher ben-
zene yield than Ni/SiO2 and Pt/SiO2 in the HDO of anisole, and had
higher toluene yield than NiFe/SiO2 and similar toluene yield to NiRe/
SiO2 in the HDO of m-cresols (Table S3, ESI). It is not ideal that the
main product in HDO of guaiacol was phenol on Ni3Ga/SiO2. The total
deoxygenation of guaiacol to benzene is very attractive, and further
investigations are required.
4. Conclusions
A NiGa(3/1)/SiO2 catalyst with high performance was prepared by
the sol-gel method. In the HDO of anisole, the anisole conversion and
selectivity to benzene reached 95.1 and 92.5% on NiGa(3/1)/SiO2,
respectively. In the HDOs of cresols on Ni/SiO2 and NiGa(3/1)/SiO2,
Ni/SiO2 gave higher conversion due to its higher activity for the clea-
vage of CAr-CH3, while NiGa(3/1)/SiO2 was more favorable for the
direct cleavage of CAr-OH. Same to the case in HDO of anisole, NiGa(3/
1)/SiO2 was more active for the cleavage of CAr-OCH3 in HDO of
guaiacol. In short, Ni3Ga IMC appears a very promising catalytic system
for the direct deoxygenation of phenolic compounds.
Scheme 2. Proposed main reaction pathway in HDO of cresols on Ni/SiO2 and
NiGa(3/1)/SiO2.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgements
Scheme 3. Proposed main reaction pathway in HDO of guaiacol on Ni/SiO2
and NiGa(3/1)/SiO2.
The authors gratefully acknowledge support from the National
Natural Science Foundation of China (No. 21576193 and 21176177).
Appendix A. Supplementary data
concluded that the cleavage of CAr-OH bond was dominant in producing
toluene on NiGa(3/1)/SiO2. The proposed reaction pathway of cresols
on Ni/SiO2 and NiGa(3/1)/SiO2 is presented in Scheme 2.
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.catcom.2020.106001.
The HDO of guaiacol was also carried out. The conversions on NiGa
(3/1)/SiO2 and Ni/SiO2 were 98.4 and 54.1%(Table 1), respectively,
and the main product was phenol with the selectivity of 72.2 and
66.6%, respectively. Methanol was produced with the selectivity of
14.3 and 12.8% on Ni/SiO2 and NiGa(3/1)/SiO2, respectively. Ad-
ditionally, the molar ratio between produced CO and converted
guaiacol were 0.23 and 0.52 on Ni/SiO2 and NiGa(3/1)/SiO2, respec-
tively. Only a small amount of anisole was detected. Clearly, the con-
version of guaiacol was largely due to the direct cleavage of CAr-OCH3
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