Self-hydrogen transfer hydrogenolysis of β-O-4 linkages in lignin catalyzed by MIL-100(Fe) supported Pd-Ni BMNPs

Article abstract of DOI:10.1039/c7gc02087b

A MIL-100(Fe) supported Pd-Ni BMNP catalyst has been fabricated, and the catalyst exhibits superior catalytic performance toward the intramolecular transfer hydrogenolysis of lignin model compounds and organosolv lignin. Alcoholic groups (C_αH-OH) of lignin were exploited as the hydrogen source, and selective cleavage of β-O-4 linkages in lignin was realized without an extra hydrogen donor. This protocol was suitable for organosolv lignin as well as model compounds; several phenols and functionalized acetophenones were detected when extracted lignin was treated in our system. The catalyst exhibits outstanding catalytic stability during the reaction process, which can be ascribed to the porous structure and the strong water stability of MIL-100(Fe). The excellent catalytic performance of Pd₁Ni₄/MIL-100(Fe) highlights the "synergistic effect" between the BMNPs and the functional synergy between MNPs and MOFs, and our work shows the bright future of BMNPs and MOFs in the development of catalysts for sustainable chemistry.

Full text of DOI:10.1039/c7gc02087b

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G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
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Self-hydrogen transfer hydrogenolysis of β-O-4 linkages in lignin
catalyzed by MIL-100(Fe) supported Pd-Ni BMNPs
Received 00th January 20xx,
Accepted 00th January 20xx
Jia-wei Zhang, Guo-ping Lu and Chun Cai*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A
MIL-100(Fe) supported Pd-Ni BMNPs catalyst has been since lignin has mainly been burned to supply energy and recover
fabricated, the catalyst exhibits superior catalytic performance pulping chemicals in the operation of paper mills,2, 10 further studies
toward intramolecular transfer hydrogenolysis of lignin model on getting higher value from lignin in an economic way are still
compounds and organosolv lignin. Alcoholic groups (CαH‒OH) of necessary due to the requirements of green and sustainable
lignin were exploited as the hydrogen source, selectively cleavage society.8, 11
of β-O-4 linkages in lignin was realized without extra hydrogen
Lignin is a natural amorphous polymer, which can be viewed as
donor. This protocol was suitable for organosolv lignin as well as a disordered polymer of phenylpropanolic units linked by ether (e.g.,
model compounds, several phenols and functionalized α-O-4, β-O-4, and 4-O-5) and C-C (β–β, β-5, and 5–5) bonds, among
acetophenones were detected when treated extract lignin under those linkages, the β-O-4 linkages comprise approximately 50% of
our system. The catalyst exhibits outstanding catalytic stability native lignin linkages.1, 12, 13 Since depolymerization is a critical step
during the reaction process, which can be ascribed to the porous for the lignin utilization process because it could provide a source of
structure and strong water stability of MIL-100(Fe). The excellent low-molecular-mass feedstocks suitable for downstream processing,
catalytic performance of Pd1Ni4/MIL-100(Fe) highlights the much attention has been focused on the dissociation of the
“synergistic effect” between the BMNPs and the functional relatively weaker β-O-4 linkages due to their high abundance in
synergy between MNPs and MOFs, and our work shows the bright lignin.10, 14 State-of-the-art strategies for β-O-4 dissociation linkages
future of BMNPs and MOF in catalysts’ development for can be broadly classified into oxidation,15-19 hydrolysis11, 20, 21 and
sustainable chemistry.
hydrotreating,22-24 amongst those different strategies, hydrotreating
process is regarded as the most promising options.25 Nevertheless,
hydrotreating processes often operate under high hydrogen
Introduction
pressures and high temperatures, which easily leads to
Increasing global awareness of the diminishing fossil energy
reserves and global efforts to reduce greenhouse gas emissions
have accelerated the study about utilization of renewable biomass
for sustainable development.1-3 Nowadays, more than 10% of the
world’s primary energy is biomass, and it is the fourth largest source
of energy in the world (following oil, coal, and natural gas).4
Lignocellulose is the most abundant form of biomass as well as a
promising renewable organic resource with abundant supplies,
which was expected to replace fossil resources in the production of
carbon based fuels.3, 5 Lignin, one of the three main constituents of
lignocellulosic biomass as well as the only large volume renewable
feedstock that comprises aromatics on the earth, has the potential
to supplement or replace coal or crude oil as the source of arenes.1,
27
dearomatization and deoxygenation of lignin.26,
In recent
breakthroughs, catalytic cleavage of C-O linkages through hydrogen
transfer reactions were also made, reductively cleaves lignin utilizing
isopropyl alcohol,28 HCOONH429 and hydrosilanes30 as mild hydrogen
donor represents another excellent options for lignin depolym-
erization.31 In fact, there are a plethora of alcohol moieties in the
natural lignin, which could act as the hydrogen source for the C-O
linkage cleavage reaction, and this provide
a potential atom
economic method for lignin depolymerization without adding
external hydrogen donor.2, 9
Ellman and coworkers reported a redox neutral C-O bond
cleavage reaction of β-O-4 model compounds using RuH2(CO)(PPh3)3
as the catalyst and xantphos as the ligand, the reaction was
completed within 2h, affording phenolic and functionalized
acetophenone products with high selectivity, but the ruthenium
precursor was inexchangable, only RuH2(PPh3)4 showing significant
activity catalyst and the catalyst recyclability is problematic.32
Moreover, Samec and coworkers reported the first heterogeneous
C-O bond cleavage under redox-neutral reaction conditions,
6-9
However, current utilization process of lignin is still not gratifying
a.Chemical Engineering College, Nanjing University of Science & Technology,
Xiaolingwei 200, Nanjing 210094, P. R. China. E-mail: c.cai@njust.edu.cn
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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commercial available Pd/C was applied as the catalyst, the reaction No reaction happened when using Ni NPs as the catalyst (entry 4),
could proceed under air, but catalytic amounts of NaBH4 must be and this indicates that Pd was the main active for this reaction.
Table 1. Optimization for the reaction conditions.a
added in the reaction.33 Those outstanding works laid the road map
for the utilization of intramolecular hydrogen for the C-O linkage of
lignin, and inspired us to plough deeper in this area.
Our previously work has demonstrated that bimetallic
nanoparticles (BMNPs) show extraordinary catalytic performance in
Conversion
(%)b
100
0
2 or 3
(%)b
95
--
hydrogenolysis of lignin due to their unique electronic states and
structural conformations,34, and this lead us to explore BMNPs as a
potential catalyst in the redox-neutral C-O linkage dissociation
reaction.35-37 Recently, porous metalorganic frameworks (MOFs) was
Entry
Catalyst
Tem. (oC)
4(%)b
1
2
Pd1Ni4
No Catalyst
Pd
130
130
130
130
130
130
130
130
130
130
130
80
5
--
3
4c
75
60
--
40
--
emerged as a class of very promising catalyst matrix due to it’s high
42
surface area, porosity, and chemical tenability,41,
and it was
Ni
0
5
Pd1Ni2
95
83
98
96
98
80
--
17
2
reported that functional synergy between MNPs and MOFs can
6
Pd1Ni6
97
effectively synergize their respective multiple advantages, resulting
43-45
boost in catalytic performance.41,
Since catalyst carrier is
7
Pd1Ni8
100
81
4
8
Pd1Co4
2
reported to be another key factor determining the hydrodeoxy-
genation activity of catalysts,38-40 we decide to explore the
application of MOFs as catalyst carrier in the lignin depolymeri-
zation reaction. Herein, MIL-100(Fe) was chosen as the catalyst
support for the BMNPs due to it’s highly porous structure, water
stability and strong lewis acid, which was reported to promote the
O–H bond cleavage.42, 46 Several supported BMNPs were screened
for intramolecular hydrogen transfer C-O cleavage of lignin model
compounds, the Pd1Ni4/MIL-100(Fe) catalyst shown the optimal
catalytic performance, highlighting a gratifying synergistic effects
between BMNPs and MOF.41 The lignin model compounds were
transformed into corresponding phenols and functionalized
acetophenones in 6 h without adding extra hydrogen source, and
little molecules were also obtained when organosolv lignin were
treated in our system. The catalytic system exhibits a broad
substrate scope as well as excellent stability during the reaction
process, no significant loss in catalytic performance was observed
when the catalyst was recycled for five times.
9
Pd1Fe4
100
~5
20
100
18
--
10
11
12
13
14
15
16d
17
18
19
20
21
Pd1Cu4
Ru1Ni4
49
82
--
Pd1Ni4
0
Pd1Ni4
100
115
150
130
130
130
130
130
130
0
--
--
Pd1Ni4
30
40
>95
90e
--
60
<5
10
--
Pd1Ni4
100
80
Pd1Ni4
Pd1Ni4/g-C3N4
Pd1Ni4/WO3
Pd1Ni4@MIL-100(Fe)
Pd1Ni4/MIL-100(Fe)
Pd/MIL-100(Fe)
<5
~99
78
>95
91
>95
71
<5
9
~99
77
<5
29
[a] Reaction conditions: 1a (0.2mmol), catalyst (4 mol %, based on Pd), 1mL
H2O, the reaction mixture was stirred under argon for 6 h. [b] Yields and
selectivity were determined by GC and GC-MS. [c] 1.6 mol % Ni nanoparticles
was applied as the catalyst. [d] The reaction was proceed under air. [e] The
produced acetophenone was totally transformed into benzoic acid.
Results and discussion
Compositions of the BMNPs were reported to be vital for
catalytic efficiency, BMNPs with different metal ratio (entries 5-7)
and constituent (entries 8-11) were prepared and tested in this
reaction. Keeping the Pd content of the BMNPs still, BMNPs with
higher Ni contents show better activity and selectivity for the
hydrogen transfer reaction, and 1:4 was emerged to be the most
suitable Pd/Ni ratio. Besides, alloying Pd with Co can improve the
selectivity to some extent, but the conversion of the substrate is
moderate (entry 8). However, when Pd1Fe4 BMNPs was employed as
the catalyst, the substrate was equivalently transformed but the
selectivity was moderate (entry 9). Interestingly, decreased catalytic
activity was observed when Pd was alloyed with Cu (entry 10).
Ru1Ni4 BMNPs was also tested in this reaction, but the catalytic
efficiency was far inferior to Pd1Ni4 BMNPs (entry 11). Primary
attempts to lower the reaction temperature show that the reaction
do not happen when the temperature was lower than 100 oC
(entries 12-14), and the BMNPs still show excellent catalytic activity
at higher temperature (entry 15). Interestingly, the reaction can also
proceed under air, except that the produced acetophenone was
totally transformed into benzoic acid (entry 16).
At the initial stage of our study, 2-Phenoxy-1-phenethanol (1a)
was selected as the model substrate to optimize the condition for
unsupported Pd1Ni4 BMNPs catalyze hydrolytic cleavage of β-O-4
bonds, but the substrate was clearly cleaved into phenol and
acetophenone in a contrast experiment in the absence of hydrogen
gas (Table 1, entry 1). Considering that a small amount of 2-
phenoxy-1-phenylethanone (4a) was detected as the by-product, we
proposed that C-O bond cleavage may proceed via an
intramolecular hydrogen transfer way. Then, we turn to explore the
reaction conditions for self-hydrogen transfer hydrogenolysis of β-O-
4 linkages. Firstly, to verify the indispensable role of the catalyst, the
reaction was allowed to perform without a catalyst, no aimed
products was detected (entry 2). Contrast experiments using
monometallic nanoparticles as the catalyst were carried out, Pd NPs
show moderate activity and selectivity for this reaction (entry 3),
the dehydrogenation product 4a was the main by-product. Together
with our previous work,34 we could say that alloying Ni with Pd can
improve the utilization efficiency of the molecular hydrogen and
speed up the hydrogenolysis process due to the electronic effects.
Since the recycle process of the unsupported Pd-Ni BMNPs is
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not easy to handle, we than attempt to immobilized the BMNPs on experiment was also performed to track the flow of H in the
different matrices. Initially, graphitic carbon nitride (g-C3N4) was substrate, when 1a’ was used as the substrate, deuterium was
selected as the support due to it’s excellent stability and metal found in acetophenone after reaction (Eq. 2). Furthermore, to verify
immobilization ability,47 but no reaction was observed when whether the solvent participate in the reaction or not, D2O was
Pd1Ni4/g-C3N4 was applied as the catalyst (entry 17), and we think applied as a solvent in this reaction, and we found almost no
this may be owing to the extremely strong coordination between g- deuterium atom was detected in our produced acetophenone (Eq.
C3N4 and metal nanoparticles. Then, we try to use tungsten oxide as 3). Finally, no reaction was proceed when 1j was applied as the
the support, as it was reported that dissociation of H2 can happen at substrate, which highlights the importance of CαH-OH groups in this
the interface of metal NPs and tungsten oxide.48 The catalytic reaction. According to those results, a schematic pathway was
activity and selectivity of Pd1Ni4/WO3 catalyst for the transformation proposed. As shown in Scheme S1 (SI), the reaction starts with a
of model compound 1a were found to be quite outstanding (entry reversible dehydrogenation of 1 to generate 4 and chemically
18), however, at the following substrate scope stage, the adsorbed hydrogen (“hydrogen pool”) on BMNPs.33, 50 To trap the
Pd1Ni4/WO3 catalyst do not show excellent functional group hydrogen, the reaction system was linked with a tube equipped with
tolerance. Finally, MIL-100(Fe) was chosen as the matrix in our cyclooctene and a catalytic amount of Pd/C to trap the hydrogen,
system because of it’s high chemical stability and water stability,46, 49 and cyclooctane was detected after the reaction, although the
moreover, it was reported that the O–H bond cleavage is promoted amount is low, we think the result proved the existence of the
with the assistance of the Lewis acid activity metal center of the “hydrogen pool” in our reaction system. The dehydro-genation
MIL-100(Fe).42 The MIL-100(Fe) encapsulated Pd1Ni4 BMNPs ketone 4 is in fast equilibrium with its enol tautomer, which absorbs
(Pd1Ni4@MIL-100(Fe), preformed Pd-Ni BMNPs was used as to BMNPs to generate intermediate 5.29 Then, atomic hydrogen on
nucleation centers for subsequent MIL-100(Fe) growth) and Pd1Ni4 BMNPs surfaces may insert into the β-O-4 linkage, leading to ether
BMNPs immobilized on MIL-100(Fe) (Pd1Ni4/MIL-100(Fe), prepared bond cleavage.
by a impregnation-reduction method) were prepared and tested in
our reaction system, both the catalytic activity and selectivity of
Pd1Ni4/MIL-100(Fe) are better than Pd1Ni4@MIL-100(Fe) (entry 19
vs entry 20). Notably, when Pd1Ni4@MIL-100(Fe) was applied as the
catalyst, ethylbenzene was detected as the by-product after the
reaction, because BMNPs was covered by a layer of MIL-100(Fe), a
part of the produced acetophenone was trapped in the micropore
of MIL-100(Fe) and may not release from the catalyst surface on
time, so the absorbed acetophenone may be further reduced into
ethylbenzene. What’s more, Pd/MIL-100(Fe) was also employed as a
catalyst in our system, the conversion of the substrate is similar to
unsupported Pd NPs, but the selectivity is relatively better, and this
stress the importance of MIL-100(Fe) in the catalysis.
Fig. 1 (a) (b) (c) TEM images of the Pd1Ni4/MIL-100(Fe) catalyst. (d)
size distribution of Pd1Ni4 BMNPs. The inlet image of (b) was the
HRTEM image of the BMNPs.
Morphologies of the Pd1Ni4/MIL-100(Fe) were directly
observed by transmission electron microscopy (TEM). As shown in
Fig.1, the anomalously spherical BMNPs were encapsulated in the
micropores of MIL-100(Fe), this kind of structure can effectively
prevent BMNPs from aggregating, guaranteeing an excellent
stability of the catalyst. Beside, size of the BMNPs was mainly
distributed between 2~3nm, the ultrafine BMNPs provides more
Scheme 1. Control experiments to illustrate the reaction mechan-
contact opportunities between the active sites and substrates,
ism.
which means higher catalytic efficiency. What’s more, the
To study the reaction mechanism, several mechanism representative high-resolution TEM (HRTEM) image shows the
verification experiments were conducted (Scheme 1). If BMNPs have clear crystalline fringe patterns and the lattice fringes
dehydrogenation product 4a was used as the substrate, no reaction align parallel to each other, besides, the lattice distance is
occurred under the same reaction condition (Eq. 1), and this favor measured to be 0.21 nm, which could be assigned to the d-spacing
our initial speculation about this mechanism. Isotope labeling for the (111) plane of Pd-Ni alloy.51
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total Pd and 3.4% of the total Ni was lost during one cycle, which
support our proposition that the catalyst amount may influence the
selectivity of the reaction.
Table 2. Pd1Ni4/MIL-100(Fe) catalyzed β-O-4 cleavage of various lignin
models.a
Fig. 2 XPS spectrum of the as-prepared Pd1Ni4/MIL-100(Fe) catalyst:
(a) Pd 3d region (b) Ni 2p region
Entry
1
1
R1
H
R2
H
R3
H
R4
H
Yield [%]b
>95
~99
84
To ascertain the detail surface chemical states of the samples,
XPS measurements were performed. Well-defined peaks corresp-
onding to Pd and Ni species both can be detected, the doublet in
Fig. 2a with binding energies of 335.2 (Pd 3d5/2) and 340.5 eV (Pd
3d3/2) can be assigned to metallic Pd0, while the another doublets at
338.1 eV and 342.8 eV are ascribed to the +2 oxidation state of Pd,
indicating that oxidation was happened during the characterization
process. Besides, as shown in Fig. 2b, the Ni species on the surface
of the catalyst was consist of metallic Ni as well as Ni oxide and
hydroxide, indicating that surface nickel can be easily oxidized to
oxide and hydroxide when exposed to oxygen and moisture in air.
In addition, the Ni/Pd ratio contents on the catalyst surface
determined by XPS was 3.36, almost equivalent to the results
determined by ICP (Ni/Pd=3.55, SI, Table S1), showing that the Pd–
Ni BMNPs in our catalyst is in a random homogeneous alloy form.
1a
1b
1c
1d
1e
1f
2
H
H
H
OMe
OMe
OMe
H
3c
H
OMe
OMe
H
OMe
H
4c
H
87
5d
6c
OMe
OMe
OMe
Me
H
91
H
H
OMe
OMe
H
>95
81
7d
8d
1g
1h
H
OMe
H
H
93
a
Reaction conditions: 0.5 mmol of substrate, 4 mol% Pd1Ni4/MIL-
100(Fe) catalyst (based on palladium), 2 mL H2O, the reaction
mixture was stirred at 130 oC under argon atmosphere for 6 h.
b
c
Yields were determined by GC and GC-MS.
The reaction
temperature was 150 oC d The reaction temperature was 180 oC.
With the robust reaction condition in hand, we then turn to
evaluate the scope of this protocol, a range of starting materials
were explored (Table 2). Gratifyingly, no passive influence on the
yield was observed when a methoxy group was introduced at R3 or
R4 position (Table 2, entry 2). However, embarrassment occurred
when there were several methoxy groups at R2, R3, R4 position,
satisfied reaction results were obtained only when the reaction was
performed at 150 oC when 1c and 1d were used as the starting
o
material (entries 3-4). The temperature was increased to 180 C to
finish the reaction when 1e was chosen as the substrate (entry 5).
Moreover, introducing another methoxy group at R4 position of 1e
leads to an enhancement in reaction activity of the substrate, C-O
linkage of 1f was equivalently cleaved at 150 oC (entry 6). It’s worth
noting that at the same reaction condition, only minor 1f was
transformed into corresponding product when using Pd1Ni4/WO3 as
the catalyst, and we think that the difference in catalytic
performance may result from the gas enrichment function44, 52 of
MOFs and the electron transfer effect45 between the guest BMNPs
and MOFs. Even with an electron donating group at R1 position,
excellent yields were also obtained at 180 oC (entries 7-8). Together
with bumpy substrate scope process, we could conclude that
electron donating groups at R1 or R2 position may hamper the
reaction process, while substitutes at R3 or R4 position do not have
huge impact on the reaction process. As to the electronic effects of
the reaction, we proposed that an electron donating group at R1 or
R2 may lower the acidity of benzyl, which means that hydrogen
release process from the model compound was suppressed. To
verify whether the γ-C affects the cleavage of β-O-4 bond, 2-(2-
methoxyphenoxy)-1-phenylpropane-1,3-diol (1i), whose structure is
closer to the true structure of lignin, was prepared and test in our
Fig. 3 Recycling of the Pd1Ni4/MIL-100(Fe) catalyst in the self-
hydrogen transfer hydrogenolysis of C-O linkage in 1a
Once the optimal reaction conditions were established, we
turn to investigate the recyclability of the Pd1Ni4/MIL-100(Fe)
catalyst. Upon completion of the reaction, the catalyst was
separated from the reaction mixture by filtration, the catalyst was
washed with water and EtOH, dried under vacuum and then directly
reused in the next cycle under the same conditions (Fig. 3). The
BMNP catalyst could be reused up to five times without losing its
activity, the size of the BMNPs after recycle experiments was
distribute between 2~5 nm (SI, Fig. S2), no obvious agglomeration
was observed. About 20% dropping in selectivity was observed
when the catalyst was used for four times, the major by products
found was the dehydrogenation product 4a. And we propose that
the main reason for the dropping in catalytic selectivity may come
from the catalyst loss during the recycled process, so 5% of the
catalyst was added to make up the mechanical loss of the catalyst
at the fifth cycle of the catalyst, and the catalytic performance of
the catalyst almost recover to the initial level. ICP analysis of the
reaction solution after the reaction indicated that about 2.1% of the
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system. About 81% yields was obtained at 180 oC for 6h, the main We gratefully acknowledge the Nature Science Foundation of
products was identified as 2-methoxyphenol and propiophenone. Jiangsu Province (BK 20140776) for financial support. This
Finally, our reaction system was also attempted in the cleavage work was also supported by the National Natural Science
of organosolv lignin extracted from birch sawdust, organosolv lignin Foundation of China (21402093 and 21476116) and the
extracted by the similar procedure was reported to contain a high Chinese Postdoctoral Science Foundation (2015 M571761 and
proportion of β-O-4 linkages.15 1wt% Pd1Ni4/MIL-100(Fe) was 2016 T90465) for financial support. We also gratefully
applied as the catalyst, the reaction was proceed under argon acknowledge the Priority Academic Program Development of
atmosphere at 180 oC for 6h. After reaction was completed, the Jiangsu Higher Education Institutions for financial support.
catalyst was removed by filtration and the reaction solution was
extract with ethyl acetate, the organic layer was analyzed by GC and
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Conclusions
In summary, Pd–Ni BMNPs immobilized on MIL-100(Fe) was
fabricated, which was proven to be highly effective for the self-
hydrogen transfer hydrogenolysis of β-O-4 linkage in lignin. Water
was used as the green solvent, the dehydrogenation and
hydrogenolysis reaction are happened at the same time using
alcoholic groups in lignin as the hydrogen donor, offering a more
economical choice for large-scale operations of the lignin
depolymerization. The Pd1Ni4/MIL-100(Fe) catalyst show outstand-
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catalytic activity was observed after 5 cycles. Excellent stability of
the catalyst was due to the extraordinary water stability and porous
structure of the MIL-100(Fe), the BMNPs was encapsulated into the
micropores of MIL-100(Fe), no obvious agglomeration was observed
although the reaction was proceed under relatively high
temperature. Catalytic cooperation between a MIL-100(Fe) host and
guest BMNPs together with synergistic effects of BMNPs include
(i) The BMNPs was encapsulated in the micropores of MIL-
100(Fe), preventing the BMNPs from agglomeration, guaranteeing a
satisfying catalytic recyclability.
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(ii) The electron transfer between Pd and Ni in BMNPs together
with the interfacial electron transfer effect between BMNPs and
MIL-100(Fe) would result in more electron rich center, which may
spur the conversion from H• to H– in the “hydrogen pool”, thus
boosting the catalytic efficiency.
(iii) MIL-100(Fe) can cooperate with BMNPs to promote the O–
H bond cleavage, forming a “hydrogen pool”, which could be utilized
in the following hydrogenolysis process.
(iv) MIL-100(Fe) can enrich the hydrogen molecules around the
active sites to certain degree, which may greatly speed up the
hydrogenolysis process.
The excellent catalytic performance of BMNPs/MIL-100(Fe) in
our work validate the natural advantages of BMNPs and MOFs, and
we believe BMNPs/MOFs has a very bright future in the catalysis
field.
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Acknowledgements
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