Defect-Engineered Ruthenium MOFs as Versatile Heterogeneous Hydrogenation Catalysts

Article abstract of DOI:10.1002/cctc.201902079

Ruthenium MOF [Ru₃(BTC)₂Y_y] ? G_g (BTC=benzene-1,3,5-tricarboxylate; Y=counter ions=Cl^?, OH^?, OAc^?; G=guest molecules=HOAc, H₂O) is modified via a mixed-linker approach, using mixtures of BTC and pyridine-3,5-dicarboxylate (PYDC) linkers, triggering structural defects at the distinct Ru₂ paddlewheel (PW) nodes. This defect-engineering leads to enhanced catalytic properties due to the formation of partially reduced Ru₂-nodes. Application of a hydrogen pre-treatment protocol to the Ru?MOFs, leads to a further boost in catalytic activity. We study the benefits of (1) defect engineering and (2) hydrogen pre-treatment on the catalytic activity of Ru?MOFs in the Meerwein-Ponndorf-Verley reaction and the isomerization of allylic alcohols to saturated ketones. Simple solvent washing could not avoid catalyst deactivation during recycling for the latter reaction, while hydrogen treatment prior to each catalytic run proved to facilitate materials recyclability with constant activity over five runs.

Full text of DOI:10.1002/cctc.201902079

Accepted Article
Title: Defect Engineered Ruthenium MOFs as Versatile Hydrogenation
Catalysts
Authors: Roland A. Fischer, Epp Konstantin, Ignacio Luz, Werner R
Heinz, Anastasia Rapeyko, and Francesc X Llabres i Xamena
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10.1002/cctc.201902079
ChemCatChem
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Defect-Engineered Ruthenium MOFs as Versatile Heterogeneous
Hydrogenation Catalysts
Konstantin Epp,[a] Ignacio Luz,[b,c], Werner R. Heinz,[a] Anastasia Rapeyko,[b] Francesc X. Llabrés i
Xamena*[b] and Roland A. Fischer*[a]
Abstract: Ruthenium MOF [Ru3(BTC)2Yy]·Gg (BTC = benzene-1,3,5-
tricarboxylate
Y = counter ions = Cl-, OH-, OAc-; G = guest
molecules = HOAc, H2O) is modified via a mixed-linker approach,
H2O) resulting in material [Ru3(BTC)2-x(PYDC)xYy]·Gg (D).[5,6]
Therein, the catalytic properties of defect-engineered Ru-MOFs
were evaluated in the hydrogenation of olefins, whereas D
;
using mixtures of BTC and pyridine-3,5-dicarboxylate (PYDC) linkers, outperformed their untreated parent counterpart 1. This was
triggering structural defects at the distinct Ru2 paddlewheel (PW)
nodes. This defect-engineering leads to enhanced catalytic
properties due to the formation of partially reduced Ru2-nodes.
Application of a hydrogen pre-treatment protocol to the Ru-MOFs,
leads to a further boost in catalytic activity. We study the benefits of
(1) defect engineering and (2) hydrogen pre-treatment on the
catalytic activity of Ru-MOFs in the Meerwein-Ponndorf-Verley
explained by the formation of partially reduced Ru-centers
(modified PWs) which are undercoordinated due to the
incorporation of ditopic carboxylate PYDC linkers (instead of
tritopic carboxylates as in the case of BTC) and thus, better
accessible showing enhanced catalytic activity when compared
to fully coordinated Ru-centers present in the “defect-free” Ru-
MOFs. Interestingly, a pre-treatment protocol involving the
reaction and the isomerization of allylic alcohols to saturated ketones. exposure of 1 and D to hydrogen atmosphere at ~150 °C leads
Simple solvent washing could not avoid catalyst deactivation during
recycling for the latter reaction, while hydrogen treatment prior to
each catalytic run proved to facilitate materials recyclability with
constant activity over five runs.
to superior catalytic activity compared to their non-treated
analogues.[7] In-situ UHV-FTIR studies (ultra-high vacuum
Fourier transformed infrared spectroscopy), identified Ru-H
II,III
species at the mixed-valent Ru2
paddlewheels as a key-
intermediate, which formation is favored by the defectiveness of
the structure present in defect-engineered Ru-MOF. These
results broadened our understanding on how defective structure,
hydrogen pre-treatment and catalytic reactivity are interlinked
and motivated us to study the particular catalytic reactivity of
defect-engineered PYDC-containing Ru-MOFs in more detail.
Thus, we herein present our investigations regarding the effects
of PYDC incorporation into Ru-MOFs on the catalytic activity
demonstrated in both the MPV (Meerwein-Ponndorf-Verley)
reaction and the isomerization of allylic alcohols.
Introduction
Modifications at the organic linker in metal-organic frameworks
(MOFs) allows for both changes in structure, physical properties
and chemical reactivity of the materials.[1] Concerning the
reactivity of MOFs in catalysis, changes of the coordination
environment of the secondary building unit (SBU), i.e. free
coordination sites at the metal, may drastically influence their
catalytic properties.[2] A common strategy in creating defective
MOFs is to use mixed-linkers in the de-novo solvothermal
synthesis,[3,4] whereby in parallel to the introduction of the
regular linker, stoichiometric amounts of a “defect-generating
linker” featuring reduced connectivity can be incorporated into
the framework by means of a co-polymerization process.[3] Thus,
unsaturated metal sites are generated, exhibiting diverse
catalytic properties which are not present in the parent
frameworks. In our previous work, pyridine-3,5-dicarboxylic acid
(PYDC) was incorporated into the Ru analogue of HKUST-1,
4.178 Å
[Ru3(BTC)2Yy]·Gg (1) (BTC = benzene-1,3,5-tricarboxylate
;
Y = counter ions = Cl-, OH-, OAc-; G = guest molecules = AcOH,
Figure 1. Illustration of an ideal Ru paddlewheel (left) ligated by trimesate
molecules, compared to a defect-engineered Ru paddlewheel (modified PW)
with incorporated PYDC as defect-generating linker (Ru:teal, O:red, N:blue,
C:grey, H was omitted for clarity).
[a]
Dr. K. Epp, W. R. Heinz and Prof. Dr. R. A. Fischer
Inorganic and Metal-Organic Chemistry, Catalysis Research Center
and Department of Chemistry, Technical University of Munich
Ernst-Otto-Fischer-Straße 1, D-85748 Garching bei München,
Germany
E-mail: roland.fischer@tum.de
Results and Discussion
[b]
[c]
Dr. I. Luz, A. Rapeyko and Dr. F. X. Llabrés i Xamena
Instituto de Tecnología Química, Consejo Superior de
Investigaciones Científicas, Universitat Politècnica de València,
Spain.
Synthesis and Characterization
Dr. I. Luz
In accordance to our previous synthetic protocols, in this study
we synthesized defect-engineered Ru-MOF D30 with a 30%
PYDC feeding ratio.[6] The incorporation of PYDC was verified
Current address: RTI International, Research Triangle Park, NC
27709-2194, USA.
1
by H NMR of acid digested samples (supporting information,
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cctc.201902079
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FULL PAPER
S1) in combination with elemental analysis (supporting
information, S2).
catalytic activity for D30 (30% PYDC) compared to 1 the “defect
free” Ru-MOF counterpart, providing evidence of the beneficial
contribution of the incorporated PYDC defects on the catalytic
activity of the system. In particular, the yield when D30 is used
as a catalyst increases from 16 to 43% compared to parent MOF
1 after 2.5 h reaction time.
Due to the fact that no N-containing solvent or reagents were
used in the synthesis, the N-content found in the samples can
be associated with the incorporated PYDC. Both data are in
good agreement to the suggested sum formula of D30
[Ru3(BTC)1.4(pydc)0.6Clx]·AcOH2.65, showing that slightly less
PYDC than the feeding ratio was incorporated in the final solid.
D30 sample is isoreticular to parent Ru-MOF, as it is indicated
by powder X-ray diffraction (PXRD) (see supporting information,
S3). Moreover, the structural integrity is not significantly affected
by the doping, showing the tolerance of the framework to the
incorporation of PYDC. Microporous D30 sample shows a type I
isotherm (see supporting information, S4) with BET (Brunauer,
Emmett, Teller) surface area of 647 m2/g. The thermal stability
was investigated by thermal gravimetric analysis (TGA),
indicating moderate thermal stability of the defect-engineered
sample up to ~220 ºC, which is in the same region as their
“defect free” parent analogue 1 (see supporting information, S5).
D30 reveals an additional decomposition event which is close to
the decomposition temperature of BTC (~220 °C). Most likely,
this decomposition step can be associated with the
decomposition of PYDC, since both compounds have similar
decomposition temperatures. Based on the data obtained by
TGA, a BTC to PYDC ratio of 3:1 can be calculated which is in
good agreement with the feeding ratios and elemental analysis,
giving evidence of the successful incorporation of PYDC. As a
crucial procedure to trigger the hydrogenation reactivity of D30,
the sample was treated with molecular H2 at elevated
temperatures (150 ºC), which leads to the desired formation of
Ru-H, as previously reported by our group.[6] Following on from
this interesting catalytic behavior, we tested parent and defect-
engineered Ru-MOFs in two kinds of heterogeneously transition-
metal-catalyzed hydrogen-transfer reactions, namely the
reduction of carbonyl compounds to alcohols with secondary
alcohols as the hydrogen donor (MPV, Meerwein-Ponndorf-
Verley reaction) and the isomerization of allylic alcohols to
saturated ketones. Herein, we want to highlight the H2 pre-
treatment as a key tool of post-synthetic modification of the
underlying Ru-MOFs/PYDC-DEMOFs and that the reactivity of
PYDC-DEMOFs can be transferred also to other reactions types.
Figure 2. Time-yield plot of MPV reaction. Comparison of the reactivity of Ru-
MOF/PYDC DEMOF (closed symbols) and their H2 pre-treated analogues
(open symbols). The number in the brackets indicate the feeding ratios of
PYDC into parent Ru-MOF.
H2 pre-treatment causes a further positive impact on the catalytic
activity of parent as well as defective Ru-MOFs. The boost in
catalytic activity is much more pronounced in H2@D30
(hydrogen pre-treated D30) reaching 99% yield after 2.5 hthe
non-treated analog D30. Due to introduced point defects like
“missing linker”, “missing node” and modified PW” within the
framework of D30, the probability of H2 to access Ru2-nodes
should be higher than for “defect free” Ru-MOFs, where only
modulator-induced defects are present.[8] Therefore, the
formation of Ru-H species is supposed to be more likely. Based
on the drastic improvement of the activity of the H2 pre-treated
samples, the reaction mechanism shown in Scheme 1 can be
assumed, usually referred to as “hydridic route”.[9] Unlike
classical MPV reactions promoted by aluminum and other non-
transition metals involving a direct hydrogen transfer from the
alcohol to the ketone via a cyclic transition state, the hydridic
route implies the active participation of Ru-H species similar to
other hydride-catalyzed reactions like the dimerization of
olefins.[7] According to this reaction mechanism, a catalytically
active ruthenium hydride species, Ru-H, is initially formed by the
abstraction of the α-hydrogen of 2-butanol, followed by the MPV-
type reduction of cyclohexanone to cyclohexanol. It is thus
evident that H2-pretreated Ru-MOFs will show a higher catalytic
activity as compared to the corresponding non-treated
compounds, since we already demonstrated that Ru-H species
are indeed formed during H2 pretreatment.[6]
Catalytic tests
Hydrogen transfer reactions
Firstly, we investigated Ru-MOFs in the MPV reaction of
cyclohexanone to give cyclohexanol, whereby 2-butanol acts as
a hydrogen donor source which formally transfers hydrogen to
the unsaturated substrate (ketone). In a typical reaction 10 mg of
ketone (0.1 mmol), 5 mg of Ru-MOF catalyst (17 mol% of Ru),
and 1 mL of alcohol (ca. 11 eq) were placed into a closed
pressured reactor under 2 bar of N2 at 120ºC. In all the reactions
described below, cyclohexanol was the only product detected.
Therefore, full selectivity was observed in all cases. Figure 2
shows the time-yield plots obtained for D30 (30% PYDC) and
“defect free” 1 Ru-MOF compounds, both before and after H2
pre-treatment at 150 ºC. The resulting data reveal the higher
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This reaction can be considered as an intramolecular hydrogen
transfer reaction, in which hydrogen is transferred from the
alcohol to the C=C bond. Isomerization of allylic alcohols is
usually carried out in the presence of additives, such as bases
or hydrogen acceptors, to promote the reaction. Various metals
from groups 8, 9, and 10 (including Ru) are known to catalyze
this reaction.[12] As a model reaction to evaluate the activity of
Ru-MOFs, we studied the isomerization of 1-octene-3-ol to
octane-3-one in the presence of 2-propanol acting as a solvent
as well as a hydrogen donor. In a typical reaction, 40 mg of the
allylic alcohol (1-octene-3-ol, ca. 0.3 mmol) 2 mg of Ru-MOF
catalyst (2 mol% of Ru), and 1 mL of i-PrOH (ca. 13 eq) were
placed into a closed pressured reactor under 2 bar of N2 at
120 ºC. The results obtained are shown in Figure 3.
Scheme 1. Proposed reaction mechanism for the MPV reduction of
cyclohexanone through a “hydridic route”.
A number of ruthenium complexes are well known to catalyze
hydrogen transfer reactions,[9] and their activity can be
significantly boosted by the addition of a small amount of
base.[10] Note in this sense that the PYDC linkers present in D30
offer a basic pyridyl-N atom in the proximity of the reactive Ru
centers which may have a similar enhancing effect as an added
external base. This would easily explain the large difference in
catalytic activity observed for compounds 1 and D30 (see Figure
2). Secondly, it was investigated if the presented Ru-H chemistry
of PYDC-DEMOFs is transferable to other related reactions,
namely the transfer hydrogenation of allylic alcohols to the
corresponding saturated ketones. Conversion of allylic alcohols
into saturated ketones is usually carried out in two steps:
hydrogenation of the C=C bonds followed by dehydrogenation of
the alcohol, which usually requires further protection and
deprotection steps. Thus, the one-pot redox isomerization
evaluated here represents an attractive alternative (see Scheme
2).[11]
Figure 3. Yield-time plot of catalytic transfer hydrogenation of 1-octene-3-ol to
octane-3-one using different Ru catalysts. Comparison between the reactivity
of Ru-MOF/PYDC DEMOF (closed symbols) and their H2 pre-treated
analogues (open symbols).
Similar to what was observed in the MPV reaction, both, the
introduction of defect-generating PYDC linkers as well as the H2
pre-treatment result in superior catalytic activity compared to
defect-free and non-treated parent Ru-MOFs (Figure 3). Defect-
engineering boosted the catalytic activity of parent Ru-MOF 1 by
a factor of about 2.5, namely, from 21 to 52% (D30) after 2h
reaction time. Upon H2 pre-treatment, we observed a 1.9-fold
increase in yield (after 2h reaction time) for 1 (yield increased
from 21% to 39%) and by a factor of 1.4 for D30 (yield from 52%
to 75%), respectively. Hence, both strategies for catalyst
optimization exhibit a cumulative increase by a factor of roughly
3.6. As it was discussed in the MPV reaction, the higher catalytic
activity of the H2 pre-treated samples and DEMOFs can possibly
be explained by the higher amount of incorporated structural
point defects resulting in a preferential formation of Ru-H
species reasoned by the lower coordination number at the Ru-
nodes. As already mentioned above for the MPV reaction, the
formation of ruthenium hydride species is a key step in the
transfer hydrogenation reaction leading to the isomerization of
allylic alcohols to the corresponding saturated ketone. In
Scheme 2. a) Two step and b) one step isomerization of allylic alcohols.
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analogy to the previous report by Yamaguchi et al. using
Ru(OH)x/Al2O3 as
catalyst between two consecutive catalytic cycles proves to be
more effective to remove adsorbed species than solvent
washing alone, which most likely explains the preservation of the
catalytic activity of these catalysts for at least five consecutive
catalytic cycles. Powder X-ray diffraction measurements and
TEM images of the collected solids indicate preserved
crystallinity (see supporting information Figure S8-9) and particle
morphology and size.
a
heterogeneous catalyst,[13] the overall
mechanism for the allylic alcohol isomerization is depicted in
Scheme 3. According to the above mechanism, adsorption of
the allylic alcohol onto the Ru sites first gives rise to the
corresponding alcoholate, followed by the formation of the Ru-H
hydride key species and α,β-unsaturated ketone. Then, hydride
transfer to the unsaturated ketone gives rise to the
corresponding enolate, which is finally desorbed as the
saturated ketone upon adsorption of a new allylic alcohol
molecule. In order to verify the heterogeneous nature of the
catalyst, and to exclude leaching of Ru-species, a hot filtration
test has been conducted at low conversion rates showing no
further reaction progress as soon as the catalyst was filtered off
(see supporting information, S6).
RUN 1
RUN 2
80
RUN 3
RUN 4
60
40
20
0
RUN 5
H2@1
H2@D30
1
D30
Catalyst
Figure 4. Recyclability tests of the Ru-BTC catalysts, showing the yield of
saturated ketone obtained after 2 h of reaction with solvent wash (1 and D30)
or repeated activation via H2 pre-treatment (H2@1 and H2@D30).
Scheme 3. Reaction mechanism for the isomerization of allylic alcohols to
saturated ketones over Ru-MOFs.
Conclusions
In summary, we demonstrate defect-engineering as an effective
synthetic tool for the introduction of structural point defects into
ruthenium MOFs and highlight their superior catalytic activity
compared to their parent analogues. Additionally, we show that
a hydrogen pre-treatment procedure has a strong impact to
further boost the catalytic activity of Ru-MOFs which we
demonstrated in the MPV reaction (Meerwein-Ponndorf-Verley)
and the isomerization of allylic alcohols. A similar beneficial
effect of the hydrogen pretreatment of the Ru-MOFs was already
described for the dimerization of ethylene by Agirrezabal-Telleria
et al. and the hydrogenation of olefins in our previous report.[6,7]
Moreover, the presence of a basic pyridyl-N atom in the PYDC
linkers allowed us to carry out the hydrogen transfer reactions
under base free conditions with excellent results and given
recyclability.
Recyclability
We selected the isomerization of the allylic alcohol 1-octene-3-ol
as a test reaction to evaluate the stability and reusability of the
catalysts. To this end, the reaction was first carried out for 2 h
following the same procedure as described above. At this point,
the catalysts were recovered by filtration, thoroughly washed
with 2-butanol and dried at room temperature. Catalysts 1 and
D30 were directly used on consecutive catalytic cycles, while H2
pre-treated catalysts H2@1 and H2@D30 were submitted again
to a hydrogenation treatment with H2 at 150 °C prior to use. The
results obtained for five consecutive catalytic cycles are shown
in Figure 4. As can be seen, the catalytic activity (viz., yield of
saturated ketone obtained after 2 h of reaction) decreases
progressively with the use in the case of catalysts 1 and D30.
This is most likely due to the progressive accumulation of
adsorbed species on the solid catalyst like products from
previous runs that are not completely removed during washing.
This results in an increasing poisoning of the catalytically active
sites. Thus, an almost complete loss of activity of the catalysts is
observed after already three catalytic cycles. Conversely,
catalysts deactivation is not observed for the H2 pre-treated
catalysts H2@1 and H2@D30. This H2 pre-treatment of the
Experimental Section
Materials and Synthesis
RuCl3·xH2O, LiCl, benzene-1,3,5-tricarboxylic acid (H3BTC), and pyridine-3,5-
dicarboxylic acid (PYDC) and all solvents [CH3COOH, H2O, CH3OH, acetic
anhydride, acetone, hexane, tetrahydrofuran, toluene, EtOH, acetonitrile and
MeOH] were used as commercially received unless otherwise noted.
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Synthesis
N2-physisorption (BET)
N2-physisorption measurements were performed on
a
Micromeritics
ASAP 20120 device using N2 at 77 K. Before the measurement the
samples (~100 mg) were degassed for 12 h at 120 °C under dynamic
vacuum.
[Ru2(OOCCH3)4Cl]
Tetraaceto-diruthenium (+II, +III) chloride was synthesized following a
slightly modified synthesis description which was introduced by Mitchel et
al.[14] 0.5 g RuCl3 · xH2O (~2.4 mmol), 0.5 g LiCl (12 mmol) and 3.5 mL
acetic anhydride was mixed with 17.5 mL acetic acid (99.5%) in a 50 mL
preheated Schlenk flask. The reaction mixture was stirred and refluxed
for 24 h at 140 °C in argon atmosphere. The black suspension turns
brown/red after a few hours. Afterwards, it was allowed to cool down to
room temperature and the precipitated brown/red solid was filtered
(membrane filter) and washed manually using 3x acetone (≥99.8%).
Yield: 0.35 g (62%). 1H NMR δ (298 K, 200 MHz, DMSO-d6) 1.9 (s, 3H, -
CH3) ppm.
Gas Chromatography (GC)
Gas chromatography measurements were performed on
a Agilent
Technologies 7890A with FID (flame ionization detector) using a capillary
column HP-5 (5% phenylmethylpolysiloxane) of 30 m length and 0.32
mm internal diameter as well as BP20(WAX) of 15 m length and 0.32 mm
internal diameter as another column. Thereby, the samples were
measured in high dilution using volatile organic solvents (usually ethanol
or acetone).
Nuclear magnetic resonance (NMR)
Liquid phase 1H-NMR measurements were performed using a Bruker
RMN AVANCE (AVANCE III) 300 MHz at 298 K and Bruker Avance
DPX-200 spectrometer at 293 K in DCl/DMSO-d6 for the digested
activated MOF samples. Thereby, approximately 5 mg samples were
digested in 4 droplets of DCl, placed in an ultrasonic bath for at least
30 min, and 0.7 mL DMSO-d6 were added. For better digestion, the
samples were carefully heated until the solution became clear.
RuMOF, [Ru3(BTC)2Yy]·Gg (1)
0.17 g Ru2(OOCCH3)4Cl (1.5 eq.; 0.36 mmol) and 0.1 g H3BTC
(benzene-1,3,5-tricarboxylic acid) (2 eq.; 0.48 mmol) were dispersed in
4 mL H2O (HPLC grade) and 0.7 mL glacial acetic acid, transferred to a
PTFE vessel, which was sealed with a stainless steel autoclave and
placed in a preheated oven at 150 °C for 72 h. No temperature-controlled
program was applied. The reaction mixture was allowed to cool down to
r.t. and the liquid was separated from the solid by centrifugation
(7830 rpm, 15-20 min). The suspension was decanted and sonicated for
10 min and washed twice with ~20 mL H2O (HPLC grade) and acetone
with subsequent centrifugation (7830 rpm, 15-20 min). The dark brown
solid was dried in vacuum (~10-3 mbar) and was digested in 4 droplets
DCl and around 0.5 ml DMSO-d6 for 1H NMR measurement. 1H NMR δ
(298 K, 200 MHz, DMSO-d6) 8.6 (s, 3H, C-HAr) ppm, 1.9 (s, 3H, -CH3).
Acknowledgements
Funding by the Spanish Government is acknowledged through
projects MAT2017-82288-C2-1-P and Severo Ochoa (SEV-
2016-0683). This project is further funded by the Deutsche
Forschungsgemeinschaft grant no. FI-502/32-1 (“DEMOFs”). KE
and WRH would like to thank TUM Graduate School and the
Gesellschaft Deutscher Chemiker (GDCh) for financial support.
KE gratefully acknowledges support from the colleagues Olesia
Halbherr (neé Kozachuk) and Wenhua Zhang.
[Ru3(BTC)2-x(PYDC)xYy]·Gg, (D30)
The defect-engineered Ru-MOF was synthesized in accordance to the
synthesis for the parent Ru-MOF, besides adding specific amounts of
pydrine-3,5-dicarboxylic acid (PYDC) into the reaction solution. In the
synthesis of D30, 1.4 eq. of H3BTC (71 mg, 0.34 mmol) and 0.6
eq. PYDC (24 mg, 0.14 mmol) were dispersed in 4 mL H2O (HPLC
grade) and 0.7 mL glacial acetic acid. Afterwards, the mixture was
transferred to a PTFE vessel, which was sealed with a stainless steel
autoclave and placed in a preheated oven at 150 °C for 72 h. No
temperature-controlled program was applied. The reaction mixture was
allowed to cool down to r.t. and the liquid was separated from the solid by
centrifugation (7830 rpm, 15-20 min). The suspension was decanted and
sonicated for 10 min and washed twice with ~20 mL H2O (HPLC grade)
and acetone with subsequently centrifugation (7830 rpm, 15-20 min). The
black solid was dried in vacuum (~10-3 mbar) and was digested in 4
droplets DCl and around 0.5 ml DMSO-d6 for 1H NMR measurement 1H
NMR δ (298 K, 200 MHz, DMSO-d6) 8.6 (s, 3H, C-HAr) ppm, 1.9 (s, 3H, -
CH3).[6]
Keywords: Metal-Organic Frameworks, defects, ruthenium, Ru-
BTC, Ru-MOF, HKUST-1, Defect-Engineering, MOF catalysis,
DEMOF,
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Thermogravimetric analysis (TGA)
Thermogravimetric studies were conducted using
TGA/SDTA851e apparatus with an applied heating ramp of 10 °K/min
under oxidizing conditions in a N2/O2 (80/20%) flow in Al2O3 crucibles.
a Mettler Toledo
Powder X-ray diffraction (PXRD)
Measurements were performed using Bragg-Brentano geometry on a
PANalytical CUBIX diffractometer equipped with
a
PANalytical
X’Celerator detector. X-ray Cu Kα radiation (λ1 = 1.5406 Å, λ2 = 1.5444
Å, I2/I1 = 0.5) was used for the measurements. Voltage and intensity
were 45 kV and 40 mA, respectively. The arm goniometer length was
200 mm, and a variable divergence slit (irradiated area = 2.5 mm) was
employed. The measurement range was from 2.0º to 90.0º (2θ), with a
step size of 0.040º (2θ) and an acquisition time of 35 seconds per step.
The measurement was performed at 298 K, and the sample was rotated
during the measurement at 0.5 rps.
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