Shape and transition state selective hydrogenations using egg-shell Pt-MIL-101(Cr) catalyst

Article abstract of DOI:10.1021/cs400681s

The use of the metal organic framework MIL-101(Cr) as support for Pt nanoparticles is evaluated in three selective hydrogenation reactions. Homogenous Pt nanoparticles of ～4 nm can be formed inside the porosity of MIL-101(Cr) in close contact with the Cr trimers in an egg-shell configuration by a wet impregnation procedure combined with sonication. The catalyst is applied in the selective hydrogenations of olefin mixtures, benzonitrile, and linoleic acid. In the case of an olefin mixture, 1-octene is selectively hydrogenated over 1-hexadecene, attributed to diffusion limitations that favor the hydrogenation of the smaller substrate. In the case of benzonitrile hydrogenation, benzylamine is selectively formed over dibenzylamine attributed to transition state selectivity. In the hydrogenation of linoleic acid, selectivities were similar to that for platinum on alumina.

Full text of DOI:10.1021/cs400681s

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Article
Shape and Transition State Selective Hydrogenations
using Egg-Shell Pt-MIL-101(Cr) Catalyst
Hossein Khajavi, Hans A. Stil, Herman P.C.E. Kuipers, Jorge Gascon, and Freek Kapteijn
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 02 Oct 2013
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ACS Catalysis
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Shape and Transition State Selective Hydrogenations using
Egg-Shell Pt-MIL-101(Cr) Catalyst
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†
‡
‡
†
†
Hossein Khajavi* , Hans A. Stil , Herman P. C. E. Kuipers , Jorge Gascon* , Freek Kapteijn
†
Catalysis Engineering, Chemical Engineering Department, Delft University of Technology, Julianalaan 136, 2628 BL,
Delft, The Netherlands
‡
Shell Global Solutions, Projects and Technology, Innovation & Research/Team Experimentation (PTI/TX), Shell Technolꢀ
ogy Center Amsterdam, Grasweg 31, 1031 HW, Amsterdam, The Netherlands.
Keywords: Metal Organic Frameworks, MILꢀ101, catalysis, Platinum nanoparticles, Selective hydrogenation, benzonitrile.
Supporting Information Placeholder
1
, 5, 7, 8, 9, 35
3
4, 37
tive metals
, (metalꢀ) organics
, postꢀsynthetically
ABSTRACT: The use of the metal organic framework MILꢀ
101(Cr) as support for Pt nanoparticles is evaluated in three selecꢀ
tive hydrogenation reactions. Homogenous Pt nanoparticles of ~4
nm can be formed inside the porosity of MILꢀ101(Cr) in close
contact to the Cr trimers in an eggꢀshell configuration by a wet
impregnation procedure combined with sonication. The catalyst is
applied in the selective hydrogenations of olefin mixtures, benzoꢀ
nitrile and linoleic acid. In the case of an olefin mixture, 1ꢀoctene
is selectively hydrogenated over 1ꢀhexadecene, attributed to diffuꢀ
sion limitations that favor the hydrogenation of the smaller subꢀ
strate. In the case of benzonitrile hydrogenation, benzylamine is
selectively formed over dibenzylamine attributed to transition
state selectivity. In the hydrogenation of linoleic acid, selectivities
were similar as for platinum on alumina.
7
functionalized linkers and the combination of several functionꢀ
3
8
alities in one single MOF catalyst . The use of MOFs as nanoꢀ
molds for hosting functional inorganic nanoparticles and their
application in catalysis and hydrogen storage attracted increasing
39
attention during the last few years . Depending upon the method
and the conditions applied for the loading and transformation of
precursors, nanoꢀparticle encapsulation might only be partially
successful. Three possible caseꢀscenarios have been defined when
3
9
classifying metal nanoꢀparticle distributions in MOFs : (i) in
class A, most of the nanoꢀparticles are preferentially deposited at
the outer surface of a MOF crystal, resulting in a wide particle
size distribution and a poor metal dispersion, especially in the
case of high loadings; (ii) in class B, most of the nanoꢀparticles
are deposited in the pore space of the MOF but they display a
rather broad particle size distribution that might arise from partial
destruction of the MOF skeleton during impregnation and (iii) in
class C, nanoꢀparticles with a homogeneous particle size distribuꢀ
1
. Introduction
tion close to that of the MOF pores or cavities are evenly distribꢀ
uted throughout the porosity of the host
Metal Organic Frameworks (MOFs) have become a familiar term
in the world of ordered porous solids. With nearly two decades of
research into this category of materials, we are now seeing a wide
range of potential applications being assessed at both academic
and industrial levels. These potential applications range from
5, 7, 8, 10, 37ꢀ47
. A critical
evaluation of most presented results demonstrates that MOF enꢀ
capsulated metal nanoꢀparticles do not display an outstanding
activity. The relatively low activity should not be surprising since
in most cases catalytic reactions have been explored where the use
of a MOF as support does not present any advantage (e.g. strucꢀ
ture insensitive reactions) and may even add undesired diffusion
limitations. In contrast, for catalytic applications where control of
nanoparticle size and morphology is needed, or where well deꢀ
fined pores may favor shape selective conversions or certain tranꢀ
sition states, MOFs may offer unique advantages over other nanoꢀ
structured supports, as demonstrated in this work.
1
ꢀ6, 7ꢀ11
(
size/shape selectiveꢀ) catalysis
, adsorption/separation proꢀ
12ꢀ17
18ꢀ25
cesses
photoluminescence
, to advanced applications like semiconductors
,
2
6ꢀ31
32ꢀ34
and drug delivery
. The lattice strucꢀ
ture of a MOF consists of inorganic nodes that are bridged by
multidentate organic linkers, often resulting in highly porous crysꢀ
tals with a high degree of tunability. By virtue of the vast amount
of possible combinations of organics and inorganics, a countless
number of structures are conceivable; this is reflected in the nearꢀ
ly twenty five thousand structures that have been identified to date
3
4
,
many of them exhibiting unprecedented pore volumes.
In this paper, the introduction of platinum nanoparticles in MILꢀ
1
01(Cr) is reported. A high dispersion is achieved and the applicaꢀ
tion of the resulting catalyst in the hydrogenation of 1ꢀoctene, 1ꢀ
hexadecene, benzonitrile, and linoleic acid is demonstrated. The
selected reactions are intended to demonstrate both substrate and
product selectivity. These reactions are well understood in terms
of mechanisms and kinetics, so highly suited for this type of
study. The simultaneous hydrogenation of two linear alpha oleꢀ
fins, 1ꢀoctene and 1ꢀhexadecene, with a significant difference in
chain length, demonstrates how mass transport limitations can
favor substrate selectivity (shape selectivity) in MOFs. In the
When it comes to catalytic applications, several routes can be
followed, with the MOF acting as the active catalyst and/or as the
support for the species of interest. The immobilization of homoꢀ
geneous catalysts on MOFs to heterogeneous catalysts is of high
interest and has been pursued due to the intrinsic advantages hetꢀ
9
erogeneous catalysts have . The coupling of shape selectivity and
3
catalysis has also been demonstrated using MOFs alongside
7
catalysis by the inorganic nodes , incorporated catalytically acꢀ
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ꢀ
4
hydrogenation of benzonitrile restrictive transition state selectivity
is demonstrated; whereby the formation of side products is supꢀ
pressed. Linoleic acid hydrogenation occurs similar as over a
conventional Pt catalyst.
After a pretreatment at 443 K under vacuum (10 mbar) overꢀ
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night, N adsorption at 77 K (Quantachrome Autosorbꢀ6B) was
2
used to determine the specific BET surface area (calculated from
data between 0.05 and 0.2 relative pressures). Pore volume was
calculated at 0.5 relative pressure. For elemental analysis samples
were digested in a mixture of 1 % hydrofluoric acid and 1.25 %
sulfuric acid and analyzed with an ICPꢀOES Perkin Elmer Optima
3000 dv for platinum and chromium. Active phase loss has been
studied by the analysis of the tested reaction mixtures for Pt after
filtering of the PtꢀMILꢀ101(Cr) Catalyst. The crystalline structure
of the catalyst composite has been analyzed using a BrukerꢀAXS
D5005 theta/theta diffractometer equipped with incident beam
CuKꢀalpha1 monochromator. The range of 1 to 20 2θ (°) has been
scanned for a period of 90 minutes. Unless stated explicitly all
scans were done under ambient conditions.
2. Experimental
2
.1. Materials
All chemicals, unless explicitly specified, were purchased from
Sigma–Aldrich and used without any further purification: terephꢀ
thalic acid (97%), chromium (III) nitrate nonahydrate (99%),
hexachloroplatinic acid (37.4 wt% Pt basis), hydrofluoric acid (47
ꢀ 51 wt%), ethanol (99.8%), tetrahydrofuran anhydrous and inꢀ
hibitor free (≥99.9%), formaldehyde solution (36.5ꢀ38% aqueꢀ
ous), 1ꢀoctene (98%), 1ꢀhexadecene (≥99%), benzonitrile anhyꢀ
drous (≥99%), linoleic acid (>99.0%) and NꢀMethylꢀNꢀ
0
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0
(
trimethylsilyl)trifluoroacetamide (MSTFA, suitable for silylaꢀ
Using FTIR analysis of CO adsorption at low temperature,
Brønsted and Lewis acid sites in the samples were distinguished.
For this, samples were prepared by pressing the MOF or MOF
tion). A 1 wt.% platinum on alumina catalyst (Sigma–Aldrich)
was used as a reference in the catalytic performance testing.
ꢀ
2
composite powder and KBr at 1 tonꢂin . The pellets were preꢀ
treated under high vacuum at 423 K initially to remove adsorbed
species. After this, the samples were reduced inꢀsitu in a flow of
2
.2. Catalyst preparation
For the synthesis of MILꢀ101(Cr) a microwave procedure was
optimized. A solution composed of chromium (III) nitrate noꢀ
nahydrate (9.765 g, 24.5 mmol), terephthalic acid (3.652 g, 22.0
mmol), hydrofluoric acid (0.90 g, ≈22 mmol) and water (90.0 ml)
was heated using a MycroSYNTH Plus ACT38. A program was
applied which ramped the temperature from ambient to 483 K
within 5 min; subsequently this temperature was maintained for
45 minutes. The microwave oven was operated at 600 W, with a
ꢀ
1
1
5 ml min of 2% diluted hydrogen at 373 K, which was followed
by a repeat of the pretreatment step. Subsequently, the samples
were cooled down to 143 K still under vacuum and CO was dosed
to 5 mbar. After this the sample was brought to room temperature,
helium was charged into the sample holder, equipped with two
CaF windows. Using a Thermo Nicolet Nexus 6700 and iS50R
2
FTꢀIR spectrometer, Diffuse Reflectance Infrared Fourier Transꢀ
formed (DRIFT) spectra were recorded. These spectrometers are
equipped with a DRIFT cell with conical pellet holders, KBr
5
0 RPM autoclave rotation and 120 rpm stirring rate for the magꢀ
netic stirrer inside of the autoclave reactor. After this the autoꢀ
clave was allowed to cool and settle overnight without agitation,
stirring or opening. The resulting product is vacuum filtered using
a 0.1 ꢁm regenerated cellulose filter and washed with ethanol
under reflux overnight. A second washing step is applied with
tetrahydrofuran in a soxhlet for at least 24 hours. Finally, the
sample is filtered off and dried at 423 K for a minimum of 12
hours under a mild vacuum (≈100 mbar) to produce ‘MILꢀ101(Cr)
as prepared’.
ꢀ
1
beam splitter, DTGSꢀTEC detector (range 11 000 ꢀ 375 cm ;
Nicolet 6700), liquid nitrogen cooled MCTꢀB detector (range 11
ꢀ
1
000 ꢀ 400 cm ; Nicolet iS50R) and a 633ꢀnm monochromatic
−1
laser beam. The spectra were recorded from 4000 to 400 cm
after an accumulation of a minimum of 64 scans and a resolution
−1
of 4 cm . KBr was used to perform all background measureꢀ
ments. CO chemisorption experiments were done in the same
setup at room temperature.
XPS spectra were recorded on an AXIS Ultra HSA spectrometer
For the platinum impregnation: 0.657 g of the prepared MILꢀ101
was suspended in 10 ml of ethanol. A second solution containing
4
prepared. The hexachloroplatinic acid solution is added dropwise
to the MILꢀ101 slurry and stirred at room temperature for several
hours before adding 0.44 ml of aqueous formaldehyde. The resultꢀ
ing slurry is then ultrasonicated in a sealed round bottom flask
overnight at 308 K. This treatment is continued for an additional
ꢀ
9
(
operating pressure <10 mbar) with a 165 mm radius Hemiꢀ
Spherical Analyzer (HSA) in rapid unꢀscanned mode using a Deꢀ
layꢀLine Detector (DLD). This was done to reduce potential damꢀ
age due to sample irradiation which was observed during scanned
mode. Spectra obtained used an aluminum anode (Al K alpha =
1486.6 eV). The coaxial charge neutralizer ensures uniform
charge compensation over the sample despite inhomogeneity.
Samples were deposited on a sample holders using doubleꢀsided
adhesive and subsequently evacuated under high vacuum. After
degassing samples were transferred to the analysis chamber. Reꢀ
gion scans were measured at 40 eV and survey scans at constant
pass energy of 160 eV, all at room temperature. Binding energies
calibration was referenced to the C1s line at 284.6 eV from adꢀ
ventitious carbon. Surface atomic ratios have approximated using
the integrated intensities of peaks corrected by the atomic sensiꢀ
0 mg (0.10 mmol) of hexachloroplatinic acid in 5 ml of water is
2
4 hours with the round bottom flask open in a fume hood and
after that at 343 K until the majority of the solvent has evaporated.
While still warm the inside of the round bottom flask is scratched
and left to cool so as to crystalize unadsorbed platinum onto flask
walls. The resulting material is recovered by filtration and washed
with tetrahydrofuran in a soxhlet overnight and dried in air in
multiple stages at temperatures of 323, 343 and 373 K with each
temperature being maintained for a minimum of 5 hours (‘MILꢀ
48
tivity factors
.
1
01(Cr) Pt partially reduced’). An additional reduction step using
ꢀ
1
a flow of 15 ml min of 2% diluted hydrogen at 373 K results in
‘MILꢀ101(Cr) Pt fully reduced’ (also referred to as ‘PtꢀMILꢀ
101(Cr) catalyst’). An additional sample has been prepared by
omitting the reducing steps; ‘MILꢀ101(Cr) Pt loaded’.
High resolution (Scanningꢀ)Transmission Electron Microscopy
(SꢀTEM) was performed on a JEOL 2100F equipped with a Gatan
Erlangshen ES500W, an Orius SC1000 CCDs, a Gatan Tridiem
energy filter system, and a Gatan 806 HighꢀAngle Annular Darkꢀ
Field (HAADF) STEM detector. The microscope was operated at
an accelerating voltage of 200 kV (FEG, range 80ꢀ200 kV), with a
2.3. Characterization
0
.17 nm point resolution. For the STEM analysis, a 0.7 nm of
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probe size, 40 ꢁm of condensor aperture, and 7 cm of camera
The hydrogenation of linoleic acid and its product oleic acid is
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length of HAADF detector were used. HighꢀAngle Annular Darkꢀ
Field (HAADF) and Secondary Electron Imaging (SEIꢀ
Components) images were taken with a nominal spot size of 0.5
nm. Energy Dispersive Xꢀray (EDX) spectrum profile scanning
was performed using the STEM attachment. For all techniques
low intensity beam conditions were applied to minimize the elecꢀ
tron dose and beam damage to the sample (using the maximum
possible magnification, minimal beam intensity, and long expoꢀ
sure durations).
the third reaction investigated. The reaction was carried out using
a reagent to catalyst ratio of 26 mmol linoleic acid/mg Pt, under
20 bar of hydrogen atmosphere at 308 K. Scheme 2 illustrates
simplified reaction pathways of hydrogenation and isomerization
60ꢀ67
of linoleic acid using a heterogeneous catalyst
.
O
O
(CH2)7
C
(CH2)8
OH
transꢀ9,transꢀ11ꢀCLA
(CH2)4
OH
transꢀ10,cisꢀ12ꢀCLA
(CH2)5
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2
.4. Catalytic performance testing
The selective hydrogenation of 1ꢀoctene and 1ꢀhexadecene was
carried out in semiꢀbatch mode at a constant pressure of 1.5 bar
absolute of hydrogen, at 308 K and at a concentration of 40.5
mmol 1ꢀoctene/mg Pt and 40.5 mmol 1ꢀhexadecene/mg Pt. Here
the reaction selectivity ratio is quantified and is defined as the
ratio of converted 1ꢀoctene to converted 1ꢀhexadecene.
O
(CH2)7
(CH2)5
OH
cisꢀ9,transꢀ11ꢀCLA
O
(CH2)4
(CH2)7
Linoleic acid
The selective hydrogenation of pure benzonitrile was carried out
at 36.5 mmol benzonitrile /mg Pt at 20 bar and 308 K. Primary
(aromaticꢀ) amines are important chemical and pharmaceutical
intermediates, solvents, paints, herbicides and textiles. They are
produced by heterogeneously catalyzed hydrogenation of aroꢀ
OH
+
H2
O
(
CH2)7
(CH2)7
O
Oleic acid
49ꢀ54
OH
matic nitriles
. The hydrogenation of benzonitrile often yields
+H2
various products, namely benzylamine (primary amine), dibenzylꢀ
amine (secondary amine), Nꢀbenzylidenebenzylamine (ternary
amine), benzylideneimine, alpha aminodialkylamine and toluene
(CH2)16
Stearic acid
OH
55
52–59
.
Reaction Scheme 1 presents the possible pathways
.
Scheme 2. A simplified scheme of possible reaction pathways
to the various products formed in the hydrogenation and isomꢀ
erization of linoleic acid (boxed) as typically described in litꢀ
6
1
BN
BA
BI
erature for noble metal heterogeneous catalysts . Products
such as elaidic acid and cisꢀ/transꢀ vaccenic acid have not
been included in this schematic.
+H2
+
H2
H2
ꢀH2
ꢀ
H2N
N
HN
The initial rate of consumption of reagents is presented as a turnꢀ
over frequency (TOF) defined here as:
ꢀBA +BA
+H2
NH3
ꢀ
ꢄꢅ. ꢅꢆꢇꢈꢉꢊꢋꢌꢍꢉ
ꢀ
ꢁꢂ ꢃ
ꢎꢏꢐꢅ.ꢅꢅꢑꢒꢓꢐꢔꢒ
BIBA
H
N
ꢀ
1 ꢀ1
Ratio of the reaction rate (r, with units; mol g s ) multiplied by
Pt
ꢀ1
Avogadro’s constant (NAvogadro; mol ) to the specific surface area
of platinum (A , with units; m g ) multiplied by active site denꢀ
sity per Pt surface area (ρSites, with units; sites m ). The reaction
NH2
+H2
ꢀNH3
2
ꢀ1
Pt
ꢀH2
+H2
ꢀ2
+NH3
ꢀ
NH3
+NH3
ꢀNH3 or ꢀBA
rate is defined here as:
ꢕꢖꢍꢔꢋꢊꢔꢗꢐ
ꢕꢘ
1
+H2
ꢀH2
ꢄ ꢃ
ꢅ.
H
N
ꢖꢏꢐ
N
Thus, the reaction rate is given by the initial rate of reagent conꢀ
sumption divided by the mass concentration of platinum per reaꢀ
DBI
DBA
ꢀ
3
gent volume (C , with units; g m ). Reagent conversion (X) is
Pt
Scheme 1. Possible reaction pathways in the hydrogenation of
benzonitrile (BN). The hydrogenation of BN results in the
formation of benzylamine (BA) through the intermediate benꢀ
zylideneimine (BI). Condensation of BA and BI occurs
through the intermediate alpha aminodialkylamine (BIBA) and
Nꢀbenzylidenebenzylamine (DBI) to dibenzylamine (DBA).
Hydrogenolysis yields toluene from DBA and BA. The direct
hydrogenolysis of BIBA to DBA is also possible. The reagent
and main products have been boxed.
defined as a ratio of the consumed reagent (C – C) to the initial
0
concentration (C0):
ꢖ ꢛ ꢖ
ꢚ
ꢖꢚ
ꢙ ꢃꢅ
3
3
. Results
.1 Textural characterization
6
8
The use of microwave synthesis for MILꢀ101(Cr)
results in
very homogeneous MOF crystals, making separation of the MOF
69ꢀ70
phase from unreacted terephthalates
straightforward. The
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optimized procedure for the impregnation of the metal precursor
0.05 the supertetrahedra of MILꢀ101 are filled, with increasing
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involved the use of waterꢀethanol mixtures in combination with
ultrasonication. The latter was found crucial: without the use of
ultrasonication during the wet impregnation step, the majority of
platinum was deposited on the outer surface of MILꢀ101(Cr) crysꢀ
tals (Fig. S6a).
pressure, the medium cavities start being filled at P/P = 0.1,
while the larger cavities are filled at relative pressures of 0.2.
0
The apparent BET surface areas are listed in table 1 along with
ICP Pt/Cr and XPS Pt/Cr atomic ratio analysis. Loadings of 1
wt% of Pt hardly result in any surface area loss. In contrast, a
considerable loss is observed for the used catalyst, and this loss
increases with the catalyst usage. After 180 h of use the 1.2 wt%
platinum impregnated MILꢀ101 loses ~ 23% of its surface area.
This area loss was most noticeable in the case of linoleic acid
hydrogenation, in other cases the largest area loss was less than 11
% for the hydrogenation of pure hexadecene (solvent free) after
100 h. The spent catalyst could be reactivated by means of an
overnight heat treatment at 443 K under hydrogen atmosphere,
this resulted in the elimination of weakly adsorbed hydrocarbons,
as followed from the TGA analysis (For TGA before and after
reactivation please refer to the supporting information; S2).
Xꢀray diffraction patterns of the unmodified MILꢀ101(Cr) (MILꢀ
1
01(Cr) as prepared), partially reduced hexachloroplatinic acid
impregnated MILꢀ101 (‘MILꢀ101(Cr) Pt partially reduced’), platꢀ
inum impregnated MILꢀ101 catalyst (‘MILꢀ101(Cr) Pt fully reꢀ
duced’) and the used platinum impregnated MILꢀ101 catalyst
0
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0
1
2
3
4
5
6
7
8
9
0
(‘MILꢀ101(Cr) used catalyst’) are illustrated in figure 1. Here,
partial reduction refers to reduction by formaldehyde, while comꢀ
plete reduction refers to the use of an additional step with a hyꢀ
drogen gas stream at 373 K (For the full diffraction pattern please
refer to the supporting information; S1). The collected diffraction
patterns match that of the simulated extended MTN topology of
69ꢀ71
MILꢀ101(Cr) found in literature
in all cases. The crystallinity
of the produced samples is affected by the hexachloroplatinic acid
impregnation, although this change is subtle. It can also be deꢀ
duced that the used catalyst maintains its phase structure even
after extensive usage. The diffraction peak height ratios are the
same in all samples; however after the wet impregnation step
samples have less clearly defined peaks while peak intensities are
unaffected.
1000
750
500
250
0
MIL-101(Cr) Pt
used catalyst
MIL-101(Cr) Pt
fully reduced
MIL-101(Cr) as prepared
MIL-101(Cr) Pt fully reduced
Used catalyst - 24 hours
Used catalyst - 180 hours
MIL-101(Cr) Pt
partially reduced
0
0.2
0.4
0.6
0.8
1
P / P0
MIL-101(Cr) as prepared
MIL-101(Cr) Calculated
Figure 2. Nitrogen adsorption isotherms for MILꢀ101(Cr) as preꢀ
pared, fresh platinum impregnated MILꢀ101 catalyst (MILꢀ
1
01(Cr) Pt fully reduced) and used platinum impregnated MILꢀ
101 catalyst after 24 and 180 h for the hydrogenation of linoleic
acid. Solid black data points represent adsorption, grey data points
represent desorption.
2
4
6
8
10
12
14
16
2θ / o
67 ꢀ
N adsorption
2
ICP
XPS
Figure 1. Xꢀray diffraction patterns of MILꢀ101(Cr) calculated
6
9
, the unmodified MILꢀ101(Cr) (MILꢀ101(Cr) as prepared), parꢀ
tially reduced hexachloroplatinic acid impregnated MILꢀ101
MILꢀ101(Cr) Pt partially reduced), platinum impregnated MILꢀ
01 as the prepared catalyst (MILꢀ101(Cr) Pt fully reduced) and
BET surface area
2
ꢀ1
Pt/Cr
ꢀ
Pt/Cr
(m g )
(
1
MILꢀ101(Cr)
as prepared
MILꢀ101(Cr) Pt
fully reduced
Used catalyst
24 hours
2210
ꢀ
the used platinum impregnated MILꢀ101 catalyst after 180 h for
the hydrogenation of linoleic acid (MILꢀ101(Cr) used catalyst) .
2180
0.12
0.11
0.09
0.261
2
120
ꢀ
ꢀ
The nitrogen adsorption isotherms for MILꢀ101(Cr) as prepared
and Milꢀ101(Cr) Pt fully reduced, before and after catalytic testꢀ
ing, shown in Figure 2, all correspond well with previously reꢀ
ported isotherms for MILꢀ101(Cr). At low relative pressures (P/P0
Used catalyst
180 hours
1680
Table 1. Calculated BET surface areas, atomic ratio Pt/Cr
calculated from XPS data and the Pt/Cr atomic ratio obtained
from ICP for unmodified MILꢀ101 (MILꢀ101 as prepared),
=
0.2), two steps are observed which are attributed to the filling of
the two different cavities in MILꢀ101. At relative pressures below
ACS Paragon Plus Environment

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platinum impregnated MILꢀ101 catalyst (MILꢀ101(Cr) Pt fully
reduced) and used platinum impregnated MILꢀ101 catalyst
after 24 and 180 h for the hydrogenation of linoleic acid (used
catalyst – 24 and 180 h).
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
In Figure 3, the three characteristic ν(CO) bands can be observed
ꢀ
1
at 2193, 2200 and 2207 cm to various degrees in all measured
3+
samples attributed to the presence of open Cr sites. The heteroꢀ
3+
geneous nature of Cr sites is ascribed to the presence of fluoride
77
ions on the chromium trimers (HF being the source of fluoride
ions during MOF synthesis). These bands are assigned to CO
coordinated at Lewis acid sites. By increasing the reduced platiꢀ
3
.2 FTIR spectroscopy
Figure 3 illustrates the measured spectra in the region of interest
ꢀ1
ꢀ
1
(
2060 – 2220 cm ) for a single batch of prepared sample after
num content in the sample bands at 2193 and 2207 cm become
less distinct; this has been associated with the formation of platiꢀ
num nanoparticles in close proximity of chromium trimers. The
various treatments. In Figure 3; MILꢀ101(Cr) Pt loaded refers to
hexachloroplatinic acid adsorbed by MILꢀ101(Cr), this is done by
removing the formaldehyde reducing agent from the wet impregꢀ
0
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
area of these bands also decreased as the Pt becomes the domiꢀ
ꢀ
1
nation procedure. The band observed at 2099 cm is associated
nant form of platinum present in the sample. The average size of
the Pt nanoparticles in the fresh catalyst has been determined by
CO chemisorption to be 4.3 nm, corresponding with a dispersion
0
72ꢀ76
with Pt ꢀCO species
and is only visible in samples that conꢀ
tain the reduced hexachloroplatinic acid. The physisorption of CO
ꢀ
1 77
ꢀ1
70–81
is observed at 2138 cm
Bands observed at 2148 cm are asꢀ
of 27%
, assuming a CO/Pt ratio of unity. This calculated size
signed to cationic platinum species and are a strong indicator for
of the platinum nanoparticles exceeds the size of a single MILꢀ
2+
72–76
the formation of Pt ꢀCO upon CO dosing
. It is interesting
1
01 cage.
2+
that ν(Pt ꢀCO) bands are only clearly observed in the partially
reduced platinum loaded sample, and almost not at all in the hexꢀ
achloroplatinic acid loaded MILꢀ101(Cr). We associate this pheꢀ
3
.3 X-ray photoelectron spectroscopy
ꢀ
nomenon with the fact that Cl ligands are removed upon treatꢀ
The surface composition of partially and fully reduced platinum
loaded MILꢀ101 catalyst has been analyzed by XPS. The comꢀ
plete spectral survey showing Pt 4f, C 1s, N 1s, O 1s and Cr 2p is
shown in Figure 4, including the deconvolution of the Pt 4f range.
ment with H at moderate temperatures, allowing coordination of
2
CO.
0
Three different platinum species can be found, namely Pt (72.20
2160
and 75.53 eV), PtO (73.70 and 77.03 eV) and PtCl (80.28 eV).
The formation of PtO is due to the exposure of the sample to amꢀ
bient air atmosphere (70 ꢀ 74), while the presence of PtCl indiꢀ
cates that the sample has not been fully reduced under the experiꢀ
mental conditions (MILꢀ101(Cr) Pt partially reduced). Using the
sensitivity factors, the atomic percentages of Cl to platinum has
been calculated to be less than 0.01. Typical binding energy valꢀ
ues have been observed for C 1s at 284.5 (CꢀC/CꢀH), 285.66 (Cꢀ
O), 288.52 (OꢀC=O) and 290.76 (C=O) eV. The N 1s and O 1s
peaks have also been observed, although little information can be
taken from these peaks. The binding energy values observed for
Cr 2p are 577.19, 586.78eV both correspond to typical binding
MIL-101(Cr) Pt
fully reduced
2099
2
148
MIL-101(Cr)
Pt partially
reduced
2207
2
157
MIL-101(Cr)
Pt loaded
3+
energies for Cr . Other oxidation states of chromium are not
2200
observed, so the chromium trimers are not chemically modified
by the platinum precursor during impregnation or during the reꢀ
ducing steps. The fully reduced sample (MILꢀ101(Cr) Pt fully
reduced) shows a binding energy of 75.53 eV for the Pt 4f 7/2 and
2
193
2
138
MIL-101(Cr)
as prepared
7
2.20eV for the 4f 5/2.
a)
O 1s
2220
2180
2140
2100
2060
O KW
Wavenumber / cm-1
Cr 2p
C 1s
Figure 3. Inꢀsitu FTIR spectra of CO adsorption at 143 K on
MILꢀ101(Cr) as prepared, MILꢀ101(Cr) Pt loaded, MILꢀ101(Cr)
Pt partially reduced, and MILꢀ101(Cr) Pt fully reduced are measꢀ
ured.
N 1s
C 1s
Pt 4f
Cl 1p
1
200 1100 1000
900
800
700
600
500
400
300
200 100
0
Binding Energy / eV
ꢀ1
The band centered at 2160 cm corresponds to CO interacting
b)
c)
Pt 4f
Pt 4f
with Brønsted acid species found in the samples (75), this band is
ꢀ
1
red shifted to 2157 cm in samples where hexachloroplatinic acid
is present. The OH groups identified could arise from strongly
bound ethanol molecules that remain in the sample after the wet
impregnation step, despite vacuum treatments. It is highly unlikeꢀ
ly that these are terminal OH groups found from PtO formed on
PtO
Pt0
Pt0
PtO
PtCl
0
0
Pt
PtO
Pt
the surface of Pt nanoparticles, as these are generally observed at
ꢀ1 78
3
497 and 3544 cm
. Due to the inert atmosphere measured
samples have been exposed to, and the pretreatment of samples
ꢀ
1
prior to measurements, such bands at 3497 and 3544 cm have
not been observed.
85
80
75
70
65
85
80
75
70
65
Binding energy / eV
Binding energy / eV
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The unmodified MILꢀ101(Cr) was inactive for all test reactions
Figure 4. a) XPS survey spectrum of the MILꢀ101(Cr) Pt partialꢀ
ly reduced catalyst and the deconvolution of Pt 4f region (70ꢀ80
eV) showing the various platinum oxidation states for b) the MILꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
under the selected conditions. In the case of olefin hydrogenation,
platinum on alumina demonstrated hardly selectivity for octene
over hexadecene, but the reaction run time was significantly
shorter, with complete conversion achieved within 90 minutes.
Figure 6 illustrates one of the runs carried out with the 1.2 wt%
platinum loaded MOF composite catalyst. The conversion of ocꢀ
tene and hexadecene is plotted along with the ratio of this converꢀ
sion (integral selectivity). Clearly, at the reaction start a high seꢀ
lectivity is shown for octane hydrogenation (at octene conversion
of 7% the octene/hexadecene selectivity ratio is 28). This preferꢀ
ential hydrogenation changes rapidly within the first two hours of
the reaction when more than 60% of octene is consumed. After
this point, the consumption rate (slope of the plotted conversion)
of hexadecene becomes comparable to that of octene as the reacꢀ
tion proceeds further. After four hours, just over 97% of octene is
hydrogenated and after about six hours the reaction is completed.
Only after four reaction hours the octene/hexadecene selectivity
matches that initially observed for platinum on alumina: 1.5. For
the octene/hexadecene hydrogenation, the reference catalyst TOF
1
01(Cr) Pt partially reduced and c) the MILꢀ101(Cr) Pt fully
reduced.
3
.4 Scanning-transmission electron microscopy (STEM)
Figure 5 shows a STEM micrograph obtained from a 1.2 wt%
platinum MILꢀ101(Cr) Pt fully reduced catalyst. The platinum
nanoparticles all are dispersed throughout the sample with mean
diameters of 5 ±0.5 nm, which are in agreement with the values
found by FTIR transmission spectroscopy combined with CO
adsorption. The platinum nanoparticles are almost exclusively
found inside the MILꢀ101 crystal and mostly in the outer region.
By the comparison of ICP and XPS results, the bulk distribution
of Pt across the framework can be deduced. Comparison between
the measured Pt/Cr atomic ratio in the bulk (0.12), with XPS
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(Pt/Cr=0.261), widely accepted as a surface analysis based techꢀ
nique, indicates that the vast majority of platinum in the (inner)
cages is close to the outer surface of the MILꢀ101 crystals, in an
eggꢀshell configuration. Additionally, the comparison of SEIꢀ
components, a technique applied here to show platinum nanoparꢀ
ticles (white spots) at the external surface of the MILꢀ101 crystal,
with the HAADF images that show all platinum nanoparticles in
the crystal, evidences the scarcity of platinum nanoparticles at the
outer surface of the crystals. Inꢀdepth analysis using Energy Disꢀ
persive XꢀRay Analysis (EDX) confirms that platinum nanopartiꢀ
cles are being imaged.
ꢀ
1
amounted to 21.0 s (at ≈16 min, octene conversion of 27%)
ꢀ
1
while that for the platinum loaded MOF composite was 9.3 s (at
20 min, octene conversion of 12%) (for the details of the referꢀ
≈
ence catalyst please refer to the supporting information; S3).
In the selective hydrogenation of pure benzonitrile, toluene and
ammonia were not observed when using the MOF based catalyst,
while over Pt/alumina toluene these were formed. Only benzylaꢀ
mine and dibenzylamine were observed for the MOF catalyst
(Fig. 7) At the start of the reaction the integral benzylaꢀ
mine/dibenzylamine selectivity is 15. This value declines steeply
over the duration of 100 h that the reaction was allowed to proꢀ
ceed and comes to a value of 2. A maximum yield of 60% is
achieved for benzylamine with a selectivity ratio of 6.5 at approxꢀ
imately 50 h. In literature supported platinum has been extensiveꢀ
5
2, 56
ly shown to be highly selective towards dibenzylamine
. This
has been is confirmed for the reference Pt on alumina catalyst,
where dibenzylamine was the major component of the products,
with a maximum integral DBA/BA selectivity of 4.2 at approxiꢀ
mately 9.5 h. Byproducts ammonia and toluene where detected in
nearly all samples. It is striking that this selectivity is reversed in
favor of benzylamine when hydrogenation occurs using PtꢀMILꢀ
101(Cr) catalyst (sample MILꢀ101(Cr) Pt fully reduced) (comparꢀ
ison made at 50% conversion of benzonitrile, 42% yield of benꢀ
zylamine). The TOF of the platinum on alumina was calculated to
ꢀ
1
53
be 0.8 s at 92 min (from literature ) while the platinum loaded
ꢀ1
MOF composite performed slightly worse with 0.5 s (at 5.5
hours).
In the hydrogenation of linoleic acid, cis/trans isomerization was
not observed during the course of the reaction. The initial product
ratio oleic acid/stearic acid started initially at 12 but this deꢀ
creased to 1.5 after 50 h (Fig. 8). This oleic acid is obtained diꢀ
rectly after the reaction start, while stearic acid shows a sigmoidal
profile, indicating being a consecutive reaction product. After 25
h, the production rate of stearic acid is in the same order of magꢀ
nitude as that of oleic acid. When comparing results in figure 8
with reference runs performed using platinum on alumina, there is
no significant difference to distinguish the two catalysts. TOF
numbers for the reference alumina and the MOF catalyst were
Figure 5. (S)TEM images showing HAADF (left) and SEIꢀ
components (right) of 1.2 wt% MILꢀ101(Cr) Pt fully reduced
catalyst at various magnifications.
ꢀ4 ꢀ1
found to be 1.5 x 10
s (at 9 h, oleic acid yield of 9.1%) and 8.4
ꢀ5 ꢀ1
x 10 s (taken at ≈25.5 h, oleic acid yield of 2.1%), respectively.
For reference run profiles and repeated runs using PtꢀMILꢀ
101(Cr) catalyst please refer to supporting information; S4.
3.5 Catalytic performance testing
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a) 1.0
30
a) 1.0
0.8
20
15
10
5
Benzylamine
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Dibenzylamine
2
2
5
0
0
0
0
0
.8
.6
.4
.2
0.6
15
0.4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Octene
1
5
0
0
Hexadecene
0.2
0.0
0.0
0
5
0
1
2
3
4
5
6
0
25
50
75
100
t / h
t / h
b) 0.6
b) 1.0
2
Benzylamine
Dibenzylamine
Toluene
0
0
0
0
0
.8
.6
.4
.2
.0
4
3
2
1
0
0.4
0.2
0.0
1
Octene
Hexadecene
0
0
1
2
3
0
5
10
t / h
t / h
Figure 6. Conversion (primary yꢀaxis) and the integral selectivity
conversion ratio octane/hexadecene, secondary yꢀaxis) versus
Figure 7. Yield (primary yꢀaxis) and the integral selectivity
BA/DBA or DBA/BA ratio; secondary yꢀaxis) versus time proꢀ
(
(
time profiles for the hydrogenation of a 1:1 mixture of 1ꢀoctene
and 1ꢀhexadecene over a) PtꢀMILꢀ101(Cr) catalyst and b) platiꢀ
num on alumina. Conditions: 91 mmol total olefin/mg Pt at reacꢀ
tion start, 1.5 bar hydrogen, 308 K.
files for the solvent free benzonitrile hydrogenation over a) Ptꢀ
MILꢀ101(Cr) catalyst and b) platinum on alumina. Conditions:
3
3
6.5 mmol benzonitrile/mg Pt at reaction start, 20 bar hydrogen,
08 K.
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Page 8 of 12
1
1
5
0
5
ty associated to open Cr(III) sites decreases with the introduction
of platinum nanoparticles, indicating that platinum is preferentialꢀ
ly accommodated in close proximity to the chromium trimers.
Oliec acid
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Stearic acid
0
0
.2
.1
The selectivity observed for the hydrogenation of selected alpha
olefins over platinum impregnated MILꢀ101(Cr) catalyst is atꢀ
tributed to the difference in chain length of substrate molecules
and the relative molecular masses. Shape of substrate molecules
does not and should not play any major role in the achieved reꢀ
sults as the windows are sufficiently large to allow substrate molꢀ
0
69–72, 84
ecules to enter the cages
. With the WheelerꢀWeisz moduꢀ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
lus greater than 0.15 for the range of characteristic lengths for the
produced catalyst, the criterion for negligible intraparticle mass
85ꢀ87
transport effects in steady state is not fulfilled
. So, that the
reaction is operated in the mass transport limiting regime, is
abundantly clear from the significantly longer duration that it
takes for MOF composite catalyst to complete the reaction comꢀ
pared to platinum on alumina (For the WheelerꢀWeisz calculation
please refer to the supporting information; S6). The factor two
difference in the chain lengths of the olefins used determines fastꢀ
er transport of 1ꢀoctene to the active sites and thus a preferential
selectivity for 1ꢀoctene is observed until this substrate is depleted.
0.0
0
50 100 150 200 250 300 350
t / h
Figure 8. Yield (primary yꢀaxis) and integral selectivity oleꢀ
ic/stearic acid (secondary yꢀaxis) versus time profiles for the solꢀ
vent free linoleic acid hydrogenation over a PtꢀMILꢀ101(Cr) cataꢀ
lyst. Conditions: 26 mmol linoleic acid/mg Pt at reaction start, 20
bar hydrogen, 308 K.
Such high selectivities have not been reported before under solꢀ
88–92
vent free conditions
.
The striking selectivity for benzylamine when hydrogenating
using PtꢀMILꢀ101(Cr) catalyst can be interpreted when considerꢀ
ing the limited space (steric hindrance) caused by the deposition
of Pt nanoparticles in the cages. The result is the blocking of reacꢀ
tion pathway by steric constraints; which has resulted in dibenzylꢀ
amine being marginally formed. A small fraction of Pt nanopartiꢀ
cles at the outer surface of the catalyst, as observed in SEIꢀ
components images, is primarily responsible for the formation of
dibenzylamine. When comparing results to what have been previꢀ
ously reported for platinum based catalysts, it becomes apparent
4. Discussion
Platinum can be encapsulated in the MILꢀ101(Cr) metal organic
framework with minimal localized damage of the support scafꢀ
fold. The obtained Pt particles are slight bigger than the size of the
82
cavities of the material, inferring that some partial structure
collapse takes place upon reduction and formation of the nanoparꢀ
ticles, as observed by the slight loss of crystallinity. However, this
partial collapse does not seem to affect accessibility of the catalytꢀ
ic sites. Even after extensive usage little loss of crytallinity is
observed; the loss that is observed is caused mostly by attrition
due to stirring in the reactor vessel. The resulting catalyst is active
in the solvent free hydrogenation of double bonds in alkenes and
unsaturated fatty acids and of benzonitrile. Differences in selectivꢀ
ities have been observed in comparison with a Pt on alumina cataꢀ
lyst and depending on the reactant, while the activity (TOF) is
slightly lower. This is attributed to shape selectivity aspects and to
the structure of the MOF catalyst, as substantiated further below.
It has been found that sonication is critical for achieving the reꢀ
ported desirable high Pt dispersion inside the MOF . Removing
the sonication from this procedure produces comparable disperꢀ
sions as that of purchased platinum on alumina catalyst. (For an
overview of a sonication free prepared MILꢀ101(Cr) catalyst
please refer to the supporting information; S5). The combination
of an acidic treatment and growth of nanoparticles in the cages
that exceed their size can result in local damage of the framework
during the catalyst preparation. This alongside interference from
the MOF’s high surface area and the presence of poorly crystalꢀ
that this selectivity has been turned around. Conventionally, platiꢀ
53, 55ꢀ57
num favors dibenzylamine over benzylamine
been extensively shown for various supports.
which has
The evolution of observed products for the hydrogenation of linoꢀ
leic acid shows the similar behavior of the PtꢀMILꢀ101(Cr) and
the reference catalyst, although at a much lower rate. The similar
product scope is attributed to the small differences in size between
the possible reaction products. These results are in line with other
catalysts such as palladium on carbon, for which products of douꢀ
85
ble bond migration are also observed . Under the pressures conꢀ
sidered here these byproducts are not observed, but the oleic and
stearic acid profiles are undoubtedly the same for both catalysts.
Solvent free hydrogenation of linoleic acid is strongly limited by
the accessibility of the platinum, which in this case is exclusively
the Pt located on the outer surface of the catalyst. Platinum on
alumina is better accessible and thus resulting in the observed
higher rate.
8
1ꢀ83
line oxide Pt phases (so called ‘XRD amorphous’ Pt)
has
For all reactions, the observed selectivities were found to be indeꢀ
pendent of the number of runs a batch of catalyst had been used
for. This is despite a small lose in the turnovers, clearly observed
in the case of the alpha olefin mixture and benzonitrile hydroꢀ
genation. Even in combination with the loss of surface area and
slight loss of crystallinity; no significant change in the relevant
selectivities has been observed. It is thus justified that the accessiꢀ
bility to the active sites in the catalyst has not been altered during
the course of catalytic testing.
resulted in the loss of XRD pattern quality when comparing preꢀ
and postꢀimpregnation results. Based on the absence of surface
area loss it can be inferred that the acidic treatment and nanopartiꢀ
cle growth did not have a significant effect on the overall integrity
of the framework. With the comparison of XPS, ICP results and
the applied imaging techniques, the bulk distribution of Pt across
the framework has been deduced. From the calculated Pt/Cr atomꢀ
ic ratios, we conclude that the vast majority of platinum in the
MOF cages is close to the outer surface of the MILꢀ101 crystals,
in an eggꢀshell configuration. Brønsted and Lewis acid sites have
been identified in all MOF samples using inꢀsitu IR spectroscopy
with CO as probe molecule. It can be concluded that Lewis acidiꢀ
5. Conclusions
Highly dispersed platinum nanoparticles have been successfully
incorporated in the MILꢀ101(Cr) framework using wet impregnaꢀ
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tion in combination with a twoꢀstage reduction step. It has been
10. Horike, S.; Dinca, M.; Tamaki, K.; Long, J. R. J. Am. Chem.
Soc. 2008, 130, 5854ꢀ5855.
1. Corma, A.; García, H.; Llabrés i Xamena, F. Chem. Rev. 2010,
110, 4606–4655.
2. Adamsa, R.; Carsona, C.; Warda, J.; Tannenbaumb, R.; Koros,
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shown that platinum catalysts with a loading of 1.2 wt% and an
average particle size of 4.3 nm according to CO chemisorption
can be easily prepared. These particles are larger than cages of
MILꢀ101. It has been deduced that the platinum nanoparticles
reside inside of the pores of the framework and are in close proxꢀ
imity to the chromium trimers found in MILꢀ101(Cr) and close to
the particle surface, in an eggꢀshell configuration. The oxidation
state of platinum was determined using XPS, which showed the
presence of a minute amount of PtCl as well as PtO that had
1
1
W. Micropor. Mesopor. Mater. 2010, 131, 13–20.
13. Gu� cu� yener, C.; van den Bergh, J.; Gascon, J.; Kapteijn, F.
J. Am. Chem. Soc. 2010, 50, 17704ꢀ17706.
1
4. Pan, Y.; Lai, Z. Chem. Commun. 2011, 47, 10275ꢀ10277.
0
formed from the reduced Pt .
1
5. Remi, J. C. S.; Rémy, T.; Van Hunskerken, V.; van de Perre,
0
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S.; Duerinck, T.; Maes, M.; De Vos, D.; Gobechiya, E.;
Kirschhock, C. E. A.; Baron, G. V.; Denayer, J. F. M. Chem. Sus.
Chem. 2011, 4, 1074ꢀ1077.
The selective hydrogenation of an olefin mixture of 1ꢀoctene and
1
ꢀhexadecene demonstrated mass transport limitations giving rise
to enhanced selectivities. This selectivity was observed prior to 1ꢀ
octene depletion and is attributed to the difference of the chain
lengths of substrate molecules that results in mass transport limiꢀ
tations in the MOF pores. In the hydrogenation of benzonitrile,
selectivity of supported platinum nanoparticles toward dibenzylꢀ
amine was flipped towards benzylamine by placing the active
sites inside the MOF pores structure. This sudden change in selecꢀ
tivity has been attributed to transition state selectivity. The selecꢀ
tive hydrogenation of linoleic acid was also investigated, however
higher selectivities could not be achieved by the platinum MOF
catalyst when compared to platinum on alumina.
1
6. van den Bergh, J.; Gucuyener, C.; Pidko, E. A.; Hensen, E. J.
M.; Gascon, J.; Kapteijn, F. Chem. Eur. J. 2011, 17, 8832–8840.
17. Zou, X.; Zhang, F.; Thomas, S.; Zhu, G.; Valtchev, V.;
Mintova, S. Chem. Eur. J. 2011, 17, 12076–12083.
1
8. Llabrés i Xamena, F. X.; Corma, A.; Garcia, H. J. Phys.
Chem., C 2007, 111, 80ꢀ85.
9. Alvaro, M.; Carbonell, E.; Ferrer, B.; Llabrés i Xamena, F. X.;
1
Garcia, H. Chem. Eur. J. 2007, 13, 5106ꢀ5112.
20. International Roadmap for Semiconductors, Semiconductor
IndustryAssociation, 2007.
2
1. Srivastava, S.; Kotov, N. A. Soft Matter 2009,5, 1146–1156.
Author information
2
1
2. Zhang, W. X.; Yang, S. H. Acc. Chem. Res. 2009, 42, 1617–
627.
Tel.+31 (0)15 278 9820, Fax.+31 (0)15 278 5006, Eꢀmail:
H.Khajavi@tudelft.nl, J.Gascon@tudelft.nl
23. Toksoz, S.; Acar, H.; Guler, M. O. Soft Matter 2010, 6, 5839–
5
849.
Notes
2
4. Allendorf, M. D.; Schwartzberg, A.; Stavila, V.; Talin, A. A.
The authors declare no competing financial interest
Chem. Eur. J. 2011, 17, 11372ꢀ11388.
5. Khajavi, H.; Gascon, J.; Schins, J. M.; Siebbeles, L. D. A.;
Kapteijn, F. J. Phys. Chem. C 2011, 115, 12487ꢀ12493.
6. Wang, M.; Guo, S.; Li, Y.; Cai, L.; Zou, J.; Xu, G.; Zhou, W.;
Zheng, F.; Guo, G. J. Am. Chem. Soc. 2009, 131, 13572–13573.
7. Harbuzaru, B. V.; Corma, A.; Rey, F.; Jordá, J. L.; Ananias,
D.; Carlos, L. D.; Rocha, J. Angew. Chem. Int. Ed. 2009, 48,
476ꢀ6479.
2
Acknowledgements
The authors would like to thank Shell for hosting this research at
Shell Technology Centre Amsterdam, and Shell Researcher Sipke
Wadman for fruitful discussions and his support.
2
2
6
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