Preparation of SBA-15 supported Pt/Pd bimetallic catalysts using supercritical fluid reactive deposition: How do solvent effects during material synthesis affect catalytic properties?

Article abstract of DOI:10.1039/c6gc02490d

Supercritical fluid reactive deposition (SFRD) using supercritical carbon dioxide (scCO₂) as the solvent and the reaction medium was employed to generate mono- and bi-metallic Pt and Pd nanoparticles (NPs) on SBA-15 as a mesoporous support material. Highly uniform particles in the 5 nm range were deposited preferentially inside the pores detected by transmission electron microscopy (TEM). The materials were further characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). Coupling of Scanning Transmission Electron Microscopy (STEM) with EDX demonstrated the formation of alloy-type structures for the bimetallic Pt/Pd particles. Comparison of the SFRD-process using scCO₂ with the impregnation method using conventional liquid solvents showed that the material characteristics were similar to deposition from n-pentane, but significantly different from deposition from toluene or THF. The differences could be rationalized on the basis of characteristic physico-chemical solvent properties. Notably, the choice of solvent during the preparation was also reflected in the catalytic performance of the materials for hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL), whereby the nature of the support and the Pt/Pd ratio were additional parameters controlling the activity with the SFRD approach. Bimetallic Pt/Pd particles were found to result in superior activity as compared to either of the individual monometallic species. Thus, the use of SFRD allows one to avoid organic solvents during the catalyst preparation, leading even to improved catalytic properties in favourable cases.

Full text of DOI:10.1039/c6gc02490d

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Qiao, N. Said,
M. Rauser, K. Yan, F. Qin, N. Theyssen and W. Leitner, Green Chem., 2016, DOI: 10.1039/C6GC02490D.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 11
View Article Online
DOI: 10.1039/C6GC02490D
Preparation of SBA–15 supported Pt/Pd bimetallic nano–catalysts
using supercritical fluid reactive deposition and their application
in hydrogenation of levulinic acid to γ–valerolactone: How do
solvent effects during material synthesis affect catalytic
properties?
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Y. Qiao,a, † N. Said,a,b, † M. Rauser,b K. Yan,a,b F. Qin,a,b,c N. Theyssen,a and W. Leitner*a,b
Supercritical fluid reactive deposition (SFRD) using supercritical carbon dioxide (scCO2) as solvent and reaction medium
was employed to generate mono- and bimetallic Pt and Pd nanoparticles (NPs) on SBA–15 as mesoporous support
material. Highly uniform particles in the 5 nm range were deposited preferentially inside the pores according to
transmission electron microscopy (TEM) and further characterization including X–ray diffraction (XRD), energy–dispersive
X–ray spectroscopy (EDX), and X–ray photoelectron spectroscopy (XPS). Coupling of Scanning Transmission Electron
Microscopy (STEM) with EDX demonstrated the formation of alloy-type structures for the bimetallic Pt/Pd particles.
Comparison of the SFRD-process using scCO2 with the impregnation using conventional liquid solvents showed that the
materials characteristics were similar to deposition from n–pentane, but significantly different from toluene or THF. The
differences could be rationalized on basis of characterstic physico-chemical solvent properties. Notably, the choice of
solvent during preparation was also reflected in the catalytic performance of the materials for hydrogenation of levulinic
acid (LA) to γ–valerolactone (GVL), whereby the nature of the support and the Pt/Pd-ratio were additional parameters to
control the activity with the SFRD approach. Bimetallic Pt/Pd particles were found to result in superior activity as
compared to either of the individual monometallic species. Thus, the use of SFRD allows to avoid organic solvents during
the catalyst preparation leading even to improved catalytic properties in favourbale cases.
dride methods (BM),11 photo–assisted depositions,12 sonoche-
mical approaches13 and deposition–precipitation techniques
(DPM).14
1. Introduction
The use of supported noble metal catalysts for hydrogenation
processes is ubiquitous in industrial application and academic
research.1 The performance of the catalyst for specific appli-
cations is fundamentally determined by the composition and
structure of the metal component and its interaction with the
support, which in turn can be influenced strongly by the prepa-
ration method.2 As support materials, mesoporous silica com-
bining uniform pore size distribution with a large surface area
are finding widespread interest.3 SBA–15 is one of the most
extensively studied mesoporous materials since its discovery in
1998.4 Corresponding metal catalysts are of considerable inte-
rest and have been successfully implemented for many tasks,5
whereby metal nanoparticles (NPs) based on Pt and Pd are
being widely studied due to their versatile application profile.6
The deposition of NPs on mesoporous supports can be achie-
ved using a range of techniques, such as post–grafting,7 incipi-
ent wet impregnation (the most common technique em-
ployed),7,8 homogeneous deposition precipitation (HDP),9
chemical vapor deposition,10 formic acid (FAM) and borohy-
Supercritical fluid reactive deposition (SFRD) has been
introduced as an attractive method for the generation of well-
defined nanoscale structures.5c,15 This process involves the
generation of metal deposits by hydrogenation of suitable
metal precursors (mostly organometallic complexes) from
their solutions in a supercritical fluid (SCF), mostly supercritical
carbon dioxide (scCO2). The formed “naked” metal can agglo-
merate in a controlled way to metallic films as shown in the
pioneering work by Watkins16, 17 or to NPs of a wide variety of
metals including Pt, Pd, Ru and Rh. Originally, this process was
called chemical fluid deposition (CFD). Major contributions to
the preparation of NPs by this approach originated from the
groups of Erkey,5b,18 Wai19 and others20. Potential benefits for
the control of the seeding and particle growth processes have
been associated with the combination of gas-like and liquid-
like properties in the supercritical state. Since supercritical
fluids have good transport properties, these media facilitate
the impregnation of the solutes into complex and finely struc-
tured architectures. At the same time, the complete miscibility
of hydrogen with scCO2 avoids any additional phase boundary
leading to a very efficient reduction. The reason why scCO2 has
been used in most of these studies, is related to its favorable
properties21: It has significant solubilizing power for suitable
metal precursors, is cheap, non–toxic, and non–flammable. In
addition, its relatively low critical temperature and pressure (Tc
= 31oC, pc = 73.8 bar) make the handling quite straightforward
using standard high pressure technology.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 11
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
Journal Name
In the present study, we focused on the deposition of aim to derive structure/activity-relationships that could be
mono- and bimetallic Pt and Pd NPs inside the pores of SBA– corroborated with the physico-chemical properties of the
15.5d–5f Monometallic depositions of Pd on SBA-15 using the media. The influence of the silica support and the Pd/Pt-ratio
SFRD approach were reported previously by the groups of in bimetallic systems was also assessed.
Beyon22 and Cabañas23 using palladium hexafluoroacetylace-
tonate [Pd(hfac)2] as “CO2-philic” precursor complex.24 Beyon
2. Results and discussion
et al. generated initially PdO that was reduced post-synthesis
under hydrogen atmosphere. A preferred particle formation
2.1. Catalyst preparation and material characterization
inside the pores was observed as compared to the use of EtOH
The principle of the applied SFRD process is illustrated in
or THF as liquid solvents, but no studies on catalytic activity
Scheme 1. The synthesis of mesoporous SBA–15 and the metal
were reported. Cabañas et al generated the particles by SFRD
precursors were carried out according to literature procedures
with independent impregnation and reduction steps and
as described in the supporting information (SI). SBA–15 with a
demonstrated catalytic activity of the materials for standard
pore size of 6 nm was chosen as the standard support materi-
hydrogenation reactions. Bimetallic PtPd depositions were
al. Both the support material and the metal complexes were
done in a sequential manner on carbonic supports for synthe-
sizing electrocatalysts by the group of Erkey.25 We chose the
filled into a stainless-steel high pressure reactor which was
sealed, pressurized with a weighed amount of CO2 to adjust a
direct co-reduction with H2 as method for the generation of
bimetallic particles using (η3–allyl)(η5–cyclopentadienyl)palla-
density of 0.7 g/mL and heated to 50 °C under continuous
stirring at the final pressure of roughly 150 bar. Details of the
dium(II), [CpPd(allyl)], and dimethyl(1,5–cyclooctadiene)plati-
apparatus and the experimental procedure are summarized
num(II), [(COD)PtMe2], as metal precursors since both com-
also in the SI. Under these conditions, the metal precursors
pounds have a sufficient solubility in scCO2 and the hydrogena-
were dissolved in scCO2, transported into the pores, and
tion products of the labile ligands can easily be removed
adsorbed on the support material. After 2 h, the pressure was
during the depressurization due to their volatility and high
CO2-solubility.16b, The catalytic properties of the materials
26
increased further by addition of hydrogen, whereby the
amount was adjusted with a mass-flow controller to achieve a
with different Pt:Pd ratios were assessed for the hydroge-
ten-fold excess of molecular hydrogen relative to the precur-
nation of levulinic acid (LA) to γ-valerolactone (GVL) as a
sor. The reduction of the precursors lead to metallic deposits
of nanoscale particles that are preferentially located inside the
pores of the SBA-15 material (vide infra).
prototypical process for the conversion of lignocellulosic
biomass substrates.27 In particular, the SFRD approach using
scCO2 was compared to conventional impregnation using liquid
organic solvents such as n–pentane, toluene, and THF with the
Scheme 1 Synthesis of SBA–15 supported bimetallic Pt/Pd NPs by supercritical fluid reactive deposition (SFRD) using scCO2 as transport and
reaction medium.
As prototypical potential catalysts, the characterization of the the hydrogenated ligands with the SCF upon venting as
bimetallic materials 3% Pt1–Pd3/SBA–15 (metal loading: 3 wt%; confirmed by further reduction of the organic content by 40%
n(Pt) : n(Pd) = 1 : 3) obtained with this method was carried out upon post-synthesis extraction with scCO2 (Table S1).
in detail. In order to get a deeper insight into the effect of the
Low angle and wide angle XRD patterns revealed the
supercritical medium in this process, the data are directly characteristic intensive peaks at 2θ = 0.9 - 1.0° corresponding
compared to materials obtained from impregnation with liquid to the (100) diffraction peak of the two–dimensional hexago-
organic solvents under otherwise identical conditions. N2 nal structure of SBA–15 together with the well–resolved (110)
adsorption and desorption curves confirmed the uniform and (200) diffraction peaks for all metal deposited materials
mesoporous structure of the synthesized SBA–15 (BET surface (Figure 1), indicating that the mesoporous structure was not
area: 705 m2/g, pore diameter: 6 nm).28
Only trace amounts of organic residues were detected by range from 25–55° 2
affected during the deposition process. High angle XRD in the
further corroborated the dispersion of
θ
elemental analysis on the material prepared by the SFRD Pt and/or Pd on the SBA–15 support. Relative sharp peaks
method.29 This can be attributed to the efficient removal of were observed for the material synthesized in THF, indicating
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 3 of 11
Journal Name
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
the formation of larger metal crystallites by deposition from and incomplete deposition. The XPS spectra (Figure S1)
this solvent as compared to the other media.
revealed signals corresponding to Pd (340.0 eV: 3d3/2 and
335.0 eV: 3d5/2) and Pt (71.0 eV: 4f7/2 and 74.3 eV: 4f5/2) in
their metallic state only, indicating that oxidized species are
not present in appreciable amounts. Comparison of the data
from bulk sensitive EDX with surface sensitive XPS analysis
reveals that the metal content is significantly lower on the
surface (Table 1). This demonstrates that the depositions occur
preferentially inside the pores with very little differentiation
between the different media. However, there are some
differences between the distributions of the individual metals.
Most significantly, the surface spectra of the sample synthe-
sized with THF showed almost exclusively the characteristic
peaks for Pt. This indicates a significant segregation between
the two metals in the final material when this solvent is used
during the preparation.
The characterization of the materials by transmission
electron microscopy (TEM) revealed very significant
differences in the structure of the NPs. Representative TEM
images of 3%Pt1–Pd3/SBA–15 synthesized in scCO2 and
different organic solvents are displayed in Figure 2a–2d. The
pore size of the support material determined from TEM (5-6
nm) correlates very well with that from N2 sorption analysis (6
nm). The materials obtained via the SFRD technique from
scCO2 were found to contain well–dispersed spherical NPs of
small size with a quite uniform distribution. The mean
diameters were determined to 5.0 +/- 1.1 nm, which matches
quite well with the pore diameter (Figure 2a/2a’). The
obtained bimetallic particles showed a significant narrower
size distribution than the ones obtained by Erkey and
Figure 1 Low angle (top) and wide angle (bottom) XRD patterns of
3%Pt1-Pd3/SBA-15 synthesized in (a) scCO2; (b) n-pentane; (c) toluene;
(d) THF and (e) pure SBA-15 before deposition.
The total metal loading and metal ratio in the bulk material as coworkers in a sequential deposition approach on carbon.25
determined by EDX analysis reflect within experimental error Particles of similar shape and size (4.3 +/- 1.0 nm) were
largely the amounts adjusted during the preparation method obtained by liquid phase impregnation using n–pentane as
(Table 1). The higher Pt:Pd ratio detected in the SFRD solvent (Figure 2b/2b’). In sharp contrast, the micrographs of
approach does not mirror the applied precursor composition materials obtained by use of toluene and THF revealed the
in a perfect manner. This might be the result of a lower presence of much larger agglomerates. The metal ensembles
solubility of the Pd complex in scCO2 compared to the one of are not spherical anymore, but rod–shaped structures of
the Pt precursor (both solubilities were not measured). In case substantial length are formed (Figures 2c and 2d). In particular
of toluene as solvent, the data indicate a slightly lower loading with THF, these wire-type structures extend to up 100 nm in
than expected which might result from less efficient reduction length, consistent with the results from XRD measurement.
Table 1 Results from EDX and XPS analysis: Metal loading and metal ratio in the bulk material and on the surface for 3% Pt1–Pd3/SBA–15 as
synthesized using SFRD and liquid phase processes with different solvents.a
EDX (bulk)
XPS (surface)
Solvent
deposition
efficienyb
97%
metal loading [wt%]
n (Pt) : n (Pd)
metal loading [wt%] n (Pt) : n (Pd)
b
scCO2
2.9
2.7
2.4
2.9
1.0 : 2.3
1.0 : 3.3
1.0 : 3.3
1.0 : 2.7
1.5
1.4
1.1
1.3
1.0 : 2.0
1.0 : 2.3
90%
n–Pentane
Toluol
80%
97%
1.0 : 4.3
1.0 : ≤ 0.5c
THF
a) Conditions: m (SBA–15) = 300 mg, m [(COD)PtMe2] = 6.0 mg (97% purity, 17.5 µmol), m [CpPd(allyl)] = 11.2 mg (52.8 µmol), T = 50 °C, t
(impregnation) = 2 h, t (reduction) = 30 min, p (H2) = 0.3 bar, V (solvent) = 20 mL; b) m (CO2) = 39.0 g (ρ = 0.7 g mL–1); c) the Pd signal is just above
the detection limit making a quantitative analysis impossible. b) The percentage values describe the ratio between the metal amount detected
by EDX and the amount of metal applied for deposition (3 wt% in total) in form of the given precursors and ratios.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 11
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
Journal Name
a
b
c
a
b
d
Figure 2 TEM analysis of 3%Pt1–Pd3/SBA–15 synthesized in (a) scCO2 (including NP size distribution e); (b) n–pentane (including NP size
distribution f); (c) toluene; (d) THF.
The internal structure of the spherical bimetallic particles The formation of the bimetallic particles is a complex process
obtained from scCO2, n–pentane and THF was analyzed with a involving transport and reactivity phenomena, both of which
combination of Energy–Dispersive X–ray spectroscopy (EDX) may be significantly influenced by the physico-chemical
and Scanning Transmission Electron Microscopy (STEM) (Figure properties of the different media. Corroborating the data of
3). Composition analysis for 10 individual particles synthesized the material characterization with typical solvent parameter
by SFRD using scCO2 revealed that the Pt-Pd composition reveals some interesting trends (Table 2). The formation of
varied between 1:1 and 1:9, consistent with an average 1:3 well-dispersed spherical particles can be plausibly associated
ratio. Analysis of 17 individual particles obtained by impregna- with the low surface tension and low viscosity scCO2 and n–
tion using n-pentane showed a slightly larger variation of Pt-Pd pentane that certainly facilitate the transport of the precursors
ratios between 1:1 and 1:17 (Figure S2). This observation is into and within the mesopores. Both solvents are also readily
even more pronounced in THF: Analysis of 8 individual partic- removed from the materials, leaving no or very little chance
les showed a Pt-Pd ratio between 1:0.7 and 1:250 (Figure S2). for post-synthesis agglomeration of primary particles during
Whereas the particles obtained from n-pentane show a Pd-rich work-up. The significantly higher H2 availability in these two
core and a Pt-rich shell, the particles produced by the SFRD media might be beneficial for the reduction step. Interestingly,
method have an almost perfectly random distribution of the a higher partial pressure of hydrogen is reported to control
two metals in an alloy-type structure. THF behaves again quite particle growth of Pd to a higher extend than Pt.31 The
different here, resulting preferentially in a separated structure extremely low polarity and negative values for polarizability
with monometallic domains and, to a much lesser extent, in are also distinct common features of these solvents. It has
particles of an alloy structure (please see also Figure S3).30
been shown that polar/non-polar interfaces are beneficial
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 5 of 11
Journal Name
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
for controlled particle growth in liquid/liquid systems under reflected in these criteria contributes favorably to the most
32
phase-transfer conditions or in micelles.31, Related effects uniform distribution and reaction of the precursors as
might apply between the highly polar solid phase and the non- indicated by the close to perfect homogeneity in size, shape,
polar medium. The property profile of the supercritical fluid and alloy-type structure.
EDX PdL_ROI
EDX PtL_ROI
Overlay
EDX PdL_ROI
EDX PtL_ROI
Overlay
EDX PdL_ROI
EDX PtL_ROI
Overlay
EDX-image
EDX-image
EDX-image
Figure 3 STEM-EDX analysis of 3%Pt1–Pd3/SBA–15 synthesized in scCO2 (left), n–pentane (middle) and THF (right).
In sharp contrast, the solvents with a surface tension in the an organometallic point of view, this difference might at least
range of 25-30 mN m-1 lead to significant larger aggregates in part be responsible for the distinct deposition behavior of
that tend to cluster in certain areas of the mesoporous support the two metal precursors observed in this solvent. Whereas
materials. This reflects the reduced possibility to penetrate the [CpPd(allyl)] is a coordinatively and electronically fully satu-
porous structure resulting in transport limitation for precur- rated 18e complex, the platinum precursor [(cod)PtMe2] is a
sors as well as for the reducing agent hydrogen. A striking square planar 16e species. This opens the possibility for strong
difference between THF and the other solvents is the fact that solute-solvent interactions between the Pt-complex and THF
the cyclic ether is a coordinating solvent that can undergo that are not possible in any of the other combinations.
strong interactions with transition metal complexes. This is Although other factors can clearly also play a role, this may
reflected indirectly by the hydrogen-acceptor value of the contribute to the very high Pt/Pd ratio at the outer surface of
Kamlet-Taft parameters as proxy or directly in the coordina- the material from this solvent as evidenced by the XPS data.
tion ability scale according to Díaz-Torrez and Alvarez.37 From
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 11
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
Journal Name
Although the corroboration with individual parameters correlated with the catalytic properties of the materials. We
does of course not capture the entire complexity of the have chosen the hydrogenation of levulinic acid (LA) to
γ
–
preparation process, it may help to choose the most valerolactone (GVL) to probe this in the present case, because
appropriate solvents for the decoration of finely structured this reaction is of significant current interest in the area of
materials with (bi-)metallic particles. This becomes particularly selective biomass conversion.
relevant if the observed material characteristics can be
Table 2 Characteristic solvent properties of the media used for catalyst synthesis.
Hydrogen
solubility
ratio at
25 °Ca
Hydrogen-
bond accep-
ting ability
Β34
Surface
tension33
/ mN m-1
Viscosity
at 50 °C
/ µPa s
Polarity /
Coordinating
Solvent
Polarizability ability index
π*34
α37
[fully
miscible]d
scCO2
[0]
57b, c
– 0.07e
– 0.47e
n.d.
n–Pentane
Toluene
THF
15.5
28.5
26.4
177c
424[32]
359[32]
2.734,35
1.135
1.035
0.00
0.11
0.55
– 0.08
0.54
– 2.1
– 1.2
– 0.3
0.58
a) Given are ratios of Henry constants normalized on H2 solubility in THF (the mole fraction of hydrogen in THF with the dosed hydrogen amount
of 0.7 mmol at 25 °C is calculated as 8.1 • 10-5 [36]). b) Value is given for a pressure level of 15 MPa. c) Data is calculated via the NIST webpage
“Thermophysical Properties of Fluid Systems” which can be found under http://webbook.nist.gov/chemistry/fluid/. d) Hydrogen is fully miscible
in CO2 at temperatures ≥ 31 °C. In terms of the normalization this accounts for a factor of 9.8 in comparison to the hydrogen concentration in
THF. e) Determined at 9 MPa and 60 °C.
2.2. Catalytic performance of the materials
Using the standard material 3% Pt1–Pd3/SBA–15 synthesized
by the SFRD approach led to a nearly quantitative yield for the
hydrogenation of LA to GVL in aqueous solution under a
standard set of reaction conditions (p = 100 bar H2 at r.t.; T =
220 °C; t = 4 h; see SI for details). A stirring speed of 400 rpm
was found to be sufficient to operate in the kinetic regime in
the given set-up (Figure S4). The reaction resulted still in a high
yield of 90.4% at an initial hydrogen pressure as low as 20 bar.
Nevertheless, the higher pressure was adjusted throughout
the further investigations for practical reasons to provide
enough equivalents of H2 for the standard scale (5 g LA, 5 mL
H2O, in a 28 mL reactor vessel). The general procedure proved
highly reproducible and very robust, giving under different
conditions uniformly excellent selectivities >99.5% over more
than 60 independent experiments. Compared with values from
literatures,40, 43 the materials 3% Pt1–Pd3/SBA–15 synthesized
in scCO2 showed favorable activity achieving total TON values
up to 7200 and total TOF values up to 3600 h-1 in the
hydrogenation of LA to GVL.
Levulinic acid has been identified as a key platform chemical
accessible from lignocellulosic biomass38 and significant pro-
gress has been made recently towards industrial scale produc-
tion.39 In particular, its sequential hydrogenation to GVL, 1,3-
pentanediol, and 2-methyltetrahydrofurane offers access to
interesting chemical products and fuels.40 The selective hydro-
genation to GVL (Scheme 2) was proposed as promising
pathway for the valorization of lignocellulosic materials in
particular by seminal work of Horvath.41 Numerous catalysts
have been developed meanwhile for this transformation, with
Ru-based systems being particularly active even at ambient
temperature.27a Productivities and activities as measured by
turnover numbers (TON) and turnover frequencies (TOF) for
standard palladium and platinum catalysts were found to be
significantly lower,42 however, they offer very high selectivity
even under forcing conditions as hydrogenation beyond the
ester level is typically not pronounced with these metals.
Operating at high temperatures might be a preferred process
window as it allows efficient heat integration for exothermic
hydrogenation reactions.
The mesoporous SBA-15 support proved superior when
compared to amorphous silica and SBA with a larger pore size
of 12 nm (Figure S5). Whereas the larger pore size SBA
provided also excellent conversion and selectivity after 4 h
under standard conditions, a significantly higher yield was
obtained with SBA-15 (6 nm) when both materials were
employed at lower catalyst loadings and shorter reaction times
of 2 h (6 nm: 80.8%; 12 nm: 31.5%).
Scheme 2 Hydrogenation of LA to GVL applying the SBA–15 supported
Although we cannot fully exclude a certain degree of
degradation of SBA-15 under the given reaction conditions,44
the bulk material appeared to be entirely intact retaining the
bimetallic Pd/Pt catalysts.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 7 of 11
Journal Name
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
mesoporous structure at least after four catalytic runs showed almost no effect. At higher Pd-ratios, however, the
according to TEM measurements (Figure 4). The average size bimetallic systems showed significantly higher conversion and
of the nanoparticles increased a little bit and were determined
as 6.7 +/- 1.6 nm.
yields. Pure Pd, in contrast, was again less effective. In general,
the data indicate an increase in activity by about 50% for the
Pt/Pd = 1:1 and Pt/Pd = 1:3 composition as compared to the
Figure 4 TEM images of 3%Pt1–Pd3/SBA–15 synthesized in scCO2 after
two individual monometallic catalysts. Interestingly, a physical
four catalytic runs.
mixture of the pure Pt and Pd materials in 1:3 ratio gave
similar results than the pure systems (45% GVL yield), clearly
Furthermore, metal leaching into solution was found to be
demonstrating that the higher activity results from the
small amounting to 5 ppm Pt (detection limit 1.5 ppm) and 1
presence of bimetallic particles.
ppm Pd (detection limit 0.3 ppm) measured in a collected
product mixture of four consecutive runs with the same
Figure 6 Activity tests of LA to GVL using different metal compositions
catalyst. These data correspond to 16% (Pt) and 2.5% (Pd) of
supported on SBA–15. Reaction conditions were identical as described
the original metal loading on the support. The stability was
in Figure 5 except m (catalyst) = 25 mg and t = 2 h. In each case GVL
also reflected in the catalytic performance, whereby only a
selectivity exceeds 99%. All activity tests were reproduced at least two
small decrease of activity was observed after the first recycling
times; ranges are indicated.
with constant yields over at least the next three runs (Figure
5).
Most significantly, the differences in material properties
resulting from the use of different solvents were also reflected
clearly in the catalytic performance (Figure 7). Only 30% yield
could be achieved with the catalyst materials synthesized
using toluene or THF, all other factors being identical. As these
two solvents lead to larger metal ensembles, the ratio of
metals exposed on the surface is obviously reduced. In
addition it is expected that the observed formation of large
agglomerates or wires blocks the pores completely, thus
hindering the necessary substrate and product transport to
and from the active centers to a higher extend.
In contrast, the catalysts synthesized in scCO2 and n–pentane
gave ca 80% yield after 2 h reaction time with very little – if
any – difference in activity (see Figure 8). This provides direct
evidence for the claimed benefits of a SFRD approach for
Figure 5 Reusability of 3% Pt1–Pd3/SBA–15 synthesized in scCO2 for LA
catalyst preparation, leading to a homogeneous distribution of
hydrogenation to GVL. Reaction conditions: m (catalyst) = 100 mg;
small particles within confined environments. However, it also
m (LA) = 5.0 g; 5.0 mL deionized water; 100 bar H2 at r.t.; T = 220 °C; t =
demonstrates that these effects can be achieved in a similar
4 h; stirring speed: 400 rpm; V (autoclave) = 28 mL. In each case GVL
way by choosing a liquid organic solvent with very similar key
selectivity exceeds 99%. All activity tests were performed at least two
properties (viscosity, polarizability, and coordination ability).
times, ranges are indicated.
The observed more uniform mixing of the two metals within
the individual particles in case of the supercritical fluid appears
to be less critical in the present reaction, but might be an
The influence of the Pt/Pd-ratio on the catalytic performance
additional discrimination factor in other cases.
is depicted in Figure 6. Doping the Pt-catalyst with 25% Pd
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 8 of 11
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
Journal Name
pressure equipment due to the use of compressed hydrogen in
the reduction step. Thus, the advantageous use of non-
flammable and not VOC rated scCO2 as solvent can be
achieved in similar or even identical equipment. In comparison
to other liquid solvents such as toluene or THF, the SFRD
approach proved even significantly superior as these solvents
resulted in large agglomerates of the NPs and hindered
formation of alloy-type bimetallics, leading to reduced
catalytic performance. We hope that our findings stimulate
further research activities on the use of scCO2 as medium both
in material science and catalyst development.
Acknowledgements
This work was performed as part of the Cluster of Excellence
‘‘Tailor–Made Fuels from Biomass’’, which is funded by the
Excellence Initiative of the German federal and state
governments to promote science and research at German
universities. The authors gratefully acknowledge the following
people from the Max–Planck–Institut für Kohlenforschung for
support with analytical measurements and data analysis:
Corinna Heidgen (GC), Bernd Spliethoff (TEM), Hans-Josef
Figure 7 Activity tests of LA hydrogenation to GVL using 3% Pt1–
Pd3/SBA–15 synthesized in different media. Reaction conditions were
identical as described in Figure 6. In each case GVL selectivity exceeds
99%. All activity tests were performed at least two times, ranges are
indicated.
Bongard (STEM
/ EDX), Dr. Claudia Weidenthaler, Jan
Ternieden and Ulrich Holle (XRD and XPS), Dr. Guanghui Wang
and Dr. Wolfgang Schmidt (N2 sorption), as well as Dr. Dong Gu
for helpful and enthusiastic discussions. Fruitful scientific
exchange with Prof. Regina Palkovits, RWTH Aachen
University, is also gratefully acknowledged.
References
a) G. Ertl, H. Knözinger, J. Weitkamp, Handbook of
Heterogeneous Catalysis, Wiley–VCH, Weinheim, 1997,
1277. b) B. C. Gates, Supported Metal Cluster Catalysts, in
Preparation of Solid Catalysts (eds G. Ertl, H. Knözinger
and J. Weitkamp), Wiley–VCH, Weinheim, 1999, 371; c) B.
Corain, G. Schmid, N. Toshima, Metal Nanoclusters in
Catalysis and Materials Science: The Issue of Size Control,
Elsevier B.V.: Amsterdam, 2007, 3.
1
Figure 8 Reaction time profile of LA hydrogenation with catalysts
synthesized in scCO2 and n–pentane. Ranges of experimental results
are indicated by error bars (partially very small, which some of them
are not exceeding the shown data point of the arithmetic mean).
2
a) J. M. Thomas, B. F. G. Johnson, R. Raja, G. Sankar, P. A.
Midgley, Acc. Chem. Res., 2003, 36, 20; b) X.–F. Yang, A. Q.
Wang, B. T. Qiao, J. Li, J. Y. Liu, T. Zhang, Acc. Chem. Res.,
2013, 46, 1740; c) U. Jung, A. Elsen, Y. Y. Li, J. G. Smith, M. W.
Small, E. A. Stach, A. I. Frenkel, R. G. Nuzzo, ACS Catal., 2015,
5, 1539; d) J. T. Feng, Y. F. He, Y. N. Liu, Y. Y. Du, D. Q. Li,
Chem. Soc. Rev., 2015, 44, 5291; e) C. Copéret, A. Comas–
Vives, M. P. Conley, D. P. Estes, A. Fedorov, V. Mougel, H.
Nagae, F. Núñez–Zarur, P. A. Zhizhko, Chem. Rev., 2016, 116,
323.
Conclusions
The synthesis of supported NPs by SFRD is an interesting
approach for noble metal catalyst production avoiding the use
of organic solvents. Our results presented here show that
mono- as well as bimetallic NPs can be easily deposited
uniformly on mesoporous supports. The obtained composite
materials synthesized by combined impregnation and
reduction from scCO2 in a sequential operation in a single
processing unit showed high activity for hydrogenation of LA
to GVL, achieving high TON and TOF values at almost perfect
selectivity. Using n-pentane instead of scCO2 provided
materials with similar material characteristics and catalytic
properties. Notably, both preparation methods require high
3
4
a) F. Q. Tang, L. L. Li, D. Chen, Adv. Mater., 2012, 24, 1504; b)
W. M. Xuan, C. F. Zhu, Y. Liu, Y. Cui, Chem. Soc. Rev., 2012,
41, 1677; c) I. I. Slowing, J. L. Vivero–Escoto, B. G. Trewyn, V.
S.–Y. Lin, J. Mater. Chem., 2010, 20, 7924; d) N. Song, Y. W.
Yang, Chem. Soc. Rev., 2015, 44, 3474.
a) D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chmelka, G. D. Stucky,
J. Am. Chem. Soc., 1998, 120, 6024; b) D. Y. Zhao, J. L. Feng,
Q. S. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelka, G. D.
Stucky, Science, 1998, 279, 548; c) M. Vallet–Regí, L. Ruiz–
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 9 of 11
Journal Name
González, I. Izquierdo–Barba, J. M. González–Calbet, J. Mater.
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
Smirnova, U. Kitkamthorn, M. Aindow, L. Türker, İ. Eroğlu, C.
Erkey, J. Power Sources, 2008, 179, 532.
Chem., 2006, 16, 26; d) F.–S. Xiao, Top. Catal., 2005, 35, 9; e)
D. M. Ford, E. E. Simanek, D. F. Shantz, Nanotechnology,
2005, 16, S458; f) V. Alfredsson, H. Wennerström, Acc. Chem.
Res., 2015, 48, 1891.
19 a) X. R. Ye, Y. Lin, C. M. Wai, Chem. Commun., 2003, 642; b) X.
R. Ye, Y. Lin, C. Wang, M. H. Engelhard, Y. Wang, C. M. Wai, J.
Mater. Chem., 2004, 14, 908; c) C. H. Yen, K. Shimizu, Y.–Y.
Lin, F. Bailey, I. F. Cheng, C. M. Wai, Energy & Fuels, 2007, 21,
2268.
5
a) I. Lee, M. A. Albiter, Q. Zhang, J. P. Ge, Y. D. Yin, F. Zaera,
Phys. Chem. Chem. Phys., 2011, 13, 2449; b) Y. Zhang, C.
Erkey, J. Supercrit. Fluids, 2006, 38, 252; c) J. D. Holmes, D. M.
Lyons, K. J. Ziegler, Chem. Eur. J., 2003, 9, 2144; d) C. Liu, R.
Tan, N. Y. Yu, D. H. Yin, Microporous Mesoporous Mater.,
2010, 131, 162; e) L. Wang, C. Li, S. H. Jin, W. Z. Li, C. H. Liang,
Catal. Lett., 2014, 144, 809; f) J. Zhu, T. Wang, X. Xu, P. Xiao,
J. Li, Appl. Catal. B: Environ., 2013, 130–131, 197.
a) I. Eryazici, C. N. Moorefield, G. R. Newkome, Chem. Rev.,
2008, 108, 1834; b) W. T. Yu, M. D. Porosoff, J. G. G. Chen,
Chem. Rev., 2012, 112, 5780.
20 a) M. Türk, Particle Formation with Supercritical Fluids in
Supercritical Fluid Science and Technology Series (Ed. E. Kiran)
Vol. 6, Elsevier Amsterdam, 2014; b) J. Bu, J.–L. Liu, X.–Y.
Chen, J.–H. Zhuang, S.–R. Yan, M.–H. Qiao, H.–Y. He, K.–N.
Fan, Catal. Commun., 2008, 9, 2612; c) C. S. Lyn, F. L.–Y. Lam,
X. Hu, W. Y. Tam, K. M. Ng, J. Phys. Chem. C., 2008, 112,
10068; d) M. Hiramatsu, T. Machino, K. Mase, M. Hori,
K. Kano, J. Nanosci. Nanotechnol., 2010, 10, 4023.
21 a) N. Tanchoux, W. Leitner, Handbook of Green Chemistry
and Technology (eds J. Clark, D. Macquarrie), 2002, 482; b)
W. Leitner, Acc. Chem. Res., 2002, 35, 746; c) M. Chatterjee,
T. Ishizaka, H. Kawanami, ACS Symposium Series, 2015, 1194,
191.
6
7
8
C.–H. Tu, A.–Q. Wang, M.–Y. Zheng, X.–D. Wang, T. Zhang,
App. Catal., A, 2006, 297, 40.
a) S. Abate, P. Lanzafame, S. Perathoner, G. Centi, Catal.
Today, 2011, 169, 167; b) S. Boujday, J. Blanchard, R.
Villanneau, J.–M. Krafft, C. Geantet, C. Louis, M. Breysse, A.
Proust, ChemPhysChem, 2007, 8, 2636.
22 S.-S. Lee, H.-I. Park, B.-K. Park, S.-H. Byeon, Mater. Sci. Eng.,
B, 2006, 135, 20.
9
D. H. Yin, L. S. Qin, J. F. Liu, C. Y. Li, Y. Jin, J. Mol. Catal. A:
Chem., 2005, 240, 40.
23 a) J. Morère, M. J. Tenorio, M. J. Torralvo, C. Pando, J. A. R.
Renuncio, A. Cabañas, J. Supercrit. Fluids, 2011, 56, 213; b) M.
J. Tenorio, C. Pando, J. A. R. Renuncio, J. G. Stevens, R. A.
Bourne, M. Poliakoff, A. Cabañas, J. Supercrit. Fluids, 2012,
69, 21.
10 A. Q. Zhao, X. F. Zhang, X. Chen, J. C. Guan, C. H. Liang, J.
Phys. Chem. C, 2010, 114, 3962.
11 J. R. C. Salgado, J. J. Quintana, L. Calvillo, M. J. Lázaro, P. L.
Cabot, I. Esparbé, E. Pastor, Phys. Chem. Chem. Phys., 2008,
10, 6796.
24 S. Kainz, D. Koch, W. Baumann, W. Leitner, Angew. Chem.,
1997, 109, 1699.
12 a) K. Fuku, T. Sakano, T. Kamegawa, K. Mori, H. Yamashita, J.
Mater. Chem., 2012, 22, 16243; b) P. S. Qiao, S. H. Zou, S. D.
Xu, J. J. Liu, Y. L. Li, G. C. Ma, L. P. Xiao, H. Lou, J. Fan, J.
Mater. Chem. A, 2014, 2, 17321.
25 A. Bayrakҫeken, B Cangül, L. C. Zhang, M. Aindow, C. Erkey,
Int. J. Hydrogen Energy, 2010, 35, 11669.
26 O. Aschenbrenner, N. Dahmen, K. Schaber, E. Dinjus, Ind. Eng.
Chem. Res., 2008, 47, 3150.
13 N. Perkas, Z. Y. Zhong, J. Grinblat, A. Gedanken. Catal. Lett.,
2008, 120, 19.
27 a) W. R. H. Wright, R. Palkovits, ChemSusChem, 2012, 5, 1657;
b) D. M. Alonso, S. G. Wettstein, J. A. Dumesic, Green
Chem., 2013, 15, 584; c) W. Luo, M. Sankar, A. M. Beale, Q.
He, C. J. Kiely, P. C.A. Bruijnincx, B. M. Weckhuysen, Nat.
Commun., 2015, 6: 6540.
14 S. Ajaikumar, M. Golets, W. Larsson, A. Shchukarev, K.
Kordas, A. R. Leino, J. P. Mikkola, Microporous Mesoporous
Mater., 2013, 173, 99.
15 a) J. X. Yang, T. Hasell, D. C. Smith, S. M. Howdle, J. Mater.
Chem., 2009, 19, 8560; b) C. Erkey, J. Supercrit. Fluids, 2009,
47, 517; c) A. H. Romang, J. J. Watkins, Chem. Rev., 2010, 110,
459.
28 J. J. Zhu, K. Kailasam, X. Xie, R. Schomaecker, A. Thomas,
Chem. Mater., 2011, 23, 2062.
29 J. M. Blackburn, D. P. Long, J. J. Watkins, Chem. Mater., 2000,
12, 2625.
16 a) J. J. Watkins, J. M. Blackburn, T. J. McCarthy, Chem. Mater.,
1999, 11, 213; b) D. P. Long, J. M. Blackburn, J. J. Watkins,
Adv. Mater., 2000, 12, 913. c) J. M. Blackburn, D. P. Long, A.
Cabañas, J. J. Watkins, Science, 2001, 294, 141.
30 B. J. Hwang, L. S. Sarma, J. M. Chen, C. H. Chen, S. C. Shih, G.
R. Wang, D. G. Liu, J. F. Lee and M. T. Tang, J. Am. Chem. Soc.,
2005, 127, 11140.
31 C. Petit, C. Salzemann, A. Demortiere, Platinum and
Palladium Nanocrystals: Soft Chemistry Approach to Shape
Control from Individual Particles to Their Self-Assembled
Superlattices in Complex-Shaped Metal NPs: Bottom-Up
Syntheses and Applications (Edited by T. P. Sau and A. L.
Rogach), Wiley-VCH, Weinheim, 2012, 305.
17 a) “Chemical Fluid Deposition: Reactive Deposition of Thin
Metal Films from Supercritical Carbon Dioxide Solutions.''
PhD thesis of J. M. Blackburn, 2001; b) “Supercritical fluid
deposition of thin metal films: Kinetics, mechanics and
applications.'' PhD thesis of C. F. Karanikas, 2008.
18 a) C. D. Saquing, T. T. Cheng, M. Aindow, C. Erkey, J. Phys.
Chem. B, 2004, 108, 7716; b) C. D. Saquing, D. Kang, M.
Aindow, C. Erkey, Micro. Meso. Mater., 2005, 80, 11; c) Y.
Zhang, D. Kang, M. Aindow, C. Erkey, J. Phys. Chem. B, 2005,
109, 2617; d) A. Bayrakceken, U. Kitkamthorn, M. Aindow, C.
Erkey, Scr. Mater., 2007, 56, 101; e) A. Bayrakçeken, A.
32 a) M. Brust, M. Walker, D. Bethell, D. J. Schiffrin, R. Whyman,
J. Chem. Soc., Chem. Commun., 1994, 801; b) C. Petit, M. P.
Pileni, J. Phys. Chem., 1988, 92, 2282; c) M. Yashima, L. K. L.
Falk, A. E. C. Palmqvisit, K. Holmberg, J. Colloid Interface Sci.,
2003, 268, 348; d) N. Zhao, W. Nie, J. Mao, D. Wang, Y. Lin, Y.
Fan, Z. Zhao, H. Wei, X. Ji, Small, 2010, 6, 2558.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 10 of 11
View Article Online
DOI: 10.1039/C6GC02490D
ARTICLE
Journal Name
33 D. R. Lide, Handbook of Chemistry and Physics, 84th edition,
CRC Press, 2003.
34 Values for scCO2 are taken from: P. G. Jessop, D. A. Jessop, D.
Fu, L. Phan, Green Chem., 2012, 14, 1245; values for conven-
tional solvents are taken from: Y. Marcus, Chem. Soc. Rev.,
1993, 22, 409.
35 C. L. Young, Solubilizy data series, Volume 5/6, Hydrogen and
Deuterium 1980, 358.
36 E. Brunner, J. Chem. Eng. Data, 1985, 30, 269.
37 R. Díaz-Torres, S. Alvarez, Dalton Trans., 2011, 40, 10742.
38 J. J. Bozell, G. R. Petersen, Green Chem., 2010, 12, 539.
39 http://www.gfbiochemicals.com
40 F. M. A. Geilen, B. Engendahl, A. Harwardt, W. Marquardt, J.
Klankermayer, W. Leitner, Angew. Chem., 2010, 122, 5642;
Angew. Chem. Int. Ed., 2010, 49, 5510.
41 a) I. T. Horvath, H. Mehdi, V. Fabos, L. Boda, L. T. Mika, Green
Chem., 2008, 10, 238; b) H. Mehdi, V. Fabos, R. Tuba, A.
Bodor, L. T. Mika, I. T. Horvath, Top. Catal., 2008, 48, 49.
42 a) K. Yan, T. Lafleur, G. S. Wu, J. Y. Liao, C. Ceng, X. M. Xie,
Appl. Catal., A, 2013, 468, 52; b) L. Corbel-Demailly, B.-K. Ly,
D.-P. Minh, B. Tapin, C. Especel, F. Epron, A. Cabiac, E.
Guillon, M. Besson, C. Pinel, ChemSusChem, 2013, 6, 2388; c)
P. P. Upare, J.-M. Lee, D.-W. Hwang, S. B. Halligudi, Y.-K.
Hwang, J.-S. Chang, J. Ind. Eng. Chem. (Amsterdam, Neth.),
2011, 17, 287.
43 a) L. Deng, J. Li, D.–M. Lai, Y. Fu, Q.–X. Guo, Angew. Chem.
Int. Ed., 2009, 48, 6529; b) L. Deng, Y. Zhao, J. Li, Y. Fu, B. Liao,
Q.–X. Guo, ChemSusChem, 2010, 3, 1172; c) F. M. A. Geilen,
B. Engendahl, M. Hölscher, J. Klankermayer, W. Leitner, J.
Am. Chem. Soc., 2011, 133, 14349; d) J. M. Tukacs, D. Kirάly,
A. Strάdi, G. Novodarszki, Z. Eke, G. Dibó, T. Kégl, L. T. Mika,
Green Chem., 2012, 14, 2057; e) A. M. R. Galletti, C. Anto-
netti, V. De Luise, M. Martinelli, Green Chem., 2012, 14, 688;
f) A. M. Hengne, C. V. Rode, Green Chem., 2012, 14, 1064; g)
Y. Yang, C.-J. Sun, D. E. Brown, L. Q. Zhang, F. Yang, H. R.
Zhao, Y. Wang, X. H. Ma, X. Zhang, Y. Ren, Green Chem.,
2016, DOI: 10.1039/C5GC02802G; h) H. X. Zhang, M. Zhao, T.
J. Zhao, L. Li, Z. P. Zhu, Green Chem., 2016, 18, 2296; i) W. J.
Yang, H. Y. Cheng, B. Zhang, Y. Li, T. Liu, M. L. Lan, Y. C. Yu, C.
Zhang, W. W. Lin, S.-i. Fujita, M. Arai, F. Y. Zhao, Green Chem.
2016, DOI: 10.1039/C6GC00019C; j) Q. Xu, X. L. Li, T. Pan, C.
G. Yu, J. Deng, Q. X. Guo, Y. Fu, Green Chem., 2016, 18, 1287;
k) A. M. Ruppert, M. Jędrzejczyk, O. Sneka-Płatek, N. Keller,
A. S. Dumon, C. Michel, P. Sautet, J. Grams, Green Chem.,
2016, 18, 2014.
44 a) F. Zhang, Y. Yan, H. Yang, Y. Meng, C. Yu, B. Tu, D. Zhao, J.
Phys. Chem. B, 2005, 109, 8723; b) R. A. Pollock, G. Y. Gor, B.
R. Walsh, J. Fry, I. T. Ghampson, Y. B. Melnichenko, H. Kaiser,
W. J. DeSisto, M. C. Wheeler, B. G. Frederick, J. Phys. Chem.
C, 2012, 116, 22802; c) R. A. Mayanovic, H. Yan, A. D. Brandt,
Z. Wang, M. Mandal, K. Landskron, W. A. Bassett,
Microporous Mesoporous Mater., 2014, 195, 161; d) Y. Tang,
Y. Chen, Y. Wu, M. Zheng, C. Zhang, M. Yang, G. Cao,
Microporous Mesoporous Mater., 2016, 224, 420.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 11
Green Chemistry
View Article Online
DOI: 10.1039/C6GC02490D
The choice of reaction media for catalyst synthesis has a
tremendous influence in the hydrogenation of levulinic
acid (LA) to γ–valerolactone (GVL).