Zeolite-Encapsulated Pt Nanoparticles for Tandem Catalysis

Article abstract of DOI:10.1021/jacs.8b09568

Encapsulation of metal nanoparticles in a zeolite matrix is a promising route to integrate multiple sequential reactions into a one-pot and one-step tandem catalytic reaction. We report a cationic polymer-assisted synthetic strategy to encapsulate Pt nanoparticles (NPs) into MFI zeolites. Degrees of encapsulation of Pt NPs in the synthesized catalysts exceeding 90% were demonstrated via kinetic studies of model reactions involving substrates with different molecular dimensions. HZSM-5 zeolite-encapsulated Pt NPs are able to selectively mediate the tandem aldol condensation and hydrogenation of furfural and acetone to form hydrogenated C₈ products with a combined yield of 87%. In contrast, hydrogenation and decarbonylation of furfural dominate on Pt NPs supported on HZSM-5 at otherwise identical conditions. The high selectivity toward the tandem reaction on the encapsulated catalyst is attributed to the distribution of metal and acid sites, which limits the access of furfural to Pt sites and promotes the acid-catalyzed aldol condensation. This is the first demonstration that the product distribution in a tandem reaction is manipulated by tailoring the architecture of catalytic materials via encapsulation.

Full text of DOI:10.1021/jacs.8b09568

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Article
Zeolite Encapsulated Pt Nanoparticles for Tandem Catalysis
Hong Je Cho, Doyoung Kim, Jing Li, Dong Su, and Bingjun Xu
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b09568 • Publication Date (Web): 24 Sep 2018
Downloaded from http://pubs.acs.org on September 24, 2018
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Zeolite Encapsulated Pt Nanoparticles for Tandem Catalysis
Hong Je Cho,† Doyoung Kim,† Jing Li,‡ Dong Su,‡ and Bingjun Xu*,†
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†Department of Chemical and Biomolecular Engineering, University of Delaware, Newark,
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Delaware 19716, United States
‡Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973,
United States
*Email: bxu@udel.edu
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ABSTRACT
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Encapsulation of metal nanoparticles in a zeolite matrix is a promising route to integrate
multiple sequential reactions into a one-pot and one-step tandem catalytic reaction. We report a
cationic polymer-assisted synthetic strategy to encapsulate Pt nanoparticles (NPs) into MFI
zeolites. Degrees of encapsulation of Pt NPs in the synthesized catalysts exceeding 90% were
demonstrated via kinetic studies of model reactions involving substrates with different molecular
dimensions. HZSM-5 zeolite-encapsulated Pt NPs are able to selectively mediate the tandem
Aldol condensation and hydrogenation of furfural and acetone to form hydrogenated C8 products
with a combined yield of 87%. In contrast, hydrogenation and decarbonylation of furfural
dominate on Pt NPs supported on HZSM-5 at otherwise identical conditions. The high selectivity
towards the tandem reaction on the encapsulated catalyst is attributed to the distribution of metal
and acid sites, which limits the access of furfural to Pt sites and promotes the acid-catalyzed
Aldol condensation. This is the first demonstration that the product distribution in a tandem
reaction is manipulated by tailoring the architecture of catalytic materials via encapsulation.
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INTRODUCTION
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Tandem catalysis, which enables multiple consecutive reactions to be conducted in a single vessel
and at similar or identical conditions, is an effective process intensification strategy for chemical
processes by eliminating costly separation steps and increasing energy efficiency.1-3 Catalytic
materials with two or more types of active sites are typically needed to facilitate individual steps
in tandem reactions. Further, to selectively drive tandem reactions, the distribution of different
types of active sites must be tailored for specific reactions.4-11 Metal-acid bifunctional catalysts
are frequently employed to mediate tandem reactions because metal and acid sites each catalyze a
broad but distinct range of reactions.3, 5, 7, 9, 12, 13 However, not all catalytic materials with both acid
and metal sites could guide the tandem reaction with steps catalyzed by these two types of sites in
the desired sequence.5, 7, 13, 14 This could be caused by the exposure of reactants to both acid and
metal sites from the beginning of the reaction, and both metal and acid catalyzed conversions
would occur in parallel rather than in any specific order. This scenario is quite common in
biomass upgrading processes because substrates are often multifunctional and require several
consecutive steps to be converted to desired products.3, 5, 15, 16 Thus, the tailoring distribution of
catalytic sites is an essential element in the catalyst design for tandem reactions.
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One potential strategy of manipulating the distribution of catalytic sites in metal-acid
bifunctional catalysts is to encapsulate metal nanoparticles (NPs) into zeolite matrices, because
this architecture allows a predetermined sequence of reactants accessing different type of catalytic
sites, i.e., reactants have to encounter acid sites in zeolite pores before accessing sites on metal
NPs encapsulated in the zeolite matrix. In addition, encapsulation could suppress the growth and
leaching of metal NPs, thus enhancing the stability of metal sites.13, 17-25 Zeolites are ideal
encapsulating materials due to the high thermal and chemical stability, well-defined microporous
structure, and the versatility to introduce different types of acid sites.19-26
The most reported method to encapsulate metal NPs into zeolites is through post-synthetic
treatments such as ion-exchange and wet impregnation, however, the resulting metal NPs were
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located both in channels/cavities and on the external surface after the calcination and/or reduction
steps.27-31 Recently, much effort has been devoted to developing synthetic strategies for metal NP
encapsulation into zeolites, including a mercaptosilane-assisted synthesis, stabilization of ligands
of metal precursors and zeolite transformation from two-dimension to three-dimension,20, 22-25, 32,
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which typically require special silica source and metal precursors, or only apply to a specific
subset of framework types. Interzeolite transformation has been pioneered by Iglesia and Zones
as an encapsulation strategy by converting larger pore zeolites such BEA and FAU with
imbedded Pt clusters into MFI zeolites with encapsulated metal clusters.21 This method requires a
two-step procedure, as the MFI seeds needed to facilitate the transformation are synthesized in a
separate step.
Herein, we report a cationic polymer-assisted synthetic strategy, which is facile and
potentially general, to directly encapsulate Pt NPs into zeolite matrices with >90% of exposed Pt
surface on encapsulated NPs with a ~95% yield based on the mass of initial synthesis gel. The
sequential Aldol condensation of furfural with acetone and the hydrogenation of the adduct are
employed as the model tandem reaction, which has been proposed as a promising route to
produce renewable fuels.7,
Pt NPs encapsulated in HZSM-5 effectively promotes the
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formation of the hydrogenated Aldol adduct, i.e., products of the tandem reaction, while Pt NPs
supported on HZSM-5 favors the hydrogenation of furfural prior to Aldol condensation under
identical conditions, demonstrating the potential of encapsulated catalysts to facilitate tandem
reactions.
RESULTS AND DISCUSSION
The formation of zeolite-encapsulated metal NPs is attained by introducing cationic polymers as
the linking agent to bind metal precursors to zeolite crystallization domains via electrostatic
interactions (Scheme 1). Polydiallydimethylammonium chloride (PDDA) can electrostatically
2-
interact with both anionic metal precursors, e.g., PtCl6 , and the negatively charged silicate or
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aluminosilicate building blocks of zeolites in the alkaline environment, thus promoting the
encapsulation of the metal precursors into the zeolite matrix during crystallization. Steam-assisted
crystallization is employed to minimize the segregation of the polymer-protected metal
complexes from zeolite lattice by limiting the mobility of metal precursors.37-40 The as-obtained
solid after crystallization is calcined in air to remove all organics, followed by reduction under the
hydrogen atmosphere. Details of the synthesis procedures are provided in the Supporting
Information.
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Scheme 1. Schematic of the strategy for encapsulating Pt nanoparticles into zeolite matrices.
Pt NPs are successfully encapsulated in both siliceous and aluminosilicate MFI zeolites
(denoted as Pt@Si-MFI and Pt@HZSM-5, respectively). The yield of Pt@Si-MFI and
Pt@HZSM-5 based on the mass of the initial synthesis gel is consistently around 95%, which is
significantly higher than that of the interzeolite transformation method.21 Scanning electron
microscope (SEM) images of Pt@Si-MFI and Pt@HZSM-5 show approximately 300 nm sized
zeolite nanocrystals consisting of primary nanoblocks (~50 nm), which are further aggregated
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into larger crystals (Figures 1a, b and S1). X-ray diffraction (XRD) patterns of both samples
confirm the MFI structure, without any phase impurity (Figure 1c).21, 41-43 The Pt loadings of
Pt@Si-MFI and Pt@HZSM-5, determined by X-ray fluorescence (XRF) spectroscopy, are 0.23
wt% and 0.22 wt%, respectively (Table S1). Notably, the peaks associated with metallic Pt (39.8°
and 46.2°) are not observed in the XRD patterns,44, 45 which is attributed to the low Pt loading and
well-dispersed Pt NPs. Energy dispersive spectroscopy (EDS) analysis of Pt@Si-MFI and
Pt@HZSM-5 reveals that the Pt NPs are uniformly distributed throughout the zeolite crystals
(Figures S2 and S3). The average size of Pt particles encapsulated in both Pt@Si-MFI and
Pt@HZSM-5 is around 5.4 nm, estimated from transmission electron microscopy (TEM) images
(Figures 1d, 1e and S4), which is consistent with results determined by the CO chemisorption
(Table S1). Most Pt NPs are larger than the pore dimension of the MFI framework (0.56 nm),41, 42
which is expected to effectively prevent the particles from migrating onto the external surface
through zeolite pores. 27Al MAS NMR spectrum of Pt@HZSM-5 (Figure S5) shows a strong
band centered at 55 ppm, which is assigned to tetrahedrally coordinated Al in zeolites, and a weak
band at -2 ppm, corresponding to extra-framework Al sites.41, 46, 47 This result indicates that the
majority of Al atoms are incorporated in the MFI framework. Further, a similar spectrum is
obtained on HZSM-5 prepared using the same PDDA-assisted method without the addition of the
Pt precursor, indicating that the presence of Pt NPs does not affect the incorporation of
framework Al atoms. EDS analysis of Pt@HZSM-5 show that Al atoms are uniformly distributed
throughout the zeolite crystals (Figure S3). Micropore volumes of Pt@Si-MFI and Pt@HZSM-5
are determined to be 0.13 cm3 g-1 and 0.14 cm3 g-1 by N2 physisorption, which are consistent with
zeolites with an MFI topology.48, 49 Notably, the two encapsulated catalysts exhibit the hysteresis
loops at P/P0 of 0.45-0.90, corresponding to ‘ink-bottle’ type mesopores.50, 51 The mesopores in
the encapsulated zeolites were created by the use of PDDA polymers in the synthesis, as
evidenced by the presence and absence of the hysteresis in the adsorption isotherms of the Si-MFI
zeolite samples prepared with and without PDDA polymers, respectively, with otherwise
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identical procedures (Figures 1f, S6 and S7). TEM images of the as-crystallized samples indicate
that Pt NPs have been formed prior to calcination (Figure S8). It should be noted that the PDDA
polymer, in addition to interacting electrostatically with the Pt precursor and zeolite building
blocks, also functions as a reducing agent to reduce the Pt precursors to form Pt NPs during
zeolite crystallization.44, 52 Density of Brønsted acid of Pt@HZSM-5 is determined to be 68 µmol
g-1 by quantitative transmission FT-IR spectroscopy with pyridine as the probe molecule (Figure
S9 and Table S1).
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Figure 1. SEM images of (a) Pt@Si-MFI and (b) Pt@HZSM-5, (c) XRD patterns of Pt@Si-MFI
and Pt@HZSM-5, high-resolution TEM images of (d) Pt@Si-MFI and (e) Pt@HZSM-5, and (f)
N2 physisorption isotherms of Pt@Si-MFI, Pt@HZSM-5, Si-MFI-PDDA and Si-MFI-no PDDA.
On the plot (f), the isotherms of Pt@Si-MFI and Si-MFI-PDDA and the one of Pt@HZSM-5 are
shifted upward by 2 mmol g-1 and 4 mmol g-1, respectively.
Model reactions with substrates of different sizes provide direct evidence that the
majority of Pt NPs are encapsulated in zeolite matrices. Oxidation of cyclohexanol (Cy6-ol,
kinetic diameter = 0.60 nm) and cyclododecanol (Cy12-ol, kinetic diameter = 0.84 nm) with tert-
butyl hydroperoxide in acetonitrile are employed as model reactions to determine the degree of
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encapsulation of Pt NPs.53 The smaller Cy6-ol can access Pt NPs located on both internal and
external surfaces of the MFI zeolites, whereas the bulkier Cy12-ol can only access Pt NPs located
at the external surface (Figure 2a). To accurately probe the degree of encapsulation of the metal
NPs of the samples, the turnover frequencies (TOFs) normalized by the amount of exposed Pt
atoms, quantified by CO chemisorption, are determined by conducting the model reactions in the
kinetic regime (differential conversions). The ratio between TOFs for Cy6-ol and Cy12-ol (Xsample
= TOFCy6-ol /TOFCy12-ol) can be used as a measure of the extent to which Pt NPs are confined
within zeolite pore structures.21, 22 To control for the slight differences in reactivity of the two
substrates, ratio between TOFs is also determined on Pt NPs supported on non-porous SiO2
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support (XPt/SiO2) (Table S2). The degree of Pt NPs encapsulation (Zsample) is quantified by Zsample
=
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1 – 1/Ysample, in which Ysample = Xsample/XPt/SiO2
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ZPt@Si-MFI and ZPt@HZSM-5 are determined to be
0.91 and 0.92, respectively (Figure 2b, c and Table S2), indicating that >90% of the exposed Pt
metal surface is on Pt NPs encapsulated within the zeolite matrix. In contrast, Pt NPs supported
on HZSM-5 (Pt/HZSM-5) displays a Z value of 0.02, which is consistent with the expectation that
the majority of Pt NPs are located on the external surface of the zeolite when prepared by
impregnation (Figure 2c and S10-S12, and Table S2). Our results are on par with the state-of-the-
art zeolite encapsulated metal NP catalysts in the literature that adopts a similar methodology in
quantifying the degree of encapsulation (Table S3).18, 20, 21, 23, 24 Nevertheless, a small fraction of
Pt NPs is observed on the external surface of Pt@Si-MFI and Pt@HZSM-5 (Figure S13). The
average size of the Pt NPs located on the external surface (~12 nm) is significantly larger than
that of those encapsulated NPs (5.4 nm) based on TEM images, suggesting that encapsulation
limits the particle growth.
The importance of the electrostatic interaction between the cationic PDDA and anionic
Pt precursor is evidenced by the lack of NP encapsulation with a cationic Pt precursor. When
2-
2+
replacing PtCl6 with Pt(NH3)4 as the Pt precursor in the PDDA-assisted synthesis under
otherwise similar conditions, a Z value of 0.17 is obtained for the resulting sample. In addition, a
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substantial amount of Pt NPs that are detached from the zeolite matrix are observed (Table S2 and
Figure S14). This is likely the result of the poor interaction between PDDA and the Pt precursor
in the synthesis gel, leading to the exclusion of Pt from the zeolite matrix. Pt supported on
HZSM-5 prepared by impregnating the cationic Pt precursor on the zeolite leads to a sample with
a Z value of 0.03, confirming that impregnation cannot produce zeolite encapsulated metal NPs.
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Figure 2. (a) Schematic of selective oxidation of cyclohexanol and cyclododecanol over Pt@MFI
and Pt/SiO2, (b) equations used to quantify the degree of Pt NP encapsulation, and (c) Z values
for Pt@Si-MFI, Pt@HZSM-5 and Pt/HZSM-5.
The ability of zeolite encapsulated metal NPs to mediate tandem reactions is
demonstrated with the model system of Aldol condensation of furfural with acetone and the
subsequent hydrogenation of the adduct on Pt@HZSM-5 (Figure 3 and Table S4). A combined
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yield of 87% for hydrogenated Aldol adduct, i.e., 4-(2-furyl)-butan-2-one (FAc-H, 3%) and FAc-
HH (84%), is achieved on Pt@HZSM-5 at 160 °C and 600 psi of H2 for 20 h. The Aldol adduct
4-(2-furyl)-buten-2-one (FAc) from the acid catalyzed Aldol condensation between furfural and
acetone undergoes the hydrogenation of the aliphatic C=C bond to form FAc-H and then the
ketonic C=O bond to FAc-HH (Figure 3a). To the best of our knowledge, this is the highest yield
of C8 hydrogenated Aldol adducts achieved via a one-pot and one-step tandem reaction. Only 6%
of the converted furfural is consumed in the production of furfuryl alcohol (FurOH), 2-
methyltetrahydrofuran (MTHF) and gamma-valerolactone (GVL) before it participates in the
Aldol condensation. The tandem reaction over Pt@HZSM-5 is accelerated at 180 °C for 3 h, with
a slightly lower combined yield of FAc-H and FAc-HH (81%). No C13 product, derived from the
Aldol condensation of FAc and furfural and further hydrogenation, is detected, which could be
attributed to the spatial constraint of the pores in the MFI topology.54 In contrast, Pt/HZSM-5 is
much less selective towards the tandem reaction, with a combined yield of C8 compounds of only
24%. The HZSM-5 support is prepared via the same method used in the synthesis of Pt@HZSM-
5 except for the absence of the Pt precursor to allow a fair comparison (Figures 2c, S5, S9 and
S10, and Table S1). In the case of Pt/HZSM-5, the majority of furfural undergoes
decarbonylation (Group A) or hydrodeoxygenation (HDO, Group B) under identical reaction
conditions to produce 2-methylfuran (MF, 41%), cyclopentanone (CPO, 13%), furan (Fu, 5%)
and levulinic acid/isopropyl levulinate (LA/IL, 4%). The observed difference in product
distribution can be attributed to the different distribution of Pt NPs in the encapsulated and
supported catalysts. Pt NPs in Pt/HZSM-5 are located on the external surface of the zeolite crystal
(Figure 3c), which leads to efficient metal-mediated furfural conversion before the acid-catalyzed
Aldol condensation could occur on the internal surface of the zeolite. In contrast, furfural and
acetone have to encounter acid sites en route to the encapsulated Pt NPs in Pt@HZSM-5, leading
to the preferential conversion of furfural via the Aldol condensation pathway. To support this
interpretation, TOF for the Aldol condensation between furfural and acetone, as well as furfural
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hydrogenation, is determined. TOFs of the Aldol condensation reaction on Pt@HZSM-5,
Pt/HZSM-5 and HZSM-5 are similar (~18 h-1; Figure S15a), suggesting that properties of acid
sites on all three samples are similar. This is expected as all zeolites are synthesized following a
similar procedure. Similarly, TOFs for furfural hydrogenation are also comparable within
experimental errors for Pt@HZSM-5, Pt@Si-MFI, Pt/HZSM-5 and Pt/SiO2, indicating that all
exposed Pt sites are similarly active and encapsulation does not alter the hydrogenation capability
of Pt sites (~2400 h-1, Figure S15b). Thus, the distribution of Pt NPs in different samples must be
responsible for the observed difference in product distribution. The metal-mediated furfural
conversion is much more facile than the acid-catalyzed Aldol condensation (TOFs of the former
are more than two orders of magnitude higher than those of the latter pathway), which is
consistent with the preferential furfural conversion on Pt/HZSM-5 before the Aldol condensation.
Control experiments further confirm that the high yields for the hydrogenated Aldol
adducts on Pt@HZSM-5 cannot be achieved by varying the ratio between metal and acid sites on
non-encapsulated catalysts (Figure 3d). Ratio of Pt and acid sites is varied by preparing a series of
Pt NPs supported on HZSM-5 with varying metal loadings. These samples are denoted as
Pt/HZSM-5-XPt, in which X represents the percentage of Pt weight loading with the values of
0.02, 0.04 and 0.06. We only prepare supported samples with lower Pt loadings than Pt/HZSM-5
(0.25 wt% Pt) because metal mediated furfural conversion prior to Aldol condensation already
dominates on Pt/HZSM-5 (Figure 3b). TOFs of metal mediated furfural conversion on all
supported samples are comparable (Figure S15), indicating that exposed Pt sites are identical
catalytically regardless of the Pt loading. Lowering the Pt loading while maintaining the density
of acid sites mainly reduces the furfural conversion at 180 °C for 3 h at 600 psi H2 from 92.4% on
Pt/HZSM-5 to 51.2% on Pt/HZSM-5-0.02Pt with the yield of the target products (FAc-H and
FAc-HH) consistently lower than 25% (Table S5). A ~30% yield of the target products is
achieved by increasing the conversion of furfural on Pt/HZSM-5-0.04Pt to >90% by running the
reaction for 9 h, which is substantially lower than the >80% yield reached on Pt@HZSM-5 (Table
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S5). Thus, the catalytic performance on encapsulated catalysts cannot be reproduced by varying
the ratio of metal to acid site density, which is consistent with our interpretation that the unique
distribution of metal and acid sites in encapsulated catalysts is responsible for steering the
reaction towards tandem catalysis. Physical mixtures of Pt/SiO2 and HZSM-5 results in similar
product distributions as Pt/HZSM-5 (Figure 3b, and Table S4 and S6), suggesting that Pt
supported on the external surface of HZSM-5 is functionally similar to that of the physical
mixture of metal and acid sites. This is reasonable because metal and acid sites are physically
separated on Pt/HZSM-5, with the former on the external surface while the latter residing
predominantly on the internal surface. To exclude the possibility that encapsulated Pt NPs are
intrinsically more selective for tandem reactions, a physical mixture of Pt@Si-MFI and HZSM-5,
with the amounts of acid and metal sites comparable to those of Pt@HZSM-5, is employed in the
tandem reaction of furfural with acetone in the presence of hydrogen under otherwise identical
conditions. The main products are FAc (22%) and FurOH (36%), indicating that both the Aldol
condensation of furfural with acetone and the hydrogenation of furfural proceed in parallel. This
is expected, because the two types of active sites are spatially separated from each other. The
combined yield for the target products is significantly lower than Pt@HZSM-5, Pt/HZSM-5, and
the physical mixture of Pt/SiO2 and HZSM-5. This is likely due to the transport limitation of the
bulky FAc in MFI pores, as evidenced by the lower TOFs of FAc hydrogenation on encapsulated
catalysts (Figure S16). 54
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Figure 3. (a) Proposed reaction pathways, (b) catalytic results for sequential Aldol condensation
and hydrogenation of furfural with acetone over the tested catalysts, (c) schematic illustration for
sequential Aldol condensation and hydrogenation of furfural with acetone over Pt@HZSM-5 and
Pt/HZSM-5, and (d) catalytic results for sequential Aldol condensation and hydrogenation of
furfural with acetone over Pt/HZSM-5 with different Pt loadings. Reaction conditions in the plot
(b) are as follows: 1 mmol of furfural, 20 mmol of acetone and 2 mL isopropanol; 600 psi H2;
furfural/Al (mol mol-1) = 43; furfural/Pt (mol mol-1) = 1232; 180 °C for 3 h, except Pt@HZSM-5*
(160 °C for 20 h). Reaction conditions on the plot (d) are the same as those on the plot (b), except
for the furfual/Pt molar ratio. Compounds involved in the reaction are denoted as following:
furfural (Fur); 4-(2-furyl)-buten-2-one (FAc); 4-(2-furyl)-butan-2-ol (FAc-HH); 4-(2-furyl)-
butan-2-one (FAc-H); furan (Fu); tetrahydrofuran (THF); furfuryl alcohol (FurOH), 2-
methylfuran (MF); 2-methyltetrahydrofuran (MTHF); 1-pentanol (PenOH); cyclopentanone
(CPO); levulinic acid (LA, when R = H); isopropyl levulinate (IL, when R = CH(CH3)2); gamma-
valerolactone (GVL).
In addition to the outstanding performance of Pt@HZSM-5 in catalyzing the tandem
reaction, Pt@HZSM-5 possesses high thermal stability during regeneration, while preventing Pt
NPs from sintering and leaching. After the tandem reaction is performed, the spent catalyst is
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washed with acetone and dried, followed by calcination at 550 °C for 6 h and reduction at 400 °C
for 2 h. Physical and chemical properties of the regenerated catalyst remain unaltered, evidenced
by multiple characterizations, i.e., TEM, CO chemisorption, SEM, XRD and N2 physisorption
(Figure S17 and Table S7). XRF analysis reveals that the regenerated catalyst has the same Pt
content as the fresh one, indicating no detectable level of leaching of Pt NPs from Pt@HZSM-5
during regeneration (Table S7). Importantly, a Z value of 0.91 is determined for the regenerated
catalyst (Table S8), confirming that Pt NPs in Pt@HZSM-5 do not sinter during reaction and
regeneration conditions.
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CONCLUSIONS
In summary, we developed a direct cationic polymer-assisted synthetic strategy to encapsulate Pt
NPs into MFI zeolites, which produces catalysts with >90% Pt NPs encapsulated in the zeolite
matrix. Pt@HZSM-5 shows high selectivity for tandem reaction of Aldol condensation and the
subsequent hydrogenation with a combined yield of FAc-H and FAc-HH of up to 87%, while
Pt/HZSM-5 favors the conversion of furfural via metal mediated hydrogenation, decarbonylation
and hydrodeoxygenation. The performance of Pt@HZSM-5 on tandem catalysis cannot be
reproduced by varying the ratio of metal and acid sites over Pt supported on HZSM-5. Kinetic
studies indicate that the distribution of Pt NPs in the zeolite, i.e., encapsulated vs. supported on
the external surface, plays a decisive role in determining the product distribution. Further, zeolite
encapsulated Pt NPs exhibit excellent sintering and leaching resistance.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:
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Detailed description and data of materials synthesis and characterization and catalytic evaluation
are included.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: bxu@udel.edu
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We acknowledge support from the Catalysis Center for Energy Innovation, an Energy Frontier
Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic
Energy Sciences under Award No. DE-SC0001004. This research used resources of the Center
for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven
National Laboratory under Contract No. DE-SC0012704.
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