Elucidation of Diels-Alder reaction network of 2,5-dimethylfuran and ethylene on HY zeolite catalyst

Article abstract of DOI:10.1021/cs300673b

The reaction of 2,5-dimethylfuran and ethylene to produce p-xylene represents a potentially important route for the conversion of biomass to high-value organic chemicals. Current preparation methods suffer from low selectivity and produce a number of byproducts. Using modern separation and analytical techniques, the structures of many of the byproducts produced in this reaction when HY zeolite is employed as a catalyst have been identified. From these data, a detailed reaction network is proposed, demonstrating that hydrolysis and electrophilic alkylation reactions compete with the desired Diels-Alder/dehydration sequence. This information will allow the rational identification of more selective catalysts and more selective reaction conditions.

Full text of DOI:10.1021/cs300673b

Letter
pubs.acs.org/acscatalysis
Elucidation of Diels−Alder Reaction Network of 2,5-Dimethylfuran
and Ethylene on HY Zeolite Catalyst
Phuong T. M. Do,†,§,⊥ Jesse R. McAtee,‡,⊥ Donald A. Watson,*,‡ and Raul F. Lobo*,†
Catalysis Center for Energy Innovation, †Department of Chemical & Biomolecular Engineering, and ‡Department of Chemistry and
Biochemistry University of Delaware, Newark, Delaware 19716, United States
S
* Supporting Information
ABSTRACT: The reaction of 2,5-dimethylfuran and ethylene
to produce p-xylene represents a potentially important route
for the conversion of biomass to high-value organic chemicals.
Current preparation methods suffer from low selectivity and
produce a number of byproducts. Using modern separation
and analytical techniques, the structures of many of the
byproducts produced in this reaction when HY zeolite is
employed as a catalyst have been identified. From these data, a
detailed reaction network is proposed, demonstrating that
hydrolysis and electrophilic alkylation reactions compete with
the desired Diels−Alder/dehydration sequence. This information will allow the rational identification of more selective catalysts
and more selective reaction conditions.
KEYWORDS: p-xylene, biomass, 2,5-dimethylfuran, ethylene, 2D-NMR, reaction network, zeolite
xylene, depicted in Figure 1, proceeds through a two-step
reaction: Diels−Alder cycloaddition of DMF and ethylene,
1. INTRODUCTION
The high cost, market volatility, and limited availability of
petroleum-based feedstocks for fuel and chemical production,
in addition to the pressing need to find energy sources that
minimize societal impact on climate change, have motivated
much research into developing second-generation biomass or
nonfood lignocellulosic feedstocks as substitutes for fossil
fuels.1,2 Processing of biomass, however, has many challenges,
including the effective conversion of biomass-derived oxygen-
ates into valuable products, the identification of novel catalytic
routes to produce useful chemicals, and the design of effective
catalysts for these chemistries.3 Another challenge is that the
reaction database and analytical capabilities that have been
established for traditional hydrocarbon processing are not
effective for dealing with oxygen-containing compounds such as
biomass oxygenates. The analytical methods needed to
determine the reaction intermediates, products, and byproducts
rank then as one of the highest priorities in biomass process
engineering and design. In other words, the conceptual design
of a biomass process cannot be achieved without knowing
many details of the reaction network that takes reagents to
products.
Figure 1. Synthesis of p-xylene from 2,5-dimethylfuran and ethylene
on HY zeolite (Si/Al = 2.55).
followed by the dehydration of the oxa-norbornene inter-
mediate. The use of Brønsted acid zeolites provides much
higher yields of p-xylene compared with results reported in the
literature.9,10 On HY zeolite at 573 K, ∼60% selectivity for p-
xylene is observed at 95% conversion of DMF. Further
enhancement of the selectivity (75% based on DMF) was
observed using n-heptane as solvent; however, similarly to other
reactions related to the processing of biomass-derived
compounds,11−13 a fraction of uncharacterized byproducts
was formed. These unknown byproducts result in a reduction
of the selectivity to p-xylene.4
Recently,4 one of our groups has reported a “green” route to
catalytically convert 2,5-dimethylfuran (DMF) and ethylene to
p-xylene, an important precursor for the manufacture of
polyethylene terephthalate.5 Both ethylene and DMF can be
derived from lignocellulose feedstocks.6,7 An important
characteristic feature of this catalytic route is that p-xylene is
the sole xylene isomer that is synthesized, reducing the high
costs of mixed xylene purification required by the existing
production infrastructure.8 The pathway from DMF to p-
Establishing an experimental protocol that, in combination
with state-of-the-art analytical tools, can identify the chemical
structure of the unknown byproducts and thereby elucidate the
Received: October 15, 2012
Revised: December 3, 2012
© XXXX American Chemical Society
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ACS Catalysis
Letter
reaction pathways leading to these side products is crucial. This
new information will also clarify how best to select the reaction
operating variables and rationally choose catalysts to maximize
the production of p-xylene. In addition, a report by the DOE
Office of Basic Science identified the understanding of
mechanisms and dynamics of catalyzed transformations as the
first grand challenge in general catalysis, particularly for biomass
conversion.14
through a 0.2 μm syringe filter, and diluted with methylene
chloride for analysis using a Shimadzu GC 2010 Plus equipped
with a Thermo Scientific TR-1 column (10 m × 0.1 mm, i.d. 0.1
μm film).22
To isolate the polar compounds from the crude reaction
mixture, the volatile components (including DMF and xylene)
were removed on a rotary evaporator. The residue was then
subjected to preparative flash chromatography on silica gel.
Isolated products were then analyzed by a combination of
techniques to determine their chemical structure.
1
In fact, H and 13C nuclear magnetic resonance (NMR)
spectroscopy and gas chromatography/mass spectrometry
(GC/MS) are common analytical techniques in organic
synthesis, natural products isolation, and other fields.15−19
However, for mixtures of closely related isomers or polymer
1
2.2. Analytical. 400 MHz H and 100 MHz 13C NMR
spectra were measured on a 400 MHz FT-NMR spectrometer
equipped with a Bruker S2 CryoPlatform in the indicated
deutero solvent and at ambient temperature. Chemical shifts
are reported in parts per million. Residual CHCl31 (from
CDCl3) was used as a reference for chemical shifts. H/13C
HMBC (heteronuclear multiple bond correlation), 1H/13C
1
structures, overlapping of H NMR or 13C NMR signals often
occurs, complicating the identification of important side
products of the reaction mixture. The combination of organic
separation techniques and two-dimensional NMR (based on
homonuclear and heteronuclear correlations) are effective in
resolving the issues associated with overlapping signals;
however, these sophisticated analytical techniques have been
applied only to a limited extent in the identification of
uncharacterized products and intermediates and generally to
the overall reaction network of biomass derived compounds.20
For example, the tools used to identify the compounds
produced during fast pyrolysis of carbohydrate and cellulosic
feedstocks have been characterized solely by electron ionization
in GC/MS and retention-time validation with commercial
standards.12,21
Here, for the first time, we report the determination of a
(nearly) complete reaction network for the cycloaddition
reaction of 2,5-dimethylfuran and ethylene on the heteroge-
neous catalyst HY zeolite using a combination of classical
separation techniques, high-resolution GC/MS, and multi-
dimensional NMR spectroscopy. The objective has not been to
maximize the yield of p-xylene, but rather, to capitalize on the
formation of dominant side products using mild reaction
conditions. The dominant side products were found to result
from the electrophilic reactions of cationic intermediates with
DMF and other nucleophiles in the reaction. The observed
chemistry on acidic HY zeolite includes Diels−Alder,
dehydration, Friedel−Crafts-type alkylation, and hydrolysis via
Brønsted acid sites. Finally, solutions to operating modes and
zeolitic catalyst design principles to minimize side product
formation have been proposed.
1
HMQC (heteronuclear multiple quantum correlation) and H
COSY (homonuclear correlation spectroscopy) NMR experi-
ments were recorded, as well.
Two-dimensional NMR cross-signals were assigned by
combining the results of the different experiments. Structural
elucidation of some compounds was obtained from 1D- and
2D-NMR spectral data in combination with GC/MS data
collected using an Agilent 6850 series GC and 5973 MS
detector. High-resolution (HR) MS was obtained at the
University of California (UC), Irvine, using their Micromass
Autospec with EI+ used to provide exact chemical formulas.
The separation of most compounds was achieved using flash
silica gel chromatography eluting with hexanes, followed by a
gradient to 50% ethyl ether in hexanes. Analytical thin-layer
chromatography (TLC) was performed on precoated glass
plates and visualized by UV or by staining with KMnO4 or ceric
ammonium molybdate. Further flash silica gel chromatographic
purification was necessary for many of the minor isolates, as
described in the Supporting Information.
3. RESULTS AND DISCUSSION
3.1. Product Identification. Figure 2 shows a typical gas
chromatogram of the reaction mixture after the reaction of
2. EXPERIMENTAL SECTION
2.1. Catalytic Reactions. It is essential to purify DMF
(99% from Sigma-Aldrich) by distillation to eliminate heavy
contaminants. The distillate is stored in an oxygen- and water-
free glovebox prior to reaction measurements. Zeolite HY (25
mg, Si/Al = 2.55 from Zeolyst International, CBV 600) and
DMF (8 mL) were charged into a 45 mL closed Parr reactor
(series 4703-4714, General Purpose Pressure Vessels) under Ar
atmosphere inside a dry and oxygen-free glovebox. The
container was then filled with ethylene to a total pressure of
4.69 MPa (Scotts Specialty Gas, Inc., 99.5% purity) and heated
using a Chemglass oil-bath unit to 493 or 528 K for 6 h. Mixing
inside the reactor was accomplished by using a magnetic stirrer.
A reaction using a mixture of 3 mL of deuterated d10-p-xylene
and 8 mL of DMF and a reaction using 8 mL of pure 2,5-
hexanedione were also carried out using the same protocol. At
the end of the reaction period, the reactor was cooled in an ice
bath for 30 min, and the products were collected, filtered
Figure 2. (A) Gas chromatogram of all liquid products from reaction
of 2,5-dimethylfuran and ethylene over HY (Si/Al = 2.55) at 528 K.
(B) Expanded region showing heavy products. Peak numbers
correspond to compounds listed in Table 1.
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ACS Catalysis
Letter
DMF with ethylene on HY zeolite over a range of temperatures
(493−528 K). A total of 22 compounds (including DMF) were
identified in the mixture using this analytical technique. The
GC area percentile, chemical structure, and chemical formulas
are summarized in Table 1.
analyses can be found in the Supporting Information (Figures
SI-5, SI-6, SI-7, and SI-8). The presence of these compounds in
the crude reaction mixture was also confirmed using 1H NMR.
For compounds 4 and 5, the use of coinjection standards to
confirm identity was not possible; however, GC/MS
(Supporting Information Figure SI-8) revealed a parent ion
of 124 m/z, with similar fragmentation patterns for both
compounds. This molecular ion corresponds to a molecular
formula of C8H12O, which is consistent with the intermediate
oxa-norbornene or isomers thereof. On the basis of the
retention time, we tentatively assign compound 4 as the oxa-
norbornene, as shown in Table 1. On the basis of analysis of the
other reaction products (described below), we have assigned
compound 5 as the isomeric alcohol resulting from protolytic
ring-opening of the bridging ether and loss of proton from the
sterically accessible methyl group. This compound is a possible
intermediate en route to p-xylene. Consistent with this
assignment, attempts to isolate compound 5 were unsuccessful
and resulted in only the isolation of p-xylene (as determined by
1H NMR), which strongly suggests that it is, in fact, an
intermediate en route to the final product.
Table 1. Product Distribution of Reaction of 2,5-
a
Dimethylfuran and Ethylene over HY Zeolite
For less volatile components, we were successful in isolating
several compounds using flash column chromatography. These
included compounds 10, 12, 14, 18, and 20, which were of
sufficient purity for subsequent structural assignment. Compar-
1
ison of the GC/MS and H NMR spectra of the isolated
materials with those of the crude reaction mixtures confirmed
that the isolated compounds were significant components of
the crude mixture. Single- and multidimensional NMR spectra
1
of these species were collected (including H, 13C, COSY,
NOESY, HMQC, HMBC).
These spectra can be found in the Supporting Information.
The NMR correlations for compound 12 are summarized in
Table 2 and are representative of the data collected in this
study. From this analysis, we have assigned compound 12 as
the bicyclic diene shown. Using similar techniques, the
Table 2. Summary of 1D and 2D NMR Data of Compound
12
carbon
number
1H NMR
(ppm)
13C NMR
(ppm)
type
COSY
HMBC
1
2
3
4
5
6
CH3
CH2
CH2
CH2
CH2
CH2
1.75
2.08
2.08
2.17
2.21
3.00
23
27
29
12
14
33
6, 7, 8
3, 7, 8, 11
3, 7, 8, 11, 12
2, 7, 8, 11, 12
10, 13
6
6
9
9, 14
a
n.d. = not determined; % area determined using GC-FID and are
1, 2, 3,
7, 8
2, 7, 8, 9, 12,
13
uncorrected. Where structure is unknown, molecular formulas are
proposed on the basis of GC/MS analysis of the crude reaction
mixture.
7
CH
5.58
119
1, 2, 3, 6 2, 3, 6, 8, 11,
12
8
9
CH
CH
C
5.58
5.74
119
108
117
133
135
146
149
1, 2, 3, 6
5
1
10, 13, 14
A number of compounds, particularly those that were
volatile, were identified by coinjection of commercial standards
using both GC/FID and GC/MS. These include DMF (1), p-
xylene (2), 2,5-hexanedione (3), and 1-methyl-4-propylben-
zene (6). The retention times and mass patterns of these
compounds matched the known standards; the details of these
10
11
12
13
14
C
C
C
C
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Figure 3. Detailed reaction network of 2,5-dimethylfuran and ethylene at 4.69 MPa of ethylene and 528 K.
structures of compounds 10, 14, 18, and 20 were assigned. The
structures of these compounds are given in Table 1.
The Diels−Alder reaction leads to oxa-norbornene intermedi-
ate 4.
Dehydration of intermediate 4 requires an acid catalyst; in
this case, the HY zeolite. Protonation of the ether of 4 and
subsequent ring-opening leads to allylic cation A. Deprotona-
tion of A at the exocyclic methyl group is expected because it is
the least sterically encumbered position adjacent to the cation.
This pathway leads to formation of alcohol 5. Alternatively,
cation A can participate in a Friedel−Crafts-type reaction with
DMF, leading to compound 14. The regiochemistry in this
reaction is explained as the addition to the less-substituted site
of the allyl cation.
The intermediacy of compound 5 is further supported by the
structures of downstream products. Protonation of the alcohol
of 5, followed by dehydration, leads to the highly stabilized
pentadienyl cation B. Deprotonation of this cation leads to the
desired p-xylene (2). Our hypothesis is that the site of kinetic
deprotonation is the exocyclic methyl group, leading to the
extended triene C; however, we cannot rule out the formation
of D as the intermediate. In either case, both C and D would be
expected to quickly isomerize to p-xylene under the acidic
conditions, driven by the exothermicity of aromatization.
This desired pathway to 2 also generates an equivalent of
water, likely responsible for the observed formation of 2,5-
hexanedione (3). It is well-known that DMF can be hydrated in
acidic media to give this diketone.24 Further, dione 3 is also
prone to acid-catalyzed aldol polymerization, which may explain
the observed polymeric surface condensates.
Finally, we observed that as samples of the crude mixture
were allowed to age under air, compounds 13 and 21 appeared
to increase in abundance at the expense of compounds 12 and
20. We were able to isolate samples of 13 and 21 and assign
their structures as the aromatic compounds shown in Table 1.
In addition, we note that isolated samples of 12 and 20 were
also converted to 13 and 21 upon standing in air.
For the other components of the crude reaction mixture, we
were unable to isolate samples of sufficient quantity and purity
to allow structural assignment; however, the majority of the
remaining compounds are relatively minor components of the
crude reaction mixture. Further, although we were unable to
fully assign the structures of these products, GC/MS analysis of
the reaction mixtures revealed mass spectral fragmentation
patterns of the unassigned materials similar to those
compounds shown in Table 1, suggesting that these minor
components are closely related isomers and likely produced via
similar mechanistic pathways.
In total, we were able to identify 13 of 22 compounds in the
crude reaction mixture, including 10 of 11 of the most
abundant components from the reactions performed at 528 K.
3.2. Analysis of Reaction Network of 2,5-Dimethylfur-
an and Ethylene over HY Zeolite. The structures of the
assigned compounds allow understanding of the reaction
network of this transformation (Figure 3). As shown in a
previous report, the Diels−Alder reaction of DMF and ethylene
is enhanced by the confinement effect inside the zeolite pores.23
Cation B can also react through a number of undesired
electrophilic pathways. Alkylation at the terminus of the
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pentadienyl cation by ethylene would result in triene E.
Although we did not observe triene E, acid-catalyzed
isomerization of this intermediate would result in the observed
4-propyltoluene (6). If the intermediate B instead reacts with
DMF in a Friedel−Crafts-type reaction, the observed major
byproduct 12 arises. As in the reaction with ethylene, this
electrophilic reaction would be expected to occur at the
terminus of the extended cation, which is consistent with the
observed products. Subsequent Diels−Alder reactions of 12
with ethylene, either at the dimethylfuryl group followed by
dehydration or at the cyclohexadiene, lead to the formation of
20 and 18, respectively. We can exclude the direct formation of
20 from cation B because reactions performed with added d10-
p-xylene did not result in an increased deuterium content in 20,
as judged by GC/MS (see the Supporting Information).
Finally, we have also observed several byproducts that are
consistent with secondary oxidation of initially formed
products. For example, the formation of 13 and 21 is readily
explained by the aerobic oxidation of cyclohexadienes 12 and
20, respectively, after the reactor is opened to air.25,26 Likewise,
dehydration of alcohol 14, followed by aerobic oxidation of the
resulting diene, gives rise to substituted xylene 10.
3.3. Discussion of Reaction Network. The proposed
reaction network is consistent with two major deleterious
pathways leading to decreased yields of p-xylene. The first
pathway involves the hydrolysis of DMF by water to generate
2,5-hexanedione (3). This side reaction is particularly plaguing
because it not only consumes starting material, but the
hydrolysis product is also subject to polymerization via aldol
reactions in the acid environment. We believe that polymeric
aldol byproducts from this pathway most likely explain the
surface condensates observed at the end of the reaction and
may also explain the darkening of the zeolite catalyst during the
course of the reaction. Indeed, subjection of diketone 3 to the
zeolite catalyst at 528 K resulted in considerable darkening of
the catalyst surface, likely due to the formation of surface-
bound polymers. Interestingly, however, very few soluble aldol-
type products were observed in this control reaction, as
determined by GC/MS analysis. This suggests that the
hydrolysis pathway is not a significant contributor to the
observed (soluble) product mixtures, as shown in Figure 2 and
Table 1.27
Unfortunately, because water is generated in the final step of
the desired reaction pathway, complete suppression of the
hydrolytic decomposition of DMF may be difficult to avoid.
Further, it is clear from Table 1 that temperature plays a role in
the hydrolytic reaction because more of diketone 3 is produced
at higher temperatures, but this may simply be a result of
greater conversion of DMF to p-xylene. One obvious strategy
that may suppress the hydrolytic reaction is the removal or
sequestration of water from the reaction media, such as by the
addition of stoichiometric desiccants. Such studies will be
undertaken in the near future.
The second nonproductive pathway involved in this reaction
sequence appears to be a number of related Friedel−Crafts-
type reactions resulting from side reactions of the highly
electrophilic cationic intermediates en route to the product.
Indeed, it appears that both allyl cation A as well as pentadienyl
cation B participate in such side reactions. In particular,
pentadienyl cation B appears to be a particularly serious branch
point in the reaction network because it undergoes both
Friedel−Crafts-type reactions (with ethylene or DMF). The
increased stability of B, compared with A, due to its extended
conjugation would be expected to lead to a longer-lived
intermediate. This stability and the resulting increase in steady
state concentration may explain why more side products appear
to derive from the latter intermediate.
In addition, one can easily envision a number of other
regioisomeric byproducts arising from electrophilic reactions
similar to those shown in Figure 3. The products from those
pathways would be expected to provide compounds with
similar or identical molecular formulas and mass spectroscopic
fragmentation patterns highly similar to the identified
compounds. As mentioned above, many of the unassigned
compounds have GC/MS features closely resembling the
Friedel−Crafts products shown in Figure 3; thus, we believe
that the remaining byproducts also result from related
electrophilic pathways.
Unfortunately, because the pathway leading to the desired p-
xylene requires the intermediacy of both cations A and B, it is
not possible to avoid the formation of these reactive
intermediates. Likewise, one might consider controlling the
concentration of the nucleophiles (i.e., ethylene and DMF) that
participate in the electrophilic side reactions as a way to
modulate the rates of formation of side products. However,
both ethylene and DMF are required in the upstream Diels−
Alder reaction, meaning that a reduction in their concentrations
would likely have deleterious effects on the overall rate of p-
xylene production. Consistent with this, we have previously
observed that high operating pressures facilitate the rate of p-
xylene production.4
Fortunately, however, the proposed reaction network does
suggest a means for limiting the production of side products
from electrophilic pathways. For both cations A and B, the
undesired Friedel−Crafts-type pathways directly compete with
productive deprotonation leading to p-xylene. One alternative is
to use zeolite materials that contain higher concentrations of
framework aluminum (i.e., lower Si/Al ratios), such as zeolite
X, that are known to have lower effective acidity.28
Alternatively, zeolites containing other framework heteroatoms
(such as Ga(III) and Fe(III)) are also known to have lower
effective acidity and could potentially aid in reducing the
relative rates of the undesired reaction channels.29,30 Finally, an
optimal selectivity window for p-xylene might be achieved by
tuning the dielectric properties of the solvent. In fact, our
previous results have shown that the use of n-heptane as solvent
increases the selectivity of p-xylene from 55% to 75% on HY
zeolite.4 One would expect that such a nonpolar solvent would
destabilize cationic intermediates, which might result in a faster
deprotonation step and increased rate of desired product
formation. Future studies will be directed toward optimization
of the zeolite catalyst as well as understanding solvent effects in
the reaction.
4. CONCLUSION
Using advanced separation and analytical techniques, including
extensive 1D and 2D NMR, we have been able to identify the
majority of compounds produced in the reaction of 2,5-
dimethylfuran (DMF) and ethylene over catalytic HY zeolite.
In addition to the desired p-xylene, we have found that
hydrolysis of the DMF and a number of electrophilic reactions
of cationic intermediates lead to a range of side products. With
detailed knowledge of byproduct structures, we have been able
to propose a reaction network that is consistent with the
observed product distribution. These studies suggest that active
removal of water from the reaction, as well as the modulation of
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Letter
(15) Kalsi, P. S. Spectroscopy of Organic Compounds; New Age
International (P) Ltd.: Tunbridge Wells, U.K., 2007.
the acidity of the zeolite catalyst, will result in higher selectivity
for the desired p-xylene. This study constitutes one of the first
examples of the application of modern analytical and separation
techniques to understanding a reaction involved in the
conversion of biomass-derived oxygenates into valuable feed-
stock products. We believe that application of such techniques
to other problems in biomass conversion will have a significant
and positive effect on developing more efficient and selective
routes to commodity chemicals in the postpetroleum era.
(16) Claridge, T. D. W. High-Resolution NMR Techniques in Organic
Chemistry; Elsevier Science: London, Amsterdam, 2008,
(17) NMR Spectroscopy in Pharmaceutical Analysis; Wawer, I.; Diehl,
B.; Holzgrabe, U., Eds.; Elsevier Science: Oxford, 2008,
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Determination, 2nd ed.; Colegate, S. M.; Molyneux, R. J., Eds.; Taylor
& Francis: 2007.
(19) Hubschmann, H. J. Handbook of GC/MS: Fundamentals and
̈
Applications; John Wiley & Sons: New York, 2008.
́
(20) Gonzalez Maldonado, G. M.; Assary, R. S.; Dumesic, J.; Curtiss,
ASSOCIATED CONTENT
■
L. A. Energy Environ. Sci. 2012, 5, 6981.
S
* Supporting Information
Spectral data for isolated compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
(21) Ronsse, F.; Bai, X.; Prins, W.; Brown, R. C. Environ. Prog.
Sustainable Energy 2012, 31, 256.
(22) Reactions run to higher levels of conversion contained similar,
although somewhat more complex, mixtures of byproducts (as judged
by GC/MS). We believe that the increase in complexity of the
byproducts under these conditions is predominately due to further
reactions of the side products facilitated by longer reaction times.
(23) Dessau, R. M. J. Chem. Soc., Chem. Commun. 1986, 15, 1167.
(24) Stamhuis, E. J.; Drenth, W.; Van den Berg, H. Recl. Trav. Chim.
Pays-Bas 1964, 83, 167.
(25) Hendry, D. G.; Schuetzle, D. J. Am. Chem. Soc. 1975, 97, 7123.
(26) McGraw, G. W.; Hemingway, R. W.; Ingram, L. L.; Canady, C.
S.; McGraw, W. B. Environ. Sci. Technol. 1999, 33, 4029.
(27) Other byproducts resulting from the self-reaction of either DMF
or ethylene were not detected.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: dawatson@udel.edu (D.A.W.), lobo@udel.edu
(R.F.L.).
Present Address
§UOP-Honeywell Research Center, 50 E. Algonquin Rd., Des
Plaines, IL 60017.
Author Contributions
⊥These authors contributed equally.
(28) Ravenelle, R. M.; Schussler, F.; D’Amico, A.; Danilina, N.; van
̈
Notes
Bokhoven, J. A.; Lercher, J. A.; Jones, C. W.; Sievers, C. J. Phys. Chem.
C 2010, 114, 19582−19595.
The authors declare no competing financial interest.
(29) Corma, A. Chem. Rev. 1995, 95, 559.
ACKNOWLEDGMENTS
(30) Shamzhy, M. V.; Shvets, O. V.; Opanasenko, M. V.; Yaremov, P.
■
S.; Sarkisyan, L. G.; Chlubna,
M.; Cejka, J. J. Mater. Chem. 2012, 22, 15793.
́
P.; Zukal, A.; Marthala, V. R.; Hartmann,
Data were acquired on instruments obtained via NSF and NIH
funding (NSF MIR 0421224 and CRIF MU CHE0840401,
NIH P20 RR017716). This work was supported as part of the
Catalysis Center for Energy Innovation, an Energy Frontier
Research Center funded by the US Department of Energy,
Office of Basic Energy Sciences under Award No. DE-
SC0001004
̌
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