Mechanism of Phenol Alkylation in Zeolite H-BEA Using in Situ Solid-State NMR Spectroscopy

Article abstract of DOI:10.1021/jacs.7b02153

The reaction mechanism of solid-acid-catalyzed phenol alkylation with cyclohexanol and cyclohexene in the apolar solvent decalin has been studied using in situ ¹³C MAS NMR spectroscopy. Phenol alkylation with cyclohexanol sets in only after a majority of cyclohexanol is dehydrated to cyclohexene. As phenol and cyclohexanol show similar adsorption strength, this strict reaction sequence is not caused by the limited access of phenol to cyclohexanol, but is due to the absence of a reactive electrophile as long as a significant fraction of cyclohexanol is present. ¹³C isotope labeling demonstrates that the reactive electrophile, the cyclohexyl carbenium ion, is directly formed in a protonation step when cyclohexene is the coreactant. In the presence of cyclohexanol, its protonated dimers at Br?nsted acid sites hinder the adsorption of cyclohexene and the formation of a carbenium ion. Thus, it is demonstrated that protonated cyclohexanol dimers dehydrate without the formation of a carbenium ion, which would otherwise have contributed to the alkylation in the kinetically relevant step. Isotope scrambling shows that intramolecular rearrangement of cyclohexyl phenyl ether does not significantly contribute to alkylation at the aromatic ring.

Full text of DOI:10.1021/jacs.7b02153

Subscriber access provided by CORNELL UNIVERSITY LIBRARY
Article
On the Mechanism of Phenol Alkylation in Zeolite H-
BEA Using In Situ Solid-State NMR Spectroscopy
Zhenchao Zhao, Hui Shi, Chuan Wan, Mary Y. Hu, Yuanshuai Liu,
Donghai Mei, Donald M. Camaioni, Jian Zhi Hu, and Johannes A. Lercher
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 19 Jun 2017
Downloaded from http://pubs.acs.org on June 19, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 9
Journal of the American Chemical Society
1
2
3
4
5
6
On the Mechanism of Phenol Alkylation in Zeolite HꢀBEA Usꢀ
ing In Situ SolidꢀState NMR Spectroscopy
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
†,1
†,1
†
†
‡
†
Zhenchao Zhao, Hui Shi, Chuan Wan, Mary Y. Hu, Yuanshuai Liu, Donghai Mei, Donald M.
†
†,*
†,‡,*
Camaioni, Jian Zhi Hu, Johannes A. Lercher
†
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352 (United
States)
‡
Department of Chemistry and Catalysis Research Center, TU München, Lichtenbergstrasse 4, 85748 Garching (Germany)
KEYWORDS: in situ NMR spectroscopy, reaction mechanism, alkylation, zeolites
ABSTRACT: The reaction mechanism of solidꢀacidꢀcatalyzed phenol alkylation with cyclohexanol and cyclohexene in the apolar
13
solvent decalin has been studied using in situ C MAS NMR spectroscopy. Phenol alkylation with cyclohexanol sets in only after a
majority of cyclohexanol is dehydrated to cyclohexene. As phenol and cyclohexanol show similar adsorption strength, this strict
reaction sequence is not caused by the limited access of phenol to cyclohexanol, but is due to the absence of a reactive electrophile
13
as long as a significant fraction of cyclohexanol is present. C isotope labeling demonstrates that the reactive electrophile, the
cyclohexyl carbenium ion, is directly formed in a protonation step when cyclohexene is the coꢀreactant. In the presence of cycloꢀ
hexanol, its protonated dimers at Brønsted acid sites hinder the adsorption of cyclohexene and the formation of a carbenium ion.
Thus, it is demonstrated that protonated cyclohexanol dimers dehydrate without the formation of a carbenium ion, which would
otherwise have contributed to the alkylation in the kinetically relevant step. Isotope scrambling shows that intramolecular rearꢀ
rangement of cyclohexyl phenyl ether does not significantly contribute to alkylation at the aromatic ring.
INTRODUCTION
classical FriedelꢀCrafts alkylation chemistry in a homogeneous
phase, or inferred from insufficient and less informative ex
situ analyses of reaction products. In particular, for Brønsted
acidic zeolites, the mechanism for phenol alkylation with
alcohol (e.g., methanol, tertꢀbutyl alcohol) is significantly
more controversial, compared to phenol alkylation with olefin
The catalytic conversion of ligninꢀderived phenolic comꢀ
pounds is a critical pathway for maximizing the utilization of
lignocellulosic biomass. While hydrodeoxygenation increasꢀ
1ꢀ3
es the H/C ratio and decreases the O/C ratio in the products,
(hydro)alkylation adjusts the carbon number and improves the
4ꢀ10
(e.g., propene, 1ꢀoctene). For example, the contribution of
carbon retention in the liquid products. Moreover, alkylated
phenols have been widely used as additives in gasoline, lubriꢀ
cants, and consumer products.
alkyl phenyl ether rearrangement to Cꢀalkylation has been
controversially discussed. While some studies reported that an
alkyl aryl ether (the kinetically favored product) can undergo
1
1ꢀ15
Alkylation of phenols, such as phenol or mꢀcresol, is an elecꢀ
trophilic aromatic substitution. Both olefins and alcohols can
be alkylating agents. In the case of alkylation of phenol with
olefins, the electrophile is the carbenium ion formed via proꢀ
tonation of the olefin by a Brønsted acid site (BAS) of a solid
acid, while in the case of alkylating phenol with alcohol, it is
generally a consensus that the electrophile can be the protoꢀ
nated alcohol (an alkoxonium species) or a carbenium ion
derived from alcohol dehydration. Electrophilic attack on the
phenolic OH or π electrons in the aromatic ring yields Oꢀ
alkylation or ringꢀalkylation (Cꢀalkylation) products, respecꢀ
tively. It has also been suggested that Cꢀalkylation products
could be formed through intramolecular rearrangement of the
kinetically favored Oꢀalkylation product, i.e., via an aryl alkyl
facile intramolecular rearrangement to directly produce alꢀ
17,18,27
kylphenols,
others negated this pathway, concluding
instead that Cꢀalkylation products arise from alkylation of
phenol with olefin formed via decomposition of the Oꢀ
24
alkylation product. From a theoretical point of view, the
prevalent mechanism has also remained elusive. Much like the
proposals for alkylation of benzene and toluene with methaꢀ
29,30
nol,
stepwise (i.e., formation of carbenium ion or a covaꢀ
lent surface alkoxide from alcohol, followed by electrophilic
substitution) and concerted (i.e., coꢀadsorption of phenol and
alcohol on acid sites and direct conversion in one single eleꢀ
mentary step, without the formation of alkoxide or carbenium
ion) routes have been proposed for phenol alkylation in zeoꢀ
31,32
16ꢀ18
lites and examined by quantum chemical calculations.
ether intermediate product.
Both phenolꢀmethanol alkylation on faujasite zeolite (HꢀFAU)
and tertꢀbutylation of phenol on Beta zeolite (HꢀBEA) preferꢀ
entially proceed via a direct, concerted mechanism, rather than
Alkylation of phenols with olefins and alcohols has been exꢀ
tensively studied, in vapor and liquid phases, over a wide
12ꢀ14,19ꢀ28
3
1
range of solid catalysts.
The hypothesized mechanisms
via a stepwise mechanism mediated by surface methoxide or
32
from these experimental studies were, however, seldom based
on rigorous rate measurements and direct spectroscopic eviꢀ
dence, but rather, almost always “borrowed”/adapted from the
tertꢀbutyl carbenium ion. Thus, these theoretical studies
appear to challenge the conventional view, at least for the
alcohols and zeolites investigated, that carbeniumꢀionꢀtype
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 9
intermediate is involved as the direct electrophile in the major and alkylates, that the carbenium ion (electrophile) is, in fact,
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
alkylation pathways. However, we note that none of these
predictions have been experimentally verified so far for zeoꢀ
liteꢀcatalyzed phenol alkylation. Of particular note is the largeꢀ
ly missing application of in situ spectroscopies able to unravel
mechanistic pathways for this class of reactions in zeolite
not produced directly from the adsorbed cyclohexanol
(Scheme 1, path A) in the pore of a BEA zeolite, because the
dominant surface species is an alcohol dimer that does not
dehydrate via an E1 mechanism. It is also established that
intramolecular rearrangement of cyclohexyl phenyl ether is, at
best, a minor pathway to cyclohexylphenols (Scheme 1, path
B), and that alkylation occurs via a stepwise route initiated by
olefin protonation (Scheme 1, path C), instead of a concerted
one (Scheme 1, path D). Olefin (reꢀ)adsorption and protonaꢀ
tion is the dominant pathway of generating the electrophile for
phenol alkylation, regardless of the starting alkylating coꢀ
reactant (cyclohexanol or cyclohexene). To the best of our
knowledge, this work represents the first example of using
NMR to study this class of reactions under steadyꢀstate and
3
0
pores or on solid surfaces in general.
1
3
We use in situ C solidꢀstate NMR spectroscopy to probe, at a
molecular level, reaction pathways for this type of solidꢀacidꢀ
catalyzed reaction, specifically, alkylation of phenol with
3
3ꢀ38
cyclohexanol on a largeꢀpore zeolite HꢀBEA,
using a miꢀ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
croautoclave MAS NMR rotor developed for studying multiꢀ
phase processes at high temperature, high pressure
39,40
conditions.
The present study was carried out in decalin, a
nonꢀpolar solvent, which is typical for the environment in
30
24,41
realistic conditions.
which such a reaction would be practically performed.
We
13
demonstrate, via analysis of the C label distribution in olefin
Path A
Rδ+
H
O
ROH
H
O
E1ꢀelimination
Oδꢀ
Si
Al
Si
Al
Si
Al
H O
2
Carbenium ion
or alkoxide
Path B
H
O
Si
Al
Sequential 1,2ꢀshifts
H
Oꢀalkylation product
Protonated ether
deprotonate
O
Si
Al
Cꢀalkylation products
Path C
Rδ+
H
Olefin reꢀadsorption
protonation
Oδꢀ
O
Si
Al
Si
Al
(RꢀH)=
Carbenium ion
or alkoxide
H O
2
H
O
ROH
Si
Al
Path D
H
ROH +
H
O
O
Si
Al
Si
Al
H O +
2
=
Scheme 1. Postulated mechanisms for Cꢀalkylation of phenol with alcohol (ROH) on zeolitic protons. (RꢀH) stands for olefin.
2
ACS Paragon Plus Environment

Page 3 of 9
Journal of the American Chemical Society
1
RESULTS AND DISCUSSION
adsorption constants of 44 and 73 (at 25 °C) for phenol and
cyclohexanol, respectively (data not shown).
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
3
Variable temperature C MAS NMR measurements of
phenol and cyclohexanol adsorption on H-BEA from de-
calin solutions. Figure 1 shows the C MAS NMR spectra
13
13
Alkylation of 1- C-phenol with 1- C-cyclohexanol. During
13
the first ~400 min, cyclohexanol dehydration was almost the
13
13
acquired after reaching adsorption equilibria of 1ꢀ Cꢀphenol
only reaction taking place (Figure 2). 1ꢀ Cꢀcyclohexanol
13
13
and 1ꢀ Cꢀcyclohexanol, from their respective decalin soluꢀ
(70.2 ppm) dehydration led to 1ꢀ Cꢀcyclohexene (127.2 ppm)
1
3
13
13
tions, on HꢀBEA at different temperatures. Cꢀisotope scramꢀ
bling within each molecule was not detected at these temperaꢀ
tures. In each spectrum, a relatively sharp peak representing
the mobile species in decalin and a broad peak representing
the species adsorbed in HꢀBEA pores are observed. Specificalꢀ
as the primary product, while the 3ꢀ C and 4ꢀ C isotopomers
of cyclohexene increased in concentration at longer residence
times. A weak signal of dicyclohexyl ether at 74.8 ppm disapꢀ
peared quickly (Figure S3, Supporting Information). The rate
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ꢀ
5
ꢀ1
of phenol alkylation started to increase (~4×10 mol gHꢀBEA
13
ꢀ1
ly, the 1ꢀ C of phenol in decalin solution appeared at 156.3
min at 127 °C) only after most cyclohexanol was dehydrated.
For monoꢀalkylation, the ortho to para substitution occurred
initially in a 1:1 ratio, but gradually increased to values larger
than 1. This ratio was still lower than the statistical ratio (2:1),
indicating that the pore constraints of HꢀBEA influence the
product selectivity (see also Table S4, Supporting Inforꢀ
mation). Metaꢀsubstitution was not detected. Diꢀalkylation
occurred much later, producing only 2,4ꢀdicyclohexyl phenol.
13
ppm, while the 1ꢀ C of cyclohexanol in decalin was at 69.8
ppm. The corresponding adsorbed species for cyclohexanol
was at ~71.6 ppm, downfield relative to the mobile species.
The adsorbed species for phenol at ~155.5 ppm, upfield relaꢀ
1
3
tive to the solution species. Thus, the 1ꢀ C signals of cycloꢀ
hexanol and phenol appear more deꢀshielded and shielded,
respectively, relative to their liquid phase states in decalin.
Firstꢀprinciple calculations of NMR chemical shifts for solvaꢀ
tion structures of phenol and cyclohexanol in decalin (strucꢀ
tures shown in Figure S1) and in the pore of zeolite HꢀBEA
a)
0.5
(
Figure S2) are qualitatively consistent (Table S2) with the
experimental observations.
OH
0.4
0
0
0
.3
.2
.1
0
0
200
400
600
800
1000
Time/min
1
3
Figure 1. Variable temperature C MAS NMR spectra of 1ꢀ
1
3
13
b)
Cꢀphenol (a) and 1ꢀ Cꢀcyclohexanol (b) adsorption on a Hꢀ
0.5
BEA catalyst (Si/Al = 75).
0
.4
.3
The peak area ratio of adsorbed and mobile phase phenol
decreased from 16.4 to 6.6, while that ratio for cyclohexanol
decreased from 34.6 to 11.2, with increasing adsorption temꢀ
perature from 25 to 82 °C. This indicates that the uptake from
decalin into HꢀBEA pores is exothermic for both molecules.
The solution concentrations at adsorption equilibria (C ) and
uptakes (q) for phenol and cyclohexanol at different adsorpꢀ
tion temperatures are compiled in Table S3, Supporting Inꢀ
0
0.2
eq
0.1
ꢀ1
formation. The uptake values (1.0–1.3 mmol gHꢀBEA ) were allꢀ
0
much higher than a 1:1 coverage of BAS (~0.15 mmol gHꢀBEA
1
0
200
400
600
800
1000
), indicating that most of the adsorbed species were present
Time/min
physisorbed in the pores without directly interacting with the
BAS. The molar ratios of adsorbed and solution species are
comparable for cyclohexanol and phenol at any given temꢀ
perature, suggesting that the adsorption constant and enthalpy
of adsorption in HꢀBEA pores were very similar for the two
molecules. Consistent with these in situ measurements, indeꢀ
pendent exꢀsitu measurements for the same mixtures provided
Figure 2. Concentrationꢀtime profiles of (a) reactants and
alkylation products as well as (b) dehydration products during
the in situ NMR investigation of phenolꢀcyclohexanol reaction
catalyzed by HꢀBEA at 127 °C.
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 9
1
3
The series of in situ C MAS NMR spectra in the aromatic
carbon region (Figure 3) as a function of reaction time shows
copy under the present alkylation conditions (i.e., higher temꢀ
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
perature and an 18ꢀtime larger substrateꢀtoꢀcatalyst ratio than
used in adsorption experiments; see Experimental).
1
3
that the signal at 156.5 ppm representing 1ꢀ Cꢀphenol started
to decrease after 400 min, with the appearance of cyclohexyl
phenyl ether, 4ꢀcyclohexylphenol, 2ꢀcyclohexylphenol, and
,4ꢀdicyclohexyl phenol at 158.8, 154.5, 153.6, and 151.6 ppm
all at 1ꢀC position for phenol), respectively, without label
13
Alkylation of 1- C-phenol with cyclohexene. When cycloꢀ
hexene (unlabeled) was used to alkylate phenol, the concentraꢀ
tion of phenol decreased exponentially with the reaction time
(Figures 4, S5 and S6). Both Oꢀ and Cꢀalkylation were obꢀ
served from the beginning of the reaction. Similar to the case
of phenol alkylation with cyclohexanol, cyclohexyl phenyl
ether quickly reached the maximum and then disappeared,
whereas all Cꢀalkylation products continued to grow until
cyclohexene was fully consumed after 250 min. The formation
of cyclohexyl phenyl ether was kinetically favored and reꢀ
versible. The reversibility of Oꢀalkylation is also shown by the
rapid formation of cyclohexene, phenol and alkylation prodꢀ
ucts when cyclohexyl phenyl ether was used as reactant (Figꢀ
ure S7). 2,4ꢀDicyclohexyl phenol, the only diꢀalkylation prodꢀ
uct observed, increased more rapidly than in phenolꢀ
cyclohexanol alkylation. The final ratio of orthoꢀ and paraꢀ
monoalkylation was ~1.5, similar to that obtained in phenolꢀ
cyclohexanol alkylation and lower than the statistical ratio of
2:1.
2
(
scrambling in phenol.
*OH
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
*
*
*
*
853.6
640.2
n
i
/
m
e
i
m
426.8
T
213.4
1
60
158
156
154
152
150
a)
ppm
0
.4
.3
1
3
Figure 3. Stacked plot of in situ C MAS NMR spectra (aroꢀ
1
3
13
matic carbon region) of 1ꢀ Cꢀphenol alkylation with 1ꢀ Cꢀ
cyclohexanol at 127 °C. The initial concentrations of phenol
and cyclohexanol were 0.54 and 0.51 M (based on density of
solution at room temperature), respectively. For other carbon
regions, see Figure S3.
0
0.2
0.1
While the concentration of cyclohexyl phenyl ether (peak at
58.8 ppm) gradually decreased after reaching the maximum
concentration at 600 min, the Cꢀalkylation products continued
to increase with increasing residence time (see Figure S4 for
C signals at chemical shifts of 20–45 ppm related to the
carbons on the cyclohexyl ring). This shows that ethers formed
by the kinetically faster Oꢀalkylation are converted further,
while the ring alkylation products (Cꢀalkylation) are stable end
products.
1
0
1
3
0
200
400
Time/min
600
800
b)
0
0
0
.6
.5
.4
The fact that phenol alkylation did not start until cyclohexanol
was almost completely consumed suggests that either phenol,
or the direct alkylating agent (electrophile), or both, are signifꢀ
icantly weaker in interacting with acid sites than cyclohexanol
0.3
0.2
(
or its derived surface intermediate). As phenol and cyclohexꢀ
anol have similar adsorption constants in the zeolite pores, the
lack of phenol alkylation before most cyclohexanol was dehyꢀ
drated (Figure 2) is concluded not to result from the absence
of phenol at the BAS. Instead, we hypothesize that only cycloꢀ
hexene forms the reactive intermediate (while cyclohexanol
does not) for ring alkylation and that the adsorption constant
for cyclohexene at the BAS is too low for it to compete with
cyclohexanol at appreciable concentrations of the latter. Alcoꢀ
hol molecules are known to form protonated dimers
BAS, which are dominant surface species even at low concenꢀ
trations or partial pressures.
alcohol dimer, phenolꢀalcohol adsorption complex) in HꢀBEA
pores, however, were not directly observed by NMR spectrosꢀ
0
.1
0
0
200
400
600
800 1000 1200 1400
Time/min
4
2ꢀ44
at
Figure 4. Concentrationꢀtime profile of compounds during the
in situ NMR investigation of HꢀBEAꢀcatalyzed alkylation of
phenol with cyclohexene (unꢀlabeled) only (a) and with
4
2,43
Such adsorbed species (i.e.,
13
equimolar cyclohexene and 1ꢀ Cꢀcyclohexanol (b) at 127 °C.
4
ACS Paragon Plus Environment

Page 5 of 9
Journal of the American Chemical Society
signals associated with the solvent, decalin. Moreover, the
13
1
chemical shifts for Cꢀlabels at 3ꢀ and 4ꢀpositions in the cyꢀ
clohexyl ring significantly overlap with each other (Table S1),
and thus, the two could not be unequivocally differentiated
from each other. In an attempt to subtract the solvent peak, it
was found that the sum of the integrated intensities for 3ꢀ and
With cyclohexanol initially added together with cyclohexene,
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
all alkylation reactions were drastically retarded and became
faster only after a major fraction of cyclohexanol was dehyꢀ
drated (Figure 4). This, combined with the initial lack of alꢀ
kylation for the phenolꢀcyclohexanolꢀdecalin mixture (0ꢀ400
min in Figure 2a), allows us to conclude hat: (a) the electroꢀ
phile for alkylating phenol is not formed in the reaction path
of cyclohexanol dehydration; (b) the presence of cyclohexanol
inhibits the formation of the electrophile from the olefin. Note
that the concentration of phenol hardly changed in the zeolite
pores as alcohol dehydration progressed.
13
4
ꢀ Cꢀcyclohexylphenols (nonꢀsolvent peaks in the 26ꢀ28 ppm
13
range) was approximately 1.4 times that for the 2ꢀ Cꢀ
cyclohexylphenols (in the range of 33ꢀ36 ppm) after complete
13
scrambling of C labels in the olefin.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
20
a)
18
16
14
13
Nature of the alkylating agent. Figure 5 shows the C signal
intensities for all the products (dehydration product: cyclohexꢀ
ene; alkylation products: cyclohexyl phenols and cyclohexyl
phenyl ether) present in the reaction mixture of 1ꢀ Cꢀphenol
alkylation with 1ꢀ Cꢀcyclohexanol. During alkylation, the
1
2
1
3
1
3
13
10
8
C
label in phenol did not undergo scrambling, while a small
extent of label scrambling was observed for cyclohexanol
6
(
Figures S4 and S8).
4
1
3
13
2
As mentioned before, the 3ꢀ C and 4ꢀ C isotopomers of
cyclohexene were essentially secondary products (Figures 2b
and S9). Two possible reaction paths for the observed
0
13
C
ꢀ2
1
3
scrambling in cyclohexene during 1ꢀ Cꢀcyclohexanol dehyꢀ
0
200
400
600
800
1000
1
3
dration exist: (1) C scrambling via hydride shifts in an interꢀ
mediately formed carbenium ion via E1ꢀtype elimination of
water from a protonated cyclohexanol, and (2) cyclohexene reꢀ
adsorption and protonation at the BAS, forming cyclohexyl
carbenium ion with the C label at either the 1ꢀ or 2ꢀposition,
which may also scramble the labels by hydride shift. If
scrambling occurs by hydride shift of the 1ꢀ Cꢀcyclohexyl
carbocation directly formed from E1ꢀtype elimination, then
rapid hydride shifts of this carbenium ion would form 2ꢀ, 3ꢀ,
and 4ꢀ Cꢀcyclohexyl carbocations and subsequent deprotonaꢀ
tion steps would lead to 3ꢀ and 4ꢀ Cꢀcyclohexene accompanyꢀ
ing 1ꢀ Cꢀcyclohexene even at the initial stage. This is indeed
the case for aqueous phase dehydration of cyclohexanol on the
same HꢀBEA catalyst. However, as illustrated in Figure 2b
and Figure 5a, there was little formation of 3ꢀ or 4ꢀ Cꢀ
cyclohexene during the initial 200 min. The negligible scramꢀ
bling at the initial stage indicates that the dominant surface
Time/min
7
6
b)
13
13
5
C
1
3
4
3
1
3
OH
1
3
2
1
3
1
OH
4
0
0
13
ꢀ1
0
200
400
600
800
1000
Time/min
species at this concentration, the protonated cyclohexanol
dimer,
42ꢀ44
13
does not form a carbenium ion during dehydration.
Figure 5. Integrated C signal intensities of (a) dehydration
13
As the C scrambling rate increased significantly only after
00 min, when most cyclohexanol was consumed, it is conꢀ
and (b) orthoꢀ and paraꢀalkylation products during phenol
13
5
alkylation with 1ꢀ Cꢀcyclohexanol on HꢀBEA in decalin
13
cluded that C scrambling in cyclohexene occurs via reꢀ
adsorption and protonation of cyclohexene. We conclude also
that reꢀadsorption of cyclohexene is significantly hindered by
(unlabeled) as a function of reaction time at 127 °C. The relaꢀ
tively large scatters in (b) at the beginning originate from the
subtraction of the intensities of decalinꢀrelated peaks (which
overlap with some of the naphthenic carbon signals in cycloꢀ
hexyl) from the total signal intensities.
13
the presence of cyclohexanol, but not by phenol. The
C
labels in olefin products were fully randomized after ~700 min
(Figure 5a), suggesting rapid protonationꢀdeprotonation equiꢀ
librium for the olefin.
13
For both oꢀ and pꢀmonoalkylation, the concentrations of 2ꢀ Cꢀ
1
3
13
Figure 5b shows the integrated C signal intensities for orthoꢀ
and paraꢀsubstituted 1ꢀ and 2ꢀ Cꢀcyclohexylphenols as a
function of reaction time. The 3ꢀ and 4ꢀ Cꢀlabeled isotoꢀ
pomers of oꢀ and pꢀcyclohexylphenols were also detected in
significant concentrations (26ꢀ28 ppm, Figure S4), but were
not included in Figure 5b because of the difficulty in comꢀ
cyclohexyl phenols were generally higher than 1ꢀ Cꢀ
1
3
cyclohexyl phenols. This became evident at t > 200 min, and
1
3
13
by the end of the experiment, 2ꢀ Cꢀcyclohexyl phenols had
reached concentrations nearly twice (~ 1.8ꢀfold) those of the
13
1ꢀ Cꢀcyclohexyl counterparts. If phenol reacted with the
1
3
intermediate directly generated from dehydration of 1ꢀ Cꢀ
13
pletely separating their signals from natural abundance
C
5
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 9
cyclohexanol, before significant hydride shift had occurred, philic attack step, would lead to equal distribution of labels
13
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
most of the Cꢀalkylation products would have contained 1ꢀ Cꢀ
cyclohexyl. Even if rapid hydride shifts had occurred, the
among all positions for a given monoalkylation product, not in
line with the observations. Taken together, we conclude that
phenol must be in the vicinity of the acid site and the carbeniꢀ
um ion so that the carbenium ion is trapped before extensive
label shifts can occur.
1
3
transient concentration of the 2ꢀ Cꢀcyclohexyl carbocation, or
any other secondary carbocation intermediate (e.g., 3ꢀ and 4ꢀ
1
3
Cꢀcyclohexyl carbocations), at any given time should always
be lower than, or at most equal to (fully equilibrated hydride
1
3
shifts, see Figure S10), that of the 1ꢀ Cꢀcyclohexyl carboꢀ
cation (a primary kinetic intermediate from E1ꢀelimination).
Consequently, alkylation of phenol by intermediates directly
produced from cyclohexanol dehydration is not able to acꢀ
1ꢀ13Cꢀolefin
+ H+Z-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
13
count for the observed preference for 2ꢀ Cꢀcyclohexyl pheꢀ
nols (Figure 5b). The results are fully consistent, however,
with reꢀadsorption and protonation of cyclohexene at the BAS
13
13
that forms more 2ꢀ Cꢀcyclohexyl carbenium ion than 1ꢀ Cꢀ
cyclohexyl carbenium ion at all reaction times. A concerted
mechanism, with coꢀadsorbed phenol and alcohol reacting in a
3ꢀ13Cꢀolefin
+ H+Z-
3
0ꢀ32
single step to form alkylates,
it would require that the Cꢀ and Oꢀalkylates should contain1
can also be excluded, because
1
3
C
3
labels at the same position as in the alcohol, i.e., 1ꢀ Cꢀ
cyclohexanol in this case. Note that the concerted mechanism
is also inconsistent with the negligible alkylation as long as
cyclohexanol is present (Figure 2a).
Scheme 2. Reꢀadsorption and protonation of cyclohexene at
the BAS leads to oꢀ and pꢀsubstituted Cꢀalkylation products
(Oꢀalkylation and diꢀalkylation products not shown) that conꢀ
13
tain more 2ꢀ Cꢀcyclohexyl (upper and lower paths) than 1ꢀ
1
3
+ ꢀ
Finally, if a major part of the Cꢀalkylation were formed via
intramolecular rearrangement of cyclohexyl phenyl ether
Cꢀcyclohexyl (upper path only). H Z stands for a BAS of
zeolite. Hydride shift pathways are not shown.
1
3
(
Scheme 1, path B), the C position of the cyclohexyl group
should not change during cyclohexyl group migration accordꢀ
1
7
CONCLUSION
ing to the alkyl group migration mechanism. Figure 5a
1
3
Phenol alkylation with cyclohexanol in decalin occurs primariꢀ
ly via electrophilic attack of a cyclohexyl cation, not an alkoxꢀ
onium ion, on the phenolic OH or π electrons in the aromatic
ring. As cyclohexanol needs to be almost completely dehyꢀ
drated before the rate of alkylation is measurable, the dehydraꢀ
tion of cyclohexanol is concluded not to involve a surface
intermediate able to alkylate the aromatic ring of phenol. Inꢀ
tramolecular rearrangement of the kinetically favored, reversiꢀ
bly formed cyclohexyl phenyl ether is also not a significant
pathway leading to Cꢀalkylation products. At the initial stage
of phenolꢀcyclohexanol alkylation, the presence of cyclohexaꢀ
nol hinders the adsorption of cyclohexene at the Brønsted acid
site and the subsequent formation of the carbenium ion. The
latter is generated upon reꢀadsorption and protonation of cyꢀ
clohexene, with increasing propensity with decreasing alcohol
concentrations. The carbenium ion is only generated via proꢀ
tonation of cyclohexene. Thus, with cyclohexene used as
alkylating agent, higher rates of alkylation were observed than
shows that the concentration of 1ꢀ Cꢀcyclohexyl phenol ether
1
3
was similar to 2ꢀ Cꢀcyclohexylphenol ether for the first 400
1
3
min and became slightly lower than 2ꢀ Cꢀcyclohexylphenol
13
ether afterwards. Since 2ꢀ Cꢀcyclohexyl phenols remained to
13
be significantly higher in concentration than 1ꢀ Cꢀcyclohexyl
phenols, intramolecular rearrangement of Oꢀalkylation prodꢀ
ucts is excluded to be a major pathway for Cꢀalkylation.
Thus, phenol alkylation with cyclohexanol occurs via a stepꢀ
wise mechanism, where the carbenium ion from olefin protoꢀ
13
nation is the main alkylating agent (Scheme 1, path C). 1ꢀ Cꢀ
cyclohexyl carbenium ion is only produced from reꢀadsorption
1
3
13
and protonation of 1ꢀ Cꢀcyclohexene, whereas 2ꢀ Cꢀ
cyclohexyl carbenium ion can be produced from reꢀadsorption
1
3
and protonation of both 1ꢀ and 3ꢀ Cꢀcyclohexenes, as shown
in Scheme 2. The lack of alkylation, until most cyclohexanol
was dehydrated (0–400 min in Figure 2a), is concluded to be a
consequence of the acid sites interacting with cyclohexanol
dimers, which eliminate water via a pathway not involving
carbenium ionꢀtype intermediate (by inference, an E2ꢀ
pathway). The rate acceleration of alkylation at t > 400 min is,
therefore, attributed to the increased concentration of carbeniꢀ
um ions produced from olefin reꢀadsorption and protonation at
the BAS, once the alcoholꢀderived species are significantly
depleted by dehydration. After the labels in olefins were fully
13
when cyclohexanol was the coꢀreactant. The C label distribuꢀ
tion in the alkylation products indicates that the carbenium ion
generated from olefin protonation is rapidly trapped by phenol
before extensive label scrambling occurs. The observations in
this work imply that for industrial realization, as well as for
synthetic purposes, the use of two catalyst beds, one for dehyꢀ
dration and a second for alkylation, may allow the optimizaꢀ
tion of an overall alkylation process.
13
13
randomized, the estimated ratio between 1ꢀ C, 2ꢀ C and
13
(
3+4)ꢀ C labeled cyclohexylphenols was 1.0: 1.8(±0.1):
2
1
.6(±0.2). This ratio was independent of the temperature (119ꢀ
42 °C) and reasonably close to the theoretical ratio (1: 2:
EXPERIMENTAL SECTION
(
2+1)) for the Cꢀalkylation products that are proposed to form
The HꢀBEA (Si/Al = 75) sample was provided by Clariant and
via quasiꢀequilibrated olefin protonation followed by electroꢀ
philic attack (Figure S10). Rapid scrambling of the labels
within the carbenium ion (e.g., via hydride shifts or multiple
deprotonationꢀprotonation events), compared to the electroꢀ
40,45
was used and characterized previously.
The choice of this
material allowed us to attribute the measured activity excluꢀ
sively to Brønsted acid sites, as it contains very low concentraꢀ
6
ACS Paragon Plus Environment

Page 7 of 9
Journal of the American Chemical Society
4
5
tions of Lewisꢀacidic extraframework Al species. All chemiꢀ
cals were purchased from SigmaꢀAldrich and used as received.
AUTHOR INFORMATION
Corresponding Author
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
13
Adsorption measurements and catalytic reactions of 1ꢀ Cꢀ
cyclohexanol (99 atom % Cꢀenriched) and 1ꢀ Cꢀphenol (99
1
3
13
*Jianzhi.Hu@pnnl.gov
1
3
atom % Cꢀenriched) on HꢀBEA were conducted in a homeꢀ
made high temperature high pressure MAS NMR rotor, where
decalin (> 99%, anhydrous mixture of cis + trans) was used as
the solvent. Other chemicals included cyclohexene (≥ 99%)
and cyclohexyl phenyl ether (95%).
*
Johannes.Lercher@ch.tum.de, johannes.lercher@pnnl.gov
Author Contributions
1
These authors contributed equally to this work. The manuscript
was written through contributions of all authors. All authors have
given approval to the final version of the manuscript.
Typically, for variable temperature (VT) adsorption experiꢀ
13
13
ments, 10 mg 1ꢀ Cꢀcyclohexanol or 10 mg 1ꢀ Cꢀphenol
mixed with 177 mg decalin and 82 mg HꢀBEA were loaded in
the rotor. The adsorption temperature was varied from 0 to
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Notes
The authors declare no competing financial interest.
1
15 °C for phenol and from 0 to 82 °C for cyclohexanol, and
maintained at each set point for 0.5ꢀ1 h until no change could
ACKNOWLEDGMENT
1
3
be observed in the C signals of adsorbed or dissolved pheꢀ
nol/cyclohexanol. The temperature and the amount of zeolite,
decalin and reactants loaded in the rotor were somewhat difꢀ
ferent for the various reaction experiments: 1) cyclohexanolꢀ
The authors would like to thank Prof. Gary L. Haller for his careꢀ
ful reading of the manuscript. This research was supported by the
U. S. Department of Energy (DOE), Office of Basic Energy Sciꢀ
ences, Division of Chemical Sciences, Biosciences and Geosciꢀ
ences. All of the NMR experiments were performed in the Enviꢀ
ronmental Molecular Sciences Laboratory (EMSL), a national
scientific user facility sponsored by the DOE’s Office of Biologiꢀ
cal and Environmental Research, and located at Pacific Northwest
National Laboratory (PNNL). PNNL is a multiꢀprogram national
laboratory operated for the DOE by Battelle Memorial Institute
under Contract DEꢀAC06ꢀ76RLO 1830.
13
phenol alkylation: 127 °C, 10.6 mg 1ꢀ Cꢀcyclohexanol, 10.1
13
mg 1ꢀ Cꢀphenol, 178 mg decalin and 4.6 mg HꢀBEA; 2)
13
cyclohexanol dehydration: 126 °C, 9.6 mg 1ꢀ Cꢀ
cyclohexanol, 194 mg decalin and 4.6 mg HꢀBEA; 3) cycloꢀ
hexeneꢀphenol alkylation: 128 °C, 8.1 mg cyclohexene (unlaꢀ
1
3
beled), 10.2 mg 1ꢀ Cꢀphenol, 182 mg decalin and 4.9 mg Hꢀ
BEA; 4) cyclohexeneꢀcyclohexanolꢀphenol alkylation: 128 °C,
1
3
9 mg cyclohexene (unlabeled), 9.2 mg 1ꢀ Cꢀcyclohexanol,
REFERENCES
13
11.3 mg 1ꢀ Cꢀphenol, 178 mg decalin and 5.3 mg HꢀBEA; 5)
cyclohexyl phenyl ether decomposition: 142 °C, 100 mg cyꢀ
clohexyl phenyl ether (unlabeled), 88 mg decalin and 4.1 mg
HꢀBEA.
(
1)
044.
2)
Huber, G. W.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106,
4
(
Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckꢀ
huysen, B. M. Chem. Rev. 2010, 110, 3552.
13
(3)
Besson, M.; Gallezot, P.; Pinel, C. Chem. Rev. 2014, 114,
In situ C MAS NMR measurements were carried out on a
Varian 500 MHz NMR spectrometer using a 7.5 mm HX
MAS probe with a spinning rate of 3.1 kHz at a resonance
frequency of 125.7 MHz. The VT experiments were conducted
using a commercially available heating stack provided by
Varian, and the actual temperature in the rotor was calibrated
using ethylene glycol using a protocol reported in the literaꢀ
1
2
827.
(
(
4)
5)
Demirbas, A. Energ. Convers. Manage. 2009, 50, 2782.
Zhao, C.; Camaioni, D. M.; Lercher, J. A. J. Catal. 2012,
88, 92.
(6)
Zhao, C.; Song, W.; Lercher, J. A. ACS Catal. 2012, 2,
2714.
(7)
Lett. 2014, 144, 434.
Xu, W.; Miller, S. J.; Agrawal, P. K.; Jones, C. W. Catal.
46 13
ture.
C MAS NMR spectra were recorded using a π/2 pulse
1
(
(
8)
9)
Nie, L.; Resasco, D. E. Appl. Catal. A 2012, 447, 14.
Xu, W.; Miller, S. J.; Agrawal, P. K.; Jones, C. W. Appl.
with pulse width of 5.5 ꢁs and H TPPM decoupling during
data acquisition. For each spectrum, 64 scans were accumulatꢀ
ed with a 10 s recycle delay, which we conclude to be suffiꢀ
cient for quantification purposes based on the equal intensities
of signals collected using 10ꢀ30 s recycle delays. The carbon
balance was better than 96% throughout the reaction, based on
the total integrated intensities of signals corresponding to all
the compounds (except decalin). The chemical shifts were
referenced to adamantane with the upfield methine peak at
29.5 ppm. All the alkylation products were quantified based
Catal. A 2013, 459, 114.
(10) Zhang, Z.; Wang, Q.; Tripathi, P.; Pittman Jr, C. U. Green
Chem. 2011, 13, 940.
(
(
11) Velu, S.; Swamy, C. S. Appl. Catal. A 1994, 119, 241.
12) Lee, S. C.; Lee, S. W.; Kim, K. S.; Lee, T. J.; Kim, D. H.;
Kim, J. C. Catal. Today 1998, 44, 253.
(13) Hu, C. W.; Zhang, Y. F.; Xu, L.; Peng, G. Appl. Catal. A
1999, 177, 237.
(
14) Sato, S.; Takahashi, R.; Sodesawa, T.; Matsumoto, K.;
1
3
Kamimura, Y. J. Catal. 1999, 184, 180.
on the signal of 1ꢀ C in the aromatic ring. A table compiling
all the chemical shift values of pertinent compounds is preꢀ
sented in the Supporting Information (Table S1).
(
(
15) Schmidt, R. J. Appl. Catal. A 2005, 280, 89.
16) Dewar, M. J. S.; Puttnam, N. A. J. Chem. Soc. (Resumed)
1
959, 4086.
(17) Ma, Q. S.; Chakraborty, D.; Faglioni, F.; Muller, R. P.;
ASSOCIATED CONTENT
Goddard, W. A.; Harris, T.; Campbell, C.; Tang, Y. C. J. Phys. Chem.
A 2006, 110, 2246.
Supporting Information.
(
18) Bregolato, M.; Bolis, V.; Busco, C.; Ugliengo, P.; Bordiga,
S.; Cavani, F.; Ballarini, N.; Maselli, L.; Passeri, S.; Rossetti, I.;
Forni, L. J. Catal. 2007, 245, 285.
Additional figures, tables and details for the theoretical calculaꢀ
tions of chemical shifts. This material is available free of charge
via the Internet at http://pubs.acs.org.
(19) Choi, W. C.; Kim, J. S.; Lee, T. H.; Woo, S. I. Catal. Today
2
000, 63, 229.
7
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 9
(
20) DeCastro, C.; Sauvage, E.; Valkenberg, M. H.; Hölderich,
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
W. F. J. Catal. 2000, 196, 86.
(
(
21) Hajipour, A. R.; Karimi, H. Appl. Catal. A 2014, 482, 99.
22) Anand, R.; Gore, K. U.; Rao, B. S. Catal. Lett. 2002, 81,
3
3.
(
(
23) Beltrame, P.; Zuretti, G. Green Chem. 2004, 6, 7.
24) GonzálezꢀBorja, M. Á.; Resasco, D. E. AICHE J. 2015, 61,
598.
(
25) Mathew, T.; Vijayaraj, M.; Pai, S.; Tope, B. B.; Hegde, S.
G.; Rao, B. S.; Gopinath, C. S. J. Catal. 2004, 227, 175.
(
26) Ronchin, L.; Vavasori, A.; Toniolo, L. J. Mol. Catal. A
012, 355, 134.
27) Ronchin, L.; Quatarone, G.; Vavasori, A. J. Mol. Catal. A
2012, 353ꢀ354, 192.
28) Wang, W.; De Cola, P. L.; Glaeser, R.; Ivanova, I.;
Weitkamp, J.; Hunger, M. Catal. Lett. 2004, 94, 119.
29) Vos, A. M.; Nulens, K. H. L.; de Proft, F.; Schoonheydt, R.
A.; Geerlings, P. J. Phys. Chem. B 2002, 106, 2026.
30) Svelle S.; Visur, M.; Olsbye, U.; Saepurahman, S.;
Bjørgen, M. Top. Catal. 2011, 54, 897.
31) Jansang, B.; Nanok, T.; Limtrakul, J. J. Phys. Chem. C
008, 112, 540.
32) Nie, X.; Janik, M. J.; Guo, X.; Liu, X.; Song, C. Catal. Toꢀ
day 2011, 165, 120.
33) Radhakrishnan, S.; Goossens, P.ꢀJ.; Magusin, P. C. M. M.;
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
(
(
(
(
2
(
(
Sree, S. P.; Detavernier, C.; Breynaert, E.; Martineau, C.; Taulelle, F.;
Martens, J. A. J. Am. Chem. Soc. 2016, 138, 2802.
(
34) Ivanova, I. I.; Kolyagin, Y. G. Chem. Soc. Rev. 2010, 39,
018.
35) Haw, J. F.; Song, W.; Marcus, D. M.; Nicholas, J. B. Acc.
5
(
Chem. Res. 2003, 36, 317.
(36) Haouas, M.; Walspurger, S.; Taulelle, F.; Sommer, J. J.
Am. Chem. Soc. 2004, 126, 599.
(
37) Wang, W.; Jiang, Y.; Hunger, M. Catal. Today 2006, 113,
02.
38) Wang, C.; Wang, Q.; Xu, J.; Qi, G.; Gao, P.; Wang, W.;
1
(
Zou, Y.; Feng, N.; Liu, X.; Deng, F. Angew. Chem. Int. Ed. 2016, 55,
2507.
(39) Hu, J. Z.; Hu, M. Y.; Zhao, Z.; Xu, S.; Vjunov, A.; Shi, H.;
Camaioni, D. M.; Peden, C. H. F.; Lercher, J. A. Chem. Commun.
2
015, 51, 13458.
40) Vjunov, A.; Hu, M. Y.; Feng, J.; Camaioni, D. M.; Mei, D.;
(
Hu, J. Z.; Zhao, C.; Lercher, J. A. Angew. Chem. Int. Ed. 2014, 53,
479.
(41) Espeel, P. H. J.; Vercruysse, K. A.; Debaerdemaker, M.;
Jacobs, P.A. in: Studies in Surface Science and Catalysis,
J.Weitkamp, H.G. Karge, H. Pfeifer, W. Hölderich, Eds..; vol. 84,
Elsevier, Amsterdam, 1994, pp. 1457.
(
42) Macht, J.; Janik, M. J.; Neurock, M.; Iglesia, E. J. Am.
Chem. Soc. 2008, 130, 10369.
(43) Zhi, Y.; Shi, H.; Mu, L.; Liu, Y.; Mei, D.; Camaioni, D.
M.; Lercher, J. A. J. Am. Chem. Soc. 2015, 137, 15781.
(
44) Lee, K. Y.; Arai, T.; Nakata, S.; Asaoka, S.; Okuhara, T.;
Misono, M. J. Am. Chem. Soc. 1992, 114, 2836.
45) Vjunov, A.; Fulton, J. L.; Camaioni, D. M.; Hu, J. Z.; Burꢀ
(
ton, S. D.; Arslan, I.; Lercher, J. A. Chem. Mater. 2015, 27, 3533ꢀ
3545.
(
46) Ammann, C.; Meier, P.; Merbach, A. J. Magn. Res. 1982,
4
6, 319.
8
ACS Paragon Plus Environment

Page 9 of 9
Journal of the American Chemical Society
For Table of Contents Only
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
9
ACS Paragon Plus Environment