Initial Carbon–Carbon Bond Formation during the Early Stages of the Methanol-to-Olefin Process Proven by Zeolite-Trapped Acetate and Methyl Acetate

Article abstract of DOI:10.1002/anie.201608643

Methanol-to-olefin (MTO) catalysis is a very active field of research because there is a wide variety of sometimes conflicting mechanistic proposals. An example is the ongoing discussion on the initial C?C bond formation from methanol during the induction period of the MTO process. By employing a combination of solid-state NMR spectroscopy with UV/Vis diffuse reflectance spectroscopy and mass spectrometry on an active H-SAPO-34 catalyst, we provide spectroscopic evidence for the formation of surface acetate and methyl acetate, as well as dimethoxymethane during the MTO process. As a consequence, new insights in the formation of the first C?C bond are provided, suggesting a direct mechanism may be operative, at least in the early stages of the MTO reaction.

Full text of DOI:10.1002/anie.201608643

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International Edition: DOI: 10.1002/anie.201608643
German Edition: DOI: 10.1002/ange.201608643
Heterogeneous Catalysis Very Important Paper
Initial Carbon–Carbon Bond Formation during the Early Stages of the
Methanol-to-Olefin Process Proven by Zeolite-Trapped Acetate and
Methyl Acetate
Abhishek Dutta Chowdhury+, Klaartje Houben+, Gareth T. Whiting, Mohamed Mokhtar,
Abdullah M. Asiri, Shaeel A. Al-Thabaiti, Suliman N. Basahel, Marc Baldus,* and
Bert M. Weckhuysen*
Abstract: Methanol-to-olefin (MTO) catalysis is a very active
field of research because there is a wide variety of sometimes
conflicting mechanistic proposals. An example is the ongoing
pool” (HCP) mechanism, originally proposed by Dahl and
Kolboe.[2,7] However, the exact route for the formation of the
À
first carbon–carbon (C C) bond in this mechanism still
discussion on the initial C C bond formation from methanol
remains elusive.[8] For a long time, the commonly acknowl-
edged assumption was that the presence of traces of
impurities (e.g. in the used methanol, catalyst, and/or carrier
À
during the induction period of the MTO process. By employing
a combination of solid-state NMR spectroscopy with UV/Vis
diffuse reflectance spectroscopy and mass spectrometry on an
active H-SAPO-34 catalyst, we provide spectroscopic evidence
for the formation of surface acetate and methyl acetate, as well
as dimethoxymethane during the MTO process. As a conse-
À
gas) is responsible for the first C C bond formation. An
alternative option, known as the direct mechanism (e.g.
coupling of two methanol or dimethyl ether molecules), still
lacks clear experimental support.[9] Interestingly, Hunger and
co-workers showed already in 2006 that traces of organic
impurities neither have any significant influence on product
distribution, nor do they govern the formation of HCP
species.[10] Since then, the research groups of Hunger,[10–15]
Kondo,[16] Fan,[17,18] Copꢀret and Sautet,[19] and Lercher[20]
have provided both experimental and theoretical evidences
in support of the direct mechanism during the initial stages of
the MTO process.
À
quence, new insights in the formation of the first C C bond are
provided, suggesting a direct mechanism may be operative, at
least in the early stages of the MTO reaction.
T
he growing concern on climate change stimulates both
academia and industry to develop more sustainable chemical
processes. The methanol-to-olefin (MTO) process over H-
SAPO-34 and H-ZSM-5 is one of these promising catalytic
routes, which provides a means to indirectly produce impor-
tant chemical building blocks, such as propylene, from natural
gas, biomass and waste.[1–5] Owing to the inherent complex
nature of the MTO process, more than 20 different mecha-
nisms have already been proposed in the literature.[6] Among
them, the most experimentally verified one is the “dual-cycle”
mechanism, which is a modified version of the “hydrocarbon
The earlier proposed direct MTO routes include the
a) oxonium ylide, b) carbene, and c) methane–formaldehyde
mechanisms.[2,6] Although, these mechanisms still have their
(limited) experimental evidences in literature, the theoretical
probability of such direct coupling is anticipated to be low
because of their higher activation energies and unstable
reaction intermediates.[2,21] However, a surface methoxy
species (SMS), formed upon adsorption of methanol onto
a Brønsted acid site, is the most experimentally verified
intermediate of the MTO process.[14,22] Moreover, some
recent reports identified that several initial hydrocarbon
species can be directly generated as a result of coupling
between SMS and methanol/dimethyl ether (DME). For
instance, with the help of IR and GC-MS spectroscopy Kondo
et al. proposed that propylene can be generated as a result of
the coupling between SMS and ethylene.[16] Based on both
[*] Dr. A. D. Chowdhury,[+] Dr. G. T. Whiting, Prof. Dr. B. M. Weckhuysen
Inorganic Chemistry and Catalysis group
Debye Institute for Nanomaterials Science, Utrecht University
Universiteitsweg 99, 3584 CG Utrecht (The Netherlands)
E-mail: b.m.weckhuysen@uu.nl
Dr. K. Houben,[+] Prof. Dr. M. Baldus
NMR Spectroscopy, Bijvoet Center for Biomolecular Research
Utrecht University, Padualaan 8, 3584 CH Utrecht (The Netherlands)
E-mail: M.Baldus@uu.nl
À
experimental and theoretical evidences, the direct C C bond-
Prof. Dr. M. Mokhtar, Prof. Dr. A. M. Asiri, Prof. Dr. S. A. Al-Thabaiti,
Prof. Dr. S. N. Basahel
Department of Chemistry, King Abdulaziz University
P.O. Box 80203, 21589 Jeddah (Saudi Arabia)
forming route proposed by Fan et al. involves: i) the forma-
+
tion of a methoxymethyl cation (CH3OCH2 from SMS and
À
DME) and ii) its subsequent direct C C coupling with
another DME or methanol molecule to form
CH3OCH2CH2OR (R = H, CH3) moiety, which is considered
to be a precursor for olefins.[17] An interesting study was
reported by the research groups of Copꢀret and Sautet, where
[+] These authors contributed equally to this work.
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201608643.
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. This is an open access article under the terms of the Creative
Commons Attribution Non-Commercial License, which permits use,
distribution and reproduction in any medium, provided the original
work is properly cited, and is not used for commercial purposes.
À
the formation of the first C C bond from DME was proposed
to be catalyzed by extra-framework Al atoms in acidic
zeolites.[19] Their experimental and theoretically verified
À
proposal involves the C C bond formation over Al2O3
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À
through the C H activation of methane in an alumino-
10 minutes of reaction (Figures S3b). Interestingly, the online
MS data presented in Figures S2c,d reveal the presence of
methane, DME, lower olefins (i.e., ethylene, propylene, and
butylene) and also traces of DMM. The existence of DMM is
supported by its characteristic m/z of 75, which exclusively
belongs to DMM (Figure S3c). The gradually increasing
amount of DMM with increasing time-on-stream could be
attributed to the formation of a higher quantity of its
precursor, the surface formate species, during the course of
reaction. This is consistent with the work of Kubelkova et al.,
who used temperature-programmed desorption to identify
DMM.[24]
+
=
oxonium (AlO CH2 )/methane adduct, which has conceptual
resemblance with the “methane–formaldehyde” mechanism
proposed by Hutchings et al.,[23] Kubelkova and co-workers[24]
and Hirao and co-workers.[25] Independently from each other,
the research groups of Copꢀret and Sautet[19] and Lercher
et al.[20] postulated the involvement of formate and acetate
À
species bound to the zeolite surface during the first C C bond
formation at the early stages of the MTO reaction. This
surface formate species could lead to the formation of
dimethoxymethane (DMM, CH3OCH2OCH3) during the
course of the MTO reaction, as suggested by the research
groups of Kubelkova,[24] and Chang.[26] Within this context it is
important to mention that Lercher and co-workers very
recently postulated that methyl acetate (CH3CO2CH3) is the
In the second stage of our study, we have performed
advanced ssNMR spectroscopy on H-SAPO-34 after being
exposed to the MTO reaction for 30 minutes at 673 K using
13C-enriched methanol. Such isotope enrichment not only
greatly increased ssNMR signal intensities but also enabled
a detailed analysis of two-dimensional ssNMR correlation
À
very first C C bond-containing intermediate (derived from
surface-bound acetate species) during the MTO reaction over
ZSM-5.[20] Despite these encouraging results, no direct
evidence has been presented for the existence of DMM as
well as surface-bound acetate and methyl acetate species
during the zeolite-catalyzed MTO reaction.
1
experiments discussed below. The H-13C cross-polarization
(CP) and 13C direct excitation (DE) ssNMR spectra at 10 kHz
MAS of the MTO-reacted catalyst are presented in Figure 1.
In this work, we provide spectroscopic evidence for the
À
direct formation of the first C C bond during the H-SAPO-
34-catalyzed MTO reaction, through the identification of
surface-trapped formate and acetate species and methyl
acetate as well as DMM. This has been made possible by
using a combination of UV/Vis diffuse reflectance spectros-
copy (DRS), mass spectrometry (MS), and magic angle
spinning (MAS)[27] solid-state nuclear magnetic resonance
(ssNMR) studies using a 13C-methanol reacted catalyst. The
multispectroscopic approach, illustrated in Figure S1 in the
Supporting Information, allows the investigation of the initial
stages of the MTO reaction, consisting of the formation of
surface formate/acetate, methyl acetate and DMM from SMS.
In the first stage of our study, operando UV/Vis DRS with
online MS was used to identify and differentiate between
neutral and carbocationic HCP-type species, as well as gas-
phase products formed during the MTO reaction over zeolite
H-SAPO-34 at
a reaction temperature of 673 K for
Figure 1. 13C DE (black) and 1H-13C CP (blue) ssNMR spectra of
trapped products obtained after the methanol-to-olefin (MTO) reaction
over H-SAPO-34 at 673 K for 30 minutes (*=spinning sideband).
60 minutes. The results of this approach are summarized in
Figures S2 and S3. Figure S2a reveals major spectral changes
during the first 10 minutes of the MTO reaction, as absorption
bands at 297, 350, 387, 414, and 640 nm increase in intensity
with increasing time-on-stream (Figure S3b). After 7 minutes
of reaction, a decrease in intensity was observed only in the
case of the 350 and 640 nm bands, implying the existence of
intramolecular transformations within the zeolite framework.
The observed bands at 297, 350, 479, and 640 nm are
attributed to neutral methylated benzenes, dienylic carbocat-
ionic/methylbenzenium (up to three methyl groups) ions,
trienylic and methylated poly-arenium ions, respec-
tively.[10–12,28–30] Similarly, the 387 nm band is characteristic
for a hexamethylbenzenium ion (HMB+) and its bathochro-
mic shift to 414 nm with increasing time-on-stream can be
explained by the further methylation of HMB+ to, for
example, hepta-methylbenzenium ions.[31] We propose that
the cracking of polyaromatics into trienylic carbenium species
and olefins are responsible for the concomitant increase and
decrease of the 479 and 640 nm bands, respectively, after
The following features were observed: i) 18–22 ppm aliphatic
methyl groups, ii) 50–65 ppm methoxy groups, iii) 90–105 ppm
acetal moiety, iv) 120–155 ppm (methylated) aromatic/ole-
finic groups, and v) 170–185 ppm carbonyl groups.[2,11–13,32–35]
Because of the overlap with spinning side bands, we employed
higher MAS rates to unambiguously identify weak signals at
200 and 220 ppm, indicative for poly-methylbenzenium ions
(Figure S4 and Table S1). Interestingly, we do not observe
strong signals around 40 ppm, which indicates the absence of
typical sp3 CH2 groups. The strongest aliphatic signal at
52 ppm was due to the methanol, whereas the peaks at 55, 57,
and 62 ppm are due to acetate, methoxy/SMS, and adsorbed
(side-on) DME, respectively (Table S1). Moreover, the
strongest peak at 132 ppm suggests the presence of neutral
methylated benzenes and HMB+ as the dominating HCP
intermediate.
2
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In order to elucidate in more detail the zeolite-trapped
species, additional 2D ssNMR spectra were recorded: i) 13
was previously characterized by Kondo et al. and Hunger
et al. by IR and NMR spectroscopy, respectively.[15,40] The
C
PDSD (Proton-Driven Spin-Diffusion) spectra[36] with short
(30 ms) and long (150 ms) mixing times for short- and long-
range 13C–13C correlations, respectively, and ii) proton-
detected 2D 13C–1H CP-HETCOR (HETCOR: HETero-
nuclear CORrelation spectroscopy)[37] with a short (50 ms)
and long (500 ms) CP contact time for the second 13C–1H CP,
for short- and long-range 13C–1H correlations (Figure S5). In
those spectra we can clearly distinguish between the broad
signals of trapped/immobile aromatic species, and sharp
signals for mobile non-aromatic/small molecules. The latter
signals remain visible under (dipolar-based) CP experiments
because of their restricted molecular mobility in H-SAPO-34.
Because of the large difference in NMR signal behavior, the
NMR spectra were processed to either focus on the broad
signals (using only initial points and applying additional line-
broadening) or on the sharp signals (using full dataset and
additional linear prediction). The strong signal at 52.2 (13C)
and 3.59 (1H) ppm can easily be assigned to surface adsorbed
methanol, while the signal at 57.7 (13C) and 3.54 (1H) ppm is
due to surface-adsorbed methoxy species (Figure 2a,b).[14,15,22]
Interestingly, a strong cross-peak between these C signals is
observed already at short (13C,13C) mixing times (Figures 2a
and S5), which indicates the close proximity of surface
adsorbed methanol and SMS. Such close proximity could be
a possible signature of their reaction through the polarization
existence of such carbene-like SMS was experimentally
confirmed as well, by a trapping experiment with cyclohexane
as a probe molecule at ꢀ 493 K, where methylcyclohexane
was formed through an insertion reaction of carbene/ylide
3
[14,15]
À
into the sp C H bond of cyclohexane.
Therefore, we
believe the strong cross-peak at short (13C,13C) mixing times
between 57.7 and 52.2 ppm is an indication of a similar type of
carbene/ylide insertion into the sp3 C H of the incoming
methanol, as shown in Figure 2c. It should be noted that SMS
À
À
is highly capable of forming C C bonds at higher reaction
temperatures, which is well established in zeolite chemis-
try.[1,3,14,16,22] Only at a long mixing time, an additional cross-
peak with 57.7 was observed at 100.1 ppm, whose correspond-
ing 1H resonates at 4.72 ppm, which can be assigned to
dimethoxymethane (DMM).[41–43] Remarkably,
a second
minor signal at 101.3 ppm is observed for the DMM-CH2
group, that shows an exchange cross-peak with 100.1 at longer
mixing times (Figure 2a). This is an indication of exchange
between anomeric DMM structures on a sub-second time-
scale (trans, trans and gauche, gauche, Figure 2d).[42,44]
Although the plausible existence and/or influence of DMM
during MTO was already proposed by Kubelkova et al.,[24]
Chang et al.[26] and Lercher et al.,[20] these results provide the
first spectroscopic evidence that DMM is indeed formed
during MTO. The acetal signal at 93 ppm also has a cross-peak
in the CH spectrum at 4.7 ppm, but lacks a correlation with
other C signals, hence identified as methanediol, as the
hydrolyzed product of DMM (Figure 2e).[41]
À
of the C H bond of SMS by a neighbouring adjacent oxygen,
as observed independently before by the groups of Kondo,
Anderson, and Senchenya (Figure 2c).[16,38,39] As a result,
SMS of a carbene/ylide nature are likely to be formed, as it
In the carbonyl region of the 13C–13C spectra, clear cross-
peaks to methyl carbon atoms were observed at
both long and short mixing times (Figure 3),
indicative for acetate species.[20] While the signal
at 180.5 ppm shows no additional cross-peaks, in
accordance with surface-bound acetate, the signal at
178.5 ppm has a clear cross-peak with a 13C signal at
55.1 ppm at longer mixing times. This 13C signal
correlates with a H signal at 3.82 ppm and has an
additional very weak signal with the methyl signal
À
at 22.3 ppm at longer C C mixing times. This cross-
peak pattern is typical for methyl acetate (Fig-
ure 3a). Similarly, in the 2D 1H–13C ssNMR spectra,
the C signl at 173 ppm correlates with a H signal at
8–8.5 ppm, which is compatible with surface for-
mate (Figure 3b).[19] Actually, two signals were
observed in this region, which could be indicative
for different resonance structures for surface for-
mate. Together, these observations support the
existence of surface-bound formate/acetate spe-
À
cies-assisted C C bond formation route during
MTO, as has recently been proposed by the
research groups of Copꢀret and Sautet,[19] and
Figure 2. ssNMR spectra of methanol, methoxy, and acetal species in H-SAPO-34
after the methanol-to-olefin (MTO) reaction for 30 minutes at 673 K. a) Zooms
from 2D 13C–13C (blue) and 13C–1H (red) ssNMR spectra with long mixing (150 ms)
or CP contact time (500 ms), respectively. b) NMR assignment of surface species.
c) Identification of a surface adduct between SMS and methanol (normal arrows:
electron flows, dotted arrows: 13C-13C NMR correlation). d) Chemical exchange of
anomeric conformations of DMM observed in 13C–13C spectra. e) Identification of
methanediol in 13C–1H spectrum (light blue) with short CP contact time (50 ms).
Lercher et al.[20] Our study provides evidence for
À
the formation of the first C C bond-containing
intermediates (i.e., methyl acetate and surface
acetate) during the MTO reaction over H-SAPO-
34. Several other correlations between aliphatic
(13C/1H: 20–30/2.2–2.4 ppm) and aromatic moieties
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(Figure 2a–c) could also be consistent with the
existence of the oxonium ylide mechanism
(Scheme S2). However, considering the reported
theoretical calculations based on the oxonium mech-
anism and the observed carbene/ylide features of
SMS in our study, we favor the carbene/ylide
insertion pathway.[2,6] Moreover, our NMR data is
not fully compatible with the intermediates of
oxonium mechanism, as was discussed in Scheme S2.
Species B alternatively could also be derived from
À
the direct C H bond activation of the CH3 group of
SMS by methanol, as computationally confirmed by
Blaszkowski and van Santen (path b in Scheme 1).[45]
Here, the additional water or methanol can act as an
assisting molecule to allow favorable transition-state
geometry and reduce the energy barrier.[45]
However, Hirao and co-workers indicated that
the spectroscopic detection of surface species B
would be very difficult as the final conversion to
Figure 3. ssNMR correlations of acetate, formate, and methylated polyene/ben-
zene in H-SAPO-34 after the methanol-to-olefin (MTO) reaction for 30 minutes at
673 K. a) Zooms from 2D 13C–13C (blue) and 13C–1H (red) MAS ssNMR spectra
with long mixing (150 ms) or CP contact time (500 ms), respectively, indicating
surface acetate and methyl acetate resonances. b) ssNMR signals of surface-
bound formate in the 13C–1H spectra (light blue) with a short CP contact time
(50 ms). c) Zoom of aromatic signals from 2D 13C–13C (blue) and 13C–1H (light
blue) MAS NMR spectra with long mixing (150 ms) or short CP contact time
(50 ms), respectively.
ethylene is expected to be fast.[25] Next, the first C C
À
bond could also be derived from surface-bound
acetate species (C in path c, Scheme 1), which is
a “Koch-type” carbonylation product of SMS (Fig-
ure 3a).[20,46] Methyl acetate is formed from the
surface-bound acetate species, which initiates the
formation of HCP species and hence, produces an
(13C/1H: 132–154/ 6–10 ppm) in Figure 3c reveal the presence
of various HCP-type intermediates; that is, conjugated
polyenes, methylated neutral benzenes and benzeniums,
which are known to be formed in the alkene and arene
cycles of the HCP mechanism (Scheme S1 and
Table S1).[2,11–13,32–35] However, the lack of signals in the 65–
90 ppm region signifies the absence of a CH3OCH2CH2OR
(R = H, CH3) moiety, as previously proposed by Fan and co-
workers.[17]
Based on the above-described results, we propose in
À
Scheme 1 a pathway for the formation of the first C C bond
during the initial stages of the MTO process. First, the CH3
group of SMS, formed by methylation of a Brønsted acid site
(denoted as ZeOH, Scheme 1), interacts initially with another
molecule of methanol/DME (Species A in path a, Scheme 1).
Scheme 1. Plausible catalytic cycle of the “direct mechanism” for the
À
The methyl C H of SMS is then polarized because of its
À
first C C bond formation during the early stages of the MTO reaction.
À
interaction with a neighboring O and the first C C bond
The reaction products and intermediates indicated in blue have been
À
formation step is assisted by hydrogen bonding with the C H
À
experimentally observed in this work. The first C C bond in paths a/b
is highlighted in bold.
proton (species A in path a, Scheme 1). As a result, the first
À
C C bond formation takes place through the typical insertion
3
À
reaction of carbene/ylide from SMS into the sp C H bond of
methanol/DME during MTO (species A/A’ in path a,
Scheme 1 and Figure 2c).[14,38–40] In addition to our ssNMR
observation (Figure 2a–c), the existence of such neighboring
oxygen group-assisted SMS-type species has been character-
ized by Hunger et al.[14,15] and Kondo et al.[16,40] Species A’
eventually led to surface-ethanolic species (B in path a,
Scheme 1), which undergoes dehydration (through protona-
tion of alcohol/ether oxygen atoms by Brønsted acid sites of
the zeolite) to form ethylene and regenerates ZeOH.[17] In
principle, the presence of two adjacent methoxy groups
olefin (path c, Scheme 1 and Section SIII in the Supporting
Information). Therefore, the present work also provides
À
evidence in support of the first C C bond formation route
through methanol carbonylation of SMS (path b, Scheme 1),
as also recently proposed by Lercher and co-workers.[20]
Indeed, the observed microscopic reversibility between
methanol and methyl acetate (Section SIII in the Supporting
Information) provides justification in support of the forma-
tion of methyl acetate, DMM, surface formate, and acetate
4
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MTO reaction.
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Similar “Koch-type” carbonylation of the zeolite surface
could also lead to the formation of surface formate
(Scheme S3),[19] as observed by ssNMR spectroscopy (Fig-
ure 3b).[46] The highly electrophilic surface formate species
then becomes available for a nucleophilic attack by methanol
to form an acetal of formaldehyde, DMM, on the solid acid
(Scheme S2 and Figure 2a,d).[24] Therefore, in addition to the
existence of methyl acetate, DMM, surface formate and
acetate, the spectroscopic identification of surface intermedi-
ate A/A’ (Schemes 1 and Figure 2c) provides evidence in
À
favor of the direct C C bond formation route from methanol
during the early MTO stages. The first few olefins from the
“direct mechanism” (paths a and b in Scheme 1) then
participate in the alkene part of the HCP mechanism
(Scheme S1 and Table S1) and hence, initiate the auto-
catalytic part of the MTO process.
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In conclusion, our data provide direct spectroscopic
evidence for the formation of surface-bound acetate (i.e.,
À
a direct C C bond-containing reaction intermediate), methyl
À
acetate (i.e., the first C C bond containing molecule) as well
as dimethoxymethane during the MTO process over H-
SAPO-34. We propose the surface species-assisted “direct
mechanism”, as outlined in Scheme 1 as the most likely
À
candidate for the formation of the first C C bond during the
initial stages of the MTO process.
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Acknowledgements
This research work was funded by a European Research
Council (ERC) Advanced grant (number 321140 to BMW)
and supported by NWO (Middelgroot program, grant number
700.58.102 to MB) as well as a grant from the Deanship of
Scientific Research (DSR) of King Abdulaziz University
(grant number T-002-431 to BMW). We thank Dr. Pie-
ter C. A. Bruijnincx for fruitful discussions.
Keywords: methanol-to-olefin reaction ·
operando spectroscopy · reaction mechanisms ·
solid-state NMR spectroscopy · zeolites
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ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
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Received: September 4, 2016
Revised: October 18, 2016
Published online: && &&, &&&&
6
www.angewandte.org
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 7
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Heterogeneous Catalysis
Direct formation of a C–C bond: By using
a combination of UV/Vis spectroscopy,
mass spectrometry, and advanced NMR
spectroscopy, evidence was found for the
formation of methyl acetate, dimethoxy-
methane and surface acetate species
during the methanol-to-olefin (MTO)
reaction over the zeolite catalyst H-SAPO-
34. New insights in the formation of the
first carbon–carbon bond during the
MTO process are provided.
A. D. Chowdhury, K. Houben,
G. T. Whiting, M. Mokhtar, A. M. Asiri,
S. A. Al-Thabaiti, S. N. Basahel,
M. Baldus,*
B. M. Weckhuysen*
&&&& — &&&&
Initial Carbon–Carbon Bond Formation
during the Early Stages of the Methanol-
to-Olefin Process Proven by Zeolite-
Trapped Acetate and Methyl Acetate
Angew. Chem. Int. Ed. 2016, 55, 1 – 7
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7
These are not the final page numbers!