A Highly Stable Copper-Based Catalyst for Clarifying the Catalytic Roles of Cu0 and Cu+ Species in Methanol Dehydrogenation

Article abstract of DOI:10.1002/anie.201710605

Identification of the active copper species, and further illustration of the catalytic mechanism of Cu-based catalysts is still a challenge because of the mobility and evolution of Cu⁰ and Cu⁺ species in the reaction process. Thus, an unprecedentedly stable Cu-based catalyst was prepared by uniformly embedding Cu nanoparticles in a mesoporous silica shell allowing clarification of the catalytic roles of Cu⁰ and Cu⁺ in the dehydrogenation of methanol to methyl formate by combining isotope-labeling experiment, in situ spectroscopy, and DFT calculations. It is shown that Cu⁰ sites promote the cleavage of the O?H bond in methanol and of the C?H bond in the reaction intermediates CH₃O and H₂COOCH₃ which is formed from CH₃O and HCHO, whereas Cu⁺ sites cause rapid decomposition of formaldehyde generated on the Cu⁰ sites into CO and H₂.

Full text of DOI:10.1002/anie.201710605

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: A Highly Stable Cu-based Catalyst for Clarifying the Catalytic
Roles of Cu0 and Cu+ Species in Methanol Dehydrogenation
Authors: Huanhuan Yang, Yanyan Chen, Xiaojing Cui, Guofu Wang,
Youliang Cen, Tiansheng Deng, Wenjun Yan, Jie Gao,
Shanhui Zhu, Unni Olsbye, Jianguo Wang, and Weibin Fan
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201710605
Angew. Chem. 10.1002/ange.201710605
Link to VoR: http://dx.doi.org/10.1002/anie.201710605
http://dx.doi.org/10.1002/ange.201710605

10.1002/anie.201710605
Angewandte Chemie International Edition
COMMUNICATION
A Highly Stable Cu-based Catalyst for Clarifying the Catalytic
Roles of Cu0 and Cu+ Species in Methanol Dehydrogenation
Huanhuan Yang, Yanyan Chen, Xiaojing Cui*, Guofu Wang, Youliang Cen, Tiansheng Deng, Wenjun
Yan, Jie Gao, Shanhui Zhu, Unni Olsbye, Jianguo Wang and Weibin Fan*
Abstract: Identification of active copper species, and further
illustration of catalytic mechanism of Cu-based catalysts is still a
challenge because of the mobility and evolution of Cu0 and Cu+
species in the reaction process. Thus, an unprecedentedly stable
Cu-based catalyst was fabricated by uniformly embedding Cu
nanoparticles in mesoporous silica shell for clarifying the catalytic
roles of Cu0 and Cu+ with dehydrogenation of methanol to methyl
formate by combining isotope-labeling experiment, in situ
spectroscopy and DFT calculations. It is shown that Cu0 sites
promote the cleavage of O–H bond in methanol and C–H bond in the
reaction intermediates of CH3O and H2COOCH3 formed from CH3O
and HCHO, whereas Cu+ sites cause rapid decomposition of
formaldehyde generated on the Cu0 sites into CO and H2.
Dehydrogenation of methanol (DOM) into methyl formate
(MeF) could be considered as a prototype C1 chemical reaction
as it generates CH3O and HCHO intermediates and COx
byproducts, and consequently, involves in the cleavage of both
O–H and C–H bonds.[11] Therefore, a clear understanding of the
catalytic roles of Cu0 and Cu+ in this reaction would be highly
useful for unraveling the catalytic mechanism of Cu-based
catalysts in C1 chemical reactions. To achieve this goal, a highly
stable Cu-based catalyst needs to be prepared. Recently, active
metal NPs encapsulated in porous shells show high thermal and
chemical stabilities in the reaction process.[12] This simulates us
to develop a method to prepare a CuO core-mesoporous silica
shell catalyst (designated as xCu@mSiO2, Figure S1) that
shows not only significantly high catalytic stability but also
adjustable activity and selectivity in the DOM into MeF. In
particular, the catalytic roles and pathways of Cu0 and Cu+
Cu-based catalysts have been widely used in large numbers of
industrially important reactions, including synthesis of alcohols
from syngas,[1] steam reforming of methanol,[2] oxidation of CO
and hydrocarbons,[3] water-gas shift reaction,[4] and selective
hydrogenation of carbonyl compounds[5] and dehydrogenation of
alcohols.[6] Therefore, Cu-based catalysts have attracted broad
research interest, and many excellent Cu-based catalysts have
been prepared.[5a,5c,7] However, the active sites and the catalytic
pathway of Cu-based catalysts have not been unambiguously
clarified despite that extensive studies have significantly
deepened these fundamental issues.[1a,2a,4,8] A major challenge
in these studies is that Cu nanoparticles (NPs) restructure,
agglomerate, and even sinter in the reduction and reaction
processes.[9]
species are clarified with such
a catalyst by elaborately
designing experiments and employing in situ spectroscopy,
isotope-labeling experiment and DFT calculations.
Another overwhelming problem is that Cu0 and Cu+ species
always coexist at real reaction conditions, and particularly, the
chemical state of Cu species dynamically evolves in the reaction
process.[1a,3a,5c] As a consequence, in some reactions, the active
component in the Cu-based catalyst is considered to be metallic
copper activated by hydrogen molecules,[4,6b,10] whereas in
another type of reactions such as CO oxidation, the interfacial
Cu+ or the dispersed CuOx (x = 0.2 – 0.5) species on the surface
are proposed to be the crucial active sites.[3a,3b] Recently, it was
assumed that a synergetic effect probably existed between Cu0
and Cu+ species in the carbon-oxygen bonds hydrogenolysis
reactions.[5c]
Figure 1. (a) TEM and STEM (inset) images of 7Cu@mSiO2; (b) HRTEM
images of the section marked with dotted circle in (a) and the typical CuO NPs
in the core with exposed (111) surface (inset); (c) CuO NPs size distribution of
7Cu@mSiO2; (d) catalytic results of 7Cu/SiO2, 7Cu/mSiO2 and 7Cu@mSiO2
for DOM to MeF and (e) catalytic results for long-term test of DOM to MeF on
7Cu/mSiO2 and 7Cu@mSiO2 (circle: 7Cu/SiO2; triangle: 7Cu/mSiO2; square:
7Cu@mSiO2; reduction conditions: 300 oC, 10 h, 10%H2/Ar (30 mL/min);
reaction conditions: 230 oC, 1 atm, WHSV = 4 h-1, n(Ar)/n(CH3OH) = 3.7 (V/V)).
[*] H. Yang, Dr. Y. Chen, Dr. X. Cui, G. Wang, Y. Cen, Dr. T. Deng, W.
Yan, J. Gao, Dr. S. Zhu, Prof. J. Wang, Prof. W. Fan
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry
Chinese Academy of Sciences
Figures 1a and S2 show that the uniform spherical particles
of as-synthesized xCu@mSiO2 have a core-shell structure with
size in the region of 500 – 700 nm. TEM images reveal that the
core consists of highly dispersed 3 – 4 nm CuO NPs, which is
confirmed by the XRD results that no diffraction peaks
characteristic of CuO were observed for the samples with Cu
loading  9.4 wt.% (Figures 1b,c, S2 and S3a). The small-angle
XRD patterns of all the samples display a peak at 2θ of 2.4o
although it broadens with the CuO content (Figure S3b). In
27 South Taoyuan Road, Taiyuan 030001, (P. R. China)
E-mail: cuixj@sxicc.ac.cn; fanwb@sxicc.ac.cn
H. Yang, Y. Cen, J. Gao
University of Chinese Academy of Sciences
Beijing 100049, (P. R. China)
Prof. U. Olsbye
Department of Chemistry, inGAP Centre of Research-based Innovation
University of Oslo
P.O. Box 1033 Blindern, 0315 Oslo, Norway
Supporting information for this article is given via a link at the end of the
document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201710605
Angewandte Chemie International Edition
COMMUNICATION
particular, all the samples exhibit a typical IV N2 physisorption
isotherm (Figure S4), indicating that their silica shell has a
mesoporous structure,[13] which facilitates the diffusion of
reactant and product molecules in/out of the sample.
high MeF selectivity. This confirms that the support, Cu+ and
Cu2+ are not the active species, while Cu0 is responsible for the
formation of MeF. This is further verified by the experimental
results of 7Cu@mSiO2 reduced at 200, 300 and 450 oC. The
N2O titration, CO-TPD and in situ XPS results reveal that Cu+
Table S2 shows that the optimum Cu loading in
xCu@mSiO2 is 6.6 wt.% in terms of the MeF yield. Interestingly,
7Cu@mSiO2 gave higher MeF yield than 7Cu/mSiO2 and
7Cu/SiO2 prepared by the impregnation method. Figure 1d
shows that 7Cu@mSiO2 and 7Cu/mSiO2 are much more stable
than 7Cu/SiO2. A further comparison of their catalytic results
reveals that 7Cu@mSiO2 and 7Cu/mSiO2 exhibit similar catalytic
activity within 136 h despite that a monotonic decrease was
observed for both of them (Figure 1e). However, unexpectedly,
the activity of 7Cu@mSiO2 can be nearly recovered after
regeneration by calcining at 550 oC in air, while 7Cu/mSiO2
decreases from  40% to 17% in methanol conversion. This
indicates that the deactivation of 7Cu@mSiO2 is probably
caused by deposition of carbonaceous materials on surface, not
agglomeration/growth of Cu NPs. Indeed, the average sizes of
Cu NPs in the fresh, spent and regenerated samples were
almost the same (Figures 1c, S3a,d,e and S7). In contrast, that
of 7Cu/mSiO2 increased from 3.9 to 4.4, and further to 5.3 nm
after reaction for 136 h and regeneration. Particularly, the Cu
NPs on the external surface of mesoporous silica sintered to 100
nm (Figure S8a,c,e). This phenomenon is more severe for
7Cu/SiO2 (Figure S8b,d) as a result of the absence of significant
geometric confinement effect. Consequently, a more severe
deactivation occurred.
o
species dominate the surface of the sample reduced at 200 C,
whereas Cu0 species are prevalent on the surface of the
o
samples reduced at 300 and 450 C (Figures S11i,j, S13b and
Tables S1, S5). Thus, both methanol conversion and MeF yield
are higher than 30% for the latter two samples, while that
reduced at 200 oC gave a methanol conversion < 6% (Table S2).
Deposition of carbonaceous materials on the spent
7Cu@mSiO2 is confirmed by IR spectroscopy, TGA result and
the decrease in the surface area and pore volume (Figure S9
and Table S1). The spent sample shows four bands between
2800 and 3000 cm-1, which are typical for the C–H vibrations in
carbonaceous materials,[14] and all disappeared after
regeneration. TGA shows that it has a wight loss of 2.71 wt.%
at > 390 oC. The similar phenomena were observed for
7Cu/mSiO2. Thus, 7Cu/mSiO2 deactivated by not only the
agglomeration of Cu NPs but also the deposition of
carbonaceous materials. In addition, some Cu species leached
(Table S1).[15] In contrast, the deactivation of 7Cu@mSiO2
primarily arises from the carbon deposition. The unexpectedly
high stability of 7Cu@mSiO2 in the structure, morphology and
compositions during the reaction and regeneration processes
results from not only encapsulation of Cu NPs in mesoporous
silica shell but also formation of copper phyllosilicate (Figures
1a-c, S3a-e, S7, S10 and S11a,b).
Figure 2. In situ DRIFT spectra of (a) 7Cu@mSiO2 reduced at 300 oC for
DOM at 230 oC at different time (red and blue labels signal for MeF and HCHO
respectively) and band intensity of MeF at 1766 cm-1 with TOS (inset), and (b)
adsorbed methoxy species on 7Cu@mSiO2 reduced at 200, 300 and 450 oC.
The DOM reaction over Cu-based catalysts involves many
elementary steps, mainly including O–H and C–H bonds
cleavage. In addition, several side reactions also occur with
formation of COx.[8b,8c,11b,11c,16] Nonetheless, the catalytic roles of
different types of copper species in these elementary steps have
not been made clear. The 7Cu@mSiO2 samples reduced at 200,
300 and 450 oC have similar Cu particle size (Figure S3f) but
different surface Cu0/Cu+ ratios, and thus, provides the
opportunity for studying this point. Figures 2a and S17b,d show
the in situ DRIFT spectra of the samples reduced at 300 and
450 oC for DOM at 230 oC. The bands for HCHO species quickly
appeared after exposure to methanol, and drastically increased
in intensity at 40 min. Meanwhile, those for MeF were visible and
intensified with increasing reaction time to 60 min.[17] The DRIFT
results are in line with the catalytic results at the initial stage
(Table S7), implying that HCHO is one of the key intermediates
in DOM process. It has been proposed that HCHO is generated
through dehydrogenation of CH3O group formed by methanol
dehydrogenation.[8b,11b,11c] Indeed, the bands characteristic of Si–
OCH3 and Cu–OCH3 groups were observed at 2997, 2958, 2856,
1466, 1267 and 1109 cm-1, and 2926, 2825 and 1445 cm-1,[18]
respectively, in the in situ DRIFT and FTIR spectra (Figures 2b
and S16g). This indicates that the O–H bond of methanol splits
In situ XPS and XAFS results show that both Cu0 and Cu+
species are present on the surfaces of reduced xCu@mSiO2,
7Cu/mSiO2 and 7Cu/SiO2, and their relative amount does not
change at steady stage (Figures S11c-f, S12 and Table S5). By
combining their CO-TPD, N2O titration and DOM results (Figure
S13a and Tables S1, S2), it can be found that MeF yield
increases with Cu0 surface area, and particularly, a nearly
positive correlation exists between Cu0/Cu+ ratio and MeF
selectivity (Figure S14). These results indicate that Cu0 may be
the most active site for producing MeF.
Table S2 shows that no product was detected on the mSiO2
support, unreduced 7Cu@mSiO2 and Cu2O, while purified
metallic copper gave a moderate methanol conversion and a
This article is protected by copyright. All rights reserved.

10.1002/anie.201710605
Angewandte Chemie International Edition
COMMUNICATION
into H and CH3O that further converts into HCHO through
breaking of C–H bond. In accordance with the catalytic results,
no bands characteristic of HCHO and MeF were detected over
the sample reduced at 200 oC (Figure S17c) due to formation of
small amounts of –OCH3 species (Figures 2b and S16g). This
gives another piece of evidence for Cu+ not to be the active site.
To exclude the Cu+ species, purified metallic Cu was used
as model Cu0 catalyst for studying the transformation of HCHO
into MeF. Table S8 shows that the HCHO produced from
decomposition of paraformaldehyde (Figure S18) was
completely converted over metallic Cu with MeF selectivity of
62% – 70%. This reveals that Cu0 leads to the transformation of
HCHO into MeF. Notably, methanol was simultaneously
generated at the initial stage and its selectivity increased to 
19% at the steady state. This makes the formation of MeF via
HCHO dimerization (Tishchenko mechanism)[8b,10] doubtful as
MeF may be also generated from HCHO and CH3O that formed
over Cu0 species by DOM or hydrogenation of HCHO.
Figure 3. (a) MS spectrum of isotope-labeled MeF obtained in the reaction of
DCDO-2%H2 over metallic Cu, and (b) standard MeF MS spectrum.
The product MS spectrum shows two intense signals at m/z of
33 and 63 (Figures 3 and S21), which are attributed to CD2HO+
fragment and DCOOCD2H respectively, thus unambiguously
evidencing that CH3O species comes from the HCHO
hydrogenation, and MeF is formed via the hemi-acetal route.
As we know, Cu0 and Cu+ species generally coexist in the
Cu-based catalysts. Thus, HCHO molecule formed on and
subsequently desorbed from the Cu0 species possibly contact
with Cu+ sites. Therefore, the transformation route of HCHO on
the Cu+ sites should be also investigated. Table S9 shows that
no MeF was generated over pure Cu2O, and HCHO was mainly
converted into CO with a selectivity of  85%. This indicates that
Cu+ species enables the decomposition of HCHO into CO and
H2, while the byproduct CO2 (Selec. = 15%) results from the
participation of H2O in the reaction (Table S9).
Figure S25 shows the most probable route obtained by DFT
calculations for DOM into MeF over Cu(111) and Cu2O(111)
surfaces (Figures S23, S24, S26 and Table S10). Clearly, the
elementary steps on the metallic Cu(111) include the DOM to
CH3O, and further to HCHO. These two species subsequently
react to generate H2COOCH3 that dehydrogenates to MeF. The
overall reaction rate is determined by the dehydrogenation of
CH3O to HCHO. Nonetheless, its energy barrier (143 kJ/mol) is
far lower than that (200 kJ/mol) of HCHO dimerization to
HCOOCH3 (Table S10), further substantiating that DOM to MeF
occurs via the hemi-acetal mechanism. The high adsorption
energy (-107 kJ/mol) and reaction energy (82 kJ/mol) make the
CH3O, and thus, the HCHO species impossible to be generated
on the Cu2O(111) surface (Figure S24). Regardless of this, the
HCHO formed on Cu0 sites has a weak interaction with the Cu0
sites, and hence, could easily desorb and approach the Cu+
sites. The DFT calculation results indicate that these HCHO
molecules directly decompose into CO and H2 on Cu2O(111)
(Figures S24, S25 and Table S10). In addition, it was found that
no synergetic effect exists between Cu0 and Cu+ in the MeF
formation process (Figure S26), and HCHO dimerization to
HCOOCH3 on Cu2O(111) is not possible either because of the
unrealistically high energy barrier (386 kJ/mol, Table S10).
To unambiguously illustrate the catalytic mechanism of
xCu@mSiO2 for DOM into MeF, the initial stage of the reaction
must be investigated. Figures 2a and S6a show the presence of
an induction period. Obviously, it is not caused by the structure
changes of xCu@mSiO2 since their structure is highly stable
(Figures 1a-c, S3a-e, S7, S10, S11a,b and Table S1). In situ Cu
K-edge XANES spectroscopy results show that a drastic shrink
The decomposition of paraformaldehyde generated
a
mixture of 97 wt.% HCHO and 3 wt.% H2O (Figure S18). The
production of H2O causes it possible of formation of methanol
via hydrolysis of MeF. Figure S19a shows that considerable
amounts of H2 were produced in the HCHO transformation
process. Thus, methanol could be also formed through the
hydrogenation of HCHO.[16] To investigate the possibility for
formation of methanol from MeF hydrolysis, a similar content (4
wt.%) of water was added in the MeF hydrolysis system. It was
found that the methanol yield from MeF hydrolysis decreased
from 15.5% to 8.1% with increasing reaction time from 5 min to 4
h (Table S8). This is contrary to the change of that observed in
the HCHO transformation process, which is in line with the result
obtained by increasing H2 pressure in the HCHO-H2 reaction
(Table S8). Thus, it is reasonable to deduce that methanol does
not mainly come from MeF hydrolysis but from HCHO
hydrogenation.
In order to illustrate that MeF is formed through the hemi-
acetal route (reaction of HCHO and CH3O) or the Tishchenko
mechanism,[8b,8c,10,11b,11c] a series of experiments was done over
metallic Cu by changing the H2 amount in the HCHO-H2 reaction.
If the reaction occurs via the Tishchenko mechanism, the MeF
yield would be independent of H2 pressure because an
intermolecular transfer of H atom between two HCHO molecules
is involved (Figure S20-Route b). In contrast, when the hemi-
acetal route dominates the reaction process, H2 would play a
detrimental role. High H2 pressure promotes the hydrogenation
of HCHO to methanol, whereas it hinders the dehydrogenation
of H2COOCH3 to MeF. Thus, feeding of large amounts of H2
would suppress the MeF formation (Figure S20-Route a). Table
S8 shows that the methanol yield significantly increased from
15.9% to 93.5% with concurrence of a drastic decrease of the
MeF yield from 62.1% to nearly 0 when the H2 concentration
was increased from 0 to 50% in the HCHO-H2 reaction system.
This suggests that MeF should form via the hemi-acetal route.
To clarify this point, an isotope-labeling experiment was
conducted by replacing HCHO with DCDO obtained through
decomposition of paraformaldehyde-D and introducing 2% H2 in
the HCHO-H2 system. If the reaction follows Tishchenko
mechanism, DCOOCD3 would be the major product. Otherwise,
DCOOCD2H would be mainly generated (Figure S20-Route c,d).
This article is protected by copyright. All rights reserved.

10.1002/anie.201710605
Angewandte Chemie International Edition
COMMUNICATION
occurred to the Cu0 peak at 8979.1 eV in the first derivative
curve after the reduced xCu@mSiO2 was exposed to methanol
for just 1 min (Figures 4 and S27), while the peak of Cu+ at
8981.0 eV greatly increased in intensity. This indicates that most
of Cu0 species was promptly oxidized to Cu+ species.
Interestingly, as the reaction went on, these oxidized Cu+
species were gradually reduced back to Cu0 species, leading to
a Cu0/Cu+ ratio very similar to that of the reduced catalyst (Table
S5). Thus, the induction period results from the prompt oxidation
of Cu0 to Cu+, but a gradual reduction of Cu+ to Cu0. The rapid
oxidation of Cu0 to Cu+ is most likely due to the strong
adsorption of CH3O on the Cu0 site, while the gradual recovery
of Cu+ to Cu0 is caused by the dehydrogenation of CH3O to
HCHO that is rate-limiting step and accelerated by adding H2
(Table S10 and Figures S28, S29). This is supported by greatly
increasing methanol conversion by pulsing HCHO due to
acceleration of CH3O consumption that results in the release of
Cu0 sites (Figure S30 and Table S10).
Conflict of interest
The authors declare no conflict of interest.
Keywords: core-shell structure • Cu-based catalyst • induction
period • methanol dehydrogenation • reaction mechanisms
[1]
[2]
a) S. Kuld, M. Thorhauge, H. Falsig, C. F. Elkjær, S. Helveg, I.
Chorkendorff, J. Sehested, Science 2016, 352, 969-974; b) M. Gupta,
M. L. Smith, J. J. Spivey, ACS Catal. 2011, 1, 641-656.
a) S. Sá, H. Silva, L. Brandão, J. M. Sousa, A. Mendes, Appl. Catal. B
2010, 99, 43-57; b) H. Xi, X. Hou, Y. Liu, S. Qing, Z. Gao, Angew.
Chem. Int. Ed. 2014, 53, 11886-11889; Angew. Chem. 2014, 126,
12080-12083.
[3]
a) B. Eren, C. Heine, H. Bluhm, G. A. Somorjai, M. Salmeron, J. Am.
Chem. Soc. 2015, 137, 11186-11190; b) W.-W. Wang et al., ACS Catal.
2015, 5, 2088-2099; c) D. Delimaris, T. Ioannides, Appl. Catal. B 2009,
89, 295-302.
[4]
[5]
A. A. Gokhale, J. A. Dumesic, M. Mavrikakis, J. Am. Chem. Soc. 2008,
130, 1402-1414.
a) L. Chen, P. Guo, M. Qiao, S. Yan, H. Li, W. Shen, H. Xu, K. Fan, J.
Catal. 2008, 257, 172-180; b) G. Onyestyák, S. Harnos, D. Kalló, Catal.
Commun. 2012, 26, 19-24; c) H. Yue, Y. Zhao, S. Zhao, B. Wang, X.
Ma, J. Gong, Nat. Commun. 2013, 4, 2339-2345.
[6]
a) F. Wang, R. Shi, Z.-Q. Liu, P.-J. Shang, X. Pang, S. Shen, Z. Feng,
C. Li, W. Shen, ACS Catal. 2013, 3, 890-894; b) E. D. Guerreiro, O. F.
Gorriz, J. B. Rivarola, L. A. Arrúa, Appl. Catal. A 1997, 165, 259-271; c)
A. G. Sato, D. P. Volanti, D. M. Meira, S. Damyanova, E. Longo, J. M.
C. Bueno, J. Catal. 2013, 307, 1-17.
[7]
[8]
[9]
a) T. Lunkenbein, J. Schumann, M. Behrens, R. Schlögl, M. G.
Willinger, Angew. Chem. Int. Ed. 2015, 54, 4544-4548; Angew. Chem.
2015, 127, 4627-4631; b) A. Reinsdorf, W. Korth, A. Jess, M. Terock, F.
Klasovsky, R. Franke, ChemCatChem 2016, 8, 3592-3599.
a) M. Behrens et al., Science 2012, 336, 893-897; b) N. W. Cant, S. P.
Tonner, D. L. Trimm, M. S. Wainwright, J. Catal. 1985, 91, 197-207; c)
M.-J. Chung, D.-J. Moon, K.-Y. Park, S.-K. Ihm, J. Catal. 1992, 136,
609-612.
Figure 4. (a) In situ Cu K-edge XANES curves of 7Cu@mSiO2 during DOM,
and (b) their corresponding first derivative profiles: Ⅰ) reduced sample; Ⅱ–Ⅶ)
after reaction at 230 oC for 1, 10, 20, 30, 40 and 60 min, respectively.
In summary, Cu NPs encapsulated in mesoporous silica
shell shows unexpectedly high stability in the DOM to MeF. The
catalytic performance of deactivated sample could be nearly
a) B. Eren, D. Zherebetskyy, L. L. Patera, C. H. Wu, H. Bluhm, C. Africh,
L.-W. Wang, G. A. Somorjai, M. Salmeron, Science 2016, 351, 475-
478; b) S. Zhao, H. Yue, Y. Zhao, B. Wang, Y. Geng, J. Lv, S. Wang, J.
Gong, X. Ma, J. Catal. 2013, 297, 142-150.
o
recovered after calcination at 550 C in air. Cu0 sites enable the
cleavage of O–H in methanol to CH3O, and further to HCHO by
breaking C–H bond, while Cu+ species are unable to catalyze
these steps, but immediately decompose HCHO generated on
Cu0 into CO and H2. The MeF is formed through the reaction of
CH3O and HCHO over the Cu0 sites, not via the Tishchenko
mechanism. The induction period originates from a prompt
oxidation of Cu0 to Cu+ by strong adsorption of CH3O species,
and a gradual recovery of Cu+ to Cu0 by consuming CH3O by
generated H* and HCHO.
[10] T. Sodesawa, M. Nagacho, A. Onodera, F. Nozaki, J. Catal. 1986, 102,
460-463.
[11] a) J. Lee, J. C. Kim, Y. G. Kim, Appl. Catal. 1990, 57, 1-30; b) S. Lin, D.
Xie, H. Guo, ACS Catal. 2011, 1, 1263-1271; c) R. Zhang, Y. Sun, S.
Peng, Fuel 2002, 81, 1619-1624.
[12] a) S. H. Joo, J. Y. Park, C.-K. Tsung, Y. Yamada, P. Yang, G. A.
Somorjai, Nat. Mater. 2009, 8, 126-131; b) W. Li, D. Zhao, Adv. Mater.
2013, 25, 142-149.
[13] X. Guo, Y. Deng, D. Gu, R. Che, D. Zhao, J. Mater. Chem. 2009, 19,
6706-6712.
[14] F. Bauer, H. G. Karge, Mol. Sieves 2007, 5, 249-364.
[15] a) K. M. Valkaj, A. Katovic, S. Zrnĉević, J. Hazard. Mater. 2007, 144,
663-667; b) S. Lee, A. Sardesai, Top. Catal. 2005, 32, 197-207.
[16] L. L. Mueller, G. L. Griffin, J. Catal. 1987, 105, 352-358.
[17] G. J. Millar, C. H. Rochester, K. C. Waugh, J. Chem. Soc. Faraday
Trans. 1991, 87, 2785-2793.
Acknowledgements
This work is supported by the National Natural Science
Foundation of China (21303240, 21573270, U1510104,
21773281), the Shanxi Youth Science Foundation (2014021014-
5) and Talent Scientific and Technological Innovation Program
[18] a) I. A. Fisher, A. T. Bell, J. Catal. 1999, 184, 357-376; c) G. J. Millar, C.
H. Rochester, K. C. Waugh, J. Chem. Soc. Faraday Trans. 1991, 87,
2795-2804; d) S. J. Mcgovern, B. S. H. Royce, J. B. Benziger, Appl.
Surf. Sci. 1984, 18, 401-413.
(201605D211001),
Partnership Program for Creative Research Teams. The Beijing
and Shanghai Synchrotron Radiation Facilities are
acknowledged for measuring in situ XAFS spectra.
and
the
CAS/SAFEA
International
This article is protected by copyright. All rights reserved.

10.1002/anie.201710605
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
An unprecedentedly stable Cu-based
catalyst was prepared by embedding
highly dispersed Cu nanoparticles in
mesoporous silica shell for clarifying
the catalytic roles of Cu0 and Cu+ sites
with dehydrogenation of methanol to
methyl formate. It is shown that Cu0
catalyzes the cleavage of O–H bond
in CH3OH to CH3O and C–H bond in
CH3O to HCHO that reacts with
another CH3O species to form
HCOOCH3, while Cu+ converts the
HCHO into CO and H2.
H. Yang, Y. Chen, X. Cui,* G. Wang, Y.
Cen, T. Deng, W. Yan, J. Gao, S. Zhu,
U. Olsbye, J. Wang, W. Fan*
Page No. – Page No.
A Highly Stable Cu-based Catalyst for
Clarifying the Catalytic Roles of Cu0
and Cu+ Species in Methanol
Dehydrogenation
This article is protected by copyright. All rights reserved.