Low-Temperature Transformation of Methane to Methanol on Pd1O4Single Sites Anchored on the Internal Surface of Microporous Silicate

Article abstract of DOI:10.1002/anie.201604708

Direct conversion of methane to chemical feedstocks such as methanol under mild conditions is a challenging but ideal solution for utilization of methane. Pd₁O₄single-sites anchored on the internal surface of micropores of a microporous silicate exhibit high selectivity and activity in transforming CH₄to CH₃OH at 50–95 °C in aqueous phase through partial oxidation of CH₄with H₂O₂. The selectivity for methanol production remains at 86.4 %, while the activity for methanol production at 95 °C is about 2.78 molecules per Pd₁O₄site per second when 2.0 wt % CuO is used as a co-catalyst with the Pd₁O₄@ZSM-5. Thermodynamic calculations suggest that the reaction toward methanol production is highly favorable compared to formation of a byproduct, methyl peroxide.

Full text of DOI:10.1002/anie.201604708

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201604708
German Edition: DOI: 10.1002/ange.201604708
Methane Oxidation
Low-Temperature Transformation of Methane to Methanol on Pd O
1
4
Single Sites Anchored on the Internal Surface of Microporous Silicate
Weixin Huang, Shiran Zhang, Yu Tang, Yuting Li, Luan Nguyen, Yuanyuan Li, Junjun Shan,
Dequan Xiao, Raphael Gagne, Anatoly I. Frenkel, and Franklin (Feng) Tao*
Abstract: Direct conversion of methane to chemical feedstocks
such as methanol under mild conditions is a challenging but
ideal solution for utilization of methane. Pd O single-sites
a high temperature; the oxygen atoms in this bent mono(m-
oxo)di-metal structure oxidize methane to methanol at
a temperature higher than 2008C in the gas phase. Unfortu-
nately, once these uniquely anchored oxygen species are
1
4
anchored on the internal surface of micropores of a micro-
porous silicate exhibit high selectivity and activity in trans-
forming CH to CH OH at 50–958C in aqueous phase through
consumed by CH , they have to be regenerated through an
4
oxidation step of O or N O at a high temperature. The
4
3
2
2
partial oxidation of CH4 with H O . The selectivity for
regeneration can be done only after CH OH is removed from
2
2
3
methanol production remains at 86.4%, while the activity for
methanol production at 958C is about 2.78 molecules per
Pd O site per second when 2.0 wt% CuO is used as a co-
the internal surface of those micropores. The removal is
typically done by soaking the used catalyst in a solvent and
then dissolving methanol molecules in the solvent. Thus, the
1
4
catalyst with the Pd O @ZSM-5. Thermodynamic calculations
transformation of CH to methanol by these unique oxide
1
4
4
suggest that the reaction toward methanol production is highly
favorable compared to formation of a byproduct, methyl
peroxide.
species anchored in ZSM-5 at high temperatures in the gas
phase is mainly an oxidation reaction instead of a continuous
catalytic process.
[
3c]
In contrast to the above chemical transformation of CH4
[
1]
M
ethane is a relatively inexpensive resource. Hydraulic
to CH OH at a solid–gas interface in ZSM-5, metal cations of
3
fracturing supplies much of this earth-abundant source from
shale, which make chemical and energy transformations
Fe, Cu, and Ni encapsulated in ZSM-5, and even commercial
[4]
ZSM-5 alone, are active in the direct oxidation of CH to
4
[
2]
economical. One application of methane is the production
of methanol. Currently, chemical industries use a two-step
process in methanol production from methane, including
steam reforming to generate synthetic gas (CO and H ) and
a following synthesis of methanol from CO and H . The first
formic acid or even CH OH at a solid–liquid interface when
3
H O is used as an oxidant. The conversion rate of CH to
2
2
4
CH OH at a solid–liquid interface pioneered by Hutchings
3
[
4a,5]
et al.
face,
is typically higher than these at a solid–gas inter-
though the rate is still relatively low.
2
[
3a,b]
2
step is performed at a high temperature of 600–8008C. The
durability of catalysts at such a high temperature is quite low.
In addition, a significant amount of energy is needed to
perform the catalysis at such a high temperature. An ideal
Although catalytic activity for direct oxidation of CH to
4
CH OH on these catalysts at solid–gas and solid–liquid
3
[
1,3–6]
interfaces was reported,
challenges remain before
a direct oxidation process under mild conditions could be
considered as a potential approach in the chemical industry.
One challenge is that the activity and selectivity for produc-
approach for utilization of CH is a direct conversion of CH4
4
to CH OH under mild conditions at a relatively low temper-
3
ature because this transformation is thermodynamically
feasible even at low temperature. Unfortunately, realization
of this approach has remained challenging.
tion of methanol from CH are far below the requirement of
4
industrial production; another is the lack of fundamental
understanding of the catalytic mechanism performed at
a solid–liquid interface. To address these challenges, develop-
ment of new catalysts with higher activity and selectivity
under mild conditions, together with a fundamental under-
standing of the catalytic mechanism, is necessary. Herein,
It has been reported that Cu-, Fe-, or Ni-exchanged ZSM-
5
can form unique oxide species, including a bent mono(m-
[3]
oxo)di-metal structure upon activation with O or N O at
2
2
a catalyst consisting of Pd O single-sites anchored on the
[*] W. Huang, Dr. S. Zhang, Y. Tang, Y. Li, Dr. L. Nguyen, Dr. J. Shan,
1
4
Prof. Dr. F. Tao
internal surface of micropores of ZSM-5 was synthesized. Its
Department of Chemical and Petroleum Engineering and
Department of Chemistry, University of Kansas
Lawrence, KS 66045 (USA)
performance in the catalytic transformation of CH at a solid/
4
liquid/gas interface was explored. Thermodynamic calcula-
tions for the formation of methanol or methyl preoxide were
performed to understand the transformation of CH4 to
methanol from a thermodynamics point of view.
E-mail: franklin.feng.tao@ku.edu
Dr. Y. Li
Department of Physics, Yeshiva University
New York, NY 10016 (USA)
Singly dispersed precious metal atoms anchored on oxides
could offer a distinctly different electronic state in contrast to
continuously packed metal atoms on the surface of a metal
nanoparticle, and thus could exhibit a distinctly different
Prof. Dr. D. Xiao, R. Gagne
Department of Chemistry and Chemical Engineering
University of New Haven
[2b,7]
West Haven, CT 06516 (USA)
catalytic activity or/and selectivity.
Herein, we prepared
catalysts with singly dispersed Pd O sites anchored on the
1
4
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
internal surface of micropores of ZSM-5. As described in the
experimental section, the amount of loaded Pd cations is
important for the preparation of singly dispersed Pd O sites
in ZSM-5. TEM images (Figure S1a), the Pd 3d XPS
spectrum (red line in Figure S2), and the XRD pattern
Table 1: Coordination number of O or Pd atoms to a Pd atom, and bond
lengths of OꢀPd or PdꢀPd in 0.04 wt%Pd/ZSM-5 studied with EXAFS.
1
4
Sample
N
N
R(PdꢀPd)
R (PdꢀO)
(PdꢀPd)
(PdꢀO)
[ꢀ]
[ꢀ]
Pd foil
12
0
2.740ꢁ0.002
–
(
Figure S3) suggest that there are no PdO nanoparticles
formed on ZSM-5 of 0.01 wt% Pd/ZSM-5. This suggests that
the Pd atoms of 0.01 wt% Pd-ZSM-5 are singly dispersed on
the internal surface of the micropores of ZSM-5. However,
PdO nanoparticles were formed on 2.0 wt% Pd/ZSM-5
0.04 wt%
Pd/ZSM-5
0
4.12ꢁ0.49
–
2.001ꢁ0.009
(
Figures S1b, S2, and S3).
Pd K-edge Extended X-ray Absorption Fine Structure
EXAFS) experiments were performed to identify the
reference PdO sample (red line in Figure 1), however, the r-
space spectrum of 0.04 wt% Pd/ZSM-5 (blue line in Figure 1)
does not have such a distinct peak with the similar intensity as
the PdꢀPd peak in PdO at ~ 3.1 ꢀ. Therefore, there is no
(
coordination environment of Pd atoms anchored in ZSM-5.
Unfortunately, owing to the low signal/noise ratio of the Pd K
edge absorption spectra of 0.01 wt% Pd/ZSM-5, no conclu-
sive information was acquired. A reasonable signal/noise
ratio was obtained on 0.04 wt% Pd/ZSM-5. XPS studies of
evidence that any species or structure in 0.04 wt% Pd/ZSM-5
contains PdꢀOꢀPd species, which indicates the absence of
PdO nanoclusters. In addition, the measured coordination
number of oxygen atoms to a Pd atom, 4.12 ꢁ 0.49 suggests
the lack of the potential bent mono(m-oxo)dipalladium
structure since the coordination number of oxygen atoms
around a Pd atom CN(Pd-O) in a mono(m-oxo)dipalladium
0
.04 wt% Pd/ZSM-5 (Figure S2) showed that no PdO nano-
particles were formed for 0.04 wt% Pd/ZSM-5. This suggests
that the Pd atoms could be singly dispersed. Figure 1 presents
[
3c,4a]
(Figure S4a) is expected to be 3 instead of 4.
Based on
1
) the lack of a PdꢀPd bond, 2) the lack of a PdꢀOꢀPd bond,
and 3) the measured coordination number of oxygen atoms
coordinating to a Pd atom, we conclude that the Pd atoms in
0
.04 wt% Pd/ZSM-5 exist as singly dispersed Pd O species in
1 4
ZSM-5 (Figure S4b).
Temperature-dependent catalytic performances of Pd/
ZSM-5 were measured in the range of 50–958C which is lower
than the boiling point of H O at a high pressure of 30 bar of
2
2
CH (Table S1). As shown in Table S1, the yield of total
4
products is highly dependent upon the temperature. For
example, the total yield is about 399.4 mmol (about
0
.40 mmol) produced from 0.01 wt% Pd/ZSM-5 (28 mg
catalyst) at 958C within 30 minutes (entry 5 of Table S1),
which is about 3 times larger than the same catalyst at 508C
(entry 1 of Table S1). The amounts of each product formed at
50, 70, and 958C are listed in Table S1.
2
Figure 1. Fourier transform magnitudes of k -weighted EXAFS data of
0
.04 wt% Pd/ZSM-5 (blue) and reference samples, including Pd foil
(
red) and PdO nanoparticles (black).
Figure S5 presents the products formed from methane
partial oxidation on 0.01 wt% Pd/ZSM-5 at 508C, which are
mainly formic acid, methyl peroxide, methanol, and carbon
dioxide with yields of 60.82, 39.48, 7.39, and 4.22 mmol,
respectively, with a total yield of 111.91 mmol. Blank experi-
ment of pure H-ZSM-5 at 508C (pink bars in Figure S5)
showed that the activity for oxidation of CH with H O by
2
Fourier transform magnitudes of k -weighted EXAFS data of
.04 wt% Pd/ZSM-5 (blue line), pure Pd foil (black), and
0
pure PdO nanoparticles (red). The Pd atoms in 0.04 wt% Pd/
ZSM-5 exhibited a coordination environment distinctly
different from metal Pd foil and PdO nanoparticles. In
metallic Pd foil, the main peak at 2.58 ꢀ is assigned to PdꢀPd
4
2
2
pure H-ZSM-5 was lower than 0.01 wt% Pd/ZSM-5 under the
same conditions at 508C. In addition, the total yields of these
products on 28 mg of 0.01 wt% Pd supported on Al O
bonds. There is no such peak in this r-range in the spectrum of
0
.04 wt% Pd/ZSM-5 (blue line), showing no evidence for
2
3
formation of metallic Pd nanoparticles on the catalyst,
nanoparticles and 28 mg of 0.01 wt% Pd supported on SiO2
nanoparticles at 508C are only a few mmol, respectively
(Figure S5). These studies suggested that Pd cations anchored
on open surfaces (surface of Al O or SiO nanoparticles) are
0
.04 wt% Pd/ZSM-5.
The average coordination number of O atoms to a Pd
atom of 0.04 wt% Pd/ZSM-5 is 4.12 ꢁ 0.49 (Table 1). In both
2
3
2
[6a]
the reported r-space EXAFS spectra of PdO nanoparticles
not active for this transformation at 508C.
and our studies of reference PdO sample, a peak at 3.1 ꢀ was
clearly identified, comparable in intensity to be the first
nearest neighbor PdꢀO contribution; this peak at 3.1 ꢀ
With the same synthesis steps as 0.01 wt% Pd/ZSM-5,
catalysts of ZSM-5 loaded with different amounts of Pd
precursors were synthesized. Figure 2 presents the yields of
the four main products including formic acid, methyl perox-
represents the contribution to EXAFS from the two closest
Pd atoms in a PdO nanoparticle, bridged by an oxygen atom
ide, methanol, and CO catalyzed by 0.01, 0.02, 0.10, and
2
[
6a]
(
PdꢀOꢀPd). Compared to other PdO nanoparticles and the
2.0 wt% Pd/ZSM-5 at 508C. Interestingly, these catalysts
2
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
Figure 3. Pressure-dependent catalytic performance in partial oxidation
of CH on 0.01 wt% Pd/ZSM-5 at 958C. 28 mg of catalyst, 0.01 wt%
4
Pd/ZSM-5 was added to a Parr reactor; 10 mL de-ionized H O was
2
added; H O (5 mmol) was added to H O before CH was introduced
2
2
2
4
Figure 2. Yields of products of transformation of CH catalyzed by
4
to the Parr reactor. The plotted yield of a product formed on 28 mg
.01 wt%Pd/ZSM-5 is the value after subtraction of the yield of the
0
5
.01, 0.10, and 2.0 wt% Pd/ZSM-5 for methane partial oxidation at
08C.
0
products formed on 28 mg ZSM-5 (without Pd sites) under the same
catalytic conditions.
exhibit quite similar yields of the four products, although their
loadings of Pd precursor were very different. The similarity in
catalytic performances on ZSM-5 with quite different load-
ings suggests that the extra Pd atoms likely remain on the
external surface of ZSM-5 particles and do not play any role
in the generation of these products. TEM image (Figure S1b),
XPS (Figure S2), and XRD (Figure S3) clearly showed the
formation of a large number of small PdO nanoparticles on
the external surface of ZSM-5 particles when the loading of
Pd precursor was 2.0 wt%. Because the yield of the four
products from 2.0 wt% Pd/ZSM-5 was similar or even lower
than 0.01 wt% Pd/ZSM-5 (Figure 2), we can deduce that the
PdO nanoparticles are not active in these chemical trans-
formations.
Figure 4. Catalytic performance of a) 0.01 wt% Pd/ZSM-5 at 50, 70,
and 958C, and b) 0.01 wt% Pd/ZSM-5 loaded with 2 wt% CuO at 50,
7
0
0, and 958C. The plotted yields of products formed on 28 mg
.01 wt%Pd/ZSM-5 or 0.01 wt%Pd/ZSM-5 loaded with 2.0 wt%CuO
Methane-pressure-dependent catalytic performances
including conversion of CH (red segment line in Figure 3)
4
are the values after subtraction of the yields of the products formed on
8 mg ZSM-5 (without Pd sites) under the same catalytic conditions.
and amount of total products (blue bars in Figure 3) formed
on the same catalyst 28 mg of 0.01 wt% Pd/ZSM-5 at 958C
were studied. As shown in Figure 3, the total yield is about
2
2
34 mmol and the conversion is about 12.3% when the CH4
pressure was 3 bar. This shows that the partial oxidation of
methane can be performed on 0.01 wt% Pd/ZSM-5 even at
a low pressure of CH4.
decreased the concentration of initially formed methanol and
thus significantly increased the concentration of formic acid.
Thus, removal of the extra H O could prevent methanol from
2
2
As shown in Figure 4a, the molecular fraction of meth-
anol among the total product (formic acid, methyl peroxide,
being oxidized to formic acid by H O and could promote the
2 2
selectivity for production of methanol. Here, CuO was used to
catalyze the dissociation of H O2 to H O and O . We
methanol, and CO ) on 0.01 wt% Pd/ZSM-5 is quite low, with
2
2
2
2
formic acid being the major product. As methanol could be
oxidized to formic acid by H O under mild conditions, the
confirmed that the decomposition of H O to H O and O
2 2 2 2
can be catalyzed by CuO (Section 6 in the Supporting
Information). Next, 2.0 wt% CuO was impregnated in
0.01 wt%Pd/ZSM-5 as a co-catalyst for dissociating extra
H O after formation of methanol.
2
2
observed formic acid in Figure 4a could be formed from
further oxidation of methanol by H O after methanol was
2
2
produced on 0.01 wt% Pd/ZSM-5. In fact, our control
experiments confirmed that the formed methanol can be
readily oxidized to formic acid by H O (see Section 5 of the
2
2
Compared to 0.01 wt%Pd/ZSM-5 without CuO
(entries 1, 3, and 5 of Table S1), the selectivities for produc-
tion of methanol on 0.01 wt% Pd/ZSM-5 loaded with 2 wt%
CuO at 50, 70, and 958C (entries 2, 4, and 6 of Table S1) were
78.48, 85.46, and 86.35%, respectively, indicating that the
CuO co-catalyst significantly increased the selectivity for
methanol production. The preservation of selectivity in 78–
86% in the temperature range of 50–958C suggests that 78–
86% is the selectivity for production of CH OH from CH on
2
2
Supporting Information).
Based on the conversion of CH (Figure 3), the amount of
4
the introduced H O is more than the oxidant needed for
2
2
formation of these detected products. Thus, there was extra
H O after the formation of methanol. Unfortunately, the
2
2
extra H O oxidized the methanol to formic acid (see Section
2
2
5
of the Supporting Information). The facile oxidation of
3
4
methanol to formic acid at 958C by H O in fact largely
Pd O sites.
2
2
1
4
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
Turn-over frequency (TOF) is used as a scale to evaluate
catalytic activity, although it is challenging to accurately
measure the number of active sites Pd O anchored in ZSM-5.
The details of the calculations of TOFs were described in
Section 8 of the Supporting Information. Table 2 lists the
evaluated TOFs of 0.01 wt%Pd/ZSM-5 at different temper-
atures with (or without) the CuO co-catalyst. TOFs of
To understand the high activity and selectivity for the
production of CH OH on Pd O of 0.01 wt%Pd/ZSM-5, DFT
3
1
4
calculations of thermodynamics of the formation of methanol
and methyl peroxide were performed as described in Sec-
tion 9 of the Supporting Information. Based on our calcu-
lations, the formation of methanol is thermodynamically
favorable over methyl peroxide. This is consistent with the
higher catalytic selectivity for methanol compared to methyl
peroxide (entries 2, 4 and 6 of Table S1).
1
4
Table 2: TOFs for methane partial oxidation on 0.01 wt% Pd/ZSM-5 and
other catalysts that convert CH to CH OH and other organic oxygenates
4
3
at solid–liquid interfaces.
Acknowledgements
[
a]
[b]
TOF
all
TOF
Entry
Catalyst
Temp. [8C]
methanol
[
c]
[c]
This work was supported by KU research fund, Chemical
Sciences, Geosciences and Biosciences Division, Office of
Basic Energy Sciences, Office of Science, U.S. Department of
Energy, under Grant No. DE-SC0014561. The EXAFS
studies were supported by DE-FG02-03ER15476 (to AIF).
Beamline X18B of the NSLS was supported in part by
Synchrotron Catalysis Consortium under the U.S. DOE Grant
No. DE-SC0012335.
products
only
[
d]
1
2
3
4
0.01 wt%Pd/ZSM-5
0.01 wt% Pd/ZSM-5
0.01 wt% Pd/ZSM-5
0.01 wt% Pd/ZSM-5
50
70
95
50
2.45
6.68
8.30
1.46
N.A.
N.A.
N.A.
[
d]
d]
[
1.53
2.72
2.33
+
2 wt% CuO
0.01 wt% Pd/ZSM-5
2 wt% CuO
0.01 wt% Pd/ZSM-5
5
6
70
95
3.19
2.78
+
+
2 wt% CuO
Keywords: methane · methanol · oxidation · palladium ·
single-sites
moles of all organic prodcuts
moles of methanol
moles of metalꢂtime ðin secondÞ
[
[
a] TOF ¼
. [b] TOF ¼
.
moles of metalꢂtime ðin secondÞ
1
6
c] The number of Pd O active sites is 1.58ꢁ10 . [d] As the amount of
1
4
the produced methanol is up to 13 mmol (see Table S1), the error bars of
the TOFs of these catalysts are large. [e] The detailed calculations of the
TOFs and comparison with other reported values is discussed in
Section 8 of the Supporting Information.
[
1] S. R. Golisz, T. B. Gunnoe, W. A. Goddard, J. T. Groves, R. A.
Periana, Catal. Lett. 2011, 141, 213 – 221.
[
2] a) Exxonmobil,
2013,
http://corporate.exxonmobil.com/en/
producing CH OH from CH on reported catalysts, including
3
4
energy/energy-outlook; b) X. Guo, G. Fang, G. Li, H. Ma, H.
Fan, L. Yu, C. Ma, X. Wu, D. Deng, M. Wei, D. Tan, R. Si, S.
Zhang, J. Li, L. Sun, Z. Tang, X. Pan, X. Bao, Science 2014, 344,
2
.5 wt% Fe/ZSM-5 and Au-Pd/TiO , were evaluated for
2
[
4a,5]
comparison
(see Sections 8.2 and 8.3 of the Supporting
616 – 619.
Information). The TOFs for producing organic compounds
methanol, formic acid, and methane peroxide) catalyzed by
[
3] a) E. V. Starokon, M. V. Parfenov, L. V. Pirutko, S. I. Abornev,
G. I. Panov, J. Phys. Chem. C 2011, 115, 2155 – 2161; b) M. H.
Groothaert, P. J. Smeets, B. F. Sels, P. A. Jacobs, R. A. Schoon-
heydt, J. Am. Chem. Soc. 2005, 127, 1394 – 1395; c) J. Shan, W.
Huang, N. Luan, Y. Yu, S. Zhang, Y. Li, A. I. Frenkel, F. Tao,
Langmuir 2014, 30, 8558 – 8569.
(
0
2
.01 wt% Pd/ZSM-5 without CuO at 50, 70, and 958C were
.45, 6.68, and 8.30 molecules on a Pd O site per second,
1
4
respectively (entries 1–3 in Table 2). Formic acid was the
major product. The TOFs of the CH OH produced on
3
0
9
.01 wt%Pd/ZSM-5 with loaded 2.0 wt%CuO at 50, 70, and
[4] a) C. Hammond, M. M. Forde, M. H. Ab Rahim, A. Thetford, Q.
He, R. L. Jenkins, N. Dimitratos, J. A. Lopez-Sanchez, N. F.
Dummer, D. M. Murphy, A. F. Carley, S. H. Taylor, D. J. Willock,
E. E. Stangland, J. Kang, H. Hagen, C. J. Kiely, G. J. Hutchings,
Angew. Chem. Int. Ed. 2012, 51, 5129 – 5133; Angew. Chem. 2012,
58C (entries 4–6 in Table 2) are 1.53–2.33 CH OH molecules
3
per site per second, were higher than those of reported
catalysts at solid–liquid interfaces
Supporting Information). These TOFs of this work were
obtained by using the amounts of products generated on
Pd O4 sites after subtracting the products formed on the
substrate (ZSM-5) under the corresponding catalytic condi-
tions.
As the size of ZSM-5 particles used in this work are in the
range of 100–300 nm, the length of the micropores in these
ZSM-5 particles is in the scale range of ZSM-5 particles. In
the liquid phase, the diffusion of Pd cations to deep parts of
these micropores is limited. Both the diffusion of CH from
the aqueous phase to Pd O sites anchored on the internal
surface of microspores and the diffusion of product molecules
from catalytic sites in micropores to the aqueous phase are
limited by the long micropores to some extent. These limits
[
4a,5]
(see Section 8.1 of the
124, 5219 – 5223; b) T. Sheppard, C. D. Hamill, A. Goguet, D. W.
Rooney, J. M. Thompson, Chem. Commun. 2014, 50, 11053 –
11055; c) M.-L. Tsai, R. G. Hadt, P. Vanelderen, B. F. Sels, R. A.
Schoonheydt, E. I. Solomon, J. Am. Chem. Soc. 2014, 136, 3522 –
1
3529; d) C. Hammond, N. Dimitratos, R. L. Jenkins, J. A. Lopez-
Sanchez, S. A. Kondrat, M. H. Ab Rahim, M. M. Forde, A.
Thetford, S. H. Taylor, H. Hagen, E. E. Stangland, J. H. Kang,
J. M. Moulijn, D. J. Willock, G. J. Hutchings, ACS Catal. 2013, 3,
689 – 699; e) E. V. Starokon, M. V. Parfenov, S. S. Arzumanov,
L. V. Pirutko, A. G. Stepanov, G. I. Panov, J. Catal. 2013, 300, 47 –
54.
4
[
5] M. H. Ab Rahim, M. M. Forde, R. L. Jenkins, C. Hammond, Q.
He, N. Dimitratos, J. A. Lopez-Sanchez, A. F. Carley, S. H. Taylor,
D. J. Willock, D. M. Murphy, C. J. Kiely, G. J. Hutchings, Angew.
Chem. Int. Ed. 2013, 52, 1280 – 1284; Angew. Chem. 2013, 125,
1
4
1318 – 1322.
are closely relevant to the limited conversion of CH here.
4
[6] a) K. Takao, K. Suzuki, T. Ichijo, S. Sato, H. Asakura, K.
Teramura, K. Kato, T. Ohba, T. Morita, M. Fujita, Angew.
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
Chem. Int. Ed. 2012, 51, 5893 – 5896; Angew. Chem. 2012, 124,
995 – 5998; b) S. Grundner, W. Luo, M. Sanchez-Sanchez, J. A.
Lercher, Chem. Commun. 2016, 52, 2553 – 2556; c) M. V. Parfe-
nov, E. V. Starokon, L. V. Pirutko, G. I. Panov, J. Catal. 2014, 318,
Zhang, Z. L. Wu, W. X. Huang, S. B. Zeng, P. Hu, Nat. Commun.
5
2015, 6, 7798; c) L. Nguyen, S. R. Zhang, L. Wang, Y. Y. Li, H.
Yoshida, A. Patlolla, S. Takeda, A. I. Frenkel, F. Tao, ACS Catal.
2016, 6, 840 – 850; d) L. Wang, S. R. Zhang, Y. Zhu, A. Patlolla,
J. J. Shan, H. Yoshida, S. Takeda, A. I. Frenkel, F. Tao, ACS Catal.
2013, 3, 1011 – 1019.
1
4 – 21; d) P. J. Smeets, R. G. Hadt, J. S. Woertink, P. Vanelderen,
R. A. Schoonheydt, B. F. Sels, E. I. Solomon, J. Am. Chem. Soc.
010, 132, 14736 – 14738; e) N. V. Beznis, B. M. Weckhuysen, J. H.
2
Bitter, Catal. Lett. 2010, 138, 14 – 22.
[
7] a) S. Zhang, L. Nguyen, J.-X. Liang, J. Shan, J. Liu, A. I. Frenkel,
A. Patlolla, W. Huang, J. Li, F. Tao, Nat. Commun. 2015, 6, 7938;
b) F. F. Tao, J. J. Shan, L. Nguyen, Z. Y. Wang, S. R. Zhang, L.
Received: June 9, 2016
Revised: August 21, 2016
Published online: && &&, &&&&
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Methane Oxidation
Single site Pd O anchored in micro-
1 4
spores of zeolite with 2.0 w% CuO is
active for transforming of CH to CH OH
in aqueous solution in the temperature
W. Huang, S. Zhang, Y. Tang, Y. Li,
L. Nguyen, Y. Li, J. Shan, D. Xiao,
R. Gagne, A. I. Frenkel,
4
3
range of 50–958C. Selectivity for produc-
F. Tao*
&&&& — &&&&
tion of CH OH in this temperature range
3
was found to be 78%-86% at 50–958C,
offering an obvious improvement over
harsh alternative conditions.
Low-Temperature Transformation of
Methane to Methanol on Pd O Single
1
4
Sites Anchored on the Internal Surface of
Microporous Silicate
6
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!