Acid-base cooperative catalysis over mesoporous nitrogen-rich carbon

Article abstract of DOI:10.1002/cctc.201402537

WO_x nanoclusters (2-3 nm) embedded on a mesoporous nitrogen-rich carbon material were synthesized by using novel methodology. This material was very effectively capitalized as a new carbon-based acid-base cooperative catalyst for sequential acetal hydrolysis and Knoevenagel condensation reactions. The protocol was also explored for the nitroaldol condensation reaction.

Full text of DOI:10.1002/cctc.201402537

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DOI: 10.1002/cctc.201402537
Acid–Base Cooperative Catalysis over Mesoporous
Nitrogen-Rich Carbon
Reena Goyal,[a] Bipul Sarkar,[a] Nishita Lucus,[b] and Ankur Bordoloi*[a]
WOx nanoclusters (2–3 nm) embedded on a mesoporous nitro-
gen-rich carbon material were synthesized by using novel
methodology. This material was very effectively capitalized as
a new carbon-based acid–base cooperative catalyst for se-
quential acetal hydrolysis and Knoevenagel condensation reac-
tions. The protocol was also explored for the nitroaldol con-
densation reaction.
the wall of the matrix and basic groups embedded into the
pores by using a solid matrix have been reported.[6,8,9]Another
route for the preparation bifunctional catalysts involves the
use of an inorganic material as the support with basic moieties
and different acidic groups such as acidic silanols in silica,
Brønsted acid sites in silica, and silica–alumina incorporat-
ed.[5,10] However, these catalysts have limitations to protection–
deprotection procedures and to changes in the chemical envi-
ronment owing to their weak acidity, and they also show limit-
ed catalytic efficiency as a result of steric hindrance.[2,7,9,11] Re-
cently, amine-functionalized graphene oxide was also explored
for cascade reactions.
Multifunctional materials have a unique potential impact on
future scientific inventions by improving efficiency and versatil-
ity while minimizing cost.[1] Ample examples can be found in
nature; therefore, researchers have now engaged themselves
in the design of materials that can perform dramatic “tailor-
able” functions in laboratories. In recent years, a wide variety
Mesoporous nitrogen-rich carbon materials and metal-sup-
ported mesoporous nitrogen-rich carbon materials are getting
considerable attention owing to their unique structural and
surface properties. Mesoporous nitrogen-rich carbon materials
offer a wide range of applications in the photocatalysis,
oxygen reduction reaction, organic transformations, and semi-
conductors.[12] The Lewis basicity of nitrogen-doped carbon
materials is achieved by pyridine-type N atoms in the CNx
framework.[13] However, controlling the N content in the CNx
matrix with the use of amines and imines offers tunable Lewis
basicity.[14] Thus, the controlled synthesis of mesoporous nitro-
gen-rich carbon materials certainly incorporates Lewis basicity
for its catalytic application.[15] Additionally, as a result of the
structural richness of tungsten oxide species, several atomic ar-
rangements can exhibit the strong acidity that is required for
catalytic reactions at low temperature.[16]
of multifunctional material systems have been proposed.[2]
A
simplified synthetic process with the least amount of waste
and a lower operational cost can be achieved with a logically
designed cascade approach.[3] Over the last two decades, re-
searchers have been focusing on the field of heterogeneous
catalysis to mimic enzymes[1] that can catalyze cascade pro-
cesses and provide a very selective product.[3,4] The complexity
of separation of functional groups under practical catalytic
conditions has left a very limited scope for homogeneous cat-
alysis.[5] Nevertheless, very few examples of heterogeneous cat-
alyst systems can be found in the current literature owing to
the ruggedness of designing matrices having both acidic and
basic catalytic functions.[6] Complexity in the synthesis proce-
dure, low acidity, and sequential arrangement of the acidic and
basic functionalities in the catalyst systems restricts the applic-
ability of such catalysts in organic synthesis protocols.[7]
Hence, in this report an innovative way to prepare well-
structured new WOx nanocluster-embedded mesoporous nitro-
gen-rich carbon (MNCx) materials with different tungsten load-
ings [2.5 and 5 mL represented as WOx/MNCx (2.5) and WOx/
MNCx (5), respectively; see details in the Supporting Informa-
tion] with tunable acidic and basic functionalities is investigat-
ed, and the activity of these catalysts in acid–base-catalyzed
cascade reactions is outlined.
To date, many bifunctional catalysts have been prepared
that consist of both acidic and basic groups with different
strengths, that is, amines, thiols, ureas, heteropolyacid-func-
tionalized silanols or Lewis/Brønsted acids and bases hosted
on silica, clay, and polymer matrices.[2,6,8,9] However, a solid
silica matrix such as SBA-15, mesoporous silica nanoparticles,
and periodic mesoporous organic silica having acidity within
WOx/SBA-15 was synthesized by using tetraethylorthosilicate
as the silica source and the triblock copolymer poly(ethylene
oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)
(average molecular weight=5800 gmolÀ1) as a structure-di-
recting agent. The detailed synthesis procedure is elaborated
in the Supporting Information. WOx/MNCx was prepared by
using a newly synthesized hard template WOx nanocluster em-
bedded SBA-15[17] with two different loadings of tungsten,
WOx/MNCx (2.5) and WOx/MNCx (5). In a typical synthesis of
WOx/MNCx, dehydrated WOx/SBA-15 (1.0 g, 2.5 mL) was treated
with a mixture of ethylenediamine (NH2C2H4NH2, 4.5 g) and
carbon tetrachloride (CCl4, 11 g). The mixture was heated at
reflux at 908C for 6 h. Then, the obtained solid (polymer silica
[a] R. Goyal, B. Sarkar, Dr. A. Bordoloi
Refinery Technology Division
CSIR—Indian Institute of Petroleum
Dehradun-248005 UK (India)
E-mail: ankurb@iip.res.in
[b] N. Lucus
Inorganic and Catalyst Division
CSIR—National Chemical Laboratory
Pune-411008 Maharashtra (India)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402537.
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composite) was dried and pyrolyzed at 6008C for 6 h
under an inert gas atmosphere. The as-prepared py-
rolyzed composite was repeatedly washed with
2.5 wt% NaOH solution in ethanol/water (1:1) with
vigorous stirring at 908C for 3 h to remove the silica
framework. Finally, the product was filtered and
washed with a water/ethanol mixture until the filtrate
had a pH value of 7.0, and it was then dried. The ma-
terial was characterized by using low-angle X-ray dif-
Table 1. Physicochemical parameters of WOx/MNCx.
[a]
[b]
[c]
Catalyst
XBET
[m2 gÀ1
XP
XPd
ICP
CHN [wt%]
XPS [wt%]
]
[mLgÀ1
]
[nm] [WppmÀ1
]
C
N
C
N
WOx/MNCx (2.5) 552
WOx/MNCx (5) 422
0.52
0.23
3.7
2.3
262.5
456.6
62.7 13.3 65.8 14.02
61.4 14.7 64.1 12.04
[a] BET surface area. [b] Pore volume. [c] Pore diameter.
fraction (XRD), N2 physisorption isotherms, high-resolution
transmission electron microscopy (HRTEM), field-emission scan-
ning electron microscopy (FESEM), X-ray photoelectron spec-
troscopy (XPS), and inductively coupled plasma atomic emis-
sion spectroscopy (ICP-AES). The low-angle XRD measurements
(Figure 1) revealed a peak in the range between 2q=0.5 and
The presence of WOx nanoparticles was demonstrated by
using the HRTEM image shown in Figure 2. In addition, the 2D
structure can also be seen from the HRTEM image (Figure S2,
Supporting Information). The wheatlike fibrous morphology of
WOx/MNCx (2.5) was demonstrated by using SEM (Figure 2,
inset; see also Figure S3).
Figure 2. HRTEM and SEM images (inset) of the WOx/MNCx (2.5) catalyst.
Figure 1. a) Small-angle X-ray diffraction patterns of the WOx/MNCx materi-
als. b) N2 physisorption isotherm of WOx/MNCx (2.5). EDS elemental dot map-
ping of c) WOx/MNCx 5 and d) WOx/MNCx (2.5).
The X-ray photoelectron (XP) C1s spectra of WOx/MNCx (2.5)
and WOx/MNCx (5) are shown in Figure 3. The spectra were de-
convoluted into five components. The two main peaks at
283.9 and 284.9 eV were assigned to sp2-hybridized graphite-
like carbon (CÀC sp2) and sp3-hybridized diamond-like carbon
(CÀC sp3) overlapping with an sp2 carbon atom bound to a ni-
trogen atom (NÀC sp2). The peaks centered at 286.5, 288.2,
and 289.5 eV were attributed to surface oxygen groups desig-
nated as CÀO, C=O, and ÀCOO, respectively. These assign-
ments are in good agreement with the reported literature. The
N1s region (Figure 3) exhibits three main contributions. The
lowest binding energy of 398.7 eV could be assigned to pyri-
dine nitrogen. The peak at 401.0 eV is related to the nitrogen
atom bound to two sp2 carbon atoms in the graphite rings,
and the peak at 399.9 eV is assumed to be due to the contri-
butions from the nitrogen atom bound to three sp2 carbon
atoms (Nb) and nitrogen bound to a carbon atom in a terminal
ÀCꢀN group (Nt).[18] The surface atomic concentration ratio
was derived from the XP spectra, as shown in Figure 3. Upon
increasing the tungsten content, a small decrease in the CÀC
sp3 atomic surface concentration and an increase in the CÀC
sp2 atomic surface concentration were observed. This behavior
is in accordance with the XRD results evidencing a well-or-
dered graphite-like surface structure for WOx/MNCx (2.5) and
58 for the WOx/MNCx (2.5) and WOx/MNCx (5) catalysts, which
was indexed to the (100), (11 0), and (200) reflections of the
hexagonal p6mm space group. These observations are in good
agreement with the XRD pattern of the pure hexagonally or-
dered SBA-15 material, which indicates that the WOx/MNCx ma-
terials have a well-ordered two-dimensional (2D) mesoporous
structure with a hexagonal porous network. This was further
confirmed by using N2 physisorption studies (Figure 1, inset).
The N2 physisorption isotherm of WOx/MNCx (2.5) exhibits
type IV isotherm patterns with a H1 hysteresis loop and a capil-
lary condensation at a relative pressure (P/P0) of approximately
0.4–0.8, which is characteristic of ordered mesoporous materi-
als. WOx/MNCx (2.5) possesses
a maximum BJH (Barrett–
Joyner–Halenda) pore diameter of 3.7 nm and a specific BET
(Brunauer–Emmett–Teller) surface area of 552 m2 gÀ1 (Table 1).
The purity of WOx/MNCx (2.5) is depicted as the background of
the N2 physisorption isotherm obtained from energy-dispersive
X-ray spectroscopy (EDS) elemental dot mapping. The pres-
ence of four elements (i.e., W, O, C, N) in the WOx/MNCx (2.5)
and WOx/MNCx (5) catalysts can be clearly seen in Figure 1c,d.
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to that obtained at 908C, and
this could be due to the forma-
tion of various side products.
The optimum catalyst weight
was found to be 0.05 g, and any
additional increase in the cata-
lyst loading had no effect on the
conversion or on the product
yield. One of the interesting pa-
rameters ascertained was the
water content of the reaction;
we needed an optimum water
content to obtain good conver-
sions with good yields of the de-
sired products. Thus, we found
that 16.6 mm water was necessa-
ry to maintain >99% substrate
conversion with 96% product
yield. WOx/MNCx (2.5) was found
to be the best catalyst under
the optimized conditions with
>99%
dimethoxymethylben-
zene conversion and an excel-
lent product yield of 96%. As we
Figure 3. The XP C1s spectra (left) and XP N1s spectra (right) of WOx/MNCx (2.5) and WOx/MNCx (5).
WOx/MNCx (5). It can be assumed that the WOx/MNCx surfaces
Table 2. Catalytic activity of the MNCx and WOx/MNCx materials in the
are composed of sp2 carbon atoms. The signal at 285.3 eV is
mainly due to carbon atoms bound to nitrogen atoms (NC
sp2). The atomic surface concentration of nitrogen is represent-
ed in a bar diagram (Figure 3), in which a small decrease in all
of the nitrogen surface species can be observed.
Knoevenagel
condensation
of
dimethoxymethylbenzene.[a]
The bifunctional activity of the WOx/MNCx catalyst was inves-
tigated for the single-pot conversion of dimethoxymethylben-
zene (DMMB, 1) into benzylidene ethyl cyanoacetate (3), which
involved acid-catalyzed hydrolysis followed by base-catalyzed
acetal Knoevenagel condensation (Table 2). The reaction was
performed in a round-bottomed flask under a N2 atmosphere.
Aliquots were successively collected by using disposable sy-
ringes at regular intervals. The reaction product was identified
by GC–MS (HP 5890 GC coupled with 5972 MSD). The identi-
fied product was analyzed with an Agilent 7890, fitted with an
Equity 1 (30 mꢁ0.28 nm i.d., 0.25 mm film thickness) capillary
column and a flame ionization detector. The reaction proceed-
ed through deacetalization of 1 to benzaldehyde (2) followed
by reaction with the methylene compound to give the deace-
talization Knoevenagel condensation product. The optimized
reaction conditions were obtained after performing a series of
experiments by varying the temperature, water content, cata-
lyst weight, and so on (Figure S4). The time-on-stream experi-
ment clearly indicated that the reaction was almost complete
(>99% conversion of substrate) after 22 h. The conversion of
dimethoxymethylbenzene gradually increased as the tempera-
ture was increased in the range from 70 to 908C, and there
was no further increase in the conversion of the substrate with
a further increase in the reaction temperature up to 1008C.
Moreover, at 1008C the desired product yield was low relative
Entry
Catalyst
Conversion
[mol%]
Yield [%]
2[b]
TON[c]
4
1
2
3
4
5
6
7
8
SBA-15
WOx/SBA-15
MNCx
10.2
43.4
–
48.9
>99
100
97.2
96.6
95.9
95.7
45.5
10
43
–
–
–
–
–
144
–
WOx/MNCx (1)
WOx/MNCx (2.5)
WOx/MNCx(5)
first recycle
second recycle
third recycle
fourth recycle
WOx MNCx
1
3
2
1
1
1
1
9.4
48
96
70
96
95
95
95
36.9
1325
1194
680
1170
1169
1164
1157
219
9
10
11
[a] Reaction conditions: Dimethoxymethylbenzene (5.54 mmol), ethyl cya-
noacetate (5.45 mmol), catalyst (0.05 g), toluene (15.2 mL) as solvent con-
taining water (16.6 mmol), 908C, N2. [b] Yield of 2 was calculated with re-
spect to the conversion of substrate 1. [c] Determined after 22 h. The
TON was calculated with respect to the conversion of dimethoxymethyl-
benzene.
increased the amount of tungsten in the WOx/MNCx (5) cata-
lyst, 100% conversion of dimethoxymethylbenzene was ob-
served. However, the selectivity towards product 3 (Table 2,
entry 5) decreased; this could be due to the increase in acidity
of the catalyst system, which led to the formation of ethanol
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as a side product. Moreover, we lowered the amount of tung-
sten by using the WOx/MNCx (1) catalyst, and the conversion
was lower (48.9%) than that provided by WOx/MNCx (2.5). Cata-
lyst stability and reusability were evaluated by collecting the
sample from the round-bottomed flask (see the Supporting In-
formation), and the results are summarized in Table 2.Certainly,
some weight loss of the catalyst occurred, which resulted in
a slight decrease (of 4.2%) in catalytic activity of the catalyst.
Moreover, leaching of tungsten species into the mixture was
also checked by the hot filtration test (see the Supporting In-
formation). The catalytic efficiency was calculated in terms of
the turnover number (TON) by considering the acid-catalyzed
first step (Table 2). It was observed that the value of the TON
Experimental Section
The syntheses of SBA-15 and WOx/SBA-15 are detailed in the Sup-
porting Information. Mesoporous nitrogen-rich carbon (MNCx) ma-
terials were synthesized by using SBA-15 as a hard template by
using the following procedure: Dehydrated SBA-15 (1.0 g) was
treated with a mixture of ethylenediamine (NH2C2H4NH2, 4.5 g) and
carbon tetrachloride (CCl4, 11 g). The mixture was heated at reflux
at 908C for 6 h. Then, the obtained solid mixture (polymer silica
composite) was dried and pyrolyzed at two different temperatures
(600 and 8008C) for 6 h under an inert gas atmosphere. The pyro-
lyzed silica/nitrogen/carbon composite was washed with a 2.5 wt%
NaOH solution in ethanol/water (1:1) with vigorous stirring at 908C
for 3 h to remove the silica framework. This process was repeated
two times. Then, the product was filtered and washed with water/
ethanol (1:1) until the filtrate was pH 7.0, and it was then dried.
À
increased as the loading of WO3 was increased. Moreover,
a plausible mechanism is depicted in Scheme S1. The whole re-
action proceeds through a two-step process involving acid-cat-
alyzed hydrolysis of dimethoxymethylbenzene (1) to benzalde-
hyde (2), which then undergoes base-catalyzed Knoevenagel
condensation in the presence of ethyl cyanoacetate. On the
Acknowledgements
R.G. acknowledges the Council for Scientific and Industrial Re-
search (CSIR), India, and B.S. acknowledges the University Grant
Commission (UGC), India, for a fellowship. We also acknowledge
the Director CSIR-IIP for his support. The authors thank the Ana-
lytical Science Division, Indian Institute of Petroleum, for analyti-
cal services.
À
basis of the results, we believe that acidic WO3 effectively at-
taches to the ÀOEt group of dimethoxymethylbenzene
through a weak van der Waals attraction followed by hydroly-
sis to form benzaldehyde. Benzaldehyde then takes part in the
Knoevenagel condensation in association with the enol inter-
mediate formed during the keto–enol tautomerism of ethyl cy-
anoacetate over the base-catalyzed CNx material. The resulting
enolate attaches to benzaldehyde to form unstable intermedi-
ate C1. The resulting intermediate accepts a proton from the
mixture to form benzylidene ethyl cyanoacetate (4) as the
product.
Keywords: cooperative catalysts · Knoevenagel condensation ·
mesoporous materials · nanostructures · nitro aldol reaction
[1] a) N. R. Shiju, A. H. Alberts, S. Khalid, D. R. Brown, G. Rothenberg, Angew.
Chem. Int. Ed. 2011, 50, 9615–9619; Angew. Chem. 2011, 123, 9789–
9793; b) M. J. Climent, V. Fornes, R. G. Lopez, S. Iborra, A. Corma, Adv.
Synth. Catal. 2002, 344, 1090–1096.
[2] a) S. Shylesh, A. Wagener, A. Seifert, S. Ernst, W. R. Thiel, Angew. Chem.
Int. Ed. 2010, 49, 184–187; Angew. Chem. 2010, 122, 188–191; b) M. J.
Climent, A. Corma, H. Garcia, R. G. Lopez, S. Iborra, V. Fornes, J. Catal.
2001, 197, 385–391; c) R. K. Zeidan, S. J. Hwang, M. E. Davis, Angew.
Chem. Int. Ed. 2006, 45, 6332–6335; Angew. Chem. 2006, 118, 6480–
6483; d) K. K. Sharma, R. P. Buckley, T. Asefa, Langmuir 2008, 24, 14306–
14320.
To check the versatility of the material we also studied the
nitro aldol condensation by taking nitromethane as the meth-
ylating agent (Table S1). Greater than 95% conversion of nitro-
methane was observed for a reaction time of 18 h (Table S1,
entry 3) with the multifunctional WOx/MNCx (2.5) material.
Upon increasing the loading of WOx over the MNCx support,
the activity reached 100%; however, a significant loss in selec-
tivity (of the condensation product) was also noted. The recy-
clability of the material was also examined: the used catalyst
was washed repeatedly with toluene, dichloromethane, and
distilled water, and it was then dried under vacuum at 1208C
for 2 h. The regenerated material showed no loss in activity;
>87% conversion of nitromethane was observed even on the
third recycle, and the product yield was 87%.
[3] a) E. Gianotti, U. Diaz, A. Velty, A. Corma, Catal. Sci. Technol. 2013, 3,
2677–2688; b) M. J. Climent, A. Corma, S. Iborra, M. J. Sabater, ACS
Catal. 2014, 4, 870–891.
[4] F. Zhang, H. Jiang, X. Li, X. Wu, H. Li, ACS Catal. 2014, 4, 394–401.
[5] K. Motokura, M. Tada, Y. Iwasawa, J. Am. Chem. Soc. 2007, 129, 9540–
9541. V. Polshettiwar, S. Varma, Green Chem. 2010, 12, 743–754.
[6] a) S. Huh, H. T. Chen, J. W. Wiench, M. Pruski, V. S. Y. Lin, Angew. Chem.
Int. Ed. 2005, 44, 1826–1830; Angew. Chem. 2005, 117, 1860–1864;
b) K. Motokura, M. Tada, Y. Iwasawa, J. Am. Chem. Soc. 2009, 131, 7944–
7945; c) M. Bouhrara, C. Ranga, A. Fihri, R. R. Shaikh, P. Sarawade, A. H.
Emwas, M. N. Hedhili, V. Polshettiwar, ACS Sustainable Chem. Eng. 2013,
1, 1192–1199.
[7] a) E. L. Margelefsky, R. K. Zeidan, M. E. Davis, Chem. Soc. Rev. 2008, 37,
1118–1126; b) A. Sinhamahapatra, P. Pal, A. Tarafdar, H. C. Bajaj, A. B.
Panda, ChemCatChem 2013, 5, 331–338.
[8] a) S. Shylesh, W. R. Thiel, ChemCatChem 2011, 3, 278–287; b) J. D. Bass,
A. Solovyov, A. J. Pascall, A. Katz, J. Am. Chem. Soc. 2006, 128, 3737–
3747; c) J. D. Bass, A. Katz, Chem. Mater. 2006, 18, 1611–1620; d) D.
Coutinho, S. Madhugiri, K. J. Balkus, J. Porous Mater. 2004, 11, 239–254;
e) S. Huh, H. T. Chen, J. W. Wiench, M. Pruski, V. S. Y. Lin, J. Am. Chem.
Soc. 2004, 126, 1010–1011.
Conclusions
WOx nanocluster-embedded mesoporous nitrogen-rich carbon
materials were prepared through a novel approach. The newly
synthesized materials were found to be excellent bifunctional
carbon-based catalyst systems for one-pot cascade reactions
comprising sequential acetal hydrolysis and Knoevenagel con-
densation. WOx/MNCx (2.5) exhibited a conversion of dimethox-
ymethylbenzene that was >99% with excellent (96%) product
yield. The catalyst also showed good bifunctional activity for
the nitroaldol reaction with 95% conversion of dimethoxyme-
thylbenzene and 100% product selectivity.
[9] a) K. Motokura, M. Tomita, M. Tada, Y. Iwasawa, Chem. Eur. J. 2008, 14,
4017–4027; b) Y. Huang, B. G. Trewyn, H. T. Chen, V. S. Y. Lin, New J.
Chem. 2008, 32, 1311–1313; c) K. Motokura, M. Tada, Y. Iwasawa, Chem.
Asian J. 2008, 3, 1230–1236.
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 3091 – 3095 3094

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
[10] a) Y. Xie, K. K. Sharma, A. Anan, G. Wang, A. V. Biradar, T. Asefa, J. Catal.
2009, 265, 131–140; b) A. Corma, U. Diaz, T. Garcia, G. Sastre, A. Velty, J.
Am. Chem. Soc. 2010, 132, 15011–15021.
[11] Y. L. Huang, S. Xu, V. S. Lin, Angew. Chem. Int. Ed. 2011, 50, 661–664;
Angew. Chem. 2011, 123, 687–690.
[12] a) Y. Zheng, J. Liu, J. Liang, M. Jaroniec, S. Z. Qiao, Energy Environ. Sci.
2012, 5, 6717–6731; b) C. N. Tharamani, A. Bordoloi, W. Schuhmann, M.
Muhler, ChemSusChem 2012, 5, 637–641; c) F. Su, S. C. Mathew, S. Ble-
chert, G. Lipner, X. Fu, X. Wang, M. Antonietti, J. Am. Chem. Soc. 2010,
132, 16299–16301; d) Y. Li, Y. Gong, X. Xu, P. Zhang, H. Li, Y. Wang,
Catal. Commun. 2012, 28, 9–12.
Chem. 2009, 121, 8024–8027; b) X. H. Li, J. S. Chen, X. Wang, J. Sun, M.
Antonietti, J. Am. Chem. Soc. 2011, 133, 8074–8077.
[15] S. van Dommele, K. P. D. Jong, J. H. Bitter, Chem. Commun. 2006, 4859–
4861.
[16] D. G. Bartona, S. L. Soled, E. Iglesia, Top. Catal. 1998, 6, 87–99.
[17] A. Bordoloi, A. Vinu, S. B. Halligudi, Chem. Commun. 2007, 4806–4808.
[18] a) N. Fairley, Casa XPS Version 2.3.15, copyright 1999–2009 Casa Soft-
ware Ltd.; b) C. D. Wagner, W. M. Riggs, L. E. Davis, J. F. Moulder, G. E.
Muilenberg, Handbook of X-ray Photoelectron Spectroscopy, PerkinElmer
Corp., Eden Prairie, USA, 1979.
[13] a) B. Frank, J. Zhang, R. Blume, R. Schlçgl, D. S. Su, Angew. Chem. Int. Ed.
2009, 48, 6913–6917; Angew. Chem. 2009, 121, 7046–7051; b) Z. Zhao,
Y. Dai, J. Mater. Chem. A 2014, 2, 13442–13451.
Received: July 15, 2014
[14] a) X. Jin, V. V. Balasubramanian, S. T. Selvan, D. P. Sawant, M. A. Chari,
G. Q. Lu, A. Vinu, Angew. Chem. Int. Ed. 2009, 48, 7884–7887; Angew.
Published online on September 26, 2014
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