Carbonate-promoted catalytic activity of potassium cations for soot combustion by gaseous oxygen

Article abstract of DOI:10.1002/cctc.201300736

The possible mechanism of soot combustion catalyzed by potassium carbonate loaded on aluminosilicate was elucidated to understand the surface reaction in solid-solid-gas triphasic catalysis. Potassium species on aluminosilicate showed high catalytic performance for the oxidation of carbon black by gaseous oxygen. Aluminosilicate helped in stabilizing the alkali cation on the surface. The carbonate ion played a critical role in enhancing the catalytic performance by acting as a supplier of active electrons to gaseous oxygen. To the best of our knowledge, this is the first report on the essential role of carbonate on the catalytic activity of an alkali cation for an oxidation reaction, although carbonate (carbon dioxide) is widely recognized to hinder the catalytic performance of the alkali compound for base-catalyzed reactions. Oxidizing carbon: The mechanism of carbon oxidation by gaseous oxygen on potassium carbonate species with/without loading on a nepheline surface with the aim of identifying the active catalytic centers is reported. The overall catalysis mechanism is clarified by considering the role of the carbonate anion in the oxidation reaction, although this anion is widely recognized to hinder the catalytic performance of alkali compounds in base-catalyzed reactions. Copyright

Full text of DOI:10.1002/cctc.201300736

CHEMCATCHEM
COMMUNICATIONS
DOI: 10.1002/cctc.201300736
Carbonate-Promoted Catalytic Activity of Potassium
Cations for Soot Combustion by Gaseous Oxygen
Masaru Ogura,*[a, b] Riichiro Kimura,[c] Hiroshi Ushiyama,[b, c] Fumiya Nikaido,[c]
Koichi Yamashita,[b, c] and Tatsuya Okubo[c]
The possible mechanism of soot combustion catalyzed by po-
tassium carbonate loaded on aluminosilicate was elucidated to
understand the surface reaction in solid–solid–gas triphasic
catalysis. Potassium species on aluminosilicate showed high
catalytic performance for the oxidation of carbon black by gas-
eous oxygen. Aluminosilicate helped in stabilizing the alkali
cation on the surface. The carbonate ion played a critical role
in enhancing the catalytic performance by acting as a supplier
of active electrons to gaseous oxygen. To the best of our
knowledge, this is the first report on the essential role of car-
bonate on the catalytic activity of an alkali cation for an oxida-
tion reaction, although carbonate (carbon dioxide) is widely
recognized to hinder the catalytic performance of the alkali
compound for base-catalyzed reactions.
porous wall of the honeycomb, in the emission system of
diesel automobiles is an efficient means of removing more
than 95% of the emitted PM.[4] However, to avoid frequent re-
generation or replacement of such filters, a catalyst that elimi-
nates carbonaceous PM by combustion is required.[5] In the
continuously regenerating trap (CRT) system, developed by the
Johnson Matthey Company, NO is oxidized by the first catalyst
with a large amount of Pt to obtain NO2, which in turn catalyz-
es PM oxidation at approximately 3008C; this corresponds to
the emission temperature in the diesel combustion system.
The DPF is installed in the second stage of the catalyst system,
where PM is captured and oxidized by NO2 generated in the
first stage. A third catalyst is required to remove NO that is
used as NO2 for the oxidant of the PM, in which urea is neces-
sary as the reductant of NO.
Gaseous oxygen is not used as the oxidant for PM because
of the high temperatures (exceeding 6008C) required. To pro-
mote the oxidation of PM by oxygen present in diesel emis-
sion, many researchers have tried to find catalysts that require
a temperature as low as the emission temperature. Although
potassium species are promising candidates for catalyst com-
ponents,[6] they have several disadvantages: potassium is vola-
tile at the temperatures required for carbon oxidation and
easily dissolves in water to afford a highly alkaline solution
that can damage the ceramic honeycomb. We found that po-
tassium carbonate stabilized on a tectoaluminosilicate such as
sodalite zeolite or a nepheline mineral shows excellent catalyt-
ic performance, which is similar to that of bulk potassium car-
bonate and is durable against rinsing in water.[7–9]
Despite the increasing demand for electric cars, automobiles
with an internal combustion system continue to be the pre-
ferred mode of transportation because of the high energy den-
sity of liquefied fuel. Because of its high energy-conversion effi-
ciency, the diesel-engine combustion system may contribute
to the reduction of CO2 emission per unit travel distance. More
than 70% of the new automobiles sold in European markets
are based on diesel engines. The combustion mechanism en-
tails the inhalation of a large quantity of air into the engine
and the release of a high concentration of oxygen in the ex-
haust. Therefore, installation of a three-way catalyst (TWC) in
the emission suppression system for NOx emission control in
the presence of an excess amount of oxygen is difficult.[1] In
addition, reducing particulate matter (PM) emission is also im-
portant for diesel-emission management.[2,3] Installation of
a diesel particulate filter (DPF), which comprises a semiplugged
ceramic honeycomb with a wall-flow system on the partitioned
In this study, we elucidated the mechanism of carbon oxida-
tion by gaseous oxygen on potassium carbonate species with/
without loading on a nepheline surface, with the aim of identi-
fying the active catalytic centers. To the best of our knowledge,
this is the first attempt at clarifying the overall catalysis mecha-
nism by considering the role of the carbonate anion in the oxi-
dation reaction.
[a] Dr. M. Ogura
Institute of Industrial Science
The University of Tokyo
Komaba 4-6-1, Meguro, Tokyo 153-8505 (Japan)
Fax: (+81)3-5452-6322
Catalytic performance of bulk alkali carbonates
E-mail: oguram@iis.u-tokyo.ac.jp
Figure 1a shows the typical CO2 elution curves detected by
a mass spectrometer (m/z=44) during carbon black (CB) com-
bustion in air. CO2 is generated during the combustion without
any formation of CO, and the temperature at which the curve
starts to steepen correlates well with the catalytic activity.
Alkali carbonates catalyzed this reaction at a low temperature
upon mixing CB in the so-called tight contact state. Upon per-
forming the combustion with various alkali metal carbonates,
[b] Dr. M. Ogura, Dr. H. Ushiyama, Prof. K. Yamashita
Unit of Elements Strategy Initiative for Catalysts & Batteries
Kyoto University
Katsura, Nishikyo, Kyoto 615-8510 (Japan)
[c] Dr. R. Kimura, Dr. H. Ushiyama, Dr. F. Nikaido, Prof. K. Yamashita,
Prof. T. Okubo
Department of Chemical System Engineering
The University of Tokyo
Hongo 7-3-1, Bunkyo, Tokyo 113-8656 (Japan)
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 479 – 484 479

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
catalytic activity of the strongly basic alkali carbonate could be
due to the activation of oxygen by the donated electron(s).
Performance of alkali carbonates on crystalline aluminosili-
cate
Basically, the catalytic performance of alkali carbonate on soda-
lite corresponds to that of the bulk alkali carbonate. Sodalite
showed very low activity for CB combustion with gaseous
oxygen, as previously reported.[6] An excess amount of sodium
on the surface of sodalite might lead to the formation of
sodium carbonate by reaction with ambient CO2 to afford
Na2CO3/Na–sodalite, which showed high catalytic activity for
the reaction. Further, as mentioned in our previous report, po-
tassium carbonate loaded sodalite underwent a phase change
to a nepheline group upon heating at high temperatures of
approximately 8008C,[7] and the exact phase was determined
by the amount of potassium loaded on sodalite prior to heat
treatment. The formed nepheline held sodium carbonate on
the surface through solid ion exchange during the treatment.
The catalytic performance of the nepheline was compared
with that of sodium and potassium carbonates, as summarized
in Figure 2, by measuring the activation energy for CB oxida-
Figure 1. a) CO2 detected at m/z=44 by mass spectrometry during CB com-
bustion on different alkali carbonates under an air stream. b) DRIFT spectra
of each alkali carbonate.
Figure 2. Activation energy for CB combustion in air with and without a cata-
lyst (Na2CO3, K2CO3, and K2CO3-loaded Na–nepheline).
the combustion initiation temperature decreased in the order
sodium>potassium>rubidium>cesium; this implies that the
catalytic activity increased with the atomic weight of the alkali
metal. Furthermore, the higher the basicity of the alkali ele-
ment, the higher the catalytic performance for carbon combus-
tion by oxygen. Given that alkali metal oxides are generally
basic, acidic CO2 hinders their basic catalytic performance.[10] In
contrast, alkali metal carbonates are not pyrolyzed into oxides
in the temperature range tested for the combustion reaction,
and this indicates that the catalytic activity originated from
each carbonate. The diffuse reflectance infrared Fourier trans-
form (DRIFT) spectra of the carbonates are illustrated in Fig-
ure 1b. The broad absorption band at 1600–1400 cmꢀ1 could
be assigned to the asymmetric vibration of the carbonate spe-
cies for each carbonate, whereas the sharp band at 1800 cmꢀ1
corresponds to the symmetric vibration of carbonate. Interest-
ingly, the broad band split into two or three bands upon
changing the alkali element carbonate from sodium to cesium.
The vibration mode of the carbonate is affected by alkalinity/
basicity, which can be referred to as a polarizing effect.[11]
Given that strong basicity favors electron donation, the high
tion as a function of carbon conversion. To speculate the
active species on the surface of the calcined nepheline, the ap-
parent activation energy of soot oxidation was determined by
using the Ozawa method[12] and Equation (1):
d log b
ꢀ ꢁ
1
E
R
¼ 0:4567
ð1Þ
d
Ta
in which b represents the heating rate; Ta is the temperature
corresponding to a carbon conversion of a%, as calculated
from the thermogravimetric curve; and E is the apparent acti-
vation energy in kJmolꢀ1. E can be estimated from the slope of
the least-squares straight-line fit of the logb versus 1/Ta plot.
The measured E values, 100–120 kJmolꢀ1, were much lower
than those obtained without using
a
catalyst, 140–
150 kJmolꢀ1. A high E was necessitated at a higher conversion
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 479 – 484 480

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
of CB on alkali carbonates; this indicates that com-
bustion of the residual carbon during the last stage
of the reaction is difficult. On the contrary, there was
no notable conversion dependence on the nepheline
catalyst, which showed the characteristics of both
sodium and potassium carbonates. Nevertheless, we
can conclude that the carbonate species on the sur-
face of the nepheline grains acted as the catalytically
active sites. Notably, the IR spectra of the carbonate
on nepheline, as displayed in Figure 3, differed from
those of the bulk carbonate. As compared with the
carbonate species in sodium carbonate, the band as-
signable to carbonate was shifted to a lower fre-
quency, which is indicative of further donation of
electron(s) or an increase in the basicity of sodium/
potassium carbonate on nepheline. The enhanced
catalytic activity observed upon potassium carbonate
loading on aluminosilicates compared with that on
sodium carbonate also supports this observation.
Notably, other potassium salts such as sulfates and
nitrates on crystalline aluminosilicate showed a high
catalytic performance, which was comparable to that
of potassium carbonate. Interestingly, only carbonate
remained on the surface after the combustion (re-
sults not shown). Raman spectroscopic studies re-
vealed that the nitrate anion was pyrolyzed, whereas
the sulfate anion remained in trace amounts and car-
Figure 3. DRIFT spectra of Na2CO3, Na–nepheline, K2CO3-loaded Na–nepheline, and
calcined one.
bonate was the major anion. Legutko et al. also suggested that
K2CO3 was the best precursor for PM oxidation among KOH,
K2CO3, KNO3, CH3COOK, and K2SO4.[20]
Effect of contact with carbon grains on the performance of
carbonate catalysts
Silver[13] or platinum[14] on ceria shows high catalytic activity for
soot combustion by gaseous oxygen through a solid–solid–gas
triphasic reaction. Effective contact between the catalyst sur-
face and CB is important for this type of reaction. Unlike the
previously mentioned tight contact mode, the loose contact,
observed in the case of the typical Ag catalyst for PM combus-
tion, Ag/CeO2, and also in the typical Pt automobile catalyst,
Pt/CeO2–ZrO2 with CB resulted in a CO2 elution curve much
broader than that resulting in the case of the potassium cata-
lyst, as shown in Figure 4. On Ag/CeO2 and Pt/CeO2–ZrO2,
active oxygen generated from bulk CeO2 moves to the surface
of silver or platinum to react with CB only if it is adjacent to
the surface oxygen species. In other words, the active oxygen
species never flies into the gaseous phase, which could be the
main reason for the need for the tight-contact mode for this
type of triphasic catalysis. Upon using a potassium catalyst, on
the contrary, the contact mode used does not critically affect
the catalytic performance, which raises the possibility that the
active species probably flies into the gaseous phase.
Figure 4. CB combustion on Ag/CeO2, Pt/CeO2–ZrO2, and K2CO3-loaded
Na–nepheline for different mixing modes.
The catalytic performances of platinum and potassium spe-
cies for CB oxidation in a helium stream are demonstrated in
Figure 5. Even though gaseous oxygen was absent, CO2 was
detected for the platinum catalyst at 250, 500, and 7008C, at
which point the lattice oxygen of the CeO2–ZrO2 support start-
ed to desorb. This finding indicated that the active oxygen
was derived from the platinum support, as the lattice oxygen
could easily desorb at such low temperatures. Cobalt(II,III)
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 479 – 484 481

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
electron density of the carbonate. Interestingly, the frequency
was further decreased if the carbonate was located on the
nepheline surface. The intrinsic catalytic activity of potassium
carbonate increased if it was supported on the surface of crys-
talline aluminosilicate, and this is indicative of the vital role of
the carbonate ion in the activation of gaseous oxygen.
The results of investigations performed thus far on coal
gasification and carbon oxidation by oxygen and by potassium
suggest that an electron is transferred from carbon to gaseous
oxygen through potassium.[17–19] Direct removal of the electron
from its orbital electron requires very high energy; therefore, it
is reasonable to propose that the alkali species aids the pro-
cess by forming a conjugated orbital with the carbonate. Thus,
we can conclude from Figure 6a that an active electron is lo-
Figure 5. CB oxidation under He stream on Pt/CeO2–ZrO2, K2CO3-loaded
Co3O4, and K2CO3-loaded Na–nepheline.
oxide (Co3O4) is known to catalyze the oxidation of carbon
monoxide by using the lattice oxygen present in Co3O4.[15] The
work function of the catalyst was lowered by the addition of
potassium,[16] and this resulted in higher catalytic activity for
the oxidation reaction. Distinct bands for CO2 generated by CB
oxidation on K/Co3O4 were seen at 580 and 7508C, and even
at higher temperatures. On the contrary, potassium-containing
nepheline did not show catalytic activity at a low temperature
of approximately 3008C under the conditions used in the pres-
ent study. Therefore, potassium on nepheline uses oxygen in
the gas phase to catalyze CB oxidation; that is, the active
oxygen for this reaction is derived from the gas phase and it
flies back to the gas phase to attack carbon. Nevertheless, we
should consider the possibility that the potassium species may
also fly; potassium may be vaporized at a high temperature,
which decreases the catalytic performance. During the labora-
tory-scale tests to 8008C, which were repeated 10 times, the
catalytic activity of potassium carbonate on nepheline re-
mained unchanged, and the decrease in the amount of potas-
sium was negligible.
Figure 6. a) Possible mechanism for carbon combustion with gaseous
oxygen on an alkaline carbonate supported aluminosilicate surface. b) The
electron structure of potassium carbonate on the aluminosilicate surface.
The balloon shown in the figure indicates the SOMO of potassium
carbonate.
cated at the carbonate site and that this electron is released
from the carbonate through potassium for the generation of
a nucleophilic oxygen species. Here, the alkali aluminosilicate
plays an indirect role in stabilizing such a carbonate species.
Potassium shows high catalytic activity for carbon oxidation,
because it allows better contact with carbon owing to its elu-
tion.[17] Although potassium might be volatilized during the ox-
idation of carbon, it is electrostatically stabilized on aluminosili-
cate, as also suggested by Su and McGinn.[21] The high-energy
active electron in the singly occupied molecular orbital
(SOMO) of potassium carbonate located on nepheline (Fig-
ure 6b) can attack an oxygen molecule and reduce it to
a more active oxygen species.
Mechanism for carbon oxidation catalyzed by potassium
carbonate
We then attempted to investigate how gaseous oxygen was
activated. For the oxidation of a carbonaceous compound,
oxygen should be reduced to gain nucleophilicity. Two differ-
ent mechanisms have been considered for the reaction: elec-
tron donation to carbon and oxygen transfer to carbon.[17] In
the latter case, for example, transition metals that show redox
capacity or oxygen-storage capacity, such as CeO2, act as cata-
lytically active centers, whereas such a redox mechanism
might be difficult in the case of the potassium carbonate cata-
lyst. Only the carbonate can act as the electron donor for
oxygen. As indicated by the IR spectra in Figure 1b, the elec-
tron density of the carbonate increased with the atomic
weight of the alkali metal, and the band corresponding to the
carbonate shifted to a lower frequency with an increase in the
We also found that oxygen activated by potassium carbon-
ate on sodalite/nepheline never catalyzed the oxidation of hy-
drocarbons and carbon monoxide and that its oxidation ability
was uniquely selective to carbon oxidation. The oxygen species
generated through this mechanism might be less nucleophilic
than O2ꢀ, which can attack CꢀH and CꢀO species; this results
in complete oxidation into carbon dioxide and water mole-
cules.
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 479 – 484 482

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
QA200TS, Anelva Japan. Carbon black #2600 (CB, Mitsubishi Chemi-
cals Co.) particles with a diameter of 13 nm were used as a refer-
ence for the carbonaceous soot found in diesel exhaust. Laborato-
ry-scale examination of the catalytic activity was conducted on two
types of contacts: one is “loose contact”, for which the soot is
mixed with the catalyst by using a spatula, and the other is “tight
contact”, for which the soot and catalyst are mixed in an agate
motor. It has long been known that the “loose-contact” scenario is
more reflective of DPF under practical conditions. In this research,
the catalysts and carbon black were simply mixed together with
a spatula to achieve a loose contact, which was similar to that ob-
served under pseudopractical conditions. The CB/catalyst mixtures
had weight ratios of approximately 1:10, so that the possible mass
and heat transfer limitation described in the literature could be
prevented. The mixtures were heated to 8008C at 10 Kminꢀ1 in
a flow of 10% oxygen in helium. The catalytic activity for CB com-
bustion was typically evaluated on the basis of the temperature,
the point at which the CO2 (m/z=44) elution curve starts to
appear. A weight loss and an exothermic peak attributed to the
combustion of CB and to the generation of CO2 were simultane-
ously detected by using thermogravimetry–differential thermal
analysis (TG–DTA) and mass spectrometry, respectively. The weight
of the sample decreased and evidence for CO2 elution were simul-
taneously observed in the mass spectrum. An exothermic peak in
the DTA measurements was clearly visible after a slight delay from
the time of CO2 elution. Therefore, the catalytic activity for carbon
combustion could be evaluated on the basis of temperature.
Finally, we focus on a base catalyst derived from alkali ion
exchanged zeolites such as potassium zeolites. Ambient
carbon dioxide adheres strongly on the surface of the alkali
ion on a zeolite, which thus prevents the adsorption of other
molecules on the active basic oxygen adjacent to the alkali
cation, and this results in carbonate formation on the sur-
face.[11] Researchers have reported that in base catalysis, deacti-
vation occurs by the adhesion of CO2, and hence, the catalyst
must be pretreated at temperatures as high as 800 to 9008C.
However, CO2 elimination or carbonate decomposition at such
high temperatures may cause sintering of the catalyst. Howev-
er, the “cumbersome” carbonate, as an oxidation catalyst, plays
an important role as an electron pool and electron donor to
promote the activation of gaseous oxygen.
Experimental Section
Catalyst preparation
Sodalite was synthesized according to the procedure reported in
the literature.[6] An impregnation method was used to load potassi-
um carbonate onto the sodalite. Potassium carbonate (16 wt%)
was added to a sodalite slurry in distilled water. The obtained
slurry was vigorously stirred for 24 h at 808C and was subsequently
dried at 1008C, which resulted in the physical deposition of potas-
sium carbonate onto the support. The potassium-carbonate-sup-
ported sodalite was thermally treated by using an electric muffle
furnace, by heating to 8008C at 10 Kminꢀ1 and by maintaining at
8008C for 5 h in a stream of air. The obtained samples were
washed with water at room temperature. Each gram of thermally
treated K2CO3/sodalite was suspended in distilled water (80 mL) in
a polypropylene bottle, and the suspension was vigorously stirred
for 24 h at room temperature. The obtained samples were filtered
and dried at 608C.
Acknowledgements
A part of this work was performed under management of “Ele-
ments Strategy Initiative for Catalysts & Batteries (ESICB)” sup-
ported by the MEXT program “Elements Strategy Initiative to
Form Core Research Center” since 2012, Ministry of Education,
Culture, Sports, Science and Technology (MEXT), Japan. A part of
this work was also supported by Nippon Soken, Inc., DENSO Cor-
poration. M.O. would like to express appreciation to Editage for
providing editorial assistance.
Characterization of catalysts
Powder X-ray diffraction (XRD) patterns were recorded to confirm
the formation of the active component “nepheline” by using
a M03X-HF diffractometer, Bruker AXS, Germany, with CuKa radia-
tion (l=1.54 ꢁ) at 40 kV and 30 mA. The 2q values ranged from 5
to 458. IR spectra were recorded by using an FTIR-4100 single-
beam FTIR, (JASCO, Japan) that was connected to a diffuse-reflec-
tance IR cell by using a KBr diluent. The spectra were generated at
a resolution of 4 cmꢀ1. Raman spectroscopy was performed at
room temperature by using a NR-1800, JASCO, with a l=532 nm
green laser. The measurement was performed at cumulated twice
and the exposure time was 60 s. The chemical composition of the
solid or liquid samples was characterized by using an inductively
coupled plasma atomic emission spectrometer, P4010, Hitachi,
Japan.
Keywords: aluminosilicates
potassium · soot combustion
·
carbonates
·
oxygen
·
[1] M. V. Twigg, Catal. Today 2011, 163, 33.
[2] R. M. Heck, R. J. Farrauto, Appl. Catal. A 2001, 221, 443.
[3] D. Fino, V. Specchia, Powder Technol. 2008, 180, 64.
[4] A. P. Walker, Top. Catal. 2004, 28, 165.
[5] C. Gçrsmann, Monatsh. Chem. 2005, 136, 91.
[6] M. Ogura, K. Morozumi, S. P. Elangovan, H. Tanada, H. Ando, T. Okubo,
Appl. Catal. B 2008, 77, 294.
[7] R. Kimura, J. Wakabayashi, S. P. Elangovan, M. Ogura, T. Okubo, J. Am.
Chem. Soc. 2008, 130, 12844.
[8] R. Kimura, S. P. Elangovan, M. Ogura, H. Ushiyama, T. Okubo, J. Phys.
Chem. C 2011, 115, 14892.
Ab initio quantum chemistry calculations were performed by using
DFT. The B3LYP hybrid function and the 3-21G basis set were used
for the calculations.
[9] R. Kimura, D. Thanh-Nghia, J. Wakabayashi, S. P. Elangovan, M. Ogura, T.
Okubo, Bull. Chem. Soc. Jpn. 2012, 85, 527.
Catalytic activity test
[10] H. Hattori, Chem. Rev. 1995, 95, 537.
[11] J. W. Ward, H. W. Habgood, J. Phys. Chem. 1966, 70, 1178.
[12] T. Ozawa, Thermochim. Acta 1992, 203, 159.
[13] K. Shimizu, H. Kawachi, A. Satsuma, Appl. Catal. B 2010, 96, 169.
[14] J. P. A. Neeft, M. Makkee, J. A. Moulijn, Appl. Catal. B 1996, 8, 57.
[15] X. Xie, Y. Li, Z.-Q. Liu, M. Haruta, W. Shen, Nature 2009, 458, 746.
The catalytic activity of the samples used for soot combustion was
evaluated by using temperature-programmed oxidation (TPO) on
a thermogravimetric/differential thermal analyzer (Thermoplus TG-
8120, Rigaku, Japan) directly connected to a mass spectroscope M-
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 479 – 484 483

CHEMCATCHEM
COMMUNICATIONS
www.chemcatchem.org
[16] a) P. Stelmachowski, G. Maniak, A. Kotarba, Z. Sojka, Catal. Commun.
2009, 10, 1062; b) P. Legutko, P. Stelmachowski, M. Trebala, Z. Sojka, A.
Kotarba, Top. Catal. 2013, 56, 489.
[21] a) C. Su, P. J. McGinn, Appl. Catal. B 2013, 138–139, 70; b) C. Su, P. J.
McGinn, Catal. Commun. 2014, 43, 1.
[17] Z. Zhu, G. Q. (Max) Lu, J. Finnerty, R. T. Yang, Carbon 2003, 41, 635.
[18] C. Janiak, R. Hoffmann, P. Sjovall, B. Kasemo, Langmuir 1993, 9, 3427.
[19] D. Lamoen, B. N. J. Persson, J. Chem. Phys. 1998, 108, 3332.
[20] P. Legutko, T. Jakubek, W. Kaspera, P. Stelmachowski, Z. Sojka, A. Kotar-
ba, Catal. Commun. 2014, 43, 34.
Received: August 30, 2013
Revised: November 16, 2013
Published online on December 12, 2013
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 479 – 484 484