COST Chemistry D36
“Molecular Structure-Performance Relationships at the Surface of Functional Materials”
1
stWORKSHOP
and 3
rdManagement Committee Meeting
Espoo, Finland
Saturday, September 1
st– Sunday, September 2
nd, 2007
Meeting place address: Helsinki University of Technology, TUAS-house, Otaniementie 17, FI-02150 Espoo, Finland
Organizers: Dr. Sanna Airaksinen and Ms. Satu Korhonen Helsinki University of Technology
Laboratory of Industrial Chemistry P.O. Box 6100 (Kemistintie 1, Espoo) FI-02015 TKK
Finland
Saturday, September 1st, 2007
9:00 REGISTRATION
9:30 SESSION 1 Chair: Lubomir POSPISIL
9:30 – 9:40 Welcome Sanna AIRAKSINEN, Symposium Organizer Miguel A. BAÑARES, Action Chair
9:40 – 10:30 KEY–1 Günther RUPPRECHTER
Vibrational spectroscopy during catalytic reactions: UHV-based model systems vs. technological catalysts
10:30 – 10:55 O–1 David J. FERMIN
Modulating the reactivity of electrode surfaces with poly- electrolyte/nanoparticle heterostructures
10:55 – 11:15 COFFEE BREAK
11:15 SESSION 2 Chair: David FERMIN 11:15 – 11:40 O–2 Klaus SCHIERBAUM
Nanosized Pt-cluster at TiO2(119) surfaces: Effect of oxygen studied by an STM-based point contact technique
11:40 – 12:05 O–3 Maria MIGUEL
Manipulation of DNA with surfactants and lipids: Compaction and decompaction
12:05 – 12:30 O–4 Robert SCHOONHEYDT Basicity of zeolites
12:30 – 13:30 LUNCH
13:30 SESSION 3 Chair: Anna-Maria VENEZIA 13:30 – 14:20 KEY–2 Björn LINDMAN
Mixed colloid systems: Fundamentals and applications in hair care, paints, gene delivery and more
14:20 – 14:45 O–5 Lubomir POSPISIL
Fullerene-γ-cyclodextrin complex as redox mediator for electrocatalytic nitrogen fixation at mild conditions
14:45 – 15:05 COFFEE BREAK
15:05 SESSION 4 Chair: Hubert GIRAULT 15:05 – 15:30 O–6 Jean-Pierre GILSON
Advances in in situ & operando IR spectroscopy applied to heterogeneous catalysts
15:30 – 15:55 O–7 Jacques FRAISSARD
Mathematical modeling and visualization of gas transport in a zeolite bed using a slice selection procedure
15:55 – 17:30 POSTER SESSION
17:00 – 18:30 3rd MC MEETING
19:00 WORKING DINNER
Sunday, September 2nd, 2007
9:00 SESSION 5 Chair: Robert SCHOONHEYDT 9:00 – 9:50 KEY–3 Gianfranco PACCHIONI
Nitrogen doping of TiO2: theory and experiment 9:50 – 10:15 O–8 Elizabeth SANTOS
Unified model for electron transfer in electrocatalysis 10:15 – 10:40 O–9 Mònica CALATAYUD
Combining theoretical description with experimental in situ studies on the effect of alkali dopants on the structure and reactivity of titania-supported vanadium oxide catalyst
10:40 – 11:00 COFFEE BREAK
11:00 SESSION 6 Chair: Maria Rosa INFANTE 11:00 – 11:25 O–10 Maria ZIOLEK
The strategy for the synthesis of hexagonally ordered mesoporous metallosilicate materials with the desired new surface properties 11:25 – 11:50 O–11 Guillaume CLET
Role of the initial form of the support in the development of Brönsted acidity and n-hexane isomerization activity of tungstated zirconia and tungstated titania catalysts
11:50 – 12:15 O–12 Viorica PARVULESCU
Metal-organic hybrid catalysts obtained by functionalization of mesoporous silicas and organic polymers
12:15 – 13:15 LUNCH
13:15 SESSION 7 Chair: Guido MUL
13:15 – 13:40 O–13 Anna E. LEWANDOWSKA
Molecular structures and catalytic properties of alumina supported niobia and niobia-vanadia catalysts
13:40 – 14:05 O–14 Lyuba ILIEVA
Gold catalysts supported on CeO2 and CeO2-Al2O3 for NO reduction by CO
14:05 WORKSHOP END
Authors Title V. Ferreira, A. C. Cascalheira,
L. M. ABRANTES
A new strategy toward self-doped polyaniline:
copolymerization of luminol with aniline P. Gonzalez-Navarrete, L. Gracia, J. Andrés,
M. CALATAYUD, C. Minot
Methanol oxidation to formaldehyde on vanadium oxide: a theoretical study G. DI CARLO, L. F. Liotta, G. Pantaleo,
A. M. Venezia Effect of TiO2 loading in the activity and SO2
tolerance of Pd supported on silica M. O. GUERRERO-PEREZ, M. A. Bañares Propane ammoxidation on V-Sb-O based
catalysts, effect of additives A. LEWANDOWSKA, L. Ortega Perez,
M. A. Bañares Influence of the chromium and molybdenum
loading on the polymerization degree on the alumina supported catalysts
G. MUNTEANU, C. Miclea Quantum chemical calculations regarding the effect of some metal transitional impurities on the reducibilities of NiO and MgO
A. M. RUPPERT, B. M. Weckhuysen Catalytic conversion of glycerol over basic oxides
E. SANTOS Experimental and theoretical studies of L-
cysteine adsorbed at Ag(111) electrodes I. SOBCZAK, A. Kusior, M. Ziolek Gold supported on mesoporous silicates and
metalosilicates as active catalyst in the oxidation processes
J. A. SULLIVAN, K. A. Flanagan, H. Hain Selective H-D exchange catalysed by aqueous- phase Pd nanoparticles
F. TIELENS, S. Dzwigaj, M. Trejda, M. Ziolek Investigation of the vanadium and niobium sites in substituted silica zeolites; a periodic DFT study
M. TREJDA, P. Decyk, D. Duczmal, J. Kujawa, M. Ziolek
Radical active species in silicate ordered mesoporous materials
A. M. VENEZIA, R. Murania, G. Pantaleo,
G. Deganello Pd and PdAu on mesoporous silica for methane
oxidation: effect of SO2
J. L. VIOTA, M. Lopez-Viota, S. Strnad, K. Stana-Kleinschek
Thermodynamics characterization of xylan- organic modified clay films
I. WALZEL, G. Mestl Development of new iron-molybdate based
catalysts for the selective oxidation of glycerol
Keynote lectures
Vibrational spectroscopy during catalytic reactions:
UHV-based model systems vs. technological catalysts
Günther Rupprechter
Institute of Materials Chemistry, Vienna University of Technology, Veterinärplatz 1, A-1210 Vienna, Austria
Model catalysis has come a long way. The development of planar nanoparticle model catalysts, consisting of well-defined ultrahigh vacuum-grown metal particles supported on thin oxide films, now provides a route to mimic an increasing number of technical catalysts [1,2]. The planarity and electrical/thermal conductivity of the model systems allows applying a wide range of surface sensitive spectroscopic and imaging techniques (e.g. XPS, IRAS, SFG, TPD, STM, etc). To date, various combinations of Pd, Pt, Rh, Ag, Au, Pd/Co, etc nanoparticles supported by Al2O3, SiO2, TiO2, Fe3O4, Nb2O5, etc have been examined.
In parallel, significant advances have been made in carrying out surface analysis under ambient pressure and photon-based methods such as polarization-modulated infrared reflection absorption spectroscopy (PM-IRAS) or sum frequency generation (SFG) vibrational spectroscopy, together with high-pressure X-ray photoelectron spectroscopy (HP-XPS) allow for studies of catalytic reactions on functioning model surfaces [2,3].
A systematic comparison of model and industrial-grade supported catalysts under reactive conditions is still an interesting topic that has not been touched too often [4,5]. In this contribution the effect of the metal oxidation state on CO and methanol oxidation activity [6] and the mechanism of carbonate formation [7] are discussed, both for Pd-Al2O3 model and technological catalysts.
1. M. Bäumer, J. Libuda, K.M. Neyman, N. Rösch, G. Rupprechter, H.-J. Freund, Phys. Chem. Chem. Phys. 9 (2007) 3541
2. 2. G. Rupprechter, Adv. Catal. 51 (2007) 133; Catal. Today 126 (2007) 3.
3. G. Rupprechter, C. Weilach, Nano Today 2 (2007) 20.
4. T. Lear, R. Marshall, J.A. Lopez-Sanchez, J.M. Winfield, S.D. Jackson, T.M. Klapötke, M. Bäumer, G. Rupprechter, H.-J. Freund, D. Lennon, J. Chem. Phys. 123 (2005) 174706-1.
5. H. Borchert, B. Jürgens, V. Zielasek, G. Rupprechter, S. Giorgio, C.R. Henry, M. Bäumer, J. Catal. 247 (2007) 145.
6. H. Gabasch, A. Knop-Gericke, R. Schlögl, M. Borasio, C. Weilach, G. Rupprechter, S. Penner, B. Jenewein, K. Hayek, B. Klötzer, Phys. Chem. Chem. Phys. 9 (2007) 533.
7. K. Föttinger, R. Schlögl, G. Rupprechter, Chem. Comm., submitted.
KEY–2
Mixed colloid systems:
Fundamentals and applications in hair care, paints, gene delivery and more
Björn Lindman, Tommy Nylander, Maria Miguel, Filipe Antunes
Physical Chemistry 1, Lund University, PO Box 124, 221 00 Lund, Sweden and Department of Chemistry, Coimbra University, Coimbra, PORTUGAL
The interaction between polymers and surfactants involves a combination of hydrophobic and electrostatic forces. A review of polymer-surfactant association in bulk is given, discussing the conditions needed for association of a surfactant to a polymer. While ionic surfactants bind broadly to polymers in aqueous solution, nonionics only do so if the polymer has a lower polarity and can interact by hydrophobic interactions. Water-soluble polymers, which have hydrophobic groups, form physical cross-links, hence their important use as thickeners. The rheological behaviour is strongly influenced by various cosolutes; especially strong effects are due to surfactants and both a decrease and an increase in viscosity can occur. This can be referred to mixed aggregate phenomenon and a simple model is presented. When the polymer-surfactant interactions are particularly strong, an associative phase separation can occur; this and other types of phase separation phenomena are described. Finally, the behavior of these mixed systems on solid surfaces is discussed. In particular, we consider the adsorption of mixtures of polyelectrolytes and oppositely charged surfactants on polar and nonpolar surfaces as studied by in situ null ellipsometry. It is found that, depending on concentration, an ionic surfactant can either induce additional polyion adsorption or induce desorption. Kinetic control of adsorption and, in particular, desorption is typical. Important consequences of this include an increased adsorption on rinsing and path dependent adsorbed layers. Special attention is also put on the effect of hydrophobic modification of the polymer. There is in general a correlation between adsorption and associative phase separation as deduced from phase diagram work. DNA-surfactant systems show strong analogies to systems used in haircare, as shown by studies related with the deposition of DNA on solid surfaces.
Nitrogen doping of TiO
2: theory and experiment
Gianfranco Pacchioni, Cristiana Di Valentin, Emanuele Finazzi, Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca,
Via R. Cozzi, 53, 20125, Milano, Italy
Annabella Selloni,
Department of Chemistry, Princeton University, Princeton N.J. 08540 USA Stefano Livraghi, Maria Cristina Paganini, Elio Giamello
Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I - 10125 Torino, Italy
Nitrogen doped titanium dioxide is attracting a continuously increasing attention because of its potential as material for environmental photocatalysis. In this paper we review experimental and theoretical work done on this system in our groups in recent years. The analysis is largely based on electron paramagnetic resonance (EPR) spectra and on their interpretation based on high-level ab initio calculations. N-doped anatase TiO2 contains thermally stable single N-atom impurities either as charged diamagnetic Nb−
centers or as neutral paramagnetic Nb• centers (b stays for bulk). The N atoms can occupy both interstitial or substitutional positions in the solid, with some evidence for a preference for interstitial sites. All types of Nb centers give rise to localized states in the band gap of the oxide, thus accounting for the related reduction of absorption band edge. The relative abundance of these species depends on the oxidation state of the solid. In fact, upon reduction, oxygen vacancies form and transfer electrons from Ti3+ ions to the Nb• with formation of Ti4+ and Nb−
. EPR spectra measured under irradiation show that the Nb centers are responsible for visible light absorption with promotion of electrons from the localized N-impurity states to the conduction band or to electron scavengers like O2 adsorbed on the surface. These results provide an unambiguous characterization of the electronic states associated with N-impurities in TiO2 and a realistic picture of the processes occurring in the solid under irradiation with visible light.
Oral presentations
Modulating the Reactivity of Electrode Surfaces with Poly- electrolyte/Nanoparticle Heterostructures
Christopher R. Bradbury, Jianjun Zhao, Gabriela Kissling and David J. Fermín*
Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
The electronic communication between nanoparticles and metal surfaces is a fundamental aspect in determining the reactivity of hybrid electroactive materials. In polymer/nanoparticle systems, the electronic communication is affected by a wide range of parameters such as the electron occupancy across the heterostructure, the effective distance between the nanoparticles and the electrode, as well as the electronic properties of the nanoparticles and the polymer framework. In the present contribution, we shall address some of these issues by examining the electrochemistry of nanoparticle monolayers attached to metal electrodes by polyelectrolyte multilayer (PEM) films.
Two classes of nanostructures will be discussed. Au nanoparticles and CdTe quantum dots (Q-dots).
Both nanomaterials are chemically synthesised and the colloids are stabilised by adsorbed negatively charged organic species. The nanoparticle monolayer formation is performed by electrostatic adsorption on poly-L-lysine (PLL) terminated PEM films. The modification of the Au electrodes is initiated by self-assembly of a carboxyl terminated alkane thiol monolayer, followed by layer-by-layer electrostatic adsorption of PLL and poly-L-glutamic acid (PGA) ultrathin films.
The structure and charge transport properties of the system are studied by in-situ scanning force microscopy and electrochemical impedance spectroscopy. Our results in the presence of the hexacynoferrate redox probe clearly show that:
1.- in the absence of metal nanoparticles, the electron transfer kinetics are controlled by long- distance tunnelling across the initial thiol layer,
2.- nanoparticle mediated electron transfer appears independent of the length of the alkane thiol and the thickness of the PEM film over distances as large as 6 nm.
The unique long-range electronic communication observed in this system is a consequence of the interplay of parameters associated with the PEM film structure, the permeability of the film with respect to the redox probe and the electronic properties of the nanoparticles. For instance, it is shown that modification of the PEM film by cross-linking generates significant changes in the electrochemical behaviour of the system. Finally, it is also demonstrated that CdTe Q-dot monolayers exhibit rectifying behaviour due to the relative position of the redox probe energy and the band edges of the dots.
O–2
Nanosized Pt-Clusters at TiO2(110) Surfaces: Effect of Oxygen Studied by an STM-based Point Contact Technique
Klaus Schierbaum and Micha Kölbach
Institut für Physik der kondensierten Materie, Abteilung Materialwissenschaft, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, Gebäude 25.23,
40225 Düsseldorf, Germany
Schottky diodes, revealing sensing properties, are known for silicon (PdAg/thin SiO2/Si for H2 sensing and Pd/SiC)1 and also for oxide semiconducting materials (e.g. Pt/ZnO for CO sensing)2. Recently, Somorjai and Xiaozhong Ji has constructed a nanoscale Schottky diode, based upon a 150-nm-thick layer of TiO2 and a 5- nm-thick platinum film, which is used to measure a continuous flow of hot electrons generated by catalytic surface reactions.3
We have studied nanosized Pt clusters deposited on (110) single-crystalline titanium dioxide surfaces under ultra-high vacuum conditions. We used the so-called “seeding and growing” technique. Small amounts of Pt are evaporated, followed by an anneal at 1000 K, thus forming very small nucleation centres for a subsequent Pt evaporation at a high temperature (1000 K). This procedure circumvents the problem of surfaces that are covered with a great number of smaller clusters at a high density.
We explore the use of the following software-controlled procedure to determine local current-voltage curves of the Pt/TiO2 structures under tunneling and under point-contact conditions; after positioning the W tip over the Pt cluster, the feedbacks stabilizes the current at a constant value (0.6 nA) which corresponds to an initial tip-cluster spacing, z0. A large number of current-voltage curves are taken, to provide a better statistics of the I-V data. The distance is then decreased by a small value ∆z of 0.1 Å and I-V-curves are determined. This is repeated until a contact between the tip and the cluster is formed. By doing so, a series of ln I-V-curves as a function of tip-cluster spacing ∆z are obtained.
We have applied the following oxygen source to expose the “nanodiode” to O2. The source is based on an ion pump-type, attached to the uhv chamber, that utilizes the high oxygen diffusion of a heated yttria- stabilized zirconia single-ended tube. The oxygen flow can be controlled by the temperature and the voltage that is applied over the internal and the external Pt contacts of the tube. This set-up avoids any mechanical disturbance so that no significant tip-cluster displacements occur during the point-contact measurements.
The I-V-curves indicate that the nanosized diode structures change their electrical behaviour as the result of oxygen exposure. It shows that the structures behave like non-linear circuit units in uhv (as expected for reduced TiO2) but converts into Schottky-diodes upon O2 interaction. The net effect corresponds to the behaviour of macroscopically Pt contacts.
To summarize, we have been able to prepare “prototypical” nano-sized Pt/TiO2 structures, image them with scanning tunneling microscopy and build an experimental set-up for contacting individual Pt clusters, localized on-top of the TiO2 surface. I-V-curves can be determined of such nanostructures. An oxygen pump, necessary to expose oxygen to the nanostructures, was developed and implemented to the STM chamber.
First results of the oxygen sensing properties of such nanoscopic diode structures have been received.
1 Hughes et al. Appl. Phys. A. 62 (1987) 1074 2 Kang et al., Appl. Phys. A. 80 (2005) 259
3 X. Ji, A. Zuppero, J. M. Gidwani, and G. A. Somorjai, Nano Lett. 5 (2005) 753
Manipulation of DNA with surfactants and lipids: Compaction and decompaction
Maria Miguel, Björn Lindman, Carmen Morán, Diana Costa, Rita Dias
Physical Chemistry 1, Chemical Center, University of Lund, P.O. Box 124, S-221 00 Lund, Sweden and Chemistry Department, Coimbra University, 3004-535 Coimbra, Portugal, [email protected] The interaction between DNA and a cationic surfactant is strong and leads in bulk solution to cooperative binding and to condensation of DNA from an extended to a compact conformation. It also leads to an associative phase separation with a concentrated DNA-surfactant phase in equilibrium with a dilute solution. Phase diagrams are found to depend strongly on surfactant and also on DNA conformation. The difference in phase diagrams between single- and double-stranded DNA show the role of hydrophobic interactions in surfactant binding. Particles formed from DNA- surfactant solutions have different sizes and shapes depending on the stoichiometry. The particles, as well as the macroscopic phases formed, have a regular internal structure as demonstrated by small angle X-ray diffraction and cryogenic transmission electron microscopy. There is typically a 5-10 nm periodicity and the major structures formed are lamellar and reversed or normal hexagonal, structure formed mainly determined by the surfactant chemical structure. By controlled mixing of solutions of DNA and surfactant, globular transparent gel-like particles can be formed. By chemical cross-linking of DNA, macroscopic gels can be prepared. These gels are very useful in studying DNA-cosolute interactions from simple volumetric measurements. Thus, on addition of a simple electrolytes, polycations or cationic surfactants, the gels shrink; this effect is reversible as reswelling occurs as the DNA-cosolute association is eliminated.
Regarding the covalent gels, denaturation of cross-linked DNA gels has been induced by changes in temperature. This process, studied by fluorescence using ethidium bromide, appears to be reversible when a heating/cooling cycle was performed. The swelling behaviour on addition of different cosolutes, such as metal ions, polyamines, charged proteins and surfactants was investigated for different DNA gel samples, which include long and short ds-DNA and long and short ss-DNA. The DNA molecular weight has only a slight effect on the deswelling curves, while conformation shows a more pronounced one. In general, single stranded DNA gels exhibits a larger collapse, in the presence of cations, than double stranded does. This has been attributed to differences in linear charge density, chain flexibility and hydrophobicity. The swelling of DNA gels appears to be reversible and this process does not depend on the DNA conformation. No macroscopic separation of collapsed and swollen region is observed at intermediate degrees of binding for ds-DNA gels, whereas a dense surfactant-rich surface phase (skin) is found to co-exist with a swollen core network for ss-DNA gels with ß >0.5. One explanation to this difference is the large deformation energy required for the compression of the very stiff ds-DNA chains.
Keywords: DNA, surfactant, gels, particles, compaction
O–4
Basicity of zeolites
P. Mignon1, E. Pidko2, P. Geerlings3, R. van Santen2 and R. Schoonheydt1
1 Centrum voor Oppervlaktechemie en Katalyse, K.U.Leuven, Kasteelpark Arenberg 23, BE-3001 Leuven, Belgium
2 Schuit Institute of Catalysis, Eindhoven University of Technology, P.O.Box 513, NL-5600 MB Eindhoven, The Netherlands
3 Eenheid Algemene Chemie, Vrije Universiteit Brussel, Pleinlaan 2, BE-1050 Brussels, Belgium Basicity of zeolites can be considered in the frame of the Brønsted-Lowry acid-base definition (1) or of the Lewis electron donor-electron acceptor concept (2):
(1) ZOH + B <> ZO- + BH+ (2) Mn+ + B <> Mn+ -- B
Where ZOH = zeolite framework with bridging hydroxyl group, Mn+ is an exchangeable cation and B is a base.
Basicity of zeolites is governed by two empirical rules: (1) basicity increases with decreasing Si:Al ratio; (2) basicity increases with the size of the exchangeable cations, both in the alkali cation series and in the alkaline earth cation series. Usually probe molecules are used to probe basicity: CO2, pyrrole, CH3OH, CH3I, N2O4. Here we present data of theoretical studies (DFT) of basicity on the basis of the following reactions:
(3) ZOM + CH3OH <> ZOCH3 + MOH (4) ZOM + CH3I <> ZOCH3 + MI (5) ZOM + N2O4 <> ZO-NO+ + MNO3
With ZO = faujasite lattice and M= alkali cation.
Reactions (3) and (4) involve the CH3-OH and CH3-I bond dissociation and the ZO-CH3 bond formation. The bond dissociation is governed by the hardness of the alkali cation and the activation energy increases with the size of the alkali cation. The bond formation involves the basicity of the zeolitic oxygen. In the case of methanol the role of the alkali in the bond dissociation is dominant, because of the hardness of the hydroxyl group. In the case of methyliodide the bond formation is dominant i.e. the activation energy decreases with the size of the alkali cation. In summary the role of the Lewis acids (alkali cations) and that of the oxygen basicity can be separated and their relative importance depends on the type of probe molecule.
In the case of reaction (5) the cooperative effect of the alkali cations in the supercages of zeolites X and Y is prominently present. The NO3- is indeed stabilized by 3 alkali cations in the supercages.
This is only possible when some cations are sited in site III. Also the larger the size, the easier is the stabilization of the nitrate anion. This stabilization of the nitrate anion by exchangeable cations frees the way for NO+ to interact with the basic oxygens.
Fullerene-γ-Cyclodextrin Complex as Redox Mediator for Electrocatalytic Nitrogen Fixation at Mild Conditions
Lubomír Pospíšil
J. Heyrovský Institute of Physical Chemistry of ASCR, v.v.i., Dolejškova 3, 18223 Prague The joint activity within the COST network initiated the research of water-soluble derivatives of fullerene. New conjugates of fullerene and cyclodextrins retain the redox activity of the fullerene moiety even in aqueous medium. This enables electrochemical generation of highly reactive fullerene anions in water. This new finding prompted us to use the fullerene-cyclodextrin complex as a redox mediator for the reduction of N2. The gaseous dinitrogen is a very inert molecule. Its conversion to other nitrogen-containing compounds is called the nitrogen fixation. Special attention is made to the conversion of dinitrogen to ammonia. The reaction involves the transfer of six electrons and six protons. It requires rather high energy-demanding conditions1 and it is the base of annual production of about 100 million of tons of ammonia.
The same reaction catalyzed by the enzyme nitrogenase proceeds at ambient conditions. This intrigues chemists to find a catalyst performing the nitrogen fixation more efficiently. We explored highly reactive reduced forms of fullerene as mediators transferring electrons to dinitrogen under conditions of a preparative electrolysis. The conversion of N2 to NH3 requires not only a strong reductant but also a protic medium (water), where fullerene is insoluble. The inclusion of C60 in the molecular cavity of γ-cyclodextrin yields a water soluble complex, which we used for the conversion.
The electrochemical impedance spectroscopy (EIS) and other electrochemical techniques were used for characterization of redox properties of the encapsulated fullerene. Fullerene can accept up to six electrons in subsequent steps2. Indeed, a single-frequency AC polarography of the [C60.(CD)2] complex in aqueous solutions (Fig.1) shows that at least the first four electron transfers can be observed. In order to asses the conditions for a possible nitrogen fixation we performed a series of EIS measurements under the atmosphere of argon and nitrogen. Indeed the charge transfer resistance substantially decreases in solutions saturated with nitrogen (compared to solutions kept under argon). A preparative electrolysis performed under nitrogen atmosphere at elevated temperature 60o C yielded ammonia3. The fingerprint of NH3 was proven by the IR and photo-
acoustic spectroscopy (Fig.2). Currently we search for optimum reaction conditions.
1. Shilov, A.E. in New Trends in the Chemistry of Nitrogen Fixation, ed. J. Chatt, Academic Press, London, 1980;
Russian translation Moscow, 1983, Chap. 5.2.
2. Dubois,D.; Kadish,K.M.; Flanagan,S.; Haufer,R.E.; Chibante,L.P.F.; Wilson,L.J. J. Am. Chem.Soc. 1991, 113, 4364.
3. Pospíšil, L.; Bulíčková, J.; Hromadová, M.; Gál, M.; Civiš, S.; Cihelka, J.; Tarábek, J. Chem. Commun. 2007, 2270- 2272.
4 3 5 8 . 5 4 3 5 9 . 0 4 3 5 9 . 5 4 3 6 0 . 0 b
a
~ 1 6 2 p p m
1 0 0 0 p p m
ν ν ν ν / c m- 1
-0.5 -1.0 -1.5
0 1
Re Im
Admittance / 1E-6
1.6 Hz
E / V vs. Fc
Fig.1 Phase-sensitive AC polarogram of [C60.(CD)2] in aqueous 0.1M KCl.
Fig.2 IR spectrum of gas from electrolysis (a) and of
authentic ammonia (b).
O–6
Advances in in-situ & operando ir spectroscopy applied to heterogeneous catalysts
Jean-Pierre Gilson
LCS - Laboratoire Catalyse et Spectrochimie, ENSICAEN / Université de Caen / CNRS, 6 bd du Maréchal Juin, 14050 FRANCE Cedex,
Tel. Secrétariat +33 (0) 2 31 45 28 21 Fax. +33 (2) 31 45 28 22 Email : [email protected]
In-situ and operando IR spectroscopy is becoming ever more popular as it brings unique insights on the working catalysts. The latest work at the “Laboratoire Catalyse et Spectrochimie” in Caen shows that the limits of this technique are far from being reached. Three examples will illustrate the almost untapped potential of such advances:
1. In-situ IR spectroscopy of Selective Ring Opening (SRO) Catalysts: a classical but in-depth characterization of these important bi-functional catalysts (transformation of low value LCO from FCC units in high quality diesel fuel) by CO adsorption on both acidic (77 K) and metallic sites (RT) gives a clear picture of their mode of operation. These quantitative results, together with a detailed kinetic assessment of the transformation of a test molecule enabled the design of a very effective SRO catalyst.
2. In-situ IR spectroscopy of HDS catalysts activated under high pressure: the inhouse development of a high pressure cell working under realistic conditions (flow of sulfiding agent, T up to 450°C, P up to 50 bar) shows that the promotion level (CoMoS phase) of HDS catalysts is a function of the sulfidation pressure. A higher level of promotion is reached at 40 bars vs. 1bar.
These in-situ spectroscopic results correlate very well with the catalytic activity of test molecules and real feedstocks. This development highlights the need to bring the operando conditions as close as possible to the real operating conditions of the catalyst.
3. Step-Scan IR and pulsed laser for operando at 33 ns in Catalysis: The reaction of carbon monoxide and nitrogen monoxide on the surface of a silver catalyst was triggered by a femtosecond pulsed laser, and monitored by in situ FT-IR spectroscopy. The mechanism of this catalytic reaction was shown by 33ns IR detection of the flip of a cyanide group from silver nanoparticles to the alumina support in less than 3µs. So far, no clear evidences for intermediates between CN and NCO species could be shown probably because of too short a lifetime on the surface of the solid. Only a higher time resolution afforded such deeper insights on such important pollution abatement catalysts.
Mathematical modeling and visualization of gas transport in a zeolite bed using a slice selection procedure
Michael Petryk1, Sébastien Leclerc2, Daniel Canet2 and Jacques Fraissard3
1 Modélisation du Transfert de Masse en Milieu Hétérogène et Nanoporeux, Université Technique d’Etat Ivan Pul’uy, Ternopil, 46001, Ukraine,
2 Méthodologie RMN, Nancy University, Bd des Aiguilettes, Vandoeuvre-les-Nancy, 54506, France
3 Université P. et M. Curie and ESPCI, Laboratoire de Physique Quantique,10 rue Vauquelin, Paris, 75005,France
We present the analytical solution of the equations of gas diffusion in a heterogeneous zeolite bed. The problem is handled by assuming that the bed consists of a large number of very thin layers of solid, perpendicular to the direction of propagation of the gas. The results allow the theoretical determination of the time dependence of the concentration profiles and the inter- and intra-crystallite diffusion coefficients of a gas in each layer of the bed.
This figure presents the calculated profiles of C H6 6 concentrations in crystallites, ( , , )
Q t X z , as a function of dimensionless distance from the crystallite center X (=x/R with R=radius) for different times t (min) and four distances from the bottom of the crystallite bed z (mm). The concentration gradient ( , , )Q t X z depends of course on the adsorption time but also, very much, on the position of the crystallites in the bed as well as on the abscissa of these latter.
These coupled investigations give a better understanding of the diffusion process in this multilayer material. This new type of NMR imaging should be very interesting for studying the co- diffusion of several gases in a catalytic bed, since it make it possible to detect the characteristic spectra of each gas at every moment and position in the bed.
Vertical movement
nt
1
z
Excitation profile
The numerical application concerns the diffusion of benzene in a cylindrical bed of ZSM5 (15mm height) displaced vertically and rapidly, step by step, inside the NMR probe in the direction of the applied magnetic field B0. Thus we can obtain the time dependence of the concentration of gas absorbed at the level of each slice.
O–8
Unified model for electron transfer in electrocatalysis
E. Santos* and W. Schmickler+
*Facultad de Matemática, Astronomía y Física. University of Córdoba. Argentina.- Zentrum für Sonnenenergie und Wasserstoff-Forschung Ulm. Germany
+Department of Theoretical Chemistry, University of Ulm. Germany.
We propose a unified theory for electrochemical electron transfer, which combines concepts from the Marcus theory of electron transfer in solution, from the tight-binding model with an extended Anderson–Newns Hamiltonian, and from gas phase catalysis. This model explicitly accounts for the electronic structure of the electrode and the stabilization of ions by the solvent. It applies both to the reduction or oxidation of simple and to bond-breaking reactions of either homonuclear or heteronuclear molecules. Generally, the breaking of the bond requires a strong catalytic effect of the electrode. Interactions with narrow d-bands lead to changes in the local density of states of the reactant as its electronic level fluctuates due to solvent reorganization. More importantly, it can significantly reduce activation barriers, and in extreme cases induce dissociative adsorption. We have performed model calculations for different reactions of interest and constructed adiabatic potential energy surfaces, using the solvent coordinate q and the bond distance r as reaction coordinates. On these surfaces, the reaction proceeds in the following way: Initially the system consists of a molecule situated in the valley near q = 0, r = r0, where r0 is the equilibrium bond distance. The final state, two cations, or two anions corresponds to the valley centred near q = −2, q=+2 respectively. The initial and the final state are separated by a barrier, whose saddle point determines the energy of activation. The nature of the metal has a pronounced effect on the shape of the surfaces. In particular, due to d-band catalysis the barrier on metals with d-bands is very much lower than on sp-metals.
Explicit model calculations for some reactions, such as the hydrogen oxidation on a series of metals, are in line with experimental data, and explain in particular why platinum is such a good catalyst. Thus our theory makes it possible to predict the catalytic properties of metals by relatively simple calculations.
A2→ 2A+ + 2 e- A2 + 2 e-→ 2A-
Combining theoretical description with experimental in situ studies on the effect of alkali dopants on the structure and reactivity of titania-supported vanadium
oxide catalyst
M. Calatayud1, A. E. Lewandowska2, E. Lozano Diz2, C. Minot1 and M. A. Bañares2
1Université Pierre et Marie Curie-Paris6, UMR CNRS 7616 LCT, Paris, F-75005, France
2Instituto de Catálisis y Petroleoquímica, CSIC; Marie Curie, 2; E-28049-Madrid, Spain
The influence of alkali ions on the structure and reactive properties (vs. H2 and vs. methanol) of V2O5/TiO2 has been studied by periodic and cluster DFT calculations and measured experimentally by operando Raman-MS during reaction, in situ TP-Raman spectroscopy and TPR. Alkali ions coordinate to surface vanadia altering its structure but it does not form bulk compounds. Theory and experiments agree on the weakening of the terminal V=O bond due to this interaction; and on the decrease of the reducibility of V2O5/TiO2. Calculations confirm that the bridging V-O-Ti bond appears directly associated to the reactive properties of surface vanadia species on titania. For methanol, the dissociative adsorption modes are preferred to the molecular one, in agreement with Raman spectroscopy during reaction.
Keywords: methanol, alkali, DFT, in situ, Raman, vanadia, titania, TPR, methanol
O–10
The strategy for the synthesis of hexagonally ordered mesoporous metallosilicate materials with the desired new surface properties
Maria Ziolek, Izabela Sobczak, Maciej Trejda, Piotr Decyk, Beata Kilos
Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland; [email protected]
A new area in templating synthesis began with the discovery of periodic mesoporous materials (M41S family) by Beck et al. in 1992. Liquid crystal templating (LCT) mechanism of these materials formation bases on the specific type of electrostatic interaction between a given inorganic precursor (I) and surfactant head group (S). Silicate or metalosilicate walls are located around intercalated surfactant molecules. One of the most popular LCT mechanism could be categorised as the S+I- pathway. By extension, the other charge- interaction pathways are S-I+, S+X-I+ (X- is a counteranion), and S-M+I- (M+ is a metal cation). The
incorporation of a metal into the skeleton is seemingly straightforward in light of the various mechanistic pathways, but the amount of dopant incorporation is difficult to predict. In the creation of the catalysts it is important to localize the metal species in the uniform sites. Therefore, it is very important to design the synthesis conditions necessary for the location of relatively high amount of metal in the walls of ordered mesoporous materials with the elimination of extra framework located metal species.
In this contribution the focus is on the incorporation of some transition metals (Fe, Nb, V, Mo, Au) important for catalytic oxidation processes into hexagonally ordered mesoporous materials (MCM-41, SBA- 3, SBA-15). The most important parameters for the successful location of metals in the silicate walls will be considered. Some new proposals for the increase of the amount of metal in the framework will be shown.
Moreover, the consideration of the specific conditions for the formation of active oxygen and/or defect holes in the mesoporous walls will be performed. To characterise all these features a wide spectrum of techniques were applied: XRD, TEM, SEM, N2 adsorption, FTIR, UV-VIS, ESR, test reactions.
Some of the most important conclusions can be drawn as follows.
1. The preparation conditions, (e.g. the proper relationship between the metal source and pH of the gel) play a crucial role in the efficiency of metal incorporation into the walls of mesoporous materials.
2. The amount of transition metal included into MCM-41 (prepared at pH=11) changes in the order: Fe (nitrate) > Nb (oxalate) > Cu (acetate) >> V (vanadyl(IV) sulphate(V)>> Mo (ammonium molybdate(IV) (the metal sources are given in the brackets). This sequence is not related to the oxidation state of metals which was estimated in calcined materials as Fe3+, Nb5+, Cu2+, V5+, Mo6+. More or less metal species were located in the extra framework positions.
3. The turning from MCM-41 to SBA-15 and SBA-3 (both prepared in the acidic medium) allows the location of niobium preferentially in the walls when NbCl5 is used as niobium source and Si/Nb is relatively high (up to 64).
4. The increase of Nb incorporation (up to Si/Nb =10) into the walls of SBA-15 can be reached by the elimination of hydrochloric acid from the reaction medium and the use of NbCl5 as niobium source.
5. Vanadium can be easily included into SBA-15 walls in the presence of H2O2.
6. The preference of metal in the formation of tetrahedrally coordinated complexes is an important feature for its effective including into the framework positions.
7. Au species surrounded by chloride can be generated in silicate MCM-41 matrix prepared by one step synthesis with Si (sodium silicate) and Au (HAuCl4) sources. Such catalyst exhibits an excellent performance in the electron transfer to oxygen in oxidation processes.
8. Nb included in the basic medium into MCM-41 structure creates defect holes active in the generation of oxygen radicals.
The unique surface redox properties will be shown for the selected catalysts in the gas and liquid phase oxidation procresses.
Role of the initial form of the support in the
development of Brønsted acidity and n-hexane isomerization activity on tungstated zirconia and tungstated titania catalysts.
Vanessa Lebarbier, Guillaume Clet, Marwan Houalla
Laboratoire Catalyse et Spectrochimie, CNRS-ENSICAEN-Université de Caen, 6 bd. du Maréchal Juin, 14050 Caen (cedex), France; [email protected]
Tungstated oxides have shown interesting properties for several acid-catalyzed reactions including n-alkane isomerization. According to Hino and Arata [1,2], these materials were thought to be active for n-alkane isomerization only when obtained by impregnation of an amorphous zirconium oxyhydroxide. Catalysts synthesized from a crystallized oxide were thought to be essentially inactive. However, recent results from our laboratory indicate that the actual influence of the support may not be straightforward [3,4]. The present work describes the influence of the initial state of the support, oxyhydroxide (amorphous) or oxide (crystallized) on the surface structure, acidity and catalytic performance of tungstated zirconia and titania.
Tungstated zirconias or titanias were prepared by impregnation of the support in both forms (zirconia / zirconium oxyhydroxide, titania / titanium oxyhydroxide). The texture and structure of the catalysts were investigated by BET, XRD, Raman and infrared spectroscopy. The acidity was monitored by adsorption of 2,6-dimethylpyridine (lutidine) and CO probes followed by FTIR. The catalytic activity was tested for isopropanol dehydration and n-hexane isomerization.
For a given W surface density, no significant differences in acidity, structure and catalytic activity were observed between the solids prepared from oxyhydroxide form of the support and those synthesized from crystalline Zr or Ti oxides. The Brønsted acidity measured by lutidine adsorption was correlated to the activity for isopropanol dehydration and the presence of polymeric W species.
Adsorption of CO brings additional information on the acidic sites involved in n-hexane iomerization. Activity for n-hexane isomerization appears to be associated with the presence of a limited number of very strong Brønsted acid sites. The lack of the influence of the initial form of the support was tentatively attributed to the structural similarity between the amorphous oxyhydroxide and the crystallized oxides used as supports. The apparent discrepancy with the literature is ascribed to the crystalline form of the oxide support with which the comparison is made (monoclinic ZrO2 , rutile TiO2 vs. tetragonal ZrO2 and anatase TiO2 in the present study).
References
[1] Arata, K., Hino, M. in Proc. 9th I.C.C.; Philips, M. J., Ternan, M., Eds., (1988), pp 1727-1734 [2] Hino, M., Arata, K. J. Chem. Soc., Chem. Commun. (1988), 1259-1260
[3] Lebarbier, V., Clet, G., Houalla, M. J. Phys. Chem. B, 110 (2006), 13905-13911 [4] Lebarbier, V., Clet, G., Houalla, M. J. Phys. Chem. B, 110 (2006), 22608-22617
O–12
Metal-organic hybrid catalysts obtained by functionalization of mesoporous silicas and organic polymers
V. Parvulescu1, R. Ene1, M. Muresanu2 and A. Popa3
1 Institute of Physical Chemistry, Spl. Independentei 202, 77208 Bucharest, Romania
2University of Craiova, Faculty of Chemistry,A.I. Cuza St, Craiova, Romania
3 Institute of Chemistry Timisoara of Romanian Academy, 24 Mihai Viteazul Blv., Timisoara, Romania
Discovery of mesoporous molecular sieves with silica has stimulated a renew interest in adsorbents and catalyst design because of their unique large surface area, well-defined pore size and pore shape. Functionalization of porous solids plays an important role in many technical aspects such as enzyme, metal and organometallic complex immobilization. We report the synthesis and properties of metal-organic hybrid catalysts obtained by non-ionic templating of silica,
functionalization of silica materials and chloromethylated styrene-divinylbenzene copolymers supports and immobilization of copper and manganese cations.
The preparing route was the electrically neutral assembly pathways based on the hydrogen-bonding interactions between the polyethylene oxide groups (N0) of surfactants and the hydroxylated tetraethylortosilicate (I0). Ordered mesoporous structures were synthesized by hydrothermal treatment. The mesoporous silica supports were functionalized freshly with 3- aminopropyl-triethoxysilane, 3-aminopropyltrimethoxysilane and salicylaldehyde and copolymer support with phosphonates and aminophosphonates groups. The synthesis of organic inorganic hybrids from polymer support was performed by two methods: one and two steps condensation. The metallic cations were immobilization from aqueous solution of precursors. The obtained materials were examined by means of several experimental methods such as: X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, FT-IR and UV-Vis spectroscopy.
The results show an ordered and large-pore mesoporous structure for silica and a same morphology for copolymer. SEM images present a spherical morphology and agglomeration of particles. A typical mesoporous structure for materials obtained with nonionic surfactant was confirmed by nitrogen sorption isotherms and pore distribution. The isotherm shows a sharp step with a hysteresis loop corresponding to the filling of the ordered mesopores at a relative pressure in the 0.5-0.6 range. Pore size of the materials depends on polycondensation of the silica, temperature and the surfactant conformation. The surface area and pore diameter are the results of interaction of ethoxy oxygens with the silanol groups. It was proved that the porous structures that retain a
significantly open framework after functionalization of their pore walls are likely more effective for adsorption of metal ions. The degrees of functionalization with phosphonates groups are relatively high, ranging from 1.19 – 2.78 mmoles of functional groups / g. of copolymer, ensuring a sufficient concentration of active centers per unit mass of the copolymer and being well suited for application as catalytic and chelatting agent. The obtained materials by functionalization of silica show a high loading capacity for adsorption of the metal ions.
The hybrids materials obtained by the functionalization of mesoporous silica and chloromethylated styrene-divinylbenzene copolymers will be used for immobilization of metal- organic complexes and enzymes and the obtained catalysts for biomimetic oxidation of organic compounds.
Molecular structures and catalytic properties of alumina supported niobia and niobia-vanadia catalysts
A.E. Lewandowskaa, O.B. Lapinab, M. Ziolekc, D.F. Khabilulinb, M.A. Bañaresa
aInstituto de Catalisis y Petroleoquimica, CSIC, E-28049-Madrid, Spain, [email protected]
b Boreskov Institute of Catalysis SB RAS, Prosp. Akad. Lavrentieva 5, 630090 Novosibirsk, Russia, c A. Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, PL-60-780 Poznan,
Poland
The molecular structures and reactive properties of alumina-supported V-Nb-O system are reported.
The molecular structure of surface niobium and vanadium oxide species were studied by Raman spectroscopy, 51V, 27Al, 93Nb and 1H MAS NMR. The reducibility was evaluated by TPR/TPO and in situ TPR/TPO-Raman. The surface sites were probed methanol test reaction. Vanadia on alumina remains dispersed by interaction with surface OH groups (1H NMR); however, Nb interacts more strongly with alumina: 93Nb- and 27Al-NMR evidence incipient formation of Nb-Al-O phase.
Furthermore, V species are affected by Nb while Nb is not affected by V sites; thus, vanadia species disperse on alumina and Nb-alumina systems. Such interplay between V, Nb and Al modulates reducibility and acid-base-redox properties, so that activity ranges between acidic to redox character and catalyst performance can be tuned based on composition and preparation methods. Combined multinuclear NMR, Raman spectroscopy and TPR data probe the tuning of (V-Nb-O)/Al2O3 system in several reactions, like ammonia remediation by selective catalytic oxidation.
Keywords: 93Nb, 51V, 27Al and 1H MAS NMR, in situ Raman, TPR/TPO cycle, methanol
probe reaction, ammonia SCO
O–14
Gold catalysts supported on CeO
2and CeO
2-Al
2O
3for NO reduction by CO
L. Ilieva*a, G. Pantaleo b, I. Ivanov a, A.M. Venezia b, D. Andreeva a
a Institute of Catalysis, BAS, “ Acad. G. Bonchev” Str. Bl. 11, 1113 Sofia, Bulgaria
b Istituto per lo Studio di Materiali Nanostrutturati, CNR, Via Ugo la Malfa, I-90146, Palermo, Italy
Up to now there are not a lot of studies on the widely applied method for NOx removal by catalytic reduction over gold catalysts, however the already published results have shown that supported gold catalysts are active in NOx reduction by H2, CO or hydrocarbons at low temperatures. The present study deals with NO reduction by CO on nanosructured gold supported on CeO2 and CeO2-Al2O3. A high and stable catalytic activity of this type of catalysts has been already shown by some of us in the reactions of WGS and complete benzene oxidation. In this study the co-precipitation method was chosen for the mixed support preparation. The effect of pre- treatment conditions and gas feed composition on the catalytic activity and selectivity of NO reduction by CO was investigated. The gold-based catalysts were characterised by several techniques - XRD, TPR, XPS and Raman spectroscopy aiming to look for a relationship between the structural features and catalytic behaviour and especially to clarify the role of alumina for the catalytic activity and stability. A series of three catalysts was studied: Au supported on ceria and on ceria-alumina, containing 10 or 20% alumina. The mixed supports were prepared by co- precipitation. The gold (3 wt%) was loaded by deposition precipitation method. The catalysts were tested in a wide temperature interval using IR and UV analysers as well as mass spectrometer for monitoring of the reactants and the products. The results have shown that the pre-treatment in hydrogen, oxygen or inert atmosphere did not have a substantial effect on the catalytic activity, which could be significantly improved by H2 addition to the gas feed. Several factors such as the gold and ceria particle size as well as the formation of oxygen vacancies have importance for the reactivity. The addition of alumina led to a slight enlargement of the gold particles, while the ceria particle size was decreased. The TPR and Raman spectroscopy results confirmed that higher amount of oxygen vacancies was generated adding increasing amount of alumina. The decrease of ionic gold component and the increase of the Ce (3+) species, as observed by XPS of gold catalyst on mixed support with 20 wt% alumina, was also indicative of the oxygen vacancy creation. In correspondence of this structural change, a higher catalytic activity was observed for gold catalyst on the mixed support with 20 wt % alumina as compared to the corresponding sample with 10 wt%
alumina. Moreover, the presence of alumina prevented catalysts agglomeration during the catalytic operation. The 100% selectivity towards N2, obtained at about 200 oC makes the studied gold catalysts promising for DeNOx process, concerning emissions immediately following the start-up of the vehicle’s engine (“cold start” phase).
Poster presentations
A new strategy toward self-doped polyaniline: copolymerization of luminol with aniline
V. Ferreiraa, A. C. Cascalheirab and L. M. Abrantesa,b
a CQB, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
b LBEQ, Instituto de Ciência Aplicada e Tecnologia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
Among other conducting polymers, polyaniline (PAni) has found numerous applications as a result of its straightforward polymerization, chemical stability and relatively high conductivity.
However, PAni is electroactive only in acidic conditions, normally pH < 4, which greatly confine its operation at near pH neutral or slightly acidic solutions, usually required for an adequate biomolecules (enzymes) operation [1].
In order to overcome this problem, self-doped polyaniline films have been used to extend the redox activity and conductivity of the polyaniline films over a wider pH range [2].
Recently, luminol has been regarded as an aniline monomer derivative, which means that electropolymerization can be used as useful method for polyluminol films deposition at solid electrode surfaces [3-5].
This work describes a new strategy to obtain self-doped polyaniline films through the electrochemical polymerisation of luminol in the presence of aniline. Cyclic voltammetry in combination with electrochemical quartz crystal microbalance (EQCM) have been used to study both the in situ growth and redox switching process. In monomer free solution, the deposited polymers are stable and electrochemically active but distinct behaviour is shown by poly(luminol- aniline) films obtained from solutions with different monomers concentration ratio. In acidic medium, the current-voltage profiles range from a polyluminol to a polyaniline like redox conversion as the aniline concentration increases. Unlike polyaniline, all prepared copolymers display well expressed electroactivity in sodium carbonate medium (pH=8), which also extends with the aniline content. The self-doping role assured by luminol moiety in the copolymer is also retrieved from the simultaneously recorded EQCM data.
[1] Oleg A. Raitman, Eugenni Katz, Andreas f. Bückmann, Itamar Willner, J. Am. Chem. Soc. 124 (2002) 6487.
[2] Albertas Malinauskas, J. Power Sources 126 (2004) 214.
[3] Shen-Ming Chen, Kuo-Chiang Lin; J. Electroanal. Chem. 523 (2002) 93.
[4] Guo-Fang Zhang, Homg-Yuan Chen, Anal. Chim. Acta 419 (2000) 25.
[5] V. Ferreira, A.C. Cascalheira, L.M. Abrantes, Thin Solid Films (2007) (Accepted).
.
a theoretical study
P. Gonzalez-Navarrete1, L. Gracia1, J. Andrés1 M. Calatayud2, C. Minot2
1 Dept. Q. Física i Analítica, Universitat Jaume I, P.O. Box 224, E-12080 Castelló, Spain
2Université Pierre et Marie Curie-Paris6, UMR CNRS 7616 LCT, Paris, F-75005, France
The oxidation of methanol to formaldehyde is studied at the B3LYP/6-311(2d,p) level on a pyramidal OV(OH)3 cluster model. Several reaction paths leading to CH2O, H2 and H2O are investigated. The first step is the dissociative adsorption of methanol. Next, a hydrogen transfer takes place to a hydroxyl group forming H2 or H2O. This step is accompanied by an electron transfer that, in the case of H2O formation, takes place to the vanadium atom reducing it. The barriers calculated for the rate-limiting steps are very similar for those two paths and around 50 kcal/mol, irrespective of the sites involved. Finally, the addition of potassium atom is studied. The main effect is observed in the stability of the methoxy intermediate, which is less stable than in the corresponding undoped system. As a result, the doped system is less active but more selective since the residence time of the methoxy intermediate is reduced.
Keywords: methanol, alkali, DFT, vanadia, methanol
Effect of TiO
2loading in the activity and SO
2tolerance of Pd supported on silica
G. Di Carloa, L. F. Liottab , G. Pantaleob, A. .M. Veneziab,a Dipartimento di Chimica Inorganica ed Analitica “Stanislao Cannizzaro”, Università di Palermo, Viale delle Scienze, Palermo I-90128; bIstituto dei Materiali Nanostrutturati (ISMN-CNR via Ugo
La Malfa, 153, Palermo, I- 90146
G. Melaetc, N. Krusec
Université Libre de Bruxelles (ULB) Chemical Physics of Materials, Campus de la Plaine, C.P.
243, Bld du Triomphe, B-1050 Bruxelles Belgique
Supported PdO catalysts for the methane combustion at low temperaturestend to sinter and to be poisoned by sulfur containing molecules1. The suitability of sulfating or not sulfating supports is still a debatable matter. As we had recently shown, a chemically inert support like silica with appropriate morphology may give rise to active PdO catalysts which have good tolerance versus SO2 poisoning, and most importantly they can be easily regenerated2. In the present work the combined effect of a large surface area silica and of the chemically active TiO2, on the methane oxidation activity of PdO catalysts, was investigated. To this aim, a series of catalysts with 1 wt%
Pd impregnated on sol-gel mixed supports with different TiO2/SiO2 ratio were prepared. The catalysts were characterized by XPS, XRD and BET measurements. For the activity test a mixture of 0.3 vol.% of CH4 + 2.4 vol.% O2 in He was led over the catalyst (50 mg) with a weight hourly space velocity (WHSV) of 60 000 ml g−1 h−1. The effect of SO2 addition to the reactant mixture was studied. In Fig.1 the methane conversion curves at different conditions, obtained with the palladium catalyst supported on the mixed oxide with 10 wt% of TiO2 are plotted. The catalyst performed quite well in terms of the light off temperature (T50= 312 °C), SO2 tolerance and thermal stability.
Based on the characterization results, the superiority of these mixed oxide supported catalysts with respect to the analogous ones on pure silica and pure titania are attributed to the SO2 scavenger effect by TiO2 and to the increased dispersion over the large surface area supports.
200 300 400 500 600
0 20 40 60 80 100
fresh
I cycle with 10 ppm SO2 II cycle
III cycle after SO2 pretreatment IV cycle
V cycle VI cycle CH4 conversion (%)
T (°C)
Fig.1 Methane conversion over Pd/TiO2(10%)-SiO2
1) P. Gelin, M. Primet, Appl. Catal. B, 39, 1 (2002).
2) A. M. Venezia, R. Murania, G. Pantaleo, G. Deganello, submitted.
