ANNEX V. STSM reports (14)

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ANNEX V. STSM reports (14)

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Realized Short Term Scientific Missions (STSM), COST Action D36; Jan 2009-Dec 2009

Period STSM Beneficiary Home Institution Host Budget

(Euro) 1 WG 6 20/02/2009 to 08/03/2009 COST-STSM-D36-4271 Anna E Lewandowska Post doc M. Banares, ICP, CESIC, Madrid, SP M. Calatayud, UPMC, Paris, FR 1830

2WG 1 17/02/2009 to 17/03/2009 COST-STSM-D36-3961 Giorgio Volpi Post Doc C. Nervi Univ. Torino, IT L. Pospisil, Heyrovsky Inst. Prague, CZ 2300

3 WG 5 01/03/2009 to 30/04/2009 COST-STSM-D36-3903 Markus Vogelsang PhD student E.Santos, Ulm Univ.DE R. Dryfe, Univ. Mamchester, UK 2500

4 WG 3 15/04/2009 to 15/05/2009 COST-STSM-D36-4037 Ivan Bogev Ivanov Post Doc D. Andreeva,Inst. of Catal., BAS, Sofia,BG A.M.Venezia, Inst. of Nanostructured Mat. Palermo, IT 2300

5 WG 3 09/03/2009 to 21/03/2009 COST-STSM-D36-4089 Gèrôme Malet PhD student N.Kruse ULB, Brussels, BE A.M.Venezia, Inst. of Nanostructured Mat. Palermo, IT 1250

6 WG 6 14/04/2009 to 31/05/2009 COST-STSM-D36-4307 Ricardo Medina PhD student M. Banares, ICP, CESIC, Madrid, SP M. Ziolek, Univ. Poznan, PL 1500

7 WG 6 15/05/2009 to 15/07/2009 COST-STSM-D36-4354 Elisabeth Rojas Garcia PhD student M. Banares, ICP, CESIC, Madrid, SP M. Calatayud, UPMC, Paris, FR 2500

8 WG 6 08/06/2009 to 10/07/2009 COST-STSM-D36-4576 Daniela Plana PhD student R. Dryfe, Univ. Mamchester, UK M. Koper, Leiden University,Leiden,NL 2450

9 WG 6 20/07/2009 to 16/08/2009 COST-STSM-D36-4802 Mazharul M.Islam Post Doc M. Calatayud, UPMC, Paris, FR Paccino, Univ. Milano, IT ACTION D43 2400

10 WG 6 14/09/2009 to 23/09/2009 COST-STSM-D36-4798 Elisabeth Santos Post Doc Universität Ulm,Ulm, DE F.Tielens,UPMC, Paris, FR 1100 11 WG 6 14/09/2009 to 13/11/2009 COST-STSM-D36-4845 Ana Rita Almeida PhD student TUDelft,Delft Frederik Tielens,Université Pierre et Marie Curie Paris(FR), 2500 12 WG 6 15/10/2009 to 15/12/2009 COST-STSM-D36-5153 Noelia Beatriz Luque Post Doc Universität Ulm,Ulm(DE) Monica Calatayud,Université Pierre et Marie Curie,Paris(FR), 2500 13 WG 3 12/09/2009 to 16/12/2009 COST-STSM-D36-4772 Gabriella Di Carlo Post Doc CNR,Palermo(IT) Magali Boutonnet,KTH Stockholm (SE) 3500 14 WG 8 09/12/ 2009 to 23/12/ 2009 COST-STSM-D36-5478 Jordi Morros PhD student CSIC,Barcelona Maria Miguel,Faculdade de ciencias e tecnologia,Coimbra(PT), 1200

Total : 14 STSM at total cost: 29830

Magali Boutonnet STSM coordinator 2010-01-25

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COST STSM D36-04450

Electrocatalytic activity of particles deposited at liquid/liquid interface

Scientific Report

Markus Vogelsang, University of Ulm

STSM within the COST workgroup D36/005/06: Structure-Reactivity Relationships of Pt and Pd Nanoarrays

Host: Prof. Robert Dryfe, The University of Manchester 01.03.2009 – 30.04.2009

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COST STSM D36-04450 Manchester, UK, March/April 2009

1. Introduction

Electrodeposition of metal particles e.g. Pt, Pd, Au, Ag and Cu or bimetallic particles e.g. Pd-Pt, Au-Pd, Au-Pt at the polarised interface between two immiscible electrolyte solutions (ITIES¹) has become an important research field during the last years. The ITIES formed between an aqueous solution containing mainly hydrophilic ions and an organic solution containing mainly lipophilic ions represents an ideal background for the metal nucleation because of the absence of a solid support². Also the metal deposition at ITIES is a novel method to prepare catalysts³ or photocatalysts⁴ in comparison to traditional chemical or electrochemical techniques.

The deposition of metal and bimetallic particles at ITIES was studied in detail by Dryfe et al.^{3, 5, 6} (Pd, Pt, Pd-Pt), Kontturi et al.^{2, 7, 8} (Pd) and Unwin et al.⁹ (Ag).

Catalysis by electrochemically prepared nanoparticles at the ITIES has been investigated by Samec et al.¹⁰ and Kontturi et al.¹¹ The deposited nanoparticles were used to catalyse various reactions e.g. the dehalogenation of bromoacetophenone to acetophenone at the water/1,2-dichloroethane (DCE) interface by Pd¹¹, the reduction of oxygen in aqueous solution by decamethylferrocene in DCE by Pt¹⁰ or the photoreduction of tetracyanoquinodimethane by Pd⁴.

In this work the deposition of Pd nanoparticles at the water/DCE interface and the usage of the synthesised nanoparticles as a catalyst for proton reduction have been investigated.

2. Experimental section and results

All deposition experiments were realised in a four electrode electrochemical cell, shown schematically in figure 1. The glass cell contained about 2 mL of each phase and the diameter of the liquid/liquid interface was about 10 mm.

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Figure 1: Scheme of the electrochemical cell

In both phases platinum mesh electrodes were used as the counter electrodes. The reference electrodes were silver/silver chloride electrodes freshly prepared by oxidation of a silver wire in a potassium chloride solution. All potentials are indicated in relation to these reference electrodes and all experiments were run with an Autolab PGStat100 potentiostat (Eco Chemie B.V., Utrecht, The Nederlands).

The first deposition experiments of Pd nanoparticles at the water/DCE interface were realised with the following electrochemical cell (1):

The aqueous phase comprised of ammonium tetrachloropalladate(II) (1mM) and lithium chloride (100 mM) as aqueous electrolyte (both Sigma-Aldrich, Dorset, United Kindom). The organic phase consisted of the electron donor decamethylferrocene (DMFc, 10 mM, Sigma-Aldrich, Dorset, United Kingdom) and Bis(triphenyl- phosphoranylidene)ammonium tetrakis(pentafluorophenyl)borate (BTPPA TPFB, 20 mM) as the organic electrolyte. The BTPPA TPFB was synthesised by metathesis of equimolar amounts of BTPPACl (Sigma-Aldrich, Dorset, United Kingdom) and

Ag (s) AgCl (s) 10 mM LiCl

1 mM BTPPACl (aq)

AgCl (s) Ag (s)

100 mM LiCl 1 mM (NH4)2PdCl4 (aq)

10 mM DMFc 20 mM BTPPA TPFB

(DCE)

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LiTPFB ^. n Et2O (Boulder Scientific Company, Mead, USA)¹². Pure water (resistance

> 18 MΩ^.cm) was generated with a Millipore Milli-Q water purification system and 1,2-dichloroethane (DCE, HPLC grade) was obtained from Lancaster Synthesis (Heysham, United Kindom).

The black cyclic voltammogram (CV) in figure 2 shows the electrochemical cell (1) in the absence of the palladium salt. The straight baseline in the potential window indicates that there is no ion transfer through the interface at an applied potential between 0 and +0.6 V. At lower and higher potentials the electrolytes begin to pass through the water/DCE interface. The red CV done in the electrochemical cell with the ammonium tetrachloropalladate(II) shows the current produced from the reduction of the Pd salt by the DMFc.

Figure 2: Cyclic voltammograms without (black) and with (red) ammonium tetrachloropalladate(II), scan rate 100 mV/s

For the deposition of the Pd nanoparticles a constant potential of 0.55 V was applied for 2 min. Then the aqueous solution was acidified with HCl to see if the deposited Pd nanoparticles at the water/DCE interface would be able to catalyse the reduction of protons to hydrogen. The obtained CV (blue line), which shows an irregular but reproducible response, is shown in figure 3.

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Figure 3: CV after deposition of Pd and acidification of the aqueous phase (blue), scan rate: 100 mV/s

Because, without acidification, the same response appeared due to a gradual alteration of the deposited Pd nanoparticles (> 2 hours) the response does not depend on the acidification, but on the slow, spontaneous aggregation of the nanoparticles which occurs more quickly in an acidic aqueous phase.

The obtained nanoparticles were characterised by high resolution TEM with the help of the School of Chemical Engineering and Analytical Science at The University of Manchester. The particles were directly collected from the interface with a carbon coated Cu grid. The images (figure 4) show a particle size of about 5 nm which is corresponding with previous reported particle sizes for Pd nanoparticles in the literature⁵.

Figure 4: TEM images of the deposited Pd nanoparticles

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To reduce the effects of aggregation of the nanoparticles we wanted to stabilise the Pd particles. In the literature there are many reported methods to stabilise nanoparticles in solution, but we are not aware of any corresponding methods for particles at liquid/liquid interfaces. The most common solution phase stabilising agents are polymers^{13, 14} (e.g. PVP = polyvinylpolypyrrolidone), ligands^15-17 (e.g.

citrate), surfactants¹⁸ (e.g. SDS = sodium dodecyl sulfate) or tetraalkylammonium salts^19-23.

The first attempt to stabilise the electrodeposited Pd particles at the water/DCE interface was realised by adding sodium citrate to the aqueous phase.

The related CVs are shown in figure 5. The black CV originates from the cell in the absence and the red one from the cell in the presence of the Pd salt. The green CV shows the response after the deposition of the Pd particles by applying a constant potential of 0.55 V for 2 min. The response is similar to the one without citrate in the aqueous solution. However no aggregation was visible to the eye at the interface, nor did the CV response become unstable by allowing the cell to stand for more than 2 hours. But after adding HCl to acidify the aqueous solution, there was a visible aggregation of the Pd particles at the interface most likely caused by protonation (and consequent removal) of the stabilising citrate ligands. The blue CV shows the response after the aggregation.

Ag (s) AgCl (s) 10 mM LiCl

1 mM BTPPACl (aq)

AgCl (s) Ag (s)

100 mM LiCl 1 mM (NH4)2PdCl4

2 mM Na3C6H5O7. 2 H2O

(aq)

10 mM DMFc 20 mM BTPPA TPFB

(DCE)

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Figure 5: Deposition of Pd nanoparticles in the presence of citrate, scan rate: 100 mV/s

The TEM images (figure 6) show also a particle size of about 5 nm for the citrate stabilised Pd nanoparticles.

Figure 6: TEM images of the citrate stabilised Pd nanoparticles

Due to the fact that the Pd nanoparticles deposited in the presence of citrate still aggregate when acidifying the aqueous solution, stabilisation of the Pd with tetraoctylammonium ions was attempted. Therefore the organic electrolyte was changed to tetraoctylammonium tetrakis(penta-fluorophenyl)borate (TOA TPFB).

This electrolyte was synthesised by metathesis of TOACl (Sigma-Aldrich, Dorset, United Kingdom) and LiTPFB ^. n Et2O (Boulder Scientific Company, Mead, USA) according to a reported method²⁴. Because the previously used tetrachloropalladate(II) ion formed an insoluble salt with the tetraoctylammonium ion the Pd salt had also to be changed to tetraamminepalladium(II) chloride.

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Figure 7 shows the related CVs. The black CV was measured in the cell without the Pd salt and the red CV with the Pd salt. The green CV shows the response after the deposition of the Pd particles by applying a constant potential of 0.55 V for 2 min. In contrast to the previous measurements, there was no visible aggregation at the water/DCE interface seen either by allowing the cell to stand for a longer time nor by adding HCl to acidify the aqueous solution.

Figure 7: Deposition of Pd nanoparticles in the presence of tetraoctylammonium ions, scan rate:

100 mV/s

This indicates that the tetraoctylammonium ions stabilise the deposited Pd nanoparticles at the water/DCE interface.

Again the TEM images (figure 8) show a particle size of the deposited tetraoctylammonium stabilised Pd nanoparticles of about 5 nm. Also it can be seen that aggregation of the Pd nanoparticles still occurs, but that the aggregates visible in the TEM images have a diameter of at most 100 nm. In contrast the aggregates resulted without the tetraoctylammonium stabilisation (figure 4) are much larger.

AgCl (s) 100 mM LiCl

1 mM Pd(NH3)4Cl2. H2O

(aq)

10 mM DMFc 20 mM TOA TPBF20

(DCE)

10 mM LiCl 1 mM TOACl

(aq)

AgCl (s) Ag (s)

Ag (s)

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Figure 8: TEM images of the tetraoctylammonium stabilised Pd nanoparticles

For additional characterisation of the deposited Pd nanoparticles XRD mesurements (with help of the X-Ray Crystallography Facility, School of Chemistry) and XPS measurements (with help of the School of Chemical Engineering and Analytical Science) were carried out.

However the present XRD measurements showed no observable diffraction peak in the expected region of the diffraction angle (2θ) of about 40 degrees. To estimate the particle size by XRD a longer measurement should be done with the deposited Pd nanoparticles to see if there is a broad peak in this region related to small particles with a diameter in the lower nm range.

The XPS measurements were done by the School of Chemical Engineering and Analytical Science at The University of Manchester with prepared Pd nanoparticles after finishing the STSM. The results of these measurements should be transferred within the next weeks.

After the deposition of stabilised Pd nanoparticles at the water/DCE interface we wanted to investigate if these particles are able to catalyse the reduction of protons to hydrogen in the acidified aqueous solution. Small visible gas bubbles at the platinum counter electrode in the aqueous phase after a large amount of recorded CVs indicated that hydrogen evolution occurred. Therefore a conventional three-electrode configuration was incorporated into the aqueous phase of the electrochemical cell, to

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oxidise the emerging hydrogen back to protons. However, applying this method the problem occurred that a large current was obtained in the CVs of the three-electrode setup only with an acidic aqueous solution of the used Pd salt in the potential region where the hydrogen reduction was expected. Thus until the end of the STSM we were unable to verify that the stabilised Pd particles at the water/DCE interface can catalyse proton reduction.

3. Conclusion and Outlook

Stabilised Pd nanoparticles have been synthesised at the water/DCE interface by electrochemical reduction of tetraamminepalladium(II) chloride in the presence of tetraoctylammonium chloride. The obtained nanoparticles were characterised by TEM, XRD and XPS resulting in a particle size of about 5 nm.

Investigation of the catalytic activity of the deposited nanoparticles for proton reduction in the aqueous phase could not be completed until the end of the STSM period. Further experiments to this topic are scheduled both in the group at the University of Ulm and at The University of Manchester.

The group in Ulm will also try to investigate the electrochemical deposition of nanoparticles at liquid/liquid interfaces with spectroscopic methods e.g. evanescent wave cavity ring-down spectroscopy. This would be a new method to measure simultaneously electrochemical and spectroscopic information at liquid/liquid interfaces.

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4. Literature

(1) Vanysek, P.; Ramirez, L. B.: Interface between two immiscible liquid electrolytes: a review. J. Chil. Chem. Soc. 2008, 53, 1455-1463.

(2) Johans, C.; Lahtinen, R.; Kontturi, K.; Schiffrin, D. J.: Nucleation at liquid-liquid interfaces: electrodeposition without electrodes. J. Electroanal. Chem. 2000, 488, 99- 109.

(3) Platt, M.; Dryfe, R. A. W.; Roberts, E. P. L.: Controlled deposition of nanoparticles at the liquid-liquid interface. Chem. Commun. (Cambridge, U. K.) 2002, 2324-2325.

(4) Lahtinen, R. M.; Fermin, D. J.; Jensen, H.; Kontturi, K.; Girault, H. H.: Two-phase photocatalysis mediated by electrochemically generated Pd nanoparticles.

Electrochem. Commun. 2000, 2, 230-234.

(5) Platt, M.; Dryfe, R. A. W.: Structural and electrochemical characterisation of Pt and Pd nanoparticles electrodeposited at the liquid/liquid interface: Part 2. Phys. Chem.

Chem. Phys. 2005, 7, 1807-1814.

(6) Platt, M.; Dryfe, R. A. W.; Roberts, E. P. L.: Structural and electrochemical characterisation of Pt and Pd nanoparticles electrodeposited at the liquid/liquid interface. Electrochim. Acta 2004, 49, 3937-3945.

(7) Johans, C.; Kontturi, K.; Schiffrin, D. J.: Nucleation at liquid-liquid interfaces:

galvanostatic study. J. Electroanal. Chem. 2002, 526, 29-35.

(8) Johans, C.; Liljeroth, P.; Kontturi, K.: Electrodeposition at polarisable liquid-liquid interfaces: The role of interfacial tension on nucleation kinetics. Phys. Chem. Chem.

Phys. 2002, 4, 1067-1071.

(9) Guo, J.; Tokimoto, T.; Othman, R.; Unwin, P. R.: Formation of mesoscopic silver particles at micro- and nano-liquid/liquid interfaces. Electrochem. Commun. 2003, 5, 1005-1010.

(10) Trojanek, A.; Langmaier, J.; Samec, Z.: Electrocatalysis of the oxygen reduction at a polarized interface between two immiscible electrolyte solutions by electrochemically generated Pt particles. Electrochem. Commun. 2006, 8, 475-481.

(11) Lahtinen, R.; Johans, C.; Hakkarainen, S.; Coleman, D.; Kontturi, K.: Two-phase electrocatalysis by aqueous colloids. Electrochem. Commun. 2002, 4, 479-482.

(12) Fermin, D. J.; Dung Duong, H.; Ding, Z.; Brevet, P. F.; Girault, H. H.: Photoinduced electron transfer at liquid/liquid interfaces Part II. A study of the electron transfer and recombination dynamics by intensity modulated photocurrent spectroscopy (IMPS).

Phys. Chem. Chem. Phys. 1999, 1, 1461-1467.

(13) Toshima, N.; Wang, Y.: Polymer-protected Cu/Pd bimetallic clusters. Adv. Mater.

1994, 6, 245-247.

(14) Henglein, A.: Physicochemical properties of small metal particles in solution:

"microelectrode" reactions, chemisorption, composite metal particles, and the atom- to-metal transition. J. Phys. Chem. 1993, 97, 5457-5471.

(15) Schmid, G.: Large clusters and colloids. Metals in the embryonic state. Chem. Rev.

1992, 92, 1709-1727.

(16) Poulin, J. C.; Kagan, H. B.; Vargaftik, M. N.; Stolarov, I. P.; Moiseev, I. I.: Scanning tunneling microscopy observation of giant palladium-561 clusters. J. Mol. Catal. A:

Chem. 1995, 95, 109-113.

(17) Amiens, C.; de Caro, D.; Chaudret, B.; Bradley, J. S.; Mazel, R.; Roucau, C.:

Selective synthesis, characterization, and spectroscopic studies on a novel class of reduced platinum and palladium particles stabilized by carbonyl and phosphine ligands. J. Am. Chem. Soc. 1993, 115, 11638-11639.

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(18) Toshima, N.; Takahashi, T.: Colloidal dispersions of platinum and palladium clusters embedded in the micelles. Preparation and application to the catalysis for

hydrogenation of olefins. Bull. Chem. Soc. Jpn. 1992, 65, 400-409.

(19) Boennemann, H.; Brijoux, W.; Brinkmann, R.; Dinjus, E.; Joussen, T.; Korall, B.:

Production of colloidal transition metals in organic phase and their use as catalysts.

Angew. Chem., Int. Ed. Engl. 1991, 30, 1312-1314.

(20) Boennemann, H.; Brijoux, W.; Brinkmann, R.; Fretzen, R.; Joussen, T.; Koeppler, R.;

Korall, B.; Neiteler, P.; Richter, J.: Preparation, characterization, and application of fine metal particles and metal colloids using hydrotriorganoborates. J. Mol. Catal.

1994, 86, 129-177.

(21) Reetz, M. T.; Helbig, W.: Size-Selective Synthesis of Nanostructured Transition Metal Clusters. J. Am. Chem. Soc. 1994, 116, 7401-7402.

(22) Reetz, M. T.; Helbig, W.; Quaiser, S. A.; Stimming, U.; Breuer, N.; Vogel, R.:

Visualization of surfactants on nanostructured palladium clusters by a combination of STM and high-resolution TEM. Science 1995, 267, 367-369.

(23) Reetz, M. T.; Quaiser, S. A.: A new method for the preparation of nanostructured metal clusters. Angew. Chem., Int. Ed. Engl. 1995, 34, 2240-2241.

(24) LeSuer, R. J.; Buttolph, C.; Geiger, W. E.: Comparison of the Conductivity Properties of the Tetrabutylammonium Salt of Tetrakis(pentafluorophenyl)borate Anion with Those of Traditional Supporting Electrolyte Anions in Nonaqueous Solvents. Anal.

Chem. 2004, 76, 6395-6401.

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COST PROJECT PRAGUE 17/02-17/03-2009

Giorgio Volpi 20/03/2009

COST REPORT

 Purpose of the visit:

During the period of the COST STSM project, we intended to study the electrochemical properties of seven Rhenium complexes, synthesized in the Turin group, containing 1- pyridylimidazo[1,5-a]pyridine ligands and 2-dipyridil ketone. The electrochemical behaviour of these transition metal complexes is crucial for their possible application in luminescent and electrochemiluminescent devices. Here are reported the structures of the seven complexes studied:

N Re

OC OC

Cl

CO N

R

N

ReGVn°

R= phenyl=GV6 R= methyl=GV16 R= 4-nitro phenyl=GV8

R= 4-dimethylamino phenyl=GV26 R=4-trif luoromethyl phenyl=GV34 R=4-tertbuthyl phenyl=GV38

N Re

OC OC

Cl CO

N

ReDPK

O DPK=Di-2-pyridyl ketone

Further task was to functionalize glassy carbon electrodes with different molecule, following the different method reported in literature^1,2,3. For this purpose we wanted to employ four different aromatic ammines: 4-nitroaniline, 1,10-phenanthrolin-5-amine (NH2- pnt), 9-diazo4,5-diazafluorene (DPPZ) and 4-((4-((dipyridin-2-ylmethoxy)methyl) phenyl)- ethynyl)aniline (GV148).

The first molecule is for comparison with the literature results^1,2,3 while the other molecules available are possible ligands for transition metals (the corresponding complexes are

1 Allan Hjarbæk Holma, Karina Højrup Vase, Bjørn Winther-Jensen, Electrochimica Acta 53, 2007, 1680–1688.

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already known in the literature). The aim is to bond these four ligands on the electrode surface before complexation. GV148 is a new ligand synthesized from 2-dipyridyl ketone (that we have also used previously as ligand) in Turin group; the presence of the amino aromatic group gives the possibility to functionalize this ligand on the GC electrode.

N O

N H

NH₂

4-((4-((dipyridin-2-ylmethoxy)methyl)phenyl)ethynyl)aniline GV148=

 Description of the work carried out during the visit:

During the first fortnight we studied all the Rhenium compounds; the electrochemical behaviour of these complexes was checked with cyclic voltammetry, polarography and in same cases with IR spectroelectrochemistry (ReGV6, ReGV8, ReDPK).

In all cases, cyclic voltammetry measurement was repeated at different scan rate to check the reversibility of the electrochemical process and possible coupling to a chemical reaction. Redox potentials of each compound was referred to the ferrocene/ferrocenium redox couple and in some cases the measurement was repeated in different solvent (CH3CN, CH2Cl2 and EtOH).

During the second fortnight we tried to functionalise glassy carbon electrodes with different amminoaromatics compounds. We tested different ways because in the literature there is not a uniform procedure for this kind of functionalization.

We tried different solvents for every molecule (CH3CN, absolute ethanol, ethanol 96%, CH3CN 80% in water and CH2Cl2) and increasing concentrations of the substrate (from 0.5 to 10 mM).

Functionalization have been carried out during simple scan rate or during time delay at fixed potential (from 10 second to 45 minute); to avoid interferences due to adsorption effects, before and after every measurement the electrode was washed with solvent (CH3CN, ethanol, CH2Cl2 or water) and sonicated (for 1 to 15 minute). We checked also the presence of adsorption effect by means of measurement at different scan rates and plotting the current vs. scan rate (or square root) to distinguish adsorption or diffusion controlled process.

 Description of the main results obtained:

The results relative to the Rhenium complexes are summarized in the following table. We used CH3CN as solvent for every complexes with tetrabutylammonium hexafluorophosphate 0.1 M as electrolyte. The concentration of the complexes was about 1.0 mM as well as the concentration of the ferrocene used as reference. All data in the table are from measurements at a scan rate 200 mV/sec.

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Compound V (vs

FC) type Compound V (vs FC) type Compound V (vs FC) type

ReGV6 ReGV38 ReGV26

cathodic -2.175 irr cathodic -2.244 irr cathodic -2.216 irr

-2.43 irr -2.565 irr -2.927 irr

-2.872 irr -3.008 irr anodic 0.542 rev

anodic 0.916 irr anodic 0.877 irr 0.819 rev

1.114 irr 1.07 irr 1.307 irr

1.47 irr 1.408 irr polarography -2.165

polarography -2.136 polarography -2.13 -2.541

-2.835 -2.496 -2.869

-3.151 -2.833

ReGV8 ReDPK ReGV34

cathodic -1.353 rev cathodic -1.289 rev cathodic -2.147 irr

-2.043 irr -1.903 rev -2.734 irr

-2.269 irr -2.588 irr -2.926 irr

-2.966 irr anodic 1.087 rev anodic 0.943 irr

anodic 0.959 irr 1.793 irr 1.167 irr

1.183 irr polarography -1.284 1.591 irr

1.565 irr -1.912 polarography -2.092

polarography -1.365 -2.616 -2.612

-1.988 -2.242 -2.885

ReGV16 4-nitroaniline V (vs

CoFC) DPPZ V (vs

CoFC)

cathodic -2.185 irr cathodic -0.632 rev cathodic -1.148 irr

-2.893 irr anodic 2.258 irr -2.359 irr

anodic 0.926 irr 2.397 irr anodic 1.557 irr

1.074 irr

1.464 irr (NH2-pnt) V (vs CoFC)

polarography -2.147 cathodic -1.268 irr

-2.513 -1.58 irr

-2.82 anodic 1.878 irr

2.187 irr

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Following picture shows an example of CV of the ReGV26 complex (1.06 mM, CH3CN, Fc 0.84mM):

Three IR stretching frequencies of the carbonyl groups of the complexes ReDPK, ReGV8 and ReGV6 were monitored during electrochemical reduction by means of IR spectroelectrochemistry. The compounds exhibit three separated absorptions (one sharp absorption at high energy and two broader absorptions at lower energies) as expected for non-symmetrically substituted fac-Re(CO)3 moieties. For example, the CV of ReDPK is reported in the voltammogram below. The IR spectroelectrochemistry performed at a potential of about 0.05 V more negative than the first mono electronic cathodic peak (E°=1.289 V vs. Fc/Fc⁺) confirms a simple charge-transfer character of the process. The presence of an isosbestic point outlines the reversibility and the total conversion into the corresponding anion [ReDPK]^–.

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Similar results were obtained for the other compounds.

With the aim to functionalize the GC electrode, we tested the electrochemical behaviour of the ligands 4-NO2-aniline and 1,10-phenanthroline-5-amine. An example of CV measurement (1° and 2° scan) after functionalization (at 1.7V for 20sec) of 4-NO2-aniline (1.5 mM, in CH3CN, electrolyte tetrabutylammonium hexafluorophosphate 0.1 M, scan rate 200mV/sec) is shown in the figure.

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The amino compounds were always functionalized in the anodic region. After functionalization, it is possible to check the different signals derived from the molecules bonded on the electrode surface, in a clean solution. In difference from 4-aminobenzoic acid reported earlier² the layer formed on the electrode was not stable after polarization to negative potentials and also not after sonication. Therefore we cannot yet unambiguously confirm, if a covalent bond to the electrode was formed or the observed effects was due to an adsorption only.

As third molecule, we tried the 9-diazo-4,5-diazafluorene (DPPZ). This molecule could be able to bond GC electrode as mostly employed diazonium salts do, releasing N2 during reductive functionalization.

The DPPZ compound gave promising results. The current profile during functionalization decreases in a similar way as reported in the literature^1,2,3. A strong surface interaction is observed since the CV peak current decreased during functionalization does not increase after sonication. After functionalization it’is possible to see irreversible waves, in the cathodic region, stable and reproducible also after cleaning with solvents or sonification.

This layer, formed on the electrode, changes the reference ferrocene wave profile already after the first functionalization cycle.

We discover, with surprise, that for this molecule the functionalization happens only in anodic region, this suggests possible different mechanism from the diazonium salts reported in the literature.

The next figure shows the CV of functionalization cycles of DPPZ (1.07mM, EtOH 96%, LiClO4 1M) performed with a delay of 10 second at 1.7V, in presence of ferrocene. It’s possible to see a significant decrease of the current (attributable to increasing of the covered surface) and a modification of ferrocene signal.

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We noted that the functionalized layer was destroyed during scan in the cathodic region where in a clean solvent appeared a new peak (about -1.2V) attributable at the new layer on the surface.

The modification of GC electrode was carried out also with a new ligand GV148 (see above), synthesized in Turin group, which involves amino aromatics group. This ligand bonds the GC surface in the anodic region (about 1.3V) with strong interaction that cannot be eliminated by sonication (15 minute in the same solvent used during the functionalization process). The layer on the electrode in clean solution shows an irreversible peak in the cathodic region. The next two figures illustrate the observed effects. When CV scanning in the solution of the ligand and ferrocene is performed up to cathodic region (first figure) the influence on the ferrocene wave is smaler, because the layer is partially destroyed at negative potentials. However, continued scanning only in anodic region (second figure) completely inhibits the ferrocene redox process.

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 Future collaboration with host institution:

We hope to investigate the possibility to use the bonded ligands on the GC surface for complexation of Re and Ir precursors. Furthermore we’d like to investigate the presence of this complexes on the electrode surface by mean of electrochemistry measurement.

Moreover in Turin group we have already synthesized six new Iridium complexes and three new Rhenium complexes that show interesting properties for luminescent and electrochemiluminescent devices. The study of the electrochemical properties of these compounds is essential for their possible application in the luminescent field.

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 Projected publications/articles resulting or to result from the STSM (if applicable):

A joint manuscript based on the electrochemical and spectroelectrochemical data obtained in Prague is in preparation.

 Confirmation by the host institute of the successful execution of the mission:

This is to confirm that Mr. Giorgio VOLPI of University of Turin completed the STSM at the J. Heyrovsky Institute of Physical Chemistry, Acad. Sci. of the Czech Republic His mission was part of the COST project D36/001. The work program included an electrochemical characterization of new transition metal complexes designed as possible compounds for electroluminescent devices. After a thorough electrochemical study he attempted several procedures for modification of the graphite surface in such a way that luminescent

compounds could be attached to the surface. Spectroelectrochemical in-situ techniques were used for evaluation of redox processes. Series of investigated compounds is a good starting point for finding correlation between the activity and the structure of new

complexes. Participating institutes plan further work in the future. It is realistic that soon a joint communication will be completed.

Dr. Lubomir Pospisil,

Coordinator for the host institute

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Scientific report

of Dr. Ivan Ivanov

Institute of Catalysis, BAS, Sofia

REFERENCE: Short Term Scientific Mission, COST D36 Host: Prof. Anna Maria Venezia, Institute of Nanostructured Materials, CNR, Palerm, Italy

Project 06/0003/06 “Interfacial functionalization of (bi)- metallic nanoparticles to prepare highly active and

selective catalysts: understanding synergy and/or promotion effect”

Period: from 15/04/2009 to 15/05/2009 Place: 90146 Palermo (IT)

Reference code: COST-STSM-D36-04455

I received a STSM grant from COST and I did experiments at the host Institute of Nanostructured Materials, CNR, Palermo, Italy. I was accepted at the laboratory of Prof. Anna Maria Venezia, coordinator of our common project 06/0003/06 “Interfacial functionalization of (bi)-metallic nanoparticles to prepare highly active and selective catalysts: understanding synergy and/or promotion effect”. We did all the experimental works with Chem.

Eng. Giuseppe Pantaleo from the same laboratory using the apparatus for catalytic activity tests - the catalytic test was PROX process on gold based catalysts. The PROX process is very important in connection with hydrogen purification of CO traces for application in PEM fuel cells. Two series of gold catalysts based on ceria, doped by the different reducible metal oxides (CoO

x

, SnO

x

, Fe

2

O

3

, MnO

x

), have been prepared in the Institute of Catalysis, BAS, Sofia. The 1

^st

route of the mixed oxide supports synthesis included co-precipitation technique (CP) and the 2

^nd

one – mechano chemical activation (MA).

During my stay at the Institute of Nanostructured Materials I studied

the apparatus for PROX catalytic tests: the scheme for connecting the

modules for measuring concentrations of N

₂

O, NO, CO, H

₂

O and

CO

2

, and of O

2

and CH

4

as well.

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The research work has included the following steps:

First, it was studied the influence of the pretreatment of the catalysts before catalytic test on the catalytic activity and selectivity of the samples. The pretreatment was carried out in the presence of oxygen at 150

^о

С for 30 min, or in the presence of hydrogen at 150

^о

С for 30 min. After each pretreatment, the PROX reaction in the temperature range from 20

^о

С to 300

^о

С was carried out. The obtained results have showed that the pretreatment with oxygen at 150

^о

С, has a little influence on the catalytic activity in PROX process in comparison to the pretreatment with hydrogen at 150

^o

C. On the basis of these experiments and the preliminary obtained TPR data the optimal conditions for the pretreatment with oxygen was chosen.

All the catalysts have been tested applying the above described conditions of pretreatment in the PROX reaction. On the basis of registered CO, CO

2

and oxygen, the selectivity of each catalyst has been calculated.

In Fig.1 - A, B are presented the PROX activity and selectivity of the samples doped by iron oxide, prepared by the both methods.

The highest PROX activity was obtained for gold catalysts, prepared by MA – 99.8 % conversion of CO at the lowest temperature - 51

^о

С and this conversion was above 99 % in all range to 150

^о

С, the selectivity was at about 38 %.

A - Au/CeFeCP B - Au/CeFeMA

0 20 40 60 80 100 120

0 200 400

Conv. %, Sel. % Form. %

T [°C]

Conv. CO Conv. O2 Selettività

0 20 40 60 80 100 120

0 100 200 300 400

Conv. %, Sel. % Form. %

T [°C]

Fig.1. PROX catalytic activity and selectivity obtained for gold

catalysts doped with Fe

2

O

3

, prepared by CP – A and prepared by MA

– B.

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Another very interesting result - the highest PROX selectivity was obtained for gold catalysts doped with MnO

x

(Fig.2). For the sample, prepared by MA, very high value of selectivity was registered - 61.5 % at the temperature very close to the condition in PEM Fuel Cells - 75

^о

С.

A - Au/CeMnCP B - Au/CeMnMA

0 20 40 60 80 100 120

0 200 400

Conv. %, Sel. % Form. %

T [°C]

0 20 40 60 80 100 120

0 100 200 300 400

Conv. %, Sel. % Form. %

T [°C]

Fig.2. PROX catalytic activity and selectivity obtained for gold catalysts doped with MnO

x

, prepared by CP – A and prepared by MA – B.

In Fig.3 there are summarized the all studied catalysts at T=75

^о

С.

AuCeCoCPcon

AuCeCoCPsel

AuCeCoMAsel

AuCeFeCPcon

AuCeFeMAcon

AuCeFeMAsel AuCeMnCPcon

AuCeMnCPsel AuCeMnMAcon

AuCeMnMAsel AuCe_con

AuCe_sel AuCeCoMAcon

AuCeSnCPcon

AuCeSnCPsel AuCeSnMAcon

AuCeSnMAsel AuCeFeCPsel

0 20 40 60 80 100 120

Catalysts

CO conversion, selectivity %

Fig.3. PROX catalytic activity and selectivity at 75

^о

С on gold

catalysts prepared with different methods CP (co-precipitation) and

MA (mechano chemical activation).

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The best catalysts are tested also in the presence of water and

CO

2

. On the contrary to literature data, we do not obtain improving of

the activity and selectivity in the presence of water. The addition of

CO

2

additionally decreases the activity and selectivity. The obtained

interesting results will be summarized in a common publication of the

both teams.

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Melaet Gérôme’s STSM Report:

About the effect of water and sulphur dioxide on palladium

based catalysts in the frame of methane complete oxidation.

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1. Formal Introduction

As the global warming is one of the first worldwide preoccupations, many countries all over the world apply an environmental politics forcing most of the industries to lower their pollutant emission. When politics think about pollution, its main concern is to work on the abatement of exhaust gas pollution from cars. Therefore, all the automotive companies compete, creating less consuming engines or developing solution for automotive exhaust emission such as the Three Way Catalyst converter on gasoline engines or the particles filters on diesel engines.

Solutions such as methane propelled vehicles are a solid alternative to lower the emission from cars. Nevertheless, the lean-burn conditions of these engines lead to the emission of small quantities of methane. Unburned methane is quite a problem since it is more harmful to the greenhouse effect than the carbon dioxide. In fact, its activity as a greenhouse gas is more significant - about twenty times - than CO2. Therefore, the use of catalytic exhaust system is a good mean to follow the ecologic standards increasing more drastically.

Nowadays scientists agree on the fact that palladium is maybe the best suited metal to be used in exhaust system to burn methane slips coming form the engine. An important drawback comes with the use of such metal as it is known to be quickly deactivated in presence of poisons such as sulphur oxide and/or water.

2. Work plan

In a previous STSM at the ISMN in Palermo, we obtained modified catalysts using titanium(oxide) to dope the SiO2 support. These catalysts were produced by the sol-gel method varying the quantity of Ti loading from 5 to 20 wt%. Importance of this modification has been observed on the methane oxidation performance and on the tolerance to SO2. The results of this collaboration have been published in the journal Applied Catalysis B: Environmental⁽¹⁾ and therefore will not be discussed here.

Regarding this new STSM, we plan to study the effect of water on our most active catalyst:

palladium supported on titanium 10% doped silica (Pd-Ti10Si). To study this influence, we suggested to feed the catalyst with water in different conditions similarly to those used to study the SO₂poisoning effect. The process is divided in eight different cycles, the first cycle is a reference cycle under reactive conditions (0,3%CH4 + 2,4%O2 diluted in He). During the second run, 5% of water is co-fed to the reactive flow in order to observe the deactivation of our catalyst in the presence of water. A subsequent run, which can be associated to a regeneration cycle, is operated in lean burn conditions to observe if the catalyst regains its activity. The third cycle consists of co-feeding both water and

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sulphur dioxide together in the reactive flow in order to observe if the deactivation is more severe in the presence of both these compounds. Again, a regeneration cycle is done in lean-burn condition, and the methane conversion is measured. A fifth cycle will consist in an overnight treatment in which the catalyst is fed with water and SO2 during 15 hours. Finally to understand the impact of H2O and SO2 ageing, we will operate cycle seven and eight in lean burn condition aiming to observe if the catalyst regains its activity.

3. Results and Discussion

The first step in this collaboration was to determine if the conversion observed was not dependent on effects such as an inhomogeneous temperature distribution or transport limitation of diffusing gaseous reactants and products inside the catalytic bed. In order to see if such effects can be avoided we ran two cycles under lean-burn conditions, increasing the temperature step wise during the first one while decreasing the temperature in the second cycle. As one can observe in Figure 1, Cycle I is different from Cycle II and this second one seems more active as the T50% (temperature of fifty percent conversion) is 34°C lower than in the first cycle. While increasing the temperature (Figure 1 Cycle III curve) in a third run, we observed that this latest cycle is identical to the second cycle, concluding that we now have a stable catalyst. Therefore, cycle III will serve as a reference cycle in order to compare the effect of a wet feed in presence or absence of SO2. This cycle III will be later referred as "Cycle I (Reference)".

These first tests lead us to the conclusion that to have a stable catalyst a first cycle under lean-burn condition must be run as a mean of an activation cycle. At this point of time, we do not know if this activation is chemically induced or if we face a temperature activation as we are reaching 600°C in that first cycle where we only pre-treat the catalyst under O2 at 350°C for an half hour. Further experiments should allow us to determine the predominant factor of this activation.

Finally, the lack of hysteresis between Cycle II and III suggests that there are no diffusion effects, thus the conversion observed is supposedly due to the catalytic activity only.

Figure 1 : Conversion versus temperature under lean-burn condition (0,3%CH4 + 2,4%O2 in Helium). Cycle I increasing the temperature, Cycle II decreasing the temperature and Cycle III increasing the temperature

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Figures 2 represent the conversion of methane against temperature in different conditions.

One can observe that a wet feed leads to a partial deactivation of the catalyst (Cycle II) but it will regain its activity while running a regeneration cycle under lean- burn conditions (Cycle III).

Furthermore, combining the effect of water with that of sulphur in the reaction mixture does not lead to a higher deactivation than in the presence of water only - see Figure 2, conversion curve from Cycle II and IV are overlapped.

The activation energies have been calculated from the data obtained, supposing a first order reaction in methane and a pseudo-zero order reaction with respect to oxygen. These data have been reported in the Table 1.

Condition Ea(kJ/mol) E_a^(a)(kJ/mol) Ln A R² T50%(°C)

Cycle I (Reference) 70 17 0.9917 289

Cycle II – ^{Wet feed} 101 31 23 0.9975 327

Cycle III – Regeneration 74 4^(b) 18 0.9915 289

Cycle IV – Wet feed + 10ppm SO2 101 31 22 0.9975 329

Cycle V – Regeneration 70 0 17 0.9954 298

Cycle VI – ¹^st cycle after overnight

(350°C 10ppm SO2 + 5%vol. H2O) 168 99 33 0.9997 373

Cycle VII – 2^nd cycle after overnight

(350°C 10ppm SO2 + 5%vol. H2O) 77 7^(b) 18 0.9915 288

Table 1. Activation energy (Ea) and pre-exponential factor A calculated (a) Ea obtain by subtracting the Ea of a given Cycle and the one from the reference Cycle. (b)Value falling into the calculation error.

According to the results listed in Table 1, one can draw two foremost conclusions: firstly the effect of the presence of both water and sulphur dioxide are not more severe than the presence of water alone. This conclusion can be made because the Ea calculated either during Cycle II or Cycle IV are very similar (101 kJ/mol). Furthermore, comparing the Ea of these precedent cycles (=31kJ/mol) to the one obtained formerly in the presence of sulphur dioxide alone in the reactive flow (Ea = 35kJ/mol), we can conclude that the presence of water has neither a positive nor a negative effect on the activity of our catalyst.

The second conclusion, less obvious but nevertheless important, is the high stability of our catalyst. In fact, one can observe that the Ea calculated from Cycle I, III and VII is quite similar thus the effect of poisons can be considered reversible. So as to recover the activity, a single cycle under lean- burn conditions is sufficient. At this time, literature has never reported on regeneration during lean- burn reaction conditions. Instead, either a reducing atmosphere or a high temperature treatment was necessary.

Figure 2: Conversion versus temperature under different conditions.

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4. Conclusion

The conclusion can be made that the mixed oxide catalyst is highly active and suffers neither from the contact with water, nor from that with sulphur dioxide. To this end, it seems extremely stable.

As we demonstrate it during this collaboration, the adsorption of water or/and sulphur seems reversible as the original activity can always be reproduced. Furthermore, the fact that the catalyst recovers its activity, even after multiple cycles, shows that this catalyst is highly stable. Finally, one should point out that the regeneration step is identical to a lean-burn cycle. This latter fact has its importance since it was never before reported in the literature.

Future studies and collaborations should be done to understand why the use of combined sulphatable and non-sulphatable supports helps prevent severe deactivation by water and SO2.

(1)Applied Catalysis B: Environmental, In Press, Corrected Proof, Available online 8 November 2008 A.M. Venezia, G. Di Carlo, G. Pantaleo, L.F. Liotta, G. Melaet, N. Kruse, doi:10.1016/j.apcatb.2008.10.023

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REPORT

Short Term Scientific Mission, COST D36

Beneficiary: Dr Anna Elzbieta LEWANDOWSKA, Institute of Catalysis, CSIC Host: Mònica CALATAYUD, Laboratoire de Chimie Théorique - UMR 7616 UPMC/CNRS

Period: from 20/02/2009 to 08/03/2009 Place: Paris (FR)

Reference code: COST-STSM-D36-04271

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The objective of the COST-STSM-D36-04271 was to get acquaint with theoretical calculation methodologies to describe catalytic systems of titania supported vanadia system in the hydration/dehydration conditions and use in combination with experimental analysis of their reactivity and structure. The work was focused on two goals:

• Training in theoretical modelling and apply it to study hydration process

• Comparing the modelling and experimental results

Methods and models

All calculations are performed with the ab initio plane-wave approach implemented in the VASP code ^{1, 2}. The Perdew-Burke-Ernzerhof (PBE) functional ^{3, 4} is used. The valence electrons (O:2s² 2p⁴, Ti:4s² 3d², V 4s² 3d³, H: 1s¹) are treated explicitly while their interactions with the ionic cores are described by the Projector Augmented-Wave method (PAW) ^{5, 6}. A cut off equal to 400 eV is used for the plane-wave basis. A (3 x 3 x 1) k-point grid is used in the Brillouin-zone. A vacuum of at least 8 Å prevents interactions between successive slabs. The positions of all the atoms in the super cell are relaxed with the conjugate gradient method.

Vibrational spectra have been calculated for selected surface species within the harmonic approximation. The vanadia unit, water molecules and first support layer are relaxed, the bottom support layers are kept fixed. The Hessian matrix is computed by the finite difference method followed by a diagonalization procedure. The eigenvalues of the resulting matrix lead to the frequency values. The assignment of the vibrational modes is done by inspection of the corresponding eigenvectors.

The model used in the calculations has been successfully employed for describing reactivity of vanadia supported on titania catalysts ^{7, 8, 9}. It contains a V2O5 unit deposed on an anatase (001) slab support as shown in Figure 1. The cell dimensions are 7.57 × 7.57 × 25 Å³. This model simulates dehydrated conditions and exhibits representative features of the vanadia/titania catalyst: presence of vanadyl V=O groups, interface V-O-Ti bonds, vanadium in its highest oxidation state (+V), vanadium coverage is 0.5 monolayers (3.5 V atoms nm^-1).

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Figure 1. side view of the slab used in the calculations for dehydrated conditions (triple unit cell). The vanadia V2O5 units are deposed on an anatase (001) five TiO2 layers thick. OT: terminal oxygen (vanadyl group). Selected distances in Å.

Hydration is modeled by the addition of water molecules to this slab. First, one water molecule is added to the cell in different geometries: dissociated, molecular, in interaction with vanadyl V=O, interface V-O-Ti, support Ti-O groups. A set of 10 geometries has been tested. Rather than a systematic study, we have focused on the analysis of trends and preference for certain spatial arrangements. For the most stable structures, a second water molecule is added and a set of possible geometries is studied. Again, the most stable structures are retained for the addition of a third water molecule. The most representative structures obtained are described below, and their stability is tested by molecular dynamics simulations at 273 K.

Sample preparation

The catalysts were prepared by wet impregnation with an aqueous solution of ammonium metavanadate (Sigma, 99.99%) of titanium (IV) oxide (Alfa Aesar, 100% anatase, SBET = 166 m²/g) ¹⁰. Oxalic acid (Panreac, 99.5%) was added to an aqueous solution of NH4VO3 to facilitate dissolving the salt. Dissolution of vanadium precursor mixture was carried out by stirring at 323 K for 50 min. The suspension was evaporated in rotatory evaporator at 338 K.

The obtained materials were dried at 383 K for 16 h and the samples were calcined at 673 K

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for 4 h in air (heating rate = 3 K min^-1). The total vanadium content were calculated to corresponds 1.2 and 3.5 V atoms/nm² of TiO₂ support. Catalysts are labeled as xV/TiO2, where ‘‘x’’ indicates the number of atoms per nm² of vanadia.

In situ Raman

Raman spectra were run with a single monochromator Renishaw System-1000 microscope Raman equipped with a cooled CCD detector (-73 ^oC) and holographic super-Notch filter for removing the elastic scattering. The powder samples were excited with the 488 nm excitation line; spectral resolution was near 4 cm^-1 and spectrum acquisition consisted of 5 accumulations of 33 s. The spectra were obtained under in situ conditions in a hot stage (Linkam TS-1500). The samples were previously hydrated in humid synthetic air flow at room temperature for 20 min. Subsequently catalyst was gradually dehydrated in a flow of dry synthetic air. Dehydration process was carried out from 323 K to 673 K with a Raman spectrum acquisition each 50 K. The rate of the heating was 10 K min^-1. Vanadia catalysts dehydration process were compared to pure titania catalyst support.