COST Chemistry D36 3rd Workshop and
5th Management Committee Meeting
Structure-performance relationships at the surface of functional materials
Benahavís (Málaga, Spain), 21
stto 23
rdof October, 2009
The main objective of the COST D36 Action is to increase the fundamental knowledge and understanding of the chemistry occurring at surfaces and interfaces and the factors that tune it. An interdisciplinary, combined effort is the approach. A fundamental approach is advocated, even for industrially oriented research projects. This requires precisely defined problems at all levels and an interdisciplinary approach i.e. synthesis and activation of the materials;
measurement of the surface properties; understanding surface properties at the atomic, molecular or cluster level and theoretical understanding of these properties in relation to chemical composition and the structure of the surface.
As a consequence, the secondary objective is to gain advanced knowledge for
modelling/predicting of the structure/composition reactivity/surface properties
relationships of the materials, by means of characterisation of the bulk and
surface properties under real operation conditions and for preparing materials
with tuneable properties.
Sponsors and collaborating institutions:
COST (European cooperation in science and technology) http://www.cost.esf.org/
Universidad de Málaga http://www.uma.es/
Ayuntamiento de Benahavís http://www.benahavis.es/inicio.asp
Junta de Andalucía
http://www.juntadeandalucia.es/index.html
Ayuntamiento de Ronda http://www.turismoderonda.es/
PID Eng&Tech
http://www.pidengtech.com/
Organizers
Dr. M. Olga Guerrero Pérez Universidad de Málaga
Prof. Dr. José Rodríguez Mirasol Universidad de Málaga
Local Committee
Dr. Jorge Bedia Universidad de Málaga
Dr. Juana M. Rosas Universidad de Málaga
Mr. Ricardo López Medina Instituto de Catálisis y Petroleoquímica
Ms. Elizabeth Rojas García Instituto de Catálisis y Petroleoquímica
Mr. Ramiro Ruiz Rosas Universidad de Málaga Ms. M. José Valero Romero
Universidad de Málaga
BOOK OF ABSTRACTS
Section I:
Scientific
Program
Wednesday 21st
17:00 – 17:15 Welcome
Miguel A. Bañares, Action Chair
M. Olga Guerrero-Pérez, Local Organizer 17:15 – 18:00 Keynote 1
Chair: Miguel A. Bañares, Instituto de Catálisis y Petroleoquímica (CSIC) (Spain)
K1 José Manuel López-Nieto, Instituto de Tecnología Química (CSIC) (Spain) “Synthesis, Characterization and Catalytic behaviour in partial alkane oxidation of Multicomponent mixed oxidic”
18:00 – 20:00 Oral Session 1
Chair: Sanna Airaksinen, Helsinki University of Technology (Finland) O1 Maria Ziolek, Adam Mickiewicz University (Poland)
“The effect of porosity of niobosilicate supports and VSbOx loading on the ammoxidation of propane”
O2 James Sullivan, University College Dublin (Ireland) “Towards 4-way catalysis”
O3 Gerhard Mestl, SÜD-CHEMIE AG (Germany)
“Towards an optimization of MoVNbTe-catalysts for C3-oxidation”
O4 Maricarmen Capel, Instituto de Catálisis y Petroleoquímica (CSIC) (Spain) “Silylation of titanium-containing amorphous silica catalyst: Effect on the alkenes epoxidation with H2O2”
O5 Lyuba Ilieva-Gencheva, Institute of Catalysis (BAS) (Bulgary)
“Preferential oxidation of CO in H2 rich stream over gold catalysts supported on doped ceria: effect of preparation method and dopants nature”
O6 Stanislaw Dzwigaj, Université Pierre et Marie Curie (France)
“The Design of Metal-Single site Catalysts for their Application in Catalytic and Photocatalytic Processes“
20:30 Welcome Reception
Thursday 22nd 9:00 – 9:45 Keynote 2
Chair: Robert Schoonheydt, Catholic University of Leuven (Belgium) K2 Venceslav Kaucic, National Institute of Chemistry (Slovenia)
“Microporous and Mesoporous Materials”
9:45 – 11:05 Oral Session 2
Chair: Sven Jaras, Chemical Technology, KTH (Sweden)
O7 Monica Calatayud, Université Pierre et Marie Curie (France)
“Glycerol etherification over alkaline earth metal oxides”
O8 Izabela Sobczak, Adam Mickiewicz University (Poland)
“Glycerol oxidation on gold catalysts supported on group five metal oxides –a comparative study with other metal oxide and carbon based catalysts”
O9 Andrei Parvulescu, Utrecht University (Netherlands)
“Etherification of Glycerol and Other Biomass-Derived Polyols: New Routes to Valuable Bulk Chemicals”
O10 Rafael Mariscal, Instituto de Catálisis y Petroleoquímica (Spain)
“Relevance of the physicochemical properties of CaO catalyst for the methanolysis of triglycerides to obtain biodiesel”
11:05 – 11:35 Cofee Break 11:35 – 13:15 Oral Session 3
Chair: Tomás Cordero, Universidad de Málaga (Spain)
O11 J. Ángel Menéndez, Instituto Nacional del Carbón (Spain)
“Influence of porosity and surface groups on catalytic activity of carbon materials for the microwave-assisted CO2 reforming of CH4”
O12 Frederik Tielens, Université Pierre et Marie Curie (France)
“Niobium Oxide Species in and on Silica Materials; a Molecular Picture”
O13 Enrique Rodriguez-Castellón, Universidad de Málaga (Spain)
“Study of Nanoporous Catalysts in the Selective Catalytic Reduction of NOx”
O14 Anna M. Venezia, ISMN CNR (Italy)
“New HDS catalysts supported on thiol functionalized mesoporous silica”
O15 Ángel Landa-Cánovas, Instituto de Ciencia de Materiales de Madrid (Spain)
“Structural Flexibility in ~SbVO4” 13:15 – 14:15 Lunch
14:45 Visit to Ronda
Friday 23rd 9:00 – 9:45 Keynote 3
Chair: José Rodríguez-Mirasol, Universidad de Málaga (Spain) K3 Jean Michel Léger, Université de Poitiers (France)
“Carbon powder as conducting supports for electrocatalysts in low temperature fuel cells”
9:45 – 11:05 Oral Session 4
Chair: Guido Mul, Delft University of Technology (Netherlands) O16 Álvaro Colina, Universidad de Burgos (Spain)
“Synthesis of Pt nanoparticles on poly(3,4-ethylenedioxythiophene) modified electrodes for the electrocatalysis of Methanol”
O17 David Fermin, University of Bristol (UK)
“Electrochemical Hydrogen Loading in Ultrathin Assemblies of Au-Pd Nanostructures”
O18 Atilla Cihaner, Atillim University (Turkey)
“One More Step Closer to Realizing the Dream of the Polymeric RGB Electrochromics”
O19 László Guczi, Chemical Research Center (Hungary)
“Modelling of Au/FeOx interface by in situ Sum Frequency Generation Technique”
11:05 – 11:35 Cofee Break 11:35 – 13:15 Oral Session 5
Chair: Jean Michel Léger, Université de Poitiers (France)
O20 Nikolaos Tsiouvaras, Instituto de Catálisis y Petroleoquímica (Spain)
“The effect of the Mo precursor on the nanostructure and activity of PtRuMo electrocatalysts for Proton Exchange Membrane Fuel Cells”
O21 Luisa Maria Abrantes, Universidade de Lisboa (Portugal)
“Electrocatalytic activity of polypyrrole films incorporating palladium particles“
O22 Hubert Girault, Ecole Polytechnique Federale de Lausanne (Switzerland)
“Bio-inspired electrochemistry: From oxygen reduction to hydrogen evolution at soft interfaces.”
O23 Stanislas Zalis, Heyrovski Institute Prague (Czech Republic)
“Density functional and electrochemical studies of the catalytic ethylene oxidation on nanostructured Au and Pt electrodes.”
O24 Sergio García, Instituto de Catálisis y Petroleoquímica (Spain)
“An FTIR study of ternary PtSn-Rh/C for ethanol electrooxidation: effect of surface composition “
13:15 – 14:30 Lunch
14:45 – 15:30 Keynote 4
Chair: Viorica Parvulescu, Institute of Physical Chemistry I.G. Murgulescue (Romania) K4 Jaques Fraissard, Laboratoire de Physique Quantique – ESPCI (France)
“NMR of physisorbed 129Xe used as a probe to investigate porous solids”
15:30 – 17:10 Oral Session 6
Chair: Maria Ziolek, Adam Mickiewicz University (Poland) O25 Volker Ribitsch, Universitat Graz (Austria)
“Adsorption of proteins on DLC surfaces“
O26 M. Rosa Infante, Instituto de Química avanzada de Cataluña (Spain)
“Amino Acid-Based Biocompatible Surfactants”
O27 Bjšörn Lindman, University of Lund (Sweden)
“Interactions of DNA with cationic surfactants and proteins: Gels, gel nano-particles, microstructure and phase separation”
O28 Eduardo Marques, University of Porto (Portugal)
“Symmetry-asymmetry effects on the self-assembly of ion-paired surfactant systems”
O29 Julian Ross, University of Limerick (Ireland)
“Formic Acid as a Hydrogen Source for Vapor Phase Catalytic Reactions”
17:10 – 20:00 Poster Session
18:00 – 20:00 5th Management Committee Meeting 20:30 Workshop Banquet
Poster Contributions 1. Blanco, Gema Instituto de Catálisis y Petroleoquímica (Spain)
“Silylation of functionalized commercial silica for the direct synthesis of hydrogen peroxide solution”
2. Zgrablich, Jorge Instituto de Física Aplicada (INFAP) (Argentina)
“Attempts to Understand the Enantioselectivity of Chiral Propylene Oxide Adsorption on NEA- Modified Pt Surfaces”
3. Pinazo, Aurora Instituto de Química avanzada de Cataluña (CSIC) (Spain)
“Argine-based surfactants: mixtures with 1,2 dipalmitoyl-sn-glycerol-3-phosphate monosodium salt”
4. Pinazo, Aurora Instituto de Química avanzada de Cataluña (CSIC) (Spain)
“Lysine-based cationic surfactants: synthesis and study of the effect of the polar group on their biological properties”
5. Pons, Ramon Instituto de Química avanzada de Cataluña (CSIC) (Spain)
“Mono acyl lysine based surfactants: self-aggregation”
6. Ivanov, Ivan Institute of Catalysis (BAS) (Bulgary)
“Gold supported on ceria doped by Me3+ (Me=Al and Sm) for water gas shift: influence of dopant and preparation method”
7. Andreeva, Donka. Institute of Catalysis (BAS) (Bulgary)
“Redox activity of gold-molybdena catalysts: influence of the preparation method”
8. Iliopoulou, Eleni F. CPERI/CERTH (Greece)
“FTIR accessibility studies of 2,6 DTBPy adsorption on FCC catalysts”
9. La Mesa, Camilo Sapienza University (Italy)
“Supramolecular Assemblies in Association Colloids: from dilute to concentrated regimes”
10. Trejda, Maciej Adam Mickiewicz University (Poland)
“New V, Nb, Ta – FAU zeolites – texture and surface properties”
11. Ruíz-Rosas, Ramiro Universidad de Málaga (Spain)
“Lignin-based electrospun carbon microforms”
12. Bedia, Jorge Universidad de Málaga (Spain)
“2-propanol decomposition on carbon based acid and basic catalysts”
13. Valero-Romero, M. José Universidad de Málaga (Spain)
“Catalytic and non-catalytic hydrothermal carbonization of hemp biomass: the carbonaceous product“
14. Rosas, Juana M. Universidad de Málaga (Spain)
“Surface chemistry modification of carbon supported chromium catalysts alter no reduction by XPS analyses“
15. Pantaleo, Giuseppe ISMN-CNR (Italy)
“CH4 combustion activity of Pd catalysts supported on TiO2 incorporated mesoporous SiO2
(SBA-15 and HMS)”
16. Edolfa, Kristine Latvian Institute of Organic Synthesis (Latvia)
“Ketonization of aliphatic acids over zinc chromite catalyst”
17. Liotta, Leonarda ISMN-CNR (Italy)
“Supported gold catalysts for Preferential oxidation (PROX) of CO in the presence of excess H2” 18. Pospisil, Lubomir J. Heyrovsky Institute of Physical Chemistry (Czech Republic)
“Structure-Reactivity Relationships in ElectronTransfers of Helical Polyaromatic Dications”
19. Mores, Davide Utrecht University (Netherlands)
“Coke formation during the Methanol-to-Olefin Conversion: Space- and Time-resolved In-Situ Spectroscopy on H-SAPO-34 and H-ZSM-5”
20. Tirkes, Seha Atilim University (Turkey)
“A Neutral State Green Polymeric Electrochromic Based on Acenaphtho[1,2-b]quinoxaline and EDOT”
21. Boghosian, Soghomon University of Patras (Greece)
“Molecular structure and reactivity of MoO3/TiO2 catalysts for ethane oxidative dehydrogenation studied by operando Raman spectroscopy“
22. López-Medina, Ricardo Instituto de Catálisis y Petroleoquímica (Spain)
“Nanostructured MoVNbTeO Oxide Catalysts for Selective Oxidation Reactions”
23. Mikolajska, Ewelina Joanna Instituto de Catálisis y Petroleoquímica (Spain)
“Operando Studies of VPO catalysts in n-butane selective oxidation reaction. Activity, selectivity and structure transformations”
24. Tielens, Frederik Université Pierre et Marie Curie (France)
“Theoretical Study of Thiol Self Assembled Monolayer Formation on Au(111) surfaces”
25. Rojas, Elizabeth Instituto de Catálisis y Petroleoquímica (Spain)
“Theoretical Investigation of the Ammonia Adsorption Process on (110)-VSbO4 Surface”
26. Wolfgang, Grünert Ruhr-Universität Bochum (Germany)
“Peculiar response of V2O5-WO3/TiO2 DeNOx catalysts to thermal stress an investigation with catalytic and spectroscopic tools“
27. Zhang, Yongmin Université Pierre et Marie Curie (France)
“Synthesis of novel 2:1 permethylated b-cyclodextrin-fullerene conjugates “ 28. Nervi, Carlo Dipartimento di Chimica IFM (Italy)
“Electrochemical Functionalization of Glassy Carbon Electrode Surfaces by Organometallic Moieties”
29. Hromadová, Magdaléna J. Heyrovský Institute of Physical Chemistry of ASCR (Czech Republic)
“Self–assembled monolayers of atrazine–based thiolates and their interaction with anti–atrazine antibody”
30. Morán, Carmen University of Coimbra (Portugal)
“DNA gel particles from single and double-tail surfactants”
31. Dias, Rita University of Coimbra (Portugal)
“Adsorption of macromolecules to responsive surfaces”
32. Mendez, Manuel Ecole Polytechnique Fédérale de Lausanne (Switzerland)
“Proton Coupled Oxygen Reduction at Liquid-Liquid Interfaces Catalyzed by Cobalt Porphine”
33. Boutonnet, Magali KTH Chemical Science and Engineering (Sweden)
“Synthesis of crystalline CeO2 nanoparticles by a novel oil-in-water microemulsion reaction method and its use as catalyst support”
34. Beck, Andrea Chemical Research Center (Hungary)
“The effect of preparation method on the formation of highly active Au-promoter oxide perimeter in promoted Au/SiO2 catalysts”
35. Benko, Timea Chemical Research Center (Hungary)
“TiO2 and CeO2 promoted Au/SBA-15 in propene total oxidation”
36. Hernandez-Alonso, M. Dolores CIEMAT-PSA (Spain)
“Selective photo-oxidation of cyclohezane on TiO2: the role of surface characteristics“
37. Alekseev, Sergyi Kiev University (Ucrania)
“Porous silicon with gold nanoparticles as laser desorption/ionization mass spectrometry platform”
38. Gerda, Vasilyi Kiev University (Ucrania)
“Matrix synthesis and functionalisation of the ordered mesoporous carbon by palladium nanoparticles as potential sorbent for hydrogen storage”
39. Syzgantseva, Olga Université Pierre et Marie Curie (France)
“Theoretical studies of hydrogen adsorption mechanism on ZrO2”
BOOK OF ABSTRACTS
Section II:
Keynote
Communications
Synthesis, Characterization and Catalytic behaviour in partial alkane oxidation of Multicomponent mixed oxidic bronzes
José M. López Nieto
Instituto de Tecnología Química, UPV-CSIC, Avda. De los Naranjos s/n, 46022-Valencia (Spain)
Abstract
The selective oxidative functionalization of short chain paraffins is a formidable challenge for the sustainable use of alkanes as feedstock. The incorporation of several functions in an adequate structure seems to be the way to the development of active and selective catalysts for partial alkane oxidations. Nevertheless, despite there are some achievements, several aspects are still not solved for an industrial applicability, as the selectivity to partial oxidation products. This paper will present an overview on the synthesis, characterization and catalytic behaviour of multicomponent metal oxides, with special attention to metal oxidic bronzes and molecular sieves, as active and selective catalysts for the gas phase partial oxidation of hydrocarbons.
Recent examples on the new synthetic procedures and new structures will be also discussed.
Introduction
The selective oxidative functionalization of short chain paraffins is a formidable challenge for the sustainable use of alkanes as feedstock and has attracted special attention during the last two decades [1]. Two strategies have been mainly developed in alkane oxidation: i) the oxidative dehydrogenation to achieve olefins and ii) the direct oxidation of alkanes to O- or N-containing products. However, only the oxidation of n-butane to maleic anhydride is industrially applied.
The oxidative dehydrogenation of short chain alkanes has been extensively studied because it is a very attractive way for alkane functionalization. Mixed metal oxides and metal containing molecular sieves have been proposed as active and relatively selective catalysts in the activation of alkanes. Although the use of N2O rather than oxygen could improve the selectivity to olefins, these catalysts cannot be considered as competitor of steam cracking technologies.
Only a few catalytic systems for ethane oxydehydrogenation could have some interest from an industrial point of view.
The second way for the functionalization of alkanes could be to replace olefins by alkane due to its low cost. Although a first approach could be to integrate a first dehydrogenation reactor to the conventional olefin oxidation process, the research effort in the last years is being carried out towards the direct oxidation (in one stage) of propane since this could permit the reduction of the reaction steps.
Multicomponent mixed metal oxides, MoVTe(Sb)NbO catalysts, reported by Mitsubishi in the early 1990s, seem to be promising in the (amm)oxidation of propane [2] and in the oxidative dehydrogenation of ethane to ethylene [3].
Typically, the most efficient MoVTe(Sb)NbO catalysts present at least two crystalline phases [4, 5]: (i) an orthorhombic (AO)2−2x(A2O)nM20O56 (A = Te or Sb and M =Mo, V, Nb), the so-called M1 (isostructural with Csx(Nb,W)5O14) and (ii) an orthorhombically distorted Te0.33MO3.33 or (Sb2O)M6O19 phase (M = Mo, V, Nb), the so-called M2. In addition, TeMo5O16 (or Sb4Mo10Ox), (V,Nb)-containing Mo5O14, and/or tetragonal bronzes may be present, depending on the catalyst composition and the catalyst preparation procedure. However, the M1 phase itself seems to be active and selective on the partial oxidation of propane and ethane, while M2 is only active and selective in the oxidation of propene to acrolein and/or acrylic acid. A certain composition range seems to be necessary to achieve the best catalytic performance, since the formation of Te2M20O57-type phase strongly depends on both the catalyst composition and the catalyst preparation method, post-synthesis treatment should be also considered in order to prepare effective catalysts [5]. The reported results suggest a molecular structure-performance relationship at the surface of functional materials [4].
On the other hand, the different catalytic behaviour of these phases can be explained on the basis of crystal structure, MO6 octahedra form pentagonal, hexagonal and heptagonal channels in M1-phase and only hexagonal channels in M2-phase. More recently, new oxidic bronzes and synthesis strategies have been proposed. A0.5[Mo5-a-bVa4+XbO14] (A = Rb, Cs, X = no element, Nb, Ta,W, Sb, Bi, Se, Te) with a M1-type structure [6], PMo(W)VNbO mixed oxides with a tetragonal tungsten bronze structure (TTB) [7], or new synthesis procedures in the preparation of other Mo-bronzes [8], or Nb,Mo-containing mesoporous materials [9] have been reported, in which a clear structure-behaviour relationship can also be proposed.
Recently it has been proposed that some of these structures should be considered as microporous materials [10] and their catalytic performance is discussed in terms not only of the chemical composition (bulk and surface) but also in terms of catalyst structure (including the nature and size of channels in this type of materials).
Acknowledgments
Financial support was provided by the DGICYT of Spain (project CTQ2006-09358-BQU).
References
[1] J.M. López Nieto, Top. Catal. 41 (2006) 3.
[2] a) M. Hatano, A. Kayo. EP 318285B1 (1988); b) T. Ushikubo, K. Oshima, A. Kayou, A, T. Umezawa, K. Kiyono, I.
Sawaki, EP529853 A2 (1993).
[3] a) J.M. López Nieto, P. Botella, M.I. Vázquez, A. Dejoz, WO Pat 0346035 (2003); b) J.M. López Nieto, P. Botella, M.I. Vázquez, A. Dejoz, Chem. Commun. (2002) 1906.
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Oshima, Y. Koyasu, Chem Mater. 15 (2003) 2112; c) P. DeSanto, D.J. Buttrey, R.K. Grasselli, C.G. Lugmair, A.F.
Volpe, B.H.Toby, Topics Catal. 23 (2003) 23.
[5] a) P. Botella, E. García-González, J.M. López Nieto, J.M. González-Calbet, Solid State Sciences 7 (2005) 507; b) A.C Sanfiz, T.W. Hansen, A. Sakthivel, A. Trunschke , R. Schlogl, A. Knoester, H.H. Brongersma, M.H. Looi, S.B.A.
Hamid, J. Catal. 258 (2008) 35.
[5] F. Ivars, B. Solsona, E. Rodríguez-Castellón, J.M. López Nieto J. Catal. 262 (2009) 35.
[6] H. Hibst, F. Rosowski, G. Cox, Catal. Today 117 (2006) 234.
[7] P. Botella, B. Solsona, E. García-González, J:M. M. González-Calbet, J.M. López Nieto, Chem Comm. (2007) 5040.
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Shiju, V.V. Guliants, ChemPhysChem 8 (2007) 1615.
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[10] M. Sadakane, K. Kodato, T. Kuranishi, Y. Nodasaka,K. Sugawara, N. Sakaguchi, T. Nagai, Y. Matsui, W. Ueda, Angew. Chem. Int. Ed. 47 (2008) 2493.
Microporous and Mesoporous Materials Venčeslav Kaučič
National Institute of Chemistry and University of Ljubljana, Hajdrihova 19, 1000 Ljubljana, Slovenia
Summary
Transition metal-modified microporous zeolitic materials (silicate- and phosphate-based) are attractive catalysts due to their hydrothermal stability and high catalytic activity and selectivity.
Metal-modified mesoporous materials with larger pore openings have been developed for catalytic processes where larger molecules are involved. The inclusion of nanosized particles of zeolitic microporous materials with larger external surface areas and high surface activity into mesoporous matrices, i.e. the preparation of microporous/mesoporous composites, substantially enhances the catalytic activity of mesoporous materials. The important feature of nanoporous solids based on various metal oxides is also their ability to form thin films with nanometer-scale thickness. Examples of successful preparation and/or functionalisation of new nanoporous solids encompass microporous and mesoporous silicates (MnS-1, MnMCM-41, MnTUD-1), microporous and mesoporous aluminophosphates (FeAPO-36, FeHMA), microporous/mesoporous silicate composites ((Ti,Al)-Beta/MCM-41, (Ti,Al)-Beta/MCM-48, Ti- Beta/SBA-15) as well as cubic mesoporous aluminophosphate thin films. Studies of structure- property relations of new solids have included X-ray diffraction, spectroscopic (XAS, NMR) and electron microscopy characterisation techniques.
Porous materials are classified into three categories, microporous with pore openings from 0.3 to 2 nm, mesoporous having pores between 2 and 50 nm, and macroporous with pores greater than 50 nm. Microporous materials are exemplified by crystalline framework solids such as zeolites (aluminosilicates), whose crystal structure defines channels and cages, i.e. micropores, of strictly regular dimensions. Mesoporous materials, exemplified by the silicate MS41 materials family, are amorphous solids exhibiting highly-ordered pore structures and large internal surface areas.
Microporous materials are generally prepared hydrothermally from aqueous gels containing a source of the framework building elements (Si, Al, P, etc.), a mineraliser (OH-, F-) regulating the dissolution/condensation processes during the crystallization, and a structure-directing agent, usually an organic amine or ammonium salt. Transition metals can be incorporated into microporous or mesoporous materials by a post-synthetic ion-exchange treatment or by direct framework substitution by the addition of transition metal cations into the synthesis gel.
An alternative to a classical hydrothermal synthesis is a microwave oven. The microwave heating is regarded as a novel synthesis tool for microporous and mesoporous materials because it offers several benefits, such as homogeneous nucleation, the promotion of faster crystallisation, rapid synthesis, the formation of uniform crystals, and small crystallites, facile morphology control, the avoidance of undesirable phases by shortening the synthesis time and so on. Recently, it was found that it provides an effective way to control the particle size distribution, crystal morphology, orientation, and even the crystalline phase.
Microporous materials are mostly used as heterogeneous acid- and redox catalysts in petroleum industry and in the production of chemicals for various types of shape-selective conversion and separation reactions. The most common reactions, where microporous acid- catalysts are involved, are fluid catalytic cracking, hydrocracking, aliphate alkylation, isomerisation, transformation of aromatics and the conversion of methanol to hydrocarbons.
Redox microporous catalysts are also increasingly used for a variety of selective oxidations of various substrates of synthetic hydrocarbons, alcohols, and amines since these reactions can be performed under mild conditions in the liquid phase. An illustrative example is the clean production of adipic acid that is used in the production of nylon with the direct oxidation of cyclohexene with aqueous H2O2 using Ti- or Fe-substituted microporous catalysts. The discovery of mesoporous silicates attracted worldwide attention since they can incorporate relatively large-sized species inside the pores. The extensive research to expand their
functionality and improve their hydrothermal and chemical stability by modified and optimised synthetic or post-synthetic routes in recent years has already enabled their application in the field of catalysis. Intensive research efforts have also been driven by the emerging applications such as biosensors, drug delivery, gas separation, energy storage and fuel cell technologies.
Investigations in the filed of mesoporous thin films are uprising fast due to their potential applications as chemical and optical sensors, shape-selective membranes and energy-storage devices.
The incorporation of transition metals into silicate, aluminophosphate and similar inorganic frameworks generates or moderates catalytic activity of the materials. Here we report on synthesis and structural studies of new micro- and mesoporous materials with the emphasis on the preparation of metal-modified nanosized zeolitic particles, microporous/mesoporous composites and zeolitic thin films.The elucidation of structures of ordered porous materials is essential for the understanding and prediction of their macroscopic physical and chemical properties. In particular, the size and connectivity of the pores determine their molecular sieving capability. The coordination, location, oxidation state and strength of bonding of the divalent and other transition metal ions in materials are directly related to their activity/selectivity in catalytic and other reactions.
The conventional single-crystal and powder diffraction methods have been successfully used for structure determinations of crystalline microporous structures. Problems that can arise are mainly due to the small size of the crystallites that often require ab initio powder structure solutions and the low concentration and/or random distribution of metal active sites over the framework or extra-framework positions. The rapid development of synchrotron radiation sources has brought around a tremendous progress in XRD techniques and methods, e.g.
anomalous dispersion methods for metal site determination. With the availability of synchrotron radiation sources, X-ray absorption spectroscopy (XAS) techniques have also developed into a widely used tool for structural research of ordered porous materials. XAS analytical methods XANES and EXAFS provide structural information about local symmetry and the average oxidation number of selected atom. Since XAS is selective towards a particular element and sensitive only towards a short-range order, it is one of the most appropriate spectroscopic tools for microporous and mesoporous catalysts characterization. Combining in situ XRD and XAS is an excellent approach to obtain information on reaction-dependent changes of both long-range crystallographic order (XRD) as well as oxidation state and local coordination environment of particular elements (XAS) in a solid catalyst.
Nuclear magnetic resonance spectroscopy also offers a wealth of information on structural and dynamical properties of crystalline- as well as amorphous porous materials. The positions and local environments of framework and extra-framework atoms of porous solids can be determined by either studying NMR spectra of 29Si, 27Al, 31P, 69Ga or 71Ga nuclei, or nuclei of charge-compensating ions like 1H, 23Na, 7Li or 133Cs.
Carbon powder as conducting supports for electrocatalysts in low temperature fuel cells Jean-Michel LEGER
Laboratory of Organic Chemistry (LACCO), CNRS-University of Poitiers, 40 Avenue du Recteur Pineau, 86000 Poitiers France
Proton Exchange Fuel Cells (PEMFC) are now considered as the most convenient fuel cells for application in a large range of power densities. Applications from micro fuel cells (electronic devices) mid-sized fuel cells to automotive applications are scheduled in the future. However, PEMFC, which work at low temperatures (from room temperature to 100 °C) and in acidic environment (protonic electrolytic membrane) need the development of convenient electrocatalysts. This means catalysts leading to acceptable performances (kinetically speaking) and with a good stability with time.
Suitable catalysts are generally noble metals, mainly platinum, possibly modified by other metals or oxides. Due to the costs of platinum, it is obvious that the total amount of noble metal need to be limited for large scale applications. An electrocatalytic reaction is a reaction taking place at the catalyst (electrode) surface. Then the only way to increase the overall rate of the reaction is to increase the active surface of the catalyst. This can be obtained by decreasing the size of the metallic particles of the catalysts. The key problem is then to have an optimized utilization of these particles and it is one of the key roles of the supporting material used in the construction of electrode for fuel cells.
Carbon is actually the unique conducting material used for this application, even if some other alternative are explored, for example with oxides. The main key property of the carbon powder for fuel cell is the electrical conductivity. Different preparation procedures are proposed to increase it before the preparation of the catalytic layer itself. The second key point concerns the ability of the catalytic particle to be fixed on the carbon powder surface. This is important to have the highest possible utilization of the catalyst (agglomeration of particles should be limited for example), but also if we considered the stability with time. If the mobility of particle is too high at the carbon surface, fritting and agglomeration of metallic particles occur leading to a decrease of the active area and of the performances of the fuel cell.
Another problem concerns the chemical degradation of the carbon materials under the working conditions. The presence of a catalyst such as platinum and of oxygen (cathodic side) can lead to the chemical oxidation of carbon (to produce CO2). This is observed during long term experiment with significant degradation of the carbon layer and consequently migration of platinum particles though the electrolytic membrane.
The purpose of this keynote lecture is to discuss of these different points in relation with the use of carbon powder as supporting materials for catalysts in fuel cells. Several examples of the preparation of electrocatalysts and how to put and maintain them at the carbon powder surface will be given. It is important to understand that the preparation procedures are critical. These techniques can be purely chemical (colloidal precursors; micro-emulsion…), electrochemical (electrodeposition…), physical (plasma…). The pretreatment of the carbon powder is also a key point, mainly for the optimization of the utilization of the catalyst. It consist mainly developing procedures to increase the concentration of oxidized sites at the carbon powder surface. These sites allow then a strong interaction with the metallic particles and limit their mobility.
Even if some people from fuel cell development still consider that carbon supporting materials are only a secondary problem, less essential than catalyst or membrane for example, it is obvious that the interactions between catalysts and carbon are extremely important. The best catalyst not stabilized at the carbon surface leads always to low performances.
References
[1] C. Lamy, J-M. Léger , S. Srinivasan, Direct Methanol Fuel Cells: From a 20th Century Electrochemist's Dream to a 21st Century Emerging Technology, in Modern Aspects of Electrochemistry, J'O.M. Bockris, B. E. Conway and R. White (Eds), Kluwer Academic/Plenum Publishers (New-York), vol. 34, (2001) p 53-118.
[2] J-M. Léger, C. Coutanceau, C. Lamy, Electrocatalysis for Direct Alcohol Fuel Cell, in “Fuel Cell Catalysis: a surface science approach”, M.T.M. Koper (Ed), J. Wiley & Sons, New Jersey, chap 11 (2009) 343-373.
[3] C. Coutanceau, S. Brimaud, C. Lamy, J.-M. Léger, L. Dubau, S. Rousseau, F. Vigier, Review of different methods for developing Nanoelelectrocatalysts for the oxidation of organic compounds, Electrochim. Acta, 53 (2008) 6865.
[4] C. Grolleau, C. Coutanceau, F. Pierre, J.M. Léger, Effect of potential cycling on structure and activity of Pt nanoparticles dispersed on different carbon supports, Electrochim. Acta, 53 (2008) 7157.
[5] P. Brault, S. Roualdes, A. Caillard, A.-L. Thomann, J. Mathias, J. Durand, C. Coutanceau, J.-M.Leger,C. Charles R.
Boswell,Solid polymer fuel cell synthesis by low pressure plasmas: a short review, Eur. Phys. J. Appl. Phys. 34 (2006) 151.
NMR of physisorbed 129Xe used as a probe to investigate porous solids Jacques Fraissard
University P. and M. Curie, ESPCI, Laboratory ˝ Physique Quantique˝, 10 rue Vauquelin, 75231 Paris, France
The fundamental idea was to find a chemically inert molecule, detectable by NMR and particularly sensitive to physical interactions with other species, which could be used as a probe to determine the properties of its environment [1]. The 129 xenon isotope is this ideal probe.
Chemical shifts and relaxation times of xenon are solely affected by intermolecular interactions and are exquisitely sensitive to the atom’s surrounding. This sensitivity to its environment means that the Xe nucleus can report on a wide variety of attributes of the physical systems in which it finds itself: gas, liquids, cages in a zeolite, nanochannels in a molecular solid, clathrates, proteins in solution, amorphous polymers, etc. It can be used also for imaging and gas diffusion measurements. Several reviews have been published on these applications [2-3].
By using optical polarization techniques [4] the sensitivity of detection can be increased by several orders of magnitude and is particularly useful for several studies (porous materials, microimaging, polymers and elastomers, etc.).
We will present some examples of the applications of the Xe-NMR technique to the characterization of microporous and mesoporous solids, including carbon nanotubes. We will add also few words about the characterization of solid polymers and proteins interactions.
References
[1] T. Ito and J. Fraissard, Proceedings of the 5th International Zeolite Conference, Naples, 1980 L.V.C. Rees (ed.), Heyden, London, 1980, p. 510.
[2] D. Raftery, B.F. Chmelka, NMR Basic Principles and Progress. B. Blümich, Ed ; Springer-verlag, Berlin, Heidelberg, 30 (1994) 111.
[3] J.L. Bonardet, J. Fraissard, A. Gedeon, M.A. Springuel-Huet, Catal.Rev.-Sci.Eng., 41(2) (1999) 115.
[4] D. Raftery, H. Long, T. Meersmann, P.J. Grandinetti, L. Revey and A. Pines, Phys. Rev.Lett.,66 (1991) 584.
BOOK OF ABSTRACTS
Section III: Oral
Communications
The effect of porosity of niobosilicate supports and VSbOx loading on the ammoxidation of propane
H. Golinskaa,b, E. Rojasa, R. Lopez-Medinaa, M. Ziolekb,*, Miguel A. Bañaresa, M.O. Guerrero-Pérezc,*
a Catalytic Spectroscopy Laboratory, Instituto de Catálisis y Petroleoquímica; CSIC; Marie Curie 2; E-29049-Madrid (Spain); b Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6,
60-780 Poznan, Poland; cDepartamento de Ingeniería Química. Universidad de Málaga; E- 29071-Málaga (Spain)
Introduction
Vanadium-antimony oxides are well known as catalysts for selective oxidation and ammoxidation reactions [1,2]. The activity and selectivity of catalysts in these processes are greatly dependent on the loading (Sb:V atomic ratio), method of preparation, gas phase composition during the thermal treatment, and the nature of the support [3]. Moreover, the role of the nature of antimony complex used during the preparation of the catalysts was stressed [4,5]. Sb-V-Ox catalysts with an excess of V are highly active and selective for propane oxidative dehydrogenation while an excess of Sb affords Sb-V-Ox catalyst more efficient for propane ammoxidation [6,7].
The idea of this work was to use niobosilicate supports exhibiting different porosity (mesopores or macropores) as supports for VsbOx binary oxides introduced with step by step impregnation.
The effect of porosity, vanadium-antimony oxides loading, and the sequence of the impregnation (first vanadium next antimony or reverse) on the effectivness in ammoxidation of propane has been studied.
Experimental
Two niobosilicate supports were synthesized: mesoporous NbMCM-41 (denoted NbM;
Si/Nb=64) and macroporous SiNbOx. They were impregnated stepwise with antimony and vanadium precursors (NH4VO3 – BDH Chemicals Ltd. And (CH3COO)3Sb – Aldrich) using V/Sb atomic ratios of 1 or 0.5. and ~25 wt % of Sb. The other group of materials were prepared by the sequenced impregnation starting from vanadium and next antimony sources, and with the atomic excess of vanadium (3 wt % of Sb and 1.5 wt % of V). The samples used in the ammoxidation reactions and their texture parameters estimated by XRD and nitrogen adsorption, are shown in Table 1. The gas phase ammoxidation of propane in the temperature range of 623 – 773 K was studied on the prepared catalysts, which were characterized before and after reactions with Raman spectroscopy.
Results and discussion
The pristine NbMCM-41 material exhibits very well ordered hexagonal arrangement of mesopores of 2.2 nm diameter and high pore volume and surface area of ~1000 m2/g estimated from XRD and nitrogen adsorption measurements. The data in Table 1 show that the use of high loading of binary SbV oxides almost totally block mesopores in NbMCM-41 ordered mesoporous material and causes the dramatically decrease of the surface area and pore volume. The use of macroporous niobiosilica allow to leave 0.3 cm3/g free pore volume in the catalyst after VsbOx loading. These texture parameters determine the catalytic activity and selectivity in ammoxidation of propane (Table 2). The catalytic tests for acidity and basicity indicated that 0.5VSb/SiNbOx reveals lower acidity than 0.5VSb/NbM with the same oxides loading. This feature together with texture parameters cause a very high selectivity in the formation of acrylonitrile on 0.5VSb/SiNbOx catalyst.
Table 1. Composition of the catalysts and texture parameters
The order of V and Sb in the symbol of catalysts indicates
the sequence of
impregnation (e.g. SbV/M means the first vanadium was loaded and next antimony)
Table 2 . The results of ammoxidation af propene at 773 K
Taking into account the results of catalytic activity and TEM, SEM, XRD, Raman spectroscopy study one could define the following conclusions from this work.
• NbMCM-41 as support for Sb-V-Ox phase interacts strongly with vanadium when a low loading of V (1.5 wt.%) is used and vanadium is the first component introduced during the stepwise impregnation.
• The higher loading of antimony and vanadium (25 and 5 wt.% respectively) results in the formation of needle/stake Sb0.95V0.95O4 rutile crystals; the increase of vanadium content to 10 wt.% gives rise to the domination of plate shaped SbxVyO5 phase.
• The mesopores in NbMCM-41 modified by the high loading of Sb-V-Ox phases are almost completely blocked by the bimetallic oxides.
• The use of macroporous SiNbOx as the support for VsbOx phase leads to the higher selectivity in the formation of acrylonitrile.
Acknowledgements
COST action D36, WG No D36/0006/06, the Polish Ministry of Science (Grant No.
118/COS/2007/03) and . Spanish Ministry of Science and Innovation (CTQ2008/02461/PPQ) are acknowledged for the financial support
References
[1] R. K. Grasselli, Catal. Today 49 (1999) 141.
[2] S. Larrondo, B. Irigoyen, G. Baronetti, N. Amadeo, Appl. Catal. A, 250 (2003) 279.
[3] G. Centi, S. Perathoner, F. Trifiro, Appl. Catal. A, 157 (1997).
[4] M.O. Guerrero-Perez, M.A. Banares, Catal. Today 96 (2004) 265.
[5] M.O. Guerrero-Perez, J.L. G. Fierro, M.A. Banares, Top. Catal. 41 (2006) 43.
[6] M.O. Guerrero-Perez, J.L. G. Fierro, M.A. Banares, Catal. Today 78 (2003) 387.
Catalysts*
Sb/V atom.
Ratio
% wt.
Of Sb
% wt.
Of V
BET area, m2/g
Pore volume BJH, cm3/g
NbM - - - 1006 1.1
0.12Sb0.15V/NbM 0.8 3 1.5 885 1.0
0.5VSb/NbM 2 25 5 52 0.1
1VSb/NbM 1 25 10 27 0.07
SiNbOx - - - 165 0.9
0.5VSb/SiNbOx 2 25 5 92 0.3
Selectivity (%) Catalyst Propane
conversion
(%) acrylonitrile acetoni trile
acroleine propen e
ethene Cox
NbM 3.0 14.9 63.6 0 20.2 0 1.4
0.12Sb0.15V/NbM 4.4 14.1 25.6 0.3 58.9 0 1.1
0.5VSb/NbM 17.8 29.2 37.8 9.4 19.8 0 3.8
1VSb/NbM 18.6 20.7 38.3 3.0 20.3 0 17.7
0.5VSb/SiNbOx 11.4 69.7 11.7 0.1 16.3 1.1 1.1
Towards 4-way catalysis James A Sullivan
UCD School of Chemistry and Chemical Biology, Belfield, Dublin 4, Ireland.
Nox and Particulate Matter (PM) remain the two most intractable emissions from diesel engines and a goal of the automotive industry is to combine strategies for their removal into a single catalytic bed. Nox is a primary and secondary pollutant contributing directly to acid rain and causing respiratory problems while contributing indirectly to photochemical smog [1]. PM defaces urban environments, carry possible carcinogens that can lodge in the alveoli of the lung and contribute to global warming (through the reduction of the albedo of arctic ice) [2].
For the past 20 years emissions from gasoline powered vehicles have been deNOxed through reduction of Nox to N2 through reduction with CO and unburned hydrocarbons (HC) present in the exhaust mixture [3]. On diesel engines the net concentration of oxidants (NO / O2) is significantly greater than that of reductants (CO/ HC) and standard three way catalysts are unable to reduce Nox so other control strategies are required [4]. The most common and effective is the Nox Storage and Reduction (NSR) system in which NO is oxidised to NO2 over a Pt catalyst and subsequently this is stored on a Nox storage material (BaO) as a nitrate (Ba(NO3)2). Once the Nox trap is saturated, a pulse of hydrocarbons regenerates it, releasing and reducing NO2 and restarts the cycle [5].
Regarding PM control technologies, the current after-treatment system relies on a particulate filter which strains larger particles from the stream followed by oxidation either with O2 through a brief high temperature excursion or with NO2 (through a C(s) + NO2 CO + NO reaction) [6].
In systems where NO2 is used to combust the particulates a Pt catalyst is added to the formulation in order to catalyse NO (which is present in the exhaust mixture) oxidation to NO2. Note that this is the same first step that operates in the NSR system described above and therefore the combination of these two systems into one catalytic bed is a possibility. Such a combination would reduce the overall volume and mass of any after-treatment systems that a diesel exhaust would require and this would have knock on effects on the fuel efficiency (and therefore the CO2 emissions per km travelled) of the vehicle. Recently promotions in soot combustion have been reported in the presence of a Nox trap [7].
In the current work we have studied combinations of Nox trapping materials and Model PM in order to determine the mechanism of this reported promotional effect and we have also studied the effects of PM on the efficiency of a Nox trap. In the former case we have determined that the localised transient increase in NO2(g) upon periodic regeneration of the trap causes the promotional effect upon soot combustion [8] while in the latter case we have, using temperature programmed techniques, transient kinetic analysis and in-situ FTIR, demonstrated that the presence of PM decreases the efficiency of a Nox trap.
The reason for the latter finding is a competition between the NO2 generated over Pt sites. In an NSR system this should adsorb on (and react with) the NOx trapping component to generate a surface nitrate. However, in the presence of PM the NO2 is reduced to NO (in the process of combusting PM) which cannot be trapped by the Nox storage component.
This confirms that in an NSR system there is significant mobility in the NO2 generated through NO oxidation which in turn suggests that the contact between the NO oxidation component and the Nox trapping component of such systems is not crucial.
References
[1] W. Kenneth, C.F. Warner, “Air Pollution, its origin and control” Harper and Row Publishers Inc. 1976 [2] J. Hansen, L. Nazarenko, Proc. Natl. Acad. Sci. 101 (2004) 423–428.
[3] K.C. Taylor, Catal. Rev. Sci. Eng., 35, (4), 457, 1993.TWC
[4] K.C. Taylor, Cat. Sci. and Tech., Anderson, J.R., Boudart, M., Ed., Springer-Verlag, 5, (1984).
[5] S. Poulston, R.R. Rajaram, Catal. Today 81 (2003) 603.
[6] A.P. Walker, Top. Catal. 28 (1–4) (2004) 165–170.
[7] F. Jacquot, J.-F. Brilhac, P. Phillips, at the 4th International Conference on Environmental Catalysis, Heidleberg, June, 2005
[8] JA Sullivan, O Keane, and A Cassidy, Applied Catalysis B: Environmental 75 (2007) 102–106.
Towards an optimization of MoVNbTe-catalysts for C3-oxidation G. Mestl
Süd-Chemie AG
Propylene is one of the key building block petrochemicals used as feedstock for a variety of polymers and intermediates. Mayjor propylene derivatives include polypropylene, acrylonitrile, propylene oxide, cumene/phenol, oxo alcohols, acrylic acid, oligomers, and other miscellaneous intermediates used, in turn in a wide range of end-use applications including automotive, construction, consumer durables, packaging, and electronics. The global propylene demand grew form 16,4 million tons in 1980 to around 30 million tons in 1990, corresponding to an average annual growth of 6,2 percent. In the decade ending in 2000, the demand grew at an average rate of 5,7 percent per year, reaching 52 million tons. Now at the end of this decade, the propylene demand has reached about 81 million tons at a growth rate of about 5,3 percent per annum. Driven by high polypropylene and other propylene derivative demand, propylene growth rate will exceed ethylene growth rate (see Fig.1 [1]).
Based on announced cracker projects olefin expansions will fall short of increased propylene demand for next few years. Future additions of predominately gas based crackers in Middle East, motivated by low NGL prices will reduce worldwide average of propylene yield from steam cracking even further. Hence, propylene demand will remain strong. There will be an imbalance between ethylene and propylene growth rate creating a propylene supply gap. The Asian gap between supply and demand is substantial and is causing very strong propylene pricing.
The acrylic acid, currently produced from propylene in a two step process, demand showed an annual growth of 4% through 2005 and the demand for acrylic acid is forecast to increase four percent per annum. Acrylate esters such as butyl, ethyl, ethylhexyl and methyl acrylates account for the majority of acrylic acid demand. These products are utilized as the acrylic monomer component in a variety of coatings, adhesives, paper and leather finishes and as co- monomers and property modifiers in plastics production. Gains will thus be stimulated by growth in demand for these end-use products, in particular industrial and specialty coatings, paper finishes and plastics additives. The producers are expected to focus their attention on the production of higher growth specialty acrylates (such as ethylene methyl acrylate); and acrylic acid polymers. The latter include superabsorbent polymers (SAPs) used in baby diapers, adult incontinence products and feminine hygiene products; water treatment polymers and detergent additives. Growth in acrylic acid demand necessitate plant expansions throughout the coming decade, strong demand for derivatives has led to very tight acrylic acid supplies on several occasions.
This increase in propylene demand (vide supra) and its derivatives, like acrylic acid, hence implied an increasing price gap to the cheaper propane in the past, rendering processes based on propane feedstock economically more viable. This expected price gap between propylene and propane promoted heavy R&D on new catalysts for the direct conversion of propane to acrylic acid during the last 20 years both in industry and academia.
Propane as such is not produced for the sake of its own it is a by-product of two other processes, natural gas, where propane (and butane) has to be extracted, and petroleum refining, where it is produced in the steam cracker. Hence, the volume of propane made available from natural gas processing and oil refining cannot be adjusted when prices and/or demand for propane fluctuate.
The main uses of propane areas follows [2]. About 38 percent of the propane consumed in the U. S. is used in the petrochemical industry. Residential and commercial use accounts for about 45 percent of all propane used most commonly to provide energy to areas not serviced by the natural gas distribution system. Farm or agricultural uses of propane, 7% of demand, include crop drying, weed control, and fuel for farm equipment and irrigation pumps. Industrial use of propane, the fourth largest propane-consuming sector, 7%, include space heating, soldering, cutting, heat treating, etc.
The demand of natural gas [3], i.e. propane, in the US, as an example, increased and will continue to increase while its production remained nearly constant, driving the propane prices upwards.
As fact, the price gap between propylene and propane did not open up as expected 20 years ago. Hence, analysts expect that the next generation acrylic acid plants will convert propylene in one step to acrylic acid instead of the current two-reactor technology, the economic realization of the propane based, 1-step process is shifted into farther future. However, it still should be further investigated for the coming post crude oil times.
References
[1] G.M. Intille, Asia Petrochemical Industry Conference, Yokohama, Japan, 2005 [2] Energy Information Administration, DOE.
[3] GSC Energy, Energy Markets Outlook, Atlanta, 2005
Silylation of titanium-containing amorphous silica catalyst: Effect on the alkenes epoxidation with H2O2
M. C. Capel-Sanchez*, J. M. Campos-Martin, J. L. G. Fierro
Instituto de Catálisis y Petroleoquímica, CSI,. c/Marie Curie, 2, Cantoblanco, 28049 Madrid.
Spain.
Introduction
Despite numerous reports in the literature, the epoxidation of terminal alkenes remains a challenge in petrochemistry. Many different methods have been developed for the preparation of epoxides. Among the non-zeolitic substrates, Ti–SiO2-supported catalysts remain prominent for their effectiveness in the epoxidation of alkenes with organic hydroperoxides, though it is generally believed that they do not effectively epoxidize alkenes with hydrogen peroxide.
Nevertheless, we have reported a very simple route for the preparation titanium-silica-supported catalysts which are very active and selective in the epoxidation of alkenes with hydrogen peroxide [1,2]. However, it has been reported that Ti-SiO2 samples show a lower intrinsic activity and lower selectivity toward the use of H2O2 for alkene oxidation than either TS-1 or Ti-β owing to their high hydrophilicity. It has been proposed that the hydrophilic/hydrophobic property of Ti zeolites plays an important role in their activity for liquid phase oxidations [1]. We have conducted silylation of Ti-SiO2 in order to enhance their activity in epoxidation with dilute H2O2
by increasing their hydrophobicity. Here, our objective is to improve the catalytic activity in the epoxidation of alkenes with H2O2 by silylation of Ti-containing amorphous silica.
Experimental Methods
Catalysts were prepared as follows: titanium isopropoxide (Aldrich, reagent grade) (0.65 g) was dispersed in 2-propanol (25 ml), the solution was heated to 353 K under stirring and then 5 g of silica (Grace Davison, XPO 2407) were added and the suspension was stirred for 2 h. The solid was filtered out and washed twice with 25 ml of 2-propanol, dried at 383 K, and finally calcined at 773 K for 5 h. Two silylant reagents: 1,1,1,3,3,3-hexamethyldisilanaze (HMDS) and tetramethyldisilazane (TMDS) were used for the silylation of the samples. The procedure was as follows: the silylant reagent fed continuously by a syringe pump to a continuous flow of N2 on the sample bed with a temperature of 473 K for 2 h, then a nitrogen flow was fed for 2 h. The silylation reagent/catalyst ratio was of 0,23.
These solids were characterized by elemental analysis, DRS UV-Vis and X-ray photoelectron spectroscopy (XPS) techniques. The catalysts were used in the epoxidation of 1-octene and cyclohexene. In a typical run, a suspension of alkene (0.2 mol), tert-butanol (11 g) and 1 g of catalyst was heated at 333 K, and then 4 g of an organic solution of 5 wt % of H2O2 (in 1 t- butanol) were added to the reaction vessel. The organic compounds were analysed by GC-FID (Hewlett Packard 6890-plus, equipped with a HP-WAX capillary column). The hydrogen peroxide was measured by standard iodometric titration.
Results and Conclusion
The elemental analysis (Table 1) shows a higher amount of carbon deposited on the catalyst when TMDS is used. This observation indicates that silylation with TMDS is more effective than HMDS. This observation can be due to the higher volume of trimethylsilane groups than dimethylsilane. DRS UV-Vis spectra (Figure 1) of the samples are similar with only slight differences. The silylated samples showed an absorption peak centered at 220 nm, typical of isolated titanium in tetrahedral coordination [4]. The slight shift in band position and the increase in bandwidth in the spectrum of reference sample point to distorted tetrahedral environment of the titanium. Solid-state 29Si MAS-NMR (Figure 2) confirmed the presence of –SiCH3 groups bound to the surface of the samples. Distinct resonances can be clearly distinguished for the siloxane units [Q3 at ≈−104 ppm for Si(Osi)3(OH) units; Q4 at ≈−114 ppm for Si(Osi)4 units]. Only two signals are observed (Q4 and Q3) on the nonsilylated catalyst. After silylation, a new signal was detected at 12,5 ppm, which can be assigned to (CH3)3Si– (Osi) in the Cat-Sil-HMDS
sample and at 20,5 assigned to (CH3)2SiH– (Osi) in the Cat-Sil-TMDS sample. The Q3/Q4 ratio (Table 1) in the reference Catalyst was estimated as 0.081. After silylation this ratio decreases.
The Cat-sil-TMDS sample exhibited the lowest ratio which indicates that the silylation coverage in this sample is higher than in the Cat-Sil-HMDS one.
Figure 1: DRS UV–vis spectra of samples Figure 2: 29Si CP-MAS NMR spectra of samples under ambient conditions.
Table 1: Carbon and hydrogen composition and Q3/Q4 ratio of samples
%C %H Q3/Q4
Cat Reference - - 0.081
Cat-Sil-HMDS 1.85 0.73 0.045
Cat-Sil-TMDS 2.20 0.86 0.039
The silylated samples showed higher conversion of hydrogen peroxide and selectivity to epoxide than the original counterpart. This effect was more evident when higher concentration of H2O2 was employed. This effect could be attributed to the higher hydrophobicity of silylated sample. Silylation treatment of Ti/SiO2 catalysts enhances significantly the activity in the expoxidation of alkenes with H2O2. The use of TMDS in the extend of the silylation is higher with TMDS than with HMDS as a consequence of the smaller size of the former sylilating agent.
References
[1] M. C. Capel-Sanchez J. M. Campos-Martin, J. L. G. Fierro, M. P. de Frutos, A. Padilla Polo, Chem. iuse., (2000) 855-856
[2] M. C. Capel-Sanchez, J. M. Campos-Martin, and J. L. G. Fierro, J. Catal., 217 (2003) 195–202 [3] T. Tatsumi, K. A. Koyano and N. Igarashi, Chem. iuse., (1998) 325-326
[4] V. A. de la Peña O’Shea, M. C. Capel-Sanchez, G. Blanco-Brieva, J. M. Campos-Martin, J. L. G. Fierro, Angew.
Chem. Int. Ed. 42 (2003) 5851-5854
200 300 400
Cat Reference Cat-Sil-HMDS Cat-Sil-TMDS
F (R)
λ (nm) -140 -130 -120 -110 -100 -90 -30 -20 -10 0 10 20 Cat-Sil-TMDS
δδδδ (ppm) Cat-Sil-HMDS
Cat Reference O Si C H3 CH3
CH3
O Si H CH3
CH3
