Université de Poitiers SFA- IC2MP
Bâtiment B27 – Bureau 237
4, rue Michel Brunet (B27)
Tél. : +33 (0)5 49 45 34 79
Fax : +33 (0)5 49 45 33 78
Courriel : sebastien.royer[at]univ-poitiers.fr
Syntheses oxides and mixed oxides-mass (complexation, coprecipitation, combustion, non-aqueous routes …)
Synthesis of porous supports for catalysis
Optimization of deposition techniques of active phases of oxide / oxide mixed
Reactive oxygen species and surface oxides network
E1. Mixed oxides mass
Perovskites are mixed compounds of general formula ABC3, some compositions are known from the early 70s to their activities in oxidation of volatile organic compounds (Voorhoeve et al. Science 177 (1972) 353). Different mechanisms of oxidation are defined in the literature by the reaction of oxidation is carried out at low temperature (typically in the case of the oxidation of CO or light alcohols) or high temperature (the case of the oxidation of hydrocarbons refractory as CH4). The study of the mobility of oxygen species led to the development of a model (Figure 1) distinguishing between:
- Mobility of surface oxygen
- Oxygen mobility of grain boundaries, and discontinuities in crystals known to be preferential diffusional paths
- Mobility of oxygen the heart crystals, or oxygen network cristall
The CO oxidation activity correlates easily responsiveness oxygen perovskite surface. Contrary to what is observed for the oxidation of CO, methane oxidation activity is in turn connected to the mobility of lattice oxygen (3 and 3 ‘, Figure 1).
However, it is difficult to obtain pure perovskite with (ie, undoped a noble metal) activities comparable to those obtained with conventional catalysts for the oxidation of Pt and / or Pd/Al2O3 (Royer et al. Catal. Today 117 (2006) 543). Unfortunately, the addition of noble metal does not provide a significant improvement in the catalytic activity. More encouraging results have been obtained by doping type structures hexaaluminate (ABaAl10O19-y, with A = Mn, Co, Fe). Indeed, some hexaaluminate substituted by transition metals are known to exhibit interesting catalytic activities for high-temperature combustion of methane, and exhibit excellent thermal stabilities. The thermal stability is also a recurrent problem when using catalysts based on noble metal. Thus, we were able to get some combinations noble metal (mainly Pd) – pseudo hexaaluminate (Mn doped) showed catalytic activities equal to those of conventional catalysts Pd/Al2O3, but showed no deactivation observed as the catalyst for classical . The incorporation of noble metal in the mixed-oxide structure is currently underway (S. Laassiri, Catal. Sci. Technol. 2011). These materials exhibit catalytic activities in low-temperature oxidation greatly improved.
E2. Synthesis of porous supports for catalysis
Alumina is a medium widely used in heterogeneous catalysis and synthesis mesostructuring modes are much less common in the literature for the synthesis of silica. Among the results obtained on alumina include for example the use of mesostructured alumina with high specific surface areas and morphologies (nodular fibrillar 2D hexagonal porosity) (Bejenaru et al. Chem. Mater. 21 (2009 ) 522). Thus, the use of the mesostructuring provides improved physical properties of the alumina. It is possible to easily obtain, after calcination at 600 ° C, specific surface areas greater than 400 m2 / g and having pore sizes in the range of mesopores large (> 6 nm). These improvements allow the production of MoS2 sheets of smaller size, and in some cases modify the degree of stacking of these sheets. All these parameters can dramatically improve the catalyst activity.
A significant improvement in catalytic performance of catalysts CoMo-S has been obtained for the reaction of HDS of gas oils. More recently, we have developed in collaboration with Cardiff University, a synthesis method for obtaining macro-mesoporous alumina organized for the synthesis of biodiesel (Dacquin et al. J. Am. Soc. 131 ( 2009) 12896). Indeed, several studies reported diffusional problems related to the pore size of the catalyst in the case of this application. Thus, it is proposed that the addition of a macroporous network wide, and decrease the length of mesoporous channels, allows the elimination of this problem and getting more active catalysts.
We also develop laboratory composite type titanium on silica mesostructured to support applications such as hydrogenation / dehydrogenation and hydrodesulfurization. While it is difficult to prepare titanium oxides of high specific surface area (> 200 m2 / g) thermally stable (at temperatures compatible for use in heterogeneous catalysis), it is possible to prepare titania-silica composite high specific surfaces. These composites have a morphology of nanocrystals anatase dispersed in the pores of a mesoporous silica. This work was conducted as part of a thesis (M. Good, Thesis, University of Poitiers, 10/2010).
E3. Dispersion of oxides and oxide-mixed porous
One of the limitations encountered in the use of the mixed oxides in the catalyst is generally small specific surface area obtained on such compounds. The example of perovskites is speaking as obtaining surface areas greater than 20 m2 / g is rarely reported in the literature. These small surface areas are generally due to crystallite size greater than 15-20 nm, because of high calcination temperatures necessary for the crystallisation of the desired phase.
It was however observed that the decrease in crystallite size allowed an increase in specific surface area of solids, and in some cases allowed the increase of the specific activity of the oxide. Thus, a decrease in the crystallite size of LaCoO3 allowed a significant increase in the mobility of the lattice oxygen, a key parameter to obtain high catalytic activities. It is therefore understandable why the control of the growth of crystallites with their goal size limitation values below 10 nm, is a real challenge for the field of heterogeneous catalysis.
Example nanoparticle supported mixed oxide synthesized in the laboratory. TEM image and EDX spectrum obtained for Ce0.33Ni0.66Oy. Quantification is given in at.%
The approach we have developed in our laboratory is to limit the growth of crystallites in an inorganic matrix. Thus, a series of perovskite lanthanum-based position A and transition metals in position B, the crystallite sizes below 5 nm was prepared by a novel method Autoignition in a mesostructured silica HMS-type (having a pore size of about 3 nm). The compounds obtained have been extremely active than the reference compounds for the activation and diffusion of oxygen (Good et al. Chem. Commun. (2008)). This was also verified that the oxygen mobility is closely related to the particle size of the oxide. Following this work, similar syntheses were carried out in support of broader mesostructured porosity (up to 9 nm pore size).
mesoporous solids, mixed oxides, environmental catalysis, nanoparticles, oxygen mobility
– * University of Sciences and Technologies of Lille, UCCS – Prof. E. Payen, Pr J.F. Lamonier, Prof. F. Dumeignil
– * University Laval (Québec, Canada) – Professor Houshang Alamdari
– * University of Cardiff (Great Britain), SMAC Laboratory – Prof. Adam F. Lee, Professor Karen Wilson
– * Wuhan University (China), Dept. of Environmental Engineering – Prof. Zhang Hui
– * University of Chemical Technology (Beijing, China), Dept. of Chemical Engineering – Prof. Zhang Runduo
– * IFPEN, Dpt divided materials – Dr. L. Roll
– * University of IASI (Romania) – Prof. A. Ungureanu and Prof. E. Dumitriu
– * Since 2009: Associate Professor, Department of Mining, Metallurgy and Materials – Université Laval (Quebec – Canada)
– * 2011: Habilitation Research – University of Poitiers
– * 2012: Leader of the thematic cross “Natural Materials and Synthesis” IC2MP (Institute of Chemistry of materials and environments Poitiers)
– S. Royer, X. Sécordel Mr. Brandhorst, F. Dumeignil, S. Cristol, C. Dujardin, M. Capron, E. Payen, J.-L. Dubois, Amorphous oxide as a novel efficient catalyst for selective oxidation of methanol directly to dimethoxymethane, Chem. Common. (2008) 865.
– N. Bejenaru, C. Lancelot, P. Blanchard, C. Lamonier, L. Rouleau, E. Payen, F. Dumeignil, S. Royer, Synthesis, characterization and catalytic performance of CoMo hydrodesulfurization catalysts supported novel mesoporous aluminas is, Chem. Mater. 21 (3) (2009) 522.
– J-P. Dacquin, J. Dhainaut, S. Royer, D. Duprez, K. Wilson, A. F. Lee, An efficient route to Obtain highly-organized mesoporous alumina-macroporous, J. Am Chem. Soc. 131 (2009) 12896.
– M. Good, D. Sellam Dacquin J.-P., A. F. Lee, K. Wilson, A. Cognini, P. Marecot, S. Royer, D. * Duprez, In-situ autocombustion as a simple and efficient route to synthesize nanocrystalline oxides and supported mixed-oxides, Chem. Common. 47 (2011) 1509.
– S. Royer, D. Duprez, REVIEW: Catalytic Oxidation of Carbon Monoxide over Transition Metal Oxides, ChemCatChem 3 (2011) 24.
– B. Katryniok, S. Paul M. Capron, S. Royer, C. Lancelot, L. Jałowiecki Duhamel, V. Bellière-Baca, P. Rey, F. Dumeignil, Synthesis and characterization of zirconia-Grafted SBA-15 nanocomposites, J. Mater. Chem. 21 (2011) 8159.
– A. Ungureanu, B. Dragoi, A. Chirieac, S. Royer, D. Duprez, E. Dumitriu, Synthesis of highly thermostable copper-nickel nanoparticles confined in the channels of mesoporous SBA-15 ordered silica, J. Mater. Chem. 21 (2011) 12529.