108 research outputs found
The control of selectivity in rutile-type Sn/V/Nb/Sb mixed oxides, catalysts for propane ammoxidation
No full textThe control of catalytic performance of rutile-type Sn/V/Nb/Sb mixed oxides, catalysts for propane ammoxidation to acrylonitrile
No full textArcozzi, Elena Ballarini, Nicola Cavani, Fabrizio Cimini, Massimo Lucarelli, Carlo Trifiro, Ferruccio Delichere, Pierre Millet, Jean-Marc M. Marion, PhilippeInternational audienceThis paper describes the effect of the composition of rutile-type Sn/V/Nb/Sb mixed oxides catalysts on the catalytic performance in the gas-phase ammoxidation of propane to acrylonitrile. The variation in the atomic ratio between components in catalysts is the key for the control of activity and selectivity. In samples with atomic composition Sn/V/Nb/Sb 1/0.2/1/x (0 <= x <= 5) and 1/0.2/y/3 (0 <= y <= 3) several compounds formed, i.e., SnO2, Sb/Nb mixed oxide, Sb6O13 and non-stoichiometric rutile-type V/Nb/Sb/O; the latter segregated preferentially at the surface of the catalyst. Tin oxide provided the rutile matrix for the dispersion of the mixed oxides. The main role of Sb was shown to generate mixed oxides containing specific sites for the allylic ammoxidation of propylene intermediately formed. The presence of Nb enhanced the activity and selectivity of these sites. (C) 2008 Elsevier B.V. All rights reserved
The control of catalytic performance of rutile-type Sn/V/Nb/Sb mixed oxides, catalysts for propane ammoxidation to acrylonitrile
No full textThis paper describes the effect of the composition of rutile-type Sn/V/Nb/Sb mixed oxides catalysts on the
catalytic performance in the gas-phase ammoxidation of propane to acrylonitrile. The variation in the
atomic ratio between components in catalysts is the key for the control of activity and selectivity. In
samples with atomic composition Sn/V/Nb/Sb 1/0.2/1/x (0 x 5) and 1/0.2/y/3 (0 y 3) several
compounds formed, i.e., SnO2, Sb/Nbmixed oxide, Sb6O13 and non-stoichiometric rutile-type V/Nb/Sb/O;
the latter segregated preferentially at the surface of the catalyst. Tin oxide provided the rutile matrix for
the dispersion of the mixed oxides. The main role of Sb was shown to generate mixed oxides containing
specific sites for the allylic ammoxidation of propylene intermediately formed. The presence of Nb
enhanced the activity and selectivity of these sites
Hydrodeoxygenation of guaiacol Part II: Support effect for CoMoS catalysts on HDO activity and selectivity
No full text3-4 Van Ngoc Bui Laurenti, Dorothee Delichere, Pierre Geantet, ChristopheBio-oils coming from ligno-cellulosic biomass are suitable material for the production of second generation biofuels. The oxygenated compounds have to be eliminated to confer good properties to these bio-oils and to permit their addition to traditional fuels. Hydrodeoxygenation (HDO) process which allows O-elimination by C-O bond cleavage under H-2 can be realized with the same type of catalysts as those used in HDS, supported CoMoS or NiMoS phases. In this work, the support effect associated with CoMoS catalysts has been investigated in guaiacol HDO reaction. Zirconia and titania supports have been compared with the traditional industrially used gamma-alumina and it appeared that zirconia as support gave very efficient conversion of guaiacol into deoxygenated hydrocarbons with a totally different selectivity. The difference in selectivity allowed us to propose a different reaction scheme compared to gamma-alumina and titania supported CoMoS. (c) 2010 Elsevier B.V. All rights reserved
The effect of Sb and Nb content on catalytic performance of rutile-type Sn/V/Nb/Sb/O, catalysts for propane ammoxidation
No full textLocal environment of vanadium in V/Al/O-mixed oxide catalyst for propane ammoxidation: Characterization by in situ valence-to-core X-ray emission spectroscopy and X-ray absorption spectroscopy
No full textSafonova, O. V. Florea, M. Bilde, J. Delichere, P. Millet, J. M. M.The local environment of vanadium in V/Al/O amorphous oxide catalyst has been studied under propane ammoxidation reaction conditions. In situ valence-to-core X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) at the V K-edge showed that acrylonitrile production starts when vanadium in the bulk structure of the oxide material changes its formal oxidation state from +4.8 to +3.8 +/- 0.1. Exposure of the catalyst to pure NH3 at 500 degrees C leads to further reduction of vanadium. Valence-to-core XES has also proved that the level of bulk nitridation of vanadium in the active catalyst was rather small. XPS analysis performed ex situ after the catalytic tests confirmed the presence of significant amounts of N3-, NHx, and -NN- species on the catalyst surface. it can be concluded that activation of V/Al/O catalyst on-stream is mainly associated with reduction of vanadium in the bulk structure of the material and nitridation of vanadium atoms on the surface. (C) 2009 Elsevier Inc. All rights reserved
La(1-x)SrxCo1-yFeyO3 perovskites prepared by sol-gel method: Characterization and relationships with catalytic properties for total oxidation of toluene
No full textRousseau, S. Loridant, S. Delichere, P. Boreave, A. Deloume, J. P. Vernoux, P.La(1-x)SrxCo(1-y)FeyO3 samples have been prepared by sol-gel method using EDTA and citric acid as complexing agents. For the first time, Raman mappings were achieved on this type of samples especially to look for traces of Co3O4 that can be present as additional phase and not detect by XRD. The prepared samples were pure perovskites with good structural homogeneity. All these perovskites were very active for total oxidation of toluene above 200 degrees C. The ageing procedure used indicated good thermal stability of the samples. A strong improvement of catalytic properties was obtained substituting 30% of La3+ by Sr2+ cations and a slight additional improvement was observed substituting 20% of cobalt by iron. Hence, the optimized composition was La0.7Sr0.3Co0.8Fe0.2O3. The samples were also characterized by BET measurements, SEM and XRD techniques. Iron oxidation states were determined by Mossbauer spectroscopy. Cobalt oxidation states and the amount of O- electrophilic species were analyzed from XPS achieved after treatment without re-exposition to ambient air. Textural characterization revealed a strong increase in the specific surface area and a complete change of the shape of primary particles substituting La3+ by Sr2+. The strong lowering of the temperature at conversion 20% for the La0.7Sr0.3Co(1-y)FeyO3 samples can be explained by these changes. X photoelectron spectra obtained with our procedure evidenced very high amount of O- electrophilic species for the La0.7Sr0.3Co(1-y)FeyO3 samples. These species able to activate hydrocarbons could be the active sites. The partial substitution of cobalt by iron has only a limited effect on the textural properties and the amount of O- species. However, Raman spectroscopy revealed a strong dynamic structural distortion by Jahn-Teller effect and Mossbauer spectroscopy evidenced the presence of Fe4+ cations in the iron containing samples. These structural modifications could improve the reactivity of the active sites explaining the better specific activity rate of the La0.7Sr0.3Co0.8Fe0.2O3 sample. Finally, an additional improvement of catalytic properties was obtained by the addition of 5% of cobalt cations in the solution of preparation. As evidenced by Raman mappings and TEM images, this method of preparation allowed to well-dispersed small Co3O4 particles that are very efficient for total oxidation of toluene with good thermal stability contrary to bulk Co3O4. (C) 2008 Elsevier B.V. All rights reserved
caractérisation de surfaces de catalyseurs en conditions quasi in situ (conférence invitée)
No full textSSCI-VIDE+Equipe-Vide+PDENational audienceNon
caractérisation de surfaces de catalyseurs en conditions quasi in situ (conférence invitée)
No full textSSCI-VIDE+Equipe-Vide+PDENational audienceNon
An alternative route to synthesize acrylic acid: the dehydration of lactic acid and lactates over alkaline earth phosphates
No full textRMN:XPS+ECI2D+CLO:PDE:JMI:SLOInternational audienceIntroductionAcrylic acid is a key platform molecule whose main applications are superabsorbent polymers (diapers), paints, coatings, adhesives and flocculating agents for water treatment. It is produced at 4.5 Mt/year by selective oxidation of propene, whose price is growing quickly because of increasing demand and rarefaction of petroleum. Several alternative sustainable routes are investigated at the present time. Among them, dehydration of lactic acid and lactates are interesting since these reactants can be yielded both by dehydrogenation of glycerol, a by-product of bio-diesel production and directly by fermentation of sugars.In spite of first study in 1958 [1], dehydration of lactic acid (LA) and derivatives have been mostly investigated since recent years with the rise of biomass valorization. High yields to acrylic acid (AA) and derivatives were obtained using modified zeolites [2] or calcium phosphates [3-4]. However, zeolites suffer from hydrothermal instability.In this work, different alkaline earth phosphates were prepared and evaluated for dehydration of lactic acid to acrylic acid. Because of high LA reactivity, the ethyl lactate (EL) conversion was also investigated. The origin of catalytic efficiency was explained from acido-base properties and the nature of the active sites present in such catalysts. Materials and MethodsAlkaline earth ortho, pyrophosphates and hydroxyapatites were prepared by co-precipitation method. Their labeling was described elsewhere [5]. The solids were characterized by XRD, FTIR spectroscopy, BET measurements and ICP analysis. Furthermore, surface characterization was obtained crossing XPS, 1H-31P CP-MAS NMR, TEM and IR techniques. Acid-Base properties were measured by NH3/CO2-TPD respectively and adsorption of probe molecules followed by FTIR. Gas phase dehydration of ethyl lactate or lactic acid was conducted in a fixed bed reactor at atmospheric pressure. Solutions of reactant were vaporized at 160-170°C and diluted with N2 before sending to the top of the reactor. After trapping, the condensed molecules were analyzed off-line with a GC chromatograph while gas products were analyzed on line. Results and DiscussionIn first step, the influence of reaction parameters was investigated: selectivity to acrylic acid strongly depends on the reaction temperature but not on the contact time. At optimized temperature of 380°C, values ranging from 19 to 49% were measured for the different prepared phosphates catalysts that are stable for at least 24 h. The best yield (43%) was obtained from barium orthophosphate [5]. Acidâbase properties determined from NH3 and CO2 TPD measurements revealed that such phosphates contain high proportion of acidic and basic sites with same weak strength. Furthermore, correlation between selectivity to acrylic acid and the acidâbase balance was clearly established: it was 50% for balance close to 1 and decreased increasing this parameter [5]. Dehydration of ethyl lactate appeared as promising reaction in spite of lower conversions. Indeed, selectivity values in dehydration products (AA and ethyl acrylate (EA)) were much higher with maxima of 87%. The evolution of selectivity sets with the conversion revealed that AA is mainly formed by simultaneous dehydration/hydrolysis reaction. However, the catalysts were unstable vaporizing pure EL solution because of polymerization of EA leading to coke formation. Interestingly, it was shown that deactivation can be inhibited adding water to the gas phase [6]. XPS characterization of the catalysts evidenced the presence at the surface of P-rich phase that corresponds to amorphous overlayer of few nanometers as evidenced by TEM. From XPS, 1H-31P CPMAS and DRIFT spectra, it was concluded that such phase contains high quantity of POH species and could correspond to a mixture of mono and dihydrogenophosphates or polyphosphates. In situ DRIFT spectra have revealed that POH species are formed under water vapor whereas they are consumed or modified under reaction mixture for both reactants suggesting that they involved in one step of the reaction mechanism. Finally, NH3 and CO2-TPD measurements followed by in situ DRIFT spectroscopy revealed that acid base pairs (M2+; P=O) and P=O basic sites are respectively probed by these techniques. The acid-base balance of 1 obtained for the most selective catalysts was explained by the involvement of (M2+; P=O) pairs in the rate-determining step of the reaction mechanism. Finally, the monitoring of POH isotopic labeling under reaction feed revealed proton transfer to the methyl group of lactic acid. From all these results, it was proposed that (M2+; P=O) pairs would constitute the adsorption site of lactic acid which then dehydrate in acrylic acid by an E2 mechanism involving POH species. ConclusionsSelectivity to acrylic acid is limited for dehydration of lactic acid over alkaline earth phosphates. Very high selectivity to dehydration products can be obtained using ethyl lactate as reactant but high specific surface area is required to reach high yield. Water vapor has to be added to the reaction feed in good proportion to avoid catalyst deactivation and reactant hydrolysis leading to lower selectivity. Finally, crossing different techniques and from in situ experiments, it was proposed that (M2+; P=O) pairs are the active and selective sites in such catalysts. These findings will allow designing more efficient catalysts.Acknowledgements This work was supported by French ANR Program Chimie Durable â Industries â Innovation (CD2I) GALAC, a joint project between IRCELYON, UCCS, LC/ENS-Lyon and Novance company.References [1]R.E. Holmen, US Patent 2859240, 1958.[2]J.Zhang, Y.Zhao, M. Pan, X. Feng, W. Ji, C. Au, ASC Catal., 1 (2011) 32.[3]J. H. Hong, J.-M. Lee, H. Kim, Y. Kyu Hwang, J.-S. Chang, S. B. Halligudi, Y.-H. Han, App. Catal A, 396 (2011) 194.[4]V.C. Ghantani, S.T. Lomate, M.K. Dongare and S.B. Umbarkar, Green Chemistry, 15 (2013) 1211.[5]E. Blanco, P. Delichere, J.M.M. Millet, S. Loridant, Catal. Tod. 226(2014)185â191.[6]E. Blanco, P. Delichere, C. Lorentz, L. Burel, C. Pinel, M. Vrinat, J.M.M. Millet, S. Loridant, Appl. Catal. B : Environm.,180 (2016) 596
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