Direct dehydration of 1,3-butanediol into butadiene over aluminosilicate catalysts

The catalytic dehydration of 1,3-butanediol into butadiene was investigated over various aluminosilicates with different SiO2/Al2O3 ratios and pore architectures. A correlation between the catalytic performance and the total number of acid sites and acid strength was established, with a better performance for lower acid site densities as inferred from combined NH3-TPD, pyridine adsorption and 27Al-NMR MAS spectroscopy. The presence of native Brønsted acid sites of medium strength was correlated to the formation of butadiene. A maximum butadiene yield of 60% was achieved at 300 °C over H-ZSM-5 with a SiO2/Al2O3 ratio of 260 with the simultaneous formation of propylene at a BD/propylene selectivity ratio of 2.5. This catalyst further exhibited a slight deactivation during a 102 h run with a decrease in the conversion from 100% to 80% due to coke deposition as evidenced by XPS and TGA-MS, resulting in a 36% loss of the specific surface area

Novel Integrated Method for Direct Acetone Synthesis in Liquid Phase from Propane and Molecular Oxygen with in situ Generated Hydrogen Peroxide

internationa

Comparison Between SBA-15 and MCM-41 Structure on the Stability and the Selectivity of Basic Catalysts in Oligomerization of Glycerol

RAFFINAGE+LRA:CLOThe oligomerization of glycerol to di- and triglycerol is an attractive reaction because these products find many applications in cosmetics, food industry and polymer industry. To control the oligomerization degree, it is necessary to develop a selective catalyst. In this work, two cesium mesoporous silica (MCM-41 and SBA-15) are compared in the selective oligomerization of glycerol into di- and triglycerol. The catalysts were prepared by incipient-wetness impregnation. The results showed that the stability and the activity of catalysts depend on the support nature. The use of SBA-15 support instead of MCM-41 leads to a more stable catalyst without changing polyglycerols selectivity. Different characterizations showed that it is due to the larger wall thickness of SBA-15. This study also showed that the nature of catalyst could influence the diglycerol isomers distribution. In fact the glycerol activation inside or outside the pores can strongly modify the selectivity to linear or branched diglycerol isomers

Studies on MeAPSO-5: An investigation of physicochemical and acidic properties

Oliveira, Alcineia C. Essayem, Nadine Tuel, Alain Clacens, Jean-Marc Ben Taarit, Younes 20th Ibero American Catalysis Symposium SEP 17-22, 2006 Gramado, BRAZILThis work reports physicochemical and acidic properties of MeAPSO-5 (Me = chromium or iron), regardless their performance in the production of isobutane. Chromium and iron were partially introduced in SAPO-5 by direct hydrothermal synthesis. The solids were characterized by XRD, chemical analysis, N-2 adsorption isotherms, EPR, XPS, and calorimetry of ammonia adsorption. Their activity was also evaluated in the isomerization of n-butane. The purity of hydrothermally synthesized SAPO-5 was identified in all solids. EPR and XPS showed that chromium and iron exist as Cr2O3 and Fe2O3, respectively, mostly distributed on the solid surface. However, no reflections characteristic of these oxides were found in the XRD patterns. The chromium and iron cause different effects on the acidity: chromium increases the solid acidity whereas iron reduces drastically the acidic features. While distinct activity were observed between CrSAPO-5 and the FeSAPO-5 in n-butane isomerization, it is noteworthy that the pure SAPO-5 is not active in the reaction due to the too low strength of its acid sites. Results suggest that the n-C-4 isomerization activity of CrSAPO-5 may be ascribed to its enhanced acidity while, contrary to what was observed in the case of mordenite or sulfated zirconia, Iron addition to SAPO-5 did not enhance the catalytic activity via a possible participation of redox steps. (c) 2007 Elsevier B.V. All rights reserved

Structural, acidic and catalytic features of transition metal-containing molecular sieves in the transformation of C-4 hydrocarbon

MATERIAUX+ATU:NESNon

Highly selective direct amination of primary alcohols over a Pd/K-OMS-2 catalyst

A new Pd-substituted octahedral molecular sieve (Pd/K-OMS-2) catalyst has been prepared for the direct amination of alcohols with primary amines operating under the borrowing hydrogen mechanism. The catalyst offered full conversion and high selectivity toward N-benzylaniline in the model alkylation reaction of aniline with benzyl alcohol at mild temperature (160 °C) for 3 h with neither production of the tertiary amine nor toluene. Pd/K-OMS-2 performed as a tandem tri-functional catalyst, first oxidizing benzyl alcohol to benzaldehyde, behaving as a Lewis acid for imine formation, and finally reducing the imine to the secondary amine. The catalyst was characterized in depth using BET, XRD, H2-TPR, XPS, FTIR, TEM, TGA/DTG, and ICP-AES / EDX to elucidate the nature of the active sites. The unexpectedly high performance of the Pd/K-OMS-2 catalyst can be ascribed, at least partially, to the in situ generation of a very active, selective and partially recyclable Pd-substituted/supported hausmannite phase (i.e., Pd/Mn3O4) in the early stage of the reaction with a high density of surface oxygen moieties. We argue about a possible role of a Pd(IV)/Pd(II) redox pump for exchanging hydrogen during the amination reaction

Microcalorimetric measurement of the acid properties of pillared clays prepared by competitive cation exchange

International audienceThe competitive ion exchange of polycations has been used to prepare well ordered Ti, and Fe-pillared clays of high specific surface area from montmorillonite, and from a beidellitic clay either natural or acid treated. The competitor are Al polycations added to the pillaring solutions. The method has been applied to unpurified natural clays, giving PILCs with surface areas of around 250 m2/g after drying at 523 K. The thermal stability of the resulting solids is increased with surface areas as high as 130–220 m2/g after calcination at 773 K. The competitive ion exchange has been also applied to acid treated clays, with surface areas of the PILC reaching 200 m2 g−1. The acid properties of these PILC, determined by microcalorimetry using NH3 adsorption, are comparable to those of zeolites or supported heteropolyacids, with initial heats of adsorption of 150–160 kJ mol−1 and site density of around 2 μmol/m2. This acidity overpass that of pillared montmorillonites and saponites prepared by a conventional method. The acid-activated clays pillared by this procedure show a lower acidity than the pillared materials obtained from natural clays

Competitive Adsorption of NOx and Ozone on the Catalyst Surface of Ozone Converters

International audienceFour catalysts—1%Pd-2%Mn/γ-Al2O3, 1%Pd/γ-Al2O3, 2%Mn/γ-Al2O3 and γ-Al2O3—were synthesized via a sol–gel method and characterized using various techniques to evaluate their physicochemical, textural, surface and acidic properties. They were used in the catalytic transformation of ozone and nitrogen oxides using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. Different consecutive gas sequences were followed to unravel the poisoning role of nitrogen oxides and the possible reactivation by ozone. It has been proven that on palladium and manganese-based catalysts, the inhibition effect of nitrogen oxides was due to the formation of monodentate nitrites, monodentate, bidentate and bridged nitrates, which are difficult to desorb and decompose into gaseous NOx, either by oxidation or by thermal treatment. Interestingly, monodentate nitrites could be eliminated if the catalyst went through a co-adsorption of NOx and ozone prior to exposure in clean ozone flow. This transformation could be the reason why the catalytic conversion of ozone could return to its original value before the poison effect of nitrogen oxide