Enrique Sastre

Synthesis, characterization and catalytic activity of MCM-41-type mesoporous silicas functionalized with sulfonic acid

This paper reports the results obtained in the synthesis, characterization and catalytic activity of thiol-MCM-41 materials synthesized using an improved method of preparation. This novel method of synthesis includes the partial replacement of the surfactant used previously — hexadecyltrimethylammonium bromide, for a shorter chain surfactant such as dodecyltrimethylammonium bromide. It also includes the use of tetramethylammonium hydroxide (TMAOH) as co-structuring agent instead of NaOH. The materials obtained from this modified gels present a higher order in the channels arrangement confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. These materials incorporates an important amount of thiol groups which can be oxidized with H2O2 in order to obtain the corresponding sulfonic groups, with a very strong acidity. The catalysts so obtained have been tested in the esterification of glycerol with fatty acids — oleic and lauric. The results obtained indicate that the catalysts prepared with mixtures of surfactants are more selective to the monoglycerides than the ones synthesized only with hexadecyltrimethylammonium bromide, probably due to the higher order in the channels packing.

Selective synthesis of fatty monoglycerides by using functionalised mesoporous catalysts

Abstract This work describes the performance of “functionalised ordered mesoporous materials” in the esterification of glycerol with fatty acids, such as lauric and oleic acids. The influence of several properties of the catalysts on their activity and monoglyceride selectivity is discussed. For the MCM-41 structure synthesised by the co-condensation method, the influence of the gel composition, hydrophobicity, nature of the functional group and pore size is presented. The catalytic behaviour of structures like SBA-15, SBA-12 and SBA-2 functionalised with mercaptopropyl groups is also discussed.

Evidence for the presence of a bimolecular pathway in the isomerization of xylene on some large-pore zeolites

Using deuterated para-xylene as a reactant we have found that more than 20% of the meta- and ortho-xylenes, obtained when using a HY zeolite as catalyst, are formed via a bimolecular mechanism. This involves, as an intermediate complex, a molecule of trimethylbenzene and another of xylene. The bimolecular process is less important in the case of mordenite, and does not occur in Zeolite Beta at low levels of conversion. The relative proportion of uni- to bimolecular mechanism depends on: reaction conditions, zeolite composition, and zeolite structure. Some of the mechanistic conclusions, reached when using xylene isomerization and transalkylation as a test reaction on faujasite zeolites, should be revised in light of these results. Finally, transalkylation between trimethylbenzenes and xylenes is proposed as a test reaction for 12 membered-ring (MR) zeolites since structural differences can be better established than when the conventional xylene isomerization-transalkylation reaction is used.

Selective synthesis of glycerol monolaurate with zeolitic molecular sieves

The purpose of this work, is to study the selective synthesis of glycerol monolaurate from lauric acid and glycerol as starting materials, employing commercial Beta, Y and Mordenite zeolites with different Si/Al ratio as catalysts. Reaction conditions such as the stirring rate, temperature, glycerol/lauric acid ratio and catalyst mass in the reaction medium were optimized to diminish homogeneous reaction and reaction limitations due to diffusive effects. In the case of zeolite Y, an increase in glycerol monolaurate yield and selectivity for the monoester were verified at high Si/Al ratio. This behavior seems to be related to the presence of stronger acid sites present in the material with low Al content and probably also because of the higher hydrophobicity exhibited by zeolites having higher Si/Al ratio. Mordenite catalyst, on the contrary, presented low activity and selectivity to glycerol monolaurate, which can be attributed to the diffusional limitations imposes by the monodimensional channel system to the organic substrate accessing the inner catalyst sites, restricting the reaction to the sites present at the external particle surface. Zeolite Beta exhibited the best results as catalyst to obtain the mono-derivative, presenting selectivities higher than 60% at 20% yield.

Synthesis of MCM-41 materials functionalised with dialkylsilane groups and their catalytic activity in the esterification of glycerol with fatty acids

The synthesis of MCM-41-type materials functionalised with 3-mercaptopropyl(methyl)Si groups has been performed by co-condensation of the corresponding alkoxysilanes and tetramethoxysilane (TMOS), in the presence of CTAB and the amino acid leucine. The materials were oxidised to [CH3,SO3H]-MCM-41, characterised and tested as acid catalysts in the esterification of glycerol with fatty acids as lauric and oleic acids. A comparison with the performance of already reported CH3/SO3H-MCM-41 catalysts is presented.

Beckmann rearrangement of cyclohexanone oxime on zeolites

The Beckmann rearrangement of cyclohexanone oxime (1) was carried out in the liquid phase in the presence of a series of acid zeolites (HY-20, HY-50, HY-100, HYD, and HZSM-5) at different reaction temperatures. Together with e-caprolactam ( 2 ), 5-cyano-1-pentene ( 3 ), and cyclohexanone ( 4 ) were present in the reaction mixtures. From the selectivity curves of 2 and 3, it can be concluded that a Ritter equilibrium between 2 and 3 occurs under our experimental conditions, the direction of the process depending strongly on the hydrophobicity of the catalyst. The influence of the level of Na + exchange and of the framework Si/Al ratio on the total conversion and the selectivity of 2 reveals that medium and strong acid sites (p K a

Microwave-assisted synthesis of plate-like SAPO-34 nanocrystals with increased catalyst lifetime in the methanol-to-olefin reaction

Nanocrystalline SAPO-34 catalysts were obtained using microwave-assisted hydrothermal synthesis. Compared to conventional heating, the use of microwave irradiation shortened the crystallization time from days to several hours, resulted in a lower level of silicon incorporation, which led to slightly lower acidity, and modified the crystal size and morphology. The SAPO-34 catalyst synthesized in a microwave oven exhibited a longer lifetime in the methanol-to-olefin reaction due to its thin plate-like crystal morphology, which facilitates accessibility of the reactant to the acid sites.

Effect of calcination temperature on structural properties and catalytic activity in oxidation reactions of LaNiO3 perovskite prepared by Pechini method

The study presented the preparation of the perovskite oxide LaNiO3 by the complex citrate method,paying particular attention to evolution of its formation from the amorphous precursor with varied calcination temperatures.The products obtained after heat treatment under air between 200 and 800 ℃ were characterized by X-ray diffraction (XRD),thermogravimetric and differential thermal analysis (TG-DTA),Fourier transform infrared spectroscopy (FTIR),SBET measurements and X-ray photoelectron spectroscopy (XPS).The results showed the formation of a single phase with perovskite structure from ca.550 ℃.Tests on the two catalytic oxidation reactions of C3H6 and CO over the system calcined between mentioned temperatures were examined on the basis of characterization results and showed that optimum catalytic properties for such reactions were achieved for the perovskite calcined at 600 ℃.In turn,correlations between redox and catalytic properties were established on the basis of thermogravimetric temperature programmed reduction (TPR) analysis.

A novel synthesis route of well ordered, sulfur-bearing MCM-41 catalysts involving mixtures of neutral and cationic surfactants

The effect of the addition of dodecylamine in the direct synthesis of MCM-41 silica bearing propylthiol groups, and using cetyltrimethylammonium bromide as surfactant, is studied. The presence of neutral head groups with shorter chains, helps the propylthiol groups to accommodate better into the micelles improving the nucleation and the pore ordering of this mesoporous material. By further oxidation, SO3H-functionalized heterogeneous catalysts with high activity and selectivity in the esterification of glycerol with fatty acids are obtained.

High acid catalytic activity of aluminosilicate molecular sieves with MCM-41 structure synthesized from precursors of colloidal faujasite

The synthesis of micro/mesoporous aluminosilicate with a hexagonal arrangement of pores has been achieved by cationic surfactant-templating in a tetramethylammonium-containing solution precursor of colloidal faujasite; this material is zeolite nanocrystal-free and exhibits high catalytic activity in m-xylene conversion.