Influencia de las condiciones de desilicación en la síntesis de la zeolita jerárquica Y

Hierarchical zeolites were synthesized by two methodologies, following desilication procedures of commercial zeolites. Starting from USY zeolite (Zeolyst CBV720 with Si/Al=15), the effect of the amount of CTAB in the desilication media and the hydrothermal treatment time on the synthesized materials was analyzed. The results showed that the surfactant amount has a higher influence on relative crystallinity (%RC) and textural properties of the materials than synthesis time. All the samples showed a lower BET surface area compared with the starting zeolite, although mesopore surface area increased from 210.33 to 467.30 m2/g in the case of Z720-75 sample. In the case of USY zeolite with Si/Al=2.6 (Zeolyst CBV500), a previous dealumination with H4EDTA and an acid washing with Na2H2EDTA steps were included. It was found that the micropore and the mesopore surface areas increased 13.75% and 12.13%, respectively, compared with the parent zeolite; furthermore, the %RC was 99% after treatment.Se sintetizaron zeolitas jerárquicas por dos metodologías, siguiendo procedimientos de desilicación de zeolitas comerciales. Partiendo de la zeolita USY (Zeolyst CBV720 con Si/Al = 15), el efecto de la cantidad de CTAB en el medio de desilicación y el tiempo del tratamiento hidrotérmico fueron analizados. Los resultados mostraron que la influencia de la cantidad de surfactante en la cristalinidad relativa (%RC) y las propiedades texturales de los materiales fue mayor que el efecto del tiempo. Todas las muestras mostraron una menor área superficial BET comparada con el material de partida, pero el área superficial mesoporosa tuvo un incremento de 210.33 a 467.30 m2/g en el caso de la muestra Z720-75. Para la desilicación de la zeolita USY con Si/Al = 2.6 (Zeolyst CBV500), se incluyó una etapa previa de desaluminación con H4EDTA y un lavado ácido posterior con Na2H2EDTA. Se encontró que el área superficial microporosa y el área superficial mesoporosa aumentaron 13.96% y 11.23%, respectivamente, comparado con el material comercial; además, el %RC se conservó en un 99% después de los tratamientos.Se sintetizaron zeolitas jerárquicas por dos metodologías, siguiendo procedimientos de desilicación de zeolitas comerciales. Partiendo de la zeolita USY (Zeolyst CBV720 con Si/Al = 15), el efecto de la cantidad de CTAB en el medio de desilicación y el tiempo del tratamiento hidrotérmico fueron analizados. Los resultados mostraron que la influencia de la cantidad de surfactante en la cristalinidad relativa (%RC) y las propiedades texturales de los materiales fue mayor que el efecto del tiempo. Todas las muestras mostraron una menor área superficial BET comparada con el material de partida, pero el área superficial mesoporosa tuvo un incremento de 210.33 a 467.30 m2 /g en el caso de la muestra Z720-75. Para la desilicación de la zeolita USY con Si/Al = 2.6 (Zeolyst CBV500), se incluyó una etapa previa de desaluminación con H4EDTA y un lavado ácido posterior con Na2H2EDTA. Se encontró que el área superficial microporosa y el área superficial mesoporosa aumentaron 13.96% y 11.23%, respectivamente, comparado con el material comercial; además, el %RC se conservó en un 99% después de los tratamientos.Hierarchical zeolites were synthesized by two methodologies, following desilication procedures of commercial zeolites. Starting from USY zeolite (Zeolyst CBV720, Si/Al=15), the effect of the amount of CTAB in the desilication media and the hydrothermal treatment time on the synthesized materials were analyzed. The results showed that the surfactant amount has a higher influence on relative crystallinity (%RC) and textural properties of the materials than synthesis time. All the samples showed a lower BET surface area compared with the starting zeolite, although mesopore surface area increased from 210.33 to 467.30 m2/g in the case of Z720-75 sample. In the case of USY zeolite with Si/Al=2.6 (Zeolyst CBV500), a previous dealumination with H4EDTA and an acid washing with Na2H2EDTA steps were included. It was found that the micropore and the mesopore surface areas increased 13.96% and 11.23%, respectively, compared with the parent zeolite; furthermore, the %RC was 99% after treatment procedures

Kinetic study of the nopol synthesis by the Prins reaction over tin impregnated MCM-41 catalyst with ethyl acetate as solvent

ABSTRACT: The kinetics of the catalytic synthesis of nopol from b-pinene and paraformaldehyde over Sn-MCM-41 catalyst and using ethyl acetate as solvent is presented and compared with previous studies in toluene. Reaction rate data were fitted to a kinetic expression based on the Langmuir–Hinshelwood formalism, using the initial rates method. Reaction rate constant and adsorption constants were determined by regression of experimental data. The highest adsorption constant for nopol respect to reactants (KC = 14.948 M-1) allows to explain the strong inhibition effect of this compound that is experimentally observed. Solvent effects were discussed in terms of formaldehyde solubility, solvation of activated complex and reactants, and competitive adsorption on active sites. Higher solubility of formaldehyde in ethyl acetate respect to toluene, determined with Henry’s law, along with the competitive adsorption of solvent and a more probable solvation of b-pinene and nopol may explain the better selectivity in ethyl acetate. Dependency of reaction constant on temperature was evaluated between 75 °C and 90 °C, resulting in an apparent activation energy of 98 kJ mol-1, which is higher than in toluene, suggesting stabilization of carbocation intermediates by solvation in the polar ethyl acetate solvent

Kinetics of the nopol synthesis by the Prins reaction over tin impregnated MCM-41 catalyst

ABSTRACT: The kinetics of the nopol synthesis by Prins condensation of b-pinene and paraformaldehyde over Sn-MCM-41 synthesized by impregnation was evaluated using the initial reaction rate method. The reaction rate equation obtained from a kinetic model based on the Langmuir–Hinshelwood formalism with the surface reaction of adsorbed reactants on catalytic sites of the same nature as the limiting step, gave a good prediction of the experimental data. The effect of temperature on the kinetics of nopol synthesis over Sn-MCM-41 obtained by impregnation was studied between 75 and 100 °C. The robustness analysis of the kinetic model showed that the surface reaction constant, k0 sr , should be about 0.185 mol g-1 h-1 at 90 °C, while the ratio between the adsorption equilibrium constant of b-pinene, KA, and formaldehyde species, KB, is approximately 1.2:1 (KA:KB). The obtained apparent activation energy and pre-exponential factor are 78 kJ/mol and 2.3 * 1010 mol g-1 h-1, respectively, but compensation effect analysis using both experimental and simulated data gave strong evidence of the dependency in temperature of the apparent Arrhenius parameters

Nopol synthesis over Sn-MCM-41 and Sn-kenyaite catalysts

ABSTRACT: Several methods were used to prepare Sn loaded kenyaite and MCM-41 silicates: ion exchange, incipient wetness impregnation and chemical vapor deposition. Catalysts were evaluated for nopol synthesis by the Prins condensation of b-pinene and paraformaldehyde. The resulting catalysts were characterized by elemental analysis, TGA, XRD, FTIR, BET surface area and UV–vis. Kenyaite samples modified with Sn by ion exchange were more resistant to leaching than those modified by chemical vapor deposition (CVD), while Sn-MCM-41 samples prepared by CVD were more active, selective to nopol and resistant to leaching than Sn-MCM-41 prepared by impregnation. In general, Sn-MCM-41 catalysts even at low Sn loadings exhibited higher nopol yields than Sn-kenyaite. Keywords: Nopol; b-Pinene; Prins reaction; Kenyaite; MCM-41; CVD; Ion exchange; S

Synthesis of nopol over MCM-41 catalysts

ABSTRACT: MCM-41 was found to be an active heterogeneous catalyst for the synthesis of nopol by the Prins condensation of bpinene and paraformaldehyde, but Sn-MCM-41 in which Sn has been grafted on MCM-41 by chemical vapor deposition is far more active and combines high efficiency and recyclability

Preparación de catalizadores de carbón activado estructurados. Un caso de estudio : síntesis limpia de dimetil carbonato a partir de metanol y CO2

RESUMEN: Se presenta la síntesis del catalizador bimetálico de Cu-Ni soportado en pellets de carbón activado utilizando carboximetilcelulosa (CMC) como agente aglutinante. Se evaluó el efecto de las condiciones de preparación, tales como concentración de CMC, relación de CMC/Carbón activado, temperatura y velocidad de calentamiento en la pirólisis sobre el área la superficial de los pellets sintetizados. La incorporación de los metales (Cu y Ni) en los pellets se efectuó por impregnación húmeda incipiente convencional. El soporte y los catalizadores sintetizados se caracterizaron mediante adsorción de N2 , H2 -TPR, XRD y técnicas de SEM-EDS. Los catalizadores peletizados se evaluaron en la síntesis directa de dimetil carbonato DMC (caso de estudio), mostrando una actividad catalítica mejorada en comparación con el catalizador en polvo.ABSTRACT: The synthesis of Cu-Ni bimetallic catalyst supported on pellets of activated carbon using carboxymethylcellulose (CMC) as a binder is reported. The effect of preparation conditions, such as binder concentration, AC/binder ratio, temperature, and pyrolysis heating rate on the surface area of the pellets, was evaluated. Cu and Ni metals were incorporated on the pellets by conventional incipient wetness impregnation. The support and the synthesized catalysts were characterized using N2 adsorption, H2-TPR, XRD and SEM-EDS techniques. The pelletized catalysts were evaluated for the direct synthesis of dimethyl carbonate DMC (case study). An improved catalytic activity (e.g., ca. 20% increase in conversion) in structured pelletized catalyst in comparison to the powdered catalyst was found

Nopol production over Sn-MCM-41 synthesized by different procedures – Solvent effects

ABSTRACT: Nopol production over impregnated Sn-MCM-41 under several reaction conditions was examined and compared with Sn-MCM-41 materials previously synthesized by CVD or hydrothermal procedures. The effect of solvent on catalytic activity of Sn-MCM-41 materials and leaching tests of impregnated samples were also assessed. Selected materials were characterized by BET, XPS and H2-TPR. The effect of solvent was explained in terms of polarity by the solvatochromic parameter, ET(30), and paraformaldehyde solubility by the Hansen solubility parameter (HSP). Nopol selectivity was enhanced at intermediate values of ET(30), and the highest b-pinene conversion was obtained when the HSP was close to 18.2 MPa0.5. Leaching experiments confirmed that the reaction was truly heterogeneous. Catalysts characterization suggested that tin was deposited as tin oxide nanoparticles, when MCM-41 was modified by CVD and impregnation with stannic and stannous chloride, respectively. Conversely, most of the tin hydrothermally incorporated is presumably present as aggregates in the inner walls of MCM-41 and a small fraction of tin isomorphously substituted silicon atoms

Effect of Sn-MCM-41 hydrothermal synthesis conditions on nopol production

RESUMEN: Se prepararon varios catalizadores Sn-MCM-41 por síntesis hidrotérmica a temperatura ambiente usando SnCl2•2H2O como sal precursora. Los materiales se caracterizaron por difracción de rayos X (DRX), TPD de amoníaco, FTIR de piridina adsorbida y TPR con H2. La reactividad de los materiales preparados para la obtención de nopol por reacción de β-pineno y paraformaldehído se relacionó con el tipo de acidez de los catalizadores. Los materiales con acidez media fueron los más selectivos a nopol. Este tipo de acidez prevaleció en los materiales que se sintetizaron con control de pH y con la adición del precursor sólido.ABSTRACT: Several catalysts were prepared by hydrothermal synthesis of Sn-MCM-41 at room temperature using SnCl2 •2H2O as precursor salt. Catalysts were characterized by TPD of ammonia, FTIR of adsorbed pyridine and TPR of H2. The reactivity of the synthesized materials for the Prins condensation of β-pinene with paraformaldehyde to obtain nopol was explained in terms of the type of acidity. The most active catalysts showed medium strength acidity. Materials synthesized under pH control and by adding the metal source as a solid, exhibited medium strength acidity

Studying PW-Amberlite catalyst deactivation in limonene epoxidation by hydrogen peroxide

RESUMEN: El catalizador PW-Amberlita es activo para la epoxidación de limoneno en condiciones trifásicas, pero se desactiva durante la reacción. En esta contribución se evaluó la estabilidad del catalizador en la reacción y la recuperación de la actividad catalítica al tratarlo con varios solventes. Se encontró que el catalizador recupera el 99% de su actividad inicial cuando se lavó con tolueno y que la recuperación fue de 95 y 97% cuando se utilizaron etanol o acetona como solventes de lavado, respectivamente. Las pruebas de lixiviación mostraron que la reacción no continuaba al separar el catalizador de la mezcla de reacción, confirmando la ausencia de lixiviación de la fase activa del catalizador. Mediante análisis FTIR se evidenció que las especies características del complejo fosfotungstato no se modificaron con reutilizaciones sucesivas del catalizador

Estudio de la desactivación del catalizador pw-amberlita en la epoxidación de limoneno con peróxido de hidrógeno

El catalizador PW-Amberlita es activo para la epoxidación de limoneno en condiciones trifásicas, pero se desactiva durante la reacción. En esta contribución se evaluó la estabilidad del catalizador en la reacción y la recuperación de la actividad catalítica al tratarlo con varios solventes. Se encontró que el catalizador recupera el 99% de su actividad inicial cuando se lavó con to- lueno y que la recuperación fue de 95 y 97% cuando se utilizaron etanol o acetona como solventes de lavado, respectivamente. Las pruebas de lixiviación mostraron que la reacción no continuaba al separar el catalizador de la mezcla de reacción, confir- mando la ausencia de lixiviación de la fase activa del catalizador. Mediante análisis FTIR se evidenció que las especies caracte- rísticas del complejo fosfotungstato no se modificaron con reutilizaciones sucesivas del catalizador.The PW-Amberlite catalyst is active for limonene epoxidation in triphasic conditions; it becomes deactivated in reaction condi- tions. Catalyst stability during the reaction and recovery of catalyst activity when it was treated with several solvents were evalua- ted. It was found that the catalyst recovered 99% of its initial activity when it was washed with toluene and that the recovery was 95% and 97% when ethanol or acetone were used as washing solvents, respectively. Leaching tests showed that the reaction did not continue when the catalyst was removed from the reaction mixture, confirming the absence of leaching during the catalyst’s active phase. FTIR analysis revealed that the characteristic species of the phosphotungstate complex did not vary with successive reusing of the catalyst