CoMo/Zn-hydroxyapatites as catalysts for the hydrodesulfurization reaction of thiophene

403-408<span style="font-size:10.0pt; mso-bidi-font-size:12.0pt;letter-spacing:-.1pt;background:white" lang="EN-GB">CoMo/Zn-hydroxyapatites catalysts have been synthesized and characterized for the hydrodesulfuration (HDS) reaction of thiophene. At the beginning, Zn-hydroxyapatite supports have been synthesized with variable Zn content (0-15% molar Zn)<span style="font-size:10.0pt;mso-bidi-font-size: 12.0pt;background:white" lang="EN-GB"> and then these solids are calcined at 400 °C before and after impregnation with Co and Mo. Samples are characterized by different techniques such as X-ray diffraction, FTIR spectroscopy, temperature programmed reduction and BET specific surface area. Results show that the Zn proportion into hydroxyapatite plays an important role on textural properties of these potencial catalysts and in their catalytic behaviour. </span

Adsorción de urea y p-cresol mediante el uso de arcillas caolinitas venezolanas

La presente investigación involucró la adsorción de urea y p-cresol sobre una caolinita venezolana. La caolinita fue previamente caracterizada a fin de determinar sus parámetros estructurales y texturales; luego, se puso en contacto con soluciones de urea y p-cresol a diferentes concentraciones. El sistema urea-caolinita ofreció un 34,8% de adsorción; mientras que para el sistema p-cresol caolinita fue del 27,7%. Al mismo tiempo, se aplicaron los modelos de adsorción: Langmuir, Freundlich y Langmuir-Freundlich a fin de comparar los resultados del proceso de adsorción. El modelo de adsorción de Freudlich fue el que mejor se ajustó a los datos experimentales obtenidos tanto para el sistema urea-caolinita como para el sistema [email protected] work assayed the adsorption process of urea and p-cresol onto Venezuelan kaolin clay. The clay was previously characterized to determine its structural and textural parameters; then, the kaolin was contacted with urea and p-cresol solutions at different concentrations. The urea-kaolin system reached a 34.8% of adsorption; while for p-cresol-kaolin was 27.7%. The Langmuir, Freundlich and Langmuir-Freundlich adsorption models were applied to compare the best adsorption process. Obtained results showed that the Freudlich model fitted better the results for urea-kaolin and p-cresol-kaolin system

ZEOLITAS NATURALES COMO ADSORBENTE DE UREA / NATURAL ZEOLITE AS ADSORBENT OF UREA

Una zeolita phillipsita natural iran&iacute; fue caracterizada mediante las t&eacute;cnicas anal&iacute;ticas usuales: difracci&oacute;n de rayos X(DRX), infrarrojo con transformada de Fourier FT-IR, y medidas de &aacute;rea espec&iacute;fica superficial BET. Esta zeolita phillipsitafue puesta en contacto con diferentes concentraciones de la toxina ur&eacute;mica urea. Despu&eacute;s del contacto con las solucionesde urea, se aplicaron distintos modelos de adsorci&oacute;n, tales como: Langmuir, Freundlich y Langmuir-Freundlich, con elprop&oacute;sito de comparar los mejores ajustes de cada una de ellas. Los resultados revelaron una etapa inicial de la formaci&oacute;nde la monocapa para dar luego con la formaci&oacute;n de multicapa que se corresponde con el sistema de Langmuir-Freundlich.ABSTRACTAn Iranian natural phillipsite zeolite was characterized by different techniques such as: X-ray diffraction, Fourier-Transformed spectroscopy (FT-IR) and BET specific surface area measurements. The phillipsite zeolite was contactedwith urea solutions of different concentrations. After the contacting, different adsorption models were assessed such as:Langmuir, Freundlich y Langmuir-Freundlich. Results showed the formation of a urea monolayer, at an early stage andfinally a urea multilayer was formed, in concordance with the Langmuir-Freundlich model.Keywords: Adsorption isotherm, Phillipsite, Urea, Characterization, Dialysis

Caracterização e análise estrutural da hidroxisodalita sintetizada a partir de amostras de solo amazônico Characterization and structural analysis hydroxysodalite synthesized from Amazonian soil samples

As zeólitas desde sua descoberta, na forma natural, vêm promovendo grande interesse em aplicações tecnológicas como peneiras moleculares, trocadores iônicos, catalisadores e, principalmente, adsorventes. As zeólitas sintéticas geralmente são preparadas com soluções aquosas saturadas de sais de aluminatos e silicatos. Mas, rejeito industrial do processo de beneficiamento de caulim tem sido empregado para sintetizar zeólita A e hidroxisodalita, devido a razão equimolar Si/Al. Nesse trabalho foi sintetizado a zeólita do tipo hidroxisodalita [Na6(AlSiO4)6 .8H2O] a partir da fração fina de duas amostras de solo amazônico - rico em caulinita [Al2Si2O5(OH)4] que é basicamente composta de Al e Si - usando o método hidrotermal. A caracterização por espectrofotometria de absorção no infravermelho com transformada de Fourier, análise termogravimétrica e térmica diferencial e difração de raios X confirmaram que as amostras in natura são majoritariamente compostas por caulinita com 69 a 71% de abundância. O refinamento estrutural de Rietveld mostrou que o produto da síntese é constituída de uma fase cristalina de hidroxisodalita de estrutura cúbica (grupo espacial , #218) com parâmetros de rede a = 0,88468 e 0,88594 nm. Os dados ajustados permitiram estimar o tamanho médio dos cristalitos d = 57 nm (ambas amostras) e a área superficial S = 44 e 41 m².g-1.<br>Zeolites since their discovery in natural form have promoted a great interest in technological applications as molecular sieves, ion exchangers, catalysts, and especially adsorbents. The synthetic zeolites are usually prepared with saturated aqueous solutions of salts of aluminates, and silicates. But the process of industrial waste processing kaolin has been used to synthesize zeolite A and hydroxysodalite due to equimolar Si/Al ratio. In this work zeolite type hydroxysodalite, Na6[Si6Al6 O4]6.8H2O was synthesized from the fine fraction of two samples from Amazonian soil - rich in kaolinite, [Al2Si2O5(OH)4], which is basically composed of Al and Si, using hydrothermal method. Characterization by FT-IR, TGA/DTA and XRD confirmed that the samples in natura are mainly constituted by kaolinite with 69 and 71% abundance. Rietveld structural refinement showed that the synthesis product consists of a crystalline phase hydroxysodalite of cubic structure (space group , #218) with lattice parameters a = 0.88468 and 0.88594 nm. The fitted data allowed us to estimate the average crystallite size d = 57 nm (both samples), and the surface area, S = 44 and 41 m² g-1 for the samples