Evaluation of pore structural stability of mesoporous titanium silicates

Therefore one of the purposes of the work presented here is to complement the stability features by studying the hydrothermal resistance of the Ti-MCM-41 materials prepared by the same procedure. A similar study of Ti-SBA-15 materials, synthesised by conventional procedures, will also be presented and the results compared with those of Ti-MCM-41 materials. The metal content was the main parameter considered. The pore structural alterations were evaluated by characterising by X-ray diffraction and nitrogen adsorption at 77K before and after the materials were submitted to increasing temperature, increasing unidirectional pressure or after 12h in boiling water under static conditions

Effect of calcination parameters on structural properties of Ti-MCM-41 materials synthesized at room temperature

In this work is presented a study of the effect of calcination parameters namely, heating rate, calcination temperature, total calcination time and time at final temperature, on pore structural properties of Ti-MCM-41 materials. The materials were prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium alcoxides, cationic surfactants and ammonia, as previously described and were characterised by X-ray diffraction, nitrogen adsorption at 77K and DR UV-Vis absorption spectroscopy. The Si/Ti values of the final calcined materials were determined by AA (Si) and ICP (Ti)

Production and characterization of activated carbons made from sunflower stems

Activated carbons (ACs) are artificial materials, prepared from natural or synthetic precursors that are worldwide extensively used. The ACs main characteristics are the noticeable adsorption capabilities provided by the highly developed porous structure and the rich surface chemistry. Because of their versatility and properties the final material can be tailored to have specific properties suitable for a wide range of applications such as medical uses, gas storage, removal of pollutants and odours, gas separation and purification as well as in catalysis. With the increase of activated carbon demand, one of the main challenges lies in the attempt to find new precursors, which are cheap and accessible with good valorisation potential, like industrial and agricultural residues. In the present work we report the production of ACs from sunflower stems, an agricultural by-product, through a physical activation process by CO2 and H2O, using a single step carbonisation at 400ºC, which as far as it came to our knowledge was never made for this precursor

IN-SITU XRD STUDIES OF THERMAL STABILITY OF PURE SILICA AND Ti-MCM-41 MATERIALS

In this work we present a study on the thermal stability of siliceous and titanium containing ordered mesoporous materials with MCM-41 structure, prepared by direct synthesis at ambient temperature and pressure, as previously described [1]. Grades with different pore diameter and Si/Ti molar ratios were analyzed, in the form of compacted powder, to assess its influence on the order-disorder transition temperature

Templated mesoporous materials: expectations, facts and challenges

This presentation included an overview of the main types of the mesoporous structures that can be generated via template processes, addressing the role of surface chemistry on their formation and implications in their properties and applications. Some aspects considered involved the introduction of catalytic functionalities, the important contributions that these model porous solids brought to the testing of fundamentals underlying gas adsorption, previously developed with common mesoporous materials having broad pore size distributions, and also their potential as molecular sieves for big molecules in the liquid phase. Together with the beautiful aspects, some challenges still to overcome, were also mentioned

Ti-MCM-41 materials synthesised at room temperature as catalysts for cyclisation of (±)-citronellal”

In the present work we extend the applicability of those Ti-MCM-41 materials, as heterogeneous catalysts, to produce an important intermediate, isopulegol, from the cyclisation of citronellal. The use of this kind of materials appears to be a good option over homogeneous catalysts, because they offer the advantage of recovery and, consequently, contribute to environmentally friendly processes

“Estudo sistemático do efeito dos principais parâmetros de síntese nas propriedades estruturais de materiais Si e Ti-MCM-41 preparados à temperatura ambiente

No presente trabalho apresentam-se os resultados de um estudo sistemático do efeito dos parâmetros de síntese nas propriedades estruturais e químicas dos materiais Ti-MCM-41, obtidos por substituição isomórfica do titânio na matriz de sílica e de acordo com um novo método desenvolvido, nomeadamente dimensão da cadeia alifática do agente estruturante (CnTMABr, n = 8, 10, 12, 14, 16, 18), ordem de adição dos precursores de Si e Ti (conjunta ou sequencial), natureza do alcóxido metálico usado como fonte de titânio (Ti(OR)4, R=Et, Pri eBun), tipo de álcool usado na preparação da solução do Ti(OR)4, (EtOH, 2-PrOH e BuOH) e razão molar de síntese Si/Ti (100, 50, 30, 10, 5, 3.3 e 2)

Avaliação da estabilidade estrutural de materiais Ti-MCM-41 preparados à temperatura ambiente: Adsorção de N2 a 77K, e, de n-pentano e de vapor de água a 298K

No presente trabalho apresentam-se os resultados de estabilidade térmica, estabilidade em relação à exposição prolongada ao vapor de água à temperatura ambiente e estabilidade mecânica de amostras de Ti-MCM-41 preparadas, com diferentes razões molares Si/Ti, segundo um novo processo realizado à temperatura ambiente a partir do Si(OEt)4 como fonte de silício e do Ti(OEt)4 como fonte de titânio, por adição directa ou em solução de 2-PrOH, usando C16TMABr ou C18TMABr como agentes estruturantes e amónia como catalisador

Estabilidade estrutural de materiais Ti-MCM-41 preparados à temperatura ambiente: Adsorção de vapor de água a 298K

neste trabalho apresentam-se os resultados de um estudo mais abrangente onde são considerados os efeitos da dimensão da cadeia alifática dos sais de brometo de alquiltrimetilamónio, usados como agentes estruturantes de síntese, e da razão molar Si/Ti na estabilidade dos materiais Ti-MCM-41 em relação à exposição prolongada ao vapor de água a 298K. Para além da questão da estabilidade o estudo apresentado permite avaliar, em simultâneo, a química superficial e as propriedades estruturais dos referidos materiais

Efeito da aplicação de pressão externa unidireccional nas propriedades estruturais de materiais Si-MCM-41 e Ti-MCM-41 preparados à temperatura ambiente

Na presente comunicação apresenta-se um estudo referente à estabilidade mecânica de materiais Ti-MCM-41 preparados, por substituição isomórfica durante a síntese, segundo um processo realizado à temperatura e pressão ambiente, tendo sido avaliado o efeito do aumento progressivo de uma pressão externa unidireccional nas propriedades estruturais dos referidos materiais. A título comparativo são também estudadas amostras constituídas unicamente por sílica