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6th International Conference on Multifunctional, Hybrid and Nanomaterials: presenting our results on the stability of hydrophobic metallosilicates

March 12, 2019

Ales Styskalik is at the “HYMA Conference” in Sitges (Spain) to present an oral communication: «Ethanol dehydration over hydrophobic aluminum and niobium silicates: Influence of homogeneity of metal mixing on catalytic activity and stability of Si−C bonds». Here is his story, in brief.

Ethylene is widely used in chemical industry, mainly in polymer production. Nowadays it is being produced by petrochemical industry. (Bio)ethanol dehydration to (bio)ethylene is an interesting process that can become a competitive alternative to oil based production of ethylene, however catalysts for this reaction suffer from low activity and hydrothermal stability. Our intention was to improve their performance by increase of hydrophobicity. For this reason organic groups were introduced into the metallosilicate catalysts. To prepare these hybrids, we exploit the power of non-hydrolytic sol-gel chemistry.

From the very beginning we were facing serious issues with hydrothermal stability especially for materials containig aromatic groups connected via a direct Si−Caromatic bond. That was surprising because hybrid silica materials were proved to feature high stability against hydrolysis: while hydrolysis in hydrophobic silica occured at 400 °C, we have observed an extensive damage to metallosilicates already at 200 °C. We have shown that the instability is brought by introduction of partial charges to silica network due to differences in electronegativity between Si and the metal atoms incorporated. The more homogeneously were metals and thus partial charges distributed within the network, the lower was the catalyst stability. This stability issue was solved by incorporation of organic groups using precursors with stable Si−Caliphatic bonds (Figure). These are hydrothermally stable up to 350 °C. Aromatic groups can be maintained when using xylylene bridges.

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