TiO2 SiO2 Aerogel Research Articles

Role of Amine Modifiers in the Epoxidation of Allylic Alcohols with a TiO2–SiO2 Aerogel

A detailed study of the epoxidation of 3-methyl-2-cyclohexen-1-ol with tert-butylhydroperoxide revealed that the poor performance of a 20 wt% TiO2–80 wt% SiO2 aerogel was due to nonoxidative consumption of the allylic alcohol. Epoxide selectivities could be improved remarkably and acid-catalyzed side reactions suppressed by addition of small amounts of aliphatic, cycloaliphatic, or aromatic amines. The best modifier was N, N-dimethylbutylamine. Amine (1 mol%) enhanced the epoxide selectivities, related to the reactant or peroxide, from 3 to 99% and 35 to 100%, respectively. Kinetic investigations uncovered how the chemical structure and the amount of various amines influence the complex network of redox- and acid-catalyzed reactions during allylic alcohol epoxidations. The stability of amines was studied under oxidizing reaction conditions. The method of amine addition was applied also to the epoxidation of other linear and cyclic allylic alcohols and 2-hexene. The scope of this method seems to be limited to epoxidation of allylic alcohols. A model for the interaction of allylic alcohol, amine, and peroxide with the Ti active site is proposed, which can interpret the enhanced selectivity and suppressed activity in the presence of amines or other bases.

Novel amine-modified TiO2–SiO2 aerogel for the demanding epoxidation of substituted cyclohexenols

Amine additives provided high selectivity (up to 98%) in the epoxidation of sensitive alkyl-substituted cyclohexenols with a TiO2–SiO2 aerogel and ButOOH; heterogenization of the catalyst system resulted in a new bifunctional catalyst.

Microstructure and catalytic properties of Rh and Ni dispersed on TiO2-SiO2 aerogels

The influence of the preparation method on the microstructure and catalytic behavior of Rh and Ni dispersed on TiO2-SiO2 aerogels is investigated.

Ultrastructural evolution during sintering of mixed sonogels

A first approach to the ultrastructural evolution during the sintering process of TiO2-SiO2 aerogels has been done on the basis of the gelation kinetics and dried gel previous analysis, in order to tailor the mixed glass sol-gel processing.

Ultrasound as a tool for the preparation of gels: effect on the textural properties of TiO2-SiO2 aerogels

TiO2-SiO2 aerogels have been prepared by hydrolysis and polycondensation of alkoxides following two different methods: the classic one, using ethanol as a solvent, and the sonic one, by means of activation with ultrasound. The work is focused on the comparison of the textural properties of gels obtained by both synthetic routes. Nitrogen physisorption, mercury pycnometry and transmission electron microscopy have been used as characterization techniques. The sonogels present higher values of specific surfaces and apparent densities, lower pore volumes, finer and sharper pore-size distributions and lower average particle size. These properties are discussed and related to the preparation techniques.