Sankhanilay Roy Chowdhury

Fine-Tuning and Recycling of Homogeneous Tungstate and Polytungstate Epoxidation Catalysts

Publisher Summary This chapter reviews work on epoxidations with aqueous dihydrogen peroxide catalyzed by tungstate and polytungstate catalysts. The activity of the sandwich polyoxometalate (sandwich POM) in cyclooctene epoxidation is compared to other W-based catalyst systems under ceteris paribus conditions. Catalyst systems based on H 2 WO 4 display the highest activity of the 11 W-catalyst systems tested. Replacing H 2 WO 4 with Na 2 WO 4 in these systems results in a strong decrease of catalyst activity, and this points to the importance of catalyst acidity. An experimental screening of various carboxylic acids cocatalysts has generated a novel W-based epoxidation system. The sandwich POM is among the most efficient of the nonacidic W-based catalyst systems. Examples where the pH neutral nature of the sandwich POM is used advantageously in the preparation of acid-sensitive epoxides are given. Allylic alcohols are epoxidized efficiently with very high reactor yields and very low sandwich POM catalyst loadings. Allylic alcohol epoxidation also proceeds very efficiently with the vanadium containing catalyst and an organic hydroperoxide instead of H 2 O 2 as the terminal oxidant. The diastereoselectivity of the epoxidation of chiral allylic alcohols is rationalized via 1,2- and/ or 1,3-allylic strain effects. Fine-tuning of catalyst activity and selectivity is achieved by varying the relative amount and nature of phase-transfer cocatalysts. Attention is paid to practical aspects that are of relevance for large-scale, industrial use of the sandwich POM catalyst, such as catalyst preparation, handling, and recycling. For the latter, an efficient method based on nanofiltration employing an a-alumina-supported g-alumina membrane has been developed.

Nanostructured ion-selective MCM-48 membranes

Templated MCM-48 silica was prepared using CTAB as surfactant. The MCM-48 powders and thin films were characterized by different techniques. MCM-48 layers were deposited on macroporous α-alumina supports and silicon nitride microsieves. The water permeability of MCM-48 was compared with the permeability of conventional mesoporous γ-alumina membranes. The applicability of MCM-48 as ion-selective electric field-driven switchable interconnect for microfluidic devices was demonstrated.

Tailor-Made Nanostructured Ion Selective MCM-48 Membranes

Mesoporous templated MCM-48 silica was prepared using a C16 surfactant as template. The MCM-48 powders and thin films were characterized by different techniques. Two types of porous supports were used, namely macroporous ?-alumina and silicon microsieves. The supported MCM-48 layers were applied as liquid permeable membranes in pressure-driven nanofiltration and electric field-mediated ion transport experiments.