Epoxidation of soybean oil catalyzed by peroxo phosphotungstic acid supported on modified halloysite nanotubes

{PO4[W(O)(O-2)(2)](4)}(3-) was supported onto modified halloysite nanotubes (HNTs) to prepare heterogeneous catalysts and these catalysts were applied in epoxidation of soybean oil. To enhance the cohesive force between {PO4[W(O)(O-2)(2)](4)}(3-) and HNTs, quaternary amino groups were anchored onto HNTs through silylation of N-(2-aminoethyl)-3-aminopropyl trimethoxysilane and alkylation of amino groups. Further {PO4[W(O)(O-2)(2)](4)}(3-) was supported onto HNTs by ion exchange. The heterogeneous catalysts were characterized by FTIR, TGA, XRF and TEM-EDS. Then the catalytic behaviour to epoxidation of soybean oil was studied in detail. The results show that the introduction of phase transfer agent during preparation of the catalysts is very effective to improve catalytic activity and mechanical agitation combining with ultrasonic agitation is the best agitation way. The catalytic reactivity increased as reaction time increased. Moreover, the catalysts can be easily recovered from the reaction system by centrifugation as deposit and recycled three times without obviously decreasing the catalytic activity. Through re-exchange of {PO4[W(O)(O-2)(2)](4)}(3-), the heterogeneous catalyst can be regenerated without catalytic activity loss. (C) 2012 Elsevier B. V. All rights reserved.