Dehydrogenative cyclization of 1,4-butanediol over copper-based catalyst

Synthesis of gamma-butyrolactone (GBL) from 1,4-butanediol (BDO) over copper-based catalysts with ZnO, Al2O3 and ZrO2 was investigated. Catalytic activity of copper was greatly affected by the additive oxides. The highest activity was obtained at a catalyst molar ratio of CuO:ZnO:ZrO2:Al2O3 = 6:1:2:2. ZrO2 showed the highest additive effect for the GBL synthesis with enhancing dehydrogenation ability of metallic Cu and enlarging Cu surface area. Al2O3 enlarged Cu surface area, whereas a large amount of tetrahydrofuran (THF) was formed over the acid sites of Al2O3 surface, and ZnO reduced the THF yield. The reaction pathway from BDO to GBL was also clarified: BDO was initially dehydrogenated to 4-hydroxybutanal, which was immediately hemiacetalized to 2-hydroxytetrahydrofuran, followed by the dehydrogenation to GBL over metallic Cu. (C) 2003 Elsevier B.V. All rights reserved.