Tungsten–zirconia-supported rhenium catalyst combined with a deoxydehydration catalyst for the one-pot synthesis of 1,4-butanediol from 1,4-anhydroerythritol

Abstract

Efficient and reusable catalysts were developed for one-pot reduction of 1,4-anhydroerythritol (1,4-AHERY), which is a promising biomass-derived C4 platform chemical, into 1,4-butanediol (1,4-BuD) with H₂. First, various ReO_x catalysts on oxide supports were tested for reductive conversion of 2,5-dihydrofuran (2,5-DHF) to 1,4-butanediol (1,4-BuD). ReO_x/WO₃–ZrO₂ showed the best performance, and ReO_x catalysts supported on other oxides were much less active in the isomerization of 2,5-DHF to 2,3-DHF which is the first step of the 2,5-DHF conversion to 1,4-BuD. The ReO_x/WO₃–ZrO₂ catalyst was combined with the ReO_x–Au/CeO₂ catalyst for deoxydehydration (DODH) of 1,4-AHERY into 2,5-DHF to develop a one-pot conversion system of 1,4-AHERY to 1,4-BuD. The highest 1,4-BuD yield of 55% from 1,4-AHERY was obtained. Even though the yield was lower than that obtained over the combination of ReO_x/C and ReO_x–Au/CeO₂ catalysts in our previous study, the regeneration of the combination of ReO_x/WO₃–ZrO₂ and ReO_x–Au/CeO₂ is possible: calcination at 573 for 3 h of the used catalyst mixture increased the activity to the fresh level. THF was the major by-product in both 1,4-AHERY and 2,5-DHF conversions, which was due to hydrogenation of DHF, disproportionation of DHF and/or dehydration of 1,4-BuD. The W amount in WO₃–ZrO₂ greatly affected the catalytic performance of ReO_x/WO₃–ZrO₂: too much W above the monolayer level on the ZrO₂ support sharply decreased the activity in 2,5-DHF isomerization. On the other hand, WO₃–ZrO₂ with a tetragonal ZrO₂ structure prepared by co-precipitation showed comparable performance to WO₃–ZrO₂ with a monoclinic ZrO₂ structure as the support of the ReO_x catalyst, demonstrating that the crystal structure of ZrO₂ has little effect on the catalytic performance. The Re species were suggested to be highly dispersed on the WO₃ (sub)monolayer on ZrO₂ based on the effect of the Re loading amount. The dispersed Re species on monolayer WO₃ species on ZrO₂ can be the active sites for 2,5-DHF disproportionation to 2,3-DHF.