Selective dehydra-decyclization of cyclic ethers to conjugated dienes over zirconia

• Published in: Journal of catalysis Vol. 410; no. C; pp. 10 - 21
• Main Authors: Ji, Yichen, Batchu, Sai Praneet, Lawal, Ajibola, Vlachos, Dionisios G., Gorte, Raymond J., Caratzoulas, Stavros, Abdelrahman, Omar A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.06.2022; Elsevier
• Subjects: 1,3 -pentadiene; Chemistry; Conjugated diene; Cyclic ether; Dehydra-decyclization; Engineering; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Isoprene; Zirconia; Zirconia; Conjugated diene; 1,3-pentadiene; Dehydra-decyclization; Cyclic ether; Isoprene
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2022.03.023

[Display omitted] •Selective production of C5 conjugated dienes from cyclic ethers over zirconia catalyst.•Metal oxide catalysts are active for cyclic ether ring opening, but other than zirconia, are non-selective to conjugated dienes.•Conjugated and non-conjugated dienes formed through primary pathways and avoided isomerization over zirconia.•Conjugated pentenolate surface intermediate on zirconia responsible for favorable isomer selectivity. ZrO2 provides high selectivity (>90%) to conjugated pentadienes through the dehydra-decyclization of C-5 cyclic ethers, even at high conversions. 1,3-Pentadiene was the major product in both reaction of 2-methyltetrahydrofuran and tetrahydropyran over ZrO2. The reaction of 3-methyltetrahydrofuran produced nearly stoichiometric amounts of isoprene. Other catalysts, including TiO2, γ-Al2O3, and H-ZSM-5, were generally much less selective and produced a mixture of diene isomers. A combination of TPD and steady-state measurements revealed that both piperylenes are exclusively produced through primary catalytic pathways from 2-methyltetrahydrofuran, avoiding any isomerization once formed. First-principle calculations on ZrO2 imply the presence of an energetically favored, surface isomerization of ring-opened intermediates to conjugated alkenolates that selectively dehydrate to conjugated dienes, providing high selectivity to the desired products. The stabilization of the conjugated alkenolate is key for understanding the ability of ZrO2 to selectively produce conjugated dienes from cyclic ethers, without the need for the thermo-limited diene isomerization.