Direct and efficient catalytic conversion of biomass-derived 2-methyltetrahydrofuran to 1,3-pentadiene via acid-base coupling of lanthanum phosphate

Abstract

It is critical to increase the reaction selectivity and atom economy, avoid side reactions during the catalytic process, and achieve the desired single-target product. Here, an efficient and novel method of producing 1,3-pentadiene via the acid-base coupling of rare-earth phosphate-catalyzed dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF) is reported, resulting in a previously unreported 1,3-pentadiene yield of 97.2% at 350 ℃. This method efficiently addresses two significant problems encountered in the dehydra-decyclization of 2-MTHF to generate 1,3-pentadiene research: the occurrence of retro-Prins condensation and the competitive reaction of 1,4-pentadiene. Density-Functional-Theory calculations demonstrated that 2-MTHF was adsorbed on the surface of rare-earth phosphate catalysts in a multi-site parallel mode, resulting in a lower apparent activation energy and ring-opening energy barrier. Space-time investigations and in situ diffuse reflectance infrared Fourier transform spectroscopy provided evidence for direct synthesis of pentadiene on rare-earth phosphate catalysts with Lewis acid-base sites. The acid-base coupling catalysis was demonstrated by poisoning experiments. In-situ self-regeneration of Brønsted acid sites was confirmed by infrared spectroscopy of adsorbed pyridine, facilitating the isomerization of 1,4-pentadiene to 1,3-pentadiene. Therefore, a unique reaction pathway for the dehydra-decyclization of 2-MTHF on the surface of rare-earth phosphates was proposed, and a new rotational isomer was discovered.