Conversion of levulinic acid to gamma-valerolactone over Zr-containing metal-organic frameworks: Evidencing the role of Lewis and Bronsted acid sites

[EN] Zr-containing UiO-66 and MOF-808 are evaluated for converting levulinic acid (LA) into gamma-valerolactone (GVL) through various routes: (i) Step-wise esterification of LA to n-butyl levulinate (nBuL) and Meerwein-PonndorfVerley (MPV) reduction to GVL; (ii) One-pot two-steps esterification with n-butanol followed by MPV reduction with sec-butanol; and (iii) direct conversion of LA into GVL through a tandem reaction. Selection of this multistep complex reaction evidences the participation of the different acid sites (Lewis or Bronsted) of the material in each individual step: Bronsted-induced acid sites catalyze esterification reaction efficiently, while Lewis acid sites are the preferred sites for the MPV step. Sulfation of MOF-808 is used to enhance the Bronsted acidity of MOF-808, which improves the performance for esterification. However, the sulfate groups introduced are detrimental for the MPV step, since they reduce the intra-pore space available to form the required bulky transition state. These results evidence the need to find the best equilibrium between Bronsted and Lewis acid sites to optimize the outcome of this multistep reaction.Financial support by the Spanish Government is acknowledged through projects MAT2017-82288-C2-1-P and the Severo Ochoa program (SEV-2016-0683). Aula-CEMEX is also acknowledged for a fellowship to JMG.Guarinos, J.; Cirujano, F.; Rapeyko, A.; Llabrés I Xamena, FX. (2021). Conversion of levulinic acid to gamma-valerolactone over Zr-containing metal-organic frameworks: Evidencing the role of Lewis and Bronsted acid sites. Molecular Catalysis. 515:1-11. https://doi.org/10.1016/j.mcat.2021.111925S11151

Zirconium-containing metal organic frameworks as solid acid catalysts for the esterification of free fatty acids: Synthesis of biodiesel and other compounds of interest

Zr-containing metal organic frameworks (MOFs) formed by terephthalate (UiO-66) and 2-aminoterephthalate ligands (UiO-66-NH2) are active and stable catalysts for the acid catalyzed esterification of various saturated and unsaturated fatty acids with MeOH and EtOH, with activities comparable (in some cases superior) to other solid acid catalysts previously reported in literature. Besides the formation of the corresponding fatty acid alkyl esters as biodiesel compounds (FAMEs and FAEEs), esterification of biomass-derived fatty acids with other alcohols catalyzed by the Zr-MOFs allows preparing other compounds of interest, such as oleyl oleate or isopropyl palmitate, with good yields under mild conditions.Financial support from the Consolider-Ingenio 2010 (project MULTICAT), the Severo Ochoa program, and the Spanish Ministry of Science and Innovation (project MAT2011-29020-C02-01) is gratefully acknowledged.García Cirujano, F.; Corma Canós, A.; Llabrés I Xamena, FX. (2015). Zirconium-containing metal organic frameworks as solid acid catalysts for the esterification of free fatty acids: Synthesis of biodiesel and other compounds of interest. Catalysis Today. 257:213-220. https://doi.org/10.1016/j.cattod.2014.08.015S21322025