A recoverable polyoxometalate-ionic liquid catalyst for selective cleavage of lignin β-O-4 models under mild conditions

Abstract

The efficient and selective cleavage of the β-O-4 linkage under mild conditions represents a promising strategy to convert lignocellulose to value-added aromatic chemicals. In this work, a recoverable polyoxometalate-ionic liquids...

Polyoxometalate as an Effective Catalyst for Catalytic Lignin into Value‐Added Molecules

“…have proved to be exceptional solvent systems for the oxidative depolymerization of lignin or lignin model compounds. [75,[90][91][92][93][94][95][96] The POM anion can undergo electrostatic interaction with several IL cations, leading to the synthesis of unique organic-inorganic hybrid molecular compounds with similar structures. [93] A vanadium-based POM catalyst was found to depolymerize pine and willow lignin in [HC4im]-[HSO 4 ], yielding aromatic compounds such as vanillin and syringaldehyde under O 2 and H 2 O 2 .…”

“…This is very important in the design of ionic liquids. Keggin‐type POM‐ILs such as [C 2 mim][OAc]/POM, P 2 W 17 ‐[Emim]HSO 4 , [BSmim]CuPW 12 O 40 , [OMIM]H 3 PW 12 O 40 , [MIMPS] 2 H 4 P 2 Mo 18 O 62 have proved to be exceptional solvent systems for the oxidative depolymerization of lignin or lignin model compounds [75,90–96] . The POM anion can undergo electrostatic interaction with several IL cations, leading to the synthesis of unique organic‐inorganic hybrid molecular compounds with similar structures [93] .…”

“…Although the POMs display strong lignin depolymerization capabilities, their high solubility in water makes catalyst recovery difficult. To improve the recyclability of POM‐IL even further, a recoverable catalyst of HPMoV‐BMIM‐SO 3 H ILs was constructed through the interaction of H 5 PMo 10 V 2 O 40 (HPMoV) with 1‐methyl‐3‐(4‐sulfobutyl)‐1H‐imidazolium (BMIM‐SO 3 ) [75] . The catalytic activity of the HPMoV‐BMIM‐SO 3 H IL catalyst can be readily restored by introducing ethyl acetate to the reaction mixture.…”

“…The biggest problem in the above techniques is driven by the evident competition between carbonylation of C α À OH and cleavage of CÀ C/CÀ O. To limit competitive reactions, developing selective oxidation [70][71][72][73][74][75] or protection strategies [76] (introducing stabilized groups such as ethylene glycol, aldehyde and so on) is highly desired. Furthermore, the important aspect was less catalyst leaching, as well as increased lignin conversion to monomers and obvious advantages in catalyst stability.…”

“…To improve the recyclability of POM-IL even further, a recoverable catalyst of HPMoV-BMIM-SO 3 H ILs was constructed through the interaction of H 5 PMo 10 V 2 O 40 (HPMoV) with 1-methyl-3-(4-sulfobutyl)-1H-imidazolium (BMIM-SO 3 ). [75] The catalytic activity of the HPMoV-BMIM-SO 3 H IL catalyst can be readily restored by introducing ethyl acetate to the reaction mixture. The results demonstrate the efficiency of POM-IL with a Keggin structure as a catalyst for the oxidation of lignin fragments to value-added molecules in aqueous acidic IL solutions.…”