Full conversion of lignocellulose using polyoxometalate catalysts with redox sites and antagonistic acidity/basicity

Qiwen Wang; Yuhan Liu; Yuan Jiang; Yuannan Chen; Yiming Li; Yang Zhang; Xiaohong Wang

doi:10.1016/j.jcis.2024.11.189

Full conversion of lignocellulose using polyoxometalate catalysts with redox sites and antagonistic acidity/basicity

J Colloid Interface Sci. 2024 Nov 26:682:263-274. doi: 10.1016/j.jcis.2024.11.189. Online ahead of print.

Authors

Qiwen Wang¹, Yuhan Liu¹, Yuan Jiang², Yuannan Chen¹, Yiming Li¹, Yang Zhang³, Xiaohong Wang⁴

Affiliations

¹ Key Laboratory of Polyoxometalate and Reticular Material Chemistry of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China.
² State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China. Electronic address: jyuan@ciac.ac.cn.
³ Changchun Institute of Technology, Changchun 130012, PR China. Electronic address: zhangyang@ccit.edu.cn.
⁴ Key Laboratory of Polyoxometalate and Reticular Material Chemistry of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024, PR China. Electronic address: wangxh665@nenu.edu.cn.

PMID: 39622109
DOI: 10.1016/j.jcis.2024.11.189

Abstract

The full utilization of lignocellulose involves two distinct catalytic routes: i) oxidative depolymerization of lignin and ii) acid/alkaline hydrolysis of hemicellulose and cellulose. To improve efficiency and reduce costs, constructing a single-cluster catalyst represents a desirable yet challenging strategy. Herein, triple-functional molecular polyoxometalates (POMs), NLL_nH_6-nV₂Mo₁₈O₆₂ (n = 1-6) were fabricated using N-lauroyl-l-lysine (NLL) and H₆V₂Mo₁₈O₆₂ as precursors. Besides its amphiphilicity to form nano-micelles with polyanion uniformly dispersed outside and NLL inside, NLL also provided basic sites to H⁺/redox POMs to compensate the loss of acidity and enabled spatial separation of antagonistic acid/base sites within a single POM molecule. Density Functional Theory, Molecular Dynamics simulations and experiments were employed to analyze these processes. The adsorption of -OH in 2-phenoxy-1-phenylethanol (pp-ol) was achieved by interacting with polyanion and extra with NH and C = O groups in NLL. These synergistic effects resulted in concentrating and confining pp-ol and reactive oxygen species around polyanion, which turnover frequency increased by 0.066 h^-1 compared to homogeneous H₆V₂Mo₁₈O₆₂. Full conversion of various soft and hard lignocellulose was achieved using NLLH₅V₂Mo₁₈O₆₂ catalyst under gradually increasing temperature. During the conversion process, the lignin was oxidized mainly through β-O-4 bond cleavage without addition of NaOH, and the degradations of hemicellulose and cellulose were realized through acidic hydrolysis. The characteristics of this triple POMs allowed it to show higher activity than homogeneous H₆V₂Mo₁₈O₆₂ and previous BetH₅V₂Mo₁₈O₆₂ (Bet, i.e. betaine), which provided an alternative to developing new surfactant-type POMs in biomass conversion. The temperature-controlled properties in NLLH₅V₂Mo₁₈O₆₂ allowed easy separation and regeneration.

Keywords: Lignocellulose; Polyoxometalates; Single-cluster catalyst; Triple functional sites.