Modulation of Self‐Separating Molecular Catalysts for Highly Efficient Biomass Transformations

Abstract

The energetically viable fabrication of stable and highly efficient solid acid catalysts is one of the key steps in large‐scale transformation processes of biomass resources. Herein, the covalent modification of the classical Dawson polyoxometalate (POMs) with sulfonic acids (‐SO3H) is reported by grafting sulfonic acid groups on the POM's surface followed by oxidation of (3‐mercaptopropyl)trimethoxysilane. The acidity of TBA6‐P2W17‐SO3H (TBA=tetrabutyl ammonium) has been demonstrated by using 31P NMR spectroscopy, clearly indicating the presence of strong Brønsted acid sites. The presence of TBA counterions renders the solid acid catalyst as a promising candidate for phase transfer catalytic processes. The TBA6‐P2W17‐SO3H shows remarkable activity and selectivity, excellent stability, and great substrate compatibility for the esterification of free fatty acids (FFA) with methanol and conversion into biodiesel at 70 °C with >98 % conversion of oleic acid in 20 min. The excellent catalytic performance can be attributed to the formation of a catalytically active emulsion, which results in a uniform catalytic behavior during the reaction, leading to efficient interaction between the substrate and the active sites of the catalyst. Most importantly, the catalyst can be easily recovered and reused without any loss of its catalytic activity owing to its excellent phase transfer properties. This work offers an efficient and cost‐effective strategy for large‐scale biomass conversion applications.

Reactivity of metal–oxo clusters towards biomolecules: from discrete polyoxometalates to metal–organic frameworks

“…Exceptionally, a tetrabutylammonium (TBA) salt of a Wells-Dawson POM covalently functionalized with sulfonic acid groups (TBA 6 [P 2 W 17 -SO 3 H]) has been recently reported as a phase transfer catalyst for the conversion of fructose to HMF with 99% yield after 2 h at 100 1C in 1,4-dioxane (Table 4). 201 It was shown to also catalyze the conversion of glucose, sucrose, and inulin into HMF in reasonable yields, but failed to convert cellulose. Moreover, this is one of the few examples where a covalently functionalized hybrid POM was used as a catalyst in biomolecular transformations.…”

Latest progress in covalently modified polyoxometalates-based molecular assemblies and advanced materials

“…POMs exhibited excellent catalytic performance in various catalytic reactions due to their large size, low electron density, and high degree of charge dissociation, which facilitated electron transport [94] . As a homogeneous catalyst, the inherent disadvantage of POMs was their high solubility in polar solvents, which led to the difficulties in recovery, separation and recirculation.…”

“…Song et al prepared a self-separating phase transfer catalyst (TBA6-P2W17-SO3H) by covalent modification of [P2W17O61] 8with organosilane-sulfonic acid groups (Figure 13a) [94] . The super acidic and modified amphiphilic catalyst not only improved the efficiency of the esterification reaction, but also brought excellent self-separating performance to the catalytic system due to the embedded emulsion precipitation cycle (Figure 13b).…”

Interface-Confined Channels Facilitating Water Transport through an IL-Enriched Nanocomposite Membrane

“…The IL-based nanocomposite materials could be an integration of an IL and nanoparticles by chemical grafting and encapsulation, , which has been reported for absorption, catalysis, and a reactor . The metal–IL complex is also an IL-based nanocomposite material that can be formed via the coordination combination between the IL and metal ions, in which the metal could enrich and immobilize a mass of IL.…”