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<p>Halloysite (Hal) is a natural clay mineral, characterized by its tubular morphology and opposite electrical charges on its surfaces. This structure endows Hal with a suite of advantageous properties, including high thermal stability, inherent acidity, and a nanoconfined lumen, making it a compelling compound for catalytic applications. A particularly promising application lies in the acid-catalyzed conversion of saccharides into 5-hydroxymethylfurfural (HMF), a versatile and bio-based platform compound for synthesizing a wide range of value-added chemicals and biofuels. While numerous acidic catalysts have been developed for this reaction, each presents inherent limitations. Hal has recently been explored for designing advanced catalysts for HMF production, yielding acceptable results. However, to achieve high HMF yields, modification of Hal characteristics, such as its acidity, hydrophobicity, and textural properties, is imperative. To improve the acidity of Hal, various innovative strategies, including acid treatment, as well as chemical functionalization for grafting acidic moieties such as sulfonic groups, acidic ionic liquids, and polymers, and immobilization of acidic species such as heteropolyacids, metal oxides and acidic metal–organic frameworks, have been pursued. Various analyses, such as NH<sub>3</sub>-TPD and the titration method, confirmed an increase in acidity of Hal up to 2 times. To improve textural properties, acid treatment can be suggested, and BET method revealed the efficiency of this approach for improving the specific surface area and pore volume of Hal. Introduction of hydrophobic species on Hal can increase the hydrophobicity of Hal, as evidenced by measuring the contact angle. Furthermore, the introduction of basic sites on Hal can lead to bi-functional catalysts, useful for the conversion of di and polysaccharides to HMF. This mini-review article discusses the recent advances in the rational engineering of halloysite for the preparation of efficient catalysts dedicated to the synthesis of HMF. The effects of Hal modification approach on its characteristics are elaborated by discussing various analyses, such as XRD, XPS, and SEM. Furthermore, the limitations of each strategy as well as future perspectives are addressed.</p>

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Modified halloysite for heterogeneous conversion of saccharides to 5-hydroxymethylfurfural: recent advances and future trends

  • 期刊论文

  • 发表日期：

    2026年7月30日

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  • Samahe Sadjadi

摘要

Halloysite (Hal) is a natural clay mineral, characterized by its tubular morphology and opposite electrical charges on its surfaces. This structure endows Hal with a suite of advantageous properties, including high thermal stability, inherent acidity, and a nanoconfined lumen, making it a compelling compound for catalytic applications. A particularly promising application lies in the acid-catalyzed conversion of saccharides into 5-hydroxymethylfurfural (HMF), a versatile and bio-based platform compound for synthesizing a wide range of value-added chemicals and biofuels. While numerous acidic catalysts have been developed for this reaction, each presents inherent limitations. Hal has recently been explored for designing advanced catalysts for HMF production, yielding acceptable results. However, to achieve high HMF yields, modification of Hal characteristics, such as its acidity, hydrophobicity, and textural properties, is imperative. To improve the acidity of Hal, various innovative strategies, including acid treatment, as well as chemical functionalization for grafting acidic moieties such as sulfonic groups, acidic ionic liquids, and polymers, and immobilization of acidic species such as heteropolyacids, metal oxides and acidic metal–organic frameworks, have been pursued. Various analyses, such as NH3-TPD and the titration method, confirmed an increase in acidity of Hal up to 2 times. To improve textural properties, acid treatment can be suggested, and BET method revealed the efficiency of this approach for improving the specific surface area and pore volume of Hal. Introduction of hydrophobic species on Hal can increase the hydrophobicity of Hal, as evidenced by measuring the contact angle. Furthermore, the introduction of basic sites on Hal can lead to bi-functional catalysts, useful for the conversion of di and polysaccharides to HMF. This mini-review article discusses the recent advances in the rational engineering of halloysite for the preparation of efficient catalysts dedicated to the synthesis of HMF. The effects of Hal modification approach on its characteristics are elaborated by discussing various analyses, such as XRD, XPS, and SEM. Furthermore, the limitations of each strategy as well as future perspectives are addressed.