Design of Water-Tolerant Solid Acids: A Trade-Off Between Hydrophobicity and Acid Strength and their Catalytic Performance in Esterification

Abstract

Water, as a byproduct in esterification, tends to adsorb on solid acid catalysts, causing loss of active components or decomposition of framework and thereby decreasing their reactivity and durability, while the development of water-tolerant solid acids is expected to solve these problems. In this review, the recent developments of major kinds of water-tolerant solid acids including zeolite, mesoporous silica, metal organic framework-based catalyst, magnetic nanoparticles, and polymeric catalyst are discussed in detail. Special attention has been paid to understand the role of hydrophobicity, acid strength, and structure of water-tolerant solid acids in catalytic performance and their stability. From the literature survey, it is found that despite the modified zeolites have a water contact angle as large as 160°, but their acid strength need to be improved and their small micropore sizes restrict their use in catalyzing the esterification of bulky molecules. In contrast, solid acids with abundant acid sites, suitable hydrophobicity, and abundant mesopores or macropores usually exhibit high activity and reusability. Among all the known solid acids, polystyrene-supported acidic ionic liquid catalysts (PS-CH2-[SO3H-pIM] [HSO4]) show a high yield of n-butyl acetate with 99.1% and high reusability of 13 times, which is a breakthrough over the traditional. This review aims to offer a comprehensive understanding for the water-tolerant solid acid catalysts in esterification.