Effects of direct sulfonation on the catalytic activity and recyclability of novel lignin-based solid acid catalysts from agri-food waste

Current approaches, emerging developments and functional prospects for lignin-based catalysts – a review

“…in lignin fragments, being accountable for its reactivity, encourage the capacity for functionalization and chemical processing in specific catalytic applications. 50,54,60,122,123 Interestingly, the use of lignin as a natural substrate for the production of industrial catalysts is considered to be one of the most innovative and recent approaches to revalorizing biomass lignocellulosic materials. The past few years have witnessed new approaches targeting the use of lignin as a natural polymer to develop a variety of biomass-based catalysts.…”

“…47 Attractively, the design of lignin-based catalysts is an innovative approach to valorize this lignocellulosic material, due to its phenolic character, accessibility, biodegradability, and reasonable production cost, as well as the presence of desirable functional groups which are enriched in both carbon and oxygen. Lignin has been successfully applied as a renewable carrier material to produce reliable metal-free solid catalysts, 41,[47][48][49][50] as well as lignin-immobilized metal catalysts. 36,39,[51][52][53] These lignin-derived catalysts offer high product efficiency, continuous operation, a clean environment, lower corrosive impact, ease of separability, and reusability, and can significantly reduce the cost of the process.…”

“…In fact, the elaboration of lignin-based acid catalysts is an appealing concept to recover this lignocellulosic material considering its bio-polyphenolic potential, affordability, biodegradability, and acceptable production economics, as well as the availability of useful functional groups like methoxy, hydroxyl, carboxyl, ketones and aldehydes, which are enriched in carbon and oxygen, are highly reactive and can prompt the implementation of lignin-based materials in various catalyzed transformations. 47,48,50,135,137 Moreover, lignin-derived catalysts exhibit a high output of the product, continuous operation, a clean environment, a reduced corrosive footprint, facility of removal, and recoverability, and can considerably decrease the cost of the process. Indeed, the heterogeneity of lignin-based acid catalysts is of particular relevance as it allows easy extraction by filtration or centrifugation, thereby maximizing its recovery potential.…”

“…4a). 20,50,54,125,142 Sulfated lignin catalysts exhibit significant activity in a wide range of selective reactions via the acidic active sites on the surface, translating into good thermal stability and high-performance catalytic conversion.…”

“…Although these lignin-based heterogeneous catalysts exhibit good catalytic performance, they do require a high processing energy and are time-consuming. 50,150 The current novelty consists of functionalizing lignin by modifying the nature and properties of its functional groups with no prior treatment. In fact, lignin presents a great opportunity for chemical functionalization through its multifunctional structure and its reactive sites (OMe, OH, COOH, CvO, etc.).…”