Sulfonated carbon is a ‘green,’ solid-acid catalyst. For applications purposes, its surface area needs to be improved and its preparation needs to be made environmentally friendly. The objective of the present study was to provide a green and economical method of preparing a sulfonated carbon catalyst by using palygorskite (Plg) fiber as a support for sulfonated carbon. Sulfonated carbon/palygorskite solid-acid catalyst (SC-Plg) was synthesized via one-step carbonization-sulfonation by mixing palygorskite with sucrose as the carbon source and p-toluenesulfonic acid as the sulfonating agent. The catalyst was characterized by SEM, EDX, TEM, FTIR, and nitrogen adsorption-desorption isotherms. The results indicated that sucrose-derived carbon was loaded uniformly on the surface of Plg fibers and formed the SC-Plg catalyst. The inexpensive Plg fibers could replace sucrose-derived carbon and increase the surface area of the resulting catalyst. The SC-Plg shows significant catalytic performance and excellent stability when used in the esterification of oleic acid with methanol. The conversion of oleic acid reached 68.09%, even after five cycles. This work paves the way for the development of highly active, carbon-based, solid-acid composite catalysts using a natural Plg nanofiber template.

Sulfonated carbon is a green, solid acid catalyst but its surface area, separation, and recovery after utilization need to be improved. The objective of the present study was to provide an environmentally friendly and economical method to prepare magnetic sulfonated carbon composite catalyst with a large surface area using palygorskite (Plg) as the support. A magnetic sulfonated carbon/Fe3O4/Plg composite catalyst was prepared via simultaneous calcination and sulfonation of the mixture of source, p-toluenesulfonic acid (TsOH), and Fe3O4/Plg. Fe3O4 nanoparticles and Plg nanorods were encased by a carbon layer derived from sucrose and TsOH. The composite catalyst exhibited good magnetic properties and high catalytic performance for the esterification of oleic acid with methanol. Oleic acid conversion reached 88.69% after the first catalytic cycle. Plg nanorods replaced sucrose and increased the catalyst’s surface area. The introduction of Fe3O4 nanoparticles improved further the acid content and oleic-acid conversion and achieved 70.31% after five cycles. The catalyst was recycled easily using an external magnetic field and its magnetic property remained unchanged due to the protection of the carbon layer.