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Abstract
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A series of catalysts based on natural clinoptilolite zeolite were synthesized and characterized for biodiesel production through the esterification reaction of oleic acid. For this purpose, sulfur-containing functional groups were incorporated into the clinoptilolite framework through ion-exchange treatment with sulfuric acid solutions at concentrations of 0.5, 1, and 2 M. The structural properties of the synthesized catalysts were investigated using XRD, FESEM, EDX dot mapping, FTIR, as well as N2 adsorption–desorption isotherms. XRD patterns and FTIR spectra revealed that the crystallinity of clinoptilolite gradually decreased during sulfuric acid treatment, with a pronounced reduction observed for the sample modified with 2 M acid. N2 adsorption–desorption isotherms analysis demonstrated that the specific surface area of the sample treated with 1 M sulfuric acid increased by 45% compared to the raw zeolite. Furthermore, EDX dot mapping confirmed the homogeneous distribution of sulfur species across all modified samples. Catalytic performance evaluation in the esterification of oleic acid indicated that the incorporation of sulfur functionalities significantly enhanced catalytic activity, with the highest conversion of 70.6% achieved by the sample treated with 1 M sulfuric acid.
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