Synthesis of Keggin-Al13-modified bentonite materials with enhanced mesoporosity: structural and textural characterization and application in soot oxidation.

Abstract

This paper reports the preparation of a series of bentonite-based materials through sequential sodium exchange, sulfuric acid activation, Al13 polycation treatment, and subsequent cobalt (Co) and manganese (Mn) impregnation. The structural and textural properties of the resulting materials were investigated using FTIR, XRD, TEM, TGA-DTA, BET surface area analysis, and fractal analysis. The soot oxidation performance was measured using O2 with T 10, T 50 and T 90 as conversion indicators. Acid activation markedly modified the structure and texture of the bentonite, resulting in a significant increase in specific surface area, reaching 438.84 m2 g-1 for BNT-NaA, together with the development of mesoporosity. XRD analysis confirmed the expansion of the basal spacing after Al13 treatment of raw and sodium-exchanged bentonite, with d 001 values of 16.96 and 18.03 Å for BNT-P and BNT-NaP, respectively, indicating interlayer incorporation of Al13 polycations. In contrast, the acid-activated samples subsequently treated with Al13, BNT-AP and BNT-NaAP, did not exhibit a well-defined d 001 reflection, indicating substantial disruption of the original layered structure and preventing the confirmation of a well-ordered pillared framework by XRD. Nevertheless, BNT-NaAP retained a relatively high specific surface area of 210.42 m2 g-1 and pronounced mesoporous characteristics. Following metal impregnation, Co/BNT-NaAP and Mn/BNT-NaAP exhibited specific surface areas of 219.75 and 187.92 m2 g-1, respectively. Fractal analysis revealed an increase in surface heterogeneity following the modification treatments, with fractal dimension values ranging from 2.61 to 2.95. Co/BNT-NaAP had a T 50 of 510 °C, compared to 590 °C for BNT-NaAP and 660 °C for soot alone, indicating enhanced catalytic activity under the investigated conditions.

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