A Microwave-Sensitive Solid Acid Catalyst Prepared from Sweet Potato via a Simple Method

In this study, a microwave-sensitive solid acid catalyst was successfully synthesized from sweet potatoes via a simple process. The catalyst was proven to have superior microwave-sensitive and homogeneous properties. The physicochemical properties were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectra (FT-IR), thermogravimetric (TGA), scanning electron microscope (SEM) and elemental analysis (EA). Results showed that the total acid density and specific surface area for the catalyst were 6.35 mmol/g and 78.35 m2/g, respectively. The elemental sulfur content reached 7.449% after sulfonation and the catalytic activity could reach over 91% within 30 min with microwave power density of 1.0 W/mL. The catalytic reaction temperature should not exceed 200 ◦C, as shown in TGA curve, and the moisture content in the oil raw material should be within 1%–2%. The catalyst deactivated gradually to 64.38% after reutilization five times, but the catalytic activity could be simply regenerated by re-sulfonation, albeit slightly reduced (87.56%). The shift of diffraction peaks in the XRD patterns and new absorption peaks at 619.98 and 1190.49 cm−1 of FT-IR spectra demonstrated that the –SO3H group was effectively attached to the catalyst. The SEM images displayed a loose and porous amorphous structure in the end catalyst.