Efficient production of biodiesel from both esterification and transesterification over supported SO–MoO–ZrO–NdO/SiO catalysts

SO2-4–Mo O3–Zr O2–Nd2O3/Si O2(SMZN/Si O2) catalysts for the production of biodiesel via both esterification and transesterification were prepared and characterized by N2adsorption-desorption isotherms,X-ray diffraction(XRD),scanning electron microscopy(SEM),thermogravimetry analysis(TGA),ammonia adsorption Fourier transform infrared spectra(NH3-FTIR),and ammonia adsorption temperature programmed desorption(NH3-TPD) to reveal the dependence of the stable catalytic activity on calcination time. The reason for catalyst deactivation was also studied. The calcination time remarkably affected the types of active centers on SMZN/Si O2-2,and 4 h was found to be the optimal calcination time. SO4 species bonded with small size Zr O2 were found to be the stable active centers,where the leaching of SO2-4and the deposition of coke were inhibited. The deposition of coke was easier on large size Zr O2 than on small size ones. Calcination in air flow could eliminate the deposited coke to recover the deactivated catalysts.