Na-modified carbon nitride as a leach-resistant and cost-effective solid base catalyst for biodiesel production

Na-modified graphitic carbon nitrides were utilized for the transesterification of soybean oil and methanol. Graphitic carbon nitrides have not yet been widely applied in biodiesel production, despite their chemical sta-bility and basicity. The catalysts were obtained via the co-thermal polymerization of NaOH and melamine. Catalyst prepared using conventional impregnation method was applied for comparison. The copolymerized catalyst with the optimum Na content showed over 90% biodiesel yield for 10 repeated cycles. The prepared catalysts were characterized by Fourier transform infrared spectrometry, X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy, CO2-diffuse reflectance infrared Fourier transform spectros-copy, and X-ray photoelectron spectroscopy. The elaborate rigid bonds between Na and N contributed to the leaching-resistance and catalytic activity. While the majority of Na species in impregnated catalysts existed in the form of Na-O, which was easily leached out to the reaction medium showing rapid catalyst deactivation over the repeated cycles. The basicity derived from the electron transfer from the Na to N atoms was confirmed from the density functional theory and CO2-diffuse reflectance infrared Fourier transform spectroscopy.