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

Abstract: 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 stability 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 spectroscopy, 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.