Catalytic properties of selenium and phosphorus ionic liquids heterogenized on algae-based biochar

Catalytic performance of pyridinium hydrogen selenate (PHSe) and pyridinium dihydrogen phosphate (PH2P) ionic liquids immobilized on algae-based biochar (AC) was studied for the first time. For that purpose, acetic acid esterification with butanol was used as a test reaction. To investigate the surface effects, textural properties and thermal behavior for PHSe/AC and PH2P/AC, physicochemical methods such as X-ray powder diffraction (XRD), nitrogen adsorption–desorption isotherms (S_BET) scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were applied. In addition, influence of the catalyst content (5–12 wt%) and reaction temperature (60–80 °C) on the butyl acetate yield and rate constant of esterification were evaluated. S_BET and SEM measurements revealed that all of the samples (AC, PHSe/AC and PH2P/AC) obtained are mixed microporous-mesoporous materials. XRD and XPS data showed more highly dispersed PH2P particles than PHSe on the carrier surface due to stronger surface ionic liquid-support interaction for PH2P/AC in comparison with PHSe/AC. The latter was responsible for higher thermal stability of PH2P/AC with respect to PHSe/AC. In addition, more obvious PH2P sites (than PHSe) on the biochar surface favored the ester production in the presence of PH2P/AC (77.4 % and 53.26 × 10⁻⁴ l/mol × min) more evidently than PHSe/AC (58.1 % and 28.82 × 10⁻⁴ l/mol × min).