Porous Boron Nitride as a Weak Solid Base Catalyst

Porous boron nitride was synthesized by pyrolysis from boric acid and urea mixed in varying molar ratios. The boron nitride prepared had high surface areas ranging from 376 to 647 m² g⁻¹ with both microporous and mesoporous structures. The sample prepared with a urea-to-boric acid molar ratio of 5 exhibited the highest pore volume with the highest surface area of mesopores. Boron-K edge X-ray absorption fine structure spectroscopy revealed that the surface structure consisted of BN₃ sites along with BN₂O, BNO₂, and BO₃ sites. Fourier transform infrared (FTIR) spectroscopy indicated the formation of amino and hydroxyl groups on the surface. Analysis using color indicator reagents and deuterated chloroform-adsorbed FTIR results indicated that the porous boron nitride had very weak base sites of strength +7.2>H−≥+6.3. Porous boron nitride exhibited a high activity for the nitroaldol reaction with a high selectivity for nitroalkene (>97 %). A good correlation was observed between the catalytic activity of the boron nitride catalysts and their porous structures.