Synthesis of heterogeneous catalysts based on manganese oxides applied for the aerobic oxidation of p-hydroxybenzyl alcohol to p-hydroxybenzaldehyde

In order to synthesize p-hydroxybenzaldehyde from p-hydroxybenzyl alcohol under oxygen atmosphere, we prepared the new heterogeneous catalysts based on manganese oxides by in-situ growth method at different pH values. The crystal structure, phase composition, morphology, and surface groups of catalysts were characterized by powder X-ray diffraction, field emission electron scanning microscopy and Fourier transform infrared spectroscopy. According to the experimental results, the solution pH used for the preparation of the catalysts strongly affected their properties and their catalytic activities. When the pH was increased from 2 to 4, the a-Mn2O3 content increased with the dominant presence of the rod-like particles. The quantity of Mn on the surface also enhanced which might improve the conversion of p-hydroxybenzyl alcohol while maintaining the high selectivity to p-hydroxybenzaldehyde (about 70%). However, when the pH was highr than 4, the quantity of rod-like particles,a-Mn2O3 and surface Mn species decreased which lowered the catalytic activity.