Pd catalyst supported on aryl-bridged polysilsesquioxane for hydrogenation of p-nitrophenol: Effect of solvent and pH

Aryl-Bridged polysilsesquioxane (ABPS), a hydrophobic, mesoporous, hybrid silica material, was employed as a support for a palladium (Pd) catalyst for catalytic hydrogenation of para-nitrophenol (PNP) to para-aminophenol (PAP) using molecular hydrogen. The effect of protic and aprotic solvents on the catalytic hydrogenation activity of para-nitrophenol (PNP) was investigated, and water, with the highest proticity, was observed to give the highest PNP conversion. The PNP hydrogenation activity was also found to decrease with decreasing proticity of the solvent. The PNP hydrogenation activity and product stability were investigated at different pH levels. To study the effect of pH on PNP adsorption, equilibrium adsorption capacity of Pd/ABPS at varying pH was determined, and Pd/ABPS samples following PNP adsorption were characterized with Raman spectroscopy. PNP conversion was calculated using UV–Vis spectroscopy, and the products of the PNP hydrogenation were identified using 1 H Nuclear Magnetic Resonance Spectroscopy (NMR), Mass Spectrometry (MS), and Raman Spectroscopy. Additionally, the performance of the Pd/ABPS catalyst was also benchmarked using Pd/AC, a commercial activated carbon-supported hydrogenation catalyst.