Hydrophobic Pd/Al₂O₃ catalyst intensified nitrobenzene hydrogenation in flow

Designing efficient catalysts and solvent system for the multiphase hydrogenation reaction is vital in continuous flow reactors. Herein, we prepare hydrophilic Pd/Al₂O₃ and hydrophobic modified C₁₂PA-Pd/Al₂O₃ catalyst for nitrobenzene (NB) hydrogenation in micropacked bed reactors (μPBRs). By tuning the methanol-water volume ratio, reaction temperature, reaction pressure, liquid and gas superficial velocity, the NB conversion and aniline (AN) yield are optimized. The highest NB conversion of 97.1% and AN yield 95.6% are obtained in μPBRs with hydrophobic C₁₂PA-Pd/Al₂O₃ at the reaction temperature of 90 °C. The apparent kinetic model is developed in μPBRs with two types of catalysts, and activity energies of NB hydrogenation for Pd/Al₂O₃ and C₁₂PA-Pd/Al₂O₃ are 7.944 kJ·mol⁻¹ and 3.372 kJ·mol⁻¹, respectively. It indicates that the catalytic efficiency of C₁₂PA-Pd/Al₂O₃ is better than that of Pd/Al₂O₃ in the methanol-water mixed solvent in μPBRs. The value of TOF for the hydrophobic modified C₁₂PA-Pd/Al₂O₃ catalyst is twice compared with the hydrophilic Pd/Al₂O₃ catalyst. The value of STY for μPBRs is higher than that of stirred tank reactors (STRs) and fixed bed reactors (FBRs).