Experimental and theoretical analysis of selective hydrogenation of p-nitroanisole to p-anisidine over Pd/C: kinetics and catalyst deactivation

Abstract

The selective reduction of nitro compounds to the corresponding amines in multi-functional moieties is attempted in a variety of industries using polluting processes including iron–acid and sulfide/polysulfide reduction processes. In the current work, selective hydrogenation of p-nitroanisole (PNA) to p-anisidine (PA) has been carried out using supported metal catalysts. 5% Pd/C was found to be highly effective in comparison with other metal catalysts used. Kinetic interpretation has been made by studying the important process parameters using 5% Pd/C as the catalyst. The experimental results show that conversion of PNA reaches 100% under the appropriate reaction conditions. The reaction was found to be 100% selective towards PA. It was possible to determine both the rate constant and adsorption equilibrium constant for the reaction. The activation energy of reaction and free energy of adsorption were found to be 10.25 and –2.4 kcal mol^–1, respectively, indicating that the reaction is Langmuir-Hinshelwood kinetically controlled. The catalyst was found to be deactivated due to the blocking of channels by product precipitation, which was considered as independent deactivation. A deactivation model was developed and it was found to fit the data very well. A complete theoretical and experimental analysis is presented.