Activity patterns of metal oxide catalysts in the synthesis of N-phenylpropionamide from propanoic acid and aniline

The reactivities of various commercial and lab-made oxide samples (e.g., gamma-Al2O3, CeO2, ZrO2 and TiO2) in the heterogeneous catalytic synthesis of N-phenylpropionamide (T, 383 K) from aniline and propanoic acid have been investigated. All the materials studied drive the direct synthesis of the amide to an extent depending on both the chemical and structural properties. A 0th-order kinetic dependence on the substrate concentrations suggests that the reaction proceeds via a Langmuir-Hinshelwood (L-H) pathway under kinetic control of the adsorption-desorption steps (the rate determining step, r.d.s.). The comparative analysis of the activity data on the basis of the relative surface specific kinetic constant discloses a superior surface reactivity of TiO2, CeO2 and ZrO2 over the gamma-Al2O3 system, and also highlights marked differences in the catalytic functionality of the titania samples. IR spectroscopic studies of the carboxylic acids and amine adsorption and interaction patterns show the formation of the bidentate, bridging, and unidentate carboxylate intermediates accounting for the different amidation functionalities of the studied materials.