Pd-Fe/SiO2 Catalysts in the Hydrogenation of 2,4-Dinitrotoluene

Pd-Fe/SiO2 bimetallic catalysts with a constant amount of Pd and a different Fe/Pd ratio were prepared by sequential wet impregnation and the hydrogenation of 2,4-dinitrotoluene was carried out at 25°C in a batch reactor. The presence of Fe enhances the Pd catalytic activity. The formation of a dispersed Pd-Fe alloy was evidenced through X-ray powder diffraction and is consistent with the data observed by FTIR analysis, TPR, and chemisorption features. The increase of the Fe total content of the catalysts results in the increase of the dispersion of the metallic phase and in the presence of partially oxidized Fe species. FTIR analysis shows that nitrocompounds chemisorb mainly on the support rather than on the metal surface. It is suggested that the Pd-Fe alloy formation is responsible for the increase of the catalytic activity because of a cooperative effect of Fe in the hydrogen transfer step.