Support effect of Rh catalysts on the hydrogenation of m-dinitrobenzene

Abstract The effect of the support (ZrO 2 , Al 2 O 3 , and TiO 2 ) of Rh (1 wt%) catalysts for the hydrogenation of m -dinitrobenzene ( m -DNB) in liquid phase was studied. The catalysts were reduced at 300 °C and characterized by EDS, TPR, TEM, N 2 Adsorption, H 2 chemisorption, XPS and Pyr-FTIR. Occurrence of partially reduced Rh species and metallic Rh is different among catalysts as evidenced by XPS. A typical SMSI effect was observed in Rh/TiO 2 catalyst according to comparison of Hydrogen chemisorption and TEM results. Kinetic analysis of the m -DNB hydrogenation showed that the first step hydrogenation rate ( m -DNB to m -NA, kinetic constant k 1 ) is faster than the second one ( m -NA to m -PDA, kinetic constant k 2 ) and this depending on the catalyst. m -DNB preferentially adsorbs on electron deficient sites provided by Rh n+ species present in Rh/Al 2 O 3 and Rh/TiO 2 catalysts and depending on the relative amount of this sites the m -DNB is partially hydrogenated to m-NA. A direct correlation of k 2 / k 1 ratio with the amount of Rh° was found.