Hydrogenation of substituted aromatic nitrobenzenes over 1% 1.0 wt.%Ir/ZrO2 catalyst: Effect of meta position and catalytic performance

This study is based on 1%Ir/ZrO2 catalyst which was studied in the hydrogenation of aromatic meta-substituted nitrobenzene in liquid phase. The catalyst was prepared by traditional impregnation method using IrCl3 and it has been characterized in terms of temperature-programmed reduction (TPR), ICP-MS, BET area, X-ray diffraction, HR-TEM and XPS measurements. The hydrogenation was evaluated in a batch type reactor at 298 K using ethanol like a solvent. The catalyst showed the formation of zero valent and partially oxidized Iridium (Irδ+) is established post-TPR and XPS characterization. The metal particle size exhibited a wide distribution with mean size 1.8 nm. Ir/ZrO2 was active in all the hydrogenation reactions with elevated conversion and promoted exclusive NO2 group reduction, resulting in the sole formation of the corresponding amino-compound except for single bondCHO and single bondCHdouble bond; length as m-dashCH2 meta-substituted nitrobenzene. We associate this response to a reducible group competition between single bondNO2 and single bondCHO or single bondCHdouble bond; length as m-dashCH2. Reactant activation on the catalyst generates a negatively charged intermediate, consistent with a nucleophilic mechanism. The presence of electron-donating substituents is shown to decrease single bondNO2 reduction rate. This effect is quantified in terms of the Hammett relationship where a linear correlation between the substituent constant (σi) and rate is established and a reaction constant (ρ) 0.639. The data generated provide the first report of the catalytic action of supported Ir in the hydrogenation of meta-substituted nitroarenes and establish the nature of the hydrogenation en liquid phase.