Selective Gas Phase Hydrogenation of p-Nitrobenzonitrile to p-Aminobenzonitrile over Zirconia Supported Gold

The catalytic action of Au/ZrO2 in the gas phase hydrogenation of p-nitrobenzonitrile (p-NBN) to p-aminobenzonitrile (p-ABN) has been assessed against Au/Al2O3. Crystalline ZrO2 was prepared by precipitation of ZrOCl2 with aqueous NH3 and calcined to generate tetragonal and monoclinic phases. Catalyst and support were characterised by surface area/porosity, temperature-programmed reduction (TPR), H2 chemisorption/temperature programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) measurements. Higher calcination temperatures (673-973 K) increased the monoclinic ZrO2 content with a decrease in surface area and pore volume. Introduction of Au by deposition-precipitation resulted in tetragonal→monoclinic transformation with post-TPR formation of Au particles in the 3-13 nm size range and electron transfer from ZrO2. Reaction over Au/ZrO2 delivered 100% p-ABN yield with higher turnover frequency (267 h−1) than Au/Al2O3 (109 h−1) attributed to greater H2 chemisorption capacity under reaction conditions and enhanced −NO2 activation. Au/ZrO2 outperformed benchmark Pd/Al2O3 and Ni/Al2O3, which generated p-aminotoluene via subsequent hydrogenation/hydrogenolysis.