Selective gas phase hydrogenation of p-nitrobenzonitrile to p-aminobenzonitrile over zirconia supported gold

• First report of p-nitrobenzonitrile gas phase hydrogenation over supported Au.
• 100% yield of p-aminobenzonitrile over Au/ZrO2 and Au/Al2O3.
• Au/ZrO2 outperforms Au/Al2O3, Pd/Al2O3 and Ni/Al2O3.
• Tetragonal → monoclinic ZrO2 on introduction of Au by deposition–precipitation.

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.

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