Selectivity in the gas-phase hydrogenation of 4-nitrobenzaldehyde over supported Au catalysts

The effects of Au particle size and support properties have been examined in the gas-phase hydrogenation of 4-nitrobenzaldehyde over Au/ZrO2, Au/TiO2 and Au/Al2O3. Gold particle size was varied using deposition–precipitation and impregnation syntheses. The catalysts have been characterised in terms of BET area/pore volume, temperature-programmed reduction (TPR), XRD, H2 chemisorption/TPD, TEM, XPS, and pyridine adsorption FTIR measurements. Reaction exclusivity to 4-aminobenzaldehyde was achieved over Au/ZrO2 and Au/TiO2 where a decrease in Au particle size (mean from 7.0 to 4.7 nm) generated a higher turnover frequency. Pyridine adsorption coupled with FTIR analysis has revealed stronger Lewis acidity associated with Au/Al2O3, which contributes to Cdouble bond; length as m-dashO reduction via the formation of a benzoate intermediate. Selectivity to the alcohol is sensitive to Au size and reaction temperature with 100% 4-nitrobenzyl alcohol selectivity over Au/Al2O3 (mean Au size = 7.8 nm) at 423–443 K. Our results demonstrate the viability of controlling selective single bondNO2 and Cdouble bond; length as m-dashO reduction using oxide-supported Au catalysts.