Enhanced production of benzyl alcohol in the gas phase continuous hydrogenation of benzaldehyde over Au/Al2O3

•Exclusive gas phase benzaldehyde reduction to benzyl alcohol over supported Au•Au/Al2O3 synthesis by deposition delivers higher H2 uptake and hydrogenation rate.•Water as benzaldehyde carrier enhances selective hydrogenation rate.•Promotional effect of water attributed to increased surface reactive hydrogen.•100% benzyl alcohol yield over Au/Al2O3 in continuous operation

Exclusive hydrogenation of benzaldehyde to benzyl alcohol in gas phase continuous operation (393–413 K, 1 atm) was achieved over Au/Al2O3, Au/TiO2 and Au/ZrO2. Synthesis of Au/Al2O3 by deposition–precipitation generated a narrower distribution (2–8 nm) of smaller (mean = 4.3 nm) Au particles relative to impregnation (1–21 nm, mean = 7.9 nm) with increased H2 uptake under reaction conditions and higher benzaldehyde turnover. Switching reactant carrier from ethanol to water resulted in a significant enhancement of selective hydrogenation rate over Au/Al2O3 with 100% benzyl alcohol yield, attributed to increased available reactive hydrogen. This response extends to reaction over Au/TiO2 and Au/ZrO2.

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