Selective hydrogenation of nitrocyclohexane to cyclohexanone oxime by alumina-supported gold cluster catalysts

Metal oxides (Al2O3, SiO2, MgO)-supported Au cluster catalysts prepared by colloid deposition method and well established Au/TiO2 prepared by deposition–precipitation method were tested for the selective reduction of nitrocyclohexane into cyclohexanone oxime. The activity and selectivity depended strongly on the size of Au and support material. Au/Al2O3 with smaller Au particle size (2.5 nm) was the most effective catalyst, exhibiting a high cyclohexanone oxime yield (86%) under mild condition (0.6 MPa H2, 100 °C). To study the origin of support and size effects, in situ FTIR experiments for OH/D2 exchange reaction and nitrobenzene adsorption combined with poisoning experiments using pyridine and acetic acid were carried out. It is suggested that cooperation of coordinatively unsaturated Au atoms and the acid–base pair site (Alδ+–Oδ− site) plays an important role in H2 dissociation step. Alδ+–Oδ− site also acts as the adsorption site of the nitro group.

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► Au/Al2O3 shows higher selectivity of cyclohexanone oxime than the standard Au catalyst, Au/TiO2.
► This is the first successful example of heterogeneous Au catalyst for the title reaction.
► Smaller Au size and acid–base bifunctional support result in higher catalytic efficiency.
► Mechanistic studies suggest a cooperation of AuCUS sites and the acid–base pair site of Al2O3.