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 H-2, 100 degrees C). To study the origin of support and size effects, in situ FTIR experiments for OH/D-2 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 (Al delta+-O delta- site) plays an important role in H-2 dissociation step. Al delta+-O delta- site also acts as the adsorption site of the nitro group. (C) 2011 Elsevier B.V. All rights reserved.