Support effects in the selective gas phase hydrogenation ofp-chloronitrobenzene over gold

Abstract

The catalytic continuous gas phase hydrogenation of p-chloronitrobenzene (P=1 atm;T=423 K) has been investigated over a series of oxide (Al2O3, TiO2, Fe2O3 and CeO2) supported Au (1 mol %) catalysts. The application of two catalyst synthesis routes,i.e. impregnation (IMP) and deposition-precipitation (DP), has been considered where the DP route generated smaller mean Au particle sizes (1.5-2.8 nm) compared with the IMP preparation (3.5-9.0 nm). The catalysts have been characterised in terms H2 chemisorption and BET area measurements where the formation of metallic Au post-activation has been verified by diffuse reflectance UV-Vis, XRD and HRTEM analyses.p-Chloroaniline was generated as the sole reaction product over all the Au catalysts with no evidence of C-Cl and/or C-NO2 bond scission and/or aromatic ring reduction. The specific hydrogenation rate increased with decreasing Au particle size (from 9 to 3 nm), regardless of the nature of the support. This response extends to a reference Au/TiO2 catalyst provided by the World Gold Council. A decrease in specific rate is in evidence for smaller particles (< 2 nm) and can be attributed to a quantum size effect. The results presented establish the basis for the design and development of a versatile catalytic system for the clean continuous production of high value amino compounds under mild reaction conditions.