Support effects in the selective gas phase hydrogenation ofp-chloronitrobenzene over gold |
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Authors: | Fernando Cárdenas-Lizana Santiago Gómez-Quero Noémie Perret and Mark A Keane |
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Affiliation: | (1) Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand Johannesburg, Johannesburg, Wits 2050, South Africa; |
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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. |
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