Gas phase hydrogenation of p-chloronitrobenzene over Pd–Ni/Al2O3

• Published in: Applied catalysis. A, General General, 2014-03, Vol.473, p.41-50
• Main Authors: Cárdenas-Lizana, Fernando, Gómez-Quero, Santiago, Amorim, Claudia, Keane, Mark A.
• Format: Article
• Language: English
• Subjects: Bimetallic catalyst; Co-impregnation; p-Chloroaniline; p-Chloronitrobenzene; Pd–Ni/Al2O3; Selective hydrogenation
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2014.01.001

•Selective hydrogenation of p-chloronitrobenzene over Ni/Al2O3 to p-chloroaniline.•Pd/Al2O3 promotes hydrodechlorination/hydrogenation to nitrobenzene and aniline.•Reaction over Pd/Al2O3+Ni/Al2O3 physical mixtures controlled by Pd/Al2O3.•Pd–Ni/Al2O3 delivers highest activity and 100% selectivity to p-chloroaniline.•Elevated p-chloroaniline yield linked to bimetallic particles in Pd–Ni/Al2O3. The gas phase (1atm; T=393K) hydrogenation of p-chloronitrobenzene (p-CNB) has been examined over alumina supported mono-(Pd or Ni) and bi-metallic (Pd:Ni=1:3, 1:1 and 3:1) catalysts prepared by (co-)impregnation. The catalytic action of physical mixtures (Pd/Al2O3+Ni/Al2O3) was also considered. The catalysts have been characterised by temperature programmed reduction (TPR), H2 chemisorption, powder XRD, HRTEM–EDX and XPS measurements. TPR analysis has provided evidence of a more facile reduction of Pd and Ni in Pd–Ni/Al2O3 relative to Pd/Al2O3 and Ni/Al2O3. TEM–EDX and XPS measurements show Pd surface enrichment in Pd–Ni/Al2O3 with evidence of modification to Pd electronic character. Ni/Al2O3 promoted exclusive -NO2 group reduction to generate p-chloroaniline (p-CAN). Pd/Al2O3 delivered a higher specific p-CNB consumption rate, yielding undesired nitrobenzene and aniline via coupled hydrodechlorination and hydrogenation. The Pd/Al2O3+Ni/Al2O3 combination generated an overall rate and product distribution equivalent to Pd/Al2O3, i.e. the catalytic response was governed by Pd in the physical mixture. In contrast, reaction over Pd–Ni/Al2O3 resulted in exclusive production of the target p-CAN. This is consistent with lower chlorobenzene hydrodechlorination activity recorded for Pd–Ni/Al2O3 (relative to Pd/Al2O3). Reaction rate was sensitive to composition where Pd:Ni=1:1 delivered the highest p-CAN yield. We attribute the catalytic response observed for Pd–Ni/Al2O3 to bimetallic particle formation as demonstrated by TPR, XRD and XPS analyses.