Pd-promoted selective gas phase hydrogenation of p

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• 作者：Fern ; o Cá ; rdenas-Lizana ; Santiago Gó ; mez-Quero ; Antoine Hugon ; Laurent Delannoy ; Catherine Louis ; Mark A. Keane
• 关键词：p-Chloronitrobenzene ; Selective hydrogenation ; p-Chloroaniline ; Au/Al₂O₃ ; Pd– ; Au/Al₂O₃ ; DRIFTS analysis ; TPR ; H₂ chemisorption
• 刊名：Journal of Catalysis
• 出版年：2009
• 出版时间：10 March 2009
• 年：2009
• 卷：262
• 期：2
• 页码：235-243
• 全文大小：737 K

文摘

The gas phase hydrogenation of p-chloronitrobenzene has been investigated over alumina supported Au (ca. 1 % , w/w) prepared by deposition-precipitation with urea (DP) and impregnation in excess solvent (IMP). Both catalysts were 100 % selective in terms of –NO₂ group reduction, resulting in the sole formation of p-chloroaniline. Au–DP exhibited a smaller mean Au size (2.9 nm) compared with Au–IMP (4.5 nm) and delivered a higher (by a factor of 14) specific hydrogenation rate. Bimetallic Pd–Au/Al₂O₃ catalysts have also been prepared by DP and IMP with Au/Pd mol/mol = 8, 20 and 88. Catalyst activation by temperature programmed reduction has been monitored and the activated catalysts characterized in terms of H₂ chemisorption, TEM analysis and DRIFTS. DRIFTS measurements using CO as a probe molecule suggest the presence of bimetallic particles and surface Au–Pd interaction. A significant increase (by up to a factor of 3) in activity was observed for Pd–Au/Al₂O₃ (Au/Pd  20) compared with Au/Al₂O₃ where the exclusive conversion of p-chloronitrobenzene to p-chloroaniline was maintained. At a lower ratio (Au/Pd = 8), nitrobenzene was produced as a result of a Pd catalyzed hydrodechlorination step. Under the same reaction conditions, Au/Al₂O₃ + Pd/Al₂O₃ physical mixtures (Au/Pd = 20) delivered higher reaction rates but with the formation of nitrobenzene and aniline, i.e. products of hydrodechlorination and hydrogenation. We attribute the enhanced and exclusive production of p-chloroaniline over the supported bimetallics to a surface Pd–Au synergism. Our results establish the viability of Pd-promotion in the selective continuous gas phase catalytic hydrogenation of p-chloronitrobenzene over supported Au.