Collect. Czech. Chem. Commun. 2008, 73, 1149-1160

Dehydrocyclization of Diphenylamine to Carbazole Over Platinum Catalysts

Miroslav Vlčko*, Zuzana Cvengrošová and Milan Hronec*

Institute of Organic Chemistry, Catalysis and Petrochemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, Bratislava 812 37, Slovakia


The gas-phase dehydrocyclization of diphenylamine (DPA) to carbazole over alumina-supported 0.4 wt.% Pt catalysts in a fix-bed reactor has been studied. The reaction was carried out at a temperature of 550 °C in the presence of hydrogen. All catalysts became well dispersed Pt after in situ reduction. Pt catalysts prepared in the presence of a competitive adsorbate (citric acid) were reasonably active during first hours on stream (DPA conversion higher than 90%). However, later, their activity decreased rapidly, except the catalyst prepared in the presence of a higher concentration of the competitive agent. The same trend was observed for the Pt catalyst prepared by wet impregnation. The activity of the catalysts prepared by a microemulsion technique was very high and stable during testing, the conversion of DPA being higher than 93%. However, the selectivities of catalysts prepared in the presence of citric acid gradually decreased with time on stream (TOS). The initial selectivityof such prepared catalysts for carbazole was about 60%. The same trend was observed for catalysts prepared by microemulsion technique. The highest selectivities, 73%, were obtained over the catalysts prepared by wet impregnation; it dropped after 6 days of testing to about 62%.

Keywords: Diphenylamine; Carbazole; Dehydrocyclization; Platinum catalysts; Gas phase.

References: 18 live references.