Pt/Al2O3-Cl catalysts derived from ethylaluminumdichloride activity and stability in hydroisomerization of C6 alkanes

Chlorinated alumina catalysts obtained by impregnating a gamma-Al2O3 (0.25 wt.% Pt) with a solution of ethylaluminumdichloride (EADC) were tested for the hydroisomerization Of C-6 alkanes. The conversion of a n-hexane + cyclohexane feed diluted in hydrogen was performed at 423 K and 3 MPa total pressure. The EADC catalysts introduced as such in the reactor displayed a fairly high initial activity, but conversion slowly declined with time on stream. Adding CCl4 to the hydrocarbon feed improved both the initial conversion and the stability with time on stream. Superior results were found for the EADC-based catalyst pretreated under hydrogen at 673 K. The catalysts derived from EADC were also compared with other Pt/Al2O3-Cl catalysts chlorinated by reacting alumina with CCl4 or HCl/H-2. Analyzing the chlorine content on the solids at various stages of the catalyst life showed that some Cl was released from the EADC catalysts during the reaction itself. Furthermore, the amount of HCl that can be desorbed from the solids was measured by temperature programmed desorption. This revealed important modifications of surface species during the course of the reaction. (C) 2004 Elsevier B.V. All rights reserved.