Highly active, selective and stable Mo/Ru-HZSM-5 catalysts for oxygen-free methane aromatization

Highly active, selective and stable catalysts for oxygen-free methane aromitization were prepared by using ion-exchange and vapor deposition techniques rather than the conventional metal impregnation methods. Ruthenium (0.15 wt%) was incorporated first to ZSM-5 as a promoter by ion-exchange at room temperature. Then 1-3 wt% of Mo was loaded using Mo(CO)(6) as a Mo precursor. High benzene yields of 4.0-4.2% using a 1.52 wt% Mo catalyst were achieved at 600 degrees C with methane flow rate of 270 cm(3)/g h and 1 atm pressure. Effect of changes in the pretreatment conditions (carburization time) was also investigated. Slower heating rates decreased the induction time and improved benzene yield. Mo loading beyond 2.5 wt% led to lower methane conversions. Temperature-programmed oxidation technique was used to characterize the nature of coke formed on spent catalysts. The amount of coke formed was negligible, resulting in high catalyst performance. (c) 2005 Elsevier B.V. All rights reserved.