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 aromatization 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 1.5–2 wt% Mo catalyst were achieved at 600 °C with methane flow rate of 270 cm3/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.