Methane aromatization over 2 wt% Mo/HZSM-5 in the presence of O₂ and NO

In the non-oxidative aromatization reaction (temperature = 770°C, flow rate = 34 ml min^-1), 2wt% Mo/HZSM-5 deactivated after 4h due to severe coking. We observed that with a suitable amount of O₂ (≤5.3 vol%) in the methane feed, the catalyst could last for more than 6h with a ca. 4% yield of aromatics at 770°C. Depending on the concentration of O₂ or the reaction temperature, there are three reaction zones in the catalyst bed: (i) methane oxidation; (ii) methane reforming; and (iii) methane aromatization. CO and H₂ produced the first two zones are accountable for stability amelioration of the catalyst. The addition of NO exhibited similar effects on the reaction. Further increase in O₂ (≥8.4 vol%) or NO (≥14.2 vol%) concentration would result in CO and CO₂ being the predominant carbon-containing products; C₂H₄ and C₂H₆ were generated in small amounts and no aromatics were detected.