A rapid and effective method for evaluating the initial activity of Mo/HZSM-5 catalyst in the methane dehydroaromatization reaction at severe conditions

The very rapid deactivation behavior of Mo/HZSM-5 catalyst in the non-oxidative CH4 dehydroaromatization needs its cyclic or continuous regeneration operation in a practical reactor system. Design and operation of such a system requires knowledge of the kinetics of catalyst deactivation and its regeneration. The present work reports an easy, rapid and quantitative approach to follow the dynamic variation of the activity of Mo/HZSM-5 in the very initial stage of CH4 dehydroaromatization at severe conditions. This approach comprises an on-line sampling and storing of a reacted effluent into a number of volume-known loops at intervals from seconds to minutes, and an off-line analysis of the stored samples. With it a nearly continuous dynamic variation in outlet benzene concentration was observed in the first tens of minutes of the reaction for all tested catalysts with Mo loadings ranging from 1.0 to 10 wt.%. Quantitative comparison of the variation with that in the benzene formation rate measured using conventional on-line GC analysis further revealed that the variation actually exhibited the dynamic behavior of the benzene formation activity of catalyst. The approach was subsequently applied successfully to follow the intrinsic maximum activity of Mo/HZSM-5 at severe conditions and in periodic reaction–regeneration operation mode to collect kinetic data for the reactor design.

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► On-line sampling and storing of the reacted effluent at desired time intervals.
► Off-line analysis of stored samples to measure variations in concentrations.
► Dynamic catalytic behaviors of Mo/HZSM-5 at various operating conditions.
► Application of the approach for studying the reaction kinetics over Mo/HZSM-5.