Feature ArticleChloromethane to olefins over H-SAPO-34: Probing the hydrocarbon pool mechanism

- Gradual formation of methylated benzene species during the initial stages of the chloromethane to olefins reaction is confirmed using ex situ 13C NMR and in situ FTIR.
- Direct correlation between chloromethane conversion and concentration of methylated aromatics during induction period.
- Extrapolation of methanol-to-olefins hydrocarbon pool mechanism to the chloromethane-to-olefins (CTO) reaction.
- Loss of micropore volume by carbon-filling suggests that the deactivation of SAPO-34 during the CTO reaction proceeds through the growth of polyaromatics.

By means of in situ FTIR and ex situ 13C NMR studies, the initial periods of the chloromethane-to-olefins (CTO) reaction over SAPO-34 were probed in order to investigate the activation period of the reaction and to elucidate the formation of the catalyst active site. A methylated benzene species has been observed to form during the initial activation period of the reaction, and a direct positive correlation was constructed between the formation of this species and the catalytic activity. The data thus indicate that these methylated benzene species contribute to the formation of active sites within SAPO-34 for the CTO reaction. This is the first known report identifying a direct semi-quantitative correlation between the catalyst activity and growth of a methylated benzene active species, during the activation period of the chloromethane to olefins reaction. The findings here in correspond well to those reported for the methanol to olefins reaction, suggesting that a similar 'hydrocarbon pool' mechanism may be responsible for the formation of light olefins in CTO chemistry as well.

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