By means of in situ FTIR and ex situ C-13 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 cro chemistry as well. (C) 2016 Elsevier B.V. All rights reserved.