Over the past 25 years, the methanol-to-olefin (MTO) process on acidic zeolites has been subject to a vast amount of studies from both industrial and academic researchers, culminating in numerous controversies regarding the most probable reaction mechanism. Recent experimental developments [1], backed up by strong theoretical evidence [2], reveal that the commonly proposed ‘direct mechanisms' fail completely for the formation of an initial C-C bond. Special theoretical focus on oxonium ylides in particular, being the favourite intermediate of committed followers of the direct mechanisms, have shown them to be highly unstable species, even when the zeolite framework is explicitly taken into account [3]. Inspired by these calculations, labelling experiments have since confirmed our theoretical conclusions [4]. We will present a detailed reaction scheme demonstrating the failure of the direct mechanisms, which is extended to a discussion on the influence of the framework on elementary reaction steps of the ‘hydrocarbon pool' alternative [5].

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