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Operando UV/Vis spectroscopy with on-line mass spectrometry was used to study the effect of different types of impurities on the hydrocarbon pool species and the activity of H-SAPO-34 as a methanol-to-olefins (MTO) catalyst. Successive reaction cycles with different purity feedstocks were studied, with an intermittent regeneration step. The combined study of two distinct impurity types (i.e., feed and internal impurities) leads to new insights into MTO catalyst activation and deactivation mechanisms. In the presence of low amounts of feed impurities, the induction and active periods of the process are prolonged. Feed impurities are thus beneficial in the formation of the initial hydrocarbon pool, but also aid in the unwanted formation of deactivating coke species by a separate, competing mechanism favoring coke species over olefins. Further, feedstock impurities strongly influence the location of coke deposits, and thus influence the deactivation mechanism, whereas a study of the organic impurities retained after calcination reveals that these species are less relevant for catalyst activity and function as 'seeds' for coke formation only. [ABSTRACT FROM AUTHOR]

The increasing demand for light olefins and the changing nature of basic feedstock has stimulated substantial research activity into the development of new process routes. Steam cracking remains the most industrially relevant pathway, but other routes for light-olefin production have emerged. Fluid catalytic cracking only produces ethene in minor concentrations. Challenged by marked catalyst deactivation, in contrast, catalytic dehydrogenation ethane up opens a more selective route to ethene. The oxidative dehydrogenation (ODH) of ethane, which couples the endothermic dehydration of ethane with the strongly exothermic oxidation of hydrogen, would potentially be the most attractive alternative route because it avoids the need for excessive internal heat input, but also consumes valuable hydrogen. In this Review, the current state of the ODH of ethane is compared with other routes for light-olefin production, with a focus on the catalyst and reactor system variants. New catalyst systems and reactor designs have been developed to improve the industrial competitiveness of the ODH reaction of ethane. The current state of our fundamental understanding of the ODH of light alkanes, in particular in terms of catalyst and reactor development, is critically reviewed. The proposed mechanisms and the nature of the active site for the ODH reaction are described and discussed in detail for selected promising catalysts. The reported catalytic performance and the possible limitations of these ODH catalysts will be examined and the performance of the emerging approaches is compared to the currently practiced methods. [ABSTRACT FROM AUTHOR]