A descriptor for the relative propagation of the aromatic- and olefin-based cycles in methanol-to-hydrocarbons conversion on H-ZSM-5

Mechanistic studies of methanol-to-hydrocarbons conversion on diffusion-free MFI samples

“…The relative propagation of the olefins-based catalytic cycle is therefore not affected by the olefin co-feed [29]. Both Ilias et al [15,16] and Sun et al [29], in independent studies, reported that co-reacting MBs with methanol/DME on H-ZSM-5 under a wide range of reaction temperatures (548-723 K) enhances the propagation of the aromatics-based catalytic cycle and results in higher selectivity toward MBs as well as ethene.…”

“…In the olefins-based catalytic cycle, olefins methylate to form higher olefins, which can either crack to form lighter olefins or undergo cyclization and hydrogen transfer to form aromatics. Both these catalytic cycles are simultaneously active inside the pores of MFI, and the relative propagation of these two cycles determines the hydrocarbon distribution observed in the effluent [15,16]. Ethene, together with higher olefins, aromatics, and branched/linear paraffins, is one of the major products of methanol-to-hydrocarbons (MTH) conversion on MFI.…”

“…The observed product distribution in MTH conversion can be interpreted as a consequence of the relative extents of propagation of the aromatics-and the olefins-based catalytic cycles inside the pores of MFI. Ilias et al [15,16] showed that co-feeding small amounts of propene (4 kPa) with 70 kPa DME on H-ZSM-5 at 548-623 K increased the propagation of the olefins-based catalytic cycle and resulted in higher selectivity toward C 3 and C 4 -C 7 aliphatic hydrocarbons. Experimental investigation by Sun et al [29], on the other hand, showed that co-feeding C 3 -C 6 olefins (10-40 C%) with methanol at higher temperature (723 K) and higher DME conversion conditions did not selectively enhance the propagation of the olefins-based catalytic cycle, and no increase in C 3 + selectivity was observed.…”

“…At lower temperatures, C 2 -C 5 olefins were the predominant products; an increase in temperature was accompanied by an increase in the formation of aromatics suggesting that secondary reactions like hydrogen transfer and cyclization become prominent at higher temperatures [30]. Ilias et al [16] also studied the effects of temperature (573-723 K) on MTH selectivity at <100% DME conversion and showed that ethene selectivity as well as MBs selectivity decreases with an increase in the reaction temperature. Ilias et al [16] proposed that the decrease in ethene selectivity with increasing reaction temperature is a result of a decrease in the extent of propagation of the aromatics-based catalytic cycle relative to the olefins-based catalytic cycle.…”

The Role of Non-Framework Lewis Acidic Al Species of Alkali-Treated HZSM-5 in Methanol Aromatization

“…Ethylene is a tracer of the arene cycle, while C3 + hydrocarbons are produced through the alkene cycle [36][37][38]. The closely-neighboring desorption temperatures of C3 + hydrocarbons and ethylene emphasize that arene and alkene cycled proceed concurrently and are highly interwined [39]. The desorbed CH4 and H2 profiles seemed to be coherent, showing two responses in 100-300 °C and 400-700 °C ranges.…”