An Oft-Studied Reaction That May Never Have Been:  Direct Catalytic Conversion of Methanol or Dimethyl Ether to Hydrocarbons on the Solid Acids HZSM-5 or HSAPO-34

Abstract

Using highly purified reagents and careful tests, we show that methanol and dimethyl ether are apparently unreactive on the two most important methanol-to-hydrocarbon catalysts, HZSM-5 and HSAPO-34. Thus, none of the "direct" mechanisms involving two to four carbon atoms in intermediates such as oxonium ylides, carbenes, carbocations, and free radicals are applicable. Only the "indirect" route (hydrocarbon pool) is an established mechanism for this chemistry. An active catalyst requires a hydrocarbon pool that typically begins with products from organic impurities in the feed, carrier gas, or the solid acid itself. Impurities may also play important roles in other reactions catalyzed by solid acids.

The Importance of the Aging Time to Prepare Cu/ZnO/Al2O3Catalyst with High Surface Area in Methanol Synthesis

“…Methanol synthesis is focused by recent interests on methanol economy 1 and methanol utilizations such as MTO (methanol to olefin) [2][3] and bio-disel. Cu/ZnO/Al2O3 catalytic system has been used for commercial methanol synthesis.…”

Effect of Feedstock and Catalyst Impurities on the Methanol‐to‐Olefin Reaction over H‐SAPO‐34

“…Haw et al. followed this approach by suggesting that the initial bond formation proceeds not through a direct route, but rather by the presence of organic impurities 41. External “impurities”, such as toluene, ethanol, and acetone, are proven to have an effect on the MTO process 3, 41, 42, 43.…”

“…followed this approach by suggesting that the initial bond formation proceeds not through a direct route, but rather by the presence of organic impurities 41. External “impurities”, such as toluene, ethanol, and acetone, are proven to have an effect on the MTO process 3, 41, 42, 43. The complexity of the MTO reaction undoubtedly allows the (simultaneous) existence of both a direct and an indirect mechanism, in which the prevailing mechanism is dependent on the system and the tools used to observe it.…”

“…We define impurities to stem from two different sources; the aforementioned external impurities from, for example, organic impurities in the methanol feed, and internal or intrinsic impurities, which are carbon deposits that are retained in the zeolite material originating from any remaining template organics or a catalyst regeneration procedure 41. It is worth noting that impurities remaining after calcination to remove templates might differ in nature from those after regeneration as detemplation could leave the catalyst with (stable) N‐containing coke.…”

“…The extensive number of publications dealing with the effect of feedstock impurities41, 42, 43, 44, 45 is in contrast with the lack of fundamental understanding on the influence of internal impurities (i.e., hydrocarbon deposits) in reactions with zeolites or zeotypes. To the best of our knowledge, there are no studies providing detailed information about their effect on the zeolite's catalytic performance and the role of these impurities on the origin of the first active HCP species.…”