Abstract
Formaldehyde (HCHO), formed in situ by transfer dehydrogenation of methanol in methanol-to-hydrocarbon (MTH) conversion, reacts with other organic species including olefins, dienes, and aromatics to cause deactivation. The propensity of these formaldehyde-mediated pathways to cause deactivation during MTH catalysis is evaluated using site-loss selectivity and yield as numerical assessors of catalyst deactivation. The site-loss selectivity of HCHO with 0.2 kPa HCHO and 12 kPa CH3OH at 673 K decreases by 80% when co-feeding 1 kPa propylene, increases by 2× when co-feeding toluene, and increases by 150× when co-feeding 1,3-butadiene, suggesting that olefins react with HCHO in nondeactivating pathways, while aromatics and dienes react with HCHO in pathways that lead to deactivation. Further, dienes have a much higher propensity than aromatics to cause deactivation via HCHO-mediated reactions when compared on a molar basis, suggesting that dienes may be critical intermediates in HCHO-mediated deactivation pathways. This is corroborated by evidence that the site-loss selectivity of HCHO increases with increasing HCHO co-feed pressure, implying that prevalent deactivation pathways are higher order in HCHO than predominant competing nondeactivation pathways. Plausibly this occurs because HCHO reacts with itself or with a HCHO-derived species en route to deactivation, such as a diene or an aromatic, which are known products of HCHO-mediated pathways during MTH catalysis. Therefore, dienes along with HCHO should be considered as critical intermediates in fomenting deactivation in MTH catalysis and strategies to eliminate polyunsaturated species and/or intercept reaction sequences of these intermediates with HCHO will likely enhance catalyst lifetime during MTH catalysis.
Original language | English (US) |
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Pages (from-to) | 3628-3637 |
Number of pages | 10 |
Journal | ACS Catalysis |
Volume | 11 |
Issue number | 6 |
DOIs | |
State | Published - Mar 19 2021 |
Bibliographical note
Funding Information:We thank Zhichen Shi for helpful technical discussions and for assistance in obtaining experimental data and Neil Razdan for helpful technical discussions. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 00039202. We also acknowledge the National Science Foundation (CBET 1701534) for financial support. Writing of this manuscript was partially supported under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Publisher Copyright:
© 2021 American Chemical Society
Keywords
- Butadiene
- Chemical transients
- Deactivation
- Formaldehyde
- Methanol-to-hydrocarbon conversion