Direct discerning reaction pathways in methanol-to-hydrocarbons by transient operation – FASPA

Liu, Chuncheng; Uslamin, Evgeny A.; Pidko, Evgeny A.; Kapteijn, Freek

doi:10.1016/j.cej.2022.139696

Cited by 5 publications

(14 citation statements)

References 90 publications

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“…More technical details and validation of the FASPA approach in the MTH process can be found in Supporting Information and in our previous work. 15 Typical obtained product responses from FASPA tests over H-ZSM-5 are shown in Figure 1.…”

Section: ■ Resultsmentioning

confidence: 99%

“…Once the injected MeOH is rapidly depleted, the decomposition and desorption of the formed HCP species explain the long tailing of observed responses, as shown in Figure 1, demonstrating the dynamic character of the HCP in the medium-pore H-ZSM-5 zeolite catalyst. 15 However, because of measurement limitations, these HCP species cannot be directly identified during FASPA tests. In particular, a sharp first response (R1) is observed for benzene, toluene, xylenes, and TriMB (trimethylbenzenes) at a response time of ∼40 s (Figure 1b), appearing ∼4 s later than aliphatic peaks (Figure 1a), ascribed to the stronger adsorption of the former species in the zeolite catalyst.…”

Section: ■ Resultsmentioning

confidence: 99%

“…A detailed discussion on the origin of the second peak of benzene, toluene, and xylenes can be found in our previous paper. 15 It is worth noting that olefins (ethylene, propylene, and butylenes) decay relatively slower than alkanes (methane, ethane, propane, and butanes). The butanes (mainly i-C 4 and some n-C 4 ) show the highest response, demonstrating their highest product selectivity (Table S2).…”

Section: ■ Resultsmentioning

confidence: 99%

“…For the displacement peak of light aromatics upon the first 12 C-MeOH/water pulse (Figures 2 and 3), we speculate that these retarded organic species are displaced mainly by water, stemming from the fast dehydration of MeOH. The DFTcalculated adsorption energy of MeOH, water, and related hydrocarbons decreases in the order MeOH (−105 kJ/mol 31 ) > water (−83 kJ/mol 31 ) > toluene/p-xylenes (−62/−71 kJ/ mol 15,32 ) > ethylene/propylene (−37/−53 kJ/mol 33 ). Further evidence arises from the delayed appearance of water in the exit flow after olefins and aromatics upon a MeOH pulse (Figure S6).…”

Section: ■ Discussionmentioning

confidence: 99%

“…have recently employed photoion photoelectron coincidence spectroscopy as a new analytical tool that provides extensive information on the reaction intermediates, confirming the key role of dimethylpentenyl species in the MTH mechanism. 20 We herein present a quantitative analysis of HCP species in H-ZSM-5 zeolite catalysts and their reactivity with MeOH in the MTH process, relying on the isotope labeling technique and the fast scanning-pulse analysis (FASPA 15 ). This recently developed FASPA technique allows quantitative GC mapping of the fast temporal evolution of the product responses upon a MeOH pulse over the catalyst.…”

Section: ■ Introductionmentioning

confidence: 99%

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Revealing Main Reaction Paths to Olefins and Aromatics in Methanol-to-Hydrocarbons over H-ZSM-5 by Isotope Labeling

et al. 2023

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The nature of hydrocarbon pool (HCP) intermediates in the methanol-to-hydrocarbons (MTH) process has been thoroughly investigated, especially for BEA- and CHA-type zeolite catalysts like H-β and H-SAPO-34. Herein, we further reveal the dynamic mechanistic details of the MTH process over the H-ZSM-5 catalyst at 400 °C, based on the dual-cycle mechanism and HCP in this medium-pore zeolite. Application of switching sequences of 13C-labeled and unlabeled methanol pulses over a model H-ZSM-5 catalyst combined with on-line MS analysis and a recently reported technique called “fast scanning-pulse GC analysis” provides a direct and quantitative insight into the MTH reactions under quasi-steady-state conditions. The transient product responses showed the almost instant formation of hydrocarbons upon a small pulse of methanol, followed by secondary formation of light aromatics via HCP decomposition and olefin alkylation–dealkylation, especially in a long catalyst bed when methanol is quickly consumed in the initial reaction zone in the catalyst bed. The isotopic analysis of typical aliphatic C3+ product responses after switching 13C-methanol pulses to the unlabeled methanol pulses showed a fast isotope scrambling in the formation of C3+ species. MS analysis of the light aromatics indicates a complete consecutive but slower isotope incorporation process of 12C into 13C-aromatics. Results provide direct experimental confirmation of the kinetically preferred olefin-based cycle over the aromatic-based cycle. The sequential isotopic incorporation strongly suggests that the paring reaction pathway through aromatic ring contraction and re-expansion steps is operative. In the appearance of aromatics upon pulsing methanol over larger catalyst beds, four processes are directly discerned, involving the displacement of adsorbed species by formed water, isotope incorporation yielding directly labeled and unlabeled products through the paring mechanism and direct aromatization, and HCP conversion through secondary reactions.

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Section: ■ Resultsmentioning

confidence: 99%

Section: ■ Resultsmentioning

confidence: 99%

Section: ■ Resultsmentioning

confidence: 99%

Section: ■ Discussionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Revealing Main Reaction Paths to Olefins and Aromatics in Methanol-to-Hydrocarbons over H-ZSM-5 by Isotope Labeling

et al. 2023

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Ethylene Oligomerization: Unraveling the Roles of Ni Sites, Acid Sites, and Zeolite Pore Topology through Continuous and Pulsed Reactions

Abed,

Mohamed,

Hita

et al. 2023

ChemCatChem

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Herein, four catalysts, consisting of either MFI or BEA as the zeolite framework in the presence or absence of Ni, are compared to explore the individual and collective adsorptive and catalytic contributions of pore topology, Ni sites, and acid sites. Both continuous and pulsed chemisorption/reaction experiments are used to obtain a complete picture of the time‐dependent adsorption‐desorption behavior, reaction mechanisms, and deactivation steps. The methodology highlights the effect of acid sites, especially during the initial stages of reaction and in the BEA‐based catalysts, which have higher acidity at a given Si/Al ratio. In addition, Ni accelerates the reaction and improves the selectivity towards intermediate oligomers. However, the tendency for the most active Ni and acid sites to saturate and deactivate more rapidly than the less active ones may lead to misinterpretation when using the continuous reactor alone. Hence, the dominant mechanisms over the different catalyst sites and reaction times are discussed based on the combined steady and dynamic experiments.

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Green synthesis of shaped nano-ZSM-5 toward more efficient methanol-to-hydrocarbon conversion

Bu,

Wang,

Liu

et al. 2023

Applied Catalysis A: General

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Direct discerning reaction pathways in methanol-to-hydrocarbons by transient operation – FASPA

Cited by 5 publications

References 90 publications

Revealing Main Reaction Paths to Olefins and Aromatics in Methanol-to-Hydrocarbons over H-ZSM-5 by Isotope Labeling

Revealing Main Reaction Paths to Olefins and Aromatics in Methanol-to-Hydrocarbons over H-ZSM-5 by Isotope Labeling

Ethylene Oligomerization: Unraveling the Roles of Ni Sites, Acid Sites, and Zeolite Pore Topology through Continuous and Pulsed Reactions

Green synthesis of shaped nano-ZSM-5 toward more efficient methanol-to-hydrocarbon conversion

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