Lifetime improvement in methanol-to-olefins catalysis over chabazite materials by high-pressure H2 co-feeds

Arora, Sukaran S.; Nieskens, Davy L. S.; Malek, Andrzej; Bhan, Aditya

doi:10.1038/s41929-018-0125-2

Cited by 141 publications

(161 citation statements)

References 46 publications

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“…4), because the short-lived primary carbenium ion (C2H5 + ) is unstable relative to the secondary carbenium ions that can be formed from larger alkenes. Kinetic studies in H-ZSM-5 (MFI) indicate that there are not significant changes in C2H4 selectivity (16 bar H2, 0.13 bar CH3OH, 723 K), 37 which is consistent with the DFT-derived free energy barriers that indicate ethane is not a predominant hydrogenation product. Additionally, rate constants of ethene hydrogenation in H-CHA (H-SSZ-13), H-SSZ-39, H-FER, and H-BEA suggest that rate constants of ethene hydrogenation are 1.5-16× lower than rate constants of propene hydrogenation.…”

Section: Hydrogenation In H-mfisupporting

confidence: 74%

“…The increases in catalyst lifetime observed by the previously discussed kinetic studies 37,38,43 have demonstrated that hydrogenation reactions play an important role in increasing catalyst lifetime in zeolites of varying topologies. No theoretical study, however, has investigated and compared hydrogenation mechanisms across multiple alkenes, dienes, aldehydes, and arenes.…”

Section: Methodsmentioning

confidence: 82%

“…39 Benzene hydrogenation routes are insignificant at high H2 MTO conditions, so arene hydrogenation does not contribute to decreases in deactivation rates in MFI. 37,38 Rather, the formation of polyaromatics is limited through elimination of CH2O and dienes.…”

Section: Hydrogenation In H-mfimentioning

confidence: 99%

“…13 High H2 pressures significantly improve catalyst lifetime in common MTO zeolites such as H-SAPO-34, H-ZSM-5, and H-SSZ-13. 37,38 Co-feeding H2 at high partial pressures (4-30 bar H2, 0.13 bar CH3OH, 673 K) improved catalyst lifetime, as measured by turnover number, by a factor of 2.8-70 in H-SAPO- 34. Similarly, H2 co-feeds at pressures of 0.4 bar in H-SSZ-13 (CHA framework) and 16 bar in H-ZSM-5 (MFI framework), H-SSZ-39 (AEI framework), H-FER, and H-BEA improved catalyst lifetime by factors of 3-15 by measured turnovers.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms of Alkene and Diene Hydrogenation Reactions in H-MFI and H-CHA Zeolite Frameworks During MTO

DeLuca

Janes²,

Hibbitts³

2019

Preprint

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Co-feeding H2 at high pressures increases zeolite catalyst lifetimes during methanol-to-olefin (MTO) reactions while maintaining high alkene-to-alkane ratios; however, the mechanisms and species hydrogenated by H2 cofeeds to prevent catalyst deactivation remain unknown. This study uses periodic density functional theory (DFT) to examine hydrogenation mechanisms of MTO product C2-C4 alkenes, as well as species related to the deactivation of MTO catalysts such as C4 and C6 dienes, benzene, and formaldehyde in H-MFI and H-CHA zeolite catalysts. Results show that dienes and formaldehyde are selectively hydrogenated in both frameworks at MTO conditions because their hydrogenation transition states proceed via allylic and oxocarbenium cations which are more stable than alkylcarbenium ions which mediate alkene hydrogenation. Diene hydrogenation is further stabilized by protonation and hydridation at α,δ positioned C-atoms to form 2-butene from butadiene and 3-hexene from hexadiene as primary hydrogenation products. This α,δ-hydrogenation directly leads to selective hydrogenation of dienes; pathways which hydrogenate dienes at the α,β-position (e.g., forming 1-butene from butadiene) proceed with barriers 20 kJ mol -1 higher than α,δ-hydrogenation and with barriers nearly equivalent to butene hydrogenation, despite α,β-hydrogenation of butadiene also occurring through allylic carbocations. Hydrogenation of formaldehyde, a diene precursor, occurs with barriers that are within 15 kJ mol -1 of diene hydrogenation barriers, indicating that it may also contribute to increasing catalyst lifetimes by preventing diene formation. Benzene, in contrast to dienes and formaldehyde, is hydrogenated with higher barriers than C2-C4 alkenes despite proceeding via stable benzenium cations because of the thermodynamic instability of the product which has lost aromaticity. Carbocation stabilities predict the relative rates of alkene hydrogenation and in some cases shed insights into the hydrogenation of benzene, dienes, and formaldehyde, but cation stabilities alone cannot account for the poor hydrogenation of benzene or the facile hydrogenation of dienes, boosted by stabilization conferred by a,δ-hydrogenation. This work suggests that the main mechanisms of catalyst lifetime improvement with high H2 co-feeds is reduction of diene concentrations through both their selective hydrogenation and hydrogenation of their precursors to prevent formation of deactivating polyaromatic species.

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Section: Hydrogenation In H-mfisupporting

confidence: 74%

Section: Methodsmentioning

confidence: 82%

Section: Hydrogenation In H-mfimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mechanisms of Alkene and Diene Hydrogenation Reactions in H-MFI and H-CHA Zeolite Frameworks During MTO

DeLuca

Janes²,

Hibbitts³

2019

Preprint

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“…Accordingly,t his thermodynamic analysis suggests that performing the reaction at elevated pressure might lead to ad ecreased coke selectivity and, therefore,h igher catalyst productivity. [20] In this work, we show that operation of the MDAreaction at elevated pressure is an efficient way to increase catalyst lifetime and total hydrocarbon productivity,bydecreasing the coke selectivity.T ransient kinetic measurements using 13 Clabelled methane evidence the reversible nature of coke formation during the MDAr eaction. At elevated pressure, coke hydrogenation becomes faster, effectively resulting in as lower build-up of carbonaceous deposits.W ea lso present operando high-pressure X-ray absorption near-edge structure (XANES) spectroscopy results,d emonstrating that the speciation of the active Mo species is not affected by highpressure operation.…”

mentioning

confidence: 77%

Reversible Nature of Coke Formation on Mo/ZSM‐5 Methane Dehydroaromatization Catalysts

et al. 2019

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Non-oxidative dehydroaromatization of methane over Mo/ZSM-5 zeolitecatalysts is apromising reaction for the direct conversion of abundant natural gas into liquid aromatics.Rapid coking deactivation hinders the practical implementation of this technology.H erein, we showt hat catalyst productivity can be improved by nearly an order of magnitude by raising the reaction pressure to 15 bar.The beneficial effect of pressure was found for different Mo/ZSM-5 catalysts and aw ide range of reaction temperatures and space velocities. High-pressure operando X-raya bsorption spectroscopyd emonstrated that the structure of the active Mo-phase was not affected by operation at elevated pressure.I sotope labeling experiments,s upported by mass-spectrometry and 13 Cn uclear magnetic resonance spectroscopy, indicated the reversible nature of coke formation. The improved performance can be attributed to faster coke hydrogenation at increased pressure, overall resulting in al ower coke selectivity and better utilization of the zeolite micropore space.

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Recent Progress in Methanol‐to‐Olefins (MTO) Catalysts

et al. 2019

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Among the 8-MR molecular sieves, silicoaluminophosphate SAPO-34 with 3D channels and moderate acid strength represents the most interesting one, the light olefins selectivity of which could reach up to 90% or even higher. [7] The excellent MTO performance of SAPO-34 was first reported by Dalian Institute of Chemical Physics (DICP) in 1990. [8] The researchers also demonstrated the good regeneration stability and high-temperature steam stability of Inspired by these pioneering discoveries, extensive research efforts have been devoted to SAPO-34 focusing on the elucidation of its crystallization mechanism, synthesis optimization, and the relevant catalytic studies, which greatly promote the technological development of the MTO process. Although SAPO-34 exhibits high catalytic activity and high selectivity toward light olefins, it suffers a rapid deactivation due to the coke deposition. Moreover, the MTO reaction on SAPO-34 catalyst is highly exothermal. These features determine that the industrial MTO process based on SAPO-34 catalyst has to adopt fluidized bed reactor, which allows efficient heat transfer and enables the continuous regeneration of the catalyst. In 2010, the world's first commercial MTO unit was successfully commissioned in Baotou, China by DICP (named DMTO technology). [5,10] The production capacity of ethylene and propylene is 0.6 Mt a −1 . To supply commercial catalysts for the DMTO unit, a 2000 t a −1 catalyst manufacturing plant was started up in Dalian in 2008. Afterward, DICP developed the DMTO-II technology, in which the byproducts of C 4 + are separated and introduced into a fluidized-bed cracking reactor to improve the yields of ethylene and propylene. Both the cracking unit and the MTO unit share one regenerator and use the same catalyst. By the end of 2018, thirteen DMTO units have been put into operation with a total production capacity of 7.16 Mt a −1 . Moreover, DICP launched the new generation of DMTO catalyst and completed the pilot test of the DMTO-III technology in 2018, both of which aim to further improve the olefins yield of DMTO units. The catalyst and technology development of the DMTO process are summarized in Figure 1.Based on SAPO-34 catalyst, UOP and Norsk Hydro also developed an MTO process with a low-pressure fast fluidizedbed reactor. [11] In 2013, a commercialized MTO plant (0.3 Mt a −1 olefins) was commissioned in Nanjing, China, which combines the UOP/Hydro MTO process and the total/UOP olefin cracking process to enhance the yield of ethylene and propylene. In addition, Shanghai Research Institute of Petrochemical Technology Methanol conversion to olefins, as an important reaction in C1 chemistry, provides an alternative platform for producing basic chemicals from nonpetroleum resources such as natural gas and coal. Methanol-to-olefin (MTO) catalysis is one of the critical constraints for the process development, determining the reactor design, and the profitability of the process. After the construction and commissioning of the world's first MTO plant by Dalian I...

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Lifetime improvement in methanol-to-olefins catalysis over chabazite materials by high-pressure H2 co-feeds

Cited by 141 publications

References 46 publications

Mechanisms of Alkene and Diene Hydrogenation Reactions in H-MFI and H-CHA Zeolite Frameworks During MTO

Mechanisms of Alkene and Diene Hydrogenation Reactions in H-MFI and H-CHA Zeolite Frameworks During MTO

Reversible Nature of Coke Formation on Mo/ZSM‐5 Methane Dehydroaromatization Catalysts

Recent Progress in Methanol‐to‐Olefins (MTO) Catalysts

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