Methanol to hydrocarbons conversion: Why dienes and monoenes contribute differently to catalyst deactivation?

Shi, Zhichen; Arora, Sukaran S.; Trahan, Daniel W.; Hickman, Daniel A.; Bhan, Aditya

doi:10.1016/j.cej.2021.134229

Cited by 6 publications

(5 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As shown in Figure 13C, co-feeding this labeled compound along with the methanol feedstock showed that the presence of certain species inhibited methanol conversion by competing for adsorption on catalytic acid sites, where they were readily converted to heavy aromatics and coke species [138] . Notably, many subsequent reports following this pioneering work confirmed the appearance of the same O-containing compounds [Figure 13D] [39,139] . [124] .…”

Section: Oxygen-containing Species Promoting Coke Formationmentioning

confidence: 67%

See 1 more Smart Citation

Fundamentals of the catalytic conversion of methanol to hydrocarbons

Liu¹,

Huang²

2022

Chem Synth

View full text Add to dashboard Cite

For more than four decades, the methanol-to-hydrocarbons (MTH) reaction has been a successful route to producing valuable fuels and chemicals from non-petroleum feedstocks. This review provides the most comprehensive summary to date of recent research concerning the mechanistic fundamentals of this important reaction, covering different reaction stages. Mechanisms that have been proposed to explain the initial C-C bond formation during the induction stage of the MTH reaction are introduced, including the methoxymethyl cation, Koch carbonylation, carbene and methane-formaldehyde processes. At present, there is no consensus regarding these hypothetical mechanisms as a consequence of the limited amount of conclusive experimental evidence. The steady state of the MTH reaction is also examined with a focus on the widely accepted indirect hydrocarbon pool mechanism and the dual cycle concept that provides a mechanistic basis for the effects of zeolite structures and reaction conditions on product distribution. In the following section, advanced characterization techniques capable of providing new insights into the formation of coke species during the MTH reaction and innovative approaches effectively inhibiting coke formation are introduced. Finally, a summary is provided and perspectives on current challenges and the future development of this area are presented.

show abstract

Section: Oxygen-containing Species Promoting Coke Formationmentioning

confidence: 67%

mentioning

confidence: 99%

Fundamentals of the catalytic conversion of methanol to hydrocarbons

Liu¹,

Huang²

2022

Chem Synth

View full text Add to dashboard Cite

show abstract

“…These observations are rationalized by DFT calculations demonstrating that at conditions relevant to MTO, dienes are predominantly formed via CH 2 O-assisted routes over alkene disproportionation routes, implying that formaldehyde influences aromatic formation as a precursor to the formation of dienes. 39 Cyclization events during MTO chemistries (Scheme 1, yellow) have been proposed to occur via (1) direct cyclization of unsaturated compounds, [20][21][22]49,50 (2) Diels−Alder cycloaddition reactions, 51−54 and (3) formaldehyde-mediated routes 55,56 via the formation of polyene alcohols, which undergo dehydrocyclization into diene rings�each of which can form C 6 rings of varying saturation. DFT calculations on direct cyclization of 1,5-hexadiene on bare and embedded cluster (single T12-site) models suggest that C 5 and C 6 hydrocarbon rings may form from secondary and primary surface-bound dienes, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…Cyclization events during MTO chemistries (Scheme , yellow) have been proposed to occur via (1) direct cyclization of unsaturated compounds, − ,, (2) Diels–Alder cycloaddition reactions, − and (3) formaldehyde-mediated routes , via the formation of polyene alcohols, which undergo dehydrocyclization into diene ringseach of which can form C 6 rings of varying saturation. DFT calculations on direct cyclization of 1,5-hexadiene on bare and embedded cluster (single T12-site) models suggest that C 5 and C 6 hydrocarbon rings may form from secondary and primary surface-bound dienes, respectively .…”

Section: Introductionmentioning

confidence: 99%

Mechanisms and Kinetics of the Dehydrogenation of C₆–C₈ Cycloalkanes, Cycloalkenes, and Cyclodienes to Aromatics in H-MFI Zeolite Framework

et al. 2022

View full text Add to dashboard Cite

This work employs periodic density functional theory to elucidate dehydrogenation mechanisms of C6–C8 cycloalkanes, cycloalkenes, and cyclodienes into aromatics during methanol-to-olefin (MTO) chemistries in H-MFI zeolites. Aromatic compounds act as co-catalysts that predominantly form ethylene over propylene products and lead to site-blocking polyaromatic compounds; thus, understanding the formation of aromatic compounds during MTO is critical to understanding its selectivity and catalyst stability. Ring dehydrogenation reactions occur via sequential hydride transfer followed by deprotonation. The rate-controlling hydride transfer reactions were investigated with surface-bound protons (Z–H) and alkyls (Z–C n H2n+1) as hydride-accepting species. Hydride transfers via proton-mediated routes occur with intrinsic free energy barriers (623 K) of 215 kJ mol–1 for C6H12, 164 kJ mol–1 for C6H10, and 141 kJ mol–1 for C6H8, whereas methyl-mediated counterparts occur with intrinsic free barriers of 101, 95, and 81 kJ mol–1, respectively. Transition states for hydride transfer reactions prefer channel intersections within MFI networks, and their activation barriers suggest that methyl-mediated routes are favored over proton-mediated counterparts during MTO. Methyl substituents on hydrocarbon rings generally increase activation barriers for hydride transfers that occur proximal to the −CH3, partly because of steric hindrances between the hydride acceptor and ring-bound −CH3. Rapid double-bond isomerization within cyclohexenes and cyclohexadienes allows hydride transfer reactions to occur away from sterically hindering methyl substituents in methylated and dimethylated C6 ring hydrocarbons. The impact of carbocation substitution in hydride-accepting species was explored by contrasting barriers of methyl (Z–CH3), ethyl (Z–C2H5), 2-propyl (Z–C3H7), and tert-butyl (Z–C4H9) surface-bound alkyls. Intrinsic activation barriers decrease with increasing substitution of the alkyl hydride acceptor, consistent with those alkyls forming more stable carbocations. However, when accounting for steric hindrances associated with the co-adsorption of hydrocarbon rings near surface-bound alkyls, apparent free barriers are larger for more-substituted alkyls. Taking these apparent barriers into account, we predict that methyl-mediated hydride transfer reactions are responsible for the aromatization of hydrocarbon rings during MTO, leading to the CH4 formed during MTO reactions as the aromatic pool is enriched.

show abstract

“…One reaction that has been immensely affected by these methods is the catalytic methanol-to-hydrocarbons/olefins (MTH/MTO) reaction, which is a promising route to obtain petrochemicals and fuels from renewable sources using microporous-acidic catalysts [8][9][10][11]. The use of operando spectroscopy partnering with ab initio calculations has revealed steps of initiation, autocatalysis, and deactivation [12][13][14][15][16][17][18][19] during MTH/MTO reactions. In brief, acid sites are prone to form methoxy and carbocation species that dehydrate, oligomerize or alkylate/dealkylate (methylate), cyclize, and aromatize to form a whole range of products, including deactivating species [20][21][22][23][24][25][26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

Evaluating catalytic (gas–solid) spectroscopic cells as intrinsic kinetic reactors: Methanol-to-hydrocarbon reaction as a case study

Valecillos

Elordi

Cui

et al. 2022

Chemical Engineering Journal

View full text Add to dashboard Cite

Methanol to hydrocarbons conversion: Why dienes and monoenes contribute differently to catalyst deactivation?

Cited by 6 publications

References 50 publications

Fundamentals of the catalytic conversion of methanol to hydrocarbons

Fundamentals of the catalytic conversion of methanol to hydrocarbons

Mechanisms and Kinetics of the Dehydrogenation of C₆–C₈ Cycloalkanes, Cycloalkenes, and Cyclodienes to Aromatics in H-MFI Zeolite Framework

Evaluating catalytic (gas–solid) spectroscopic cells as intrinsic kinetic reactors: Methanol-to-hydrocarbon reaction as a case study

Contact Info

Product

Resources

About

Methanol to hydrocarbons conversion: Why dienes and monoenes contribute differently to catalyst deactivation?

Cited by 6 publications

References 50 publications

Fundamentals of the catalytic conversion of methanol to hydrocarbons

Fundamentals of the catalytic conversion of methanol to hydrocarbons

Mechanisms and Kinetics of the Dehydrogenation of C6–C8 Cycloalkanes, Cycloalkenes, and Cyclodienes to Aromatics in H-MFI Zeolite Framework

Evaluating catalytic (gas–solid) spectroscopic cells as intrinsic kinetic reactors: Methanol-to-hydrocarbon reaction as a case study

Contact Info

Product

Resources

About

Mechanisms and Kinetics of the Dehydrogenation of C₆–C₈ Cycloalkanes, Cycloalkenes, and Cyclodienes to Aromatics in H-MFI Zeolite Framework