Tuning the selectivity of methanol-to-hydrocarbons conversion on H-ZSM-5 by co-processing olefin or aromatic compounds

Ilias, Samia; Bhan, Aditya

doi:10.1016/j.jcat.2012.03.016

Cited by 170 publications

(153 citation statements)

References 65 publications

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“…As far as the MTA is concerned, toluene also plays an important role in remarkably enhancing the selectivity of the xylenes (ca. 8.4 times) as reported by Ilias and Bhan [42], which may also attribute to high selectivity of p-/m-xylene. Similarly, the alkane's selectivity decreases from 26.8% (with H 2 ) to 1.0% at 648 K (without H 2 ), confirming that the MTH process indeed produces partial alkanes in the co-catalytic conversion of m-cresol in spite of further hydrogenation of toluene in the presence of H 2 .…”

Section: Co-catalytic Conversion Under N 2 and The Intermediate Convesupporting

confidence: 77%

High Selectively Catalytic Conversion of Lignin-Based Phenols into para-/m-Xylene over Pt/HZSM-5

2016

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Abstract:High selectively catalytic conversion of lignin-based phenols (m-cresol, p-cresol, and guaiacol) into para-/m-xylene was performed over Pt/HZSM-5 through hydrodeoxygenation and in situ methylation with methanol. It is found that the p-/m-xylene selectivity is uniformly higher than 21%, and even increase up to 33.5% for m-cresol (with phenols/methanol molar ratio of 1/8). The improved p-/m-xylene selectivity in presence of methanol is attributed to the combined reaction pathways: methylation of m-cresol into xylenols followed by HDO into p-/m-xylene, and HDO of m-cresol into toluene followed by methylation into p-/m-xylene. Comparison of the product distribution over a series of catalysts indicates that both metals and supporters have distinct effect on the p-/m-xylene selectivity.

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Section: Co-catalytic Conversion Under N 2 and The Intermediate Convesupporting

confidence: 77%

High Selectively Catalytic Conversion of Lignin-Based Phenols into para-/m-Xylene over Pt/HZSM-5

2016

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“…A compilation of the present knowledge on the reaction mechanism of zeolite-catalyzed methylations is given by Svelle et al 29,64 Many theoretical studies available in literature assume the concerted methylation pathway, 28,35,36,56,62,65 however recent studies also account for the stepwise pathway. 21,59,[66][67][68][69][70] Experimentalists, on the other hand, encounter major challenges to distinguish the concerted and stepwise methylation pathways. 29 Experimentally defined rate laws for methylation reactions typically exhibit a zeroth order methylation rate dependence on methanol partial pressure, irrespective of the reaction path.…”

Section: Introductionmentioning

confidence: 99%

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

Wispelaere

Bailleul

Speybroeck

2016

Catal. Sci. Technol.

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Title: Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions Advanced ab initio molecular dynamics techniques enable study of the infl uence of catalyst topology and acidity, reaction temperature and the presence of additional guest molecules on methylation reactions of benzene and propene, which are crucial reaction steps in the conversion of methanol into hydrocarbons. Our advanced simulations provide detailed insight into how operating conditions impact the competition of the concerted and stepwise methylation mechanism and thus the reaction kinetics. As featured in:See and mechanism of individual reaction steps at operating conditions. Herein we use state-of-the-art advanced ab initio molecular dynamics techniques to study the influence of catalyst topology and acidity, reaction temperature and the presence of additional guest molecules on elementary reactions. Such advanced modeling techniques provide complementary insight to experimental knowledge as the impact of individual factors on the reaction mechanism and kinetics of zeolite-catalyzed reactions may be unraveled. We study key reaction steps in the conversion of methanol to hydrocarbons, namely benzene and propene methylation. These reactions may occur either in a concerted or stepwise fashion, i.e. methanol directly transfers its methyl group to a hydrocarbon or the reaction goes through a framework-bound methoxide intermediate. The DFT-based dynamical approach enables mimicking reaction conditions as close as possible and studying the competition between two methylation mechanisms in an integrated fashion. The reactions are studied in the unidirectional AFI-structured H-SSZ-24, H-SAPO-5 and TON-structured H-ZSM-22 materials. We show that varying the temperature, topology, acidity and number of protic molecules surrounding the active site may tune the reaction mechanism at the molecular level. Obtaining molecular control is crucial in optimizing current zeolite processes and designing emerging new technologies bearing alternative feedstocks.

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“…[35][36] In contrast, SAPO-34 has large 12-member-ring cavities with small (3.8 × 3.8 Å) pore openings that enrich aromatic intermediates, promoting the aromatic-based cycle to produce more ethene 37 (a termination product of this cycle, see Scheme 1). Likewise, the MTH product distribution over ZSM-5 can be tuned by varying the reaction conditions (e.g., feed compositions [38][39][40] and zeolite crystal sizes 4,[41][42] ) to adjust the relative propagation of these two catalytic cycles.…”

Section: Introductionmentioning

confidence: 99%

Investigating the Influence of Mesoporosity in Zeolite Beta on Its Catalytic Performance for the Conversion of Methanol to Hydrocarbons

et al. 2015

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Hierarchically porous zeolite Beta (Beta-MS) synthesized by a soft-templating method contains remarkable intra-crystalline mesoporosity, which reduces the diffusion length in zeolite channels down to several nanometers and alters the distribution of Al among distinct crystallographic sites. When used as a catalyst for the conversion of methanol to hydrocarbons (MTH) at 330 o C, Beta-MS exhibited a 2.7-fold larger conversion capacity, a 2.0-fold faster reaction rate, and a remarkably longer lifetime than conventional zeolite Beta (Beta-C). The superior catalytic performance of Beta-MS is attributed to its hierarchical structure, which offers full accessibility to all catalytic active sites. In contrast, Beta-C was easily deactivated because a layer of coke quickly deposited on the outer surfaces of the catalyst crystals, impeding access to interior active sites. This difference is clearly demonstrated by using electron microscopy combined with electron energy loss spectroscopy to probe the distribution of coke in the deactivated catalysts. At both low and high conversions, ranging from 20% to 100%, Beta-MS gave higher selectivity towards higher aliphatics (C 4 -C 7 ) but lower ethene selectivity compared to Beta-C. Therefore, we conclude that a hierarchical structure decreases the residence time of methylbenzenes in zeolite micropores, disfavoring the propagation of the aromatic-based catalytic cycle. This conclusion is consistent with a recent report on ZSM-5 and is also strongly supported by our analysis of soluble coke species residing in the catalysts.Moreover, we identified an oxygen-containing compound, 4-methyl-benzaldehyde, in the coke, which has not been observed in the MTH reaction before.

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Tuning the selectivity of methanol-to-hydrocarbons conversion on H-ZSM-5 by co-processing olefin or aromatic compounds

Cited by 170 publications

References 65 publications

High Selectively Catalytic Conversion of Lignin-Based Phenols into para-/m-Xylene over Pt/HZSM-5

High Selectively Catalytic Conversion of Lignin-Based Phenols into para-/m-Xylene over Pt/HZSM-5

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

Investigating the Influence of Mesoporosity in Zeolite Beta on Its Catalytic Performance for the Conversion of Methanol to Hydrocarbons

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