Product shape selectivity dominates the Methanol-to-Olefins (MTO) reaction over H-SAPO-34 catalysts

Hereijgers, Bart P. C.; Bleken, Francesca Lønstad; Nilsen, Merete Hellner; Svelle, Stian; Lillerud, Karl Petter; Bjørgen, Morten; Weckhuysen, Bert M.; Olsbye, Unni

doi:10.1016/j.jcat.2009.03.009

Cited by 365 publications

(337 citation statements)

References 36 publications

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“…This is similar to work in the group of Olsbye 14 where an (Al+P)/Si ratio of 11 was reported as optimum for MTO, showing that lower ratios contribute more actively to catalyst deactivation. This ratio corresponds to approximately one acid site (proton) per cage.…”

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confidence: 90%

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

et al. 2015

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The diffusion of olefins through 8-ring solid acid microporous zeolites is investigated using molecular dynamics simulations techniques and using a newly developed flexible force field. Within the context of the Methanol to Olefin (MTO) process and the observed product distribution, knowledge on the diffusion paths is essential to obtain molecular level control over the process conditions. Eight-ring zeotype materials are favorably used for the MTO process as they give a selective product distribution towards low carbon olefins. To investigate how composition, acidity and flexibility influence the diffusion paths of ethene and propene, a series of isostructural aluminosilicates (zeolites) and silicoaluminophosphates (AlPOs and SAPOs) are investigated with and without randomly distributed acidic sites. Distinct variations in diffusion of ethene are observed in terms of temperature, composition, acidity, and topology (AEI, CHA, AFX). In general, diffusion of ethene is an activated process for which free energy barriers for individual rings may be determined. We observe ring dependent diffusion behavior which can not solely be described in terms of the composition and topology of the rings. A new descriptor had to be introduced namely the accessible window area (AWA), inspired by implicit solvation models of proteins and small molecules. The AWA may be determined throughout the molecular dynamics trajectories and correlates well with the number of ring crossings at the molecular level and the free energy barriers for ring crossings from one cage to the other. The overall observed diffusivity is determined by molecular characteristics of individual rings for which AWA is a proper descriptor. Temperature-induced changes in framework dynamics and diffusivity may be captured by following the new descriptor throughout the simulations.

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confidence: 90%

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

et al. 2015

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“…The latter proposition was supported by Hereijgers et al 53 who, by means of isotopic experiments with the present work, we cannot support the hypothesis that a higher C2 selectivity is due to differences in diffusion between C2 and C3 through the 8-ring pores. We believe that the results obtained could be better explained on the bases of acid strength than on the bases of diffusion.…”

Section: Shape-selectivity and Thermodymanic Equilibrium Of Olefinscontrasting

confidence: 65%

Methanol to olefins: activity and stability of nanosized SAPO-34 molecular sieves and control of selectivity by silicon distribution

Martínez‐Triguero

Concepción

et al. 2013

Phys. Chem. Chem. Phys.

123

110

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Royal Society of ChemistryLi, Z.; Martínez Triguero, LJ.; Concepción Heydorn, P.; Yu, J.; Corma Canós, A. (2013 AbstractNanoSAPO-34 molecular sieve synthesized in microwave environment with 20nm of crystal size showed higher lifetime than SAPO-34 prepared by conventional hydrothermal method in the reaction of methanol to olefins. It has been found that silicon distribution strongly affects lifetime and selectivity. Thus, silicon at the border of the silicon islands gives higher lifetime and lower C2/C3 ratio. This change in activity and selectivity is better explained in terms of different silicon distribution than on preferential diffusion of ethene through the 8MR pores and agrees with transition-state selectivity. The effects of equilibrium of olefins and deactivation by coke were isolated,showing that after full formation of hydrocarbon pool, selectivity is independent of deactivation by coke.

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“…Notably, higher methanol to carrier gas (N 2 ) ratio may also contribute to the improved olefins yield, as shown in the simulated results of two atmosphere pressure reactions, with methanol to N 2 ratio of 50:1 and 3:1, respectively. It is supposed that pressure is still the main reason for the totally different aromatic and olefin product distributions in each case, which is also supported by series of previous studies [1,[3][4][5]19].…”

Section: Conflictions Between the Simulated Data And Real Experimentasupporting

confidence: 70%

“…3a-c) obtained in each reaction, showing formation of olefins is not thermodynamically favoured under the applied conditions. In the temperature range of 300-500°C, which was indicated to donate large portions of C 2 -C 4 olefins in the previous researches, [3,5,12,19], ethylene selectivity is higher than other two olefin types, and shows a gradually increasing trend. It seems C 4 H 8 (1-butene) is greatly supressed in each case, as reflected by the observed data.…”

Section: Computer-aided Simulations For Three Reactions Of Different mentioning

confidence: 79%

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A research into the thermodynamics of methanol to hydrocarbon (MTH): conflictions between simulated product distribution and experimental results

et al. 2017

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Thermodynamic calculations and analysis were carried out for a rational understanding of the results from selected laboratory MTH reactions. Simulations without solid carbons (coke), CO, CO 2 and light alkanes target on the yield of olefin and aromatic products, which has been found better referenced to the real experimental observations that occur in time-on-stream (TOS). The confliction between simulated data and real experimental results is presumably ascribed to the limited dwelling time of products in the reaction system. Hydrocarbon pool based reactions donate olefins and methyl-benzenes as primary products in a continuous-flow MTH reaction; when the dwelling time of product extends intra-conversions (H 2 transfers) between products would further adjust the composition of MTH yield, in which case alkanes and aromatic products (cokes precursors) increase. In the case of intraconversions are ignored due to limited product dwelling time, thermodynamic calculation on Gibbs free energy change of selected sub reactions shows fairly close results to the real experimental data, which well supports the above explanations. This work highlights the importance of proper choosing target products and/or sub reactions for a rational thermodynamic prediction of MTH product distribution obtained in time-on-stream.Keywords Methanol to hydrocarbon Á Hydrocarbon pool mechanism Á Thermodynamic Á Intra-conversion Á Dwelling time IntroductionAt present, the pathways of methanol to hydrocarbon reaction especially the formation of first C-C bond are still in debate. The most acceptable hypothesis by far relies on the mechanism based on a 'hydrocarbon pool' [1]. In this theory, limited trace amount of hydrocarbons introduced as impurities in the methanol feedstock formed the initial aromatics (some benzene ring structures), which play a key role as the 'scaffold' in later process [2]. Methyl groups are added onto the hydrocarbon pool molecules in alkylation steps and light olefins are subsequently formed by the corresponding de-alkylation steps. The initial olefins can be converted into alkanes by occupying H 2 , whereas continuous loss of H 2 , followed by the cyclization steps forms more aromatics [3][4][5]. In a mature MTH system, series of the above reactions proceed in a parallel way and, therefore, bring in a complexity to the products and orders of their formation; however, thermodynamics always say coke (extremely dehydrogenated products, or solid carbons) is the dominating product in MTH and most other hydrocarbon transformations [6]. Before the reaction reaches a final format of solid carbons [C (s) ], Electronic supplementary material The online version of this article

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Product shape selectivity dominates the Methanol-to-Olefins (MTO) reaction over H-SAPO-34 catalysts

Cited by 365 publications

References 36 publications

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

Methanol to olefins: activity and stability of nanosized SAPO-34 molecular sieves and control of selectivity by silicon distribution

A research into the thermodynamics of methanol to hydrocarbon (MTH): conflictions between simulated product distribution and experimental results

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