Theoretical investigation of the olefin cycle in H-SSZ-13 for the ethanol-to-olefins process using <i>ab initio</i> calculations and kinetic modeling

Amsler, Jonas; Bernart, Sarah; Pleßow, Philipp N.; Studt, Felix

doi:10.1039/d1cy02289j

Cited by 2 publications

(4 citation statements)

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“…Stepwise pathways begin with the formation of surface ethoxy species (SES) in the first step. 72 An analogous mechanism was assumed for dehydration of 1-propanol to dipropyl ether, propene, and surface propoxy species (SPS).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The considered mechanism for ethanol dehydration according to Figure includes the formation of ethene and diethyl ether from ethanol through concerted and stepwise pathways. Stepwise pathways begin with the formation of surface ethoxy species (SES) in the first step . An analogous mechanism was assumed for dehydration of 1-propanol to dipropyl ether, propene, and surface propoxy species (SPS).…”

Section: Resultsmentioning

confidence: 99%

“…The surface ethoxy species (SES) is the intermediate along the stepwise paths, whereas the concerted paths in orange, blue, and red circumvent SES formation. Adapted from Amsler et al, ref , with permission from the Royal Society of Chemistry.…”

Section: Resultsmentioning

confidence: 99%

“…Recent theoretical work on ethanol and propanol dehydration in zeolites has begun to tackle whether confinement or acidity is the key feature. Several mechanistic steps have been explored, primarily focusing on whether the direct monomolecular formation of ethene occurs via a stepwise E 1 or a concerted E 2 elimination pathway. − Experimentally, it is challenging to distinguish between the two, however, density functional theory (DFT) studies suggest that the E 2 pathway has a lower activation barrier and is likely to be the dominant pathway. − Other studies focus on the initial binding of the alcohol to the acid site. Of particular interest is whether η 2 or a η 1 binding occurs, and whether these exist as Eigen or Zundel style complexes, as this will influence which pathway is followed. , Even before this, other studies have questioned the true nature of the active site in zeolites, with recent work by Pfriem et al focusing on the influence of water clusters on hydronium ion formation and their role in catalytic activity …”

Section: Introductionmentioning

confidence: 99%

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Combining Theoretical and Experimental Methods to Probe Confinement within Microporous Solid Acid Catalysts for Alcohol Dehydration

et al. 2023

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Catalytic transformations play a vital role in the implementation of chemical technologies, particularly as society shifts from fossil-fuel-based feedstocks to more renewable bio-based systems. The dehydration of short-chain alcohols using solid acid catalysts is of great interest for the fuel, polymer, and pharmaceutical industries. Microporous frameworks, such as aluminophosphates, are well-suited to such processes, as their framework channels and pores are a similar size to the small alcohols considered, with many different topologies to consider. However, the framework and acid site strength are typically linked, making it challenging to study just one of these factors. In this work, we compare two different silicon-doped aluminophosphates, SAPO-34 and SAPO-5, for alcohol dehydration with the aim of decoupling the influence of acid site strength and the influence of confinement, both of which are key factors in nanoporous catalysis. By varying the alcohol size from ethanol, 1-propanol, and 2-propanol, the acid sites are constant, while the confinement is altered. The experimental catalytic dehydration results reveal that the small-pore SAPO-34 behaves differently to the larger-pore SAPO-5. The former primarily forms alkenes, while the latter favors ether formation. Combining our catalytic findings with density functional theory investigations suggests that the formation of surface alkoxy species plays a pivotal role in the reaction pathway, but the exact energy barriers are strongly influenced by pore structure. To provide a holistic view of the reaction, our work is complemented with molecular dynamics simulations to explore how the diffusion of different species plays a key role in product selectivity, specifically focusing on the role of ether mobility in influencing the reaction mechanism. We conclude that confinement plays a significant role in molecular diffusion and the reaction mechanism translating to notable catalytic differences between the molecules, providing valuable information for future catalyst design.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%