Designing Multi-Dopant Species in Microporous Architectures to Probe Reaction Pathways in Solid-Acid Catalysis

Abstract

The introduction of two distinct dopants in a microporous zeotype framework can lead to the formation of isolated, or complementary catalytically active sites. Careful selection of dopants and framework topology can facilitate enhancements in catalysts efficiency in a range of reaction pathways, leading to the use of sustainable precursors (bioethanol) for plastic production. In this work we describe our unique synthetic design procedure for creating a multi-dopant solid-acid catalyst (MgSiAPO-34), designed to improve and contrast with the performance of SiAPO-34 (mono-dopant analog), for the dehydration of ethanol to ethylene. We employ a range of characterization techniques to explore the influence of magnesium substitution, with specific attention to the acidity of the framework. Through a combined catalysis, kinetic analysis and computational fluid dynamics (CFD) study we explore the reaction pathway of the system, with emphasis on the improvements facilitated by the multi-dopant MgSiAPO-34 species. The experimental data supports the validation of the CFD results across a range of operating conditions; both of which supports our hypothesis that the presence of the multi-dopant solid acid centers enhances the catalytic performance. Furthermore, the development of a robust computational model, capable of exploring chemical catalytic flows within a reactor system, affords further avenues for enhancing reactor engineering and process optimisation, toward improved ethylene yields, under mild conditions.

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“…In this vein, MgSAPO-34 was also tested, containing just 0.1 wt % Mg and 3.0 wt % Si. The inclusion of magnesium was found to increase the overall acidity of the system, leading to an increase in “stronger” acid sites, compared to the regular SAPO-34 . This lowered the activation barrier of diethyl ether formation, increasing the rate of formation (Figure ).…”

“…One way this can be achieved is by modifying the acidity of the framework through the inclusion of a secondary dopant. 307 Thus far this review has purposefully limited itself to pure SAPO materials,…”

“…The inclusion of magnesium was found to increase the overall acidity of the system, leading to an increase in 'stronger' acid sites, compared to the regular SAPO-34. 307 This lowered the activation barrier of diethyl ether formation, increasing the rate of formation (Figure 26). The inclusion of magnesium was found to have less of an influence on the ethylene formation step (Figure 26).…”

“…Showing the variation in reaction rates for ethanol dehydration to ethylene, via diethyl ether, emphasizing the influence of a secondary Mg dopant, adapted from references 205,307 .…”

“…In this case, it is challenging to decouple the influence of the framework and the acidity; however, both clearly play a key role in the process. One way this can be achieved is by modifying the acidity of the framework through the inclusion of a secondary dopant . Thus far, this Review has purposefully limited itself to pure SAPO materials; however, countless examples exist of metal-doped SAPOs.…”