Isomorphous Substitution of Gallium into MFI-Framework Zeolite Increases 2,5-Dimethylfuran to Aromatics Selectivity and Suppresses Catalyst Deactivation

Abstract

The valorization of biomass-derived molecules into commodity chemicals is important for the transition to renewable feedstocks. The model platform molecule 2,5-dimethylfuran (2,5-dmf) can be converted into value-added aromatics such as benzene, toluene, and xylenes (BTX) over zeolite catalysts. To explore the role of the zeolite acid site(s) in BTX selectivity, gallium has been isomorphously substituted into the framework, resulting in a Ga-silicate. Compared to the ZSM-5 counterpart, this modification shows enhanced benzene selectivity as well as resistance to deactivation by coke in continuous catalytic performance tests.

Continuous isomerisation of 2,5‐dimethylfuran to 2,4‐dimethylfuran over Ga‐silicate

“…In brief, X-ray diffraction (XRD) confirms the MFI-type framework structure and the absence of other crystalline phases with long-range order (Figure S1) and scanning electron microscopy imaging shows highly crystalline crystals that are interconnected, resulting in a range of particle sizes. [15,16,[18][19][20] From N 2 -sorption measurements, the calculated BET-specific surface area falls within the rather narrow range of 365-412 m 2 g À 1 and likewise, the micropore volumes span the rather narrow range of 0.145-0.175 cm 3 g À 1 , which are reasonable values for these materials. [21][22][23] Further analysis of the N 2 -sorption isotherms shows a type H4 hysteresis (Figure S2) indicating that both meso-and micropores are present.…”

“…We have observed the isomerisation of 2,5‐dmf to 2,4‐dmf, 2‐methyl‐2‐cyclopentenone (2‐mcpo) and 3‐methyl‐2‐cyclopentenone (3‐mcpo) as side reactions over the H‐form of beta and MFI zeolites (with various aluminium or gallium contents) when targeting the formation of benzene, toluene and xylenes (BTX) [15,17] . While screening catalyst formulations for enhanced BTX production, we discovered that Ga‐silicate, i. e., Ga positioned in the MFI framework (Ga‐MFI), exhibits much improved long‐term activity and selectivity towards mentioned isomers, making it a suitable candidate for 2,4‐dmf production [16] …”

“…This suggests that mainly weak acid sites are responsible for isomerisation reactions, whereas strong acid sites are responsible for cracking, decarbonylation and aromatisation reactions. Ga‐silicate has, in a recent study, been shown to contain even weaker acid sites as well, on which ammonia readily adsorbs and desorbs at temperatures below 150 °C [16] . Complementary targeted studies are necessary to determine the most beneficial Ga content of the catalyst.…”

“…[14] Recently, we found 2,4-dmf to be a side product in the catalytic valorisation of biomass-derived 2,5-dimethylfuran (2,5dmf) over zeolites. [15,16] We have elaborated further on this isomerisation reaction, and herein, we communicate an alternative green approach, namely the continuous selective syn-thesis of 2,4-dmf by heterogeneous catalytic isomerisation of readily available 2,5-dmf, shown in Scheme 1d).…”

“…[15,17] While screening catalyst formulations for enhanced BTX production, we discovered that Ga-silicate, i. e., Ga positioned in the MFI framework (Ga-MFI), exhibits much improved long-term activity and selectivity towards mentioned isomers, making it a suitable candidate for 2,4-dmf production. [16] Here, we have studied Ga-MFI, using H-ZSM-5, Silicalite-1, and Ga 2 O 3 , as references. The physicochemical properties of the catalysts are summarised in Table S1.…”