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The synthesis of hierarchical lamellar zeolites with a controlled meso-/microporous morphology and acidity is an expanding area of research interest for a wide range of applications. Here, we report a one-step synthesis of a hierarchical meso-/microporous lamellar MFI–Sn/Al zeolite ( i.e. , containing both Lewis acidic Sn- and Al-sites and a Brønsted acidic Al–O(H)–Si site) and its catalytic application for the conversion of glucose into 5-(ethoxymethyl)furfural (EMF). The MFI–Sn/Al zeolite was prepared with the assistance of a diquaternary ammonium ([C 22 H 45 –N + (CH 3 ) 2 –C 6 H 12 –N + (CH 3 ) 2 –C 6 H 13 ]Br 2− , C 22-6-6 ) template in a composition of 100SiO 2 /5C 22-6-6 /18.5Na 2 O/ x Al 2 O 3 / y SnO 2 /2957H 2 O ( x = 0.5, 1, and 2; y = 1 and 2, respectively). The MFI–Sn/Al zeolites innovatively feature dual meso-/microporosity and dual Lewis and Brønsted acidity, which enabled a three-step reaction cascade for EMF synthesis from glucose in ethanol solvent. The reaction proceeded via the isomerization of glucose to fructose over Lewis acidic Sn sites and the dehydration of fructose to 5-hydroxymethylfurfural (HMF) and then the etherification of HMF and ethanol to EMF over the Brønsted acidic Al–O(H)–Si sites. The co-existence of multiple acidities in a single zeolite catalyst enabled one-pot cascade reactions for carbohydrate upgrading. The dual meso-/microporosity in the MFI–Sn/Al zeolites facilitated mass transport in processing of bulky biomass molecules. The balance of both types of acidity and meso-/microporosity realized an EMF yield as high as 44% from the glucose reactant.
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Sulfurous zeosils for dehydra-decyclization of tetrahydrofuran to renewable butadiene
Renewable 1,3-butadiene (1,3-BD, C4H6) was synthesized from the tandem decyclization and dehydration of biomass-derived tetrahydrofuran (THF) on weak Brønsted acid zeolite catalysts. 1,3-BD is a highly solicited monomer for the synthesis of rubbers and elastomers. Selective conversion of THF to 1,3-BD was recently measured on phosphorus-modified siliceous zeolites (P-zeosils) at both high and low space velocities, albeit with low per-site catalytic activity. In this work, we combined kinetic analyses and QM/MM calculations to evaluate the interaction of THF with the various Brønsted acid sites (BAS) of Boric (B), Phosphoric (P), and Sulfuric (S) acid modified silicalite-1 catalysts toward a dehydra-decyclization pathway to form 1,3-BD. Detailed kinetic measurements revealed that all three catalysts exhibited high selectivity to 1,3-BD ca. 64–96% in the order of S-MFI > P-MFI > B-MFI at a given temperature (360 °C). Notably, the S-MFI maintained a selectivity >90% for all evaluated process conditions. The computational results suggested that the nature of the Brønsted acid sites and the adsorption energetics (relative THF-acid site interaction energies) are distinct in each catalyst. Additionally, the protonation of THF can be improved with the addition of a water molecule acting as a proton shuttle, particularly in S-MFI. Overall, S-containing zeosils exhibited the ability to control reaction pathways and product distribution in dehydra-decyclization chemistry optimization within microporous zeolites, providing another alternative weak-acid catalytic material.
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- Award ID(s):
- 1901635
- PAR ID:
- 10522415
- Publisher / Repository:
- RSC
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 26
- Issue:
- 3
- ISSN:
- 1463-9262
- Page Range / eLocation ID:
- 1430 to 1442
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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1,3-Pentadiene (piperylene) is an important monomer in the manufacturing of adhesives, plastics, and resins. It can be derived from biomass by the tandem ring-opening and dehydration (dehydra-decyclization) of 2-methyltetrahydrofuran (2-MTHF), but competing reaction pathways and the formation of another isomer (1,4-pentadiene) have limited piperylene yields to <60%. In this report, using detailed kinetic measurements of 2-MTHF dehydra-decyclization on zeolites with disparate acidities (boro-, and alumino-silicates) and micropore environments (MFI, MWW, and BEA), weakly acidic borosilicates were shown to exhibit ca. 10–30% higher selectivity to dienes at about five-to-sixty times lower proton-normalized rates than aluminosilicates (453–573 K). Dehydra-decyclization site time yields (STYs) were invariant for aluminosilicates within the investigated frameworks, indicating the absence of pore-confinement influence. However, individual site-normalized reaction rates varied by almost an order of magnitude on borosilicates in the order MWW > MFI > BEA at a given temperature (523 K), indicating the non-identical nature of active sites in these weak solid acids. The diene distribution remained far from equilibrium and was tuned towards the desirable conjugated diene (1,3-pentadiene) by facile isomerization of 1,4-pentadiene. This tuning capability was facilitated by high bed residence times, as well as the smaller micropore sizes among the zeolite frameworks considered. The suppression of competing pathways, and promotion of 1,4-pentadiene isomerization events lead to a hitherto unreported ∼86% 1,3-pentadiene yield and an overall ∼89% combined linear C5 dienes’ yield at near quantitative (∼98%) 2-MTHF conversion on the borosilicate B-MWW, without a significant reduction in diene selectivities for at least 80 hours time-on-stream under low space velocity (0.85 g reactant per g cat. per h) and high temperature (658 K) conditions. Finally, starting with iso-conversion levels ( ca. 21–26%) and using total turnover numbers (TONs) accrued over the entire catalyst lifetime as the stability criterion, borosilicates were demonstrated to be significantly more stable than aluminosilicates under reaction conditions (∼3–6× higher TONs).more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D3GC03090C
