Increasing demand for sustainable chemicals and fuels has pushed academia and industry to search for alternative feedstocks replacing crude oil in traditional refineries. As a result, an immense academic attention has focused on the valorisation of biomass (components) and derived intermediates to generate valuable platform chemicals and fuels. Zeolite catalysis plays a distinct role in many of these biomass conversion routes. This contribution emphasizes the progress and potential in zeolite catalysed biomass conversions and relates these to concepts established in existing petrochemical processes. The application of zeolites, equipped with a variety of active sites, in Bronsted acid, Lewis acid, or multifunctional catalysed reactions is discussed and generalised to provide a comprehensive overview. In addition, the feedstock shift from crude oil to biomass involves new challenges in developing fields, like mesoporosity and pore interconnectivity of zeolites and stability of zeolites in liquid phase. Finally, the future challenges and perspectives of zeolites in the processing of biomass conversion are discussed.

/pdf/potential-and-challenges-of-zeolite-chemistry-in-the-2jjml8ecsr.pdf

Potential and challenges of zeolite chemistry in the catalytic conversion of biomass

The development of more carbon efficient and economically viable lignocellulosic biomass conversion technologies is critical for the sustainable production of liquid transportation fuels and chemicals. The molecule g-valerolactone (GVL) has gained attention as a versatile platform chemical for the production of liquid alkenes, as a solvent for biomass processing, as an approved fuel additive, and as a precursor for renewable polymers. Biomass-derived GVL is currently produced by the multistep processing of the carbohydrate fractions of lignocelluloses, wherein acid catalysts transform sugars into levulinic acid (LA), and noble-metal catalysts reduce LA to GVL with molecular hydrogen (H2). [5,6] This strategy suffers from several limitations that hinder the large-scale manufacture of GVL. In particular, the LA-reduction step necessitates precious-metal catalysts (e.g., Ru or Pt) or high H2 pressures (> 30 bar), which have been shown to negatively impact the economics of GVL-derived transportation fuels. Formic acid has emerged as an alternative to molecular H2, but noble metals and/or harsh conditions are still required to carry out the hydrogenation step. Inexpensive supported transition metals (e.g., Cu/ Al2O3) are active but suffer from leaching and/or sintering during the reaction. For the large-scale production of GVL, catalytic schemes are required that maximize product yields without the use of precious metals, high H2 pressure, or an excessive number of unit operations. Transfer-hydrogenation (TH) reactions, such as the Meerwein–Ponndorf–Verley (MPV) reaction, offer an attractive alternative to molecular H2 for the reduction of targeted functional groups. The interaction between the catalyst, the hydrogen donor, and the acceptor molecule can be modulated to impact activity and selectivity. Many catalysts are active for TH reactions, including organometallic compounds, transition metals, and metal oxides featuring acid/base properties. Pure-silica zeolites containing a small amount of tetravalent heteroatoms with open coordination sites (e.g., Zr or Sn) have also been used as solid Lewis acids to promote TH reactions. Wise and Williams used homogeneous Ru complexes and Chia and Dumesic used heterogeneous metal oxides to produce GVL from levulinate derivatives by TH reactions with high yields. Corma and co-workers demonstrated the efficacy of Sn-Beta and Zr-Beta zeolites for the intermolecular MPV reaction between alcohols and ketones in organic solvents. Sn-Beta and other tin-containing silicates have also been shown to transform hexoses, pentoses, and trioses through intramolecular hydride and carbon-atom shifts in both organic and aqueous media. Herein, we report an integrated catalytic process for the efficient production of GVL from furfural (Fur) through sequential TH and hydrolysis reactions catalyzed by zeolites with Bronsted and Lewis acid sites (Scheme 1). In our

Domino Reaction Catalyzed by Zeolites with Brønsted and Lewis Acid Sites for the Production of γ‐Valerolactone from Furfural

http://www.chtf.stuba.sk/~szolcsanyi/education/files/Chemia%20heterocyklickych%20zlucenin/Prednaska%207/Doplnkove%20studijne%20materialy/Cellulose/Chemical%20conversion%20pathways%20for%20carbohydrates.pdf

Chemical conversion pathways for carbohydrates

Nanocrystalline Sn-Beta zeolites have been successfully prepared via an improved two-step postsynthesis strategy, which consists of creating vacant T sites with associated silanol groups by dealumination of parent H-Beta and subsequent dry impregnation of the resulting Si-Beta with organometallic dimethyltin dichloride. Characterization results from UV−vis, XPS, Raman, and 119 Sn solid-state MAS NMR reveal that most Sn species have been successfully incorpo- rated into the framework of Beta zeolite through the postsynthesis process and exist as isolated tetrahedral Sn(IV) in open arrangement. The creation of strong Lewis acid sites upon Sn incorporation is confirmed by FTIR spectroscopy with pyridine adsorption. The Sn-Beta Lewis acid catalysts are applied in the ring-opening hydration of epoxides to the corresponding 1,2-diols under near ambient and solvent-free conditions, and remarkable activity can be obtained. The impacts of Lewis acidity, preparation parameters, and reaction conditions on the catalytic performance of Sn-Beta zeolites are discussed in detail.

Improved Postsynthesis Strategy to Sn-Beta Zeolites as Lewis Acid Catalysts for the Ring-Opening Hydration of Epoxides

Efficient valorization of biomass to biofuels with bifunctional solid catalytic materials

Carbohydrate epimerization is an essential technology for the widespread production of rare sugars. In contrast to other enzymes, most epimerases are only active on sugars substituted with phosphate or nucleotide groups, thus drastically restricting their use. Here we show that Sn-Beta zeolite in the presence of sodium tetraborate catalyses the selective epimerization of aldoses in aqueous media. Specifically, a 5 wt% aldose (for example, glucose, xylose or arabinose) solution with a 4:1 aldose:sodium tetraborate molar ratio reacted with catalytic amounts of Sn-Beta yields near-equilibrium epimerization product distributions. The reaction proceeds by way of a 1,2 carbon shift wherein the bond between C-2 and C-3 is cleaved and a new bond between C-1 and C-3 is formed, with C-1 moving to the C-2 position with an inverted configuration. This work provides a general method of performing carbohydrate epimerizations that surmounts the main disadvantages of current enzymatic and inorganic processes.

/pdf/sn-beta-zeolites-with-borate-salts-catalyse-the-lyhmf3y0nv.pdf

sn-Beta zeolites with borate salts catalyse the epimerization of carbohydrates via an intramolecular carbon shift

Sn-Beta zeolites with borate salts catalyse the epimerization of carbohydrates via an intramolecular carbon shift

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sn-Beta zeolites with borate salts catalyse the epimerization of carbohydrates via an intramolecular carbon shift

Sn-Beta zeolites with borate salts catalyse the epimerization of carbohydrates via an intramolecular carbon shift