Generation of basic centers in high-silica zeolites and their application in gas-phase upgrading of bio-oil

Protective dissolution: generating secondary pores in zeolite by mechanochemical reaction

Introduction of meso-/macropores into the intrinsic microporous framework of zeolites has raised substantial interest in catalytic reactions with bulky reactants. Herein, we report the formation of secondary meso-/macropores in Silicalite-1 zeolite by a solvent-free mechanochemical grinding process. The strategy allows the preservation of high crystallinity and microporosity of the pristine zeolite, and the generation of mesopores at room temperature and marcopores at higher temperatures. The roles of the tetrapropylammonium bromide (TPABr) and ammonium fluoride (NH₄F) have been proposed and demonstrated. A protective layer is formed by TPA⁺ ions bonded with the surficial defects to shield the outer surface from the direct attack by F⁻. Instead, F⁻ diffuses into the micropore system in a local aqueous environment within zeolite formed by the mechanochemical reaction. As a result, freely diffused F⁻ selectively dissolves zones with structural defects to form secondary pores inside the zeolite. Moreover, this strategy proves highly effective in encapsulation of nanoparticles (Pt, Co) in the meso-/macropores of Silicalite-1 zeolite, forming a yolk–shell composite catalyst for potential applications.

A novel strategy for meso-/macropores formation in zeolites by mechanochemical reaction.

Advances in porous and nanoscale catalysts for viable biomass conversion

Solid catalysts with unique porosity and nanoscale properties play a promising role for efficient valorization of biomass into sustainable advanced fuels and chemicals.

Impact of Macroporosity on Catalytic Upgrading of Fast Pyrolysis Bio-Oil by Esterification over Silica Sulfonic Acids

Fast pyrolysis bio-oils possess unfavorable physicochemical properties and poor stability, in large part, owing to the presence of carboxylic acids, which hinders their use as biofuels. Catalytic esterification offers an atom- and energy-efficient route to upgrade pyrolysis bio-oils. Propyl sulfonic acid (PrSO₃ H) silicas are active for carboxylic acid esterification but suffer mass-transport limitations for bulky substrates. The incorporation of macropores (200 nm) enhances the activity of mesoporous SBA-15 architectures (post-functionalized by hydrothermal saline-promoted grafting) for the esterification of linear carboxylic acids, with the magnitude of the turnover frequency (TOF) enhancement increasing with carboxylic acid chain length from 5 % (C₃ ) to 110 % (C₁₂ ). Macroporous-mesoporous PrSO₃ H/SBA-15 also provides a two-fold TOF enhancement over its mesoporous analogue for the esterification of a real, thermal fast-pyrolysis bio-oil derived from woodchips. The total acid number was reduced by 57 %, as determined by GC×GC-time-of-flight mass spectrometry (GC×GC-ToFMS), which indicated ester and ether formation accompanying the loss of acid, phenolic, aldehyde, and ketone components.

Recent progress on upgrading of bio-oil to hydrocarbons over metal/zeolite bifunctional catalysts

Upgrading of bio-oil over metal/zeolite bi-functional catalysts, is of high necessity and popularity in converting biomass to high-quality hydrocarbons (transportation fuels and petrochemicals) to reduce the overall CO₂ emissions of fossil based materials.

Aldol condensation of biomass-derived platform molecules over amine-grafted hierarchical FAU-type zeolite nanosheets (Zeolean) featuring basic sites

Amine-grafted FAU nanosheets exhibited the superior catalytic performance for the aldol condensation of biomass feedstocks to chemicals yielding the desired product close to 100%.

Synthesis, characterisation, and catalytic evaluation of hierarchical faujasite zeolites: milestones, challenges, and future directions

The preparation of hierarchical faujasite catalysts is challenging yet rewarding.

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

This review emphasizes the progress, potential and future challenges in zeolite catalysed biomass conversions and relates these to concepts established in existing petrochemical processes.

Selective dehydrogenation of bioethanol to acetaldehyde over basic USY zeolites

Alkali-activated zeolites are active, selective and stable catalysts for ethanol dehydrogenation to acetaldehyde. Molecular oxygen eases hydrogen abstraction from the adsorbed ethoxide intermediate boosting the catalytic performance.

A critical view on catalytic pyrolysis of biomass

The rapid heating of biomass in an oxygen-free environment optimizes the yield of fast-pyrolysis liquids. This liquid comprises a mix of acids, (dehydrated) carbohydrates, aldehydes, ketones, lignin fragments, aromatics, and alcohols, limiting its use. Deoxygenation of these liquids to replace hydrocarbons represents significant challenges. Catalytic pyrolysis is seen as a promising route to yield liquids with a higher quality. In this paper, literature data on catalytic fast pyrolysis of biomass are reviewed and deoxygenation results correlated with the overall carbon yield. Evidence is given that in an initial stage of the catalytic process reactive components are converted to coke, gas, and water, and only to a limited extent to a liquid product. Catalysts are not yet good enough, and an appropriate combination of pyrolysis conditions, reactive products formed, and different reactions to take place to yield improved quality liquids may be practically impossible.