Gas turbines operate at exhaust gas temperatures exceeding 500 °C. Vanadium-based catalysts encounter challenges in NH3-SCR denitrification due to vanadium volatilization and titanium dioxide support phase transition at high temperatures. This restricts the effective denitrification temperature range to 300~400 °C, falling short of gas turbine denitrification requirements. Zeolite-supported catalysts, known for their high specific surface area, abundant acid sites, and stable framework structure, demonstrate superior catalytic activity and hydrothermal stability at high temperatures. This review synthesizes recent advancements in high-temperature catalysts utilizing ZSM-5, Beta, SSZ-13, and SAPO-34 zeolites as supports. It elucidates the interaction mechanisms between active components (e.g., transition metals Fe, Cu, W, rare earth elements) and zeolite supports. Furthermore, it examines variations in denitrification performance through the lens of the high-temperature NH3-SCR reaction mechanism, offering valuable insights for high-temperature denitrification catalyst development.

The selective synthesis of methylamines─monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA)─via methanol ammoniation is an important industrial process. Although small-pore zeolites like CHA and RHO offer improved selectivity, their combined MMA and DMA yield (yieldMMA+DMA) remains limited to 79.3% under industrial conditions (400 °C, methanol weight hourly space velocity of 4.3 h-1). Here, we report the performance of the SSZ-39 zeolite in this reaction. H-SSZ-39 with a Si/Al ratio of 5 achieved a yieldMMA+DMA of 85.9% under industrial conditions. Partial Na+ exchange further improved the performance by selectively neutralizing strong Bro̷nsted acid sites responsible for TMA formation, increasing yieldMMA+DMA to 90.6%. Solid-state 23Na multiple-quantum magic-angle spinning (MQMAS) NMR and Rietveld refinement of powder X-ray diffraction (PXRD) showed that Na+ ions first occupy eight-membered rings (8MRs) and migrate to double six-membered rings at higher exchange levels. Acid site analysis and density functional theory (DFT) calculations revealed that Al-OH groups in 8MRs possess the strongest Bro̷nsted acidity and high Na+ affinity. These results indicate that Na+ exchange in SSZ-39 proceeds in a specific order, offering valuable insights into the rational design of zeolite-based catalytic systems.

Efficient Production of Liquefied Petroleum Gas from CO ₂ Hydrogenation by Combining Fe–Al Bimetallic Catalyst with SSZ-13 Zeolite

Two-step activation of SSZ-13 zeolite membranes for mild template removal and enhanced CO2/C2H6 separation

Fluoride-free synthesis of SSZ-13 zeolite membranes from clear-solution with reduced time

Copper-exchanged SSZ-39 zeolite catalysts have been proven to be more hydrothermally stable than Cu-SSZ-13 catalysts. However, the synthesis of high-silica SSZ-39 zeolites is still a significant challenge. The excess framework Al in Cu-exchanged Al-rich SSZ-39 catalysts leads to not only severe dealumination during hydrothermal aging but also damage to the SCR-active Cu2+ ions by the detached Al. In this work, in-depth knowledge of the stabilization of Al by Y is provided. It was found that the energy needed to break the first Al-O bond is significantly enhanced due to the Y3+ located in the eight-membered rings. Additionally, Cu2+-2Z and Y have a synergistic effect on the stabilization of the framework Al. The introduction of Y into the Cu-SSZ-39 catalyst with hydrothermally stable Cu2+-2Z as the only Cu species remarkably enhanced both the low-temperature activity and the hydrothermal stability. The catalyst maintained excellent deNOx activity even after hydrothermal aging at the extremely high temperature of 940 °C. Both stable Cu species and stable framework Al are essential for the design of hydrothermally stable Cu-exchanged zeolite catalysts.

Operando FT-IR and UV–vis spectroscopic studies emphasise the nature of coke species formed over SSZ-13 zeolite during ethanol-to-hydrocarbons process

Synthesis of discrete SSZ-39 zeolite nanosheets by solvent-free seed-assisted route for efficient CO2 capture

Economically and eco-friendly synthesis of SSZ-13 zeolite using choline chloride as template with the investigation effects of sodium ion and aging

Impact of modified acidity and diffusion on ethylene-to-propylene reaction via size and shape controlled SSZ-13 zeolite

Co-exchanged SSZ-13 zeolite membrane for boosting CO2/N2 separation

Manipulating pore structures of SSZ-13 zeolite membranes via hydrocracking activation for superior H2/CO2 separation

Rapid and Facile Synthesis of Highly Mesoporous SSZ-13 Zeolites from Interzeolite Conversion of Y Zeolite

Zeolite synthesis is known as a difficult-to-control process, with many degrees of freedom that have a partially uncharted impact on the final product. Due to this, many zeolite scientists have regarded the initial mixing (aging) stage as the only time at which the chemical composition of a zeolite synthesis mixture can be impacted without heavily disrupting the delicate equilibria that are at play during crystallization. Recently, however, this view has started to change, with innovative techniques such as charge density mismatch or electro-assisted synthesis showing that the addition of new elements to the reactor midsynthesis might lead to new and surprising outcomes. In this manuscript, we show that by intermittent removal of certain fractions, notably Al-rich solids or Si-rich liquids, from the reaction medium during an interzeolite conversion from FAU-to-CHA (and FAU-to-MFI), one can control the Si/Al ratio of the final product, without heavily impacting the reaction time, particle size, or divalent cation capacity of the final product. This approach was named "split synthesis" and has led to several insights. By removing some Si-rich liquid phase after 40 min of synthesis, the Si/Al ratio of the daughter zeolite was lowered to a value of 20 (starting from 40), while the divalent cation capacity, a performance indicator for several acid and metal-catalyzed reactions, was kept maximized. On the other hand, when Al-rich solids were removed after 40 min (and in some cases colloidal silica was supplemented), we were able to rapidly synthesize small SSZ-13 zeolites with Si/Al ratios up to 180. These high-Si SSZ-13 zeolites had particle sizes in the range 100-150 nm and are traditionally difficult to crystallize in hydroxide medium. They showed a great olefin yield (6%) in the conversion of CO2 and H2 with ZnZrOx as cocatalyst.

Zeolites are considered as promising CO2 adsorbents due to their affordability, exceptional stability, and porous characteristics, yet they are still facing the challenges of low adsorption capacity and selectivity. In this study, we present a straightforward method to significantly improve the CO2 adsorption performance of zeolites through vacuum-assisted alkaline treatment. Under alkaline conditions, the pore structure and surface functionality can be modulated through desilication, dealumination, and ion exchange. Additionally, vacuum conditions aid in releasing gas molecules trapped in the pores, facilitating the solution entry. Three typical zeolites, including SSZ-13 (CHA), T (ERI/OFF) and NaA (LTA) zeolites, are utilized through the vacuum-assisted alkaline treatment. At an optimized pH of 12, their CO2 adsorption capacities increase by 7.67% to 16.99%. The significant enhancement in the CO2 adsorption capacity is attributed to the modified pore size and pore volume. Thus, we suggest that the vacuum-assisted alkaline treatment is an effective approach for improving gas adsorption performance.

ZnZrOx coupled highly acidic zeolite H-SSZ-13 achieves an exceptional light olefin space-time yield of 7.50 mmol gcat−1 h−1 under high space velocity (21 000 mL gcat−1 h−1) and low-pressure (1 MPa) conditions via optimized oxide–zeolite synergy.

Investigation of the reaction time and hydrothermal synthesis route on the SSZ-13 zeolite particle crystallization and CO2 adsorption

Charge density-mediated crystallization kinetics for SSZ-13 transformed from coal fly ash-derived Al-rich analcite

Commercial SSZ-13 zeolite with different n(Si)/n(Al) ratios and from different suppliers were subjected to a post-synthetic treatment in order to create mesopores of up to 15 nm. Furthermore, the materials were modified with copper ions and thoroughly physico-chemically characterized. The modified textural properties varied the nature of copper species, and thus, activity in the selective catalytic reduction of NOx with ammonia (NH3-SCR-DeNOx). Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) studies with hexane as probe liquid revealed improved intracrystalline diffusion for some Cu-containing SSZ-13 materials. The NH3-SCR-DeNOx pathways are verified via in situ DR UV-Vis, in situ FT-IR and EPR, temperature-programmed studies as well as SSITKA studies that provide a mechanistic understanding of the reaction. Kinetic modelling results demonstrate the highest NH3-SCR-DeNOx reaction rates and up to 20 % lower energy barriers with n(Si)/n(Al) ratio of 6.5 for all modified forms (i. e., (NH4)Cu-SSZ-13_6.5 and Cu-SSZ-13_6.5_NaOH/0.1) and cause only negligible parasitic ammonia oxidation. The modelling of the stop-flow experiments further demonstrates that the SCR pathway via the HONO surface intermediate is present but barely contributes to the overall NO conversion compared to the dominant path between adsorbed NH3 and NO from the gas phase.

The inevitable dealumination process of zeolite Y is closely related to ultrastabilization, enhanced Bro̷nsted acidity, and deactivation throughout its life cycle, producing complex aluminum and acidic hydroxyl species. Most investigations on dehydrated zeolites have focused on the Bro̷nsted acidity of tetra-coordinated Al (Al(IV)) and Lewis acidity associated with tricoordinated Al (Al(III)) sites, which has left the penta-coordinated Al (Al(V)) in dealuminated zeolites scarcely discussed. This is largely due to the oversimplified view of detectable Al(V) as an exclusively extra-framework species with Lewis acidity. Here we report the formation of Bro̷nsted acidic penta-coordinated Al species (Al(V)-BAS) in the dealumination process. Two-dimensional (2D) through-bond and multiquantum 1H-{27Al} correlation solid-state NMR experiments demonstrate the presence of a bridging Si-OH-Al(V) structure in dealuminated Y zeolites. Different from the conventional belief that water attack leads to the breaking of zeolite framework Al-O bonds in the initial stage of zeolite dealumination, the observed Al(V) as a dealumination intermediate is directly correlated with a BAS pair because of the direct dissociation of water on the framework tetrahedral aluminum (Al(IV)), thus bypassing the cleavage of Al-O bonds. 1H double-quantum solid-state NMR experiments and theoretical calculations provide further evidence for this mechanism, whereas pyridine adsorption experiments confirm stronger acidity of Al(V)-BASs than the traditional bridging hydroxyl groups associated with Al(IV). We were also able to detect the Al(V)-BAS site from dealuminated SSZ-13 zeolite with CHA topology, suggesting that its creation is not specific to the framework structure of zeolites.