SSZ-13 Zeolite Research Articles

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

This study investigates the influence of synthesis time (1–4 days) and synthesis route for the fast production of SSZ-13 zeolites via the conventional hydrothermal method for CO2 adsorption. Two synthesis routes were examined using different Si precursors: tetraethyorthosilicate (Route T) and silica (Route L). The samples were characterized by XRD, FTIR, SEM, 29Si and 27Al MAS-NMR, and gas sorption, the results were correlated to CO2 adsorption kinetics. Route T produced fully crystalline SSZ-13 zeolite within 1 day with high yield, resulting in ultramicroporous materials through particle-mediate crystallization, transitioning from coarse spherical particles with high specific surface area (750 m2 g−1) and the highest equilibrium CO2 adsorption capacity of 81.08 mg g−1, to perfectly cubic structures for longer synthesis with decreased specific surface area (610 m2 g−1) and porosity. A disorder-to-order transition for synthesis longer than 3 days, along with the elimination of the interspaces internal, significantly decreased CO2 adsorption capacity (63.03 mg g−1). Meanwhile, SSZ-13 zeolites by Route L produced ultramicroporous crystalline particles only after 2 days, featuring intricate, layered structures formed by stacked sheets, indicating layer-by-layer mechanism. Longer synthesis times further increased particle complexity, reaching specific surface area of 858 m2 g−1 for the 4-day synthesis, along with improved CO2 adsorption capacity. However, the CO2 adsorption capacity for highly crystalline SSZ-13 samples obtained by Route L varied within 68.72–80.39 mg g−1, suggesting that structural properties also influenced CO2 adsorption performance. These findings demonstrate that conventional hydrothermal synthesis can rapidly produce SSZ-13 adsorbents, allowing fine-tuning material properties and CO2 adsorption capacity by selecting the appropriate synthesis route.

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

Interzeolite transformation (IZT) is a powerful method for controlling the framework type, aluminum distribution, and hierarchical structures of zeolite. However, the in-depth mechanisms underlying IZT remain unexplored. In this study, we reveal a distinctive nucleation pathway and structural evolution of zeolite SSZ-13 during IZT that is different from the traditional hydrothermal synthesis methods. Utilizing two aluminum sources—al-rich zeolite analcite and aluminum sulfate—we accelerated the crystallization process with SSZ-13 seed crystals and TMAda-OH. Our findings indicate that the Al content, representing the charge density of the nucleation micro-environment, plays a critical role in shaping the framework and nucleation pathway. Nucleation occurred at the interface between analcite and the silica solution during IZT, characterized by a high-silica micro-environment with low charge density. In this environment, the precursor predominantly replicated the double six rings (D6R) of SSZ-13 seed fragments, forming double four rings (D4R) and CHA cages which resulted in a short induction period, fewer nucleation sites, and larger crystals size (∼1.5 μm). Conversely, when aluminum sulfate was mixed with silica sol, a uniform, Al-rich nucleation micro-environment with high negative charge density was established. the precursor primarily interacted with TMAda+ ions for charge compensation rather than with seed fragments. This slow interaction promoted the formation of CHA cages instead of D6R and D4R, leading to a longer induction period, increased nucleation sites, and smaller SSZ-13 crystal sizes (∼150 nm). This study elucidates how the charge density of micro-environment mediated interaction between precursors, organic structure-directing agent, and seed, providing valuable insights into the crystallization kinetics of IZT.

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

Efficient CO2 capture from flue gas and natural gas is highly desirable to reduce greenhouse gas emissions. Discrete SSZ-39 zeolite nanosheets are prepared by the solvent-free seed-assisted route for the first time to capture CO2. Synthesis parameters such as H2O/SiO2 ratio and synthesis time are optimized and the formation mechanism of the SSZ-39 zeolite nanosheets is studied. The nanosheets have a thickness of 30 nm and an aspect ratio of 10. The HR-TEM characterization shows that the base face of the nanosheet corresponds to its (001) plane with a pore size of 3.8 Å × 3.8 Å. The CO2/N2 and CO2/CH4 selectivities of SSZ-39 zeolite nanosheets are as high as 1092 and 136 by Ideal Adsorption Solution Theory (IAST), respectively. Furthermore, breakthrough results indicate that SSZ-39 zeolite nanosheets have great application potential for separating CO2 from flue gas and natural gas.

Unraveling the NH3-SCR-DeNOx Mechanism of Cu-SSZ-13 Variants by Spectroscopic and Transient Techniques.

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.

Revealing the Bro̷nsted Acidic Nature of Penta-Coordinated Aluminum Species in Dealuminated Zeolite Y with Solid-State NMR Spectroscopy.

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.

Engineering In-Co3O4/H-SSZ-39(OA) Catalyst for CH4-SCR of NOx: Mild Oxalic Acid (OA) Leaching and Co3O4 Modification.

Zeolite-based catalysts efficiently catalyze the selective catalytic reduction of NOx with methane (CH4-SCR) for the environmentally friendly removal of nitrogen oxides, but suffer severe deactivation in high-temperature SO2- and H2O-containing flue gas. In this work, SSZ-39 zeolite (AEI topology) with high hydrothermal stability is reported for preparing CH4-SCR catalysts. Mild acid leaching with oxalic acid (OA) not only modulates the Si/Al ratio of commercial SSZ-39 to a suitable value, but also removes some extra-framework Al atoms, introducing a small number of mesopores into the zeolite that alleviate diffusion limitation. Additional Co3O4 modification during indium exchange further enhances the catalytic activity of the resulting In-Co3O4/H-SSZ-39(OA). The optimized sample exhibits remarkable performance in CH4-SCR under a gas hourly space velocity (GHSV) of 24,000 h-1 and in the presence of 5 vol% H2O. Even under harsh SO2- and H2O-containing high-temperature conditions, it shows satisfactory stability. Catalysts containing Co3O4 components demonstrate much higher CH4 conversion. The strong mutual interaction between Co3O4 and Brønsted acid sites, confirmed by the temperature-programmed desorption of NO (NO-TPD), enables more stable NxOy species to be retained in In-Co3O4/H-SSZ-39(OA) to supply further reactions at high temperatures.

A low-temperature regenerable catalyst for stable and selective propylene production from ethylene using Ni and P-supported SSZ-13 zeolite

Due to the increasing demand for propylene, highly selective propylene production from ethylene using small pore zeolite has received significant attention. However, rapid catalyst deactivation due to coke deposition on the catalyst impedes effective propylene production in industry. Therefore, it is essential to develop a low-temperature regeneration ethylene-to-propylene (ETP) catalyst with stable catalytic activity. To achieve such a catalyst, various hydrocracking metal species and phosphorus-supported SSZ-13 were prepared and evaluated using a one-pass ETP and ETP-Regen test. The optimized catalyst NiO(1.0)-P(0.6)-SSZ-13 exhibited a constant, excellent propylene yield of over 70 wt% with 90 wt% of propylene selectivity over ETP reaction and consecutive ETP-Regen cycles. The unprecedented catalytic performance of NiO(1.0)-P(0.6)-SSZ-13 was ascribed to the synergistic effect of NiO and P components, where nickel is responsible for catalyst recovery through effective coke removal, while phosphorus plays an essential role in size-selective diffusion.

White light-emitting Ag+-doped H-SSZ-13 zeolite

Ag+-exchanged SSZ-13 zeolites with single-phase white-emitting, especially obtained in a mild temperature (400 °C), are highly desirable for the construction of white LEDs, but rarely reported. Herein, luminescent silver nanoclusters composites were synthesized though treating H-SSZ-13 zeolites in the presence of a moderate amount of sodium hydroxide solutions, by assembling the silver nanoclusters in the modified SSZ-13 zeolites, followed by heating under mild conditions, which it bright white light emission phenomena under a 365 nm UV light. This white emitting may be ascribed to the collapse of the zeolite skeleton due to the etching of the zeolites by NaOH, thereby formation and stabilization of silver nanoclusters within modified Na-SSZ-13 zeolites. For the first time, the white-emitting Ag@Na-SSZ-13-400 zeolites phosphors were obtained at a mild temperature (400 °C) with a photoluminescence quantum yield (PLQY) of 24.45 % and the CIE chromaticity coordinate were (0.26, 0.33) under the 360 nm excitation. We believe that this work may provide a prospect for application of SSZ-13 zeolites and the preparation of luminescent AgNCs.

Post-Synthetically Treated ERI and SSZ-13 Zeolites Modified with Copper as Catalysts for NH3-SCR-DeNOx

ERI and SSZ-13 were subjected to post-synthetic treatments (depending on the zeolite topology) to create micro-/mesoporous materials. The results in terms of NH3-SCR-DeNOx show that the applied treatments improved the catalytic activity of the Cu-containing ERI-based materials; however, the NO conversion did not vary for the different materials treated with NaOH or NaOH/HNO3. For the micro-/mesoporous Cu-containing SSZ-13, a lower NO conversion in NH3-SCR-DeNOx was observed. Thus, our findings challenge the current paradigm of enhanced activity of micro-/mesoporous catalysts in NH3-SCR-DeNOx. The modification of the supports results in the presence of different amounts and kinds of copper species (especially isolated Cu2+ and aggregated Cu species) in the case of ERI- and SSZ-13-based samples. The present copper species further differentiate the formation of reactive reaction intermediates. Our studies show that besides the μ-η2,η2-peroxo dicopper(II) complexes (verified by in situ DR UV-Vis spectroscopy), copper nitrates (evidenced by in situ FT-IR spectroscopy) also act as reactive intermediates in these catalytic systems.

Achieving High Dispersion of Pd in Small-Pore Zeolite SSZ-13: A High-Efficiency Low-Temperature NOx Adsorber.

Passive NO x adsorber (PNA) materials are primarily considered for reducing nitrogen oxide emissions during the low-temperature cold start of a motor vehicle. Pd/SSZ-13 has attracted considerable attention because of its outstanding hydrothermal stability and sulfur resistance. Optimizing the dispersion of precious metal Pd in Pd/SSZ-13 is crucial for enhancing PNA performance and nitrogen oxide adsorption capability. In this study, we prepared Pd/SSZ-13 using different methods and evaluated their influence on the NO x adsorption capability. The characterization results show that the dispersion of precious metal Pd in the Pd/SSZ-13 catalyst prepared by the quantitative ion-exchange method is as high as 92.13%, and the loading amount is as high as 98.93%. Pd predominantly exists as Pd2+, achieving near-total loading and further improving the catalyst's NO x adsorption capacity. This study offers innovative approaches and methods for applying Pd/SSZ-13 as a PNA material, serving as a reference for its further optimization and performance enhancement. Continued research into the preparation and adsorption performance of Pd/SSZ-13 materials could offer solutions to reduce motor vehicle nitrogen oxide emissions.

Impact of sulfur exposure on high-temperature Cu speciation in SSZ-13 Zeolites

Metal active sites exchanged in zeolites dynamically change speciation under different reaction conditions, resulting in condition-dependent reactivity with gas molecules. This is of particular significance in chemical deactivation, such as sulfur poisoning of Cu-SSZ-13 zeolites used for NH3-assisted selective catalytic reduction (SCR) of NOx in diesel engine exhaust. Here, we employ computational techniques, combined with experiments and spectroscopies, to develop thermodynamic models for sulfur poisoning of zeolite framework-bound Cu dimers that form at high temperatures in Cu-SSZ-13 zeolites as a function of both the Al distribution and reaction conditions. Our results demonstrate that framework-bound Cu dimers that form under high temperature oxidative conditions are particularly susceptible to poisoning by SO2 and SO3. These Cu dimers react more exothermically with SOx species than Cu monomers, forming thermodynamically stable sulfur-containing Cu dimers that require high temperatures for catalyst regeneration.

Improved Synthesis of Hollow Fiber SSZ-13 Zeolite Membranes for High-Pressure CO2/CH4 Separation.

High-silica CHA zeolite membranes are highly desired for natural gas upgrading because of their separation performance in combination with superior mechanical and chemical stability. However, the narrow synthesis condition range significantly constrains scale-up preparation. Herein, we propose a facile interzeolite conversion approach using the FAU zeolite to prepare SSZ-13 zeolite seeds, featuring a shorter induction and a longer crystallization period of the membrane synthesis on hollow fiber substrates. The membrane thickness was constant at ~3 μm over a wide span of synthesis time (24-96 h), while the selectivity (separation efficiency) was easily improved by extending the synthesis time without compromising permeance (throughput). At 0.2 MPa feed pressure and 303 K, the membranes showed an average CO2 permeance of (5.2±0.5)×10-7 mol m-2 s-1 Pa-1 (1530 GPU), with an average CO2/CH4 mixture selectivity of 143±7. Minimal defects ensure a high selectivity of 126 with a CO2 permeation flux of 0.4 mol m-2 s-1 at 6.1 MPa feed pressure, far surpassing requirements for industrial applications. The feasibility for successful scale-up of our approach was further demonstrated by the batch synthesis of 40 cm-long hollow fiber SSZ-13 zeolite membranes exhibiting CO2/CH4 mixture selectivity up to 400 (0.2 MPa feed pressure and 303 K) without using sweep gas.

Mechanistic insights and the role of spatial confinement in catalytic dimethyl ether carbonylation over SSZ-13 zeolite

Mechanistic insights and the role of spatial confinement in catalytic dimethyl ether carbonylation over SSZ-13 zeolite

Embryonic zeolite-directed synthesis of ZSM-34 and SSZ-13 zeolites

The use of an organic structure-directing agent (OSDA) makes zeolite synthesis expensive and environmentally non-friendly. Seeded zeolite synthesis offers an environmentally benign alternative that avoids using an OSDA while providing a high purity, crystallinity, and yield in the product. In this study, we report using embryonic zeolites (EZs) as efficient seeds to obtain industrially important zeolites such as ZSM-34 and SSZ-13 in an OSDA-free synthesis system. Our results showed that zeolites ZSM-34, SSZ-13 and LTL could be obtained depending on the Al/Si ratio in the synthesis system. The synthesis time was considerably shorter than other ZSM-34 and SSZ-13 syntheses methods reported in the literature, achieving more than 90% crystallinity. The physicochemical analysis showed that highly crystalline zeolites with characteristics similar to the OSDA synthesized counterparts were obtained. Furthermore, the EZs seeding approach is facile, low cost, and environmentally friendly, provided the synthesis is OSDA-free. In addition, the EZs seeds can be obtained under hydrothermal synthesis conditions. The method can be potentially applied to the synthesis of other zeolite types.

Bimetallic PtZn nanoparticles anchored in high-silica SSZ-13 zeolite for efficient propane dehydrogenation

Direct dehydrogenation of propane to propylene (PDH) is a promising route to meet the ever-growing global propylene demand, but the industrial Pt-based catalysts usually suffer from serious deactivation derived from coke deposition and sintering under harsh reaction conditions. In this work, PtZn bimetallic nanoparticles encapsulated into high-silica SSZ-13 zeolites (PtZn@SSZ-13) were synthesized via a facile ligand-protected interzeolite transformation strategy. In a PDH reaction, the synthesized 0.5Pt3Zn@SSZ-13 catalyst exhibits superior catalytic performance with a propane conversion of 23.7% and a propylene selectivity of 96.8%, which is significantly better than that of PtZn supported on high-silica SSZ-13 (0.5Pt3Zn/SSZ-13). Particularly, the high catalytic activity of this catalyst can be kept during three successive oxidation–reduction cycles. Detailed characterizations including HAADF-STEM, XPS, UV–Vis, H2-TPR reveal that the remarkable improvement of PDH performance is attributed to the PtZn synergistic effect as well as the confinement of SSZ-13 zeolites. The DFT calculations and microkinetic simulations also evidenced that the Pt particles anchored on the Zn-doped SSZ-13 zeolite pore framework possessed obviously higher propane dehydrogenation activity, whereas the anti-coking ability of 0.5Pt3Zn@SSZ-13 was also stronger than Pt (111) surface, demonstrating the superior performance of 0.5Pt3Zn@SSZ-13.

Exploring the Impact of Active Site Structure on the Conversion of Methane to Methanol in Cu-Exchanged Zeolites.

In the past, Cu-oxo or -hydroxy clusters hosted in zeolites have been suggested to enable the selective conversion of methane to methanol, but the impact of the active site's stoichiometry and structure on methanol production is still poorly understood. Herein, we apply theoretical modeling in conjunction with experiments to study the impact of these two factors on partial methane oxidation in the Cu-exchanged zeolite SSZ-13. Phase diagrams developed from first-principles suggest that Cu-hydroxy or Cu-oxo dimers are stabilized when O2 or N2O are used to activate the catalyst, respectively. We confirm these predictions experimentally and determine that in a stepwise conversion process, Cu-oxo dimers can convert twice as much methane to methanol compared to Cu-hydroxyl dimers. Our theoretical models rationalize how Cu-di-oxo dimers can convert up to two methane molecules to methanol, while Cu-di-hydroxyl dimers can convert only one methane molecule to methanol per catalytic cycle. These findings imply that in Cu clusters, at least one oxo group or two hydroxyl groups are needed to convert one methane molecule to methanol per cycle. This simple structure-activity relationship allows to intuitively understand the potential of small oxygenated or hydroxylated transition metal clusters to convert methane to methanol.

Magnetic MOFs with flexibility for efficient magnetic-induced swing adsorption

Magnetic-induced swing adsorption is effective because of its easy operation, fast heat generation, and short distance of heat transfer. The energy efficiency of this adsorption method depends on the performance of magnetic adsorbents in alternative magnetic fields. In this work, we fabricated flexible MOF-based magnetic adsorbents and applied them in the magnetic-induced swing adsorption. When magnetic field is turned off, the adsorbents show open pores for C3H8 uptake at room temperature. When magnetic field is turned on, C3H8 is released because magnetic-induced heating drives the adsorbents loss their activity through conformational change of pores derived from aromatic rings tilting and rotation. The flexibility of the adsorbents decreases energy consumption to achieve desorption, which promote the energy efficiency of magnetic-induced swing adsorption. The optimal working capacity can reach 16.8 cm3 g−1, which is superior to various typical adsorbents such as F30/470 (9.32 cm3 g−1), MIL-91(Al) (3.36 cm3 g−1), and SSZ-13 zeolite (4.48 cm3 g−1). This work may open up a new avenue to address the issues caused by high energy consumption and slow heat transfer during desorption.

Exploring Cage Effects of Alkane Adsorption on SSZ-39 (AEI) and SSZ-13 (CHA) Zeolites: A Comparative Study

Exploring Cage Effects of Alkane Adsorption on SSZ-39 (AEI) and SSZ-13 (CHA) Zeolites: A Comparative Study

Effects of Cu species in Cu-SSZ-13 zeolites on the performance of NOx reduction reactions

In diesel vehicle exhaust after-treatment systems, high silica Cu-SSZ-13 has received increasing attention as a commercialized catalyst owing to its high efficiency in selective catalytic reduction reactions with NH3 (NH3-SCR). However, research on the regulation of Cu2+ species within metal active centers in the pore structure of chabazite (CHA)-type zeolite to improve catalytic performance lacks sufficient depth. Herein, SSZ-13 zeolite with various Al distributions was prepared by adjusting the proportion of N,N,N-Trimethyl-1-adamantanaminiumhydroxide (TMAdaOH) and Na in the initial gel. Moreover, three representative Cu-SSZ-13 catalysts with different Cu2+ species were synthesized via an ion exchange method. 23Na MAS NMR and NO adsorption infrared spectroscopy results revealed that with increasing Na content and decreasing TMAdaOH concentration in the initial gel, the number of paired Al in the CHA framework gradually increased. Consequently, this increased the number of Cu2+-2Z sites near six-membered ring (MR) and reduced the amount of [Cu(OH)]+-Z sites near eight-MR. The fresh Cu-SSZ-13 catalyst, with a moderate amount of Cu2+-2Z and [Cu(OH)]+-Z, exhibited optimal catalytic performance across the entire temperature window. After hydrothermal aging, Cu-SSZ-13 with a higher concentration of Cu2+-2Z species featured optimal performance among all Cu-SSZ-13 catalysts above 400 °C. These findings indicated the significance of balancing the amount of both Cu2+-2Z and [Cu(OH)]+-Z in the Cu-SSZ-13 zeolite. Additionally, the results elucidated the reaction intermediates involved in the NH3-SCR process catalyzed by Cu-SSZ-13 with various Cu species.

Development and investigation of a multilayer PDMS/zeolite composite membrane for CO2 separation applications

This work aims to investigate and develop a concept for CO2 separation based on PDMS/SSZ–13 (high-Si CHA) composite membranes. Firstly, an Al2O3 support was coated with SSZ-13 zeolite layer, then to increase the performance of the membrane, a Polydimethylsiloxane layer was effectively deposited homogeneously to cover the cracks and defects of the zeolite layer. The results of single gas permeation measurements displayed a notable increase in ideal CO2/CH4 selectivity up to 428 at the lowest PDMS concentration of 0.5 vol%. Moreover, a coating time of 10 min preserved CO2 permeance while increasing CO2/CH4 selectivity from 5 to 120. A twentyfold increase in CO2/CH4 selectivity was noted with mixed gas permeation without a reduction in CO2 permeance. Quantitative and qualitative microscopic analyses were also carried out on the coated membrane to better understand its morphology and microstructure. The outcomes indicated that PDMS layer decreased the permeation of N2 and CH4 and enhanced surface affinity toward CO2, resulting in reduced defects in the zeolite membranes and enhanced selectivity for CO2/N2 and CO2/CH4.