Stability Of Zeolites Research Articles

Improving the hydrothermal stability of zeolite Y by La3+ cation exchange as a catalyst for the aqueous-phase hydrogenation of levulinic acid.

La3+ cation exchange is shown to improve the hydrothermal stability and catalytic activity of bifunctional zeolite Pt/Y catalysts in the aqueous-phase hydrogenation of levulinic acid (LA) with formic acid (FA) as hydrogen source. La3+ cation exchange of zeolite Y (nSi/nAl = 16) was conducted both in aqueous solution and in the solid state. The hydrothermal stability of La3+-containing zeolite Y probed by exposure to the reaction mixture (0.2 mol L−1 LA, 0.6 mol L−1 FA) at 473 K under autogenous pressure for 24 h improves with increasing La content. The material exhibiting the highest La content (0.5 mmol g−1) is the most stable with a preservation of 25% of the initial specific micropore volume after the hydrothermal treatment, whereas unmodified zeolite Y completely loses its microporosity. A new procedure using DRIFTS is a useful supplementary tool for quantifying the framework degradation of Y-type zeolites after hydrothermal treatment. Bifunctional Pt/Y catalysts after La3+ cation exchange are more active than the parent Y-zeolite for the hydrogenation of LA to γ-valerolactone (GVL), with significant enhancements in LA conversion, i.e., 94% vs. 42%, and GVL yield, i.e., 72% vs. 34%., after 24 h.

The catalytic activity of microporous and mesoporous NiCoBeta zeolite catalysts in Fischer–Tropsch synthesis

Two kinds of microporous and mesoporous NiCoBeta zeolite catalysts were prepared. The effect of bimetallic zeolite preparation method, dealumination degree, the presence of micropores in the support structure and the effect of nickel addition on the activity and selectivity of cobalt-based microporous and mesoporous dealuminated and non-dealuminated zeolite catalysts in Fischer–Tropsch synthesis were determined. These catalysts were obtained by sequential impregnation (Ni3.0Co20AlBeta and Ni3.0Co20SiBeta) and co-impregnation (co-Ni3.0Co20AlBeta and co-Ni3.0Co20SiBeta). The study showed that the presence of Ni leads to a lower cobalt oxide reduction temperature and an increase in CO conversion. Nickel–cobalt zeolite systems showed high activity and selectivity throughout the lifetime of the reaction. The use of a two-step post-synthesis method and the promotion of cobalt systems with nickel allow to obtain active, selective, and stable zeolite catalysts for Fischer–Tropsch synthesis.

Benzofuran as deactivation precursor molecule: Improving the stability of acid zeolites in biomass pyrolysis by co-feeding propylene

Benzofuran (BZF) is produced during the biomass and waste pyrolysis, playing a key role in the catalytic deactivation in the processing of the resulting fractions, as well as in catalytic pyrolysis reactions. The transformation of this chemical over a typical pyrolysis catalyst (ZSM-5) is studied in this article. When this compound is processed alone, it presents a very high reactivity. At low temperature, the formation of large amount of coke precursors leads to a fast catalyst deactivation. As temperature increases, the weight of cracking reactions (yielding benzenes or naphtalenes) becomes more important, increasing the catalyst’s stability, although new polyaromatic carbon species are detected.A new strategy to minimize the deactivation caused by this compound, consisting of co-feeding propylene, is proposed. The presence of an alkene leads to the formation of alkylated derivatives of Diels-Alder condensation products, hindering their oligomerization capacity and minimizing the formation of polyaromatic coke deposits. Different temperatures and alkene/BZF ratios were tested, concluding that increasing the alkene concentration and the reaction temperature monotonously increase the catalyst’s stability in presence of BZF.

Effect of zeolite topology on NH3-SCR activity and stability of Cu-exchanged zeolites

The catalytic activity and stability of Cu-exchanged zeolites Cu-ZSM-5 (MFI topology), Cu-TNU-9 (TUN), Cu-FER (FER) and steamed Cu-Y (FAU) were evaluated in the selective catalytic NO reduction by ammonia (NH3-SCR). The NH3-SCR activity of the investigated catalysts strongly depended on the feed composition, i.e., the presence of H2O (5.0 Vol.-% of H2O). The catalysts revealed high stability during 24 h of NH3-SCR reaction, also in the presence of water vapour. DR UV–vis and FT-IR with probe molecules (CO or NO) showed the presence of isolated Cu+/Cu2+ and aggregated copper oxide species. Although Cu-ZSM-5 is less active than Cu-TNU-9 in catalysing NO oxidation to NO2, both catalysts revealed similar activity in the NH3-SCR reaction. Applying Rapid-Scan FT-IR spectroscopy and 2D COS analysis the reaction mechanism of NH3-SCR on Cu-exchanged zeolites was investigated. It is proposed that NH3-SCR over the studied Cu-exchanged catalysts proceeds via [Cu(OH)(NH3)2(NO)]+ intermediates followed by the reduction of Cu(II) to Cu(I). The differentiated speciation of copper sites is reflected in their various susceptibility for the reduction and finally affects the catalytic activity and stability of the zeolitic catalysts. The formation of the [Cu(OH)(NH3)2(NO)]+ mixed ligand species is governed by the competition between the O2− and NH3 ligands. Also the stability of the forms initiating NH3-SCR, i.e., [Cu(NH3)4]2+, [Cu(OH)(NH3)3]+ and [Cu(NH3)2]+, is ruled by the confine interaction of ammonia molecules, which can be both adsorbed on a protonic site and ligated to copper sites with the framework oxygen atoms.

Obsidian as a Raw Material for Eco-Friendly Synthesis of Magnetic Zeolites.

A sample of rhyolitic obsidian (OS) was used as raw material for zeolite synthesis by long (4 days) and fast (2 h)-aging hydrothermal processes. Zeolite synthesis was also performed by a fast (2 h) sonication method. The products were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) both immediately after and 3 years after their formation in order to determine the stability of synthetic materials according to the method used. The results confirm zeolitization of obsidian both by long-aging conventional hydrothermal heating and fast hydrothermal process. However, the data highlight the efficiency of direct ultrasound energy in achieving more stable zeolite crystals over time. These results carried out using a natural source, follow those already obtained using wastes and pure sources as raw materials thus providing a definitive validation of the different mechanisms controlling zeolite formation according to the process used. Moreover, the results confirm the effectiveness of ultrasonic energy in the formation of zeolites that are more stable over time. Due to the chemical composition of the obsidian precursor, all synthetic zeolites show good magnetic properties (i.e., saturation magnetization), in view to potential magnetic separation.

Understanding the high hydrothermal stability and NH3-SCR activity of the fast-synthesized ERI zeolite

ERI zeolite is a small-pore zeolite that has been rarely explored as a catalyst in the selective catalytic reduction of NOx with ammonia (NH3-SCR) as the performance has been considered to be limited by its insufficient hydrothermal stability. We herein report that a fast-synthesized ERI zeolite, which can be synthesized in only 2 h at a high temperature (210 °C), shows much enhanced hydrothermal stability than the conventional ERI zeolite due to the presence of less silanol defects. The fast-synthesized ERI zeolite with an optimal copper loading (equaling a Cu/Al ratio of 0.20) is demonstrated to be highly active in the NH3-SCR, which even rivals Cu-SSZ-13 – the benchmark NH3-SCR catalyst. Various characterization techniques are employed to characterize the copper species in the fast-synthesized ERI zeolite in order to understand its high hydrothermal stability and NH3-SCR activity. The results indicate that the copper species sitting at different locations exhibit variant hydrothermal stability and NH3-SCR activity, suggesting the importance of the interplay between the copper species and the zeolite host. With a deep understanding into the structure-activity relationship, this work presents that the fast-synthesized ERI zeolite holds potential to emerge as a robust NH3-SCR catalyst for emission control.

Rapid Synthesis of Hydrothermally Stable ZSM-5 in the Presence of 1-Butanol

Hydrothermal stability and productivity of zeolite are important concerns when considering its industrial applications. In this study, we used 1-butanol as an organic additive for the synthesis of ...

Effects of mesopore introduction on the stability of zeolites for 4-iso-Propylphenol dealkylation

Low rank coal- and biomass-derived liquids generally contain a mixture of alkylphenols, which can be dealkylated over zeolites into phenol as a basic chemical. Zeolites with different pore structures were evaluated for the dealkylation of 4-iso-propylphenol as a model alkylphenol, among which HZSM-5 and HMCM-22 displayed the highest phenol selectivity above 96 %. However, HZSM-5 deactivated fastest among the catalysts due to coke deposition. Thus, mesopores were introduced by desilication into HZSM-5 catalysts to improve the catalytic stability. The mesopore incorporation enhanced the connectivity of the micropores with the crystal surface, and shortened the diffusion lengths. Coke location analysis revealed that micropore occlusion by the coke shell occurred on the parent HZSM-5, whereas the acid sites in the desilicated catalysts were more accessible for fully utilization, even though the coke mainly deposited in the micropores. Furthermore, the coke on the desilicated HZSM-5 displayed a lower graphitization degree.

Effects of Lanthanum Incorporation on Stability, Acidity and Catalytic Performance of Y Zeolites

A better understanding of the roles of rare earth (RE) in heterogeneous catalysts is crucial for improving the properties of catalysts in petro-chemical industry. Fluid catalytic cracking (FCC) catalysts containing RE-incorporated Y zeolites with excellent stability and activity are continuously used to improve the conversion of heavy oil into transportation fuels. In this paper, the effect mechanism of Lanthanum (La) on stability and acidity of Y zeolites are elucidated in conjunction with their influences on catalytic performance. The improvement on stability of La-incorporated Y zeolites can be attributed to the La incorporation which bonds strongly with framework O2 and O3 atoms and strengthens the interaction between framework Al and its neighbouring O atoms. It is the enhanced stability restrains the release of framework Al and the formation of extra-framework Al, hence leads to a decrease of total L acid amount and an increase of total B acid amount, especially a clear increase in medium strength B acid amount (with 31P NMR/TMPO chemical shifts at 62 and 58) and a significant decrease in strong B acid amount (with 31P NMR/TMPO chemical shifts at 70 and 65) with the incorporation of La into Y zeolites. However, the total acid amount decreases significantly when La2O3 content is high. The increase of B acid amount and improved stability of LaHY zeolites, boost the conversion ability and isomerization ability of heavy oil, while resulting in poor olefins selectivity and coke selectivity caused by the enhancement of hydrogen transfer reactions. Therefore, Y zeolite containing appropriate La2O3 content should be considered to enhance heavy oil cracking ability while boosting light olefins production and optimizing coke selectivity.

Enhancing the Supercapacitive and Conductivity Properties of Polypyrrole via In-situ Polymerization with HY Zeolite Nanoparticles

Highly stable zeolite HY/polypyrrole composite material was successfully fabricated by applying in-situ chemical polymerization approach. The functional properties of the prepared zeolite HY particles/polypyrrole were systematically inspected using XRD and FT-IR characterization techniques. Thermal stability and optical properties were consistently studied using TGA and UV–Vis spectroscopy techniques. The value of band gap energy (Eg) of the produced zeolite HY/polypyrrole nanocomposite was lower than the values of its individual components. Cyclic voltammetry studies concluded that HY/polypyrrole electrode material with mass ratio ~ 0.4 prepared at cold polymerization conditions ~ 0 °C exhibited the highest values of specific capacitance ~ 310 F g−1 and ionic conductivity ~ 1.7 S cm−1. The fabricated zeolite HY/polypyrrole composite material at 0 °C revealed a capacitance retention ~ 93.4%, while the other composite prepared at 25 °C possessed a capacitance retention ~ 72.4% after 500 charge/discharge cycles. The electrochemical impedance spectroscopy (EIS) measurement for the optimized composite electrode materials confirmed the cyclic stability after long term cycling of about 5000 cycles as a result of higher ionic conductivity between active material and ionic species than that value before cycling.

Zeolite (In)Stability under Aqueous or Steaming Conditions.

Zeolites are among the most environmentally friendly materials produced industrially at the Megaton scale. They find numerous commercial applications, particularly in catalysis, adsorption, and separation. Under ambient conditions aluminosilicate zeolites are stable when exposed to water or water vapor. However, at extreme conditions as high temperature, high water vapor pressure or increased acidity/basicity, their crystalline framework can be destroyed. The stability of the zeolite framework under aqueous conditions also depends on the concentration and character of heteroatoms (other than Al) and the topology of the zeolite. The factors critical for zeolite (in)stability in the presence of water under various conditions are reviewed from the experimental as well as computational sides. Nonreactive and reactive interactions of water with zeolites are addressed. The goal of this review is to provide a comparative overview of all-silica zeolites, aluminosilicates and zeolites with other heteroatoms (Ti, Sn, and Ge) when contacted with water. Due attention is also devoted to the situation when partial zeolite hydrolysis is used beneficially, such as the formation of hierarchical zeolites, synthesis of new zeolites or fine-tuning catalytic or adsorption characteristics of zeolites.

Thermodynamic study of cement/rock interactions using experimentally generated solubility data of zeolites

Alteration of widespread interfaces between cements and clays in geological time scales is essential to the safety assessment of radioactive waste repositories but not well understood partly due to the low reliability of thermodynamic data for zeolites. Here, we collected and full-scale characterized Ca-based zeolites with six types of frameworks that could possibly form in the interfaces. Besides, chemical interactions between degraded cementitious phases and rock forming minerals after equilibrating for ~6 years were investigated. By using the currently generated thermodynamic data of selected zeolites, chemical interactions in the cement/rock systems were studied, showing that no equilibrium was reached after 6 years and zeolites favored in thermodynamics, such as chabazite and gismondine rather than faujasite, can be expected to form at even longer timescale. The experimentally derived thermodynamic data was verified preliminarily by establishing consistent predominance diagrams of cement-zeolite-clay minerals, helping to predict zeolite stability domains in large timescales.

Synthesis, characterization, and thermodynamic study of selected Na-based zeolites

Zeolites are crystalline aluminosilicates with three-dimensional framework structures that can form in alkali-activated cements, Roman cements, and the interaction zone of cements and clays. However, their stability domains are uncertain due to their high structural variability and the lack of experimental solubility data. Thermodynamic data were here determined for selected Na-based zeolites built from six different secondary building units that could possibly form in the interaction zones of cement/clay. The zeolites were synthesized by hydrothermal methods and full-scale characterized with respect to framework structures, extra-framework cations, Si/Al ratios, and water contents. Their thermodynamic properties were determined based on the experimental solubility products at different temperatures using GEMS. Predominance diagrams of zeolite-clay/mica-SiO2/Al(OH)3 minerals in the chemical sub-systems of Na2O-SiO2-Al2O3-H2O were successfully established using PHREEQC-PhreePlot code. The experimentally derived thermodynamic data provide insights on the early stage of the zeolite ageing and predicting zeolite stability domains during cementitious material hydration.

Strategies for Extending Zeolite Stability in Supercritical Water Using Thermally Stable Coatings

Increasing the stability of zeolites in liquid, near-critical, and supercritical water at temperatures greater than 200 °C is required for many important chemical processes, notably including hydro...

Biochar-supported natural zeolite composite for recovery and reuse of aqueous phosphate and humate: Batch sorption–desorption and bioassay investigations

Abstract The incomplete inert nature of engineered biochar and the low desorbability/recyclability of its disposals are still questionable. Herein, water hyacinth biochar-supported natural zeolite (ZB) was compared with the original biochar (OB) on the recovery and reuse of aqueous phosphate and humate under batch sorption–desorption experiments. In addition, the potential reuse of the exhausted biochar on ameliorating nutrient supply potentials of sandy soil was investigated using a bioassay on early-growth seedlings. Physicochemical analysis revealed the successful functionalization of ZB and improving its thermal stability. Physisorption and chemisorption forces participated mutually in sorption process. In this regard, precipitation mechanism showed a high contribution for chemisorption of phosphate into brushite and hydroxylapatite minerals. The calculated q m a x values of Langmuir model showed the lower affinity of ZB to phosphate and humate compared to OB due to lowering/vanishing of amine functional groups and the dramatic reduction in specific surface area through cover/clog of micro-and meso-pores by zeolite fine particles. However, phosphate desorbability from ZB was significantly higher than OB suggesting its higher renewability potentials. The exhausted biochar additives (particularly ZB-loaded phosphate and humate) stimulated plant biomass yield, photosynthetic pigments and nutrients uptake by arugula seedlings. Furthermore, the residual effect of these additives on stimulating the aforementioned parameters of the successive maize seedlings confirmed the higher phytoavailability and usability of ZB-loaded additives. The high thermal stability and desorbability of natural zeolite, therefore, support its potentiality to improve stability and recyclability of engineered biochar.

Cancrinite synthesis from natural kaolinite by high pressure hydrothermal method: Application to the removal of Cd2+ and Pb2+ from water

Abstract Zeolites were synthesized from natural Tunisian clay by hydrothermal treatment under high pressure (100 MPa H2O pressure) at different gradients of temperature in high pressure autoclaves. The natural clay was first heated at 650 °C (HC-heated clay) and then transformed to an amorphous phase at 650 °C by adding different amount of NaOH. By increasing temperature and NaOH content, low-density frameworks zeolites like faujasite are transformed into more stable zeolites having higher density frameworks like cancrinite due to dissolution and recrystallisation steps. Cancrinite (Na8(H20)2CO3[Al6Si6O24]) (IZA-code: CAN) was successfully synthesized with a good purity. The synthesized CAN was characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The removal performance of heavy metal ions (Cd2+, Pb2+) from solution by pure CAN and clays has been studied. The kinetics of adsorption of Cd2+ and Pb2+ are very fast: equilibrium is reached within 2 min at 298 K. The capacity of adsorption of CAN is higher for Pb2+ (192 mg g−1) than for Cd2+ (68 mg g−1). Adsorption equilibrium of Cd2+ and Pb2+ on CAN were well represented by Langmuir equation although the thermodynamic study reveals a more complex mechanism: thermodynamic parameters, such as equilibrium constant, free energy, entropy and enthalpy for adsorption were obtained from the experimental data, including adsorption microcalorimetry.

Recent Progress to Understand and Improve Zeolite Stability in the Aqueous Medium

The work reviewed here attempts to summarize the growing literature on zeolite stability in hot liquid water. This required to first establish the nature, structure and interactions of the active sites in Brønsted and Lewis acidic microporous materials in the presence of liquid water. This understanding was then transferred to zeolite stability and catalyst deactivation. While early results correctly established Si–O–Si hydrolysis as the dominant pathway compared to the Si–O–Al hydrolysis observed in steaming, it also focused extensively on the positive role of framework and extra-framework Al in stabilizing zeolites. However, stability was instead found to more directly correlate with the number of internal structural defects and intraporous water concentration. Stabilization protocols for Brønsted acidic zeolites are described in detail. In the case of Lewis acidic zeolites, their inherent hydrophobic behavior (Si/M >100) makes them more resistant towards water, however, issues such as reversible carbonaceous species formation as well as irreversible metal leaching and fouling remain. Finally, we summarize the most important factors in designing robust and efficient zeolite catalysts made to withstand hot liquid water.

Stability of Li-LSX Zeolite in the Catalytic Pyrolysis of Non-Treated and Acid Pre-Treated Isochrysis sp. Microalgae

This paper investigates the use of Li-LSX-zeolite catalyst over three regeneration cycles in presence of non-treated and acid pre-treated Isochrysis sp. microalgae. The spent and regenerated catalysts were characterised by surface analysis, elemental analysis (EA), SEM-EDS, and XRD to correlate their properties with the bio-oil yield and quality. The acid pre-treatment removed alkali metals, reducing gas yield in favour of bio-oil, but, at the same time, led to catalyst deactivation by fouling. Differently, the non-treated microalgae resulted in a bio-oil enriched in C and H and depleted in O, compared to the pre-treated ones, denoting higher deoxygenation activity. After 3 pyrolysis/regeneration cycles, the analyses suggest that there are no major changes on catalyst using non-treated microalgae. Regeneration at 700 °C has been shown to be able to remove most of the coke without damaging the Li-LSX zeolite structure. In summary, Li-LSX zeolite was effective in maintaining deoxygenation activity over three cycles in the pyrolysis of non-treated Isochrysis microalgae, while the algae pre-treatment with sulphuric acid was detrimental on the catalyst activity.

Extremely Stable Zeolites Developed via Designed Liquid-Mediated Treatment.

Improving the stability of porous materials for practical applications is highly challenging. Aluminosilicate zeolites are utilized for adsorptive and catalytic applications, wherein they are sometimes exposed to high-temperature steaming conditions (∼1000 °C). As the degradation of high-silica zeolites originates from the defect sites in their frameworks, feasible defect-healing methods are highly demanded. Herein, we propose a method for healing defects to create extremely stable high-silica zeolites. High-silica (SiO2/Al2O3 > 240) zeolites with *BEA-, MFI-, and MOR-type topologies could be stabilized by significantly reducing the number of defect sites via a liquid-mediated treatment without using additional silylating agents. Upon exposure to extremely high temperature (900-1150 °C) steam, the stabilized zeolites retain their crystallinity and micropore volume, whereas the parent commercial zeolites degrade completely. The proposed self-defect-healing method provides new insights into the migration of species through porous bodies and significantly advances the practical applicability of zeolites in severe environments.

Zeo19: A thermodynamic database for assessing zeolite stability during the corrosion of nuclear waste immobilization glasses

Stable, durable immobilization of radioactive wastes requires robust understanding of the sub-surface geochemical processes that occur in repository environments. For example, the accelerated dissolution (corrosion) of nuclear waste immobilization glasses (i.e., the so-called “Stage III” corrosion) following the precipitation of zeolitic phases is a significant issue that could result in radionuclide release. However, current uncertainties in establishing the tendency for the persistence of zeolites results in difficulties in estimating the chemical environments and state variables that favor zeolite precipitation. To assess the tendency for Stage III corrosion, we compiled a unified, internally-consistent thermodynamic database to estimate zeolite stability under conditions relevant to nuclear waste repositories (namely, p = 1 bar and T < 95 °C), i.e., for compounds including: analcime, clinoptilolite, mordenite, erionite, thomsonite, bikitaite, brewsterite, dachiardite, epistilbite, ferrierite, gonnardite, harmotome, leonhardite, paranatrolite, tetranatrolite, yugawaralite zeolite X, and zeolite P(Ca). The database, which features both existing and/or newly-derived thermodynamic properties, is integrated with a Gibbs (free) energy minimization (GEM) solver to estimate stable zeolite phase equilibria and their partitioning at equilibrium. The database offers favorable predictions of the solubility of the zeolite phases as a function of temperature. The validity of the database is ascertained by comparing newly-constructed equilibrium activity diagrams with experimental observations of zeolite formation during glass dissolution across conditions encompassing diverse solution chemistries, pH’s, and temperatures.