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The recycling of polyethylene terephthalate (PET) waste plastics has garnered global attention as an essential area of research to address. Chemical upcycling methods, such as glycolysis, offers a visible solution by directly converting PET wastes into high-valued monomers, enabling their reintegration into the plastic life cycle. However, the recovery of metal salt catalyst and the thermal stability of organic catalyst pose challenges in PET glycolysis. Zeolites with strong Brønsted acid are widely used in the degradation of polyolefins, but in PET glycolysis, they face the problems of acid site mismatch and difficult contact with PET. In this work, nanosized FAU-type zeolite catalysts (100-FAU) were employed to carry out PET glycolysis, which were green synthesized at low temperature without organic template. In comparison to commercial FAU-type catalysts, 100-FAU exhibits enhanced Lewis acidity and basicity along with increased accessibility to active sites. The 100% degradation of PET was achieved within 1 h, resulting in a BHET yield of 64.2%. Prolonging the reaction time to 1.5 h led to an enhanced BHET yield of 72.1%. The quality of the primary product bis(2-hydroxyethyl) terephthalate (BHET) was verified through IR, DSC, and NMR characterizations. Furthermore, as a solid catalyst with high thermal stability, zeolite can be easily recovered via filtration and demonstrated stable performance over at least 5 cycles, and proved effective for glycolysis of commercially waste PET plastics. The acid–base dual-functional catalytic mechanism of Na-form FAU in PET glycolysis was proposed. Under its guidance, the promoting effect of other Na-form nanosized zeolites on PET degradation was verified. [ABSTRACT FROM AUTHOR]

SrO has attracted attention for its use as a heterogeneous catalyst in producing biodiesel from transesterification owing to its high alkaline character and low solubility in methanol. In studies conducted in this decade, reaction conditions such as the methanol–oil molar ratio, reaction time, catalyst loading and temperature have been optimized in these systems. Furthermore, several works have been carried out to improve the physicochemical properties and increase the leaching resistance of this material. Thus, the new trends in using SrO in transesterification reactions are that this oxide should be supported or combined with Al2O3, TiO2, ZrO2, or Fe2O3, CaO, metal–organic frameworks, zeolites or La2O3. It has been observed that strontium can form mixed crystalline phases with these oxides by increasing the (M2+O2−) pairs and Lewis basicity of the oxygens, resulting in increased basicity and catalytic activity. Moreover, the transition metal oxides may provide Lewis acidity. Hence, these strontium‐containing catalytic systems have demonstrated a bifunctionality that can perform esterification and transesterification reactions at the same time. In addition, the combination of these oxides decreases the leaching of the catalyst. Other materials such as metal–organic frameworks, zeolites, and La2O3 have been studied as SrO supports, showing that they can be used in oil transesterification reactions. [ABSTRACT FROM AUTHOR]

Biomass is an attractive raw material for the production of fuel oil and chemical intermediates due to its abundant reserves, low price, easy biodegradability, and renewable use. Hydroxymethylfurfural (5‐HMF) is a valuable platform chemically derived from biomass that has gained significant research interest owing to its economic and environmental benefits. In this review, recent advances in biomass catalytic conversion systems for 5‐HMF production were examined with a focus on the catalysts selection and feedstocks' impact on the 5‐HMF selectivity and yield. Specifically, the potential of zeolite‐based catalysts for efficient biomass catalysis was evaluated given their unique pore structure and tunable (Lewis and Brønsted) acidity. The benefits of hierarchical modifications and the interactions between porosity and acidity in zeolites, which are critical factors for the development of green catalytic systems to convert biomass to 5‐HMF efficiently, were summarized and assessed. This Review suggests that zeolite‐based catalysts hold significant promise in facilitating the sustainable utilization of biomass resources. [ABSTRACT FROM AUTHOR]

A set of Sn- and Zr-BEA zeolites was obtained using Gemini-type surfactants as SDA and hierarchical BEA nanosheets as seeds. The prepared catalysts were tested in the Baeyer–Villiger oxidation of cyclic ketones with hydrogen peroxide resulting into commercially valuable monomers. The highest conversion of cyclohexanone (70.7%) and selectivity towards the desired ε-caprolactone (> 99%) were achieved over mesoporous Sn-BEA_np_75 possessing the highest concentration of Lewis acid sites and comparatively low fraction of extra framework Sn4 + species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Glucose isomerization is performed in different solvents using metal doped zeolite Y. • Ethanol favours fructose production, methanol favours alkyl fructoside production. • Nature of acid sites differs within the pore and outside of the pore. • NMR relaxation confirms that mechanism is dependent on pore uptake of solvent used. • DRIFTS measurements show that metal doping increase Lewis acidity of zeolite Y. Sn and Ga doped zeolite Y catalysts were tested for the isomerization of glucose to fructose carried out in different solvents (water, methanol and ethanol). Therein, ethanol favoured a Lewis acid site catalyzed pathway that promotes glucose isomerization to fructose, whereas methanol resulted in an equal distribution of products (mannose, fructose and alkyl fructoside). In contrast, the catalysts were totally inactive in water solvent. NMR relaxation measurements, including solvent displacement experiments, suggested that the lack of catalytic activity in water is due to the strong adsorption of this solvent within the zeolite pores blocking reactants from the Lewis acid sites active for the sugar isomerization. In comparison, ethanol adsorbs relatively more strongly than methanol, hence is retained in the pores where solvated fructose is preferentially prevented from the further reaction on Brønsted acid sites situated outside of the pore space. NMR relaxation measurements using pyridine and tetrahydrofuran (THF) and pyridine-DRIFTS measurements suggest metal doping had little effect on the overall relative acid strength of the zeolites but resulted in zeolites with increased Lewis acid strength relative to the non-doped zeolites. The results reported provide direct experimental evidence on the importance of adsorption properties of solvents within zeolites used for glucose to fructose isomerization and may serve as a starting point for a new approach towards designing and optimizing such catalytic systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • An acid-modulated isomorphous substitution method for synthesizing Ti-MWW. • Rich open Ti(OSi) 3 OH sites formed via the developed synthesis method. • The open Ti(OSi) 3 OH sites possess the stronger Lewis acidity. • The stronger Lewis acidity promotes the catalytic oxidative hydration. Although the oxidative hydration of ethylene with hydrogen peroxide (H 2 O 2) to ethylene glycol (EG) over Ti-MWW zeolites take advantages of step-saving and facile operation, both H 2 O 2 utilization efficiency and EG yield are relatively low, because some extra-framework octahedral Ti species are usually formed in the Ti-MWW zeolites synthesized by prevailing methods, which are detrimental to selective oxidation. In the present work, an acid-modulated isomorphous substitution method, i.e. , layered borosilicate MWW-type zeolite (ERB-1) treated with HNO 3 aqueous solution containing tetrabutyl orthotitanate (TBOT), is developed to synthesize a Ti-MWW zeolite without extra-framework octahedral Ti species under the optimized synthesis conditions. In combination with the results from extensive characterizations for the synthesized zeolites, it is found that in the zeolite prepared by the currently developed synthesis method there are more open Ti(OSi) 3 OH sites formed, resulting in the stronger Lewis acidity that is very helpful to EG production from the oxidative hydration of ethylene with H 2 O 2 , compared to the one synthesized by the prevailing method. Moreover, the developed catalyst is recyclable after the regeneration of the deactivated zeolite by calcination at high temperatures. Therefore, it is anticipated that the currently developed Ti-MWW might be industrially applicable in the one-pot synthesis of EG from ethylene with H 2 O 2. [ABSTRACT FROM AUTHOR]

Shape-selective stannosilicates have been post-synthesized for the hydration of epoxide to diols. A simple acid treatment has been employed to remove extensively the interlayer double four ring units, converting the three-dimensional (3D) UTL germanosilicate into a 2D layered IPC-1P intermediate. Isomorphous incorporation of tetrahedrally coordinated Sn active centers was realized via solid-liquid treatment of IPC-1P with diammonium hexachlorostannate aqueous solution, which was accompanied by the spontaneous condensation of neighboring silica-rich cfi layers upon calcination and structural construction of a 3D PCR structure. Sn-PCR stannosilicates with tunable Sn contents were thus prepared. With Sn-derived robust Lewis acidity confined in the intersecting 10- and 8-ring channels, the Sn-PCR (Si/Sn molar ratio of 77) catalyst served as a shape-selective nanoreactor for the hydration of ethylene oxide (EO) into ethylene glycol (EG), exhibiting a remarkable EO conversion (99.5 %) as well as a steady EG selectivity (>98.4 %) at greatly reduced H2 O/EO molar ratio and near-ambient reaction temperature. [ABSTRACT FROM AUTHOR]

Faujasite is one of the most industrially employed zeolite for its catalytic properties. The strong Brønsted bulk bridging Al−OH−Si sites are often thought to be the main origin of the Brønsted acidity of faujasite. However, many reactions also take place at the surface of the material and of its mesopores, where other types of acid sites exist. This study aims at unraveling the nature and strength of faujasite bulk and surface acid sites. Using Density Functional Theory (DFT), we rank the faujasite acid sites based on their stability, investigate their dehydration properties, and study their Brønsted and Lewis acidity via the adsorption of pyridine. Calculations are performed on cells with high (47 for bulk cells and about 300 for surface slabs) and low Si/Al ratio (about 3) and on cells containing defects under the form of silanol nests. These environments generate Brønsted acid sites of various strengths, and strong Lewis acid sites, even in the absence of extra‐framework species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tetrahedrally coordinated framework-associated Fe3+ species form strong Lewis acid sites. • Paraffin cracking is initiated by strong Lewis acid sites of Fe-ZSM-5. • Fe-ZSM-5 increases propene, butenes and aromatics selectivity compared with Al-ZSM-5. • Fe 2 O 3 particles does not catalyze paraffin cracking. Iron-modified Al-ZSM-5 increases selectivity to propene, a key petrochemical resulting from fluid catalytic cracking (FCC). However, the type and role of active iron species remain unclear, hindering efforts to streamline the design of selective FCC additives. Here, we investigated Al-free Fe-ZSM-5 catalysts containing iron species in the form of framework Fe3+, extra-framework Fe3+, oxidic clusters, and oxide micro aggregates in n-octane cracking (FCC model) to assess their effect on catalytic cracking. DR-UV–Vis spectroscopy, 57Fe Mössbauer Spectroscopy, FTIR studies of pyridine adsorption, and n-octane cracking tests at 500 °C revealed that framework-associated coordinatively unsaturated Fe3+ species, which induce strong Lewis acidity, are responsible for paraffin cracking initiation, whereas bulk iron oxides on the zeolite surface are inactive. In comparison with Al-ZSM-5, Fe-ZSM-5 increases the olefinicity of the valuable C 3 -C 4 fractions (selectivity to propene and butenes) and promotes aromatization reactions due to the lower relative strength of Fe-induced Brønsted acid sites and dehydrogenation properties. As shown by our 57Fe Mössbauer study (performed at −269 °C) of the catalyst in calcined, spent, and regenerated states, Fe-ZSM-5 deactivation is associated with the loss of tetrahedrally coordinated Fe3+ species. Therefore, tuning Fe-ZSM-5 C 3 -C 4 selective FCC additives requires stabilizing framework Brønsted and framework-associated Lewis acid sites while decreasing the concentration of iron oxide species. Ultimately, these findings may enable us to meet the demand for propene derived from FCC cracking, which is expected to grow in the foreseeable future. [ABSTRACT FROM AUTHOR]

The valorization of low‐grade industrial residues into valuable materials has been a way to reduce the impact of the industry on planetary boundaries. Silicon‐rich wastes have been used for zeolite synthesis while the impurities originating from wastes have a vital role in the physicochemical properties and the catalytic performance of waste‐derived zeolites. Here, the effect of steaming and the impact of impurities on waste‐derived zeolites were investigated. Steamed waste‐derived zeolite ZSM‐5 maintained their structure while their Brønsted acidity was decreased significantly due to dealumination. Electron paramagnetic resonance revealed that steaming of the samples resulted in the re‐dispersion of Fe impurities phases. The waste‐derived zeolites exhibited a high amount of weak and intermediate acidity upon steaming. Interestingly, the waste‐derived sample with a higher amount of impurities had an increase in Lewis acidity upon steaming, while catalytic testing in the Methanol‐to‐Hydrocarbons reaction exhibited 10 % higher conversion and 4 % in propylene yield. [ABSTRACT FROM AUTHOR]

Understanding the acid sites on zeolites is vital for the establishment of catalyst structure–activity relationship and exploration of their potential applications in heterogeneous catalysis. Here, we report the identification of active framework Lewis acid sites on ZSM‐5 zeolites. The structures of framework‐associated tri‐coordinated Al that is bonding with hydroxyl groups are determined by using one‐ dimensional (1D) 31P and two‐dimensional (2D) 31P‐{27Al} NMR spectroscopy of trimethylphosphine oxide probe molecule. 2D 13C‐{27Al} NMR correlation experiments allow the observation of favorable formation of methoxy species on the framework‐associated Al Lewis acid sites in methanol reaction at low temperature, which is corroborated by density functional theory calculations. These methoxy species contribute to the further conversion of methanol to hydrocarbons as active C1 species. The results provide new insights into the Lewis acidity of zeolites. [ABSTRACT FROM AUTHOR]

Levulinic acid (LA) is one of the top twelve chemicals listed by the US Department of Energy that can be derived from biomass. It serves as a building block and platform chemical for producing a variety of chemicals, fuels and materials which are currently produced in fossil based refineries. LA is a key strategic chemical, as fuel grade chemicals and plastic substitutes can be produced by its catalytic conversion. LA derivatisation to various product streams, such as alkyl levulinates via esterification, γ-valerolactone via hydrogenation and N-substituted pyrrolidones via reductive amination and many other transformations of commercial utility are possible owing to the two oxygen functionalities, namely, carbonyl and carboxyl groups, present within the same substrate. Various biomass feedstock, such as agricultural wastes, marine macroalgae, and fresh water microalgae were successfully converted to LA in high yields. Finding a substitute to mineral acid catalysts for the conversion of biomass to LA is a challenge. The use of an ultrasound technique facilitated the production of promising nano-solid acid catalysts including Ga salt of molybophosphoric acid and Ga deposited mordenite zeolite, with optimum amounts of Lewis and Bronsted acidities needed for the conversion of glucose to LA in high yields, being 56 and 59.9 wt.% respectively. Microwave irradiation technology was successfully utilized for the accelerated production of LA (53 wt.%) from glucose in a short duration of 6 min, making use of the unique synergistic catalytic activity of ZnBr2 and HCl. [ABSTRACT FROM AUTHOR]

In this work, the novel solid base Li/NaY was prepared via the solid state reaction between NaY zeolite and Li2CO3 at high temperature. When applied to the dimethyl carbonate (DMC) preparation through transesterification of ethylene carbonate (EC) and methanol, up to 89% yield of DMC with 99% selectivity can be accessed. The characterization results reveal the as‐synthesized Li/NaY possesses higher basicity than NaY. Furthermore, the Lewis acidity of the Li/NaY material is also enhanced due to the incorporation of lithium. Therefore, the Li/NaY can act as a dual functional catalyst in the transesterification reaction, thus leading to high efficiency. Notably, this catalyst can be easily recovered and reused for at least six times without obvious activity loss. This work provides a green synthetic route to DMC production and also sheds light on the development of solid basic catalysts. [ABSTRACT FROM AUTHOR]

Ultrafine nanosized ZSM-5 zeolite was synthesized by hydrothermal method promoted by hydroxyl radical at crystallization temperature of 90°C, and modified by the Ga isomorphous substitution. The effects of the introduction of active GaO+ species on the physicochemical properties and catalytic performance of the modified zeolites in the methanol-to-gasoline (MTG) process were also investigated. The results show that by the secondary synthesis method Ga atoms can be introduced into the nano-ZSM-5 zeolite's framework. The Brønsted acid strength of the prepared [xGa/Al]NZ5 series of zeolites is reduced and the acid content is increased. At the same time, active GaO+ species with strong Lewis acidity are formed, which improves the dehydrogenation activity of the catalysts in the MTG reaction and selectivity to gasoline. The [4Ga/Al]NZ5 catalyst exhibits excellent catalytic performance, the highest gasoline selectivity of 69.6 % at conversion of 96.1 % was obtained. The [xGa/Al]NZ5 is a promising efficient catalysts for the MTG reaction. [ABSTRACT FROM AUTHOR]

In refineries, one of the most important production units is Fluid Catalytic Cracking (FCC). In them, the incorporation of additives to the catalyst is a very interesting option to reduce the sulfur content of gasoline, and thus obtain commercial fuel specifications. In this study, the transformation of thiophene into a cyclohexane (HC) stream for its in-situ desulfurization has been investigated, using catalysts based on niobium or zinc (6 wt%) incorporated into three types of zeolites: HUSY, HBeta and HZSM-5. Catalytic tests were carried out at 773 K in an automatically controlled fixed-bed tubular reactor. The reaction products were analyzed online by gas chromatography, with FID detector for hydrocarbons and SCD for sulfur compounds, and the catalysts were characterized by XRD, FTIR, N 2 adsorption isotherms, HRTEM, XRF, 29Si and 27Al solid state NMR, NH 3 -TPD and FTIR-pyridine techniques. The results indicate that the addition of metals did not significantly alter the textural and structural properties of the zeolites, and that the Nb/HB and Nb/HY catalysts were the most effective in the conversion of thiophene, and selective toward paraffins and H 2 S mainly. The performance of these materials was attributed to the existence of an optimal balance between the Brønsted and Lewis acid sites, which increased the hydrogen transfer coefficient (HTC) during the cyclohexane transformation, resulting in higher desulfurization activity. The addition of zinc drastically increased the density of the Lewis acid sites and decreased the HTC, favoring the production of aromatics and thiophene condensation reactions, thus transferring sulfur to the gasoline streams. In general, the catalysts investigated are of significant interest as additives for sulfur reduction in FCC gasoline streams, either by producing easily removable H 2 S or by transferring sulfur to heavier fractions. [Display omitted] • The structural and textural properties of the zeolites were not deeply affected after incorporating the metals. • Catalysts with higher Lewis acidity (Zn-based catalyst) were more selective towards aromatics and condensed sulfur compounds. • The optimal ratio between the Brønsted and Lewis sites increases the hydrogen transfer and favors the desulfurization. • Zn-based catalysts transfer sulfur from gasoline to heavier fractions. • The Nb/HB and Nb/HY catalysts were more active in the conversion of thiophene to paraffins and H 2 S. [ABSTRACT FROM AUTHOR]

Tin-containing β zeolite exhibits excellent catalytic performance in various biomass conversions to high-value chemicals due to its strong Lewis (L) acidity produced by framework Sn4+ sites. However, it is difficult to incorporate Sn species into the framework of β zeolite due to that the ionic radius of Sn (0.69 Å) is larger than that of Si (0.40 Å). Herein, organic additives with carbonyl, hydroxyl, aldehyde or amine groups were used to stabilize Sn species in the gel and framework Sn4+ in the zeolite. Among all additives, acetone (AC) has the best stabilizing effect on Sn species. The stabilization effect between AC and Sn4+ sites was observed by FT-IR. The characterization results indicate that more tin species were incorporated into β framework and the L acid density increased due to the complexation between carbonyl group and Sn species. Compared to Sn-β-3d synthesized without additive, the L acid density of Sn-β-AC-3d increased by ∼50% (from 21 μmol g−1 to 34 μmol g−1). For the conversion of ethyl levulinate to γ-valerolactone, the reaction reached equilibrium faster over Sn-β-AC-3d than over Sn-β-3d at the investigated reaction temperatures. A yield of 98% was obtained over Sn-β-AC-3d at 110 °C. Besides, Sn-β-AC-3d exhibited good stability and reusability. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Ce/HZ5-HM and CeO 2 /HZ5-HM catalysts were prepared by hydrothermally modifying HZSM-5 zeolite with Ce3+ and CeO 2. • The n-heptane conversion and ethylene yield on Ce/HZ5-HM and CeO 2 /HZ5-HM increased by 6–11 % and 7–9 %, achieving E/P>1. • The Ce/HZ5-HM and CeO 2 /HZ5-HM catalysts perform a lifetime of 117 h and 150 h, with four-to-five times longer than others. • The acid strength, density, and B/L acid ratio enhanced by hydrothermal Ce3+/CeO 2 modification, healing the zeolite defects. Modulating zeolite acidity by conventional metal impregnation is a challenge in preparing hydrocarbon cracking catalyst, which often eliminates its intrinsic strong acidity, resulting in reduced the hydrocarbon conversion capacity and low light olefins (C 2 =-C 4 =) yield. Here, the Ce/HZ5-HM and CeO 2 /HZ5-HM catalysts were readily prepared by hydrothermally modifying HZSM-5 zeolite (HZ5) with cerium salts (Ce3+) and cerium oxide (CeO 2), respectively. Comparatively, Ce/HZ5-IW catalyst was obtained by modifying HZ5 with Ce3+ using the incipient wetness impregnation. It is revealed that, compared to HZ5, Ce/HZ5-HM and CeO 2 /HZ5-HM catalysts have an increased ratio of strong/weak (S/W) acid and Brønsted/Lewis (B/L) acid, while Ce/HZ5-IW sample has reduced strong acidity. Further, the Ce/HZ5-HM exhibits higher acid strength, acid density, and B/L value than that of CeO 2 /HZ5-HM sample. When applied to cracking n-heptane reaction, compared with HZ5 and Ce/HZ5-IW, heptane conversion and ethylene yield on Ce/HZ5-HM and CeO 2 /HZ5-HM catalysts increase by 6–11 % and 7–9 %, yielding the ratio of ethylene/propylene (E/P) more than 1. Moreover, Ce/HZ5-HM and CeO 2 /HZ5-HM catalysts perform a lifetime of 117 h and 150 h, with four-to-five times longer than that of HZ5 zeolite (∼29 h) and Ce/HZ5-IW catalyst (∼39 h). The characterization results demonstrate that, adopting hydrothermal method ensures more Ce3+ interacting with the silanol groups in Ce/HZ5-HM, generating the new Brønsted acid sites and makes CeOx species incorporating into the hydroxyl nest of zeolite, which can heal the defective sites and improve stabilization of acidity and framework structure of zeolite. Therefore, the above two catalysts can highlight the monomolecular cracking reaction, low coke deposit rate, long catalytic stability. [ABSTRACT FROM AUTHOR]

The transformations of carbohydrates into the platform substances such as furfural, hydroxymethylfurfural (5-HMF), lactic acid, etc. are actual environment-friendly processes. Herein, glucose transformation in an aqueous medium (10 wt.%) at 160 °C over synthesized nickel modified zeolites Y, M and ZSM-5 has been studied. The catalysts have been characterized by using FTIR spectroscopy, pyridine adsorption with IR-spectroscopic control, ammonia TPD, low-temperature nitrogen adsorption/desorption, and TEM. Utilizing HPLC, GC and 13C NMR the reaction products were identified. The 5-HMF molar yields over 5NiHY, 5NiHZSM-5, and 5NiHM were 8.5, 14, and 16%, respectively. Glucose conversion was practically quantitative. To investigate deactivated samples, FTIR and DTA/TG techniques have been used. The 5NiHM and 5NiHZSM-5 catalysts have showed a twice-lower weight of deposits (10 wt.%) than 5NiHY with the biggest total acidity. Bifunctional Lewis/Brønsted acid zeolite catalysts with Lewis acidity predominance demonstrate better performance in glucose transformation. The balance between acidity of the catalyst and textural properties is stated to play a key role in the transformation of glucose into 5-HMF. Nickel-containing zeolite ZSM-5 and M can be considered as promising catalysts for glucose conversion. Perspective trends in related research are provided. [ABSTRACT FROM AUTHOR]

Bifunctional catalysts on the basis of Ukrainian natural mordenite-clinoptilolite rocks modified by hydrochloric acid and by witness impregnation with nickel have been synthesized. Samples have been characterized by means of XRD, XRF, FTIR-spectroscopy, low temperature nitrogen adsorption/desorption, DTA/TG, TEM. Catalysts have been tested in micro pulse linear hexane isomerization. Hydrochloric acid treatment of natural zeolite rock leads to silica-to-alumina ratio increasing and raising the BET surface as well as the volumes of mesopores and micropores. The nickel nanoparticles deposited over zeolite crystals have a predominant size of 10 nm, but for some samples smaller ones of 5 nm and bigger ones of 20–50 nm have been found using TEM investigations. Pyridine sorption shows Brønsted and Lewis acidity of the catalysts, moreover the lower hydrochloric acid concentration using leads to practically equal Brønsted and Lewis acidity, the higher acid concentrations causes the Lewis acidity predominance. DTA/TG investigations show that water physically sorbed in the pores of the samples has been removed up to 200 °C from lager cavities of acid-treated catalysts and up to 500 °C from narrower cavities for untreated initial rock. Removing zeolite structure water up to 800 °C causes the dehydroxylation and Brønsted acidity transformation into Lewis acidity. The sample dealuminated by 1 mol dm−3 acid with nickel nanoparticles of 5–8 nm demonstrates the best performance in the isomerization of n-hexane. It is characterized by a 20% yield of hexane isomers at 250 °C and 70% selectivity. [ABSTRACT FROM AUTHOR]

DEDMS-silylation induced reduction of zeolite surface hydroxyl (z-OH) groups on USY affects the selective oxidation of benzyl alcohol to benzaldehyde over Au/USY-1 catalysts by altering adsorption effect. [Display omitted] • More Al-associated zeolite hydroxyl groups more strongly adsorb benzyl alcohols. • Stronger adsorption capacity boosted Au-catalyzed conversions of benzyl alcohol. • Diethoxydimethylsilane silylation reduced surface –OH in Al-O(H)-Si and Al-OH. • FT-IR and in-situ DRIFT results proved change in adsorption ability and acidity. Metal-zeolites catalysts are of great importance in selective organic conversions. Zeolites possess features of highly-ordered porous network, adjustable acidic properties (Brønsted/Lewis), spatial nanoconfinement effects, unique shape selectivity and the strong (hydrothermal-) stability. The role of zeolite hydroxyl (z-OH) groups, such as bridging ones in Si-O(H)-Al (B acids) and terminal ones in Al-OH and Si-OH (silanols), in catalysis is an interesting topic, particularly when they are not catalytic active sites, while they affect the catalytic performances. This study comprehensively investigated series of Au/USY catalysts in the selective oxidation of benzyl alcohol to benzaldehyde and clarified the dominating contributions of Al-associated z-OH groups to affecting catalytic conversions and selectivity via altering the Si/Al ratio and reducing z-OH groups by amorphous silica species derived from diethoxydimethylsilane under high-temperature calcination. The catalysts were characterized by XRD, BET, TEM, XPS, UV/Vis, FT-IR and in-situ DRIFT to investigate crystal structures, textural properties, morphologies, size distribution, chemical state of gold, acidity, and adsorptive properties. The experimental results proved that zeolites with a higher amount of z-OH groups tuned by Si/Al ratios or by diethoxydimethylsilane silylation exhibited higher catalytic activity because of the adsorption effect. Finally, a possible mechanism was discussed based on the experimental results and literature. [ABSTRACT FROM AUTHOR]

This study examines a selective removal of Al metal from Al-Beta (BEA), Al-Faujasite (FAU, type Y) and Al-Mordenite (MOR) whose frameworks have high and close Si/Al ratios ≥ 30. Dealumination was performed using acid leaching (nitric acid, 13 M) solution at 100 °C for 20 h. Unlike Al-BEA, Al-FAU and Al-MOR were hardly dealuminated for their ultra-stable structure. Solid-state incorporation (SSI) method was applied to incorporate Lewis acidic Sn metal in dealuminated zeolitic frameworks. Newly formed zeolites have numerous vacant tetrahedral sites with a siliceous-rich framework. These zeolites were characterized by powder XRD, elemental analysis, N2 sorption, DRIFT and 27Al MAS NMR spectroscopies. Meerwein–Ponndorf–Verley (MPV) was selected as a reaction to assess the catalytic performance of prepared zeolites. While SSI-Sn-BEA exhibited superior catalytic activity for the presence of Lewis acid-Sn, FAU and MOR showed less catalytic activity due to their confined structural effects, presence of silanol nest and inadequate Sn incorporation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new way to direct conversion of isobutyl alcohol to jet-range hydrocarbons. • We used dealuminization method to effectively adjust the pore structure and acidity of Beta zeolite. • The increased ratio of Lewis/Bronsted acidic sites was promoted the oligomerization reaction to form jet fuels. Various dealuminum methods of zeolite Beta to generate the jet fuels by converting isobutyl alcohol has been investigated in detail. And related factors of the zeolite catalyst such as acid site, pore structure, and pore size which can influence reactive activity, were also studied utilizing XRD, SEM, XRF, Nitrogen adsorption-desorption, NH 3 -TPD, Py-FTIR, and 27Al solid-state NMR. Removal of extra-framework aluminum or part of framework aluminum by hydrochloric acid dealumination, is able to improve the diffusion property of the products in the channel of zeolite Beta via increasing the ratio of Lewis/Brønsted. Consequently, isobutyl alcohol can be quantitatively oligomerized over dealuminated zeolite Beta with the selectivity of C 8−16 exceeding 50 % at a conversion of 98 %. Moreover, the deactivated catalyst can be easily regenerated by calcining it in flowing air. High conversion, high jet fuels selectivity, and facile regeneration make it an attractive potential catalyst for isobutyl alcohol oligomerization reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sn-Beta zeolite with Lewis acid sites is able to activate C-H bond. • Sn-Beta zeolite exhibits high performance in propane dehydrogenation. • Theoretical calculation suggest that the propane dehydrogenation occurs on the Lewis acid sites. The gap between supply and demand of propylene has become more and more evident, because of a large consumption of the downstream products derived from propylene. Propane dehydrogenation (PDH) constitutes an important alternative for the production of propylene, and thus considerable attention has been paid to the development of eco-friendly and cost-efficient catalysts for this process. Herein, we discover that the Sn-Beta zeolite with Lewis acid sites can activate the C-H bond, and exhibits high catalytic performance in the PDH. XRD, STEM, and XPS characterizations confirm that Sn species are incorporated into the zeolite framework, and H 2 -TPR suggests that there is a strong interaction between Sn species and zeolite framework. It is found that the Lewis acid is the active site for dehydrogenation reaction, and the Brønsted acid is responsible for cracking reaction. The dehydrogenation rate/cracking rate is positively proportional to the L/B ratio, and a high L/B ratio is beneficial for the propane dehydrogenation reaction. The Na-Sn-Beta-30 catalyst possessing the highest amount of Lewis acid but the lowest Brønsted/Lewis ratio, exhibits the best performance in the PDH, which delivers propane conversion of 40% and propylene selectivity of 92%. Most importantly, these Sn-Beta zeolites are extremely stable without any detectable deactivation under the harsh reaction condition for 72 h. Density functional theory calculations reveal that both Sn and adjacent O atom or OH group cooperatively act as the active sites. The PDH occurs through the direct reaction mechanism in which hydrogen molecule is produced by the direct coupling of H atom of primary C 3 H 7 motif with the Brønsted proton in closed sites or the proton of water in open sites. It seems that open sites are more reactive than the closed ones, and the intrinsic enthalpy barriers are calculated to be 242 ~ 301 kJ/mol depending on the hydroxylation extents. These efficient Sn-Beta zeolites could provide a new possibility for the development of a new generation of PDH catalysts with a high stability for the production of propylene. [ABSTRACT FROM AUTHOR]

A series of bifunctional platinum catalysts were prepared, supported on alumina or different zeolites, some of which were submitted to either desilication or dealumination in order to modify their acidic properties. The catalysts were characterized for their structural and textural properties, their acidic properties, including distribution of acid strength and Brønsted and Lewis acidity, their metallic properties, and used in the hydrocracking of polystyrene under kinetic control, where activity in end-of-chain scission and random scission of the polymer has been quantified as well as the distribution of products. Activation energies and pre-exponential factors have been calculated from the kinetic data, and analyzed in terms of compensation effect, in order to extract conclusions on activity, active centers and reaction pathways. Finally, activation energies, both of end-of-chain and random scissions, yield to gasoline fraction and percentage of aromatics in the gasoline fraction have been correlated with catalytic properties in order to extract conclusions on the major catalytic properties affecting catalytic performance in this process, from the point of view of catalytic design. [ABSTRACT FROM AUTHOR]

The reactions of acetone and hydroxyacetone over heteroatom doped BEA zeolites (Sn, Mo, and W) in the presence and absence of H2O vapor are investigated using infrared spectroscopy. Acetone is converted to mesityl oxide over Sn‐BEA exclusively. At higher temperatures, larger oxygenates such as phorones, aromatics, and coke form. The presence of co‐adsorbed water in Sn‐BEA suppresses tautomerization. H2O vapor is also beneficial for minimizing coke formation at high temperatures. Hydroxyacetone is converted into 2‐hydroxypropanal over Sn‐BEA, exhibiting high affinity to Sn sites up to 400 °C. Sn‐BEA catalyzes conversion of hydroxyacetone into the enol in the absence of H2O, but exposure to H2O induces the formation of 2‐hydroxypropanal and subsequent conversion to acrolein. The Lewis acid descriptors are used to rationalize the reaction pathways. For the isomerization of hydroxyacetone into 2‐hydroxypropanal, the hardness of acid sites influences the reaction and correlates with the overall Lewis acidity of the catalysts, respectively. However, the size of the exchanged metal significantly affects aldol condensation, where keto and enol forms of acetone adsorb to active sites simultaneously. [ABSTRACT FROM AUTHOR]

13X zeolite was hydrothermally synthesized and poly(vinylidene fluoride) (PVDF)/13X zeolite particles mixed matrix membranes were prepared using phase inversion method as the lithium‐ion battery separator. Hydrophilic and porous 13X zeolite loading impacts on the critical separator properties of morphology, wettability, electrolyte uptake, and high temperatures dimensional stability were investigated using scanning electron microscopy, contact angle, and thermal shrinkage analysis. Electrolyte uptake of the 13X zeolite particles loaded PVDF separators increased and also the incorporation facilitated the lithium ions migration (ion conductivity) due to the Lewis acidity of their structure. The 8 wt% 13X zeolite loaded separator (S2) revealed higher porosity (~+20%), electrolyte uptake (+80%), ion conductivity (+80%), and thermal shrinkage (~−47% at 165°C). C‐rate capability and cycle performance of a cell battery assembled using the S2 separator considerably improved compared with those of the assembled by the neat PVDF and commercial polypropylene separators. [ABSTRACT FROM AUTHOR]

• Brönsted acid attribute to the induction of hydroxyl groups by framework Sn • DHA dehydration by Brönsted acid is the rate-determining step. • HA isomerization by Lewis acid boosts the selectivity of ML. • Isotopic labeling technology verifies the proposed mechanism. To investigate the effects of the acid characteristic of Sn-MFI zeolite on catalytic performance in the transformation of dihydroxyacetone to methyl lactate, multiple characterization and experimental methods were employed. Firstly, the transformation between Lewis and Brönsted acid sites was initially confirmed by 31P-TMP NMR method, owing to the introduction of CH 3 OH by framework Sn species to donate protons. It is found that Lewis acid sites are cooperative with Brönsted acid sites to boost the primary reactions of dihydroxyacetone (DHA) to methyl lactate (ML). Yet, too high ratio of Brönsted acid sites to Lewis acid sites favors the generation of side product pyruvic aldehyde dimethyl acetal (PADA). That is because Brönsted acid sites majorly catalyze the dehydration of DHA, the addition of pyruvaldehyde (PA) with methanol and the addition of hemiacetal (HA) with methanol to PADA, whereas Lewis acidic framework Sn sites are responsible for the isomerization of HA to ML, which can be further verified by the isotopic labeling experiments. Therefore, this study provides a definite and systematical insight on the impacts of acid property on product selectivity. [ABSTRACT FROM AUTHOR]

Ga-modified zeolites represent the most effective catalyst for catalytic transformation of light alkanes to aromatics. GaO+ ions and GaOx clusters on Ga/ZSM-5 zeolites are probed by solid-state NMR. These two types of Ga species show strong Lewis acidity and are quantitatively correlated with the catalytic activity of Ga/ZSM-5 for methane C–H bond activation. The interaction between the surface Ga species and zeolite is characterized by using double-resonance solid-state NMR spectroscopy, which provides direct spectroscopic evidence for the location and distribution of active Ga species. These results provide new insight into the understanding of the nature and role of Ga species in Ga-modified zeolites for the conversion of light alkanes. [ABSTRACT FROM AUTHOR]

Here the effect of HZSM‐5 acid‐properties on the reacting‐pathways in the reaction system of toluene alkylation with methanol was studied detailedly, from the aspects of acidic type (Brönsted/Lewis), density, strength and location. A reasonable acid‐properties as following is an indispensable support to achieve a high methanol alkylation‐efficiency: not only the relatively high ratios of both Brönsted/Lewis and external/internal acid‐amount, but also both modest density and weak‐medium strength. Firstly, because alone Lewis acidity is almost inactive to aromatic alkylation, meaning Brönsted acid‐sites are indispensable. Secondly, an extremalization in either acidic density or strength is disadvantageous to aromatic alkylation, but encourages the conversion of methanol to olefins (MTO). Besides, the external acid‐sites in a relatively relaxed microenvironment are more favorable to catalyze aromatic‐alkylation than those inside channel where the strong diffusion/space restriction to aromatic‐molecules but foments MTO side‐reaction. Our work may provide a theoretical guidance for improving the methanol alkylation‐efficiency in this reaction system. [ABSTRACT FROM AUTHOR]

The chemoselective synthesis of 2‐(phenoxymethyl)oxirane from allyloxybenzene is achieved with over 90 % yield in a sustainable reaction system using titanium‐substituted silicalite‐1 (TS‐1) as a catalyst, hydrogen peroxide (H2O2) as an oxidant, and a mixture of MeOH/MeCN as a solvent at 40 °C. No acid‐catalyzed side reactions prompted by the Lewis acidity of the Ti active site in TS‐1 are observed. The TS‐1 catalyst can also promote the formation of oxiranes from various p‐substituted allyloxybenzenes in good yields. The reaction mechanism is investigated through the reaction with other allyloxy compounds. The results, which are supported by DFT calculations, indicate that an active species of Ti peroxides formed from the reaction of TS‐1 with H2O2 selectively oxidizes the allyloxybenzene to 2‐(phenoxymethyl)oxirane. [ABSTRACT FROM AUTHOR]

• MCM-56/49 zeolites were synthesized using Aerosil, Ultrasil and Ludox as silica sources. • MCM-56 synthesized with aniline showed enhanced availability of Brønsted acid centers. • Zeolites were tested in Friedel-Crafts alkylation of mesitylene with benzyl alcohol. • Catalytic activity depended on external Brønsted centers concentration. • Key role of IR spectroscopy in correlating physical characteristics with activity. Zeolite MCM-56 is a high alumina, monolayered form of the commercially useful framework MWW but it is a transient product during crystallization, so many factors influence its state and quality. This work examines properties of a series of MCM-56 and MCM-49 samples synthesized for different times using Aerosil, Ultrasil and Ludox as silica sources, hexamethyleneimine as the structure directing agent and additionally aniline as structure promoting agent. It was found that the most important parameter, governing the catalytic activity in the test reaction of Friedel-Crafts alkylation of mesitylene with benzyl alcohol, was availability of the Brønsted acid centers located at the external surfaces of the crystals. The key role in correlating physical characteristic with activity was played by infrared spectroscopy as it enabled the study of many properties of the tested materials, starting from the total concentration of acid centers, and their type (Brønsted or Lewis acids) through the concentration of centers available for the reagent molecules, to investigating the correlation of acidity with the degree of zeolite crystallinity. [ABSTRACT FROM AUTHOR]

• Tetrahydropyranylation in zeolites is catalyzed primarily by Brønsted acid sites. • Diffusion in microporous channels becomes rate-limiting for acid zeolites. • Activity of zeolite with Lewis acidity is due to defects or residual Brønsted sites. Tetrahydropyranylation (THP) has been extensively studied experimentally with both Brønsted and Lewis acid-based catalysts, such as zeolites, considered. However, our atomic-level understanding of the underlying mechanisms of different types of catalytic sites remains limited, particularly regarding zeolites. Thus, we combined an experimental catalytic study with density functional theory (DFT) calculations to identify the active sites and corresponding reaction mechanism in MFI zeolite. Both experimental and computational data clearly show that Brønsted acid sites are more reactive than Lewis acid sites. Furthermore, calculated reaction barriers for Brønsted acid site catalysis (5 kcal mol−1) are much lower than those for the diffusion of bulky products in microporous channels (approximately 20 kcal mol−1). In full agreement with theoretical calculations, the results of Madon-Boudart test clearly show that the effect of diffusion on the H-MFI catalysts performance cannot be neglected even at low temperature. Therefore, the diffusion becomes the rate-determining step. Overall, our findings suggest that designing zeolites with improved THP catalysis performance requires focusing on acid zeolites with Brønsted acid sites of average strength with facilitated diffusion, e.g., due to auxiliary mesoporous system. [ABSTRACT FROM AUTHOR]

First principles calculations are applied to find a pathway for methylation of benzene with methane into toluene and dihydrogen catalyzed by MFI type zeolite-supported Co species. On Co2+ at the α-position of MFI framework which is exposed to relatively large space, benzene is strongly adsorbed, while the adsorption on Co at the β-position is weak due to steric hindrance. Energy required for dissociation (activation) of methane was high, but the large energy evolved by adsorption of benzene on Co cancels the activation energy for the methane dissociation to suppress the energies of this step and following formation of toluene precursor. The activation energy of methane dissociation is sensitively changed by Al−Al distance also. Short distance results in difficulty of cleavage of Co–O bond, because Co is fully and strongly coordinated to basic oxygen atoms next to Al atoms, i.e., O in Al–O–Si. On the contrary, Co is partly coordinated to O in Si–O–Si with moderate Al−Al distance, and the cleavage of coordination bond is easy. Too long distance causes difficulty for hopping H+ to reach base site apart from the reaction field. At an appropriate Al−Al distance, the activation energies of the methane dissociation and toluene precursor formation are low. The latter is the rate-determining of benzene methylation with methane, and its energy, i.e., the apparent activation energy is in agreement with the experimental measurements. Experimentally, high activity at the α-position, strong dependence of activity on the framework Al content and the high activity at a moderate framework Al content were observed, supporting the theoretical conclusions. The driving force of benzene methylation with methane, a reaction between a pair of inactive reactants (methane and benzene), is thus clarified to be the strong adsorption of benzene. The origin of catalytic activity is therefore proposed to be strong electron withdrawing nature (Lewis acidity) of Co species held by the ion exchange site of zeolite. [Display omitted] • Unique mechanism in which adsorption of benzene on Co cancels the high energy for the methane dissociation. • Deep understanding on the influences of location of Co2+ and Al−Al distance showing the unique catalysis. • Agreement between the first principles calculations and experimental observations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Water presence favors formation of free extraframework aluminum (EFAl) species. • Neutral EFAl species deprotonate Brønsted acid sites under catalytic conditions. • Tetrahedral cations are the dominant EFAl form, particularly Al(OH) 2 (H2O)2+. • EFAl cations can behave as Brønsted acids and likely alter micropore shape selectivity. • Framework aluminum pairs modify EFAl character through hydrogen bonding. A systematic investigation of hydrated extraframework aluminum (EFAl) species interacting with Brønsted acid sites (BAS) in H-ZSM-5 is presented to understand the cooperative active site structure under catalytic operating conditions. Static models of EFAl species confined in the H-ZSM-5 unit cell show that isolated BAS protonate neutral EFAl species to form cations. Ab-initio molecular dynamics (AIMD) simulations and enhanced sampling performed at the temperature for methanol-to-hydrocarbon conversion reveal two regimes of stable EFAl species, namely the [Al(OH) 2 ]+ ion existing with two bonds to the zeolite scaffold or as a pore-guest in the form of [Al(OH) 2 (H 2 O) 2 ]+. Our results indicate that hydrogen-bonding plays a significant role in BAS-EFAl active site structure, especially at higher BAS density and that EFAl species can function as both Bronsted and Lewis acidic components to alter proton transfer kinetics as well as shape selectivity within these microporous solids. [ABSTRACT FROM AUTHOR]

Ab‐initio molecular dynamics simulations and transmission infrared spectroscopy are employed to characterize the structure of water networks in defect‐functionalized microporous zeolites. Thermodynamically stable phases of clustered water molecules are localized at some of the defects in zeolite Beta, which include catalytic sites such as framework Lewis acidic Sn atoms in closed and hydrolyzed‐open forms, as well as silanol nests. These water clusters compete with ideal gas‐like structures at low water densities and pore‐filling phases at higher water densities, with the equilibrium phase determined by the water chemical potential. The physical characteristics of these phases are determined by the defect identity, with the local binding and orientation of hydroxyl moieties around the defects playing a central role. The results suggest general principles for how the structure of polar solvents in microporous solid acids is influenced by local defect functionalization, and the thermodynamic stability of the condensed phases surrounding such sites, in turn, implies that the catalysis of Lewis acids will be influenced by local water ordering. [ABSTRACT FROM AUTHOR]

Metal‐exchanged zeolites are complex catalytic systems with great potential for applications in hydrocarbon conversion processes. The numerous combinations of zeotypes and metal‐based Lewis acid motifs create a vast material space that can only be effectively navigated with robust structure‐function relationships. Exhaustive modeling of extraframework metal sites in all crystallographically distinct framework positions is not practical; thus, we quantified the uncertainties arising from the use of simplified active site representations using the C−H bond activation in methane as a probe reaction. Density functional theory calculations and statistical analysis of associated error ensembles suggest that the Lewis acid identity primarily determines the reactivity of the zeolite towards methane activation, with other factors such as zeolite model characteristics deemed secondary. The error ensemble distributions were used to predict the relative probability of creating active C−H bond scission fragments in metal‐exchanged zeolites, and thus can be used to efficiently screen various metal‐exchange candidates in their efficacy towards hydrocarbon conversion. [ABSTRACT FROM AUTHOR]

• ZSM-5 organic template-free was successfully synthesized. • NH 4 -ZSM-5 zeolite was calcined by cold plasma and by conventional heating. • Cold plasma ZSM-5 activation lead to a partial dealumination. • Lewis and Brønsted acidity was improved in the case of ZSM-5 plasma-activated. • ZSM-5 plasma-activated performance in the methanol-to-DME reaction was enhanced. Dimethylether (DME) is nowadays considered as one of the most promising alternative fuels for the future. It has a very low climate impact, and can be produced in a renewable way, namely from the gas phase condensation of methanol over common acid catalysts such as γ-Al 2 O 3 or zeolites. The challenge today is to switch from high reaction temperatures (300–350 °C) to lower ones (ideally 100–150 °C) in order to operate more energy-efficiently and with 100% selectivity to DMEThe methanol conversion needs to be increased below 300 °C in order to get high yields of DME even in that low temperature range. In the present paper, we show a way to achieve this in the case of the widely studied ZSM-5 zeolite. We show that submitting the zeolite to a cold plasma treatment before using it as a catalyst allows significantly increasing the yield of DME up to 300 °C. Indeed, the plasma treatment leads to a partial dealumination of the zeolite and thereby to an increase of the number of strong Brønsted acid sites which play a key role in the methanol-to-DME reaction mechanism. [ABSTRACT FROM AUTHOR]

The role of Lewis and Brønsted acid sites and their potential synergy remains ambiguous for the production of polyoxymethylene dimethyl ethers (OME), which are suitable as a Diesel substitute. Here, this synergistic effect was investigated by using a series of beta polymorph A (BEA) zeolites with various degrees of Brønsted and Lewis acidity. Lewis acidity was introduced in dealuminated zeolites by Sn grafting in dichloromethane. These sites were only active in paraformaldehyde decomposition, OME growth, and acetalization. The Brønsted acid sites arising from bridging hydroxyl groups were active for all reaction steps, and notably for trioxane ring‐opening and dissociation to formaldehyde (FA), which did not occur on the Lewis acid sites. Presence of both Lewis and Brønsted acid sites led to a four‐fold increase in turnover frequency and a significant decrease of byproduct formation compared with the parent zeolite during OME synthesis from dimethoxymethane and trioxane. The synergistic effect between both types of acid sites is explained by FA insertion on Lewis acid sites leading to OME growth. Interaction between tetrahedral Sn and the carbonyl group of FA resulted in an activated carbonyl bond, which was likely the initial step for insertion of FA into OME. [ABSTRACT FROM AUTHOR]

The conversion of the alkali‐treated intergrowth germanosilicate CIT‐13 into the single‐crystalline high‐silica ECNU‐21 (named after East China Normal University) zeolite, with a novel topology and a highly crystalline zeolite framework, has been realized through a creative top‐down strategy involving a mild alkaline‐induced multistep process consisting of structural degradation and reconstruction. Instead of acid treatment, hydrolysis in aqueous ammonia solution not only readily cleaved the chemically weak Ge(Si)−O−Ge bonds located within the interlayer double four ring (D4R) units of CIT‐13, but also cleaved the metastable Si−O−Si bonds therein. This led to extensive removal of the D4R units, and also generated silanol groups on adjacent silica‐rich layers, which then condensed to form a novel daughter structure upon calcination. Individual oxygen bridges in the reassembled ECNU‐21 replaced the germanium‐rich D4R units in CIT‐13, thereby eliminating the original intergrowth phenomenon along the b axis. With an ordered crystalline structure of 10‐ring (R) channels as well as suitable germanium‐related Lewis acid sites, ECNU‐21 serves as a stable solid Lewis acid catalyst for the shape‐selective hydration of ethylene oxide (EO) to ethylene glycol (EG) at greatly reduced H2O/EO ratios and reaction temperature in comparison with the noncatalytic industrial process. Zeolite transformations: The structural conversion from polymorph germanosilicate CIT‐13 to the novel ECNU‐21 zeolite has been achieved for the first time by an alkali treatment strategy (see figure). With a moderate Lewis acidity, ECNU‐21 serves as a promising shape‐selective catalyst for the hydration of ethylene oxide, with a conversion of more than 97 % and selectivity towards ethylene glycol of around 96 %. [ABSTRACT FROM AUTHOR]

Zr-β zeolites were modified with second metals to catalyze the conversion of ethanol/acetaldehyde to 1,3-butadiene. The incorporation of Ta increases the Lewis acidity of Zr-β zeolite, resulting in higher catalytic activity than that of In, Y and Ce. Furthermore, the Zr-β zeolite that was first incorporated with Zr and then Ta with a Ta/Zr molar ratio of 1.5 exhibited greater catalytic activity of 57% conversion and 75% selectivity. Activity descriptors were proposed to calculate the reactivity of key reaction steps, which served as evidence that Ta incorporation enhances the aldol condensation and MPV reduction reaction activity, thus improving catalytic performance. [Display omitted] • The metals Zr and Ta were sequentially incorporated into the framework of β zeolite. • The second metal Ta was incorporated into the Zr-β zeolite to establish new Lewis acid sites. • The strengthening Lewis acidity is contributed to enhancing the activity of aldol condensation and MPV reduction. • A mathematical descriptor was defined to analyze the reactivity of aldol condensation and MPV reduction. [ABSTRACT FROM AUTHOR]

The zeolite community spent 50 years in pursuing the synthesis of high-silica LTA -type zeolites, and ultimately succeeded with the pure-silica polymorph by applying specific structure-directing agents (SDA). The high-silica zeolite A has exhibited unique properties and strong potential to be applied as an adsorbent and catalyst in several novel processes. In the present study, the high-silica polymorphs of Si/Al ratios from 15 to ∞ were synthesized and subjected to thorough characterizations using multiple physicochemical methods. It has been revealed that there exists strong interactions between the organic SDAs and the framework. Therefore, removing the SDAs by calcination in air is difficult, and can only be done above 700 °C with a certain degree of framework dealumination. The retained framework structure shows connectivity defects and a unique combination of Brønsted and Lewis acidity. Using methanol-to-olefins (MTO) as a probe reaction, the catalytic performance of high-silica LTA -type zeolites has been evaluated. Compared to the well-studied CHA and MFI -type catalysts, high-silica zeolite A exhibited a shorter life-time and higher selectivity towards C 4 olefins, while methane selectivity increased with the deactivation. [Display omitted] • The crystallization of high-silica LTA -type zeolites requires specific structure-directing agents (SDAs). • Strong SDA/framework interactions are evidenced by XRD, NMR and TG. • Complete removal of SDA by calcination accompanied by framework dealumination, while the framework structure retained. • High-silica LTA-type material possesses unique acidity that renders different catalytic performances in MTO reactions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Unit cell expansion is caused by the incorporation of Sn atoms. • Sn atoms are highly dispersed in the lattice of zeolite particles. • Lewis acidity attributes to the charge difference between framework Sn and Si atoms. • The catalytic performance of Sn-MFI is dependent on the Lewis acid property. Abstract Sn-MFI zeolite is one kind of remarkable emerging solid Lewis acid catalyst with high stability in recent years, due to its wide application in the environmental-friendly biomass conversion and catalytic oxidation processes. Herein, it is confirmed that the Sn species are highly dispersed in the matrix of zeolite, and the expansion of unit cell is attributed to the formation of crystalline Sn O Si bonds, owing to the size difference between Si and Sn atoms. Due to the charge difference, Sn-MFI zeolites possess much more Lewis acid sites than Silicalite-1 and SnO 2 /Silicalite-1, and the catalytic property is closely related to the amount of Lewis acid sites. Consequently, it is reasonable to infer that the Sn atoms are inserted into the framework of Sn-MFI zeolite, in tetrahedral coordination, which acts as the active sites in Lewis acid catalyzed reactions. [ABSTRACT FROM AUTHOR]

Abstract: For several decades, it has been known that ozone emissions are harmful to humans, plants, and animals. Heterogeneous catalytic decomposition is an efficient process for removing ozone from air. This study examines the effect of the zeolite's framework and pore width on efficiency for decomposing gaseous ozone. Four highly hydrophobic zeolites are used: a large cavity zeolite (Faujasite/H‐FAU), a medium pore zeolite with parallel channel (Mordenite/H‐MOR), and two medium pore zeolites with interconnected channels (H‐ZSM‐5/H‐MFI and Na‐ZSM‐5/Na‐MFI). Experiments were conducted in fixed‐bed flow reactors loaded with zeolite at ambient conditions (20 °C and 101 kPa). Zeolite surfaces were analyzed during the experiments in order to understand the influence of physical and chemical surface properties on the ozone decomposition mechanism. A higher amount of ozone is eliminated using H‐MOR, compared with the zeolite samples H‐FAU, H‐MFI, and Na‐MFI. Pore width and micropore framework size distribution (channel and cages) appear to be key factors. A narrow channel or cage, slightly larger than the ozone molecule size, seems to promote ozone interactions with Lewis acid sites. Fourier transform infrared spectroscopy shows that Lewis acid sites (LAS), located on the walls of zeolite pores, decompose ozone. This leads to the formation of atomic oxygen species that could react with another ozone molecule to form dioxygen. Hence, LAS are regenerated, ready to decompose another ozone molecule once more. [ABSTRACT FROM AUTHOR]

Group 4 (Ti and Zr) and 5 (Nb and Ta) atoms substituted into the * BEA zeolite framework (M-BEA) irreversibly activate hydrogen peroxide (H 2 O 2 ) and form pools of metal-hydroperoxide (M-OOH) and peroxide (M-(η 2 -O 2 )) intermediates active for the oxidation of 2,5-dimethylthiophene (C 6 H 8 S), a model reactant representative of organosulfur species in fossil reserves and chemical weapons. Sequential oxidation pathways convert C 6 H 8 S into 2,5-dimethylthiophene oxide (C 6 H 8 SO) and subsequently into 2,5-dimethylthiophene dioxide by oxidative dearomatization. Oxidation rates measured as functions of reactant concentrations together with in situ UV–vis spectra show that all M-BEA activate H 2 O 2 to form pools of M-OOH and M-(η 2 -O 2 ), which then react with either C 6 H 8 S or H 2 O 2 to form the sulfoxide or to decompose into H 2 O and O 2 , respectively. Turnover rates for C 6 H 8 S oxidation and H 2 O 2 decomposition both increase exponentially with the electron affinity of the active site, which is quantitatively probed via the adsorption enthalpy for deuterated acetonitrile to active sites. C 6 H 8 S oxidation rates depend also on the nucleophilicity of the solvent used, and rates decrease in the order acetonitrile >  p- dioxane ∼ acetone > ethanol ∼ methanol. In situ UV–vis spectra show that highly nucleophilic solvent molecules compete effectively for active sites, inhibit H 2 O 2 activation and formation of reactive M-OOH and M-(η 2 -O 2 ) species, and give lower turnover rates. Consequently, this work shows that turnover rates for sulfoxidation are highest when highly electrophilic active sites (i.e., stronger Lewis acids) are paired with weakly nucleophilic solvents, which can guide the design of increasingly productive catalytic systems for sulfide oxidation. [ABSTRACT FROM AUTHOR]

Developing highly active catalysts for bio-oil hydrodeoxygenation is of great importance in the low cost production of conventional transport alkane fuels. Toward this goal, a Ni catalyst supported on mesoporous ZSM-5 zeolite mixed with 25 wt% γ-AlO (Ni/Al-HMZSM-5) was designed for hydrodeoxygenation of phenol as model compound. For comparison, the catalytic activities of Ni catalysts on conventional microporous ZSM-5, mesoporous ZSM-5 and γ-AlO were also investigated. It was found that almost complete phenol conversion (99.6%) was achieved over the Ni/Al-HMZSM-5 catalyst along with a high cyclohexane selectivity (98.3%) under a relatively mild condition (170 °C, 4 MPa H). The open mesopores, stronger acid sites and synergism effect of Brønsted and Lewis acidities are jointly responsible for the excellent hydrodeoxygenation performance. In addition, it was shown that the catalyst was recycled several times with little loss of activity and selectivity. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The synthesis and characterization of tin, tin/aluminum, and tin/boron containing MFI zeolites are reported. It is shown that tin uptake is high (near 100%) but decreases with the introduction of a second heteroatom. Additionally, the zeolite crystal size decreases and morphology changes with the introduction of a second heteroatom as evidenced by FE-SEM and XRD. UV-Vis confirms the tetrahedral framework coordination of tin within the zeolite and the absence of tin oxide clusters. Studies of methanol adsorption using in-situ IR spectroscopy indicate that tin-MFI sample with low tin contents possess lower acidity, and that tin/aluminum samples confirm aluminum within the zeolite through the presence of a Brönsted acid site. Comparison of spectra of adsorbed d-acetonitrile on the surface of these catalysts with the silicalite-1 is consistent with the tin centers in the framework possessing Lewis acidity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nickel loaded on ZSM-5 exhibited higher catalytic performance than H-ZSM-5 zeolite in toluene disproportionation. • The Ni/ZSM-5 with Ni/Al = 0.6 showed high toluene conversion and lower benzene/xylene ratio closer to the stoichiometry. • The high catalytic performance for Ni-0.6 was supposed to be ascribed to the synergy effect of Brønsted acid sites and Lewis acid sites. Impregnation of various heteroelements on the ZSM-5 zeolite was applied to improvement of the catalytic activity in toluene disproportionation. Nickel loaded on ZSM-5 (Ni/ZSM-5) exhibited higher catalytic activity (toluene conversion) and lower benzene/xylene ratio (closer to the stoichiometry, meaning low rate of side reaction) than H-ZSM-5 zeolite. The Ni/ZSM-5 with Ni/Al = 0.6 showed the maximum in catalytic activity, and excess Ni loading caused decrease in the conversion and increase in the benzene/xylene ratio due to decrease of acid amount and acceleration of dealkylation, respectively. The detailed analysis of acidic property by means of ammonia IRMS-TPD method showed that the Ni loading generated Lewis acid sites on the zeolite. The synergy of Brønsted and Lewis acid sites, ascribed to Si-OH-Al and Ni species, respectively, is suggested to give the high activity of desired reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • A three-step process is computationally analysed for the tautomerization of phenol and catechol. • External Lewis acids of zeolite MFI effectively catalyse the tautomerization of phenol and catechol. • The calculated activation energies are smaller than 55 kJ/mol at 473 K. • The tautomerization of catechol is selective towards cyclohexa-2,4-dien-2-hydroxy-1-one. Because the structure of lignin consists mostly of inter-linked phenolic monomers, its conversion into more valuable chemicals may benefit from isomerization processes that alter the electronic structure of the aromatic rings. The tautomerization of phenolic-type compounds changes the hybridization from sp 2 to sp 3 of the carbon atom at the ortho position, which disables the aromaticity and facilitates the subsequent hydrogenation process. Here, we have performed a Density Functional Theory study of the tautomerization of phenol and catechol at the external surface of zeolite MFI. The tautomerization starts with the adsorption of the molecule on three-coordinated Lewis acid sites, followed by the dissociation of the phenolic hydroxyl group, with the transfer of the proton to the zeolite framework. The rotation of the deprotonated molecule enables a more favourable orientation for the back-transfer of the proton to the carbon atom at the ortho position. The energy barriers of the process are smaller than 55 kJ/mol, suggesting that this transformation is easily accessible under standard reaction conditions. [ABSTRACT FROM AUTHOR]

Acid catalysts including Ni, Ag and Fe-loaded zeolites of different structures were prepared either via cationic exchange or impregnation techniques from pristine H-zeolites (BEA, and MFI). Their catalytic activity was evaluated in the liquid-phase Friedel–Crafts acylation of anisole with propanoic acid. It turned out that, whatever the doping procedure was, the zeolite loaded with transition metals led to considerable decrease in propanoic acid conversion, regardless of the nature or the metal content. However, the extent of this detrimental effect followed the order: Ag + > Ni 2+ > Fe 3+ . Pristine acidic zeolites were not only found to be the most active, but also to be the most selective toward ortho - and para -acylation products. H-ZSM-5 zeolites yielded the highest intrinsic activity, with TOF values of 0.09 h −1 . The catalyst activity proved to be essentially attributed to the density and accessibility of Brønsted acid sites, playing a key role in the activation of the reactants. Brønsted sites are proposed to be the most likely catalytic species for performing this Friedel–Crafts acylation. [ABSTRACT FROM AUTHOR]