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This study reports the seeded synthesis of MFI‐type (ZSM‐5) zeolite in fluoride medium at pH = 8.5. Crystal growth kinetics of the resulting zeolite (ZSM‐5‐F) as a function of seed content and crystallization temperature is studied. The crystallization time is reduced to 1.5 h and crystals with sizes below 200 nm and a Si/Al ratio of 23.6 are obtained. A zeolite with similar characteristics but synthesized in a hydroxyl medium (ZSM‐5‐OH) is used to evaluate ZSM‐5s synthesized in different crystallization media. Their physicochemical properties are compared and particular attention is paid to the nature, number, and distribution of silanol sites. The two zeolites exhibit similar number of Brφnsted acid sites; however the material synthesized in a hydroxyl medium contains a substantially larger number of surface and internal silanols that impact significantly its catalytic performance in methanol to hydrocarbon transformation. While the two materials exhibit similar selectivity in methanol transformations, the catalyst synthesized in fluoride medium shows superior activity and resistance to deactivation. The results suggest that seeded synthesis in a fluoride medium can be used for the preparation of superior zeolite catalysts. [ABSTRACT FROM AUTHOR]

Chemical interactions occurring between zeolites and alumina binders during the critical steps of catalyst forming are the focus of this study. Three widely used and commercially significant variants of FAU zeolite, covering a wide range of Si/Al ratios, micro- and meso-porosity and acidic properties (Y [LZY-64, Si/Al = 2.3] and USY [CBV 720 and CBV 760 with Si/Al = 16 and Si/Al = 28, respectively]) were shaped by extrusion with pseudoboehmite to produce bound extrudates. These extrudates were characterized by conventional techniques (XRD, 27Al NMR and IR spectroscopy, N 2 physisorption ...) and compared to their parent powders activated under the same conditions. The catalytic performances of the zeolite powders, their derived alumina extrudates and physical zeolite/γ-Al 2 O 3 mixtures were also evaluated employing two different reactions: i) n-octane hydroisomerization, to probe all catalytic sites and ii) 1,3,5 tri-isopropyl benzene dealkylation to probe only the external/mesoporous surfaces. The bound zeolites systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. Infrared spectroscopy measurements of the number, nature and strength of the acid sites were consistent with these catalytic results demonstrating that new catalytic sites are created and located on the external or mesoporous surface of the zeolites, i.e. at the zeolite-binder interface. The work reported here clearly illustrates that binding and subsequent thermal treatment of zeolite powders to produce commercially representative forms can significantly alter the quality and quantity of active sites creating active centers not usually present in pure powders which are typically studied and reported in much of the open literature. Such a study is also a blueprint for other catalytic phases, other forming processes (spray-drying, oil-dropping, pelletizing ...) and could also be applied to the shaping of adsorbents. Image 1 • Zeolite Y were shaped by extrusion using pseudoboehmite as binder. • Acidic properties of zeolite extrudates were probed using basic probe molecule and monitored by infrared. • Zeolite shaping alter qualitatively and quantitatively the acidic properties of the final compounds. • Zeolite Y extrudates systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. • New acid sites are formed during shaping, reminiscent of amorphous silica-alumina. [ABSTRACT FROM AUTHOR]

A series of ZSM-5 zeolites (embryonic, microporous, hierarchical) is studied in the catalytic cracking of polypropylene in the framework of its chemical recycling. Two important zeolite features impact their catalytic performances and allow their design as efficient catalysts: porosity and acidity. They also play a key role in catalyst deactivation and regeneration. A detailed thermogravimetric and spectroscopic (operando FT-IR) analysis of the reaction, including catalyst coking and regeneration, shows the emergence of rules to design fit-for-purpose catalysts to be used in existing or grass-roots FCC units. [Display omitted] • Operando FT-IR-GC-MS study highlights the relative role of the micro- & mesoporous surfaces. • Complementary roles in PP cracking: porosity and acid site strength related to confinement. • Reversible embryonic zeolites deactivation makes PP recycling to fuel or petrochemicals. • The rules to design fit-for-purpose catalysts to be used in existing or grass-roots FCC units. [ABSTRACT FROM AUTHOR]

Zeolites are widely used in industrial processes, mostly as catalysts or adsorbents. Increasing their micropore volume could further improve their already exceptional catalytic and separation performances. We report a tunable extraction of zeolite framework cations (Si, Al) on a faujasite-type zeolite, the archetype of molecular sieves with cages and the most widely used as a catalyst and sorbent; this results in ca. 10% higher micropore volume with limited impact on its thermal stability. This increased micropore volume results from the opening of some of the small (sodalite) cages, otherwise inaccessible to most molecules. As more active sites become accessible, the catalytic performances for these modified zeolites are substantially improved. The method, based on etching with NH4F, is also applicable to other cage-containing microporous molecular sieves, where some of the most industrially relevant zeolites are found. [ABSTRACT FROM AUTHOR]

Natural gas will play a significant role in the transition from fossil to green(er) energy production. Its major component, methane (CH 4) is an attractive resource to co-generate hydrogen (H 2) and added value chemicals (important building blocks such as olefins and aromatics) for petrochemistry. We highlight the advantage of using a novel dual catalyst system containing a monofunctional Al-free metallic single site catalyst referred as S-Mo (Si/Al ∼ ∝) where Mo is atomically dispersed in the zeolitic framework and a monofunctional acidic H-ZSM-5 catalyst referred as S-Al (SiAl = 128) to achieve superior yields of high value products. Under severe reaction (850 ºC) and regeneration (700 ºC) conditions, the Mo-S catalyst is stable and does not suffer from irreversible structural damage by losing its Mo atomic dispersion, and deactivation by coke deposition, thus ensuring steady catalytic performances in multi-cycle catalytic tests. Conversely, the current bifunctional catalysts prepared by Mo impregnation on an acidic catalyst suffer from irreversible damage during coke combustion due to the formation of Al₂(MoO₄)₃ or AlMoO 6 Anderson entities. This new approach opens novel and promising pathways to develop methane upgrading processes based on the physical separation and operation of a non-deactivating metallic catalyst and a regenerable acidic catalyst. [Display omitted] • Catalytic systems involving single site Mo-MFI lead to a stable methane conversion and hydrocarbons production. • Best MDA performances are obtained with a dual bed configuration of two monofunctional single sites Mo-MFI and HZSM-5 catalysts. • The single site Mo-MFI in dual bed configuration displays no coke formation and a high thermal and hydrothermal stability. • Dual bed configuration allows managing separately the reactional temperature of both layers to find the best balance between activity and coke formation. [ABSTRACT FROM AUTHOR]

Abstract: Ring-opening reactions of decalin and methylcyclohexane (MCH) over bifunctional catalysts (1.2Ir/WO3/Al2O3) were investigated. A series of catalysts containing up to 5.3at. W/nm2 and 1.2wt.% Ir was prepared. The acidity of the solids was monitored by low-temperature CO adsorption followed by infrared spectroscopy. Characterization of the Ir metal phase was performed by H2 chemisorption and X-ray diffraction. The activity and product selectivity patterns obtained for the decalin ring-opening reaction were compared with those observed for MCH. For both naphthenes, ring contraction precedes ring opening, suggesting a similar ring-opening mechanism. Kinetic modeling based on the proposed reaction network allowed the determination of the activation energies and initial rates. Based on the yields and products distribution obtained for the decalin reaction, the potential for improvement of the cetane number is discussed. [Copyright &y& Elsevier]

An accessibility index (ACI) was derived from infrared spectroscopy of substituted alkylpyridines with different size (pyridine: 0.57nm, 2,6-lutidine: 0.67nm, and 2,4,6-collidine: 0.74nm) over hierarchical porous ZSM-5 crystals. The samples were prepared by selective silicon extraction of a commercial sample in NaOH (desilication), and they contained different degrees of intracrystalline mesoporosity. Our results demonstrate the enhanced accessibility of Brønsted acid sites in the hierarchical zeolites. For example, a relatively bulky molecule such as collidine, which probes practically no acid site of the parent medium-pore MFI structure, can access up to 40% of the acid sites in the mesoporous sample. The ACI is a powerful tool to standardize acid site accessibility in zeolites, and can be used to rank the effectiveness of synthetic strategies to prepare hierarchical zeolites. [Copyright &y& Elsevier]

• The use of FER as catalyst for the dehydration of iso-butanol results in an excellent selectivity for n-butenes. • The external Brønsted acid sites function as isobutanol dehydration active sites. • High external Brønsted acidity improves selectivity to n-butenes. • Use of in-situ and operando characterisation toolboxes allowed identifying the active sites. The conversion of isobutanol to light olefins over zeolites was investigated by IR operando spectroscopy. FER zeolites showed a surprisingly high selectivity for the direct conversion of iso-butanol to linear butenes, hence catalyzing dehydration and skeletal isomerization in one step. As a fundamental understanding of the separate reactions is required to design superior catalysts, an in-situ and operando FT-IR mechanistic study of the reaction was carried out. The spectroscopic data, the derived species participating and their respective role are analyzed using chemometric (PCA and MCR-ALS) tools. We highlighted the role played by the external acid sites and the requirement of a specific distance between these sites to ensure the n-butene selectivity and point that the internal Brønsted acidity has an adverse effect on the catalyst stability. Moreover, there is no correlation between the carbon species formed on the surface and the exceptional selectivity towards n-butenes, allowing to exclude a "carbon pool" mechanism. [ABSTRACT FROM AUTHOR]