Polypropylene cracking on embryonic and ZSM-5 catalysts : an operando study

International audienceA 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

Tuning zeolite properties for highly efficient synthesis of propylene from methanol

Series of nanosized ZSM-5 samples is synthesized at 170 °C, 150 °C, 120 °C and 100 °C. Experimental data show that the decrease of crystallization temperature leads to significant changes in zeolite properties. Crystals synthesized at 100 °C exhibit many framework defects with lower acid sites density, strength and larger external surface area. The selectivity to light olefins and the propylene-to-ethylene ratio increases as the crystallization temperature decreases. Propylene-to-ethylene ratio above 6 with the highest selectivity to propylene of 53 % is obtained over ZSM-5 catalyst prepared at 100 °C. Stability of the nanosized zeolite in MTO is also improved compared to industrial sample with similar Si/Al ratio. This catalytic performance is a result of the decrease in the acid sites density, strength and the crystals’ size, providing shorter diffusion path and larger external surface area. The presence of structural defects and different external surface are of the crystals has been shown to play an important role in the MTO catalyst performance

Formation mechanism of three member 1 ring containing 2 microporous zincosilicate rub-17

The crystallization process of RUB-17 (RSN-type), a zeolite-type zincosilicate, was studied in order to shed light on the zeolite crystallization mechanism. The sequence of crystallization events from the formation of the initial gel to the complete transformation into a zeolite-type material was investigated. Complementary methods, including XRD, TG/dTG, Raman, 29Si MAS NMR, SEM, that allowed studying both short and long-range order in the solids were used. RSN-type structure contains 3-, 4-, 5- and 6-member rings (MRs) that allowed following the formation of different building units in the course of zeolite formation. The set of experimental data revealed that the three-member ring (3MR) was the unit preferentially formed during the induction period. At this stage of gel evolution the presence of larger rings was not detected. The latter were observed only after the appearance of long-range order in the solid proved by X-ray diffraction analysis. Hence the formation of RSN-type structure was related with the large 3MRs population during the induction stage

Time-resolved dissolution elucidates the mechanism of zeolite MFI crystallization

Zeolite crystal growth mechanisms are not fully elucidated owing to their complexity wherein the formation of a particular zeolite can occur by more than one crystallization pathway. Here, we have conducted time-resolved dissolution experiments of MFI-type zeolite crystals in ammonium fluoride medium where detailed structural analysis allowed us to extrapolate and elucidate the possible mechanism of nucleation and crystal growth. A combination of electron and scanning probe microscopy shows that dissolution initiates preferentially at lattice defects and progressively removes defect zones to reveal a mosaic structure of crystalline domains within each zeolite crystal. This mosaic architecture evolves during the growth process, reflecting the changing conditions of zeolite formation that can be retroactively assessed during zeolite crystal dissolution. Moreover, a more general implication of this study is the establishment that dissolution can be used successfully as an ex situ technique to uncover details about crystal growth features inaccessible by other methods

A 3D Organically Synthesised Porous Carbon Material for Lithium Ion Batteries

We report the first organically synthesized sp–sp3 hybridized porous carbon, OSPC‐1. This new carbon shows electron conductivity, high porosity, the highest uptake of lithium ions of any carbon material to‐date, and the ability to inhibit dangerous lithium dendrite formation. The new carbon exhibits exceptional potential as anode material for lithium‐ion batteries (LIBs) with high capacity, excellent rate capability, long cycle life, and potential for improved safety performance

Acidic medium zeolite synthesis – an avenue to new materials

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Silicalite-1 Hollow Spheres and Bodies with a Regular System of Macrocavities

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Control of the morphology of zeolite crystals

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Core−Shell Polystyrene/Zeolite A Microbeads

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Preparation of regular macroporous structures built of intergrown silicalite-1 nanocrystals

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