Hierarchical ZSM-5 zeolites synthesized by silanization of protozeolitic units: Mediating the mesoporosity contribution by changing the organosilane type

Lignin as a Bio-Sourced Secondary Template for ZSM-5 Zeolite Synthesis

The aim of this study was to investigate the effect of the addition of lignin as a sacrificial agent in ZSM-5 zeolite synthesis. Peculiar growths of ZSM-5 crystals leading to various textural properties were observed. Hence, the behavior in acid-catalyzed conversion of methanol into hydrocarbons (MTH) shifted from high selectivity toward olefins (>55%) to the sole formation of dimethyl ether (DME). Lignin acted as a bio-sourced secondary template (BSST), impacting the zeolite crystals’ shape and, thus, their physicochemical properties.

Hierarchical HZSM-5 for Catalytic Cracking of Oleic Acid to Biofuels

Solid acid catalyzed cracking of waste oil-derived fatty acids is an attractive route to hydrocarbon fuels. HZSM-5 is an effective acid catalyst for fatty acid cracking; however, its microporous nature is susceptible to rapid deactivation by coking. We report the synthesis and application of hierarchical HZSM-5 (h-HZSM-5) in which silanization of pre-crystallized zeolite seeds is employed to introduce mesoporosity during the aggregation of growing crystallites. The resulting h-HZSM-5 comprises a disordered array of fused 10–20 nm crystallites and mesopores with a mean diameter of 13 nm, which maintain the high surface area and acidity of a conventional HZSM-5. Mesopores increase the yield of diesel range hydrocarbons obtained from oleic acid deoxygenation from ~20% to 65%, attributed to improved acid site accessibility within the hierarchical network.

Pyrolysis characteristics, kinetics, and evolved gas determination of chrome-tanned sludge by thermogravimetry-Fourier-transform infrared spectroscopy and pyrolysis gas chromatography-mass spectrometry

The pyrolysis characteristics, kinetics, and evolved gas analysis of chrome-tanned sludge were investigated by thermogravimetry (TG) with Fourier-transform infrared spectroscopy (TG-FTIR) and pyrolysis with gas chromatography and mass spectrometric detection (Py-GC/MS). Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) methods were used to calculate kinetic parameters in the kinetic study. The chrome-tanned sludge contained 7600 mg kg^-1 Cr in the form of CrOOH and 41,400 mg kg^-1 S in the form of S₈. The activation energy derived by Friedman method increased from 139.83 to 590.72 kJ mol^-1 as the temperature increased from 50 to 500 °C, much higher than those of lignocellulosic biomass and sewage sludge. The TG-FTIR results showed that the main component of the pyrolysis gases was organics that contained alkane groups, and this component reached a maximum at ∼500 °C. The Py-GC/MS results indicated that the diesel-range organics (C10-C28) accounted for more than 65% of the evolved gases; 20%-31% of the evolved gases were C16 and C18, and included mainly palmitic, stearic, and oleic acids. The evolved gases contained high contents of sulfur and nitrogen compounds, mainly in the forms of elemental sulfur (S₆ and S₈) and nitriles, respectively. Kinetics and evolved gases determining provide a better understanding of tanned sludge pyrolysis and references for pyrolysis reactor design and scale-up.

Conversion of Stearic Acid into Bio-Gasoline over Pd/ZSM-5 Catalysts with Enhanced Accessibility

Palladium supported on nanocrystalline ZSM-5 (n-ZSM-5, Si/Al = 32) and hierarchical ZSM-5 (h-ZSM-5) with different acidity (Si/Al = 33, 51, 122) were tested in the liquid-phase conversion of stearic acid under nitrogen atmosphere (6 bar). The incorporation of Pd into ZSM-5 zeolite increased significantly the share of gasoline in the reaction products due to the promotion by this metal of both decarboxylation and hydrogen transfer reactions. Likewise, the Pd nanoparticles dispersed over the zeolitic support favored the conversion of light olefins formed by end-chain cracking reactions into gasoline-range hydrocarbons according to an oligomerization/cyclization/aromatization pathway. Additionally, Pd/h-ZSM-5 gave rise to higher conversion and selectivity towards gasoline than Pd/n-ZSM-5, due mainly to the enhanced accessibility and improved Pd dispersion achieved when using the hierarchical zeolite. The decrease in the Si/Al atomic ratio in Pd/h-ZSM-5 samples resulted in a rise in the stearic acid conversion, although it was lower than expected. This finding denotes that, for supports with high acid sites concentration, the Pd availability became the limiting factor as the metal was loaded in similar amounts in all catalysts. Finally, the increase of the reaction temperature with the Pd/h-ZSM-5 (122) catalyst augmented both stearic acid conversion and gasoline selectivity, since it enhanced the conversion of the light olefins, formed as primary cracking products, into liquid hydrocarbons. Therefore, it can be concluded that Pd supported on hierarchical ZSM-5 zeolite is a convenient catalyst for obtaining bio-gasoline from oleaginous feedstock.

From 3D to 2D zeolite catalytic materials

Research activities and recent developments in the area of three-dimensional zeolites and their two-dimensional analogues are reviewed. Zeolites are the most important industrial heterogeneous catalysts with numerous applications. However, they suffer from limited pore sizes not allowing penetration of sterically demanding molecules to their channel systems and to active sites. We briefly highlight here the synthesis, properties and catalytic potential of three-dimensional zeolites followed by a discussion of hierarchical zeolites combining micro- and mesoporosity. The final part is devoted to two-dimensional analogues developed recently. Novel bottom-up and top-down synthetic approaches for two-dimensional zeolites, their properties, and catalytic performances are thoroughly discussed in this review.

Highly hydrothermal stable mesoporous molecular sieves (TZM) prepared by the self assembly of zeolitic subunits from ZSM-5 desilication and their catalytic performance for CO2 reforming of CH4

We demonstrated a new strategy for the preparation of highly stable mesoporous molecular sieves (TZM) by the desilication of ZSM-5 zeolite and self-assembly of the zeolite subunits in a Na₂O·(3.3–3.4) SiO₂ aqueous solution.

Bidimensional ZSM-5 zeolites probed as catalysts for polyethylene cracking

Lamellar and pillared ZSM-5 zeolites (L-ZSM-5 and PI-ZSM-5, respectively) were synthesized and tested in the catalytic cracking of low-density polyethylene (LDPE).

A solvent evaporation route towards fabrication of hierarchically porous ZSM-11 with highly accessible mesopores

A solvent evaporation route to generate an organosilane modified dry gel and its transformation into hierarchically porous ZSM-11 is reported. The material features good pore-connectivity and improved acid site accessibility towards bulky substrates.