Synergism of Titanium in MFI Zeolite to Acidity with Its Appliance to N-Hexane Catalytic Cracking Reaction

Catalytic cracking of naphtha is now a process of huge development potential to produce light olefins, which are important basic raw materials used in various industries, but current industrial catalysts like ZSM-5 zeolites suffer from low selectivity and high energy consumption. Here, Ti/Al-containing nanosize MFI-structure zeolites in-situly synthesized through one-pot method were applied to the catalytic cracking using n-hexane as the model reactant. The maximum mass yield of combined light olefins reaches 49.2% with 99% conversion at 600°C and 1 atm. Multiple characterizations are used to identify the Ti-related active species and their effect on the performance. It was found that a higher proportion of LAS caused by Ti was beneficial to the activation of reactant, and the slightly increased amount of BAS leaded to more alkanes converting into light olefins. This understanding may open new opportunities for design and modification of catalytic cracking catalysts.

Fabrication of titanosilicate pillared MFI zeolites with tailored catalytic activity

Titanosilicate pillared MFI zeolite nanosheets were successfully synthesized by infiltrating the mixed tetraethyl orthosilicate(TEOS)/tetrabutyl orthotitanate(TBOT)solvent into the gallery space between adjacent MFI zeolite layers.The obtained zeolite catalysts were characterized using powder X-ray diffraction,N2 adsorption/desorption isotherms,scanning electron microscopy,transmission electron microscopy,ultraviolet-visible spectroscopy,X-ray photoelectron spectroscopy,and Fouriertransform infrared spectroscopy techniques.The H2〇2 oxidation of dibenzothiophene(DBT)was used to evaluate the catalytic performance of the obtained titanosilicate pillared MFI zeolites.The conversion of DBT and selectivity of dibenzothiophene sulfone(DBTS)were most affected by the textural properties of the zeolites.This was attributed to the DBT and DBTS molecules being larger than micropores of the MFI zeolites.The conversion of DBT and yield of DBTS could be systematically tailored by tuning the molar ratio of the TEOS/TBOT solvent.These results implied that a balance between the meso-and microporosity of zeolites and tetrahedrally coordinated Ti(IV)active sites of titanosilicate pillars can be achieved for the preparation of desired catalysts during the oxidation of bulk S compounds.

Co-aromatization of methane and hexane over Pt encapsulated in ZSM-5 zeolite and the electronic effect of K promoters

The co-aromatization of methane with higher hydrocarbons represents a promising route to valorize methane, an abundant but underexploited carbon resource. In this study, we elucidate a novel approach to enhance the catalytic co-aromatization of hexane and methane by confining Pt within zeolite catalysts and modulating its electron density. Our findings show that encapsulating Pt within MFI structure is pivotal for activating the feedstock and fostering the formation of aromatic products. Interaction between K atoms and the silanol nest forms siloxy groups which are critical for the stabilization of Pt species. Tuning the K content in PtSn@MFI catalysts adeptly alters the electronic configuration of Pt clusters. This modification is corroborated by infrared and X-ray photoelectron spectroscopy analysis, and density functional theory calculations. Remarkably, the catalyst with 0.8 wt% K exhibits an optimal Pt electron density, driving its superior efficacy in the co-aromatization reaction, converting 0.78 mol of methane for each mole of hexane processed. By employing ~(13)C isotopic labeling and solid-state NMR studies, we demonstrate the participation of methane in the adsorbed species inside the zeolite channel and its incorporation to the benzyl site of the substitute group and phenyl rings in aromatic compounds, underscoring the importance of Pt encapsulation.

Forming and Gathering of SnO2 Nanoparticles on External Surface of High Silica TON, MFI and FAU Type Zeolites

Tin dioxide （SnO2） nano-particles were prepared on high silica TON, MFI and FAU type zeolites by impregnation of SnC12 solution and subsequent calcination at 873 K. XRD and SAED were used to characterize the crystalline phase, and TEM was used to characterize the morphology, the particle size and the agglomerative state of the formed nano-materials. The nano-particles, which possess 8 nm, 10-80 nm and 6 nm in size, were found to form on the outer surface of TON, MFI and FAU zeolites, respectively. SnO2 microcapsules and SnOz netlike nanostructure were obtained by decomposition of SnO2-TON and SnO2-MFI in 40% hydrofluoric acid at room temperature. Compared with the nano-particles formed on NaY zeolite, the special morphology and the agglomerative state of SnO2 nanostructures on TON and MFI type zeolites with one and two dimension channel system indicate that the heterogeneous framework, surface structure and property perform important function for forming and growing SnO2 nanostructure on the outer surface of the zeolites.

Urea-assisted morphological engineering of MFI nanosheets with tunable b-thickness

Engineering of crystal morphology affects the catalytic and adsorption properties of zeolitic materials.Considering the anisotropic diffusion of molecules derived from its topological features,MFI zeolite nanosheets with short b-axis thickness are highly desired materials to reduce diffusion resistance.However,the design and development of eco-friendly synthesis protocols with reasonable cost and high efficiency remain elusive.Herein,we reported a systematic study on the synthesis of MFI nanosheets using urea as an additive.Both silicalite-1 and ZSM-5 zeolites(MFI type framework structure)with controllable b-thicknesses ranging from 50–200 nm were achieved by optimizing the synthetic parameters including water content,urea and SDA concentrations.The concentration of hydroxide anions was found to dominate the crystallization kinetics compared with the counterpart tetrapropylammonium cations(TPA^(+)).To facilitate the crystal growth of MFI zeolites in the presence of urea,the ratio OH−/SiO_(2)has to be higher than 0.2,independent of the TPA+concentration.The role of urea in the assistance of plate-like crystal formation through the inhibition of(010)facet growth was revealed by electron microscopy and infrared(IR)spectroscopy analyses.The developed strategy for morphological engineering is not limited to the MFI-type zeolite and can be applied to other frameworks depending on the intrinsic properties of additive molecules and the interactions between them.

Sustainable Synthesis of Core-Shell Structured ZSM-5@Silicalite-1 Zeolite

Core-shell structured ZSM-5@Silicalite-1 zeolite could effectively hinder the deactivation of catalyst surface. Currently, organic structure directing agents(OSDAs) are necessary in the conventional route for the synthesis of this core-shell zeolite under hydrothermal conditions, which is costly and environmental-unfriendly. In this research, a synthesis of the core-shell structured ZSM-5@Silicalite-1 zeolite with a strategy of alcohol filling and zeolite seeding without any organic template or solvent is exhibited. The obtained products are well characterized by X-ray powder diffractometer(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), N2 sorption isotherms, solid magic angle spinning(MAS) NMR, temperature-programmed-desorption of ammonia(NH3-TPD), and X-ray photoelectron spectroscopy(XPS) techniques, in order to confirm the core-shell structure. More importantly, the core-shell structured ZSM-5@Silicalite-1 zeolite exhibits a long lifetime and a high p-xylene selectivity in the alkylation of toluene with methanol, compared with the conventional ZSM-5 catalyst.