Tao Dou

Facile fabrication of mesopore-containing ZSM-5 zeolite from spent zeolite catalyst for methanol to propylene reaction

A facile and eco-friendly approach for the synthesis of mesopore-containing ZSM-5 zeolite with small crystal size was proposed by subtly making use of a coke-deposited spent zeolite catalyst. When used in the methanol to propylene reaction again, the refabricated ZSM-5 catalyst exhibited a much higher propylene selectivity and a longer catalytic lifetime.

Synthesis of high-silica EU-1 zeolite in the presence of hexamethonium ions: A seeded approach for inhibiting ZSM-48

A seeded approach was developed to synthesize high-silica EU-1 zeolite via inhibiting the co-crystallization of ZSM-48 in the presence of hexamethonium (HM) ions. A systematic study was carried out to determine factors such as seed content and SiO(2)/Al(2)O(3) ratio, which influenced the crystallization of high-silica EU-1 and transformation of EU-1 into ZSM-48. Using EU-1 seeds, not only well-crystallized pure EU-1 zeolites with SiO(2)/Al(2)O(3) ratios more than 500 were synthesized, but also the co-crystalline of ZSM-48/EU-1 or pure ZSM-48 was obtained in control from silica-rich mixture gels. Furthermore, the kinetic features of the seeded synthesis of EU-1 zeolites with SiO(2)/Al(2)O(3) ratios of 55, 190, and 500 were examined. It was found that seeds played crucial roles in the decrease of apparent activation energy of EU-1 nucleation and inhibiting the transformation of EU-1 into ZSM-48. The HM and Al species performed synergistic roles to inhibit the formation ZSM-48 during high-silica EU-1 nucleation and crystal growth.

Characterization and Catalytic Performance in n-Hexane Cracking of HEU-1 Zeolites Dealuminated Using Hydrochloric Acid and Hydrothermal Treatments

A series of modified HEU-1 zeolites were prepared using hydrochloric acid treatment, hydrothermal treatment, and a combination of these. The parent and modified HEU-1 zeolites were characterized by X-ray diffraction, N-2 adsorption-desorption isotherms, X-ray fluorescence, temperature-programmed desorption of ammonia, Fourier-transform infrared spectroscopy of adsorbed pyridine, and Al-27 solid-state magic-angle spinning nuclear magnetic resonance techniques. The catalytic cracking performances of the modified HEU-1 zeolites were evaluated on a fixed-bed microreactor at 625 degrees C, atmospheric pressure, and an n-hexane weight hourly space velocity of 2.0 h(-1). The results showed that extra-framework alumina could be removed by directly treating with hydrochloric acid, and framework alumina could be removed by hydrothermal treatment. Acidity characterization showed that the weak acid sites of HEU-1 zeolites could be adjusted using acid treatment, and the number of strong acid sites could be reduced using hydrothermal treatment. The framework n(Si):n(Al) ratio was improved by using a combination of hydrothermal treatment and acid leaching. The acidities of the HEU-1 zeolites were adjusted and both the mesopore volume and external surface area were enhanced. In n-hexane cracking reactions, the dealuminated HEU-1 zeolite obtained by hydrothermal treatment for 4 h at 600 degrees C and then washing with hydrochloric acid exhibited the highest propylene production as a result of suppression of the hydrogen transfer reaction. At 625 degrees C, the selectivity for propylene on HEU-1(HT4-HCl) increased to 35.2% from 21.9%, and the lifetime of HEU-1(HT4-HCl) was also prolonged from not more than 10 to 40 h.

Facile control of inter-crystalline porosity in the synthesis of size-controlled mesoporous MFI zeolites via in situ conversion of silica gel into zeolite nanocrystals for catalytic cracking

We report here a strategy for the facile synthesis of hierarchical MFI zeolite nanocrystals with controllable inter-crystalline mesopores by a one-step hydrothermal synthesis method using silica gel as the silica source and tetrapropyl ammonium as the microporous template without any other mesoporous templates or zeolite seeds. Powder X-ray diffraction results show the MFI structure with high crystallinity for all as-prepared zeolites. Scanning electron microscope characterization shows that 400–1000 nm zeolite aggregates are composed of the assembly of ~100 nm zeolite nanocrystals. Transmission electron microscopy results indicate the formation of inter-crystalline mesopores in the aggregated nanocrystals among the interspace of zeolite nanocrystals. The high mesopore volume (0.13 cm3 g−1) and external surface area (93 cm2 g−1) of the aggregated MFI zeolites are observed by N2 sorption measurements. The inter-crystalline porosity of MFI zeolites varies with the change in aggregation and the size of zeolite nanocrystals by changing the sodium concentration or the type of sodium salt in aluminate–silicate gels during hydrothermal crystallization. The mesoporous MFI zeolite aggregates exhibit similar light olefin selectivities and remarkably enhanced lifetime in the catalytic cracking of hexane compared to the highly dispersed MFI zeolite nanocrystals.

Quantum chemistry of adsorption and hydrogenation of DBT and carbazole on NiMoS using ZINDO/I method

The purpose of this study was to develop a fundamental understanding of the adsorption and first-step hydrogenation mechanisms of sulfur and nitrogen compounds over molybdenum disulfide (MoS2). To do so, molecular simulation of the dibenzothiophene (DBT) and carbazole over NiMoS micro-crystal active surface was performed using Zerners intermediate neglect of differential overlap (ZINDO) program with Hyperchem software. This study discusses the adsorbed structural parameters of DBT and carbazole molecules and proposes possible reaction pathways of hydrogenation on the NiMoS catalyst surface. The most stable configuration of adsorbed DBT is with the molecular plane perpendicular to the catalyst surface, while carbazole preferably adsorbed with the molecular plane parallel to the surface. Reaction enthalpies of DBT and carbazole adsorption processes on the catalyst surface were simulated based on the different configuration structures. The conformation heats and the activation energies of first-step hydrogenation of DBT and carbazole molecules over different configuration structures were also obtained by quantum chemistry simulation. The simulations on different catalyst surface structures indicated that the less vacant sites on the surface would result in the relatively low activation energies for DBT molecule. However, the hydrodenitrogenation (HDN) of carbazole increased with more vacant sites on the catalyst surface.

Synthesis of hierarchical mesoporous zeolites based on MOR zeolite: application in the automobile tailpipe hydrocarbon trap

Hierarchical mesoporous zeolites with different levels of micro- and mesoporosity were prepared by dissolution and reassembling processes of MOR zeolite in the presence of mesoscale cationic surfactant cethyltrimethylammonium bromide. The obtained materials were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, Fourier transform infrared, Nitrogen (N2) adsorption/desorption, Temperature programmed desorption of NH3 (NH3-TPD) and Nuclear magnetic resonance techniques. Moreover, these hierarchical zeolites were tested as hydrocarbon traps using toluene as probe molecule and the temperature programmed desorption method. The results showed that the amount of microstructure and mesostructure in the composite was able to be favorably tuned by varying dissolution time at the first stage. The hierarchical materials displayed remarkably high desorption temperature in toluene-TPD, which is an expected performance of hydrocarbon trap in automobile tailpipes. The effect is due to the easier transport of bulky molecules provided by mesopores and increasing the number of available active sites via a fragmentation of the microporous framework. Therefore, the synthesized composite molecular sieve may be a novel catalyst for hydrocarbon trap in automobile tailpipes.

Quasi-solid state synthesis of EU-1 zeolite and its catalytic properties for the isomerization of C8 aromatics

In this study, EU-1 zeolite was successfully synthesized via a quasi-solid state approach and assembled to catalyst for the C8 aromatics isomerization process. The catalytic properties were tuned through careful modification of the acidity of EU-1 zeolites and metal-doping of the catalyst. It was shown that EU-1 was an excellent candidate for the C8 aromatics isomerization process due to its unique structure. In addition, steam treatment of EU-1 at 450–500 °C could optimize the acidic properties of the catalyst, hence enhance its catalytic performance. The effect of the amount of Pt on ethylbenzene conversion was studied and the optimum amount was determined to be about 0.3–0.4 wt%. It was confirmed that EU-1 zeolite prepared via a quasi-solid state approach and then dealuminated by steam treatment had better activity and selectivity than conventional mordenite (MOR) zeolite and could be an excellent candidate for C8 aromatics isomerization.

Synthesis and Characterization of Hierarchical ZSM-48 Zeolite

A series of hierarchical ZSM-48 zeolites was prepared by seed silanization. The structural and textural properties of the hierarchical ZSM-48 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N2 adsorption-desorption, 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), and Fourier transform infrared spectroscopy adsorbed by pyridine (Py-IR). It was found that the crystal size of ZSM-48 was significantly reduced by seed silanization. Due to the secondary porosity in the mesopore region generated in hierarchical ZSM-48, both the total surface area and the pore volume of the material have a considerable increase. The enhancement of the textural properties could be controlled by changing the amount of silanizaiton agent.

Green and efficient dry gel conversion synthesis of SAPO-34 catalyst with plate-like morphology

SAPO-34 catalyst with plate-like morphology was designed and synthesized for the first time, by the dry gel conversion method using cheap triethylamine as a structure-directing agent assisted with seed suspension containing nanosheet-like SAPO-34 seed. The latter played an important role in formation of SAPO-34 (CHA-type) with plate-like morphology. In addition, the yield of the product in the synthesis system containing seed suspension reached 97%, 15% higher than that obtained in the corresponding synthesis system without the seed suspension. Meanwhile, the plate-like SAPO-34 catalysts synthesized by this method exhibited higher selectivity to light olefins and longer lifetime in methanol-to-olefins (MTO) reaction than the traditional cubic SAPO-34 catalyst. This work provides a new technical route for green and efficient synthesis of SAPO-34 catalysts with improved MTO performance.

Controllable synthesis of EU-1 molecular sieve with high SiO2/Al2O3 ratios in thermodynamic stable sol system

A new green chemical route was designed in this paper for the synthesis of high-silica EU-1 molecular sieve in TEAOH–SiO2–Al2O3–HMBr2–H2O system in which tetraethylammonium hydroxide (TEAOH) substituted for sodium hydroxide (NaOH) as an alkali source. The physicochemical properties of the synthesized samples characterized by such means as X-ray powder diffraction (XRD), electrophoresis apparatus, precise pH meter, scanning electron microscope, Fourier infrared spectrometer (FT-IR), thermo gravimetric analyzer (TG) and temperature programmed desorption (NH3-TPD). The research results showed that the SiO2/Al2O3 ratio of EU-1 molecular sieve could reach 706 with TEAOH as an alkali source. The SiO2/Al2O3 ratio of the product was improved greatly to 1046 with the template agent increasing. The new synthetic route has also significantly expanded the synthetic phase region. The absolute value of zeta potential of the TEAOH sol system was obviously higher than that of the NaOH sol system, indicating the thermodynamic stability of the former sol system was higher and better for the synthesis of pure high-silica EU-1 molecular sieve. The FT-IR spectra and TG/DTG diagrams of products indicated that TEA+ occluded in the final products could balance electronegative framework. The amount of strong, weak and the total acidity reduced with the increase of SiO2/Al2O3 ratio. The catalytic results of methanol-to-hydrocarbon demonstrated that the molecular sieve prepared by the new method has better catalytic performance.