Xionghou Gao

Cation location and migration in lanthanum-exchanged NaY zeolite

LaNH4Y and LaY zeolites were prepared using a double‐exchange double‐calcination method by La exchange of NaY zeolite. The distribution of the La cations was determined by powder X‐ray diffraction with Rietveld refinement. The results indicate that the La cations are initially located in supercages, and then their hydration shells are stripped off and they migrate to small sodalite structures located at SI´ during heating and dehydration. The changes in the T-O-T angles show significant distortion of the flexible framework and instability in LaNH4 Y obtained using a one‐exchange one‐calcination process. For La cations located at SI´ and coordinated with O3, the T-O3 bond distance increased, which indicates that the rare‐earth cations not only restrain framework dealumination, suppressing condensation of the unit cell, but also have an effect on the T-O3 bond distance, increasing the unit cell volume. The role of the rare‐earth species is to ensure the hydrothermal stability of the zeolite in order to control the acid site density and catalytic activity. The effects of La cations and NH4^+ cations on the zeolite acidity were studied using infrared spectroscopy and NH3 temperature‐programmed desorption, and the mechanism of rare‐earth stabilization of the Y zeolite is described.

Creation of mesostructured hollow Y zeolite by selective demetallation of an artificial heterogeneous Al distributed zeolite crystal

Hollow zeolites have gained great interest in the last decade because of their broad applications in catalysis, drug delivery, and as membranes. Here, we demonstrate that a low silica hollow Y zeolite with mesoporous walls can be prepared by a sequential demetallation (SiCl4, HCl and NaOH) strategy without using any organic templates. It has been found that the design of a Y crystal with a Si-rich surface and an Al-rich core introduced by SiCl4 treatment is a critical factor. The inhomogeneous Al distribution structure guides the sequent HCl and NaOH treatment to the selective demetallation for the generation of a hollow cavity and mesoporous shell. The resultant hollow Y zeolite with a 200 nm shell shows an extremely high hierarchy factor (0.18), higher than that of the conventional steamed USY zeolite (0.08), due to the larger BET surface area (844.4 vs. 620.3 m2 g−1), and in particular the significantly increased mesopore surface area (415.6 vs. 76.6 m2 g−1). As such, the catalytic cracking performance in 1,3,5-triisopropylbenzene and the vacuum gas oil conversion of the hollow mesoporous Y zeolite outperforms the conventional steamed USY zeolite in terms of catalytic activity, product selectivity, and catalyst lifetime.

Desilication by Alkaline Treatment and Increasing the Silica to Alumina Ratio of Zeolite Y

The framework silica to alumina ratio, the porosity, and the acidity properties of ultrastable Y zeolites prepared by ‘steaming’ and by the ‘sequential alkaline treatment and steaming’ of NaY zeolites are compared. The adaptability of the combined alkaline treatment method and steaming toward the type of starting NaY zeolites was studied. By comparison with single steaming treatment the combination of sequential alkaline treatment and steaming affords products with an obviously increased mesopore volume. The level of framework ultrastabilization and acidity of the final products were not affected. The mesopore volume of the ultrastable Y zeolite prepared by steaming dealumination only was no more than 0.14 cm3/g. The mesopore volume of the final product prepared by sequential desilication and dealumination was 0.22 cm3/g. The sequential desilication and dealumination method is suitable for the NaY zeolite with a high framework silica to alumina ratio. A small increase in the mesopore volume and severe micropore damage were evident when the NaY zeolite with a relatively low silica to alumina ratio (SiO2/Al2O3 = 4.8, determined by nuclear magnetic resonance) was used as the starting material for the combined desilication and dealumination treatment.

Suzhou kaolin as a FCC catalyst

Abstract The chemical and mineralogical compositions, the pore-diameter distribution, and the X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy of kaolin from Suzhou, China, and the physicochemical and catalytic properties of a catalyst prepared from that kaolin, are presented in this paper. Crystallized microspheres (CMR) containing ~30% NaY zeolite can be prepared from the Suzhou kaolin. The catalyst produced performs better than a standard commercial catalyst in terms of activity, attrition resistance, resistance to passivation by Ni and V and better gasoline and coke selectivity

Hydrothermally stable mesoporous aluminosilicates with moderate acidity via degradation-assembly process and improved catalytic properties

Mesoporous aluminosilicates with hydrothermal stability and moderate acidity are synthesized via assembly of microporous zeolite precursors obtained by the degradation of zeolite NaY, denoted as “degradation-assembly” (DA) technique. By controlling the degradation degree of matrix NaY, precursors with larger spatial volume and stronger rigidity will be obtained. The characterization results showed that the walls of the mesophase in MDA (mesoporous aluminosilicate obtained by “DA” method) composed of the preformed zeolite Y building units and the moderate acidity was inherited from the introduced precursors. It was suggested that the more mature assembly units accounted for the increased acidity of MDA with more Al species retained in the framework of mesophases. The resulting aluminosilicates with simultaneously moderate acidity and hydrothermal stability showed superior catalytic properties when used in heavy oil catalytic cracking catalysts.

Study on the mechanism of zeolite Y formation in the process of liquor recycling

Abstract Crystallization of zeolite Y formation in the process of mother liquor recycling (MLR) has been studied. The zeolite crystallization mother liquor comprises a little sodium silicate as well as minor zeolite, Upon addition of aluminum sulfate, the silicate existed in the mother liquor reacts to form finely divided silica–alumina hydrogel (MLHG) which can be utilized later in zeolite Y formation. The particle of MLHG is relatively small and Si/Al of the gels framework is a little great. Since amorphous aluminosilicate gel passes through two stages of gelation, the pseudoequilibrium between solid phase and liquid phase of gel is attained rapidly and the time of zeolite Y formation is much reduced. In addition, experiments have also showed that the quantities and the properties of zeolite Y added affect the process of crystallization heavily. Minor quantities of zeolite in the mother liquor have detrimental effect on the zeolite Y formation. Based on studies of crystallization from recycling mother liquor, a model of two-phase transformation for zeolite Y formation has been proposed.

Synthesis of ZSM-5 on kaolin microspheres in the absence of an organic amine template

Abstract Zeolite ZSM-5 was synthesized successfully, in situ, on pyrokaolin microspheres (PKM) under hydrothermal conditions, without the use of an organic amine template. The utility of alkali-modified pyrokaolin microspheres (AMKM) was also evaluated. The resulting products were characterized using X-ray diffraction, scanning electron microscopy (SEM) and N2-adsorption isotherm data. The material containing ZSM-5 synthesized from the system PKM-additional silicawater had a large surface area and pore volume with significant enhancements in the micropore surface area and micropore volume. The SEM images show that the synthesis of zeolite ZSM-5 from pyrokaolin microspheres (PKM) led to the formation of polycrystalline aggregates <2 μm in size. The purity of the zeolite ZSM-5 produced was affected by both the pH value of the reactant system and the reaction temperature. In the system containing AMKM-additional silica-water, very little of the synthesized zeolite resided on the kaolin microspheres.

Hydrothermally stable macro-meso-microporous materials: synthesis and application in heavy oil cracking

Hydrothermally stable hierarchical materials with macro-meso-micropores were synthesized by combination of precursor assembly and PS/P123 dual templates. Precursor assembly aims at the formation of meso-micropores and improving the hydrothermal stability, and PS microspheres aim at the introduction of macropores. Moreover, worm-like mesopores vertical to the surface of PS microspheres were present, which achieve the full interconnection of macro-meso-micropores. The resulting aluminosilicates with hierarchical pores and high hydrothermal stability showed excellent catalytic cracking properties for heavy oil.

Kinetics study and analysis of zeolite Y destruction

A series of zeolites, including USY zeolites without sodium, Na-USY at different Na contents, La-USY with different rare earth (RE) contents and La-Na-USY with RE and Na were prepared by an ion exchange method. They were investigated to understand the activation barriers for the destruction of Y zeolite structure under hydrothermal treatment and the effect of V using the solid-state kinetic model. The results showed that the pathways for Y zeolite destruction were dealumination, desiliconization and the disappearance of La–O bonds. Zeolites were destroyed by steam through acid hydrolysis, which was accelerated by V. In addition, Na and V exerted a synergistic effect on the framework destruction, and the formation of NaOH was the rate-determining step. The presence of RE elements decreased hydrolysis and stabilized the structure of the zeolites. The interaction between V and RE destroyed zeolite structure by eliminating the stabilizing La–O [RE–OH–RE]5+ bridges in the sodalite cages.

Fabrication of intracrystalline mesopores within zeolite Y with greatly decreased templates

Zeolite Y with intracrystalline mesopores has been emerging as one of the most potential materials in the catalytic cracking of large molecules. Our group has reported the synthesis of zeolite Y with intracrystalline mesopores with the formula [(CH3O)3SiC3H6N(CH3)2C18H37]Cl (denoted as “TPOACl”). However, the fabrication of mesoporous zeolite Y with a decreased organic template remains a significant challenge. In this study, a novel surfactant [(CH3O)3SiC3H6N(CH3)2C16H33]Cl (denoted as “TPHAC”) was designed and synthesized using low-cost industrial raw materials, which was found suitable for the formation of mesoporosity utilizing greatly decreased amount of the surfactant. The possible differences in the synthesis mechanisms of TPOACl and TPHAC have been discussed. The enhanced hydrophilicity of the hydroxyl groups and the subsequent decrease in the micelle aggregation number (MAN) are proposed to be the key to underline the decreased amount of surfactant in the successful synthesis. The material shows excellent hydrothermal stability and a higher mesoporous surface area ratio than TPOACl. The prepared mesoporous zeolite Y showed much higher catalytic activity and selectivity in heavy oil cracking than that prepared from TPOACl.