Honghong Shan

Hierarchical ZSM-11 with intergrowth structures: Synthesis, characterization and catalytic properties

Abstract Hierarchical ZSM-11 microspheres with intercrystalline mesoporous properties and rod-like crystals intergrowth morphology have been synthesized using a spot of tetrabutylammonium as a single template. XRD, FTIR, SEM, TEM and N2 adsorption analysis revealed that each individual particle was composed of nanosized rod crystals inserting each other and the intercrystalline voids existing among rods gave a significant mesopore size distribution. Steam treatment result demonstrated the excellent hydrothermal stability of samples. Various crystallization modes including constant temperature crystallization (one-stage crystallization) and two-stage temperature-varying crystallization with different 1st stage durations were investigated. The results suggested that the crystallization modes were mainly responsible for the adjustable particle size and textural properties of samples while the small amount of tetrabutylammonium bromide was mainly used to direct the formation of both ZSM-11 framework and its intergrowth morphology. Furthermore, the performance of optimal ZSM-11 as an active component for the catalytic pyrolysis of heavy oil was also investigated. Compared with the commercial pyrolysis catalyst, the hierarchical ZSM-11 catalyst exhibited a high selectivity to desired products (LPG + gasoline + diesel), as well as a much lower dry gas and coke yield, plus a high selectivity and yield of light olefins (n C 3 = - C 4 = ) and very poor selectivity to benzene. Therefore, fully open micropore-mesopore connectivity would make such hierarchically porous ZSM-11 zeolites very attractive for applications in clean petrochemical catalysis field.

Synthesis of a ZSM-5(core)/SAPO-5(shell) composite and its application in FCC

A core/shell structure composite was synthesized via a new method of pre-coating one raw material. The composite was characterized by X-ray diffraction, SEM, TEM and N2 isothermal adsorption–desorption and Py-FTIR. In addition, the catalytic performance of the composite in cracking of heavy oil for producing olefin was also investigated. The characterization results show that the composite with a core/shell structure had smaller particle size, uniform SAPO-5 shell, and fewer acid sites than ZSM-5, accelerating the transport of reactant and product molecules between different zeolites. Consequently, the light olefins on the composites had high specific selectivity.

Isobutane Dehydrogenation over Metal (Fe, Co, and Ni) Oxide and Sulfide Catalysts: Reactivity and Reaction Mechanism

Silica‐supported metal oxide and sulfide catalysts of Fe, Co, and Ni were evaluated comparatively for the catalytic dehydrogenation of isobutane. The results of the activity test and temperature‐programmed reduction of hydrogen characterization indicate that metal oxides, except Fe2O3, are easily reduced to metal ensembles, which are extremely active for alkane hydrogenolysis and lead to the formation of a considerable amount of methane and coke. However, the dehydrogenation performance was significantly improved after sulfidation treatment. The introduction of sulfur affects the catalysts in two ways: one is the geometric effect, which dilutes the aggregated metallic species and reduces hydrogenolysis activity, and the other is the electronic effect, which facilitates the desorption of olefin and increases the product selectivity. Moreover, the reaction mechanism is explored by using the proposed model of the interaction between isobutane and sulfide catalysts. Finally, sulfur loss and partial coke deposition are determined to be the main reasons for catalyst deactivation.

Studies on the promoting effect of sulfate species in catalytic dehydrogenation of propane over Fe2O3/Al2O3 catalysts

The promoting effect of sulfate species in propane dehydrogenation over Fe2O3/γ-Al2O3 catalysts is systematically elucidated by using iron(III) or iron(II) sulfate as the precursor, pre-treating with SO2 or introducing SO2 with propane as the reactant. At 560 °C, up to 23 wt% propylene yield with 80% selectivity is obtained. It is demonstrated that the introduced sulfate species exist in the form of SO42− and strongly interact with the support and Fe via the Al–O–S bond and the Fe–O–S bond. On one hand, it suppresses the formation of FexC species and thus the cracking reaction. On the other hand, it leads to an enhanced adsorption capacity of propane. Meanwhile, the initial C–H bond activation and subsequent rupture with the formation of Fe–C3H7 and OH are facilitated, resulting in excellent dehydrogenation performance. Online MS, XPS, XRD and reaction–regeneration–sulfuration results show that the loss of sulfate species by the reduction to S2− and release in the form of SO2 is the main reason for the deactivation of the sulfated catalysts.

Effect of magnesium modification over H-ZSM-5 in methanol to propylene reaction

H-ZSM-5-based catalyst is a recognized catalyst which is particularly selective towards the formations of light olefins in the methanol reaction. A series of H-ZSM-5 (SiO2/Al2O3xa0=xa038) modified with different amounts of magnesium have been investigated. All the samples were characterized by X-ray diffraction instrument (XRD), temperature-programmed desorption of NH3 (NH3-TPD) and Fourier Transform Infrared Spectoscopy (FT-IR). The results indicated that the impregnation of H-ZSM-5 (SiO2/Al2O3xa0=xa038) zeolite with various magnesium loading amount significantly affected the strength of acid sites and decreased the concentration of both weak and strong acid sites. As a result of modification, magnesium mainly interacted with strong Brønsted acid sites, thus generated new medium strong acid sites and enhanced the yield of propylene. The optimum acid property for methanol to propylene (MTP) reaction was gotten over 4.0xa0Mg-ZSM-5 (4.0xa0wt% Mg) zeolite catalyst. The maximum yield of propylene was 10.62xa0wt% over 4.0xa0Mg-ZSM-5 zeolite catalyst by the 30xa0min on stream. Coke which was mostly formed on strong Brønsted acid sites, would cause the catalysts deactivation, so the reduction of strong Brønsted acid sites could enhance the catalytic stability.

Synergistic Effect of Nickel Species and γ-Alumina Added to HZSM-5 on the Methanol to Aromatics

Ni/HZSM-5 catalysts with γ-alumina were prepared by the sol–gel method. At first, reaction performances were investigated over the HZSM-5 catalysts with and without γ-alumina. Then, reaction evaluations were conducted over the Ni/HZSM (different loading amounts of nickel species were investigated) catalysts with and without γ-alumina. The addition of nickel species and γ-alumina increased the total acidity of the catalysts. Furthermore, the introduction of γ-alumina increased the amount of mesopores in the catalysts. Nickel species were much more stable with the presence of γ-alumina. Both nickel species and γ-alumina contributed the aromatization of methanol.Graphical Abstract

Synergistic effect of W and P on ZSM-5 and its catalytic performance in the cracking of heavy oil

In order to develop the conversion of heavy oil with a high yield of propylene in the catalytic cracking process, ZSM-5 zeolite was modified by tungsten and phosphorus, which was proved to be an effective method. Characterization results show that the improvement of catalytic performance could be correlated to the interaction of phosphorus and tungsten species on ZSM-5. P inhibited the aggregation of tungsten species on ZSM-5 and was conductive to convert the tungsten species with octahedral coordination into tetrahedral coordination. And this ultimately led to that more acid sites were reserved after hydrothermal treatment in the tungsten and phosphorus co-modified ZSM-5 catalyst. Phosphorus species played an important role to restrain the dehydrogenation activity of tungsten. In addition, a model reflecting the interaction between tungsten species and ZSM-5 framework was proposed.

Multifunctional two-stage riser fluid catalytic cracking process

This paper described the discovering process of some shortcomings of the conventional fluid catalytic cracking (FCC) process and the proposed two-stage riser (TSR) FCC process for decreasing dry gas and coke yields and increasing light oil yield, which has been successfully applied in 12 industrial units. Furthermore, the multifunctional two-stage riser (MFT) FCC process proposed on the basis of the TSR FCC process was described, which were carried out by the optimization of reaction conditions for fresh feedstock and cycle oil catalytic cracking, respectively, by the coupling of cycle oil cracking and light FCC naphtha upgrading processes in the second-stage riser, and the specially designed reactor for further reducing the olefin content of gasoline. The pilot test showed that it can further improve the product quality, increase the diesel yield, and enhance the conversion of heavy oil.

Effect of γ-alumina as active matrix added to HZSM-5 catalyst on the aromatization of methanol

HZSM-5-based catalyst is a recognized catalyst which is particularly selective towards the formations of aromatics in the methanol reaction. However, studies on HZSM-5-based catalyst were mainly focused on the addition of metallic or/and nonmetallic element. Quite few studies have reported the effect of active matrix such as γ-alumina on the aromatization of methanol. In this study, γ-alumina was introduced into HZSM-5-based catalyst for the purpose of investigating the effect of γ-alumina in methanol to aromatics reaction. The catalysts were characterized by X-ray diffraction, Temperature-programmed Desorption of NH3 (NH3-TPD), Pyridine adsorption FT-IR diffuse reflection spectroscopy and adsorption–desorption measurements of nitrogen, respectively. Characterizations showed that the introduction of γ-alumina increased the amount of mesopores and acid sites in the catalyst. The experimental mainly includes two parts. Firstly, separate reaction performances over the catalyst with/without γ-alumina and γ-alumina showed that γ-alumina could significantly promote the formations of aromatics. However, γ-alumina alone could merely convert methanol to dimethyl ether with a minor quantity of gaseous hydrocarbons. Acid properties showed that the introduction of γ-alumina increased the percentage of Lewis acid on catalyst surface and enhanced acid strength, as a result, promoted the production of active intermediates which was essential for aromatic formation. The rise of aromatics selectivity might be caused by the combined effect of acid site density and acid strength. Follow-up work was mainly focused on the effect of the loading amount and loading order of the catalyst with γ-alumina. Results indicated that the total aromatic yield increased gradually with the increasing amount of catalyst with γ-alumina regardless of the loading order of the catalyst with γ-alumina. Gasoline compositions showed that the increased aromatics were at the expense of paraffins, olefins, and naphthenes. Besides, all single aromatic hydrocarbons increased gradually with the increasing amount of catalyst with γ-alumina. And the aromatics had a larger variation change when methanol first passed through the catalyst with γ-alumina.

Studies on the Nature of Active Cobalt Species for the Production of Methane and Propylene in Catalytic Dehydrogenation of Propane

Co/Al2O3 catalysts with different Co3O4 loadings were studied in catalytic dehydrogenation of propane. The optimal results of 21.5 wt% propylene yield and 83.6xa0% selectivity were obtained at 5 wt% loading. XRD, DRS and XPS results showed that at loadings below 10 wt%, the “surface Co spinel” formed from tetrahedral Co2+ ions during the course of reaction constituted the active site for dehydrogenation reaction. Whereas at high loadings (above 10 wt%), only Co3O4 crystallites presented, which were easily reduced to metallic Co species, resulting in dramatically enhanced cracking reaction and the formation of abundant methane.Graphical Abstract