Xinmei Liu

One-step solvothermal synthesis of Fe3O4@C core–shell nanoparticles with tunable sizes

We report the synthesis of Fe3O4@C core-shell nanoparticles (FCNPs) by using a facile one-step solvothermal method. The FCNPs consisted of Fe3O4 particles as the cores and amorphous uniform carbon shells. The content of Fe3O4 is up to 81.6 wt%. These core-shell nanoparticles are aggregated by primary nanocrystals with a size of 10-12 nm. The FCNPs possess a hollow interior, high magnetization, excellent absorption properties and abundant surface hydroxyl groups. A possible growth mechanism of the FCNPs is proposed. The role of glucose in regulating the grain size and morphology of the particles is discussed. The absorption properties of the FCNPs towards Cr(VI) in aqueous solution is investigated. We demonstrate that the FCNPs can effectively remove more than 90 wt% of Cr(VI) from aqueous solution.

In situ synthesis, characterization and catalytic activity of ZSM-5 zeolites on kaolin microspheres from amine-free system

ZSM-5 zeolites were synthesized by an in situ hydrothermal crystallization method on kaolin microspheres from an organic template-free solution. The as-synthesized samples were characterized by using X-ray diffraction, scanning electron microscopy, Fourier Transform Infrared spectrometry, N2 adsorption and desorption, and Temperature Programmed Desorption. The results showed that small-sized ZSM-5 crystallites with less than 1 micron in diameter were effectively formed on kaolin microspheres. The synthesized products indicated high hydrothermal stability and strong acidity. By mixing the H-type ZSM-5/CMK composite with a Fluid Catalytic Cracking base catalyst, the performance of the catalyst is then evaluated. The results of catalytic performance evaluation showed that with the addition of ZSM-5/CKM, it favored the production of light olefins such as propylene and butylenes by catalytic cracking of vacuum gas oil.

Effects of synthetic conditions on the textural structure of pseudo-boehmite

Mesoporous alumina with pseudo-boehmite phase was prepared by using the cation-anion double hydrolysis method from mixed aqueous solution of aluminum sulfate and sodium aluminate. The effect of synthetic conditions on the crystal structure and textual properties of pseudo-boehmite was investigated, such as synthetic temperature, pH value and the addition of sodium silicate. With the assistance of characterization techniques, such as X-ray diffraction (XRD), N2 adsorption-desorption isotherms (BET) and (27)Al magic-angle spinning nuclear magnetic resonance (MAS NMR), the relationship between textural properties of the mesoporous alumina samples and their synthetic conditions was discussed. The results displayed that an increase in synthesis temperature promoted the formation of higher crystalline pseudo-boehmite with the increase of its surface area and pore volume. Pure pseudo-boehmite phase could be obtained in the pH value range from 6.0 to 9.0, while bayerite phase occurred when the pH value was over 10.0. The introduction of sodium silicate could greatly improve the pore volume (1.20 cm(3)/g) and surface area (480.2 m(2)/g) of pseudo-boehmite. Interestingly, pure pseudo-boehmite phase was obtained at very high pH value without formation of bayerite phase when sodium silicate was initially added into the aluminum hydroxide colloid.

Zeolite Y synthesized with FCC spent catalyst fines: particle size effect on catalytic reactions

In this study, Y zeolite with different particle sizes was synthesized with fines of Fluid Catalytic Cracking (FCC) spent catalyst. The effect of particle size on physicochemical properties of zeolite was systematically investigated. The results showed that zeolites synthesized via in situ crystallization technique exhibited large surface area, high relative crystallinity and high thermal stability. With a decrease of particle size of zeolite, both total acid density and B acid sites increased while acid L sites decreased. The cracking activity for heavy oil and coke resistance of ultra-fine zeolite catalysts were enhanced. Of note is that the desulfurization capability of superfine zeolite catalyst was found to be much higher than that of industrial catalyst.

Regulating acidity, porosity, and morphology of hierarchical SAPO-11 zeolite by aging treatment

A facile method to modify pore structure, acidic character, and morphology of SAPO-11 molecular sieve was proposed. Aging treatment (e.g., microwave irradiation or lyophilization) is introduced in the preparation of dry gel. It regulates the kinetics of zeolitic nucleation and growth. X-ray diffraction, scanning electron microscopy, N2-adsorption, temperature programmed desorption, laser particle analyzer, and (29)Si MAS NMR were employed to investigate the effects of aging treatments on SAPO-11 products. The experimental results indicate that depolymerization reaction of silicon species is enhanced aged by microwave irradiation with a higher temperature (90°C). Ratio of SM 3 to SM 2 substituting mode increases producing more strong Brønsted acid sites. Lyophilization technology, as another aging method, was employed to control the morphology of SAPO-11. Nano-sized hierarchical SAPO-11 molecular sieve (200nm in length) is obtained with an oriented growth. Activity of hydroisomerization catalysts is regulated by aging treatment. Cracking reaction attributes to a high conversion nearly 87wt% for M90. The hydroisomerization reaction is enhanced for M40 due to a large proportion of moderate acid sites.

Substituting effect of Ce3+ on the AlPO-11 molecular sieve

Substituted AlPO-11 molecular sieve with Ce3+ was first prepared. The substitution was verified by characterization techniques and density functional theory. The results showed that both Al3+ and P5+ sites could be substituted. Cerium–oxygen tetrahedron was formed when Al3+ sites were replaced via isomorphous substitution. As for substituting the P5+ sites, Ce3+ coordinated with two or three oxygen atoms to form surface defects. Bronsted and Lewis acid sites appeared from the charge compensation and structure defects, respectively. The defective surface with higher interface energy resulted in particle aggregation and oriented growth. CeAPO-11 possesses a superior hydrothermal stability, which enables its application in a steam atmosphere with severely high temperatures. It was added as the bi-functional promoter (isomerization and dehydrogenation) to a fluid catalytic cracking catalyst. The results showed that CeAPO-11 increased the reaction conversion and the selectivity of aromatics and cycloparaffins.

The effects of magnesium of Zn–Mg–Al additives on catalytic cracking of VGO and in situ reduction of sulfur in gasoline

The scope of the present study is to describe the cracking behavior of hydrocarbons and the reduction of sulfur in gasoline in fluid catalytic cracking (FCC) process using Zn–Mg–Al additives with varying the Mg/Al molar ratios. Experiments have been carried out on a micro-activity-test (MAT) reactor using high-sulfur vacuum gas oil (VGO) feed and zinc impregnated Mg–Al spinels as additive and the commercial cracking catalyst. It was found that Zn–Mg–Al additives exhibited enhanced Lewis acidity compared with the corresponding Zn-free Mg–Al spinels. The MAT results indicated that the addition of additives reduced the yields of liquid petroleum gas and coke at low Mg contents but increased the coke yield at high Mg contents. Overall, the additives improved the yields of gasoline and diesel. It has also been shown that the rich Lewis acidity had a positive effect on the conversion of aromatic sulfur species of gasoline and the maximum reduction of gasoline sulfur was achieved with Zn/Mg4.0Al2O3 due to the synergistic effect of basicity and Lewis acidity.

Mechanistic study of methane reforming with carbon dioxide on a supported nickel catalyst

The nature of activation of methane on supported nickel catalyst has been investigated by means of temperature programmed surface reaction (TPSR), temperature programmed desorption (TPD), X-ray photoelectron energy spectroscopy (XPS) and pulse reaction and a synergetic mechanism of carbon dioxide reforming with methane is tentatively postulated. TPSR, TPD and XPS results indicate that carbidic Cα carbonaceous Cβ and carbidic clusters Cγ surface carbon species formed by decomposition of methane show different surface mobility, thermal stability and reactivity. Cα and Cβ species on the nickel surface are thermally unstable and can be rapidly converted into Cγ species upon increasing temperature. The carbidic carbon is a very active and important intermediate in carbon dioxide reforming with methane and the carbidic clusters Cγ species might be the precursor of the surface carbon deposition.The nature of activation of methane on supported nickel catalyst has been investigated by means of temperature programmed surface reaction (TPSR), temperature programmed desorption (TPD), X-ray photoelectron energy spectroscopy (XPS) and pulse reaction and a synergetic mechanism of carbon dioxide reforming with methane is tentatively postulated. TPSR, TPD and XPS results indicate that carbidic Cα, carbonaceous Cβ and carbidic clusters Cγ surface carbon species formed by decomposition of methane show different surface mobility, thermal stability and reactivity. Cα and Cβ species on the nickel surface are thermally unstable and can be rapidly converted into Cγ species upon increasing temperature. The carbidic carbon is a very active and important intermediate in carbon dioxide reforming with methane and the carbidic clusters Cγ species might be the precursor of the surface carbon deposition.

Adsorption of 4,6-dimethyldibenzothiophene and collidine over MoO3/γ-Al2O3 catalysts with different pore structures

Mesoporous γ-Al2O3 supports with different pore structures were prepared by the cation-anion double hydrolysis method. Based on these samples, MoO3/γ-Al2O3 catalysts were made via impregnation. The adsorptions of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and collidine over the supports and catalysts were studied by FT-IR. The supports or catalysts with larger pores can adsorb more 4,6-DMDBT. The methyl groups on adsorbate molecules are very close to the sulfur atom, resulting in apparent steric hindrance. Increasing the pore size can promote the interaction between the adsorbates and supports or catalysts, enhancing the CC bond and weakening the CS bond of 4,6-DMDBT. 4,6-DMDBT molecules were coordinated with the unsaturated Mo atoms over the catalysts to form π-complexation adsorption. There was much difference between thiophene and 4,6-DMDBT adsorption. The adsorption of collidine over the catalysts also illustrated that there existed steric hindrance. Significantly, the catalyst with hierarchical mesopores was beneficial for the adsorbates with larger molecular dynamics diameter. Compared with the pore size, the specific surface area was not the key factor to affect the adsorptions of 4,6-DMDBT and collidine. The hydrodesulfurization reaction of 4,6-DMDBT illustrated that the catalysts with larger pore size or hierarchical pore structure presented higher desulfurization efficiency (above than 80%).

Sulfur introduction in V–K/γ-Al2O3 catalyst for high performance in the non-oxidative dehydrogenation of isobutane

Sulfur was introduced, for the first time, into V–K/γ-Al2O3 catalysts, due to which their performance in the non-oxidative dehydrogenation (DH) of isobutane was promoted remarkably. After sulfidation, the isobutene yield increased from 29.6% to 49.8%. Many attempts have been made to thoroughly explain the promoting effect of sulfidation over V–K/γ-Al2O3 catalysts towards DH activity. This study demonstrates that both properties of the vanadium species and the acid properties of vanadium-based catalysts are affected by sulfidation. The introduction of sulfur, which has lower electronegativity, made the bond energy of V–S lower than that of V–O. Therefore, the vanadium species can be reduced easily after sulfidation and hence, the availability of V3+ and V4+ species, which serve as active DH sites, increases on the catalyst surface. The increased acid strength further enables easy activation of the C–H bond in isobutane, thus contributing to an increase in isobutane conversion. Moreover, the decrease in acidic sites inhibits side reactions and confers higher isobutene selectivity to the sulfide catalyst compared to its oxidized state. The sulfide V–K/γ-Al2O3 catalyst, presenting ideal activity, stability and space–time yield, is a promising alternative to optimized industrial DH catalyst.