Xiaotong Zhang

Deep Desulfurization of Diesel Fuel by Extraction with Task-Specific Ionic Liquids

Abstract Extraction of S-compounds from diesel oil by task-specific ionic liquids has been investigated. The influences of different ionic liquids, extraction time, extraction temperature, different S-compounds, the amount, and the recycling of ionic liquid were studied. This process is capable of removing up to 56% of dibenzothiophene in model diesel oil under optimum extraction conditions. At the same time, this process was applied to the real predesulfurized diesel oils. The results indicate that such a process could be an alternative to common hydrodesulfurization for deep desulfurization.

Investigation on the mechanism of adsorption and desorption behavior in cerium ions modified Y-type zeolite and improved hydrocarbons conversion

Abstract Different types of Y zeolites (HY, USY and NaY) containing various amounts of cerium (Ce) were prepared with the method of liquid ion exchange and characterized by X-ray diffraction (XRD), intelligent gravimetric analyzer (IGA), and a molecular simulation technology (grand canonical Monte Carlo simulation, GCMC). A novel calculation method of desorption index (DI) was proposed and the influence of cerium cationic species on the processes of adsorption-desorption of hydrocarbon molecules (n-octane) on the cerium modified Y zeolites (CeY) was studied. The results indicated that Ce ion species played a key role in reducing desorption activation energy of n-octane on Y type zeolites, leading to an improvement of the desorption ability of the CeY and the regulation of the adsorption state of n-octane from aggregation to decentralization. These findings are essential factors for enhancing the product selectivity of light hydrocarbon component and the catalytic activity of rare earth modified Y zeolites (REY) catalysts in fluid catalytic cracking (FCC) process.

Selective oxidation of cyclohexane using a Co-M/Al2O3 catalyst without additives

Abstract Without any organic solvent or activator, the selective oxidation of cyclohexane with air to afford cyclohexanol and cyclohexanone was investigated over Co/Al2O3 and Co-M/Al2O3 (M = Cu, Zn, and Ni) catalysts prepared by sol-gel method. The activity of the catalysts decreases in the following order: Co-Ni/Al2O3 > Co/Al2O3 > Co-Zn/Al2O3 > Co-Cu/Al2O3. The optimum contents of cobalt and nickel are 4.0 wt% and 3.0 wt% in Co-Ni/Al2O3 catalyst, respectively. The best result was obtained over Co-Ni/Al2O3 catalyst with a conversion of 9.9% and a selectivity of 94.6% and the ratio of cyclohexanone to cyclohexanol of 2.8 when the reaction was carried out at 443 K for 120 min under 4.5 MPa, and catalytic activity did not change after five consecutive reactions.

MCl2 (M=Hg, Cd, Zn, Mn) catalysed hydrochlorination of acetylene – a Density Functional Theory study

Abstract A Density Functional Theory method has been employed in this research to conduct an in-depth study of the correlation between the conversion of acetylene to vinyl chloride catalysed by MCl2 (M=Hg, Cd, Zn, Mn) and the electron affinity. From the analysis of the adsorption energy and energy profile of acetylene hydrochlorination reaction, combined with Fukui indices and outer-shell Mulliken population change alongside reaction pathway, it can be concluded that, the outermost electron migration is the main factor affecting the catalytic property of MCl2 (M=Hg, Cd, Zn, Mn) catalyst. The Mulliken population change of the central atom M2+ (M=Hg, Cd, Zn) share similar tendency along the reaction pathway, the only difference is Hg2+ gained more electrons than the other two when acetylene got absorbed, and that proved that Hg(II) got better electron withdrawing, which is a main motivator of better catalytic properties in acetylene hydrochlorination reaction.

Effect of cerium ions initial distribution on the crystalline structure and catalytic performance of CeY zeolite

Abstract CeY samples with different cerium (Ce) ions initial distribution were prepared by diverse preparation processes. The correlative influence of Ce ions distribution on the intracrystalline structure and catalytic mechanism of Y-type zeolite was studied by X-ray diffraction (XRD), Rietveld refinement, X-ray fluorescence spectrometry (XRF), energy-dispersive X-ray spectroscopy (EDS), infrared (IR) spectra, NH3 temperature-programmed desorption (NH3-TPD), N2 physical adsorption-desorption and micro-activity test (MAT). The results indicated that Ce ions were concentrated on the surface (supercage) of CeY zeolite would reduce the number of acid sites and the ratio of Bronsted acid and Lewis acid (B/L). Once Ce ions concentrated in the sodalite cage, it would participate in the coordination with framework oxygen atoms under the condition of steric hindrance. Meanwhile, Ce ions would preferentially promote the B/L value of weak acid by retaining more intracrystalline framework Al atoms in sodalite cage, which was beneficial to the conversion of heavy oil in FCC process. The optimal initial-distribution of Ce ions could not only save the consumption of rare earth resources but also give the best catalytic performance of CeY zeolite catalysts, and these advantages and attributes enabled it to have the potential to be applied in industrial applications.

A DFT study of the effect of NNN Al atom on strength of Brönsted acid sites of HY zeolite

Abstract A density functional theory study has been employed to investigate the effect of next-nearest-neighbours aluminium (NNN Al) atom on the acid strength of Brönsted acid site in Y zeolite. Additionally, the distribution of NNN Al atom was also studied. The obtained results show that thermodynamically, the favourable sites for location of NNN Al atom are the diagonal sites of the four-membered ring and meta-position of hexagon I. Furthermore, the increase of NNN Al atoms causes the nonlinear reduction of the strength of Brönsted acid sites. When the number of NNN Al atoms is greater than two, the increasing extent of acid strength is not obvious with the reduction in the number of NNN Al atoms. But the acid strength will increase linearly with the further reduce of the number of NNN Al atoms. Compared with deprotonation energy (ED), ammonia adsorption energy (Eads) could give a more reasonable measuring result for the acid strength.

Impact of surface arrangement and composition on ethylene adsorption over Pd–Ag surface alloys: a computational study

The adsorption of ethylene on three low-index Pd–Ag bimetallic surfaces, which are the (111), (100), and (110) facets, is investigated using gradient-corrected periodic density functional calculations with dispersion correction. The surfaces have been modeled by 5 layers of Pd atoms and different Ag atomic concentrations, allowing us to study ethylene adsorption from 100% Pd to 25% Pd on the surfaces. The adsorption energy and the geometry have been computed for different adsorption sites (on top of a Pd or bridging two Pd atoms) for different facets and Ag atomic concentrations. For bare Pd surfaces and their surface alloys, the bridge site is always found to be more stable than any other site. For the surface alloys, the local density of states, charges of ethylene and Pd atom, and differential electron density have been investigated to illustrate the importance of ligand and ensemble effects of the guest metal Ag atoms. The adsorption is weakened because of the ensemble effect when the surface Ag atomic concentration increases. The amount of electrons transferred to the ethylene molecules from the surface increases slightly when the concentration of the surface atomic Ag increases. The ligand effect becomes more significant when the surface is closer, and its effect is not the same for different surface facets.

Aromatization of n-Hexane Under Microwave Irradiation

Abstract The aromatization of n-hexane over HZSM-5 and ZnNi/HZSM-5 catalysts has been investigated using two different heating methods: microwave irradiation (MW) and conventional heating (CH). The results indicate that the aromatics and BTX yields under MW are higher than those under CH. n-Hexane aromatization mechanism under MW was similar to that under CH at the temperature below 673 K. However, the mechanism of n-hexane aromatization was different at the temperature from 673 K to 753 K. The higher the reaction temperature is, the more condensed-nucli aromatics are produced. Therefore, MW requires the lower reaction temperature when equal yields of aromatics and BTX are obtained.