Youwei Cheng

Synthesis of nanocrystalline lead chalcogenides PbE (E = S, Se, or Te) from alkaline aqueous solutions

Abstract Reaction of a sulfur, selenium, or tellurium alkaline aqueous solution and Pb(CH 3 COO) 2 ·3H 2 O aqueous solution produces nanocrystalline lead chalcogenides PbE (E = S, Se, or Te) with a cubic phase at low temperature under atmospheric pressure. The products are characterized through X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analysis. The average particle size is in the range 20–35 nm. The XPS analysis indicates that the stability of the product surface in air decreases in the order PbS, PbSe, and PbTe. An advantage of this synthesis method is that the PbE crystallizes well in the alkaline solution. The mechanism for the formation of the lead chalcogenides is discussed.

Characteristics of Coke Deposition Over a SAPO-34 Catalyst in the Methanol-to-Olefins Reaction

The deactivation of SAPO-34 catalyst in the methanol-to-olefins process has been studied at temperatures of 400 to 475°C. The catalyst activity keeps stable before a rapid deactivation occurs at a critical coke content. The analysis of retained coke species showed that methylbenzenes were the most abundant species at lower temperatures (400°C and 425°C), while polycyclic aromatics became the dominant species at 475°C. The growth in the retained coke species with increasing temperature comes from the enhanced reactivity of methylbenzenes and methylnaphthalenes at high reaction temperature, where methylnaphthalenes may function as another active reaction centers.

Synthesis of nanocrystalline marcasite iron ditelluride FeTe2 in aqueous solution

Abstract Reaction of an alkaline aqueous solution dissolving elemental tellurium and iron(II) complex Na 2 [Fe(EDTA)] aqueous solution produces nanocrystalline marcasite FeTe 2 at 140°C under atmospheric pressure. All peaks in the XRD pattern of the final product can be indexed to orthorhombic FeTe 2 with the cell constants a =5.31 A, b =6.29 A and c =3.86 A. TEM image of FeTe 2 nanocrystallites shows an average particle size of 25 nm with a spherical morphology. The tellurium alkaline solution, as a tellurium source, makes FeTe 2 crystallize well in aqueous solution. The use of iron(II) complex instead of iron(II) ion greatly reduced the amount of byproduct. The mechanism of the formation of iron ditelluride was discussed.

Solubilities of Isophthalic Acid in Acetic Acid + Water Solvent Mixtures

Abstract The solubilities of isophthalic acid (1) in binary acetic acid (2) + water (3) solvent mixtures were determined in a pressurized vessel. The temperature range was from 373.2 to 473.2K and the range of the mole fraction of acetic acid in the solvent mixtures was from x2 = 0 to 1. A new method to measure the solubility was developed, which solved the problem of sampling at high temperature. The experimental results indicated that within the temperature range studied, the solubilities of isophthalic acid in all mixtures showed an increasing trend with increasing temperature. The experimental solubilities were correlated by the Buchowski equation, and the calculate results showed good agreement with the experimental solubilities. Furthermore, the mixed solvent systems were found to exhibit a maximum solubility effect on the solubility, which may be attributed to the intermolecular association between the solute and the solvent mixture. The maximum solubility effect was well modeled by the modified Wilson equation.

Kinetics of Burning Side Reaction in the Liquid-phase Oxidation of p-Xylene

Abstract During the liquid-phase oxidation of p-xylene, over-oxidation of reactant, intermediates and solvent to carbon dioxide and carbon monoxide is generally known as the burning side reaction. Batch and semi-continuous experiments were carried out, and the experimental data of the burning side reaction were analyzed and reported in this paper. The results showed that the rates of burning side reactions were proportional to the rates of the main reaction, but decreased with the increasing concentrations of reactant and intermediates. The inter-stimulative and competitive relationship between the burning side reaction and the main reaction was confirmed, and the rates of the burning side reaction could be described with some key indexes of the main reaction. According to the mechanism of the side reactions and the kinetics model of main reaction which were proposed and tested in the previous papers, a kinetic model of the burning side reactions involving some key indexes of the main reaction was developed, and the parameters were determined by data fitting of the COx rate curves. The obtained kinetic model could describe the burning side reactions adequately.

Naphthalene-2,6-dicarb­oxy­lic acid–1-methyl­pyrrolidin-2-one (1/2)

The asymmetric unit of the title compound, C12H8O4·2C5H9NO, contains one half-molecule of naphthalene-2,6-dicarboxylic acid (NDA) and one molecule of 1-methylpyrrolidin-2-one (NMP): the NDA molecules lie on the crystallographic twofold rotation axes. In the crystal, the components are linked by strong O—H⋯O hydrogen bonds and C—H⋯O interactions.

Benzene-1,4-dicarboxylic acid-N,N-dimethyl-acetamide (1/2).

The asymmetric unit of title compound, C8H6O4·2C4H9NO, contains one half-molecule (an inversion centre in P21/n generates the other half of the molecule) of terephthalic acid (TA) and one molecule of N,N-dimethylacetamide (DMAC). The DMAC molecules are linked to TA by strong O—H⋯O hydrogen bonds.