Physicochemical and catalytic properties of CoAPO-5 and CoAPSO-5 molecular sieves

The physicochemical and catalytic properties of cobalt- and silicon-substituted AlPO-5 molecular sieves were studied by means of temperature-programmed reduction, temperature-programmed desorption of ammonia and the reaction of toluene disproportionation.     

Improvement of the hydrothermal stability of MCM-48 mesoporous molecular sieves

This is a review of our recent reports about improving the hydrothermal stability of MCM-48 mesoporous molecular sieves and the related works done by other groups. It presents the different effects of direct addition of various anions, including F^?, SO₄ ^2?, NO₃ ^? and Cl^?, on the improvement of the hydrothermal stability of MCM-48. The different effects of anions on the improvement of the hydrothermal stability and the critical factors influencing the formation of hydrothermally stable MCM-48 are also explained by careful analysis and discussion.     

A study of piperidinium structure-directing agents in the synthesis of silica molecular sieves under fluoride-based conditions

This study is a continuation of our efforts to understand the interplay in the self-assembly chemistry for formation of molecular sieves from guest organocations and inorganic silicon oxide. In this particular study we focus on the competitive interplay of the organocations and the synthesis cofactor fluoride anion. The anions play a key role in structure determination, as a function of net solution concentration. They compete with the role for the space-filling organocation in determining which molecular sieve host structure will be specified. In this study we look at this competition in the synthesis for a series of 33 different organocations derived from the piperidine ring system. Derivatives were prepared which both fixed substituents on the carbon and nitrogen centers on the ring. Results were discussed in terms of product selectivity from synthesis as a function of solution concentration for the reactants. A total of 17 different host topologies were found in this series, and a correlation was seen for (a) open-framework lattices (low framework densities) under the most concentrated reaction conditions and then (b) high framework density products once the conditions were more dilute. Some surprising synthesis differences are seen in comparing the performance of these structure directing agents (SDAs) in fluoride media vs hydroxide media (the more conventional environment for zeolite/molecular sieve syntheses involving silicate chemistry). Finally molecular modeling was used to understand some of the trends in product selectivity for closely related guest (SDA) candidates.     

Synthesis and some aspects of the formation mechanism of carbon structures under hydrothermal conditions

The formation of carbon structures upon the reactions of organic compounds with strong mineral acids under hydrothermal conditions was studied. The reactions were found to give amorphous carbon, microcrystalline graphite, nanodiamonds, diamond-like carbon, diamonds, C₆₀ and C₇₀ fullerenes, and carbolite. Hydrocarbons of various compositions including aromatics and naphthenes were detected among the reaction products. A possible mechanism of the formation of carbon structures with sp ² bond hybridization under hydrothermal conditions was proposed.     

The crystallization of anatase and the conversion to bronze-type TiO2 under hydrothermal conditions

When the anatase form of TiO₂ was heated at a constant rate of 6°C/min to 450°C it crystallized from hydrated amorphous TiO₂ gel at 170°C in pure water or at <150°C in NaOH solutions. The uptake of Na⁺ ions into crystallized anatase affected the reactions subsequent to this initial crystallization while only anatase crystals continued to grow with increasing temperature in pure water. Immediately after the nearly amorphous second stage at 325°C, conversion from colloidal anatase particles to square sheet-shaped bronze-type TiO₂ crystals began at 350°C and was complete at 425°C in 0.5 M NaOH. This conversion was considered to proceed via crystallographic shear rather than via dissolution and precipitation since this also happened with thermal treatment to 700°C in air.     

Structure-inheriting solid-state reactions under hydrothermal conditions

We have explored several structure-inheriting solid-state reactions (SISSRs) under hydrothermal conditions for syntheses in the Co-Mo-O system. And we found an interesting hydrothermal SISSR from CoMoO₄·3/4H₂O to high-pressure (hp-) phase of CoMoO₄, which enabled us to considerably reduce the severe conditions for the synthesis of hp-CoMoO₄. As similar hydrothermal SISSRs are expected to be useful tools for material syntheses, we also briefly discuss them as a means of developing novel material syntheses and designs.     

An intrinsic synthesis parameter governing the crystallization of silico(zinco)aluminophosphate molecular sieves

One of the most fundamental but yet unanswered questions in the synthesis of zeolites and zeolite-like materials is whether or not any parameter controlling the microporosity of the crystallized product from synthesis mixtures with feasible chemical compositions exists. Here we report that an experimentally optimized parameter (ca. 3.3 ≤ MOH/P₂O₅ ≤ 5.3, where M is alkali metal ions) is the criterion bringing about the successful formation of various high-charge-density silicoaluminophosphate (SAPO) and zincoaluminophosphate (ZnAPO) molecular sieves, without the aid of organic structure-directing agents. The materials obtained using this empirical concept include SAPO molecular sieves with CHA and LTA topologies, as well as a SAPO FAU/EMT intergrowth, and ZnAPO ones with CZP and SOD topologies. This study demonstrates the existence of an essential factor determining not only phase selectivity but also microporosity (0.3–2 nm) in the synthesis of zeotypes with charged frameworks which may offer interesting opportunities for more efficiently producing novel zeolite structures and/or compositions.

The existence of an essential parameter (ca. 3.3 ≤ MOH/P₂O₅ ≤ 5.3, where M is alkali metal ions used as structure-directing agents) determining phase selectivity and microporosity in the synthesis of zeotypes with charged frameworks is demonstrated.     

Formation of carbon phases under hydrothermal conditions

The formation of carbon phases by reacting formaldehyde with sulfuric acid under hydrothermal conditions was studied. The final products of the reaction were found to be amorphous carbon, diamond-like carbon, α- and β-graphite phases, fullerenes C₆₀ and C₇₀, fullerites, carbolite, and chaoite. Hydrocarbons of various compositions were detected in reaction products, namely cyclic hydrocarbons, including aromatic ones, and naphthene hydrocarbons. A formation scheme is suggested for carbon structures.     

Selective capture of phosphopeptides by hierarchical Ti-aluminophosphate-5 molecular sieves

Hierarchical Ti-aluminophosphate-5 molecular sieves templated by glucose have been synthesized and applied as a potential adsorbent for the first time to selectively capture phosphopeptides from complex peptide mixtures prior to MALDI-TOF MS analysis.     

Issues in the synthesis of crystalline molecular sieves: towards the crystallization of low framework-density structures.

Fundamental and practical interest in crystalline, microporous, molecular sieves is largely a direct consequence of the fact that their bulk properties can be manipulated through variations in atomic structure. This correspondence between the macroscale and the atomic scale is due to the uniformity of these crystalline materials. Control of the atomic structure therefore is of extreme importance, and is the thesis of this Review. Synthesis mechanisms and the parameters that can direct the crystal assembly pathway and the ultimate product formed are discussed and rationalized.     

分步晶化法合成ZSM-5/SAPO-5复合材料

通过分步晶化水热处理的方式合成了ZSM-5/SAPO-5复合材料。研究了两种分子筛凝胶的混合方式、调节ZSM-5母液的酸类型、SAPO-5凝胶组成以及晶化时间对复合材料形成的影响。实验结果表明,简单将两种分子筛的合成凝胶混合不能得到复合材料。采用H₂SO₄调节ZSM-5合成母液的pH值,在ZSM-5与SAPO-5理论质量比为3.5、SAPO-5凝胶中P₂O₅与Al₂O₃摩尔比为1.2的条件下可以得到ZSM-5/SAPO-5复合材料。但样品中含有少量无定形物质,这些无定形通过延长晶化时间并不能完全消除。     

UV Raman spectroscopic study on the synthesis mechanism and assembly of molecular sieves

In the past decade, UV Raman spectroscopy has become a powerful technique for the characterization of the synthesis mechanism and assembly of molecular sieves. Ultraviolet excitation avoids fluorescence that plagues visible Raman spectroscopy and concurrently enhances the Raman signal because of the short wavelength of excitation and the resonance Raman effect. The advances of UV Raman spectroscopy, UV resonance Raman spectroscopy and in situ UV Raman spectroscopy and their applications to the characterization of zeolite assembly mechanisms are provided in this tutorial review. Using UV Raman spectroscopy, the synthesis mechanism of zeolites, including the identification of primary units, assembly through key intermediates, transition metal species, and the roles of the organic templates in framework formation have been elucidated, and are discussed herein.     

Bitumen upgrading under solvothermal/hydrothermal conditions

Bitumen is known as a mixture of organic liquids which has great importance to the chemical industry because of its great variety of special properties, which has favored the development of a wide field of applications. Bitumen has been mainly obtained as a residue of the petroleum refining process. Recently, the development of a process has been proposed to recover chemical resources from bitumen that can accomplish the destruction of the bitumen to produce harmless but useful compounds. Water at hydrothermal conditions is considered a promising and an environmentally acceptable solvent for a wide variety of chemical reactions such as organic syntheses and decomposition of hazardous waste into harmless compounds. In these works, water at supercritical conditions was applied as a solvent for upgrading of bitumen. The experiments were conducted at a temperature of 673 K and at various reaction pressures. The effect of pressure and reaction time on the decomposition process is presented. The chemical species in the aqueous products were analyzed by gas chromatography?Cmass spectrometry and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy. Ultimate analysis of solid residue was also conducted using a CHN analyzer. The results showed that the amounts of bitumen-derived compounds formed increased with increasing reaction time. In addition, the study of bitumen model compounds by using a batch reactor was also conducted. Furthermore, this method could become an efficient method for upgrading bitumen into harmless compounds with a high yield of valuable chemical intermediates on the basis of the experimental results.     

Hydrolysis of acetals in water under hydrothermal conditions

A simple method for the hydrolysis of acetals and ketals was accomplished in neutral water or aqueous media by hydrothermal treatment without using acidic reagents. The deacetalization reaction was effectively accelerated in the presence of calcium chloride. Because no acidic catalysts were employed, neutralization of the reaction mixture was not necessary after the reaction. This sequence was successfully applied to the hydrolysis of chitosan, a biodegradable polyaminosaccharide.     

Rotor-like ZnO by epitaxial growth under hydrothermal conditions

Rotor-like ZnO was grown from a mixture of rod-like ZnO powder and a saturated Zn(OH)(4)(2-) solution under moderate hydrothermal conditions at 100 degree C, in which the precursor rod-like ZnO crystal plane acts as a matrix core, and the branched nanorods showed fast epitaxial growth on the six directions around the prism core.     

酸性分子筛上甲醇催化转化反应机理研究进展

概括了甲醇转化反应机理实验和理论研究方法,介绍了甲醇脱水预平衡阶段的主要机理模型和实验理论依据,重点综述了C-C键形成过程中涉及到的直接机理和"烃池"机理的实验与理论研究进展和存在的问题,探讨了分子筛孔道结构对"烃池"物种结构和反应历程的影响.     

The molecular mechanism of low-temperature decomposition of hydrogen sulfide under conjugated chemisorption-catalysis conditions

The molecular mechanism of interaction of two hydrogen sulfide molecules with the (Co^III-H_o)₂S₂(SH₂)₄ model active center containing occluded hydrogen was studied by the density functional theory method with the B3P86 hybrid exchange-correlation functional. The reaction was found to occur in the following elementary steps: molecular adsorption of hydrogen sulfide ? dissociative chemisorption ? S-S bond formation in the surface intermediate {2Co^III ? (μ-S₂) + 2H(ads)} with the release of the first hydrogen molecule into the gas phase H₂(g) ? the release of the second hydrogen molecule into the gas phase H₂(g) ? the formation of cyclooctasulfur in the reaction 4S₂(ads) → S₈(ads). The first three steps occur spontaneously at room temperature, the thermodynamic driving force of the process being the stoichiometric reaction of S-S bond formation at the stage of conjugated chemisorption of two hydrogen sulfide molecules on two adjacent metal ions with the release of the first hydrogen molecule into the gas phase. The catalytic cycle is terminated by the recombination of molecular sulfur S₂ into cyclooctasulfur S₈ in the adsorption layer and the release of the second hydrogen molecule into the gas phase.     

Solubility of Li2WO4 under hydrothermal conditions

Experimental studies of water solubilities of Li₂WO₄ at temperatures up to 450°C and pressures up to 147 MPa show that this salts with water forms a type 2 binary system, where the solubility of the salt under the vapor pressure decreases as temperature rises to end at the critical end-point p (g=l-s) near the H₂O critical temperature. High-temperature Li₂WO₄ solutions are shown to not react with silica, but they cause corrosion of metallic walls of an autoclave accompanied with gas evolution and formation of dark-colored solid corrosion products.