New approach to the preparation of catalysts for the oxidative coupling of methane

A new approach to the preparation of systems that exhibit catalytic activity in the oxidative coupling of methane (OCM) is considered. With the use of ferrospheres separated from power-generation ashes from different sources as an example, it was demonstrated that OCM catalysts can be prepared by the crystallization/solidification of oxide melts with the formation of microspherical particles. The dependence of activity and selectivity for the oxidative reforming of methane on the ferrospheres containing from 36.2 to 92.5 wt % Fe₂O₃ into the products of deep oxidation and OCM was studied. It was found that deep oxidation reactions on ferrospheres with Fe₂O₃ contents higher than 85% were suppressed, and the main reaction path of CH₄ conversion was its oxidative coupling with the formation of C₂ products (with selectivity to 60% at 750°C); moreover, the selectivity for C₂ formation in this region was proportional to the concentration of Fe₂O₃. Phases responsible for the catalytic conversion of methane into CO _x and OCM products were considered, and it was shown that the catalytic activity and selectivity of the oxidative transformation of CH₄ on ferrospheres is determined by the position of the point that corresponds to their composition on a phase diagram of CaO-Fe₂O₃-SiO₂.     

Effect of the production conditions on the size and magnetic characteristics of iron sulfide Fe<Subscript>3</Subscript>S<Subscript>4</Subscript> nanoparticles

It was shown that the reaction of the trinuclear complex [FeFe₂O(CH₃CO₂)₆(H₂O)₃]·₂H₂O with thiourea in tetraethylene glycol leads to the formation of nanoparticles of thiospinel Fe₃S₄, the size of which depends on the reaction conditions. It was established that the formed thiospinel particles exhibit superparamagnetic characteristics. It was shown that the size of the nanoparticles has an effect on their magnetic characteristics.     

Specifics of adsorption and chemical processes on the surface of gamma-irradiated vanadium dioxide

The effect of γ-irradiation on the electrophysical properties and processes of thermal desorption of water from the surface of vanadium oxides V₂O₃-VO_2?δ-VO_2+δ-V₂O₅ were studied by the thermal analysis and electric conductivity techniques. It was shown that the amount of adsorbed water on the surface and the phase composition of the surface changed under exposure to low doses. The observed effects for vanadium oxides as semiconductors were correlated with analogous processes for alumina as a dielectric. It was found that the surface conductivity in irradiated VO_2?δ samples during the chemical reaction of ethanol with benzoic acid adsorbed after irradiation was substantially higher than that in their unirradiated counterparts. It was assumed that irradiation enhances the metal-semiconductor phase transition on the VO_2?δ surface during the chemical reaction.     

金属酞菁化合物在TiO2表面的分散研究

Dispersion of copper(Ⅱ) phthalocyanine (CuPc), copper(Ⅱ) phthalocyaninesulfonate (CuPcS) and cobalt(Ⅱ)phthalocyaninetetrasulfonate (CoPcTS) on the surface of titanium dioxide was investigated by XRD, XPS, FT-IR and UV-Vis techniques. Results show that interaction between CuPc and TiO2 was very weak and CuPc was difficult to disperse on the surface of the support. While partly sulfurized CuPcS could be dispersed on the surface of support through sulfo-groups and its dispersion capacity was determined to be 0.085 g CuPcS/g TiO2. Completely sulfurlzed CoPcTS could also be dispersed on the surface of TiO2 as a monolayer and its dispersion capacity was 0.12 g CoPcTS/g TiO2. Interactions of the sulfo-groups as well as the electrons of CoPcTS with the surface of TiO2 could be evidenced by FT-IR characterization. Therefore, it was suggested that CoPcTS molecules be adsorbed on the surface of TiO2 in a flat-lying mode while CuPcS in a slanting one. UV-Vis spectra show that the dispersed CuPcS and CoPcTS molecules exist in both forms of monomers and dimers.     

Effect of promoters on the catalytic performance of Ni/Al2O3 catalyst for partial oxidation of methane to syngas

The effect of promoters such as Ce, La and Ca on catalytic performance of Ni catalyst was measured in a continuous fixed bed reactor. The effect of promoters on Ni/a-Al₂O₃ catalyst is more significant than on Ni/g-Al₂O₃ catalyst. Ce was proved to be the best promoter among the three promoters tested and the optimum loading of Ce was 1%. The catalyst was characterized by TG, XPS, TPR and XRD techniques. TPR results showed that Ce can improve the reducibility of the Ni/Al₂O₃ catalyst. XRD results indicated that Ce was highly dispersed when its loading was low, but at higher loading it was crystallized into bulk CeO₂, thus, decreased the catalytic activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

聚合物对锆钛酸铅纳米晶须形貌的影响

本工作以(C₄H₉O)₄Ti、Pb(NO₃)₂和ZrOCl₂·8H₂O为主要原料，采用改进的水热方法合成了锆钛酸铅(PZT)纳米晶须，并考察了聚合物对锆钛酸铅晶体形貌的影响。结果表明，聚合物对于控制晶体的取向生长起着关键性作用。另外还初步探讨了不同浓度以及不同聚合物对晶体形貌的影响机理，认为聚合物起着覆盖和螯合的作用，进而影响晶体的取向生长趋势，形成纳米线。     

Role of oxidizers in the active dissolution and passivation of metals

It was established that addition of hydrogen peroxide to a solution of sulphuric acid leads to acceleration of the active dissolution of chromium and to the shift of its passivation potential in negative direction. Similar data were obtained for Fe-28% Cr alloy in H₂SO₄ solution containing H₂O₂ and for iron in sulphuric acid with K₂Cr₂O₇ additions. The conclusion was made that depending on the potential the molecules of oxygen-containing oxidizers can undergo different transmissions on the surface of the metal, including transformations connected with the direct participation of the oxidizer in the anodic dissolution of the metal or in the building of inhibiting or passivating layers on the metallic surface.     

Activity of MoSe2/Al2O3 catalysts in decomposition of thiophene and selenophene

The rate of thiophene decomposition was shown to be independent of the type of chalcogens used in catalysts MoX₂/Al₂O₃, where X = S, Se. On the contrary, the rate of selenophene decomposition was shown to be higher on catalysts MoSe₂ than that on MoS₂. This observation suggests that the decomposition proceeds on anion vacancies. The decomposition of either thiophene over MoSe₂ or selenophene over MoS₂ results in the formation of partially substituted chalcogenides. At that, the molar ratios of the substituted chalcogen to Mo were shown to coincide in both cases. The fact that the rate of the thiophene decomposition does not depend on the degree of anion exchange indicates that the decomposition is not associated with hydrogenolysis.     

Living cationic polymerization of isobutyl vinyl ether by the carboxyl group of the carbon black/zinc chloride initiating system

The effect of zinc chloride (ZnCl₂) on the cationic polymerization of isobutyl vinyl ether (IBVE) initiated by carboxyl groups on a carbon black surface was investigated. Although the polymerization of IBVE was initiated by carboxyl groups on the surface, the rate of polymerization was small and the molecular weight distribution (MWD) of poly IBVE was very broad. The rate of the polymerization was found to be drastically increased, and 100% monomer conversion was achieved in a short time by the addition of ZnCl₂. The number-average molecular weights (M_n) of the polyIBVE were directly proportional to monomer conversion in the polymerization initiated by the carbon black/ZnCl₂ system. By addition of the monomer at the end of the first-stage polymerization, the added monomer was smoothly polymerized at the same rate as in the first stage. The M_n of the polymer was in excellent agreement with the calculated value, assuming the polyIBVE chain forms per unit carboxyl group on the surface and MWD was narrow (M_w/M_n = 1.2 ～ 1.3). Based on the results, it is concluded that carbon black/ZnCl₂ system has an ability to initiate the living cationic polymerization of IBVE. Furthermore, it was found that polyIBVE was grafted onto the carbon black surface after the quenching of the living polymer with methanol. © 1995 John Wiley & Sons, Inc.     

Effect of ultra-fine gold particle addition to metal oxides in ethylene oxidation

Oxidation of ethylene was carried out over alumina-supported metal oxide catalysts and highly dispersed gold catalysts, respectively, under atmospheric pressure. The ethylene was completely oxidized to produce carbon dioxide and water with both metal oxide and gold catalysts. The activity of gold catalyst prepared by deposition method was much higher than that of supported metal oxide catalysts. Ultra-fine gold particles on Co₃O₄ were more active than on Al₂O₃. Fe₂O₃/Al₂O₃ and MnO₂/Al₂O₃ catalysts were more active than MoO₃/Al₂O₃ catalyst. The activity of the supported metal oxide catalysts was greatly enhanced by addition of gold particles. It was therefore considered that gold particles promote dissociative adsorption of oxygen and the adsorbed oxygen reacts with adsorbed ethylene on support adjacent to the active site.     

Elucidation of sulfur mobility on Cr, Mo and W-based catalysts in hydrodesulfurization using a35S pulse tracer method

In hydrodesulfurization of radioactive³⁵S-labeled dibenzothiophene catalyzed by CrO₃/Al₂O₃, it was found that sulfur on sulfided CrO₃/Al₂O₃ was more labile than those on MoO₃/Al₂O₃ and WO₃/Al₂O₃, while the amount of sulfur was less than that on MoO₃/Al₂O₃. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

Degradation of perfluorinated sulfonic acid films: An in-situ infrared spectro-electrochemical study

The in-situ Fourier transform infrared (FTIR) spectro-electrochemical method was used to evaluate the degradation mechanism of perfluorinated sulfonic acid (PFSA) polymer for the first time. The effect of H₂O₂ concentration in Fenton's reagent on the PFSA film degradation was studied. It was found that the effect of the H₂O₂ concentration on the chemical degradation of the PFSA film was limited, whereas, the electrochemical degradation was obviously enhanced at higher H₂O₂ concentrations. The chemical degradation of PFSA film in Fenton's reagent was similar to that in pure H₂O₂ solution. However, the results indicated that the electrode potential is the dominating factor affecting the degradation of the PFSA film. It is clear that the electrochemical degradation of PFSA film in Fenton's reagent is more serious than that in pure H₂O₂ solution. Moreover, it is indicated that the main cause of the membrane degradation is the instability of the backbone of the polymer chain under electrochemical conditions and secondarily the loss of sulfuric groups in the side-chains. It is concluded that the in-situ FTIR spectro-electrochemical method could be used to evaluate more objectively the degradation of the polymer film.     

Sorption of radioactive technetium on pyrrhotine

The sorption behavior of technetium on pyrrhotine was studied with batch experiments and diluted sulfuric acid (less than 2.88 mol/l) was used to dissolve the technetium adsorbed on pyrrhotine. A significant sorption of technetium on pyrrhotine was observed under aerobic and anaerobic conditions, and the sorption on the mineral was supposed to be due to the reduction of TcO₄ ^- to insoluble TcO₂ ^.nH₂O. Sorbed technetium on the mineral could be desorbed by diluted sulfuric acid. The maximum desorption ratio under aerobic conditions was much higher than that of under anaerobic conditions, meanwhile, the desorption rates under anaerobic conditions were higher than that of under aerobic conditions in the initial stage of the experiments.     

Number of surface redox sites of V-Sb-O catalysts

The NARP technique was applied for the measurement of surface redox sites of V-Sb-oxide catalysts. The profile of produced nitrogen in the NARP measurement was composed of two parts; the initial sharp peak and the tailing part, those represented the contribution of surface redox sites and regeneration step of the redox sites with lattice oxygen, respectively. The surface concentration of redox sites determined from the initial sharp peak was almost equivalent to the surface concentration of vanadium ions above surface Sb/V ratio of 1.0. The role of V-O-Sb sites on VSbO₄ surface as redox sites was suggested. The tailing part was broader than that of V₂O₅ at the same temperature range because of the faster regeneration step relative to that in V₂O₅. The surface concentration and the regeneration of redox sites strongly depend on the preparation method.     

The formation of γ‐crystal in long‐chain branched polypropylene under supercritical carbon dioxide

The crystallization behavior of long‐chain branched (LCB) polypropylene (PP) in the supercritical carbon dioxide (scCO₂) atmosphere was investigated to show the influences of LCB and CO₂ on the formation of γ‐crystal. The crystallization experiments were performed in CO₂ atmosphere with the pressure from 1.3 to 10.4 MPa and temperature between 90 and 130 °C. The effects of LCB level, CO₂ pressure, and crystallization temperature on the content of γ‐crystal were investigated. The results showed that the influence of LCB on the formation of γ‐crystal was obvious when PP was crystallized in CO₂. The content of γ‐crystal increased with LCB level and reached a maximum of 88.2%. It could be explained that, as LCB increased the chainfolding energy of PP molecular chain and hindered it from folding back into crystal lamella, which made the formation of γ‐crystal easier. However, CO₂ was the key factor in the formation of γ‐crystal, and the influence of CO₂ on γ‐crystal was much significant than that of LCB. It was believed that the increase of free volume after dissolving of CO₂ in PP was helpful in the formation of γ‐crystal. It was found that the content of γ‐crystal increased almost linearly with CO₂ pressure (CO₂ content), and the contribution of CO₂ to γ‐crystal increased with pressure, while that of LCB increased with temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 441–451, 2008     

Enhanced Photocatalytic Activity of Titanium Dioxide Supported on Hexagonal Mesoporous Silica at Lower Coverage

The photocatalytic activities of titanium dioxide (TiO₂) supported on hexagonal mesoporous silica (HMS), zeolite Y (NaY) were investigated by using the photodegradation of 2,4,6-trichlorophenol (TCP) as test reactions. It was found that the photocatalytic activity of TiO₂ on HMS was much higher than that of TiO₂ powders, and that of TiO₂ on NaY. It was also found that TiO₂/HMS had maximal photocatalytic activity at a lower Ti content. The larger the pore size of HMS used as the support of TiO₂, the better the photocatalytic activity of TiO₂ for degradating of organic pollutant. These observations suggested that the supported structure was a main factor responsible for enhancement of the photocatalytic activity of TiO₂. Characterization of the samples by TEM, XRD, BET, and UV-vis diffuse reflectance spectra indicated that the structures of HMS and TiO₂ were confirmed and TiO₂ did not enter into the HMS framework and was formed as nanoparticles on all supports.     

纳米TiO2有机表面改性的研究

利用硅烷偶联剂(KH-550)对表面包覆氧化硅的金红石相纳米TiO₂进行了有机表面改性。采用红外光谱(IR)、X射线光电子能谱(XPS)、热分析(TG-DTA)、BET、透射电镜(TEM)、润湿性和分散性实验等对表面改性前后的纳米TiO₂进行了表征。红外光谱和X射线光电子能谱表明，KH-550以化学键合的方式结合在纳米TiO₂的表面，并形成了有机包覆层。经测量，纳米TiO₂表面的KH-550的质量分数约为2.0%。讨论了产生KH-550理论包覆量与实际包覆量差异的原因。TEM、TG和BET得出的结果显示，在纳米TiO₂有机表面改性过程中存在明显的团聚现象，改进分散纳米TiO₂的方法是提高有机改性效果的关键。润湿性实验和分散性实验表明，经KH-550表面改性的纳米TiO₂同时具有亲水性和亲油性。     

Active component of supported vanadium catalysts in the selective oxidation of methanol

The structure of catalysts based on vanadium oxide supported on different oxides (SiO₂, γ-Al₂O₃, ZrO₂, and TiO₂) was investigated. Their catalytic properties in the selective oxidation of methanol in a temperature range of 100–250°C were studied. It was shown that the nature of the support determines the structure of the oxide forms of vanadium. The supporting of vanadium on SiO₂ and γ-Al₂O₃ leads to the preferred formation of crystalline V₂O₅; the surface monomeric and polymeric forms of VO_x are additionally formed on ZrO₂ and TiO₂. It was established that the crystalline V₂O₅ oxide is least active in the selective oxidation of methanol; the polymeric forms are more active than monomeric ones. The mechanism of the selective oxidation of methanol to dimethoxymethane and methyl formate on the vanadium oxide catalysts is considered.     

Role of sodium decoration on the methane storage properties of BC3 nanosheet

First-principles calculations including dispersion correction are carried out to investigate pristine and Na-decorated graphene-like BC₃ (h-BC₃) for their application as methane storage materials. Structural optimization shows that the methane is physisorbed on the pristine sheet via van der Waals forces with adsorption energy of ?2.7 kcal/mol. It was found that unlike the pristine graphene, sodium decorated sheet can effectively interact with the CH₄ molecule, so that each metal atom bound on sheet may adsorb up to four CH₄. Furthermore, no bond dissociation was observed for the adsorption of CH₄ on Na-decorated h-BC₃, which means that decorated sheet can act as a storage device for methane safety storage. The results indicate that decoration of the Na atom on surface of sheet induces significant changes in electronic properties of the sheet and its E _g is unchanged after adsorption of CH₄ molecules. Theoretical methane storage capacity of Na-decorated BC₃ nanosheet could approach 18.1 wt%.     

Investigation of opto-dielectric properties of Ti-doped Ga2O3 thin films

Several Ti-incorporated Ga-oxide (Ga₂O₃) thin films with different amounts of Ti contents have been prepared by vacuum evaporation method on glass and silicon substrates. The Ti incorporation level was measured with energy dispersion X-ray spectroscopy (EDX) method. The crystalline structure of the prepared films was determined with X-ray diffraction method. Experimental data indicate that Ti⁴⁺ ions doped in host Ga₂O₃ form solid solutions (SS) even with so large Ti% content ∼10.4% wt. All the prepared solid solutions have the known orthorhombic (ɛ-phase) phase of Ga₂O₃. The doping controls the optical and electrical properties of the host Ga₂O₃. It was found that the bandgap of the prepared undoped Ga oxide is 5.23 eV, which was decreased monotonically with increasing of Ti doping level so that it is possible to engineer the bandgap. Furthermore, the electrical measurements show that with Ti doping, it is possible to turn the high-k Ga oxide into low-k dielectric material. The optical sensitivity of the capacitance, dissipation factor, and ac-conductance of the Ga₂O₃:Ti films grown on Si was studied as a function of Ti-doping level. It was observed that the prepared Ga₂O₃:Ti film with 6–10% doping level has the highest photosensitivity among the other samples.