The role of Rh on Pt-based catalysts: structure sensitive NO + H2 reaction on Pt(110) and Pt(100) and structure insensitive reaction on Rh/Pt(110) and Rh/Pt(100)

The catalytic activity of the Pt(110) surface for the reaction of NO + H₂ was much less than that of the Pt(100) surface. However, the catalytic activity of the Rh deposited Pt(1l0) surface was almost equal to that of the Rh deposited Pt(100) surface. That is, the catalytic reaction of NO + H₂ on Pt(110) and Pt(100) surfaces is highly structure sensitive, but it changes to structure insensitive by the deposition of Rh atoms. These results are rationalized by formation of an active overlayer on the Pt(110) and Pt(100) surfaces, which is very analogous to the Rh-O/Pt-layer formed on Rh/Pt(100), Pt/Rh(100) and Pt-Rh(100) alloy surfaces during catalysis. The formation of the common overlayer of Rh-O/Pt-layer during catalysis is responsible for the structure insensitive catalysis of Rh deposited Pt-based catalysts, which is an important role of Rh in a three way catalyst.     

Highly Reactive β-Dicalcium Silicate: I, Hydration Behavior at Room Temperature

The hydration behavior at 25°C of β-dicalcium silicate synthesized from hillebrandite (Ca₂,(SiO₃)(OH)₂) at 600°C was studied over a period of 224 d. The hydration rate of the β-dicalcium silicate having fibrous crystals with specific surface area of 7 m²/g is extremely rapid. For water/solids ratios of 0.5 and 1.0, the hydration reaction is completed in 28 and 14 d, respectively. The hydrate contains almost no Ca(OH)₂, and its Ca/Si ratio is close to 2. SEM observations indicate that the hydrate forms an outer shell on the surface of β-dicalcium silicate and grows inwards. The silicate anion structure is considered to consist of dimers and single-chain structures from ²⁹Si MAS NMR. Variations of physical properties of press-formed bodies have also been discussed.     

Behavior of chlorophyll derivatives in canola oil processing

Chlorophyll derivatives in canola oil were analyzed quantitatively by reversed-phase high-performance liquid chromatography without any pretreatment. The main components were pheophytin (pheo) a and b and pyropheophytin (pyro) a and b. The factors affecting the types and concentration of chlorophyll derivatives in oil have been investigated during seed preparation, expelling, extraction, degumming and alkali-refining processes. Bleaching tests of alkali-refined canola oil with activated earth indicated the adsorption of each derivative to decrease in the following order: pheo a > pyro a >> pheo b > pyro b. In bleaching with activated carbon, however, the following order was observed: pyro b > pheo b > pheo a > pyro a.     

AlON-SiAlON复合材料的制备及特性

为提高AlON陶瓷材料的抗氧化性能 ,制备了AlON -SiAl7O2 N7复相材料。在 1 75 0℃、0 .5MPa的N2 气氛中 ,保温 2h烧成不同Al2 O3/AlN/Si3N4配比的原料得到不同AlON/SiAl7O2 N7比的复相材料。因为在烧结SiAl7O2 N7的过程中 ,蒸发-凝聚的同时伴随着SiO气体的挥发 ,因此很难得到致密的AlON -SiAl7O2 N7复相材料。研究了AlON -SiAl7O2 N7复相材料在 1 30 0℃、空气中的抗氧化性能 ,同时作为比较 ,研究了相同条件下单相的AlON材料的抗氧化性能。结果表明 ,AlON -SiAl7O2 N7复相材料显示了较之单相的AlON陶瓷材料更好的抗氧化性能 ,这是因为氧化过程中所形成的含玻璃相的表面氧化层抑制了氧的向内扩散所致。     

Electrochemical copolymerization of aniline and aniline-2,5-disulfonic acid

Electrochemical copolymerization of aniline and aniline-2,5-disulfonic acid (ADSA) was carried out in HCl solutions. The presence of ADSA inhibited significantly the growth of polyaniline (PAn), although the voltammetry of the copolymer was still similar to that of conventional PAn. As the ADSA concentration increased, the deposition rate of the copolymer decreased rapidly and finally no solid film was deposited on the electrode surface. When the ADSA concentration was lower than ˜ 5 mM, the depression effect of ADSA on the growth rate of the copolymer is mainly due to its stronger adsorption at the electrode surface. For higher ADSA concentrations, the inhibiting effect of ADSA was dominated by its termination effects, which led to more soluble oligomers and in turn resulted in lower deposition efficiency. Electrolysis of ADSA solution might result in a water-soluble fully sulfonated PAn.     

Sinterability of β-Calcium Orthophosphate Powder Prepared by Spray-Pyrolysis

Mixed solutions of Ca(NO₃)₂ and (NH₄)₂HPO₄ with Ca/P = 1.50 were spray-pyrolyzed at 600°C to produce β-calcium orthophosphate (β-Ca₃(PO₄)₂) powder; the spray-pyrolyzed powder was ground and then calcined at 600°C for 1 h. The best crystalline β-Ca₃(PO₄)₂ powder was obtained from the solution with 1.80 mol.L^–1 Ca(NO₃)₂, 1.20 mol.L^–1 (NH₄)₂HPO₄. The resulting powder was composed of primary particles with sizes of <0.5 μm. Dense β-Ca₃(PO₄)₂ ceramics with a relative density of 96.1% could be fabricated by firing this compressed powder at 1070°C for 5 h.     

碳复合耐火材料

分析了由氧化物—石墨—非氧化物—结合剂组成的含碳耐火材料在加热过程中的作用机理，论述了结合剂对气孔形成的影响、气孔对含碳耐火材料氧化的影响、非氧化物的作用及行为。通过分析耐火材料在使用过程中的反应及微观结构的变化，可对耐火材料的组成和结构进行合理的设计。     

Gasification of coal impregnated with catalyst during pulverization: effect of catalyst type and reactant gas on the gasification of Shin-Yubari coal

Shin-Yubari coal was impregnated with several catalysts of different chemical types during pulverization. The resultant system was more homogeneous and reactive than systems prepared by impregnation of coarse coal. The relative activities of the catalysts were determined as a function of gasification temperature, catalyst loading and gasifying agent. The activity sequence in steam was K ? Ba ? Ni ? Fe ? coal ash. Each catalyst had a unique reaction profile. For example, using steam the specific rate or the rate per remaining fixed-carbon weight decreased with time for the iron-catalysed reaction, whereas it increased for the potassium-catalysed reaction. A similar order of activity was observed in carbon dioxide, but a different sequence was noted for the hydrogenation reaction. Transition metal catalysts were the most active. The hydrogenation reaction profiles were different from the oxidation profiles.     

Ce4+Ce3+ redox equilibrium in Na2O-B2O3 melts by linear sweep voltammetry

New semi-empirical equations were presented to study the redox equilibria of transition metal ions in molten oxides by linear sweep voltammetry. These equations gave the relation between the peak potential and the polarographic half-wave potential, and contained the Randles-Sevcik equation as an extreme case. The measurements of $\text{Ce}{}^{\mathrm{4+}}\text{Ce}{}^{\mathrm{3+}}$ equilibrium in several Na₂O-B₂O₃ melts were used to verify the equations. The agreement between the electrochemically estimated value of the equilibrium and the other estimated from the chemical analysis of the quenched sample was quite satisfactory. The relation between the $\text{Ce}{}^{\mathrm{4+}}\text{Ce}{}^{\mathrm{3+}}$ equilibrium and the composition of the melt was discussed as the functions of the basicity.     

Effect of fiber surface modification on the mechanical properties of sisal fiber‐reinforced benzoxazine/epoxy composites based on aliphatic diamine benzoxazine

Sisal fibers were incorporated into a mixture of benzoxazine and bisphenol A type epoxy resins to form a unidirectionally reinforced composite. Surface modifications of the sisal fibers were carried out with sodium hydroxide, γ‐aminopropyltrimethoxysilane, and γ‐glycidoxypropyltrimethoxysilane. The surface treatments led to changes in the morphology, chemical groups, and hydrophilicity of the fibers. The effect of the fiber surface treatments on the fiber–matrix interfacial adhesion and mechanical properties of the composites were also studied. The results showed that surface treatments with sodium hydroxide and a silane coupling agent led to improved fiber–matrix adhesion; this could be seen in the scanning electron micrographs of the fractured surfaces from mechanical testing and the reduction in the impact strength of the composites made from treated fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007