Inhibiting and deactivating effects of water on the selective catalytic reduction of nitric oxide with ammonia over MnOx/Al2O3

The effect of water on the selective catalytic reduction (SCR) of nitric oxide with ammonia over alumina supported with 2–15 wt.-% manganese oxide was investigated in the temperature range 385–600 K, with the emphasis on the low side of this temperature window. Studies on the effect of 1–5 vol.-% water vapour on the SCR reaction rate and selectivity were combined with TPD experiments to reveal the influence of water on the adsorption of the single SCR reactants. It turned out that the activity decrease due to water addition can be divided into a reversible inhibition and an irreversible deactivation. Inhibition is caused by molecular adsorption of water. TPD studies showed that water can adsorb competitively with both ammonia and nitric oxide. Additional kinetic experiments revealed that adsorbed ammonia is present in excess on the catalyst surface, even in the presence of water. Reduced nitric oxide adsorption is responsible for the observed reversible decrease in the reaction rate; the fractional reaction order changes from 0.79 in the absence of water to 1.07 in its presence. Deactivation is probably due to the dissociative adsorption of water, resulting in the formation of additional surface hydroxyls. As the amount of surface hydroxyls formed is limited to a saturation level, the deactivating effect on the catalyst is limited too. The additional hydroxyls condense and desorb in the temperature range 525–775 K, resulting in a lower degree of deactivation at higher temperature. A high temperature treatment at 775 K results in a complete regeneration. The amount of surface hydroxyls formed per unit surface area decreases at increasing MnO_x-loading. The selectivity to the production of nitrogen is enhanced significantly by the presence of gas phase water.     

Reactivity of steam in exhaust gas catalysis III. Steam and oxygen/steam conversions of propane on a Pd/Al2O3 catalyst

A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C₃H₈ with O₂ or with O₂ + H₂O were carried out with different stoichiometric ratios S(S =[O₂]/5[C₃H₈]). The conversion profiles of C₃H₈ for the reaction carried out in substoichiometry of O₂ (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H₂ and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdO_x into Pd⁰, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdO_x into Pd⁰. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling.     

Catalytic oxidation of sulphide ions to elementary sulphur in aqueous solutions over transition metal oxides

The catalytic activity of a wide range of transition metal oxides in oxidation of sulphide ions by air in aqueous medium was studied. Some specific features of the reaction mechanism on some of the studied oxides were considered. The transition metal oxides are promising catalysts for practical application. Some of these oxides will allow the preparation of catalysts possessing activity comparable to that of the cobalt phthalocyanine based catalysts, popular in industrial practice.     

铁钴钒软磁合金损耗谱的分形结构

研究了铁钴钒软磁合金的铁芯损耗，发现铁芯损耗谱具有分形结构。讨论了带材厚度和磁感应强度对分形维数Ｄｆ的影响。     

高性能各向异性Sm2Fe17Nx磁粉的制备

本文研究了高性能各向异性Ｓｍ２Ｆｅ１７Ｎｘ磁粉的制备工艺路线与工艺参数。优化了制备与工艺参数。已制备出磁性能达到：Ｂｒ＝１．３９Ｔ，Ｈｃｉ＝８５０ＫＡ／ｍ和（ＢＨ）ｍ＝２３６ＫＪ／ｍ＾３的各向异性Ｓｍ２Ｆｅ１７Ｎ２．８８磁粉，该磁粉的各向异性场ＨＡ达到２０Ｔ。     

添加剂对尖晶石型锰酸锂性质表征的影响

以LiOH·H_20和MnO_2为原料,分别掺入H_2BO_3、Al_2O_3、SiO_2和P_2O_5等添加剂,用固相分段法制备尖晶石型锰酸锂。结果表明,SiO_2和P_2O_5可以有效地改善LiMn_2O_4的电化学性能,H_3BO_3对锰酸锂的电化学性能影响不大,而Al_2O_3破坏了LiMn_2O_4的电化学性能。面扫描结果显示,Si或P元素各自都均匀地分散于LiMn_2O_4的物相中。从元素电负性和原子半径的角度分析了B、Si、P和Al元素对尖晶石型LiMn_2O_4结构和性能的影响。     

化学沉积法制备的Ni(P)、Ni(B)纳米薄膜的结构与磁性

用化学沉积法制备了系列Ni(P),Ni(B)合金薄膜样品，用X射线衍射结构分析方法证明样品由尺寸为纳米量级的颗粒组成，样品在磁性上表现出超顺磁性，对热磁处理前后的磁学参数进行了比较研究。     

Superconductivity and magnetism in niobium doped YBa2Cu3O7 Related high Tc ceramics

Magnetic characterization has been performed on the members of the cuprateniobate RBa₂Cu₂NbO₈ (R = Pr, Nd, and La) series and R_1.5Ce_0.5Sr₂Cu₂NbO₁₀ (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12K. The PrCSCNO sample is nonsuperconducting and shows two distinct orderings at 17K and 53K. No such magnetic phase transition is observed down to 2K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of the lower critical field curve, dc irreversibility line, and critical curent densities are reported for each of the superconducting NdCSCNO, SmCSCNO, and EuCSCNO compounds.     

Effects of a Nd—Fe—B magnetic filler on the crystallization of poly(phenylene sulfide)

The crystallization of poly(phenylene sulfide) (PPS) in a polymer–magnetic Nd—Fe—B powder suspension was studied. Isothermal crystallization behavior was analyzed by way of differential scanning calorimetry, and the kinetics were described via the Avrami equation. The Avrami parameters and the crystallization times were strongly affected by both the particle size and the presence of a coupling agent coated on the filler particles. The small Nd—Fe—B particles exhibited long induction and half‐times, whereas the large particles tended to have short crystallization times. Particles ranging from 38 to 150 μ appeared to have similar crystallization times and to have no significant change in the value of Avrami index with melt crystallization temperature. As a result of these analyses, the dynamic mechanical properties were determined to correlate the fundamental polymer crystallization characteristics and the physical properties of the PPS binder. The enhancement of the wetting of the filler to the binder was promoted through the coupling agent, as confirmed by dynamic mechanical testing performed on the samples. The storage modulus typically decreased because of the presence of the uncoated small particles. Conversely, the loss modulus was enhanced because of the presence of the coated small particles in the PPS binder. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1091–1102, 2002     

Studies on the interactions of metal oxides and Na2 SO4 at 1100 and 1200 K in oxygen

The interaction of different metal oxides such as Co₃O₄, NiO, Al₂O₃, Cr₂O₃, Fe₂O₃ and SiO₂ with Na₂SO₄ at a temperature of 1100 and 1200 K in flowing oxygen has been studied. The thermogravimetric studies for each system were carried out as a function of Na₂SO₄ in the mixture. The presence of different constituents in the reaction products were identified by X-ray diffraction analysis and the morphologies of the reaction products were characterized using metallography and scanning electron microscopy (SEM). The formation of products was also investigated by thermodynamic computation of free energies of the reactions and the study of relevant equilibrium phase diagrams. The soluble species in the aqueous solutions of the reaction products were determined quantitatively using atomic absorption spectrophotometry. The high temperature interaction products usually contain a 3-phase structure namely, Na₂O·M₂O _x , M₂O _x and metal sulphide and/or metal sulphate. The formation of Na₂O·M₂O _x depends upon the solid state solubility of metal oxide in the molten salt at high temperatures. Under limited solubility conditions Na₂O·M₂O _x is invariably formed, but as soon as this condition is relaxed the oxide. M₂O _x , precipitates and forms a separate phase.