Selective oxidation of ammonia to nitrogen on transition metal containing mixed metal oxides

The selective catalytic oxidation of ammonia to nitrogen (NH₃-SCO) has been studied over hydrotalcite derived mixed metal oxides containing Cu, Co, Fe or Ni. XRD, BET, NH₃-TPD and TPR techniques were used for catalysts characterization. Results of NH₃-SCO were compared with those of selective catalytic reduction of NO with NH₃ (NO-SCR). Reaction mechanism was studied by temperature-programmed surface reaction (TPSR) and activity tests with a various contact time. Catalytic performance of the studied samples depends on both kind and loading of transition metals in the mixed metal oxide system. The Cu-containing samples have been found to be the most active catalysts of the NH₃-SCO process. Transition metal loading strongly influences distribution of ammonia oxidation products. The highest selectivity to N₂ was measured for the catalysts with the lowest transition metal content.     

Mechanisms of hydrocarbon conversion reactions on heterogeneous catalysts: analogies with organometallic chemistry

Catalysis is central to most industrial processes for chemical manufacturing. As catalytic processes have become more complex and more demanding, selectivity has become the central issue in their design. Selectivity is defined by the relative rates of competing reaction pathways available to crucial intermediates, and can be controlled by subtle changes in the nature of the catalyst, the reactants, and/or the reaction conditions. In order to be able to do this in a systematic manner, a good understanding of the catalytic reaction mechanisms is needed. Here a connection is drawn between the key elementary steps comprising hydrocarbon conversion reactions on surfaces and those known to occur on discrete organometallic complexes. This way, the hydrogenation, dehydrogenation, hydrogenolysis, chain growth, and isomerization reactions typical in heterogeneous catalysis are redefined in terms of hydride elimination, oxidative addition, reductive elimination, migratory insertion, and 1, 2-shift elementary steps, among others. It is suggested that the knowledge already available from organometallic chemistry can be used to further advance the understanding of the surface science involved in heterogeneous catalysis. Thanks to the commonality of the chemistry involved, a better synergy could also be established between homogeneous and heterogeneous catalytic development. These ideas are discussed in this article in a critical and personal way.*Invited contribution to the special volume entitled The Interface between Heterogeneous and Homogeneous Catalysis, stemming from contributions at the recent International Symposium on Relations between Heterogeneous and Homogeneous Catalysis, and dedicated to the memory of Robert L. Burwell.     

Viscoelastic Effects in a Phosphate Glass-Metal Seal

A family of phosphate glasses has been developed with thermal expansion behavior in the elastic range that nearly matches the response of 304 stainless steel. Attempts to make concentric pin-shell seals consistently have yielded fractures between 400° and 300°C during cooling. Elastic stress analyses which neglect glass transitional behavior and utilize constant glassy ("elastic") thermal expansion coefficients predict a residual stress state that is compressive. However, viscoelastic computations which include the effects of structural relaxation during glass transtion show that tensile stresses sufficient to cause failure arise during cooldown of the seal.     

Effect of alkali and alkaline earth metals on nitrogen release during temperature programmed pyrolysis of coal

Formation of HCN, NH₃, and N₂ during fixed-bed pyrolysis at 10K min⁻¹ has been studied using coal samples after partial demineralization followed by addition of metal hydroxides from aqueous systems. Without additives, NH₃ is the predominant product at ≤ 700°C, showing the two peaks in the formation rate profile, whereas N₂ is the only product at ≥ 800°C. The presence of NaOH, KOH and Ca(OH)₂ promotes considerable NH₃ formation between 450 and 600°C, but in contrast suppresses HCN formation in this region. The Ca shows the largest effect on both the promotion and suppression. It is likely that the NH₃ increased by Ca addition arises partly from HCN, but mainly from secondary reactions of tar-N. These hydroxides affect N₂ formation in quite different manners: the Na decreases the rate between 700 and 950°C, and the K changes it less significantly than the Na, but the Ca remarkably increases the rate in a low temperature region of 550–700°C. These different features are discussed in terms of solid-phase reactions of alkali metal carbonates with char-N and secondary decomposition reactions of tar-N on CaO particles. As a result, total conversion of coal-N to HCN, NH₃ and N₂ up to 1000°C increases in the sequence of Na < none < K < Ca.     

新型合成聚合物重金属离子吸附剂及其吸附性能

阐述了新型聚合物重金属离子吸附剂的合成与改性及其对水溶液中Cd(Ⅱ)、Pb(Ⅱ)、Cu(Ⅱ)、Hg(Ⅱ)等重金属离子的吸附性能。这些聚合物重金属离子吸附剂对低浓度的重金属离子表现出了较好的吸附能力，其中聚合物吸附剂PGHyFeO—COOH对mg／L级的Pb(Ⅱ)、Cd(Ⅱ)、Hg(Ⅱ)的最大吸附量分别为211．4mg／g、155．0mg／g、147．2mg／g。这些吸附剂的吸附速度也较快，平衡吸附时间一般在60min左右，有的甚至只有几分钟。新型聚合物重金属离子吸附剂在水处理工业中具有广阔的应用前景。     

Heavy metals contribution of non-aqueous fluids used in offshore oil drilling

A monitoring program was performed to investigate heavy metal content alteration due to exploratory drilling for oil using non-aqueous fluids (NAFs) in Brazilian offshore, 900 m deep. Fourteen elements were monitored in 54 sites and it was verified that after drilling activities the average Ba concentration was remarkably increased with respect to background level, even 1 year after the activity. A minor increase in Mn and a moderate increase in Al concentrations were verified. The Cd, Cr, Ni, As, Co, Cu, Pb, V, and Zn concentrations were at the background levels, ca. 1 year after the NAFs drilling materials deposition on the seafloor. The Al, Ba, Cd, Cr, Cu, Ni and Zn mean concentrations were significantly different (P<0.05) between the three sampling operations (cruises) performed, while As, Cd, Fe and Pb presented different mean values according to the distance of the oil well, independent of the sampling operation. Interaction between sampling operation and distance was observed for Mn. In all sediment samples the Hg concentration was below the detection limit (0.07 μg g⁻¹).     

Enthalpy recovery of gases issued from H2 production processes: Activity and stability of oxide and noble metal catalysts in oxidation reaction under highly severe conditions

Oxidation activity and stability under reaction was investigated for a series of mixed oxide catalysts, doped or not by a precious metal (Pd, Pt). The reaction feedstock, containing CO, H₂, CH₄, CO₂ and H₂O, simulated gases issued from H₂ production processes for fuel cells. Contrarily to conventional noble metal catalysts, mixed oxide samples present generally good stability under reaction at high temperature. The activities measured for the perovskite and hexaaluminate catalysts, are however largely lower than that of the reference Pd/Al₂O₃ catalyst. High activities were obtained after impregnation of 1.1 wt.% Pd or 0.8 wt.% Pt on the hexaaluminates samples. Even if Pd/Al₂O₃ was found to present a high activity, this sample suffered from drastic deactivation at 700 °C. Better stability were obtained on perovskite. Furthermore, doping hexaaluminate by Pt led to samples with good activities and high stability. Even if better activities were obtained by doping the hexaaluminate samples by Pd, the Pd/BaAl₁₂O₁₉ strongly deactivated, as it was previously observed for the reference catalyst. Interestingly, this Pd deactivation was not observed when Pd was impregnated on the Mn substituted hexaaluminate, leading to a stable and active catalyst. This suggests that it is possible to stabilize the palladium in its oxidized form at high temperature (700 °C) on the surface of some supports.     

Dependence of oil stability index of fatty compounds on their structure and concentration and presence of metals

During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous materials such as metals on oxidative stability.     

重金属在宽叶香蒲人工湿地系统中的分布与积累

本文通过对广东韶关凡口宽叶香蒲（Typha latifolia)人工湿地系统的进出水口，土壤剖面及四种优势植物体各部分器官中Pb,Zn,Cu和Cd含量进行分析。结果表明；重金属主要库存于土壤中。从水平上看，全量的重金属含量从进水口到出水口呈上升趋势，而有效态则相反；从土壤剖面的垂直分布上看，全量和有效态重金属含量都随土壤深度的增加而递减，四种植物都具有较强的吸收和富集重金属的能力，且主要富集在植物的地下部分。     

GaN基LED与Si键合技术的研究

采用金属键合技术结合激光剥离技术将GaN基LED从蓝宝石衬底成功转移到Si衬底上。利用X射线光电子谱(XPS)研究不同阻挡层对Au向GaN扩散所起的阻挡作用,确定键合所需的金属过渡层。利用多层金属过渡层,在真空、温度400℃和加压300 N下实现GaN基LED和Si的键合,通过激光剥离技术将蓝宝石衬底从键合结构上剥离下来,形成GaN基LED/金属层/Si结构。用金相显微镜及原子力显微镜(AFM)观察结构的表面形貌,测得表面粗糙度(RMS)为12.1 nm。X射线衍射(XRD)和Raman测试结果表明,衬底转移后,GaN基LED的结构及其晶体质量没有发生明显变化,而且GaN与蓝宝石衬底间的压应力得到了释放,使得Si衬底上GaN基LED的电致发光(EL)波长发生红移现象。