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.     

高分子铁盐絮凝剂制备及其应用研究

研究了以废铁屑和工业硫酸亚铁为原料,在常压和加热条件下,用氯酸钾作为氧化剂制取聚合硫酸铁(PFS)的工艺条件,并在PFS制备的基础上,合成了聚磷硫酸铁(PPFS)和聚氯硫酸铁(PFCS)。将所制备的聚铁用于污水处理实验,结果表明:用该方法制备的聚铁絮凝剂对实际水样具有较好的混凝处理效果,且制备工艺简单、速度快,从根本上消除了用NaNO_2催化氧化法制备聚铁对环境造成的二次污染。     

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).     

Ethanol vapor deactivation of gossypol in cottonseed meal

Most cottonseed cultivars contain gossypol, a polyphenolic antinutritional compound. “Free” gossypol is a physiologically active form of gossypol, which is toxic to young- and nonruminant animals. To utilize solvent-extracted cottonseed meal as a general feed, gossypol must be either removed or deactivated to a minimum level specified for each class of animal. Normally, deactivation is carried out prior to oil extraction; however, the desired level of deactivation is not always attained. A new supplemental method of deactivation has been found by using either ethanol or isopropanol vapors on solventextracted meal. In a bench-top set-up, ethanol vapor reduced free gossypol from 0.115 to 0.053%, and a further reduction to 0.026% has been observed with the addition of ferrous sulfate. The supplemental deactivation method can, in most cases, reduce free gossypol to significantly safer levels for feeding, thus increasing utility, and possibly demand, for cottonseed meal as a general animal feed protein source. Presented in part at the AOCS Annual Meeting, Atlanta, GA, May 8–12, 1994.     

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.     

活性染料染色废水的日光脱色降解

在太阳光照射条件下，使用铁(Ⅲ)-草酸盐络合物／H2O2对存在于水中三种中温型活性染料进行光催化降解研究，重点考察了太阳光的强度和活性染料的浓度对脱色降解反应的影响结果表明：太阳光的强度低于50001ux，染料的脱色率低于40％；在高于400001ux、照射60分钟脱色率高于98％，在高于900001ux时，照射10分钟，可使活性蓝MS脱色率接近100%，太阳光的强度越高，溶液中的染料浓度越低。