Silica-supported cobalt catalysts for the selective reduction of nitrogen monoxide with propene

Catalytic behavior of silica-supported transition metals for NO reduction with propene in the presence of oxygen was investigated. While both silica and cobalt oxides did not show any activity for the selective NO reduction, impregnated CoO/SiO₂ prepared from cobalt acetate showed good activity although the preparation conditions had significant effect on the activity. It was suggested that highly dispersed surface Co²⁺ ions on silica are responsible for the catalytic activity.     

Preparation and reaction mechanistic characterization of sol–gel indium/alumina catalysts developed for NO x reduction by propene in lean conditions

The impregnation and sol–gel preparation methods were investigated to develop high activity catalysts and understand the significance of the indium–aluminium interaction on aluminasupported indium catalysts in NO _x reduction with propene. Active In/alumina catalysts with a very high surface area (270 m²/g) and thermal stability were prepared in controlled conditions by sol–gel processing. When Al isopropoxide and In nitrate in ethyl glycol were used as precursors in aqua media, indium atoms were incorporated evenly distributed as a thermally stable form in the aluminium oxide lattice structure. In wet impregnation it was beneficial to use a certain excess of aqueous In solution (volumes of solution : pores = 2 : 1) to have the highest NO _x reduction activity. The catalyst containing dispersed Al on In oxide (58 wt% In, phaseequilibrium preparation method) showed activity at lower temperatures than any other In–Al oxide catalyst or pure In₂O₃. The adsorption of different reaction intermediates on alumina and stable In₂O₃ sites were detected by FTIR studies. In/alumina catalysts have active sites to oxidize NO to NO₂, partially oxidize HC, form the actual reductant which contains N–H or N–C bonding and react with NO to dinitrogen. The cooperation with indium and aluminium was evident even in the mechanical mixture of sol–gel prepared alumina (301 m²/g) and In₂O₃ powders (27 m²/g), where the probability for molecularscale intimate contact between indium and aluminium sites was very low (particle size 10–250 m). Shortlived gaseous intermediates and surface migration are the possible reasons for the high catalytic activities on the two physically separated active sites both necessary for the reaction sequence.     

In vitro effects of urease inhibitors on rate of urea hydrolysis in soils

We studied the effect of urease inhibitors on the urea hydrolysis in some Sundanese soils belonging to the orders of Vertisol and Entisol. The hydrolysis showed a lag period of about 3 days and its rate (Y) per unit time (t) could be described by a two constants exponential equation of the general form Y = K₁t^K ₂. Statistical analysis showed that the intercept K₁ (rate of urea hydrolysis) was significantly affected by soil type rather than treatment. It seems that K₁ is associated with the soils' initial urease activity as it closely correlates with the Michaelis constant (km).The gradient, K₂, being significantly affected by soil type as well as treatment is probably associated with the induced urease activity with time and it, therefore, varied with variations in soils and treatments. Of the so-called urease inhibitors used in this study Ca(OH)₂, p-benzoquinone (PBQ) and orthophosphoric acid (OP) only PBQ reduced urea hydrolysis while the other chemicals have effects possibly related to modifying the soil pH. Inhibitor treated soils had substantial amounts of unacounted for N which was believed to be present, presumably, in the form of carbamate.Contribution from the Department of Biochemistry and Soil Science, Faculty of Agriculture, Shambat, Sudan.     

Nitrate leaching from loamy soils as affected by crop rotation and nitrogen fertilizer application

Nitrate leaching as affected by cropping system/crop rotation, history of farmyard manure application or fertilizer nitrogen application (0 N, 0.5 N and 1 N) was studied at nine sites on loamy soils during 1986/87, 1987/88 and 1988/89. Soil solution from 80 to 90 cm soil depth was sampled every second week in the period November to May by the use of porous ceramic cups and analysed for NO₃-N and Cl. Climatical conditions were obtained from standard meteorological observations in the region. Drainage from soil profiles was calculated from measured and simulated values of precipitation and actual evapotranspiration, respectively.The results show that type of crop is of the utmost importance for the leaching magnitude of nitrate as 40% of the total variance in nitrate concentrations in the soil solution could be explained by the type of crop.The second factor of importance was the history of farmyard manure (FYM) application, which was able to explain 28% of the total variation in nitrate concentration in the soil solution. Nitrate concentration/leaching from arable land without FYM ever being applied was considerably lower than from arable land which received periodical FYM applications until the early 70's or from arable land which besides periodical FYM applications in the past presently still receives regular applications of FYM. Only about 1% of the total variation in nitrate concentration in the soil solution was explainable by the level of fertilizer nitrogen application.Differences between years explained 14% of the total variation in nitrate concentration in the soil solution due to differences between the years in soil temperatures and water run-off. The run-off during the autumn and winter of 1986/87, 1987/88 and 1988/89 was 95, 275 and 55 mm, respectively. As expected nitrate leaching increased with increasing run off. However, nitrate leaching at the 275 mm run off was considerably lower than expected, which seems explainable by a substantial denitrification. The soil at the sites in question seems thus partly to purify the soil solution for nitrate before it leaves the root zone at the observed high run off conditions.     

The availability of nitrogen following topsoil application of liquid digested sludge

Samples (375 g) of the Evesham series (clay loam) soil were incubated under aerobic conditions at 20 °C following incorporation of liquid mesophilic digested sewage sludge (1150 mg N L^–1). Simultaneously, pot trials under field conditions were also established. Total soluble N total oxides of nitrogen, ammonium N and headspace carbon dioxide samples were determined periodically over the first 480 day degrees C. Soluble organic N fractions were also calculated and it was found that the soil water concentration of available N (as nitrate N) could be predicted from summation of SON and NH₄-N on sludge application. The accumulation of nitrate N was compared with field derived data and both correlated well to a 2 pool exponential model. High rates of nitrification were observed and 70% of the organic N applied was mineralised over 480 day degrees C. The use of the relative quantity of soluble to insoluble organic N could be a possible indicator of subsequent nitrogen availability in field application.     

Coupling of dry matter and nitrogen accumulation in ryegrass

The logistic model has proven very useful in relating dry matter production of warm season perennial forage grasses to applied nitrogen. A recent extension of the model coupled dry matter and plant N accumulation through a common response coefficient c. The objective of this analysis was to apply the extended logistic model to cool season Gulf annual ryegrass (Lolium multiflorum Lam.) and to establish a common response coefficient c between accumulation of dry matter and plant N. Analysis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant N removal, and plant N concentration to applied N, with an overall correlation coefficient of 0.9954. Furthermore, the model closely described the relationship between yield and plant N removal, as well as between plant N concentration and plant N removal. The logistic equation is well-behaved and simple to use on a pocket calculator. It can be used to estimate yields and plant N removal in evaluation of agricultural production and environmental quality.     

凯氏定氮法在测试氯乙烯-丙烯腈共聚树脂中丙烯腈含量的应用

介绍了凯氏定氮法在测定氯乙烯-丙烯腈共聚树脂中丙烯腈含量的应用及反应原理,对测试结果的准确性和重复性进行了研究,并与灼烧法进行了比较。实验结果表明:采用凯氏定氮法测定氯乙烯-丙烯腈共聚树脂中丙烯腈的含量是可行的,测定结果准确,重现性较好。     

NO adsorption on Cu-ZSM-5: assignment of IR band at 2133 cm−1

The adsorption of nitrogen oxides on Cu-ZSM-5 was studied by infrared spectroscopy to elucidate the species associated with the band at 2133 cm^–1. The band was found for both NO and NO₂ adsorption. Labeling experiments with¹⁵NO revealed that the associated surface species contained nitrogen and, most likely, an N-O bond. Co-adsorption experiments of NO and oxygen produced adsorbed nitronium, NO ₂ ⁺ , as the principal, associated species. Adsorption of nitrogen oxides on dispersed CuO and the HZSM-5 support demonstrated that the 2133 cm^–1 band was not necessarily associated with copper ions. A relatively strong correlation between the bands at 2133 and 3615 cm^–1 indicates that the primary adsorption sites of NO ₂ ⁺ are the strongly protic, bridging Si(OH)Al framework hydroxyls. Once these were filled, other, weaker acid sites began to adsorb NO ₂ ^O .     

γ-Al2O3载体制备中水洗脱氯工艺的连续化

通过正交实验，研究了γ-Al₂O₃载体制备中拟薄水铝石水洗的连续化。方差分析表明，第一阶段洗水的pH是影响脱氯效果的关键因素，初步得出水洗连续化的优化条件。与国内外传统的间歇式水洗相比，收率从80%提高到99.7%，所需洗水量仅为原来的1/3，而处理500 kg物料的生产周期也从10 h缩短到2～3 h。     

粗四氯化钛除钒工艺现状及发展趋势

概述了使用铜丝、有机物、硫化氢和铝粉4种物质除去粗四氯化钛中的杂质钒方法的优缺点,通过比较指出有机物除钒法和铝粉除钒法是较理想的粗四氯化钛除钒方法。最后,对有机物除钒法目前存在的问题及解决方案进行了分析。