Understanding heterogeneous catalysis on an atomic scale: a combined surface science and reactivity investigation for the dehydrogenation of ethylbenzene over iron oxide catalysts

In order to study the dehydrogenation of ethylbenzene to styrene, epitaxial iron oxide model catalyst films with Fe₃O₄(111), -Fe₂O₃(0001) and KFe _x O _y (111) stoichiometry were prepared in single crystal quality on Pt(111). They were investigated using surface science techniques before and after atmospheric pressure reaction experiments in a newly designed single crystal flow reactor. As expected from low-pressure measurements, Fe₃O₄(111) is catalytically inactive. The catalytic activity of -Fe₂O₃(0001) starts after an activation period of about 45 min. After that, the surface is essentially clean but shows a high concentration of defects. On the potassium-promoted films, however, the activation period is much longer, the activity then is higher and the surface gets covered completely with carbon and oxygen during reaction. This indicates a different reaction pathway on the promoted films with a carbon–oxygen species as catalytically active species.     

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.     

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。     

Effect of nutrient seed coating on the emergence of wheat and oats

A series of experiments was conducted under controlled soil moisture and temperature conditions in a growth chamber to examine the effect of a range of nutrient seed coatings on the emergence to wheat (Triticum aestivum L. cv. Kite) and oats (Avena sativa L. cv. Blackbutt) sown in a coarse sandy loam soil. Final emergence of oats was not reduced by a coating containing 10 kg P ha^–1 (as monocalcium phosphate [MCP]) whereas the same coating reduced wheat emergence by 15%. The emergence of both wheat and oats was severely reduced by urea coatings (supplying 10 kg N ha^–1) to 33 and 13% respectively; this injury was lessened markedly by the inclusion of phenyl phosphorodiamidate (PPD) in the urea coatings at 1% (w/w) (emergence increased to 66 and 56% respectively).Low soil moisture (67% of field capacity [FC]) resulted in almost no emergence of wheat coated with urea (± bentonites of different pH). In soil at FC, the addition of bentonite of pH 5 (B5) to urea coatings permitted greater emergence (54%) than when bentonite of pH 9 (B9) was added (32%) which, in turn, permitted greater emergence than urea coating alone (10%). When PPD and bentonite (B5 or B9) were combined either singly or together with urea in seed coatings, PPD was more effective than either of the bentonites in reducing injury and masked the slight positive effect of B5.Coatings containing various combinations of N and P sources (at 3.6 and at 8 kg ha^–1 respectively) all reduced the emergence of wheat compared to raw seed (91% emergence). When applied alone, MCP was least damaging (74%); the combination of MCP with ammonium sulfate (AS) caused somewhat more injury (68%) whilst combination with calcium nitrate (CN) caused most injury (29%). In contrast, CN alone caused relatively little damage (73%) whilst AS alone was more damaging (50%). There was no significant regression found between percentage emergence and either the calculated partial salt index or the pH of the nutrient coatings. Further work is needed to examine the mechanisms of injury due to nutrient seed coatings so that safe but effective formulations can be developed.     

The SMSI between supported platinum and CeO2–ZrO2–La2O3 mixed oxides in oxidative atmosphere

CeO₂–ZrO₂–La₂O₃ (CZL) mixed oxides were prepared by citric acid sol–gel method. The as-received gel was calcined at 500, 700, 900 and 1050 °C to obtain the so-called C5, C7, C9 and CK, respectively. The C5, C7 and C9 powders were impregnated with H₂PtCl₆ and then calcined at 500 °C to prepare P5C5, P5C7 and P5C9, respectively. The impregnated CK powders were calcined at 500, 700 and 900 °C to prepare P5CK, P7CK and P9CK, respectively. The XRD and XPS analyses show that the surface distribution of Pt is evidently influenced by the structural and textural properties of the support. The CO adsorption followed by FTIR reveals that the dispersion and the chemisorption sites of Pt are reduced as the calcination temperature of CZL support increases. The chemisorption ability of the CK samples is even completely deactivated. The encapsulation mechanism, which has been applied to explain the so-called strong metal–support interaction (SMSI) after reductive treatment, is introduced here to demonstrate the abnormal observations though the samples were prepared in oxidative atmosphere. The HRTEM results also confirm this explanation. The effects of oxygen vacancies, the chemisorption sites on the Pt surface and Pt/Ce interfacial sites on the three-way catalytic activities are discussed.     

高效节能换热器在氮肥工业中的应用

描述了新型折流杆换热器的强化传热和降低壳层压力降的原理 ,它与传统折流板换热器相比 ,传热效率高 ,材料及能耗小。介绍了这种新型换热器在合成氨变换工段和尿素装置中的应用情况及所起的节能降耗作用 ,指出该高效节能换热器在设计和生产中的关键技术。     

High-temperature catalysts with a synergetic effect of Pd and manganese oxides

A synergetic effect in the catalytic activity has been found after palladium introduction in Mn–Al–O systems. The magnitude of the synergetic effect depends on the types of the oxidic manganese species: oxide Mn₃O₄, spinel (Mn, Mg)[Mn, Al]₂O₄ or hexaaluminate (Mn, Mg)LaAl₁₁O₁₉. The synergetic effect of Pd and manganese-containing compounds is observed only if palladium is introduced to the low-temperature precursor of the manganese alumina spinel or manganese hexaaluminate. The synergetic effect is not observed when high-temperature samples with formed spinel or hexaaluminate phases are modified with Pd.