排序方式: 共有32条查询结果,搜索用时 46 毫秒
1.
2.
G. Liberti G. Servi A. Guaglio C. Ruffino N. Pernicone 《Journal of Thermal Analysis and Calorimetry》1974,6(1-2):183-192
Results on hydrogen reduction of pure magnetite to iron at low temperature are reported as part of research on ammonia synthesis catalyst. Experimental work was carried out by thermogravimetry and by electron microscopy.The reduction has a typical S-shaped kinetic curve, with a poorly reproducible induction period. The slope of the reduction curve at 50% conversion (k
0.5) was found to depend on sample mass (2–50 mg), particle size, temperature (220–280C) and presence of moisture in the hydrogen
.The results suggest both interparticle and intraparticle (through iron ash) diffusion to be slow. Morphological examinations of the sample at various reduction degrees support this interpretation.
Zusammenfassung Die Ergebnisse der Reduktion von reinem Magnetit zu Eisen durch Wasserstoff bei niedrigen Temperaturen werden als Teil einer Forschungsarbeit über Katalysatoren zur Ammoniak-Synthese mitgeteilt. Die Versuche wurden mittels Thermogravimetrie und Elektronenmikroskopie durchgeführt.Die Reduktion verläuft nach einer typisch S-förmigen kinetischen Kurve, mit einer schlecht reproduzierbaren Induktionsperiode. Es wurde festgestellt, daß die Steile der Kurve bei 50% Konversion (k 0.5) von der Probenmenge (2–50 mg), der Teilchengröße, der Temperatur (220 bis 280) und der Feuchtigkeit des Wasserstoffes abhängt.Diese Ergebnisse lassen darauf schliessen, daß sowohl die interpartikuläre als auch die intrapartikuläre Diffusion (durch die Eisen-Asche) langsam ist. Diese Deutung wird durch morphologische Prüfung des Musters bei verschiedenen Reduktionsstufen unterstützt.
Résumé On communique les résultats obtenus en réduisant par l'hydrogène à basse température la magnétite pure en fer, travail faisant partie de recherches sur les catalyseurs pour la synthèse de l'ammoniac. Les expériences ont été effectuées par thermogravimétrie et par microscopic électronique.La courbe cinétique de la réduction présente la forme en S type, avec une période d'induction peu reproductible. Il est apparu que la pente de la courbe de réduction, pour un taux de conversion de 50% (k 0.5) dépendait de la prise d'essai (2–50 mg), de la dimension des particules, de la température (220 à 280) et de la présence d'humidité dans l'hydrogène .Ces résultats permettent de conclure que les processus de diffusion sont lents, qu'ils soient de type interparticule ou intraparticule. L'examen morphologique des échantillons pour divers degrés de réduction a confirmé cette interprétation.
, , . . S- , . , 50% (0.5) (2–50 ), , (220–280) (2)=1,2 ). , , , , . .相似文献
3.
Giovanni Fronza Claudio Fuganti Piero Grasselli Stefano Servi 《Tetrahedron letters》1985,26(40):4961-4964
Baker's yeast mediated reduction of the α-acetoxy ketones (1)–(3) proceeds with high enantio- and stereoselectivity to give the carbinols (4)–(6), easily converted into the masked chiral deoxy sugars (12)–(14), from which {=D}- and {=L}-deoxysugars have been obtained. 相似文献
4.
The present study examined the influence of synthetic N-(1,3-benzothiazol-2-yl)-N-(4,5-dihydro-1H-imidazol-2-yl) amine (2-Amdz) on levels of vitamins A, E and C and malondialdehyde (MDA) in rats. A total of 30 rats, divided into two groups, were used in the study. The control group was given only a subcutaneous injection of 250 microL 75% ethanol, every other day. The other group of rats was administered a subcutaneous injection of 2-Amdz (25 mg kg-1, dissolved in 250 microL of 75% ethanol). Injections were continued for 16 days. After the application of 2-Amdz for 16 days, the serum levels of vitamins A, E and C and malondialdehyde (MDA) were determined by HPLC. The serum vitamin A, E, and C levels decreased significantly compared to controls (p<0.05) whereas serum MDA levels were higher than control levels (p<0.005). As a result, it can be suggested that 2-Amdz induced a severe stress and more importantly, increased the amount of free radicals and significantly decreased the levels of serum antioxidant vitamins. 相似文献
5.
A new biocatalytic strategy to obtain the ethyl (R)-2-hydroxy-4-oxo-4-phenylbutyrate precursor of ethyl (R)-2-hydroxy-4-phenylbutyrate, an important intermediate in the synthesis of a variety of ACE inhibitors, has been set up. Starting from ethyl 2,4-dioxo-4-phenylbutyrate, a screen of microorganisms has been performed in order to find the best catalyst able to reduce the keto group in the α-position with high chemo- and enantioselectivity. The biotransformation catalyzed by Pichia pastoris CBS 704 gave the best results in terms of conversion and enantioselectivity. The addition of adsorbing resins in the fermentation medium is effective in controlling substrate and product concentration in the medium, thus improving both conversion and enantioselectivity of the biotransformation. Preliminary experiments in a continuous batch reactor with growing culture of P. pastoris will be also presented. 相似文献
6.
Fasoli E Arnone A Caligiuri A D'Arrigo P de Ferra L Servi S 《Organic & biomolecular chemistry》2006,4(15):2974-2978
1-O-Acyl-sn-glycero-3-phosphocholine and 1-O-acyl-sn-glycero-3-phosphoric acid have been prepared selectively and with high yields from the corresponding diols, glycerophosphoryl choline and glycerol-3-phosphate. Starting from the diols, the activated tin ketals were prepared in 2-propanol by reaction with dialkyltin oxide. The intermediates were acylated in the same solvent with long-chain fatty acid chlorides, giving the corresponding 1-acyl-lyso-phospholipids in high yield and with complete regioselectivity. The catalytic nature of the tin-mediated acylation and the relevance of the solvent are discussed. 相似文献
7.
We investigate nonlinear oscillations in a fourth-order partialdifferential equation which models a suspension bridge. Previouswork establishes multiple periodic solutions when a parameterexceeds a certain eigenvalue. In this paper, we use Leray-Schauderdegree theory to prove that if the parameter is increased further,beyond a second eigenvalue, then additional solutions are created. 相似文献
8.
Mario Servi 《Annali dell'Universita di Ferrara》1968,13(1):93-116
Riassunto Allo scopo di studiare alcuni problemi di algebra universale in una categoriaK, si definiscono, relativamente ad un oggetto diK, alcuni concetti di solito riferiti ad un insieme, quali quello di relazione binaria (in particolare di equivalenza), composizione
di corrispondenze, nucleo di un morfismo.
Lavoro eseguito nell'ambito dell'attività dei Gruppi di Ricerca Matematici del C.N.R. (programma n. 8), nell'anno 1969. 相似文献
Summary In order to study some problems of Universal Algebra in a categoryK, some set theoretic concepts are generalized to objects ofK.
Lavoro eseguito nell'ambito dell'attività dei Gruppi di Ricerca Matematici del C.N.R. (programma n. 8), nell'anno 1969. 相似文献
9.
The formula for the blocking probability for the finite capacity M/G/1/K in terms of the steady state occupancy probability distribution of M/G/1 and the system utilization is known [Keilson, J. Royal Statistical Soc. Serie B, 28 (1966) 190–201]. The validity of this relationship is demonstrated for a broad class of state dependent M/G/1 vacation systems and priority systems. New methods are employed which may also be of interest in their own right.This research was conducted while J. Keilson was a Senior Staff Scientist at GTE Laboratories Incorporated. 相似文献
10.