摘要:

AbstractThe vanadium trapping effect of Mg and La containing additives in cracking catalyst contaminated with 2300 ppm Ni and 4700 ppm V has been analyzed by microactivity test (MAT) and imaging secondary ion mass spectrometry (SIMS). The results of SIMS imaging are consistent with cracking activity data and show that the La/spinel is a superior vanadium trap for the fluid catalytic cracking of hydrocarbons (FCC) operation. La/spinel serves as a dual function additive for both vanadium trap and SOxremoval. The optimum amount of La/spinel added to the cracking catalyst is about 15% by weight. This results in an increased catalytic activity, an increase in gasoline yield, and a decrease in coke and gas factors. The MgAl2O4phase of Mg/Al2O3additive is found capable of trapping vanadium while its MgO of Mg/Al2O3phase can migrate to zeolite particles (the active component of the FCC catalyst) that, in turn, causes a decline in the activity of that catalyst.

ISSN:0009-4536    

DOI:10.1002/jccs.199700085

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractWe define θ‐ (or R‐) bonding (or antibonding) character of the molecular orbitals according to the slopes of the orbital energy curves when the internuclear angle (or internuclear distance) is varied. So far the slope of the orbital curve has only been accounted for by the qualitative argument based on two factors: the orbital overlap and the s‐p mixing.We employ the bond orbitals instead of the usual atomic orbitals as the basis set to analysis the character of the molecular orbitals. The Fock matrix in the bond orbital basis can then quantitatively account for the effects of both the overlap and s‐p mixing factors.Our analysis also show that a third factor, the orbital interaction, is essential to account for both the “typical” and “abnormal” behavi

ISSN:0009-4536    

DOI:10.1002/jccs.199700086

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA series of binary and ternary rare earth complexes with para‐substitued benzoic acids and 1,10‐phenanthroline were synthesized. The phosphorescence spectra were measured and the lowest triplet state energies of ligands were determined, the phosphorescence lifetimes were obtained and intramolecular energy transfer mechanism between ligands was studied. The luminescence properties were also measured and were in agreement with the prediction. The energy match and intramolecular energy transfer process in these binary and ternary complexes were discussed in det

ISSN:0009-4536    

DOI:10.1002/jccs.199700087

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA series of dendramines and dendramides have been synthesized and some of their “anti‐freeze” properties in diesel fuels have been tested, showing that these compounds are good oil additives for reducing the wax‐like crystals which block the fuel

ISSN:0009-4536    

DOI:10.1002/jccs.199700088

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe analytical conditions of the direct determination of bismuth in some certified reference material samples (soil and sediment) by slurry sampling Zeeman electrothermal atomic absorption spectrometry (ETAAS) with the use of automated ultrasonic slurry mixing are discussed. Palladium nitrate was used as a chemical modifier. With the use of this modifier it was possible to stabilize bismuth to the pyrolysis temperature of 1300 °C. Platform atomization was performed at 2050 °C. The results of determination are calculated from a simple, aqueous standards based calibration graph.Statistical evaluation of the results indicate that the slurry sampling method is reproducible and the accuracy of the proposed method is very good. This method is rather simple and its other advantages are good sensitivity and relatively short analysis tim

ISSN:0009-4536    

DOI:10.1002/jccs.199700089

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractSelenium concentration in serum has been proposed as the most valuable indicator of human selenium status. In this work, the concentration of selenium in serum is measured by GFAAS using longitudinal Zeeman‐effect background correction, a highly sensitive technique that can be used to determine selenium at sub‐ppb level. Standard reference materials are analyzed to verify the accuracy and precision of this technique. The direct method proposed in this study is used for the determination of selenium in human serum collected from healthy people of 19–25 years and women of 21–34 years in the First trimester of pregnancy. The method developed in this study, which can quickly and accurately measure serum selenium, is suitable for applications in clinical diagnosis or biological mon

ISSN:0009-4536    

DOI:10.1002/jccs.199700090

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractSilca‐supported Co3O4(6 wt% as Co) catalysts were prepared by pore volume impregnation of ethanol or aqueous cobalt nitrate solutions, and calcinedin vacuoto 300 °C. The catalytic performances of these catalysts for oxidation and hydrogenation of CO were examined. All Co3O4/SiO2catalysts were found to be very active in catalyzing oxidation of CO to CO2as compared to a commercial 1 wt% Pt/Al2O3. The ethanol‐prepared catalysts exhibited higher activity than those of the aqua‐prepared catalysts. Pre‐calcination of the ethanol‐prepared catalysts in oxygen at 600 °C resulted in a dramatic decrease in the activity. Temperature programmed oxidation indicated the presence of carbon deposits on the surface of used catalysts. Infrared spectra showed the continuous generation of CO2when these catalysts were exposed to CO. These indicate the primary role of CO disproportionation in catalytic oxidation of CO on Co3O4at low temperature and explain the sharp decrease in activity in the initial period. After reduction at 400 °C, the ethanol‐prepared catalysts were also found to be more active in catalyzing hydrogenation of CO, and produced less methane and olefin (C2‐C4) fraction. Higher turnover frequencies were observed after high temperature reduction (600 °C) as well, at which ethoxyl groups were removed from silica surface. In both reactions, the enhanced activity for the ethanol‐prepared catalysts can not be fully accounted for by the increase in the dispersion of Co3O4or CO metal. This suggests that the surface structures of Co3O4or CO were further modified by the carbonaceous species d

ISSN:0009-4536    

DOI:10.1002/jccs.199700091

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractProcedures for the dimerization of acrolein to form 3,4‐dihydro‐2H‐pyran‐2‐carboxaldehyde by microwave induced synthesis have been developed. Significant rate‐enhancement and yield increase were observed. 3,4‐Dihydro‐2H‐pyran‐2‐carboxaldehyde was obtained in 91% yield under microwave irradiation for 5 minutes instead of 39% yield by reacting at 190 °C for 40 min

ISSN:0009-4536    

DOI:10.1002/jccs.199700092

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractAn oligonucleotide analog containing 2′‐O‐methylpseudoisocytidine (P) and 2′‐O‐methyluridine (X) in an alternated homopyrimidine sequence (P‐X‐)7P‐T can form triplexes with d‐A‐(G‐A‐)7G single strand and [d‐A‐(G‐A‐)7G]:[d‐C‐(T‐C‐)7T] duplex in neutral conditions. An UV mixing titration showed an end point of two units of (P‐X‐)7P‐T to one unit of d‐A‐(G‐A‐)7G. This indicates that a [(P‐X‐)7P‐T]·[d‐A‐(G‐A‐)7G]·[(P‐X‐)7P‐T] is formed. The [(P‐X‐)7P‐T]·[d‐A‐(G‐A‐)7G]·[(P‐X‐)7P‐T] triplex is stable in a 0.1 M NaCl solution at neutral pH. However, the formation of triplex with [(P‐X‐)7P‐T] and a duplex [d‐A‐(G‐A‐)7G]·[d‐C‐(T‐C‐)7T] can be accomplished in solution also containing 5 mM MgCl2. CD spectra of both triplexes showed large negative bands at wavelength 210–230 nm. Both triplexes can be detected by native gel electrophoresis. The thermal dissociation/association resu

ISSN:0009-4536    

DOI:10.1002/jccs.199700093

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe synthesis of 3,11‐dioxatetracyclo[6.3.0.02,6.05,9]undecanes has been accomplished from furans in a short sequence by iodine‐induced cyclization reaction. The application of iodine‐induced cyclization reaction for the synthesis of 3,5,7‐trioxapentacyclo[7.2.1.02,8.04,11.06,10]dodecane itself was also demon

ISSN:0009-4536    

DOI:10.1002/jccs.199700094

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY